ENGINEERING STUDIES
HSC Module 1: Civil Structures
Syllabus Outline
1.1
Historical and Societal Influences and the Scope of the Profession
1.1.1
Outline the history of technological change as applied to civil structures.
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1.1.2
The first civil structures were developed using materials that were readily available such as timber.
Later bridges were constructed from stone.
During the Industrial Revolution, timber and stone were replaced in bridge construction by steel.
A beam is a member that is supported so that its supports do not carry longitudinal forces. Beam
bridges are amongst the simplest types of bridges
o There are two main types of beam bridges. A simple supported beam is has supports at both
ends. A cantilevered beam has a support at only one end.
o Early beam bridges were built by the Romans from timber and stone.
o Truss girder bridges were developed in the 1500s.
o The box girder bridge is the most common form of beam bridge today and consists of a tube
with a rectangular cross section stiffened by a series of internal walls.
Arch bridges consist of a deck or roadway supported either above or below by an arch.
o Arch bridges were originally built of stone, and later used cast iron and steel. Modern arch
bridges use concrete.
o Arch bridges distribute the load of the bridge into the abutments at either end and then into
the ground.
o Concrete shrinks while it sets, so concrete arch bridges are built with a central hinge to allow
for shrinkage.
Suspension bridges support the deck on tension members strung between two towers.
o Early suspension bridges used twine, vine or chains.
o Suspension bridges are much more lightweight than any other type of bridge and so can span
long distances.
o Cable-stayed suspension bridges are a specific type of suspension bridge in which the cables
attach directly to the pylons.
o Steel is commonly used in the manufacture of suspension bridges.
Moveable bridges are used where it is inconvenient or costly to build a bridge over a waterway high
enough so as not to impede the flow of water traffic.
o Moveable bridges can be made to lift above the roadway, lift as a cantilever to one or either
side, swing open from the middle or descend below the surface of the water.
Investigate the construction processes and materials used in civil structures from a historical
point of view.
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Early bridges were made from timber which was easy to manufacture and readily available. Timber
rots away with time but has good compressive and tensile stress properties, so bridges had to be
replaced. Because timber comes from trees, the length of the span of the bridges was limited.
Stone was used in early arch bridges. It was a more permanent building material than timber but was
only strong in compression. As such, it was only suited to arch bridges.
Bricks are sometimes used in bridge construction. They have similar properties to stone.
Cast iron is weak in tension but strong in compression. It can be cast, which saves time and money.
Steel was used in arch bridges and steel cables in suspension bridges. It allowed for much greater
spans to be constructed. Steel is also used to reinforce concrete. Steel is malleable, has a simple
construction and is strong in both compression and tension.
Concrete was not used in bridges until the problem of shrinkage was addressed. Most new bridges
use concrete of some type. Pretensioned and posttensioned concrete are common. Concrete is strong
in compression but weak in tension.
Steel I-beams have the best efficiency as they have the most material away from the neutral axis.
Box girder bridges can withstand torsional loads.
Engineering Studies – Page 1
1.1.3
Critically examine the impact of civil structures upon society and the environment.
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Primitive beam bridges and suspension bridges allowed for transport to cross rivers and ravines.
Bridges improved transportation and the economy by allowing for trade where it was not previously
possible.
Concrete has improved the stability of bridges.
Steel has improved the safety and cost of manufacturing bridges and has also allowed for longer
spans.
Bridges may affect water flow which can have social and environmental implications.
The use of timber as a material and fuel source has led to deforestation.
Stone quarried scarred the landscape and destroyed habitats for local fauna.
The use of coal for fuel in the construction of bridges has contributed to an increase in the level of
carbon dioxide in the atmosphere which is responsible for global warming.
Bricks were mined from brick pits which cause subsidence and erosion of the landscape.
Concrete requires many minerals to be mined and uses a large amount of water in product and
setting.
1.2
Engineering Mechanics
1.2.1
Apply mathematical and/or graphical methods to solve problems related to the design of pin
jointed trusses.
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1.2.2
The method of joints isolates each joint and analyses the forces on the beams connected to it.
o All forces in a truss are reaction forces.
o All forces carry axial loads. This means that if the force on one joint is in one direction, then
the force on another joint connected to the same member will be in the opposite direction.
o If the forces point towards the centre of the beam, then the beam is in compression.
o If the forces point away from the centre of the beam, then the beam is in tension.
o It is best to start on a joint with the minimum number of unknown forces.
The method of sections quickly finds the forces on a single member.
o A section is taken through the beam that is being analysed.
o The optimal section contains the fewest number of unknown forces.
o Moments should be taken around a point to eliminate any other unknown forces.
Evaluate the importance of the stress/strain diagram in understanding the properties of
materials.
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Stress is a measure of the internal reaction to an externally applied force. It is measured in Pascals
(Pa).
𝐿
𝜎=
𝐴
There are three main types of stress:
o Tensile stress is an axial stress that extends a member.
o Compressive stress is an axial stress that contracts a member.
o Shear stress is nonaxial and causes a member to slide over another.
A tension test involves the application of a load to a
material sample. It is from this test that a load-extension
graph is produced.
Shear stress is a type of stress that features one plain
sliding over another.
The area involved in the shear stress calculation is
parallel to the external force.
Single shear stress occurs when there is only one pair of
forces acting on a body.
Double shear stress occurs when there is more than one
shear plane.
Engineering Studies – Page 2
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Punching shear stress occurs when a hole is punched through a material. The shear area is the
perimeter of the hole multiplied by the thickness of the material.
Strain is a measure of how much a material or member will deform under a certain force.
Δ𝐿
𝜀=
𝐿
A stress/strain diagram gives the properties of a material when a tension test is performed.
For most stress/strain curves, the stress appears to decrease towards the end (necking down). This
is because most stress/strain diagrams show engineering stress.
Engineering stress is calculated using the original cross-sectional area even though the crosssectional area reduced during necking down.
True stress is calculated using the cross-sectional area under a particular load.
Working stress is the maximum allowable stress that a material or object will be subjected to when
in service. Working stress is always less than the ultimate tensile stress.
Safe working stress is always less than the elastic limit for a given material.
Hooke’s Law states that stress is proportional to strain up to the proportional limit.
𝜎
𝐸=
𝜀
Young’s modulus (𝐸) is a measure of the stiffness of a material. It is also known as the modulus of
elasticity or stiffness.
Materials have a constant modulus of elasticity up to the proportional limit.
Above the proportional limit, stress no longer has a linear relationship with strain.
Resilience is a measure of the ability of a material to maintain its shape after deformation. It can be
found by the area under the curve up to the proportional limit.
Yield stress is the stress value at the progressive yield point. At this point, there is no relationship
between an increase in stress and an increase in strain.
An approximation for the yield point/elastic limit for materials that do not have a definite point due
to their structure is proof stress. If a line is drawn parallel to the curve up to the proportional limit
but shifted 0.001 units to the right, the point where it intersects the curve will be the point of 0.1%
proof stress.
Toughness is the ability of a material to absorb energy. This is also called impact strength. It is given
by the area under the entire curve.
The ultimate tensile stress (UTS) is the highest amount of stress a material can withstand.
Since a material should be working at stresses under its breaking point, a factor of safety is how much
tolerance a material is given.
UTS
F of S =
𝜎max
Within a system, there is a compromise between a high factor of safety and the efficiency of the
system.
Engineering Studies – Page 3
1.2.3
Calculate and graph the bending stress and shear force of simple supported beams involving
vertical point loads only.
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Whenever a nonaxial force acts on a beam, there will usually be some resistance to bending.
This force creates bending stress internally within the beam.
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The shear force at any point on a beam is the algebraic sum of all the external forces on one side of
the beam. The shear force is the internal reaction of the material to being sheared apart by external
forces.
Shear force calculations involve working progressively along the beam and summing the external
forces to determine the shear force.
Shear force diagrams involve following the direction of the applied loads and plotting the points on
the diagram.
The bending moment at any point along a beam is equal to the total moment developed at that point
by the external force system. If the moments are summed at a given point along the beam that is in
equilibrium, then the value will be zero.
Bending moment diagrams can be calculated by summing moments about active and reactive forces
then drawing a diagram, or by plotting the area under the curve from left to right of the shear force
diagram.
When a beam bends, the top is in compression and the bottom is in tension.
The neutral axis is the approximate centre of the cross section of the beam. The further the distance
from this axis, the stronger a beam is in bending.
𝑀𝑦
𝜎𝐵 =
𝐼𝑥𝑥
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1.2.4
Describe the effect of uniformly distributed loads on a simple beam, without calculations.
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1.3
Uniformly distributed loads are spread across a region of the beam.
When calculating moments with a uniformly distributed load, treat it as a point load in the middle of
the region with the sum of the entire load.
Uniformly distributed loads cause diagonal lines on shear force diagrams.
Uniformly distributed loads cause curves on bending moment diagrams.
Engineering Materials
1.3.1 Describe basic and specialised testing conducted on materials used in civil structures and
examine the properties, uses and appropriateness of materials used in civil structures.
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Materials can be tested by destructive or non-destructive means. Destructive testing involves loading
a material until it breaks. Non-destructive testing involves using an external device to examine the
faults without destroying the test piece.
Engineering Studies – Page 4
Test
Type
Use
1.
determining the
location of cavities
X-ray
2.
3.
nondestructive
1.
dye penetrant
finding small cracks
on the surface
ultrasonic
determining the
location of cavities
2.
1.
2.
1.
determining the
tensile strength
tensile
2.
3.
1.
compressive
destructive
determining the
compressive strength
2.
3.
transverse
performance under
bending and shear
force
torsional
performance under
twisting forces
1.
2.
3.
1.
2.
Method
X-rays are passed through a material
onto a photosensitive film.
Darker areas represent areas with less
material.
The location of cavities and internal
faults can be found.
Dye is splashed onto the surface of the
material.
Under ultraviolet light, the dye becomes
fluorescent and displays any cracks.
A machine emits sound pulses.
The echo is mapped to determine the
location of any cavities on the surface.
A piece of material is stretched by a
testing machine.
The machine exerts a set load on the
material.
The elongation and load are recorded as
it breaks.
A piece of material is crushed by a
testing machine.
The machine exerts a set load on the
material.
The deformation and load are recorded
as it breaks.
Material is supported on both ends.
A load is applied on the beam.
Bending load and total deflection are
measured as it ruptures.
Material is twisted using machinery.
Twisting load, thinning and other factors
are recorded.
1.3.2 Describe the testing of concrete.
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Slump testing is used to check the fluidity of concrete before casting. The concrete is cast into a
cylindrical mould open at the top and bottom. When the mould is removed, the conical wet concrete
should slump slightly according to set specifications. If it collapses, it is too wet; if it breaks in half it
is too dry.
Compressive testing is used to test the concrete after specific time intervals to ensure that the
material was properly cast.
1.3.3 Examine how failure due to cracking can be repaired or eliminated.
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Cracks are small imperfections within a material that are created when it splits apart.
These cracks tend to propagate, causing further cracking by creating new surfaces which eventually
cause the material to fail.
The mechanical strength of a material is lower than its theoretical strength due to irregularities in
the surface that cause stress concentrations and then cracks.
Cracks usually form due to an applied load. They can be caused by machining, forging or welding
defects, thermal expansion and contraction, corrosion pitting and incorrect forming processes.
When a crack begins to grow, it releases its strain energy.
1
SE = 𝜎𝜀
2
The maximum strain energy is often referred to as resilience.
Engineering Studies – Page 5
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Crack propagation occurs as the crack approaches the critical crack length. At that length, the
imperfection concentrates the load on the object at the bond. This concentrates double the stress at
the next bond and so on until the entire material fails.
The strain energy released from a crack goes to the area adjacent to the crack. The released energy is
not concentrated at the tip of the crack and builds up until the material fails. If the energy drops below
a threshold, the crack will halt its growth.
The critical crack length of a material is the length of a crack that will cause it to propagate through
the entire material.
2𝑊𝐸
𝐿𝑔 =
𝜋𝜎 2
where 𝐸 is Young’s Modulus and 𝑊 is the work of fracture for each surface (J m−2)
The longer the critical crack length, the less likely a material is to fail.
Brittle materials have a shorter critical crack length than ductile materials.
A common cause of cracking is fatigue failure from cyclic loading.
Cracks can be prevented by:
o rounding off corners to allow for a more even distribution of load
o perforating areas susceptible to tearing open to stop crack growth
o lowering the stress in susceptible areas
o reinforcing the material to reduce brittleness
o adding expansion joints to prevent expansion cracking
o placing forces perpendicular to the crack shear plane.
Cracks can be repaired by:
o crushing small cracks together in different directions in the hope of them stopping themselves
o changing the volume of the material through injection of material through injection into the
cracks
o welding or using adhesives to patch up the cracks.
1.3.4 Investigate ceramics including glass, cement and bricks in relation to their structure and
properties.
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Ceramics are a wide range of materials which are mostly a combination of metals and non-metals.
Most ceramics consist of semi-metallic components from earthen materials such as sand and lime.
Ceramics are typically hard, brittle and have good compressive strength and insulation.
Ceramics are porous and prone to cracking.
The most commonly used ceramics are glasses, clay and cement.
Glass is an amorphous (non-crystalline material).
o Glass is brittle and optically transparent.
o Glass cannot be shaped because of its structure. It is formed.
o Glass is made by combining silica, sodium oxide and calcium oxide and heating them to the
liquid state.
o Glass can be blown against a mould.
o Float glass involves floating a layer of molten glass on a bath of tin. The glass is cooled and
passed to a cutting area on rollers.
o Glass is annealed to remove internal stress.
o It can be toughened using tempering. This is when the surface cools faster than the inside.
This causes the surface to be in compression and prevents it from cracking.
o Glass is used in windshields and windows, cups and bottles, insulation and in composite
materials such as fibreglass.
Cement is a binding agent in concrete.
o There are two types of cement: hydraulic cement, which hardens underwater, and nonhydraulic cement, which hardens through other methods.
o Portland cement hardens due to complex chemical reactions which turn the cement to silicate
gel.
o The setting of cement emits heat.
o Cement comes in powdered form. It is created by crushing limestone and shale together and
heating in a kiln. This is mixed with gypsum and refined.
Engineering Studies – Page 6
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Silica is a well-known engineering ceramic that consists of silicon dioxide (SiO2 ). The silica
tetrahedron consists of one silicon atom and four oxygen atoms. Each unit is therefore SiO42−.
Orthosilicates are formed when two metal atoms donate two electrons each and an ionic bond is
formed between the metals and the silica tetrahedron.
Chain structures are formed when oxygen atoms are shared by adjacent tetrahedral. Asbestos is an
example of this.
Sheet structures form when three oxygen atoms are jointly shared to form a layer of Si2 O52−.
Framework structures occur when every oxygen bonds with another molecule. A common form of
this is quartz.
Clay may be formed by:
o pressing, in which dry clay is powdered and pressed into a mould of the desired shape
o isostatic pressing, in which the dry powder is placed in a plastic polymer mould and high
pressure liquid or gas is forced into the container to provide more uniform packing
o hand throwing, in which the clay is shaped by hand on a rotating wheel
o extrusion, in which a plastic mixture of clay is forced through a suitably shaped orifice
o slip casting involves preparing the clay body as a creamy suspension of clay in water, called
slip, and pouring it into a Plaster of Paris mould. A layer of clay develops on the wall as water
is absorbed by the mould. Once the desired thickness has been achieved, excess slip is poured
from the mould.
1.3.5 Explain the special properties produced by composite materials.
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Composites are materials that are made from two or more constituents of differing properties.
Particulate composites consist of particles.
Laminar composites consist of layers.
Fibre composites are a textile material.
Fibre composites consist of a fibre and a matrix. Fibres carry the load of the composite and matrices
bind them together to protect the fibres from corrosion and distribute the load.
Carbon fibre composite and glass fibre composite are used in planes like plywood due to their
extremely high strength-to-weight ratio.
Timber is a composite material of cellulose fibres and a natural resin.
Hardwoods have pores, while softwoods do not. Hardwoods come from flowering plants.
Mortar is a mixture of cement, sand and lime.
Concrete is a composite material of cement, aggregate and sand. The sand fills the gaps between the
aggregate and the cement acts as a binding agent.
Asphalt is a composite of aggregate and bitumen. It is tough and crack resistant and impervious to
contamination by oil.
Laminates are materials that consist of two different substances pressed together. Plywood is a
laminate.
Bimetallic strips use two back-to-back metals with different thermal expansion rates. As the metals
expand, the strip bends in one direction. They are used in kettles and thermostats.
Geotextiles are woven polymers or ceramic fibres used for stabilising road base. They are also used
in drainage systems.
1.3.6 Compare simple reinforced, pre-tensioned and post-tensioned structures.
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Concrete is a mixture of sand, cement, aggregate and water.
It is weak in tension but strong in compression.
Reinforced concrete is concrete combined with a reinforcement structure to improve its tensile
strength.
Ferro-concrete consists of concrete with steel fibre added. Glass, plastic and graphite can also be used.
The material used to reinforce the concrete must be good in tension and have a similar expansion
rate to concrete.
Steel is usually used to tension concrete.
Engineering Studies – Page 7
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Prestressed concrete is created by casting the concrete over a series of steel rods held in tension prior
to pouring. When the concrete sets, the rods are released and try to return to their unstressed
positions, which places the concrete in compression.
Poststressed concrete is case with tubes through it. After setting, wires are pulled through the slab
and anchored to plates at each end and tensioned.
Spalling occurs when the reinforcing steel corrodes. The steel expands which causes the concrete to
crack.
1.3.7 Evaluate the significance of corrosion problems in civil structures and describe methods used to
protect civil structures against corrosion.
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Corrosion is the chemical deterioration of a material over time.
Dry corrosion occurs when a metal reacts with oxygen in the air.
This forms an oxide layer over the metal known as rust.
If the metal oxide layer forms an impervious layer that prevents contact between the underlying
metal and the air, the metal is referred to as being passive.
If the metal oxide layer is porous, corrosion can continue deep into the material. This is known as
active corrosion.
Dry corrosion is sensitive to temperature and occurs much faster under the application of heat.
Most engineering materials undergo dry corrosion.
Wet corrosion is an electrochemical phenomenon which occurs in galvanic cells.
When two metals are in contact, the more reactive metal donates electrons (oxidises) to the less
reactive metal (reduces). As it does so, the more reactive metal loses ions and corrodes.
Electroplating can be used to protect metals from corroding. This can involve accelerating the
corrosion process to form a protective oxide layer or galvanising the metal in hot zinc.
Corrosion can be prevented by coating. Some metal alloys such as stainless steel and aluminium
create an impervious oxide layer. This oxide layer can be encouraged through anodising, in which the
metal is connected to an electrical supply.
Some paints can prevent corrosion by providing a layer that would corrode slower than the parent
metal.
Phosphoric acid can be used to remove rust and replace it with a corrosion resistant film that can be
painted.
Hot dipping involves coating steel or aluminium in a layer of zinc metal. The zinc forms zinc carbonate
on the surface which is extremely corrosion resistant.
1.3.8 Describe methods used for recycling materials when civil structures are replaced.
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Disposal of waste materials is discouraged.
Used bricks can have the mortar removed and be reused.
Roofing materials such as slates and contemporary clay and concrete tiles can be reused.
Sheet glass can be reused in its original condition or crushed to be used as a raw material in the
manufacture of new glass products.
Solid wastes such as tyres can be mixed with resins and then cast, moulded or extruded into new
construction products.
Most metals can be either reused or recycled.
Asphalt and concrete can be recycled by crushing them and using them as aggregate for future
applications.
Engineering Studies – Page 8
1.4
Communication
1.4.1 Interpret and produce orthogonal assembly dimensioned drawings.
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A development is the shape formed when a sheet metal object is unfolded to form a flat surface.
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If an object or structure is to be made to a predetermined size, then the development must be made
to produce that size. True lengths can only be measured if they are parallel to the direction of view in
an orthogonal drawing.
Transition pieces join two ducts of differing sizes.
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Producing a triangulation development for transition piece involves:
1. Draw the top and front views using orthogonal projection.
2. Define the position of the seam.
3. Label the larger square the base, and, starting at the seam label the corners with the
letters a, b, c, … in an anticlockwise direction.
4. Label the smaller square the top, and, starting at the seam label the corners with the
numbers 1, 2, 3, … in an anticlockwise direction.
5. In the top view, the seam line a1 is lightly drawn, then the line b1, forming triangle a1b.
6. Lightly draw the line b2, thus forming the triangle b12.
7. Lightly draw the line b3, thus forming the triangle b23.
8. Continue to triangulate the remaining part of the top view.
9. The transition piece has now been triangulated in preparation for the development.
Engineering Studies – Page 9
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The offset method determines the true length from different views.
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If there is symmetry, only half of the development needs to be drawn.
Engineering Studies – Page 10
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Dimensions should always be provided above the line that they pertain to.
Specific standards exist for nuts and bolts.
MD × P refers to a metric (M) bolt of diameter D and pitch P.
The thread depth on a bolt is half the pitch.
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For a bolt, the distance across the flats is defined as 1.6D and the distance across the points is defined
as 1.8D. The depth of the bolt head is 0.7D. The thread depth is 0.5P or 0.1D.
For a nut, the distance across the flats is 1.6D and the distance across the points is 1.8D. For a standard
hex nut, the depth of the head is 0.8D. For a lock nut, the depth of the head is 0.5D.
For a washer, the diameter is 2D and the depth is 2 mm.
Counter bores and counter sinks are used to recess a bolt or screw head below the face of an object.
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Engineering Studies – Page 11
ENGINEERING STUDIES
HSC Module 2: Personal and Public Transport
Syllabus Outline
2.1
Historical and Societal Influences and the Scope of the Profession
2.1.1 Investigate the history of technological change related to transport and its impact on society.
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2.1.2
A bicycle is inexpensive and highly efficient. It is also environmentally friendly.
o The first bicycles consisted of a wooden toy horse. It was propelled by the operator moving
his or her feet along the ground. There were no brakes or steering.
o In 1817, the draisienne was developed which had a steerable front wheel. The frame was still
timber but had wrought iron forks.
o In 1840, the first pedal-powered bicycle was developed which consisted of rods connected to
foot stirrups.
o In 1861, cranks were fitted to the front wheel. This was called the velocipede. It had a wrought
iron frame with cast iron fittings and timber wheels.
o In 1870, bicycle manufacturers realised that a larger front wheel meant further propulsion
per revolution. Bicycles with large front wheels were called ordinaries. Riding an ordinary
was difficult and dangerous.
o In 1884, the rover safety was developed. It consisted of a steerable front wheel and rear
wheels driven by pedals linked to the rear wheel by a chain and sprocket. Different ratios of
the gears could also be achieved. This was possible due to the development of steel.
o In 1888, the pneumatic tyre became common on bicycles.
o In 1895, the derailleur gear system was developed and patented.
o The increased usage of the car saw a decline in bicycles in the 1990s. With less money spent,
there was gradual refinement on the bicycle.
o In the 1980s, mountain bikes was developed that had a low gear ratio and a thick wheel tread.
Bicycles today are manufactured from aluminium alloys, chrome-molybdenum alloys, lightweight
magnesium alloys and composite carbon fibre materials. The increased strength of these materials
has allowed bicycles to become more functional and easier to ride.
Investigate the construction processes and materials used in civil structures from a historical
point of view.
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The engine block needs to be able to be cast and machined. It needs to be resistant to high
temperatures and impact loads, thermally conductive and lightweight. Suitable materials for this
include grey cast iron and aluminium alloys.
Pistons need to be able to be machined and resistant to impact loads as well as high temperatures, be
thermally conductive and lightweight. Typically they are made of aluminium.
Crankshafts need to have high tensile and fatigue strength and good machinability. They are usually
manufactured from cast iron or alloyed steel.
Body panels need to have a good strength-to-weight ratio, good surface finish and formability,
toughness and scratch resistance and corrosion resistant. Typically they are made of mild steel
although alternatives such as aluminium alloys and thermoplastics also exist.
The frame needs to be lightweight, stiff and have good weldability, fatigue strength and corrosion
resistance. It is typically made from steel alloys or aluminium alloys.
Windscreens are made from laminated glass. Tempered glass is used in side and rear windows but
not the front as it obstructs the vision.
Wheels are made from aluminium alloys, fabricated steel or magnesium alloys.
Tyres are made from vulcanised rubber. They have good traction, wear resistance and shock
absorption.
Aluminium alloys are replacing steel where weight is important.
Carbon fibre composite materials are also being used in vehicles.
Engineering Studies – Page 12
2.1.3 Analyse the impact of developments in transport systems on the environment.
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All forms of transport create air pollution.
The bicycle is the most environmentally conscious form of personal transport. It only generates air
pollution in its manufacture.
Motor cars release carbon dioxide and sulfur dioxide gas into the atmosphere which cause global
warming and acid rain.
The impact of motors cars on the environment could be lessened by:
o increasing the price of petrol
o linking the registration fee of vehicles to the pollutants they produce
o increasing the number of bus only lanes or transit lanes on all roads
o reducing the parking available in cities
o charging a toll on all major roads
o restricting the use of vehicles during the day.
Electric trains have less of an environmental impact, but the power still needs to be generated. In
Australia, this power comes from coal-fired power stations.
Trains can move many people very quickly.
Regenerative braking in trains recaptures energy lost during braking.
Hybrid electric motor cars have not yet been a commercial success because:
o they lack the performance of petrol or diesel motor cars
o they have a small range between charges
o the batteries take up too much space and weigh too much
o they have an extremely high cost compared to conventional petrol vehicles.
All forms of personal and public transport produce noise pollution.
Noise pollution can be reduced by:
o choosing quieter alternatives where possible
o reducing the noise at the source using mufflers and sound absorbing materials
o isolating the transport system
o restricting the time of use of the transport system.
Road and rail infrastructure causes tree felling and rock blasting which disrupts the environment and
destroys local habitats.
2.1.4 Assess the social implications of engineering innovation on people’s lives.
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Personal transport has a number of advantages:
o It is available on demand.
o It has greater convenience
o It has greater levels of personal comfort and security
o It may be used for sport, fitness and pleasure.
Personal transport has a number of disadvantages:
o The owner is responsible for running and maintenance costs
o Some costs apply regardless of the use of the vehicle
o There is often a high start-up cost
o Most vehicles require special training or licensing
o Strict laws apply to most vehicles
o There is a greater change of accident or death
o There is a greater impact on the environment due to under-utilisation of private vehicles.
Public transport is shared between many users, such as trains, buses, ferries, trams and planes. Public
transport is often subsidised by the government.
Public transport has a number of advantages:
o The customer only pays when they use it
o The cost of operation is subsidised by the government
o There is no special training or licensing required
o It can be used by those unable to operate personal transport
o There is a reduced risk of accidents
o There is less air pollution per person
o There is reduced traffic on roads.
Engineering Studies – Page 13
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2.2
Public transport has a number of disadvantages:
o The customer has little control over the time or route taken
o It is not available in all areas or applications
o There is wasted dwell times
o Taxpayers’ money is used to subsidise running costs
o It has very high initial capital costs paid for by the community
o The comfort and personal security may not be as great.
There are safety issues involved in operating personal and public transport:
o Young people on bicycles are often inexperienced and unaware of the dangers particularly
from other road users.
o Bicycles must be ridden wearing a helmet to protect the rider’s head.
o Many safety features such as antilock braking systems, general car dynamics of handling and
braking and power steering help protect users of cars. These are active safety features.
o Seat belts, air bags, shock absorbing panels, collapsible steering columns and break-away
pedals are designed to protect the users of cars. These are passive safety features.
o Trains contribute to reducing the road toll. They remove many vehicles from the road.
o Aeroplanes are one of the safest methods of travel.
The production of cars has made personal transport more accessible to the public.
The development of four wheel brakes in 1922 made cars safer to use.
In the 1980s, computer systems were introduced into cars that improved their reliability and safety.
Engineering Mechanics
2.2.1 Apply mathematical and/or graphical methods to solve engineering problems related to
transport including mechanical advantage, velocity ratio and efficiency.
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Friction is often considered the enemy of efficiency.
Friction is present in all machines.
It causes wear in the individual components and causes energy to be wasted.
It can be reduced by lubrication.
The normal force (𝑁) always acts at perpendicularly to the supporting surface. It balances all forces
that have perpendicular components.
If the supporting surface is inclined, the normal force is the component of the weight force that is
perpendicular to the surface.
Frictional force (𝐹𝑅 or 𝐹𝐹 ) is the reaction force that is exerted between the contacting surfaces that
tends to prevent movement.
When a certain force is applied to a body it will only move if the applied force in the direction of
motion overcomes the frictional force. At this point, the frictional force is called limiting friction.
Static friction is the force that opposes motion in static objects.
Kinetic friction is slightly less than static friction and opposes the motion of moving objects.
The ratio of the limiting friction to the normal reaction is constant for the same material. This is called
the coefficient of friction (𝜇)
𝐹𝑅
𝜇=
𝑁
The angle that resultant force of the normal and the frictional force is equal to called the angle of
static friction (𝜙)
tan 𝜙 = 𝜇
The angle of the slope is called the angle of inclination.
The angle of repose is the angle of inclination necessary for an object to be just on the point of
sliding.
𝜃 = 𝜙 = angle of repose
Friction problems can be solved mathematically or analytically.
2.2.2 Differentiate between the concepts of energy and power and apply appropriate basic calculations.
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The work done on a body is the product of its displacement and the force applied.
Engineering Studies – Page 14
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2.3
The displacement must be in the direction of the applied force.
𝑊 = 𝐹𝑠
The unit of work is the joule (J).
When more than one force acts on a body to produce motion, the total work done is found by
calculating the resultant force on the body.
When a body is moving at a constant velocity, there is no acceleration. According to 𝐹 = 𝑚𝑎 then,
there is no force and hence no work done.
The work done can also be found using a force displacement graph. The work is given by the area
under the curve.
Energy is the capacity to do work.
Kinetic energy is the energy that a body possesses due to its motion.
1
𝐾𝐸 = 𝑚𝑣 2
2
Potential energy is the energy that a body possesses by virtue of its position.
Gravitational potential energy is due to height.
𝐺𝑃𝐸 = 𝑚𝑔ℎ
Strain energy is a form of potential energy.
1
𝑆𝐸 = 𝐹Δ𝑙
2
The slope of the line of a spring up to the elastic limit is known as the spring constant (𝑘).
If a body is under motion due to the action of external forces, then the total energy in the system is
constant.
𝐾𝐸𝑖 + 𝑃𝐸𝑖 ± 𝑊 = 𝐾𝐸𝑓 + 𝑃𝐸𝑓
Power is the rate of doing work.
𝑊
𝑃=
𝑡
Power is also the product of force and velocity.
𝑃 = 𝐹𝑣
The unit for power is the watt (W). One watt is equal to one joule per second.
Efficiency (𝜂) is less than 100% in all systems due to power losses.
Brake power is the power that is available to do useful work at the driving wheels.
brake power
𝜂=
indicated power
Engineering Materials
2.3.1 Investigate the application of testing of materials.
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Non-destructive tests do not damage the item being tested. They are used to check manufactured
items and to determine the effect of forming processes on a material’s properties.
Destructive tests test the specimens to destructions or their breaking point. This allows an easy
comparison of their mechanical properties.
The elasticity of a material is its ability to return to its original condition.
The yield strength of a material is the point at which plastic deformation occurs.
The ultimate tensile stress (UTS) is the maximum stress that can be applied to a material.
Notched-bar impact tests measure the
toughness and impact strength of a material. A
swinging pendulum simulates an impact
loading. The height that the pendulum attains
after impacting the specimen compared to its
starting height gives an indication of the amount
of energy used to fracture the specimen.
In an Izod test (right), the specimen is mounted
vertically and supported only at the base. There
is a notch at the base and the striker hits the top.
Engineering Studies – Page 15
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In Charpy test (right), the test specimen is held
between two supports 40 mm apart and the notch
is in the middle on the opposite side to the striker.
Many items are subjected to fluctuating or
changing stress. Failure due to cyclic loading is
called fatigue failure.
The ability of a material to resist fatigue can be
tested using the Wohler system. The specimen is
mounted on a revolving chunk. As the specimen
revolves, a known load causes a fluctuating
bending stress on the material.
The hardness of materials can be determined using
a hardness test.
Compressive and tensile tests measure compressive and tensile strength.
Most vehicles are collision tested.
2.3.2 Outline how changes in properties occur as a result of heat treatment processes.
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Ferrous materials are those in which the main constituent alloying component is iron.
Engineering Studies – Page 16
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Alloy steels contain additional materials that alter their properties.
Stainless steels contain 12% chromium which forms chromium oxide that protects the steel from
oxidation and improves the strength and hardness.
If more than 12% chromium is added to mild steel, it cannot be hardened except by cold working.
If more than 12% chromium is added to medium or high carbon steel, it can be quench hardened.
18% chromium 8% nickel stainless steel alloys are common in construction.
Chrome-molybdenum steels contain about 0.3% carbon, 1.1% chromium and 0.25% molybdenum.
These given good deep hardening properties, ductility and weldability.
Heat treatment is the controlled heating and cooling of a material to obtain required properties.
Steel is an interstitial solid solution.
Above 910°C, steel undergoes a change in allotropy from body centred cubic (BCC) to face centred
cubic (FCC). The face centred cubic can dissolve up to 2% carbon, while the body centred cubic can
dissolve up to only 0.008% carbon.
When steels are cooled, most of the carbon leaves the structure and forms ferrite and cementite.
Ferrite is iron with 0.008% carbon and is very soft and ductile. Cementite has 6.67% carbon and is
hard and brittle.
Full annealing involves heating into the austenite range, then soaking and slow cooling. It produces
equiaxed unstressed grains of ferrite and pearlite.
Process annealing involves heating to below the austenite range then slowly cooling. It produces
equiaxed unstressed ferrite grains but leaves pearlite in its stressed state.
Normalising is similar to full annealing but involves heating the steel to a higher temperature and
cooling in still air. This makes the grains finer and so the steel is stronger.
Hardening depends on the different solubilities of carbon in the FCC and BCC structures. Hardening
causes a martensitic structure.
Most hardened steels are tempered to remove brittleness. When martensite is heated, the trapped
carbon diffuses out to form iron carbide particles. This relieves some stress and reduces brittleness.
Surface hardening of steels hardens the surface but leaves a soft core.
o Carburising involves heating the steel to 950°C in a carbon-rich atmosphere for between
three and six hours. Carbon enters the surface layer of the steel.
o Nitriding involves heating to 500°C in a nitrogen-rich atmosphere for 40 to 100 hours. Very
hard traces of nitrides form on the surface of the steel.
o Selective hardening involves heating the surface to over 900°C then quenching which forms
martensite on the surface but leaves the core unaffected.
2.3.3 Explain the method and applications of various ferrous metal forming processes.
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Forming processes are the techniques used to shape a material.
Casting of a liquid into a metal mould cavity is convenient method of manufacturing components.
A mould cavity is made from either a reusable pattern or as a permanent metal mould. The molten
metal is cast and solidified, then removed from the mould.
In sand casting, a pattern of the item to be cast is produced and specially prepared sand with binders
is packed into a box around the pattern. The pattern is removed and the mould assembled. Molten
metal is poured through a runner into the mould. Air is allowed out through a riser. Once finished,
the item is removed and the sand reconstituted for recasting.
Shell casting is similar to sand casting, but the sand is bound together using an artificial polymer
bonding material. Each half shell is made on a metal pattern plate that is heated and covered with the
resin/sand mix. The excess mixture is tipped off and the half mould is cured in an oven. Molten metal
is poured in and the solidified casting is removed by breaking the shell.
Die casting involves the metal being cast into a permanent metal mould.
Investment casting produces a clay mould from a wax pattern that is then melted out. The metal is
poured into the ceramic which is broken when the metal solidifies and the object removed.
Hot working occurs at temperatures above the recrystallisation temperature. The final product has
small, equiaxed grains which is tougher and more ductile than the cast structure.
Common hot working procedures include:
o rolling
o forging
o extrusion
Engineering Studies – Page 17
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o piercing.
The disadvantages of hot working include poor
surface finish and poor dimensional accuracy.
Cold
working
occurs
below
the
recrystallisation temperature. The final
product has elongated stressed grains.
The advantages of cold rolling are:
o no heating is required
o improved dimensional control
o better surface finish
o increased strength properties
o directional strength properties
o reduced metal loss and tool wear
o it is the only method of hardening mild
steel and most nonferrous metals.
The disadvantages of cold working are:
o more rigid and powerful equipment is
needed
o larger forces are needed
o work hardening occurs
o undesirable directional properties may
be produced
o the metal must be free of oxides before
working.
Common col working procedures include:
o drawing
o rolling
o cold-heading or upsetting
o extrusion
i
Engineering Studies – Page 18
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The top right image is hot rolling, The next image is cold rolling, The next image is drawing. The next
macrostructure due to forging. The above image is upsetting.
In powder forming, brittle powders are mechanically or chemically disintegrated. Hardened steel or
carbide dies are filled with the powder. The component is pressed together then heated in a furnace.
2.3.4 Justify the use of non-ferrous metals in transportation parts and systems based on relevant
structure/property relationships.
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Non-ferrous metals are frequently used in transportation.
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Some properties of non-ferrous metals include:
o good formability
o low density
o corrosion resistance
o high thermal and electrical conductivity
o stiffness and strength that is usually lower than ferrous metals
o poor weldability.
Engineering Studies – Page 19
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Aluminium has an affinity for oxygen and is found only as aluminium oxide in nature.
It is separated from bauxite ore by electrolysis.
Aluminium is relatively soft.
It is used in electrical wiring as it is lighter than copper despite being less electrically conductive.
The addition of alloying elements improves the mechanical properties of aluminium such as tensile
strength, rigidity, machinability and casting properties.
Aluminium alloys can be both cast and wrought.
Some elements added to aluminium to affect its properties include:
o copper, to allow the alloy to be precipitation hardened
o magnesium, which improves electrical conductivity and corrosion resistance
o silicon, which improves electrical conductivity and corrosion resistance
o iron, which assists in precipitation hardening
o titanium and manganese, which refine the grain structure
o zinc and chromium which improve tensile strength.
Brasses are alloys of copper and up to 40% zinc plus other elements like tin, lead, manganese,
aluminium and iron.
Under equilibrium cooling 𝛼 brasses form large equiaxed grains creating a soft and malleable
structure. If they are cooled slightly faster, a cored structure is produced with the centre of each
grain richer in the higher melting point copper.
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If more than 37% zinc is added, a hard brittle 𝛽 phase also appears. This is known as Muntz metal.
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Bronzes are copper alloys that do not contain zinc.
Tin bronzes contain about 10% tin. Alloys up to 7% zinc are single 𝛼 phase which is tough and
ductile.
The hard and brittle 𝛿 phase is present in alloys containing more than 7% zinc.
Casting tin bronzes contain up to 18% tin.
Aluminium bronzes are single phase cold worked structures with up to 5% aluminium and hot
worked alloys with up to 10% aluminium.
Aluminium bronzes have the following properties:
o The ability to retain strength at elevated temperatures
o Good corrosion resistance
o High resistance to oxidation
o Good wearing properties
o Pleasing colour making/aesthetics.
Many nonferrous metals can have their properties altered by cold working.
Annealing involves soaking a metal above its recrystallisation temperature then cooling back to room
temperature. The more heavily a metal is cold worked, the more nuclei will form on recrystallisation
which will lead to a larger number of equiaxed grains.
When cooled, some non-ferrous alloys become hard due to the complete precipitation of a metal
compound. If these alloys are heated to a single phase structure then quenched, the compound is not
able to precipitate.
Duralumin consists of aluminium and 4% copper and is heat treated by precipitation hardening.
Some nonferrous alloys can be hardened and tempered. These materials have better corrosion
resistance than steels.
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Engineering Studies – Page 20
2.3.5 Justify appropriate choices of ceramics and glasses used in transportation parts and systems.
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In most vehicles, the windscreen is made from laminated glass and the other windows from tempered
glass.
Glass is tempered by heating it into the annealing range then rapidly cooling it by air blasting.
Laminated glass is produced by cutting annealed glass to side then laying polyvinyl butyl between
the layers before being heated and tested.
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2.3.6 Justify appropriate choices of polymers used in transportation parts and systems.
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Thermosoftening polymers are covalently bonded linear chains held together by weak secondary
bonds.
Polyethylene is a thermosoftening polymer.
Thermosoftening polymers have a low melting point.
Thermoplastics are amorphous and can be transparent. (Crystalline polymers are opaque.)
They are weaker than thermosetting polymers because they have fewer covalent bonds.
In natural polymers such as rubber, sulfur is introduced as a vulcanising agent to link between the
chains in a process that requires heat and pressure.
The number of cross-links determines the rigidity of the rubber.
Vulcanised elastomers are electrical insulators and have good abrasion resistance.
Thermosetting polymers consist of three-dimensional covalent lattices.
Phenol formaldehyde (Bakelite) is a thermosetting polymer.
Thermosetting polymers have a higher melting point.
They are crystalline so are opaque.
In injection moulding, polymer granules are placed in a hopper that feeds into a heating chamber. The
polymer is forced through the chamber by a screw where it is melted. The molten polymer is injected
into a cool permanent mould. Once it sets, the mould opens and the finished item is removed.
Extrusion involves melting the polymer granules and then passing them through a die as it solidifies.
Thermosoftening polymers are often extruded. Polymers can also be extruded onto another material,
like plastic insulation on wires
Blow moulding is used to make bottles. The polymer is softened then extruded. The metal mould
closes around the viscous polymer an then air is blown into the top, pushing the hot polymer against
the walls of the mould.
Calendaring involves spreading viscous molten polymer over a sheet of fabric then rolling it.
Rotational moulding is used to mould hollow items. A permanent metal mould is produced and a
small quantity of polymer granules loaded into the mould. The mould is spun and the polymer
granules are propelled against the walls where they solidify.
Polymers can be cast in the viscous state.
Compression moulding involves mixing polymer powders with fillers and placing them in a heated
mould. The closing mould compresses the polymer and this combination of heat and pressure
polymerises the item.
2.3.7 Justify appropriate choices of engineering textiles in transportation parts and systems.
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2.4
Engineering textiles are polymer fibres woven into fabrics.
They can be used for drainage, road bases and as a vandal-proof fabric for trains.
Engineering Electricity and Electronics
2.4.1 Identify the electrical systems used in the transport industry.
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AC stands for alternating current. It continuously changes direction.
The current in AC oscillates at the frequency. In Australia, the supply frequency is 50 Hz.
DC stands for direct current. It flows in one direction only.
A rectifier converts AC to DC.
Engineering Studies – Page 21
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Electrical power is used for:
o heating
o motors
o lighting
o radiation devices
2.4.2 Describe current transmission and simple circuit diagrams.
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In a coal-fired power station, coal burnt to generate heat. The heat generated is used to boil fresh
water to produce high-pressure steam. The steam is passed through the blades of a turbine at high
speed. The turbine powers a generator. Usually, multiple turbines are used of increasing diameters
to harness all the energy of the steam. The generator converts kinetic energy into electrical energy.
Hydroelectricity is generated in much the same way except that the power of natural flowing water
is harnesses instead of burning coal.
Solar power uses photovoltaic cells which provide about 2.2 V each. They are made of silicon wafers.
Wind power uses the kinetic energy of the wind to turn turbines connected to generators to produce
power.
Other forms of energy include:
o internal combustion engines
o biomass
o tidal power
o wave energy
o geothermal electricity
o nuclear power.
The grid system carries electrical energy through a network of transmission lines to major
distribution points.
Single phase power is used in domestic applications. In industrial applications, however, the pulsing
power can impose excessive torques on mechanical components leading to failure.
Three phase power is generated using three separate circuits. The sum of the voltages of three phase
power is constant.
Power stations generate power at 20 kV.
Transmission towers are often constructed of fabricated steel.
Multiple conductors are used to combat resistive losses.
Porcelain insulating discs suspend the wires. They prevent arcing from the wires to the tower.
Electrical conductors are made up of multiple thin strands twisted together to prevent uneven
distribution of electricity flowing through them. Normally, more current flows closer to the surface
than to the centre.
Transformers vary the voltage of an electrical supply.
They consist of two coils, a primary coil and a secondary coil.
The ratio of the number of windings will be proportional to the ratio of the voltages.
𝑛𝑝 𝑉𝑝
=
𝑛𝑠 𝑉𝑠
Step-up transformers increase the voltage.
Step-down transformers decrease the voltage.
Because 𝑃 = 𝐼 2 𝑉, electrical energy is transmitted at very high voltages with low currents to reduce
resistive losses in the system.
Electrical protection mechanisms in domestic devices include:
o an earth connection to prevent the external casing from becoming electrically live
o an earth leakage protection circuit to switch off the power if current flows in the earth lead
o a fuse or circuit breaker to p
o revent fire in the case of over currents caused by a short circuit.
Transmission lines have an earth wire above the wires to protect lighting from striking the main
conductors.
The transmission system is used to carry bulk electricity from the generation site to the main
population centres, from where it is distributed to consumers by the distribution network.
The distribution network is not responsible for generating power.
The distribution network operates on lower voltages.
Engineering Studies – Page 22
2.4.3 Investigate the principles and application of electric motors used in the transport industry
including motor speed control.
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A synchronous motor (right) consists of a rotating magnet or electromagnet in an induced magnetic
field.
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A three phase synchronous motor attempts to keep the torque of the system constant by using three
pairs of electromagnets around the rotor, each out of phase by 120°.
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Single phase synchronous motors are rarely used. All practical synchronous motors use three phase
stator windings.
Slip rings alloy the motor to rotate while maintaining an electrical connection between the rotor’s
winding and the direct current source.
Synchronous motors can only run at the speed of rotation of the stator’s electric field unless a gearbox
is added.
If the load torque exceeds the maximum motor torque, the rotor will lose synchronism with the
rotating field and will stall.
Synchronous motors are difficult to start with a load. This is achieved by additional windings on the
rotor which only contribute significant torque to the motor when it accelerates.
A DC motor is similar but runs on direct current.
The current in a DC motor must be reversed every half turn to prevent the motor from stopping. This
is achieved by a cylindrical switch called a commutator which consists of carbon brushes that make
contact with the individual segments of a copper cylinder mounted on the rotor.
The DC motor, being an electromechanical device, requires continuous maintenance to ensure proper
operation.
DC motors do not have a fixed speed.
In some DC motors, the stator consists of permanent magnets and in others it consists of
electromagnets.
DC motors are used in:
o older trains
o conveyer belt systems
o steel rolling mills
o model trains
o electric windows.
The universal motor can operate off either AC or DC.
When a DC motor is connected to AC, it still rotates, but:
o the torque is not constant and varies with its rotation
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Engineering Studies – Page 23
o
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the speed can only be controlled by varying the magnitude of the voltage supplied to the
motor.
Universal motors offer high torque for their size.
Universal motors have brushes that contact the rotor coils.
They are used in hand power tools such as drills, sanders and power saws.
2.4.4 Analyse the basic principles of control technology as applied to the transport industry.
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Analogue signals are both continuous in amplitude and in time.
Digital signals have been quantised and sampled. A digital signal can be represented by a regular
stream of symbols.
A signal that is represented by only two possible levels is called a binary signal. Binary signals are
used in computers.
The term logic is used to describe a set of formal relationships between input and output variables.
Input variables are factors that determine whether a particular outcome will occur or be true.
Output variables describe the particular outcome.
In the case of a lamp, the input variable is whether the light is on or off. The output variable is the
illumination of the lamp.
Boolean logic is a set of rules specifically relating to logical variables that can only take on two
possible values.
If a Boolean expression has two inputs, A and B, then there are four possible outputs AA, AB, BA and
BB.
If there are 𝑚 inputs, then there are 2𝑚 outputs in a Boolean expression.
A logic gate is an electrical circuit that is designed to implement a particular Boolean logic function.
There are three logic gates of interest: AND, NOT and OR.
Engineering Studies – Page 24
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2.5
The term fly by wire has been coined to describe a flight control system that relies solely on
electronics to function; there is no mechanical connection.
Electronics are used for navigation and communications.
Lighting is a power application. Historically, lighting systems on bicycles were powered by small
generators. More recently, bicycle lighting has been powered by rechargeable batteries.
A speedometer or odometer measure the speed and distance travelled respectively. They are
mounted to bicycles and use sensors on the wheels to detect rotations.
Motorcycles use:
o an alternator to generate electrical power
o a battery to store energy for stating when the alternator output is too low
o a rectifier to convert the AC current to DC current for storage in the battery
o a voltage regulator to limit the voltage supplied to the battery
o a spark ignition system to supply high voltage pulses to the spark plugs to ignite the fuel-air
mixture in the cylinders
o a starter motor to start the engine
o lights for illumination of the road ahead
o a horn.
The brake light system illuminates the rear brake lamps when either the front brake lever or rear
brake pedal is activated. This corresponds to an OR logical function.
The starter motor is used for power to turn the engine over sufficiently quickly to start it. The energy
for the starter motor comes from the battery. The starter motor is DC for high torque.
Antilock braking systems are used to prevent a wheel from locking up during braking. Rotating
wheels are the source of gyroscopic stability on motorcycles. The antilock braking system works by
monitoring the rotational speed of the wheels. When the system detects that a wheel has stopped
rotating under braking force, the hydraulic pressure is released by an electrically-operated servo.
Considering a train: power is fed from the overhead conductors by a catenary system and collected
by a pantograph. The system operates on 1500 V DC. Power is obtained from the grid network. Trains
motoring up grades in the network use considerable energy to lift the train mass to higher elevations.
When the train descends, the motors are used as generators to convert mechanical energy to
electrical energy. Electrical power is used by the train as it moves and is converted to kinetic energy.
Diesel-electric engines use a diesel engine to drive an electric generator.
Communication
2.5.1 Produce dimensioned, sectioned orthogonal drawings, applying appropriate Australian Standard
AS 1100.
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Third angle projection is to be used in orthogonal drawings.
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The shape of a hole can be square or round. The shape is indicated by the symbol preceding the size
of the hole.
Engineering Studies – Page 25
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A round hole is indicated as shown:
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The depth of a hole is indicated by the depth symbol followed by the required depth of the hole. The
depth of the hole is the depth of the full diameter and does not include the distance to the pointed
end.
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Countersinking of a hole widens the top to provide a tapered seat that allows the countersunk screw
to fit flush with the surface of the component.
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Counterboring of a hole is used to widen the top of the drilled hole to provide a cylindrical seat that
allows a socket head screw to fit flush with the surface of the component.
Engineering Studies – Page 26
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A spotface is used to provide a flat surface on a rough or curved area to allow a nut or bolt to fit flush
with the surface of the component. A specialised spotfacing drill is used to form the flat surface
around the top of the previously drilled hole.
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Spherical radii is indicated using the letters SR before the given size. Spherical diameter is indicated
using the letters S followed by the diameter symbol and the given size.
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Chamfers must be dimensioned so that the size and the angle of the chamfer are fully described.
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A knurl is a raised area on the surface of a cylindrically shaped component, usually a fastened, that
provides a gripping area to hold when turning the component.
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Flat surfaces on a cylindrical component are shown as:
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When drawing cylindrically shaped bars, it is often convenient to only show a portion of the length
of the bar.
Engineering Studies – Page 27
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When a hole is drilled through a cylindrical bar or shaft, a line of intersection is formed between the
hole and the cylindrical surface.
Engineering Studies – Page 28
ENGINEERING STUDIES
HSC Module 3: Aeronautical Engineering
Syllabus Outline
3.1
Historical and Societal Influences and the Scope of the Profession
3.1.1
Define the responsibilities of the aeronautical engineer.
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3.1.2
Describe legal and ethical issues of aeronautical engineering, and the importance of engineers as
managers.
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3.1.3
Engineers need to measure the impact of aeronautical engineering on the wider community and the
environment.
The development of pressurised high-capacity jet aircraft has revolutionised long distance travel and
trade. This allows people to fly across the globe in only 24 hours. This has been a positive impact on
the community.
Increased trade, tourism and employment are also positive impacts.
The aeronautical engineering industry has the potential to impact negatively on the community.
Aircraft safety, excessive noise, environmental pollution, sustainability and recycling are issues that
affect the community.
The design, construction, maintenance and operation of aircraft is tightly regulated by a range of
legislation and international conventions.
The Convention on Civil Aviation was agreed to in 1944 and recognised that aviation was an
international industry that required consistent rules that applied in all member states.
To gain airworthiness, an aircraft must be designed and maintained to comply with strict structural
and in-flight performance standards.
Engineers have an ethical responsibility to ensure that aircraft they design or maintain are airworthy
and safe.
Engineers usually work in teams and almost always supervise the work of others.
It is important for engineers to have good human relations skills. Team building skills, problem
solving skills and communications skills are all important when working on complex multidisciplinary projects.
The design of aircraft requires coordination and management of a large range of personnel.
Once an aircraft company has carried out the aerodynamic, structural and materials design of a
component, the plans are then produced for the manufacturer to build the component.
Subcontracting involves another company to form individual teams to initially assess the project,
design the component and produce it.
Examine projects and innovations from within the aeronautical profession.
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Many technologies found in the aeronautical engineering industry are not unique to the discipline.
These may include materials, such as graphite and aluminium alloys, CAD programs, wind tunnel
testing and computerised calculations.
Aircraft design is concerned with how to achieve flight safely and efficiently. Aircraft need to be:
o as light as possible, to maximise the payload and alloy it to lift off in the first instance
o made of materials that are suited to the operating conditions and the environment, and will
remain in good condition for the expected service life
o structurally sound, so that all stresses are within working limits
o made from accurate components from detailed drawings.
A modern jet aircraft may contain over a million individual components. Each one needs to be drawn.
Most components have complex shapes such as curves or holes.
Many calculations in aeronautical engineering are complex, because they involve working in three
dimensions.
Engineering Studies – Page 29
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3.1.4
Analyse the training and career prospects within aeronautical engineering.
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3.1.5
Aeronautical engineers use aircraft design software to aid them, including:
o structural analysis software
o modelling software
o aerodynamic calculation software
o CAD software.
Structural analysis software analyses the forces, stresses and moments in aircraft wings and bodies
by breaking them into sections, called elements. The conditions in each element are examined and
the results combined to produce a distribution of forces, stresses and moments.
Modelling software is used to measure the behaviour of a model under simulation.
Aerodynamic calculation software makes CFD calculations to predict the lift and drag levels for a
particular airframe, as well as stall and other performance characteristics.
Computer aided design is used to produce accurate and dimensioned drawings of parts and
components.
Modern aircraft may be tested by producing a scale model and subjecting it to wind tunnel testing.
This gives engineers an idea of how the real thing may perform under similar conditions. Most wind
tunnels compress the air to 25 atmospheres for correct scale effect.
Aircraft design is influenced by a range of constraints and factors.
When an aircraft wing is generating lift, the upper surface has a lower pressure over it than the lower
surface has under it. The air tends to migrate towards the end of the wing and spill off there. This
creates vortices behind the wing which reduce the lift. Winglets are small tips on the end of wings to
prevent the formation of vortices.
An advanced machining centre is a computer-controlled machine with hundreds of cutting tools
available. The machine use cutters to perform operations usually carried out by lathes, drills and
milling machines.
Aeronautical engineers must complete a Bachelor of Engineering in Aeronautical Engineering at
university level.
The University of Sydney and University of New South Wales offer four year undergraduate courses
in aeronautical engineering.
Graduates may follow many different career paths, including:
o the design, development and manufacture of aircraft and aircraft components
o maintenance of existing aircraft and facilities
o jobs with government authorities like the Civil Aviation Safety Authority or Australian
Defence Force.
Research the history of flight in Australia and understand that way it has impacted on people’s
lives.
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The desire to fly has been documented since the Ancient Greeks.
In 200 BC, Archimedes observed that some solids could float in liquids, and then developed the basic
principles governing floating and buoyancy.
In 1290, Roger Bacon extended these concepts to solid objects in the air.
In 1783, Etienne and Joseph Mongolfier produced large sheets of linen that was air tight and
fashioned the first air balloon.
The development from hot air to hydrogen as a source of buoyancy and lift removed the need for fire,
but the large volume of hydrogen was potentially even more dangerous.
Balloons were slow and ineffective in winds.
Early aircraft designs used flapping wings.
After years of development, the Wright brothers made the first successful powered flight. The design
allowed the wings to be flexed in torsion, permitting different amounts of lift to steer the plane.
This is now achieved by ailerons and rudders.
Engineering Studies – Page 30
3.1.6
Examine safety issues related to flight and flying.
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All employers have an obligation to provide a safe and healthy work environment for their employees.
A common regime for controlling and dealing with hazards comprises four control measures:
o eliminate the hazard
o change the equipment or materials used
o change work practices
o use personal protection equipment (PPE).
Many issues exist in the aeronautical engineering industry, including:
o Fibre dusts, which can penetrate deeply into the lungs of workers, causing discomfort and
skin irritation. Some dusts can also cause fatal lung conditions.
o Noise. Workers can be exposed to noise levels above 100 decibels when working in the
vicinity of operating jet engines or riveting processes on factories.
o Chemical hazards, including organic solvents, which are linked to cancer and other
degenerative conditions.
3.2
Engineering Mechanics
3.2.1
Apply mathematical and graphical methods to solve flight-related problems.
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An aircraft flying straight and level is being acted upon by four forces.
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If the forces are not concurrent, then the plane will experience various moments.
A pitching moment is the twisting force trying to raise or lower the nose. This can be caused by the
balance of the freight, passengers or fuel, or airflow over the tailplane and elevators.
A rolling moment is the twisting force trying to roll the aircraft. This can be caused by the ailerons.
A yawing moment is the twisting force trying to yaw the aircraft. This can be caused by the deflection
of the rudder.
The hot gases in a jet engine expand and rush out the back of the engine at great speed. According to
Newton’s law and the conservation of momentum, as the gases shoot out backwards, so the jet goes
forwards.
Momentum is the product of mass and velocity.
𝜌 = 𝑚𝑣
Thrust is the change in momentum per time.
𝑚Δ𝑣
𝑇=
𝑡
Three things must be determined prior to thrust calculations:
o the velocity of the gases on intake
o the velocity of the exhaust gases
o quantities of gases consumed by the engine.
All aerial vehicles depressurise the air above them and compress the air below.
The reduced pressure and increased rush of air over the top surface of the wing causes it to be lifted
upwards.
The pressure difference and downwash generates lift. The amount of lift depends on:
o the speed of the wing through the air
o the shape and size of the wing
o the angle of the wing to the air (angle of attack, 𝛼).
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Engineering Studies – Page 31
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3.2.2
Outline Bernoulli’s principle as applied to instrumentation and lift.
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3.2.3
Drag is the aeronautical term for air resistance experienced by the aeroplane as it moves through the
air. It opposes motion and acts parallel to the relative airflow.
Drag is detrimental to high-speed flight.
Drag can be reduced by streamlined shapes, polished surfaces and flush-fitting rivets, as well as other
design features.
Induced drag is a byproduct of the production of lift and is related to the angle of attack. Induced drag
is greatest at low speeds.
Parasitic drag comes from hangers on to the wing that do not contribute to lift, such as engines.
Parasitic drag is proportional to the square of the airspeed.
At high speeds, the drag is almost totally made up of parasitic drag.
The design of the wing contributes to its efficiency.
The ratio of lift to drag (L/D) is dependent on the design of the wing section.
Typical aerofoils achieve the best L/D ratio at an angle of attack of about 4°.
The production of lift by an aerofoil is explained by Bernoulli’s principle.
Daniel Bernoulli discovered that the total pressure in a fluid remained constant and consists of static
pressure (the weight of the molecules) and dynamic pressure (due to motion).
If air was accelerated through a venturi, at the narrowest point where the air speed was the fastest,
the static pressure was the lowest.
Bernoulli’s principle states that: as the velocity of a fluid increases, the pressure exerted by that fluid
decreases.
The pattern of the airflow past an aeroplane depends on the shape of the aeroplane and its attitude
relative to the free-stream airflow.
Streamlining occurs when succeeding molecules follow the same path in a flow.
An object moving through air will eventually cause some turbulence. This occurs when succeeding
molecules no longer follow a streamline flow pattern.
The angle of attack, 𝛼, is the angle that the camber of the aerofoil makes with the oncoming air.
An incompressible fluid which moves into a region having a different cross-sectional area (from 𝐴1
to 𝐴2 ) undergoes a change in speed (from 𝑣1 to 𝑣2 ).
For the speed to undergo change, there must be a change in force. A change in force results in a change
in pressure, but the total pressure remains constant.
1
𝑃 + 𝜌𝑣 2 + 𝜌𝑔ℎ = 𝑘
2
This is Bernoulli’s equation.
Investigate the nature and effect of bending stresses, applying appropriate mathematical
methods.
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The purpose of an aircraft structure is to transfer the lift from the wings to support the weight of the
structure and its payload.
The airframe must provide both strength and stiffness.
Frames can be constructed from pin jointed or welded joints.
Engineering Studies – Page 32
3.2.4
Describe the operational principles and use of the stated propulsion systems used in the aircraft
industry.
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3.2.5
Apply mathematical methods to solve hydraulics-related problems.
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3.2.6
Most aeroplanes have hydraulically operated systems incorporated into their design.
A basic hydraulic system consists of a pump, regulator, reservoir, relief valve, filters, plumbing, oil
and control valves, actuators and accumulators.
Wheel brakes are normally disk brakes. They are hydraulically operated by toe pedals on top of the
rudder pedals.
In the atmosphere, static pressure is exerted equally in all directions. It is a result of the weight of all
the molecules of air above that point pressing down due to gravity.
Static pressure decreases with altitude.
Static pressure does not involve the relative motion of the air.
It is sampled on the surface of an aircraft by a static vent.
Dynamic pressure is caused by relative movement.
It depends on:
o the speed of the body relative to the air
o the density of the air.
Describe the basic operation of an altimeter and pitot tube.
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3.3
Turboprop engines:
o The turboprop engine drives the propeller by a gas turbine engine.
o Compressors compress the incoming air, fuel is sprayed in behind the compressor, and the
hot gas drives the turbine which turns the propeller.
o A reduction gear reduces the speed of the propeller. Propellers waste power and make too
much noise if they spin two quickly.
Turbojet engines:
o Turbojet engines do not have propellers. They are propelled by a backward jet of hot gas.
o The compressors ensure that all the air entering the turbojet is compressed and forced into a
combustion chamber. It is heated and the hot exhaust gases propel the plane forwards.
o Some of the air passes around the engine entirely. This is accelerated to produce more thrust.
An altimeter measures the height of an aircraft above a pre-selected surface level.
The atmospheric pressure (static) is fed into an instrument from an aperture in the fuselage side so
that it is perpendicular to any airflow.
Altimeters determine how high an aircraft is above sea level by measuring the pressure of the earth’s
atmosphere.
The airspeed indicator measures the speed through the air. Oncoming air enters the forward-facing
aperture on the aircraft, called the pitot tube. It is carried to a capsule with a diaphragm that can
expand or contract.
The pressure exerted is a combination of existing static pressure and dynamic pressure.
A pitot tube has two tubes:
o an outer tube, with holes perpendicular to the direction of the flow, which senses static
pressure only
o an inner tube, which faces the direction of flow and senses static plus dynamic pressure.
Engineering Materials
3.3.1 Describe non-destructive tests used on aircraft materials and components.
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Mechanical testing of materials provides data and information that allows the most appropriate
material to be selected for the many different applications on an aircraft.
Both environmental exposure and cyclic loadings can combine to cause fatigue failure.
Engineering Studies – Page 33
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Fatigue cracks have three different growth phases:
o initiation, in which microscopic cracks form due to slip along shear planes
o stable growth, in which visible cracks develop perpendicularly to the local tensile stresses
o unstable growth, in which the cracks develop perpendicular to the local tensile stresses.
Four conditions are necessary for cracks to develop and grow:
o the material must be prone to stress cracking
o tensile stress must be present
o stress, at least at the crack tip, must be in the plastic range of the material
o the stress must have cyclically varying intensity.
Brittle materials like glass fracture suddenly, while fibres in composite structures tend to stop
cracking before they develop to any significant length.
Fatigue life can be increased by case hardening, nitriding, cold working and machining.
Fatigue life can be reduced by cladding, decarburising, chrome plating, cadmium plating or
galvanising.
Modern aircraft design allows for serious fatigue cracking, corrosion or accidental damage to occur
while maintaining the necessary strength to carry reasonable loads without failing.
Engineering Studies – Page 34
3.3.2 Analyse structure, property relationship, uses and appropriateness of materials and processes
used in aeronautical engineering applications.
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Aluminium alloys and carbon fibre are used in the aeronautical engineering industry.
Aluminium is soft and ductile and has a low modulus of elasticity.
Carbon fibre is brittle and has a high modulus of elasticity.
Both materials are easily formed around curved surfaces.
Pure aluminium is unsuitable for aircraft structural members as it is too soft and lacks strength.
However, it has very good corrosion resistance. It is often hot rolled onto the surface of an alloy sheet
to provide a corrosion resistant layer. This is called an Alclad composite.
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Aluminium is alloyed with other materials to improve its favourable properties:
o Copper is added to enhance ductility and malleability. Copper also prevents stress cracking
and makes the alloy more shock resistant.
o Manganese makes a surface that is highly resistant to wear and corrosion, and increases
strength.
o Silicon makes the alloy harder but not brittle. It is also easier to cast.
o Magnesium increases corrosion resistance, hardness and weldability.
o Zinc creates a stiffer and more brittle alloy.
The letter H is used to indicate non-heat-treatable alloys that are work hardened.
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3.3.3 Investigate the effects of heat treatment on the structure and properties of aluminium alloys.
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Stabilising is the reduction of residual stresses in a component. It is heated to 250°C, soaked for five
hours and then furnace cooled.
Annealing is similar to stabilising but is soaked a 360°C and cooled in air.
3.3.4 Justify appropriate choices of polymers for their application and use in aircraft.
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Most of the polymers used in the aircraft industry replace materials in an attempt to reduce the
weight of the component.
One of the most common uses for polymers in modern aircraft is to provide the matrix for composite
materials.
The polymer reinforces the fibres together and transfers the load between them.
It also keeps the fibres in the right orientation.
Engineering Studies – Page 35
3.3.5 Describe the uses and application of composites used in aircraft construction.
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The role of fibre reinforcement is to:
o carry the load of the composite
o provide tensile strength, flexural strength and stiffness
o determine electrical and thermal properties.
Almost all fibres have a circular cross-sectional shape.
Fibres are available in continuous and chopped forms. These prepregs must be kept under controlled
conditions until moulded.
Two-dimensional woven fabrics are often used in place of unidirectional tapes for a number of
reasons:
o the product is tougher and less likely to delaminate
o fewer layers of fabric are required, so the component is thinner
o lay-up time is much shorter
o fabrics can be woven from a mixture of fibres to provide a blending of properties.
Any matrix within a composite:
o binds the fibres together
o transfers the load between the fibres and keeps them in the correct orientation
o protects the fibres from abrasion and oxidation
o provides the overall dimensions of the component
o determines the service temperature and compressive strength.
Honeycomb cored sandwich structures have been used in aircraft since the 1940s and the
hexagonally-shaped cells are now often made from composites including Kevlar, fibreglass and
carbon fibre materials. Developments in adhesives have allowed the combination of a variety of
different materials.
Honeycomb sandwich structures are rigid and show low deflection even when very light in weight.
Syntactic cores combine microspheres with a resin matrix. They can fit contoured shapes, and offer:
o greater strength
o no issues with wrinkling of the face material
o continuous support of the face material
o fewer moisture problems.
Flexible hydraulic lines were once neoprene but now have a Teflon inner tube with stainless steel
braided external reinforcement.
Engineering Studies – Page 36
3.3.6 Understand the mechanism of corrosion common to aircraft components and identify corrosion
prevention techniques.
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There are two general forms of corrosion:
o direct chemical corrosion
o electrochemical corrosion.
Different materials are more or less likely to corrode.
Pitting occurs on unprotected metal surfaces when acids, alkalis or saline solutions chemically react
with the metal. Small holes or pits form in the material causing losses in ductility and strength.
Fretting occurs at the junction of highly loaded components subject to vibration. Lubrication can
reduce fretting.
Exfoliation is a form of Intergranular corrosion that occurs at the edge of a metal component that has
been cold worked.
Corrosion may occur due to:
o dissimilar metals coming into contact (electrochemical corrosion)
o heat treatment
o welding
o fretting
o stress
o high temperatures
o electrical equipment
o damaged protective coatings
o surface defects
o crevices.
Engineering Studies – Page 37
ENGINEERING STUDIES
HSC Module 1: Civil Structures
Syllabus Outline
4.1
Historical and Societal Influences and the Scope of the Profession
4.1.1
Describe the nature and the range of the work of telecommunications engineers.
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4.1.2
Examine projects and innovations in the telecommunications profession.
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4.1.3
Broadbanding is related to bandwidth and is concerned with transferring as much data as possible
as quickly as possible.
Compression solutions are being refined by software engineers in the internet industry.
Compressed formats exist for photographs (JPEG), video (MPEG) and music (MP3).
Asynchronous Transfer Mode (ATM) is a refinement of earlier packet switching. It is a protocol for
transferring data.
The asymmetric digital subscriber line (ADSL) features a pair of sophisticated modems: one at the
exchange and one at the end user’s premises.
Broadcast and digital media convergence is the coming together of telecommunications, television,
computing, radio, music and the internet.
Analyse training and career prospects within telecommunications engineering.
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4.1.4
Engineers involved with telecommunications work in one of the most rapidly expanding and complex
fields of engineering.
Examples of telecommunications engineering include:
o transmission media, the material or media in which the signals are transmitted or carried
o transmission and receiving equipment, the equipment which actually converts and transmits
the telecommunications signals
o transmission technology, the methods and protocols by which signals are encoded and
decoded
o switching systems, the methods of connecting and recording the connection of one piece of
terminal equipment to another.
Telecommunications engineers may be involved in:
o research
o design of equipment and systems
o supervising the manufacture of equipment
o installation and commissioning of equipment and systems
o maintenance and upgrading of installed systems
o sales, tender preparation and marketing
Most engineers in the telecommunications industry have a background in electrical engineering or
software engineering.
Research current technology used in telecommunications.
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The earlier plain old telephone system (POTS) used solid copper wire twisted in pairs to run from the
subscriber’s home to the closest exchange.
At the telephone exchange, wires were directly connected to an electromechanical switching system
that then directly connected the subscriber to the desired line.
This is known as circuit switching and occurred in Australia for over 100 years.
Twisted pairs are subject to attenuation (loss) as the length of the wire is increased. Distances of over
3000 metres attenuate the signal significantly. Today, amplification is necessary.
Engineering Studies – Page 38
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Coaxial cable consists of a single conducting material running down the axis of the cable, surrounded
by a dielectric insulating layer. A continuous shield covers the cable to prevent high frequency
radiation from leaking from the cable. A coaxial cable can carry dozens of channels in a single cable.
This means that it has a high bandwidth.
Optic fibre is being increasingly used in telecommunications. It uses the internal reflection of light
down a light guide to transmit signals. The light guide is made from a glass core enclosed in glass
cladding. Optic fibre has a higher bandwidth than coaxial cable.
The glass in optic fibre is very pure. It is possible to transmit a light signal over 100 km in optic fibre
without amplification.
The general formula for decibel gain or loss is:
dBgain/loss = 10 log(gain/loss)
The bandwidth of optic fibre is high because the carrier waveform is light, and the frequency of light
is much higher than the frequency of radio waves.
Wireless technology does not use wires or cables to connect between exchanges. This can reduce the
cost of infrastructure. Common applications use microwave networks, cellular phone systems,
geostationary satellites and low earth orbit satellites.
Ground-based microwave systems have a series of microwave towers spaced at regular intervals.
These must have line of sight to each.
Geostationary or geosynchronous satellites hold a set position above the Earth’s surface.
Large numbers of people now own and operate mobile phones.
The metropolitan area is divided into cells a few kilometres across. Each cell has a base station
operating at a different set of frequencies to nearby calls. The towers operate on low power outputs
so that the operating frequencies can be reused elsewhere.
Originally, analogue systems were used. They required more of the available frequency bandwidth
per channel. Mobile phones now all use digital systems.
Low earth orbit satellites are about 1500 km above the Earth’s surface. Satellites in low earth orbits
are equivalent to mobile phone towers in the sky.
An analogue signal on single copper wire needs to be maintained continuously during a conversation,
and only one conversation may be carried out on that particular line.
With a digital exchange, the connection is not hard wired, but virtual. It is only linked when data is
being sent or received.
o You dial your number, and the computerised telephone exchange notes down where you are
and where you want to call.
o The telephone transmits the signal to the local exchange.
o Your voice is sampled at 8000 Hz.
o The computer sends the sampled conversions into an electronic packet.
o The packet is sent to the destination exchange where it is unpacked and converted back to
analogue.
o The signal is sent down copper cables to the destination telephone.
Engineering Studies – Page 39
4.1.5
Research the history of technological change in the field of telecommunications.
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Early forms of communication required the sender to know the position of the receiver. These forms
of communication were often slow and unreliable.
Modern telecommunications rely on the ability to use and control electricity.
The development of electrostatics for transmission by modulated airwaves provided the final
revolution for the creation of telecommunications systems today.
In 1729, Stephen Gray found that some materials were electrical conductors and others were not.
Charles Du Fay found that some objects repelled each other while others showed attraction.
In 1746, Benjamin Franklin concluded that electricity was a fluid and positive objects had an excess
of this fluid and negative objects had a deficiency. Franklin also showed that lightning was electricity.
Later work introduced electrons and showed that positive objects actually had a deficiency of charge.
In 1785, Coulomb formulated the laws of attraction and repulsion between charged bodies.
In 1786, the first observations that were to lead to the invention of the battery were made. A freshly
killed frog was made to twitch due to the reaction between two dissimilar metals.
Allessandro Volta discovered that two different metals connected by a conducting liquid could
produce electricity. He produced the voltaic pile, the first battery.
In 1820, Hans Örsted noted that a strong current passing through a wire would move the needle of a
compass held near it. This discovery was electromagnetism.
The concept that electricity could produce electromagnetic waves that would travel without a
conductor at the speed of light was first suggested by James Maxwell. In the late-1880s, Heinrich
Hertz produced these waves.
In 1897, Joseph Thompson confirmed the existence of electrons.
In 1913, Robert Millikan measured the exact charge on an electron.
In 1904, John Fleming built the firs vacuum tube which allowed for thermionic emission and
transmission.
Telegraph communication was the first form of messaging to use electricity. It was the dominant form
of communication for over 100 years.
Crooke and Wheatstone in England and Morse and Vail in the US invented the telegraph
simultaneously. The telegraph used wires to provide electrical energy to five needle pointers which
would point to the letters of the alphabet.
The first public use of this system was in 1844.
The Morse telegraph generated a sound by closing metal contact points, and was simple and reliable.
This became the preferred system.
Later, positive and negative impulses would be sent instead.
The first telegraph sending and receiving instruments could transmit one message at a time. In 1871,
JB Stearnes developed a duplex transmission system that allowed sending and receiving messages to
occur simultaneously. This was an early form of multiplexing.
In 1918, modulated carriers were used to pass messages along telegraph lines. By varying the
frequency of these carriers, it became possible to send, receive and separate many messages
simultaneously.
Business requirements lead to the introduction of teletype in 1924. Messages were sent and received
immediately in printed form, removing the need for an operator. A special typewriter was used.
The facsimile telegraph was perfected in the 1930s for transmitting graphic information such as
photographs.
Telephones allow people to talk to each other. The telephone was developed by Alexander Graham
Bell.
The original Bell telephones were sold in pair and connected together directly like an intercom.
To simplify the network, telephone exchanges were built so that a user, linked to the exchange could
be connected to any business or other user that was also linked to the exchange. The last manual
exchange in Australia was closed in 1991.
In 1891, AB Strowger patented an automatic dialling system.
In 1878, the first telephones appeared in Melbourne.
Trunk lines between Sydney and Melbourne and Melbourne and Adelaide were opened in 1907 and
1914 respectively.
By 1957, nearly all telephones in capital cities were connected to automatic exchanges.
Engineering Studies – Page 40
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Microwave technology allows broadband, high quality communications. In 1958, the first microwave
trunk link was established between Melbourne and Bendigo. Microwave radio relies on line of sight
transmitting and receiving and therefore uses tall towers on high terrain.
The COMPAC transpacific undersea cable was opened in 1962.
A telephone consists of a dialling mechanism, a transmitter and a receiver.
o The dialling mechanism enables contact with a particular subscriber. At first, dial telephones
used a coded sequence of electrical pulses created on a rotary dialling mechanism.
o Modern telephones use a keypad to create a coded sequence of tones that establishes an
electrical connection with the required phone.
o The transmitter is a microphone in the handset.
o When speaking into a carbon microphone, sound waves cause a thin round aluminium
diaphragm to vibrate, which acts on a chamber containing small grains of carbon. Electrical
contacts on either side of the chamber allow a low voltage to pass through the carbon. When
the grains are compressed by the vibration, more current is allowed to pass through.
o Modern telephones use foil electret microphones which are smaller and more sensitive. They
use a diaphragm and a backing plate. An electric field is established between the diaphragm
and backing plate. Vibrations change the strength of the field and these correspond to changes
in an electric current for transmission along a telephone line.
o The receiver consists of an iron diaphragm with a permanent magnet around it. The varying
electrical signal creates a magnetic pull on the diaphragm from the electromagnet and this
causes the diaphragm to vibrate.
Modern telephones have relied on multiplexing systems to allow many connections simultaneously
through one line.
The cordless telephone and mobile telephone use radio signals to remove the need for a physical
connection.
The first mobile telephones appeared in the 1930s, but they were large and heavy. Improvements in
miniaturisation have allowed the transformation of these devices.
In the early-1800s, Joseph Henry and Michael Faraday showed that a current travelling along one
wire could produce a current in another.
Hertz proved the existence of these waves using a loop of wire.
Radio waves are reflected by the ionosphere and bounce back to Earth, allowing their transmission
around the globe.
By 1905, radiotelegraphy between ship and shore was becoming common.
In 1918, radio transmission was fully realised with the development of the super heterodyne circuit.
This increased selectivity and sensitivity.
Television is the transmission of pictures as well as speech by radio waves.
Telecommunications are now controlled by a computer or microprocessor.
The change from analogue to digital transmission is now underway.
Mobile phones use digital communication.
Engineering Studies – Page 41
4.2
Engineering Materials
4.2.1 Analyse structure, properties, uses and appropriateness of materials in telecommunications
engineering applications.
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The voltage (V) of a circuit is measured using a voltmeter. It must be placed in parallel to the
component it is measuring. The voltmeter has a high resistance so that almost no current flows
through it.
The cathode ray oscilloscope is an important measuring instrument in electronics.
Current (I) is the number of electrons moving from one point to another. The current, in amps (A), is
measured by an ammeter. It must be connected in series with the component it is measuring. The
ammeter must have a very low resistance.
Specialised non-destructive tests have been developed to assess the condition of electrical insulation.
A Megger test measures:
o the relative amount of moisture in the insulation
o leakage current over the dirty or moist surface of the insulator
o winding breakdowns or faults as a measure of resistance versus time.
The Megger meter uses a high DC voltage applied to the insulator. Small amounts of current will be
conducted within the structure of the insulator and may leak to the surface. When a voltage is applied,
readings are taken of the insulation resistance and graphed against time.
The insulating qualities of a material can be measured by an ohmmeter.
The lower the resistivity of a material, the smaller the amount of material that is needed to carry
current. It also means there is less insulating material needed because the wires are thinner,
sheathing costs are lower and transport costs are reduced.
For a material to be made into wire, it must exhibit ductility and be able to withstand tensile stresses.
Joining conductors may be achieved by twisting, soldering or welding.
Copper has traditionally been used for communications wires and cables, because it is ductile, has
suitable tensile strength and is a good conductor.
Electrolytic tough pitch copper is used for wires. This has a minimum copper content of 99.9 percent.
Cadmium increases the strength and wear resistance of a copper cable without significantly altering
the electrical resistance.
Aluminium is lighter, less expensive and more abundant than copper.
It is normally used for aerial power transmission cables, but is not as conductive as copper.
Aluminium is also poorer in ductility, tensile strength, joining properties and corrosion resistance.
Aluminium alloys are sometimes used for cables. A common alloy is 99%Al/0.5%Fe/0.5%Co.
The conductivity of gold is similar to copper. It is normally used as linkage in semiconductor devices.
Gold is ductile and does not oxidise.
The outer layer of communications cables is the sheath and is designed to create a stable environment
for the core. Lead has good corrosion resistance, good strength and flexibility. It has been replaced by
polymers because lead suffers from fatigue failures, is heavy and expensive. It is also toxic.
Polyethylene has superior insulation resistance to paper and is suitable for high frequency cables. It
is, however, costly and has a low softening temperature. It also allows water vapour to penetrate and
is difficult to join.
Polyvinyl chloride (PVC) has poor electrical properties but is tougher and withstands higher
temperatures than polyethylene.
Polypropylene is tougher than polyethylene.
Nylon is used as an insect resistant outer layer on cables that are used underground.
4.2.2 Describe the uses and applications of polymers and fibre optics in telecommunications.
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Polyvinyl chloride (PVC) has poor electrical properties but is tougher and withstands higher
temperatures than polyethylene.
Polypropylene is tougher than polyethylene.
Nylon is used as an insect resistant outer layer on cables that are used underground.
Typical optical fibres are very fine fibres of glass made of pure silica. The cladding of the cable has a
different refractive index to the core, which causes the light energy to be refracted off the corecladding interface.
Engineering Studies – Page 42
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Only silica glass and some polymers are suitable for use as optical fibres.
The light used in fibre optic systems is normally at the red end of the spectrum. This is less susceptible
to attenuation in the glass. The light is generated by a semiconductor laser made from gallium,
aluminium or arsenic.
Any decrease in the intensity of the light in an optic fibre is known as attenuation. This occurs because
of:
o atomic absorption of the light by the glass
o the scattering of light by flaws and impurities
o the reflection of light by splices and connectors.
To overcome attenuation, the signal is boosted at regular intervals.
Optical fibres are:
o lightweight
o have very wide bandwidths
o are not affected by electromagnetic interference because glass does not conduct electricity
o glass does not spark like metals
o it is more secure than coax
o it is inert in corrosive environments
o the raw materials are relatively inexpensive.
Optical fibres are made by modified chemical vapour deposition. A pure silicon tube with a high
refractive index is filled with a special gas and heated by an external heat source. This deposits an
inner layer of silicon dioxide with 10% germanium oxide. The composite tube is heated to 2400°C
and collapsed to achieve a solid cored fibre.
Glass fibres are passed through a bath of molten polymer to form a protective outer skin.
A loose polymer sleeve may be fitted and the gap between the sleeve and the fibre filled with a gel
material.
To protect cables from tensile stress during insulation, internal strength members can be added when
multiple fibre cables are constructed.
In a step-index fibre, the refractive index is constant within the core and steps to a lower value
towards the cladding.
Engineering Studies – Page 43
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In a graded-index (multimode) fibre, the refractive index of the core changes from the centre
outwards. The refractive index of the core is proportional to the square of the distance from the
centre.
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Polymers can be formed into optic fibres, but suffer from greater attenuation. Polymer fibres are
usually of the multimode step-index type.
Common examples include:
o polystyrene core with polymethymethacrylate cladding
o polymethymethacrylate core with fluoro alkyl methacrylate cladding.
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4.3
Engineering Electricity and Electronics
4.3.1 Describe the basic concepts and
telecommunications.
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application
of modulation and
demodulation
in
The performance of a telecommunications network is generally governed by:
o the power of the signal being transmitted
o the power of the electrical noise in the system
o the bandwidth of the system
An analogue signal is continuously variable in amplitude and time.
Digital signals can only be one of a set number of possible levels.
Sampling of an analogue signal means taking a series of measurements at regular instants in time.
Quantisation is the process of approximating a measurement of amplitude by the nearest value from
a set of possible values.
The time domain representation of a signal shows the amplitude of the signal as it varies with time.
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All telecommunications links contain electrical noise. Electrical noise is signals that are undesirable
in the system.
The size of a radio antenna is a function of the wavelength of the signal it is designed to transmit or
receive.
The wavelength of a signal also determines its ability to propagate over and around objects in its path.
An object whose principal dimensions are the same as or larger than the wavelength of the signal will
effectively block it.
Sources of electrical noise include interference from other electrical appliances such as fluorescent
lights and electric drills, nearby lightning, radio signal interference and faulty connections.
Electrical noise is usually measured in terms of its amplitude relative to the signals of interest.
An analogue signal is more susceptible to noise than a digital signal. The process of reconstructing
the original digital signal from a received noisy digital signal is called regeneration.
The main benefits of digital transmission are:
o immunity to noise
o cost of digital equipment
o channel capacity utilisation
o security
o privacy
o integration of formats
Bandwidth is the range of frequencies that can be sent through the link. The bandwidth of a
communications link is dependent on its electrical and electronic properties.
Signal power is a measure of the power of the signal that is sent across the link. Noise power is a
measure of the electrical noise or interferences in the channel.
In order to avoid errors in transmission across a channel:
o the power can be increased
o the electrical noise can be decreased
o the bandwidth of the system can be increased.
Most images use a digital format. In digitising an image, it is sampled at regular intervals down and
across the image. Each of the samples is called a picture element, or pixel.
The sampling of an image is normally measured in pixels per unit distance. A common unit is dots per
inch (dpi).
The RGB system measures relative quantities of red, green and blue at each pixel.
Baseband is used to describe a telecommunications system in which the message to be sent is
converted directly to an electrical signal and then sent over a cable to its destination.
A baseband link only requires the signal to be converted to an electrical impulse, transmitted and
then converted back into the signal.
A carrier wave is a pure sinusoidal wave at some predetermined frequency.
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In amplitude modulation, the amplitude of the carrier wave is varied to carry the message signal.
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Demodulation is the process of separating the message signal and the carrier wave at the receiving
end.
AM transmission is relatively cheap, but the quality of the sound if not as good as FM.
AM demodulation is achieved with an envelope detector. A diode is used to select only one half of the
modulated signal. A resistor and capacitor together form a smoothing filter that extracts the envelope
of the signal from the modulated carrier.
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Frequency modulation involves varying the frequency of the carrier wave to transmit information.
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FM radio is less susceptible to noise because the signal to noise ratio is reduced.
The circuitry for FM demodulation is more complex and expensive than AM.
FM is used for the sound track on televisions and for some radio stations.
Phase modulation (PM) varies the instantaneous phase, or angle, of the carrier wave to represent the
message.
Amplitude shift keying (ASK) involves switching the carrier wave between two different amplitudes.
In more sophisticated systems, multilevel ASK may be used.
Frequency shift keying (FSK) involves switching the carrier wave between two or more frequencies
to convey information.
Phase shift keying (PSK) uses different phases of the carrier wave to convey digital data.
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More commonly, several keying schemes are used concurrently.
4.3.2 Describe the types and methods of radio and digital television transmission and reception
systems in telecommunications.
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The electromagnetic spectrum describes all of the frequencies used for telecommunications.
It is illegal to transmit information in bands for which you are not licensed.
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Guided media refers to transmission media that carry signals along a conductor.
Unguided media transmit signals through air or space.
A twisted pair cable is two parallel insulated copper wires that are twisted together. The interweaving
reduces electrical noise.
Multiple pairs of wires may be twisted together into a single cable.
The most common way of using the mains power to switch on off-peak devices is audio frequency
injection, or ripple control. This involves sending coded pulses of audio frequency signals along the
power lines. This is amplitude shift keying.
Waveguides are a special cable used for high frequency signals. Current has a tendency to concentrate
close to the surface of conductors. A waveguide is a hollow rectangular metal tube.
Mobile communications use microwaves, VHF and UHF ranges.
Navigation systems use VLF, LF, VHF and UHF ranges.
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ENGINEERING STUDIES
HSC Module 1: Civil Structures
HISTORICAL AND SOCIETAL INFLUENCES
Beam Bridges
A beam is a member that is supported in such a way that the supports do not carry longitudinal forces. Beams
that are supported at both ends are called simply supported beams. Beams that are supported at one end only
are cantilevered beams. A beam is not necessarily solid; it may be a truss or a tube. The Greek historian Herodotus
wrote of a multispan beam bridge in Babylon in the fifth century BC. Early beam bridges used timber. In 55 BC,
Julius Caesar built a 550 m long wooden beam bridge that incorporated 50 spans. By 1570, Italian architect
Andrea Palladio had developed a truss girder bridge. In the nineteenth century, English engineer James Warren
developed a truss girder bridge that would be extensively used by railway engineers.
In America in 1820, Ithiel Town developed a truss girder bridge with diagonals and in 1847, Squire Whipple
developed the iron truss. He also pioneered a method for determining the force in each member of a truss. In
1849, Robert Stephenson developed the bowstring girder, which consisted of an arch, the bow, and a horizontal
tie, the string, that constrained the bow from spreading. Stephenson designed the bowstring girder for his high
level bridge to cross the River Tyne at Newcastle. In 1850, Stephenson collaborated with others to develop the
Britannia Bridge to carry the railway over the Menai Straight in Wales. It consisted of wrought iron tubes that
trains could run through. In 1867, Heinrich Gerber built the first cantilever bridge, the Forth Bridge in Scotland.
1948 saw the development of one of the most commonly used beam bridges today: the box girder bridge. This
bridge is a tube with a rectangular cross section stiffened by a series of internal walls, creating a box. Bridges
may use a box girder on each edge of the roadway, or there may be a central girder with the roadway forming
cantilevers on each side.
Arch Bridges
Arch bridges date back thousands of years. There are a number of different designs of arch bridge.
Stone Arch Bridges
The stone arch bridge was extensively used by Roman engineers from about 200 BC to 400 AD. After the fall of
the Roman Empire, Europe entered the Dark Ages, a period of little learning. Much of the information on Roman
technology and engineering was lost. Medieval bridges were not up to the standard of Roman bridges. London
Bridge was typical of these and its 276 m length consisted of 20 spans, between 7.5 and 10.4 metres in length.
The Renaissance followed the Middle Ages and bridge development started in earnest. Renaissance designers
developed lower arches to reduce the height of bridges. Low arches put much larger loads on the piers, but this
is offset by the adjacent pier pushing in the opposite direction. The load on the abutments is still very high. If an
arch bridge is to be built over a low bank river on flat ground, the challenge is to attain very low rise.
Cast Iron and Steel Arch Bridges
Although some societies had entered the Iron Age by about 1500 BC, the Europeans could not yet melt iron and
cast it. Cast iron was not widely used until the Industrial Revolution in about 1750. Cast iron has similar
properties to stone being strong in compression and weak in tension. However, cast iron arch bridges can be
made with an open frame, which reduces their weight compared to stone arch bridges. The first cast iron arch
bridge was the Coalbrookdale Bridge over the River Severn in Shropshire in 1779. Steel later replaced cast iron
in the manufacture of arch bridges.
Concrete Arch Bridges
Concrete is now the most commonly used material in bridge design. It is very strong in compression and so is
ideal for arch bridges. With steel reinforcing, it is suitable for beam or cantilever use. As a concrete bridge sets,
which can take up to a year, the bridge shrinks. Steel arch bridges are built with hinges at each end. Concrete arch
bridges have a third hinge in the middle to allow for shrinkage. This design was first suggested by Robert Maillart
and put into practice on the bridge over the River Inn in Switzerland in 1901. In 1904, Eugene Freyssinet
hypothesised prestressed concrete but it could not be manufactured until after high tensile wire was developed.
Engineering Studies – Page 48
Suspension Bridges
Suspension bridges support the deck on steel cables strung between support towers. The cables are always in
tension. Suspension bridges can be made more lightweight than any other type of bridge and thus can offer longer
spans. Early suspension bridges suffered from a lack of lateral stability. The remedy for this was to use a stiffened
deck hanging from the suspension cables with wire ropes. Thomas Telford built the first successful large-scale
suspension bridge over the Menai Strait in Wales. John Roebling was responsible for the introduction of wire
cables instead of chains when he designed the Brooklyn Bridge. After the failure of the Tacoma Narrows Bridge,
engineers returned to building rigid decks. Twenty-six years later, British engineers devised a better solution for
the Severn suspension bridge. Gilbert Roberts experimented with a finned design that would better deflect side
loading from the wind. Cable-stayed bridges are a type of suspension bridge except that the cables from the deck
each attach directly to the vertical columns.
Composite Bridges
Recently, advanced composite materials in the form of fibre-reinforced polymers have found application in
bridges. Composites are being increasingly used in applications ranging from reinforcing rods and tendons,
wraps for seismic retrofit columns and externally bonded reinforcement for strengthening of walls, beams and
slabs, composite bridge decks and structural systems. One of the most important considerations in bridge decks
is the how the weight correlates to the loadbearing capacity. Composite materials also
provide structural strength, corrosion resistance
and reduced ongoing maintenance. However,
research into composite materials is ongoing, so
engineers are cautious about their use in bridges.
Orthotropic Deck Plates
Orthotropic deck plate construction uses stiffened
steel slabs. Plain carbon steel plate, stiffened by
cells or ribs forms the basis of both the crosswise
girders and the longitudinal main girders.
Stiffeners are placed on the inside so as to achieve
a smooth outer surface, reducing the
accumulation of dust or dirt deposits.
Moveable Bridges
It is often inconvenient of excessively costly to build a bridge over a waterway high enough not to impede the
flow of water traffic. There are three such bridges in Sydney:
 The Pyrmont Bridge at Darling Harbour was originally a road bridge, then later a pedestrian and monorail
bridge, and now a pedestrian only bridge. It opens by rotating on a turntable. It is the last example of an
early DC electric powered opening bridge.
 The Spit Bridge in the northern suburbs of Sydney opens by raising a cantilevered opening section of the
bridge through an angle of 90 degrees to allow watercraft through.
 The Ryde bridge opens by the centre section being raised up by a gear system on a set of runners.
Engineering Innovations in Civil Structures and their Effect on People’s Lives
Invention is the development of something entirely new. Innovation means making an alteration to something
that has already been invented and improving upon it.
Summary of Engineering Innovations in Civil Structures
 From 10000 BC, primitive beam and suspension bridges allow transport across rivers and ravines.
 Greek development of the beam bridge improves transportation for human- and animal-drawn traffic.
 Roman engineering produces the arch bridge, which was a more stable and secure bridge than those
which preceded it and could span longer distances, which improved transportation of human- and
animal-drawn traffic and water transport.
 The Dark Ages caused receded development and more inefficient designs.
 From the 1600s, truss girders improve beam bridge design and allow for longer spans, causing greater
safety and allowing for fewer pylons.
Engineering Studies – Page 49
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Renaissance development improved arch bridge design and allowed for lower arches, reducing the
amount of stone required and the impedance of the river.
James Finlay in the 1800s designs the first modern suspension bridge, allowing long spans and little
impediment to water traffic.
From the 1800s, the bowstring girder is embraced by railway engineers for being cheap and simple to
manufacture
From the 1900s, box girders are used in freeway construction.
From the 1900s, cantilever bridges allow longer spans and less impediment to water vehicles.
The Brooklyn Bridge is the first bridge to use steel cables, which improved safety.
Concrete is used as a building material for engineering.
The Sydney Harbour Bridge is completed and reduces travel times north and speeds development into
northern Sydney.
The Tacoma Narrows Bridge failure shows the dangers of poor design and a lack of forward thinking and
leads to safer suspension bridges.
The Severn Suspension Bridge is constructed with a streamlined cross section to deal with wind.
Akashi Kaikyō Suspension Bridge opens in 1998 and is the longest spanning bridge in the world, at 1991
metres.
Construction and Processing Materials used in Civil Structures
Bridge development has been facilitated by the development of different materials that have proved suitable in
bridge construction.
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Timber was used in the earliest bridges. It offered ease of manufacture and was a readily available
resource. Over time, it rots and disintegrates away.
Rope was used in early suspension bridges. Over time, it rots and disintegrates away.
Stone was used in Roman arches and was a more permanent building material than timber or rope. Stone
is strong in compression but weak in tension.
Bricks are sometimes used in bridge manufacture. They have similar properties to stone.
Cast iron began to be used in bridges by the late-1700s. Like stone, it is weak in tension but strong in
compression. It can be melted and cast, which saves time and money. Cast iron bridges could be made of
frames which provided a strength equal to stone but with greatly reduced weight.
Wrought iron was used in early suspension bridges. Wrought iron was unreliable due to the fibrous
structure present in ferrite. When wrought iron was replaced with steel, suspension bridges could be
built much longer.
Steel was mass produced by Henry Bessemer in 1856. Steel was used in steel arch bridges and steel cables
could be used in suspension bridges which allowed greater spans to be achieved. At the beginning of the
1900s, steel was used to reinforce concrete.
Concrete was not used in bridges until the shrinkage problem was addressed by the third hinge. Due to
its weakness in tension, it is only used in reinforced steel. Most new bridges use concrete of some type.
Stainless steel is now being used in some bridges.
Environmental Implications of Materials used in Civil Structures
Since all building materials are derived at some stage from the Earth, there will always be some impact when the
raw materials are gathered.
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Timber was used as a source of heat for steam power and as a building material which resulted in
deforestation in surrounding areas. Trees take centuries to grow and old growth forests have never
recovered from the logging.
Ancient and medieval cultures mined stone by digging large quarries which scarred the landscape and
impacted natural flora and fauna.
Bricks require a large amount of clay and shale to manufacture so large pits were dug to find these
materials. Often the brickworks were alongside the pit. Subsidence is often a problem on old brick pit
sites.
Cast and wrought iron require the combustion of fossil fuels. These required iron to be mined and smelted
which used a large amount of energy.
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Steel has a greater impact on the environment than cast and wrought irons due to its proliferation
through more industries. Steel has allowed longer bridges to be built.
Concrete requires vast amounts of minerals to manufacture it such as sand, aggregate and cement.
Worldwide environmental concern has created the need for engineers to minimise the environmental impact of
a variety of materials in relation to production, construction, maintenance and demolition, and recycling or
disposal. The major environmental impact of bridges is the materials used in their construction.
The impacts of steel include:
 large amounts of water used in the steel-making processes for cooling
 quenching and pollution control
 production of toxic materials associated with the manufacture of coke used in blast furnaces
 abundance of toxic chemicals used in steel making
 galvanised steel can be a source of zinc contamination of the surrounding soil.
The impacts of concrete include:
 concrete can be recycled as aggregate only
 over six times more material is required to produce a concrete superstructure than is required for a steel
superstructure.
Maintenance
The viability and integrity of bridges depends on the continual rehabilitation and maintenance of the existing
structure. In such activities, a wide variety of materials including steel, asphalt, concrete, petroleum-based
sealants, wood preservatives and additives are used. During wet weather, there is a potential for leaching of the
chemical constituents in these materials and the possibility of transport to adjacent surface and subsurface water
bodies. Potentially toxic chemicals from these materials may result in adverse environmental effects.
ENGINEERING MECHANICS
Truss Analysis
Since the development of the truss, it has
become one of the most important
engineered structured. Trusses are built
on the strongest geometric shape, the
triangle. Solving any problem involving a
truss usually involves finding the
reactions at the supports.
Engineering Studies – Page 51
Determining the Reactions at the Supports
Determine the reaction at each of the supports in the above truss.
ΣM𝐴 ↷+ = 0
0 = 50 × 10 + 30 sin 45° × 20 − 𝑅𝐵 × 30
30𝑅𝐵 = 500 + 424.26
𝑅𝐵 = 30.8 kN ↑
ΣF𝑉 ↑+ = 0
0 = 30.81 − 50 − 30 sin 45° + 𝑅𝐴𝑉
𝑅𝐴𝑉 = 40.40 kN ↑
ΣF →+ = 0
0 = −30 cos 45° + 𝑅𝐴𝐻
𝑅𝐴𝐻 = 21.21 kN ↑
𝑅𝐴 = √40.402 + 21.212
= 45.63 kN
40.40
tan 𝜃 =
21.21
𝜃 = 62.3°
∴ 𝑅𝐿 = 45.63 kN ↗ 62.3°
𝑅𝑅 = 30.8 kN ↑
Analysing Truss Members
Although a truss is considered as a beam to determine the reactions at the supports, the frame that is the truss
also contains forces. The framework allows the truss to span greater distances than a simple beam and can
support a greater load. There are two methods for determining the reactions in the supports of a truss: method
of joints and method of sections. For these analyses, the assumption is that each joint of the truss is pinned, and
they can rotate in relation to each other. This ignores any moment in the joint. In reality, truss joints are usually
welded, riveted or bolted in such a way that rotation is prevented which complicates truss analyses.
Method of Joints
Consider the truss loaded as shown right. To find the
force in members AF and EF, examine joint AEF.
Engineering Studies – Page 52
270
𝐸𝐹
270
𝐸𝐹 =
tan 60°
tan 60° =
= 155.88 N (tension)
270
𝐴𝐹
270
𝐴𝐹 =
sin 60°
sin 60° =
= 311.77 N (compression)
The tension and compression are found by looking at the force and the way it travels. If the force is moving away
from the joint, that is, stretching it, then the member is in tension. If the force is moving towards the joint, that is
squashing it, then the member is in compression.
To find the force in members FG and BG, examine joint ABFG.
This should be determined graphically.
Note that the accuracy of the answer is
dependent on the scale and precision to
which it is drawn.
∴ 𝐹𝐺 = 35 N (compression)
𝐵𝐺 = 136 N (compression)
Method of Sections
The method of joints is a viable option for determining the reactions in truss members, however, it can be slow,
particularly if the members are in the middle of the truss. Consider the same truss as above.
The principle of this method is based on the fact that the whole truss is in equilibrium. If the truss is ‘cut’ through
at least two members the remaining system will also be in equilibrium. To solve by method of sections, pass a
section plane through the truss that cuts the members in which the force needs to be found. Consider the cut
members as external forces of one half of the truss.
Engineering Studies – Page 53
Consider the left side of the truss only. To find the force in BG, take moments.
ΣMP ↷+ = 0
0 = 270 × 1 + 300 × 0.5 − 𝐵𝐺 ×
√3
2
√3
𝐵𝐺 = 120
2
𝐵𝐺 = 138.56 N (compression)
It can be seen that the initial estimate for the direction was correct as the answer is positive. Now, to determine
the force in FG, use the sum of the vertical forces, because it is the only cut member with a vertical component.
ΣF ↑+ = 0
0 = 270 − 300 + 𝐹𝐺 sin 60°
𝐹𝐺 sin 60° = 30
𝐹𝐺 = 34.64 N (compression)
Now, to find the force in FE, use the sum of the horizontal components as it is the only force remaining.
ΣF →+ = 0
0 = 𝐹𝐸 − 138.56 − 34.64 × cos 60°
𝐹𝐸 = 155.88 N (tension)
Bending Stress Induced by Point Loads
Whenever a nonaxial acts on a beam there will usually be some bending that takes place. This force creates
bending stress that is a measure of the beam’s internal resistance to bending.
Shear Force
The shear force at any point on a beam is the algebraic sum of all the external forces on one side of the beam. The
shear force is actually the internal reaction at a given point along a beam of the material to being sheared apart
by external forces.
Bending Moment
The bending moment at any point along a beam is equal to the total moment developed at that point by the
external force system. If moments are summed at a given point along a beam that is in equilibrium, the value will
be zero.
Engineering Studies – Page 54
Calculating Shear Force
Calculating shear force involves progressively working along the beam summing the external forces to determine
the shear force.
Calculating Shear Force and Maximum Bending Moment
Calculate the shear force and bending moment at each of the points in the diagram above.
Calculating the Shear Force at Point 1
Assume that the shear force at Point 1 is downwards.
ΣFV ↑+ = 0
0 = 20 − SF1
SF1 = 20 kN ↓
Calculating the Shear Force at Point 2
Assume that the shear force at Point 2 is upwards.
ΣFV ↑+ = 0
0 = 20 − 40 + SF2
SF2 = 20 kN ↑
Calculating the Bending Moment at Point 1
ΣM1 ↷+ = 0
0 = 20 × 1 − BM1
BM1 = 20 kNm
Engineering Studies – Page 55
Calculating the Bending Moment at Point 2
ΣM2 ↷+ = 0
0 = 20 × 3 − 40 × 1 − BM2
BM2 = 20 kNm
Calculating the Maximum Bending Moment
The bending moments at these points are not, however, the maximum values. Engineers are concerned with
the maximum shear force and bending moment, because this is where the stress will be the greatest. In this
beam, the maximum bending moment occurs at the 40 kN force.
Shear Force Diagrams
Consider the beam below. To draw a shear force diagram, draw on each external force, and then link them with
horizontal lines.
Thus, it can be seen that the resulting shear force diagram is as below.
Engineering Studies – Page 56
Bending Moment Diagrams
Bending moment diagrams can be calculated by either summing up moments about active and reactive forces, as
above, then drawing a diagram, or by using the area under the curve from left to right of the shear force diagram.
The Neutral Axis and Outer Fibre Stress
When a beam is subjected to bending, not all of the beam undergoes the same types of stress. When a beam
undergoes positive bending, the upper surfaces will be in compression and the lower surfaces will be in tension.
This means that there must be a section of the beam that is undergoing no stress. This is called the neutral axis.
The greater the distance from the neutral axis, the greater the stress present. The relationship between bending
stress and other characteristics may be expressed as
bending moment in section (Nm) Young ′ sModulus for the material (Pa) bending stress at section (Pa)
=
=
second moment of area (mm4 )
radius of the curvature (m)
distance from neutral axis (m)
𝑀 𝐸 𝜎𝐵
= =
𝐼
𝑟
𝑦
The most used form of this relationship is
𝜎𝐵 =
𝑀𝑦
𝐼
The radius of curvature is a measure of the curve the beam takes on when
loaded. The smaller the value, the more bowed the beam is. It is not
constant and is affected by the bending moment at that point of the beam.
The second moment of area (I) is a measure of the resistance of a beam to
bending. The formula for the second moment of area for most crosssectional shapes is very complex. The value of the second moment of area
will always be provided in examination situations.
Uniformly Distributed Loads
Unlike a point load, a uniformly distributed load (UDL) is a load that is
evenly spread across a beam. Examples of uniformly distributed loads
include wind blowing against a building and a fish tank on a shelf. When a
beam is placed on supports, the beam itself has a mass that acts on the
supports.
Uniformly distributed loads generated angled lines on shear force
diagrams and curves on bending moment diagrams. In most UDL
situations there will be a mix of uniform and point loads. These are shown
in the diagram on the right.
Engineering Studies – Page 57
Stress and Strain
Stress is a measure of the internal reaction that occurs in response to an externally applied load. This internal
reaction is related to the original cross sectional area to quantify the nature of the reaction.
load
cross sectional area
𝑃
𝜎=
𝐴
stress =
Strain is the proportional change in length caused when a specimen is under axial load.
strain =
𝜀=
extension
original length
Δ𝐿
𝐿
In mechanically elastic structures such as bridges and buildings, stress is directly proportional to strain.
Shear Stress
Shear stress is a measure of the internal reaction to a shearing force. If the shear plane runs perpendicularly
across the object, the shear area will be the cross sectional area. However, if the shearing operation punches a
hole, then the shear force will be the area of the outside of the hole.
𝜎𝑠 =
𝑃
𝐴
Engineering and Working Stress
Stress strain curves generally fall away towards the end of the curve. This is because they show engineering
stress. Engineering stress is calculated with the load always divided by the original cross sectional area, even
though the cross sectional area reduces before failure. This type of stress does not take into account the change
in cross sectional area. The term used to describe the actual stress is true stress.
Maximum allowable stress, or safe working stress, may be defined as the maximum permissible stress than a
material or object will be subjected to in service. Working stress is usually less than the yield stress and the
ultimate tensile stress. The ratio of working stress to yield stress or UTS is called the factor of safety.
Related Terms and Definitions
Elastic Limit
The elastic limit is the stress up to which the strain is elastic. This means that if the load is removed, the object
will return to its original dimensions. Beyond this point, permanent plastic deformation occurs.
Yield Stress
Yield stress is the stress where there is a marked increase in strain without a corresponding increase in stress.
In mild steel, there are definite yield points, but most materials show a progressive yield. The yield stress is
always greater than the elastic limit, but less than the UTS.
Resilience
Resilience is the amount of stress necessary to bring about a certain amount of permanent strain in the material.
Proof stress is a measure of yield on materials that do not show a marked yield point. Usually a set amount of
strain is given such as 0.2% and the amount of stress necessary to record this strain is recorded.
Engineering Studies – Page 58
Toughness
Toughness is a measure of the ability of a material to absorb energy. Tough materials are capable of absorbing
strain energy or the energy of an impact and are the opposite of brittle materials. Toughness is found by
calculating the area under a stress/strain curve.
Hooke’s Law
Hooke’s Law states that stress is proportional to strain up to the elastic limit. This means that any increase in
stress will bring about a proportional increase in strain up to a given point. Mathematically, Hooke’s Law is
𝐸=
𝜎
𝜀
where 𝐸 is a constant
Young’s Modulus (modulus of stiffness)
Young’s Modulus is represented by the constant in Hooke’s Law. Mathematically, it is given as
𝑃⁄
𝜎
𝐴
𝐸= =
𝜀 Δ𝐿⁄
𝐿
𝑃𝐿
𝐸=
Δ𝐿𝐴
Factor of Safety
Factor of safety is the ratio of safe working stress to either yield stress or ultimate tensile stress, depending on
the type of material. It is a very important consideration in designing equipment.
For ductile materials:
factor of safety =
yield stress
maximum allowable stress
For brittle materials:
factor of safety =
ultimate tensile stress
maximum allowable stress
Stress/Strain Diagrams
Engineering Studies – Page 59
ENGINEERING MATERIALS
Testing of Materials
Type of Testing
Test
visual inspection
x-ray
non-destructive
dye penetrant
ultrasonic
tensile
compressive
destructive
transverse
torsional
Use
identifying where failure is most likely to occur or where
failure has already begun to occur
determining if cavities are present
finding small cracks in the surface by placing dye on the
surface, applying a developer and then examining (UV light
may be used)
ultrasonic pulses are used to determine if cavities are present
used to determine the tensile strength of a material; test piece
is stretched and the load and extension recorded
used to determine the compressive strength of a material; test
piece is compressed and load and deformation recorded
used to determine the performance of a material when
undergoing bending or shear
used to determine how a material will cope with twisting
forces (couples)
Testing of Concrete
Slump Test
The slump test is used to check that the concrete is of appropriate fluidity for casting. The concrete is cast into a
cylindrical mould, open at the top and bottom. The mould is then placed on a board and the concrete poured in.
Upon removal of the mould, the conical wet concrete that is remaining should slump slightly according to set
specifications. If it collapses, the concrete is too wet; if it breaks in half then crumbles, it is too dry.
Compressive Test
Concrete is strong in compression and after casting various specimens will be taken and subjected to
compression testing after specific time intervals. If the concrete fails any of the tests, then the material was a
faulty mix and it may need to be recast.
Crack Theory
Stress concentration can have a large impact on the behaviour of a material or object in service. In 1920, AA
Griffith published a paper explaining that the practical, mechanical strength of a material is lower than its
theoretical strength due to irregularities in the surface that cause stress concentrations and then cracks. The way
cracks form and grow is related to the applied stress and present strain energy.
Strain energy is closely related to potential energy and is a measure of the amount of energy stored in a material
that has undergone some strain. The strain energy per unit volume of a material is given by
1
× stress × strain
2
1
𝑆𝐸 = 𝜎𝜀
2
strain energy per unit volume =
Strain energy is proportional to the square of stress and inversely proportional to Young’s Modulus. When a crack
begins to grow, the material is releasing its strain energy and thus the strain energy present in the material will
have a large impact on the formation and propagation of cracks in the material.
Engineering Studies – Page 60
Crack Formation and Growth
A material has two methods of failure: brittle failure and ductile failure. The structure of a material depends on
how it will fail. Metal alloys such as mild steel undergo ductile failure up to a point, so they extend in length until
brittle failure takes over. Brittle materials such as glass and concrete do not undergo ductile failure; they undergo
immediate brittle failure. Crack formation and growth is a method of brittle failure.
Cracking may be divided into two phases. It starts with undamaged material through to the first appearance of
micro-cracks (crack initiation phase) and crack propagation. Crack propagation is the phase in which the crack
grows in size under cyclic loading, leading to eventual failure.
Stress concentrations may occur due to:
 weld defects
 quench cracking
 corrosion pitting
 machining marks
 mishandling damage
 arc strikes from welding
 inadequate radii at section changes
 casting defects such as porosity, shrinkage and inclusions.
In theory, glass and other ceramics should be very strong in tension. They never achieve good tensile
performance because there are tiny micro cracks in the material.
Figure A below shows a set of atoms in a material with perfect linking of the atomic planes. Figure B shows that
an imperfection is present in the top layer. This will tend to concentrate twice the stress at the next bond, as it
must do the work of two bonds. By Figure C, the crack is travelling through the bonds as they break and the
remaining bonds become more stress in Figure D. As this continues, the likelihood of the crack growing increases
until eventually the crack travels through the material.
Critical Crack Length
There is a critical length that a crack must become before it proceeds through a material. This is a particularly
important factor in the design of components in civil structures that use brittle materials. Once the critical crack
length is exceeded, under load the crack will travel through the material until failure occurs. Determining the
critical crack length is beyond the scope of the course. The critical crack length is directly proportional to Young’s
Modulus and inversely proportional to the applied stress. Materials with a higher modulus of elasticity should
have a longer critical crack length. The longer the critical crack length, the less likely the material is to fail.
Engineering Studies – Page 61
Failure Due to Cracking
Failure due to cracking is a brittle fracture mechanism. Some materials are more likely to crack than others. The
more brittle a material, the shorter its critical crack length will be. Once the critical crack length is exceeded, then
failure is inevitable if stress levels are maintained.
Cracking of a material under cyclic loading may occur well below the yield stress. Cracking
produced in this manner is called fatigue. Fatigue is the most common form of materials
failure. It has been estimated that up to 80% of machinery failure is due to fatigue. A fatigue
fracture always starts as a small crack. As the crack expands, the load carrying crosssection of the component is reduced which increases the stress on this section. Failure
occurs progressively over a number of stress cycles. One of the most characteristic features
found on fatigue fracture surfaces is the presence of ‘beach’ marks. These represent the
successive positions of the advancing crack and are centred on a common point that
corresponds to the crack origin.
Repair and Elimination of Failure Due to Cracking
In the event of crack formation, stress concentration is important. If a material is metallic, then an option to repair
the crack is welding. This can, however, cause microstructural changes around the weld that may further weaken
the material and the weld may become a point of stress concentration. The area may need to be heat treated to
avoid microstructural complications. In polymeric materials, it may be possible to use adhesive technology to
repair cracking. If the failure is in a thermoset and adhesives are not available, replacement is the only solution.
If the failure is in thermoplastic, polymer welding can be used which offers strengths close to the parent material.
Cracks can be eliminated from forming by designing items without sharp corners. Another solution is to place
interfaces within a material. An interface is an area within a material, weaker than the surrounding area that runs
perpendicularly to the expected growth of the crack. When a crack travels through the material, it reaches the
interface but is blocked from passing it.
S-N Curves
Indicative fatigue data on materials is obtained from standardised test pieces in a special test rig that applies a
cyclic load. A diagram is subsequently built up of load cycles to failure for a variety of applied loads. This is called
an S-N diagram (applied stress-number of cycles). Ferrous metals exhibit a fatigue limit. This represents a stress
below which failure does not occur. This is also called the endurance limit and is typically found in steels with
titanium alloys. Non-ferrous metals do not experience an endurance limit.
Ceramics
Typically, ceramics are a combination of one or more metallic elements with non-metallic elements. They form
ionic and covalent bonds which give them unique engineering properties. They are often categorised as silicate
ceramics, oxide ceramics, non-oxide ceramics, conventional ceramics, glasses and advanced ceramics. Ceramics
are hard, brittle and chemically inert. They are good electrical and thermal insulators. Common ceramics include
aluminium oxide, Al2 O3 , and silica, SiO2 . Ceramics have good compressive strength but have little tolerance for
cracking. Even microscopic defects can cause failure well below the theoretical tensile strength.
Engineering Studies – Page 62
Stone
Stone may come in various forms. In Sydney, many civil structures used sandstone in the early days of European
settlement. Sandstone is a sedimentary rock. Granodiorite such as that used at the ends of the Sydney Harbour
Bridge is an igneous rock with a similar structure to granite and diorite. Slate was used on many early buildings
for roof tiles. It is a metamorphic rock. All stone is weak in tension, strong in compression and brittle.
Glass
Glass has found immense use in civil structures. Glass is an amorphous solid. It does not have a regular crystalline
material. Glass cannot be shaped because of its amorphous structure. Shaping must be done at elevated
temperatures where the viscosity of glass is reduced. Glass has low toughness, so is brittle. It is also weak in
tension.
Common window glass is a mixture of silica (SiO2 ), soda (Na2 O) and lime (CaO). The soda overcomes
devitrification, which is where the glass crystallised, and the lime makes the glass insoluble in water. Toughened
glass is heat treated to increase its toughness. The glass is heated then the outer surfaces cooled quickly by blasts
of cold air. This leaves the surface gold but the interior hot. As the interior cools, it contracts and places the outer
surface in compression. Glasses may be devised to meet almost any requirements.
Cement
Cement is a ceramic material formed by complex reactions with alumina, soda and lime. Hydraulic cement
hardens underwater and nonhydrolic cement, or Portland cement, does not. Cement is a ceramic material while
concrete is a composite that consists in part of cement. Cement is produced in the following manner:
 limestone and shale are both crushed then mixed together
 the mixture is passed through grinding mills into a kiln
 in the kiln at about 1500°C, the mix fuses and forms clinker
 the clinker is ground and stored
 the clinker is mixed with up to 5% gypsum which slows down the setting time
 the mixture is reground and mixed to a very fine powder and stored in a moisture-free environment.
When Portland cement is mixed with water, a complex set of chemical reactions occur which tend to form a
silicate gel. The setting involves the evaporation of the water and the formation of silicates. The silicate gel
accounts for about half of the mass of the cement. These chemical reactions are exothermic. Setting cement is
often hosed down during curing to prevent overheating and cracking.
Bricks
Bricks are generally rectangular building blocks that were traditionally made from clay, but are now made from
concrete. Clay is formed into the brick shape and then fired in a kiln to set the clay. Bricks may be pressed,
recognised by being sold, or extruded, where they will have a number of wholes through them. Many large brick
wall sections now use besser blocks which are large concrete blocks with hollow channels in them.
Composites
Timber
Timber is a composite of cellulose fibres (tracheids) and a natural resin (lignin). Timber can be either hardwood
or softwood. Hardwood timbers have pores while softwood timbers do not. These pores run through the
structure between the tracheids to carry nutrients. Hardwoods come from flowering plants (angiosperms) while
softwoods come from pines and conifers (gymnosperms). Timber has a very good strength-to-weight ratio but is
affected by the weather and susceptible to attack from pests and termites.
Wood is far stronger when loaded parallel to the grain than perpendicularly. Timber has found extensive use
throughout history as a readily-available material for construction. Some of the factors that affect the strength of
timber are:
 moisture content
 duration of loading
 defects such as knots.
Engineering Studies – Page 63
Timber may also be affected by chemical treatment which can have an adverse effect on mechanical properties.
Timber is classified into two groups: hardwoods and softwoods. Softwoods have a simpler structure. Hardwoods
contain both vessels and pores while softwoods contain only pores.
The mechanical properties of timber vary from species to species, but as a sustainable resource, it is generally
regarded as:
 easily machined
 renewable and biodegradable
 a good thermal and electrical insulator
 exceptionally strong relative to its weight
 easily fabricated using simple hand or power tools.
Timber may also be reengineered to produce a range of manufactured products including plywood, I-beams,
hardboard, trusses and fibreboard.
Mortar
Mortar is used between bricks in buildings. Mortar now contains Portland cement, sand and lime in the ratio
3:2:1.
Concrete
Concrete is a composite material of cement, sand and aggregate. The sand fills the gaps between the aggregate
and the cement acts as a binder. The sand and aggregate bulk out the concrete to reduce the cost because less
cement is then required. They also contribute to the strength of the material. Concrete is usually mixed in a 4:2:1
ratio of aggregate to sand to cement. If too little water is added to the concrete, it will not be fluid enough to
mould. If too much water is added, then the final strength will be low and shrinkage may be a problem. The ratio
of water to cement is ideally about 1:1.
Reinforced Concrete
Because of concrete’s inherent weakness in tension, there may be problems when a concrete beam sags as the
lower surfaces, when placed in tension, cause cracks to form. To overcome this, the concrete may be reinforced
with rods or steel mesh that takes the tensile load to make the concrete more resistant to failure.
Prestressed Concrete
To improve the performance of reinforced concrete, prestressed concrete may be created by casting the concrete
over a series of steel rods that have been tensioned prior to pouring. Once the concrete sets, the rods are released
and try to return to their unrestrained state, placing the concrete in compression.
Poststressed Concrete
Poststressed concrete is formed when concrete is case with tubes running through the slab. After setting and
curing, wires are pulled through the slab and anchored to plates at one end and tensioned.
Spalling in Concrete
Spalling, or concrete cancer, occurs when the reinforcing steel corrodes. When steel corrodes, it expands and
causes the concrete to crack. Careful design and not placing reinforcing too close to the surface can reduce
spalling.
Asphalt
Asphalt or tarmacadam (tarmac) is used for surfacing roads. It is a mixture of aggregate and bitumen. It is tough
and crack resistant yet hard wearing due to the exposed aggregate. It is impervious to contamination by oil.
Asphalt is laid hot and when it cools, the bitumen solidifies. The stiffer the bitumen, the tighter the aggregates
are held together and the heavier the load the road surface is able to handle. Function-related properties of
asphalt include resistance to plastic deformation, traffic and climate-related fatigue and low temperature
cracking.
Engineering Studies – Page 64
Laminates
Laminates are materials that consist of two different substances pressed together. Plywood is a laminate where
the grain structure of the timber is arranged at 90° to the successive layers to increase strength. Laminated
veneer timber is similar to plywood by the veneers run the same direction. It is used in construction. Laminated
glass is used when a shatter-resistant glass is needed. Two layers of glass are passed through rollers that
compress a polymer sheet between them. Bimetallic strips use two back-to-back metals with different thermal
expansion rates. As the metals expand, the strip bends in one direction. They are used in kettles, thermostats and
in gas protection circuits.
Cross-laminated timber (CLT) is an engineered timber product consisting of dense panels of wood engineered
for strength through laminations of different layers. This innovative and versatile product gains its rigidity and
strength from multiple layers of boards placed crosswise to adjacent layers. The building project Forté in Victoria
Harbour is the largest timber apartment building in the world and uses CLT.
Geotextiles
Geotextiles are woven polymers or ceramic fibres. They can be used for stabilising a road base. When a road is
constructed, the asphalt is laid over a finely crushed material called the road base. Over time, the road base will
often become contaminated by clay, rock or soil. To prevent this, a geotextile sheet is placed between the subsoil
and the road base to stabilise the road surface. Geotextiles can also be used for drainage systems. In civil
engineering, geotextiles serve the four basic functions of:
 reinforcement
 filtering
 separation
 conducting planar flow, which allows water and gases to move in the plane of the textile thus reducing
pressure build-up.
Most applications of woven or non-woven geotextiles perform one or more of the following functions:
 erosion reduction
 drainage
 surface stabilisation
Corrosion
Corrosion is the chemical deterioriation of a material due to a chemical reaction caused by differences in
electrical potential on the surface. Corrosion can occur in metals, ceramics and polymers. Metallic corrosion
involves the deterioration of metals or metal alloys. In nature, most metals exist as chemical compounds but are
refined before use into the pure metal. Corrosion progressively returns them to the combined state.
Corrosion involves complex chemistry. Oxidation occurs when a metal loses electrons and occurs at the anode.
Reduction is the consumption of electrons and occurs at the cathode. Some metals are more likely to be anodic
while others are more likely to be cathodic. Cathodic metals tend to be more stable and less affected by corrosion.
Less reactive metals tend to be cathodic.
To predict the susceptibility of metals to corrosion, standard electrochemical tests are performed to determine
the electrode potential in the environment. The galvanic series shows qualitatively the relative activity of a
variety of metals in seawater. The further apart two metals are in such an electrochemical series, the greater will
be the potential difference between them.
Corrosion occurs in two basic forms: general (uniform) and localised (non-uniform). Localised corrosion occurs
in many forms such as galvanic, crevice, pitting, Intergranular, selective etching, erosion corrosion, stress
corrosion and microbially-induced corrosion.
Dry Corrosion
Dry corrosion occurs through chemical reactions of metals or alloys with gases, in furnaces at high temperatures.
This includes in steam locomotive boilers and in hot water pipes. A principle cause is a reaction of the metal with
oxygen and other molecules in flue gases.
Engineering Studies – Page 65
Wet Corrosion
Wet corrosion occurs when a metal is placed into a fluid, usually an electrolyte. An electrolyte is a solution
containing ions. Some parts of the metal will become anodic while other parts will become cathodic. The locations
of the cathode and the anode will continually change resulting in uniform corrosion.
Galvanic Corrosion
Galvanic corrosion occurs when dissimilar metals are placed together in the presence of a corrosive environment.
Different metals have a greater affinity to corrode than others, so one will become cathodic and the other will
become anodic. A concentration cell occurs when there is a difference in concentration of electrolyte material. In
a car door, for example, stagnant water becomes low in dissolved oxygen which causes a difference in oxygen
levels and sets up a concentration cell. High oxygen will create a cathode while the area of low oxygen will become
the anode. The result will be the eventual destruction of the car door. This is why a plastic coating on the outside
of a car door does not prevent corrosion.
Crevice Corrosion
Concentration cells take a particularly damaging form as crevice corrosion. Crevice corrosion is where an
electrolyte fills a crevice and there are different oxygen levels between the top and the bottom of the crevice.
Crevice corrosion can be problematic on any metal structure where joints may create crevices.
Pitting
Pitting corrosion occurs due to the non-homogenous nature of the metal surface. It may be due to inclusions,
potential differences between metal constituent phases, distortions at grain boundaries or the presence of the
surface deposits.
Corrosion in Stress Cells
Stress cells are the result of high residual stress in parts of a metal object. These areas of high stress tend to
become anodic while those of lower stress become cathodic. Often, a stressed metal will corrode when an
unstressed piece in similar conditions will not corrode as readily. Grain boundaries in metals are areas of high
stress and thus a metal with a fine grain is more likely to corrode internally than one with coarser grains. Stresses
may be caused by:
 faulty design
 vibration
 plastic deformation
 residual stresses from unequal cooling
 the presence of an ionically-conducting aqueous phase in contact with the metal.
Stress corrosion cracking (SCC) is the growth of cracks in an environment where a metal under tensile loads is
simultaneously subjected to a corrosive environment. Compressive forces may actually provide some protection
against stress corrosion cracking. It is more common in alloys than pure metals and may lead to sudden or
unexpected failure due to difficulties involved in detection. Stress corrosion cracking may be alleviated by:
 stress relieving heat treatments
 avoiding surface machining stresses
 applying external protective coatings
 peening surface treatments to induce surface compressive stresses.
Intergranular Corrosion
Under some conditions, grain boundaries specifically may be attacked. Quite often the rest of the material is left
unaffected.
Corrosive Environments
Factors affecting the rates of corrosion include:
 temperature
 velocity of corrosive media
 likelihood of deposits forming
 poor design creating crevices
 residual stresses within the metal
 microbial content of environment
Engineering Studies – Page 66





metal surface creating corrosion sites
formation and stability of protective surface films
availability of oxygen to enable reactions to proceed
existence of anodic and cathodic sites on the metal in contact with this electrolyte
presence of an ionically-conducting aqueous phase in contact with the metal.
Benefits of Corrosion
Corrosion always occurs in metals at differing rates. Some metals like steel form a porous layer called rust that
alloys corrosion to continue. Other metals like aluminium form a protective film that makes the surface of the
metal passive and inert. Metals in this situation display passivity. Passivity is a condition where a metal that
should be reactive appears inert. Examples of passive metals are aluminium, titanium and chromium. Stainless
steel is a passive alloy. Rust is the name given to the corrosion of steel. It is the antithesis of the corrosion products
on passive metals. It is porous and flaky and exposes fresh corrodible metal beneath. Most steel structures must
be protected from the atmosphere or corrosive environments to ensure their longevity.
Protecting Civil Structures from Corrosion
Most steel structures such as bridges use two protective mechanisms to stop corrosion: painting and galvanising.
Galvanising involves dipping the steel part into molten zinc which then covers the steel and protects it from
corrosion. The zinc coating very slowly corrodes away over time but protects the steel before that point. Painting
coats the steel to prevent oxidation, but also wears away given time. Products such as Zincalume™ which is an
alloy of zinc and aluminium and Colorbond™ which uses a zinc/aluminium alloy with a polyester coating are
products used to protect steel from corrosion.
Some sheet aluminium alloys used Alclad™ which is duralumin (aluminium/copper alloy) coated with pure
aluminium. The passive aluminium protects the more corrosive-susceptible alloy. Aluminium alloy window
frames are normally anodised which involves creating a thick oxide layer to further enhance the oxide aluminium
that naturally forms.
Cathodic protection involves making the object cathodic, and thus preventing it from corroding. Sacrificial
anodes are blocks of another metal that are bolted to steel or other reactive materials that causes the steel to
become cathodic. Sacrificial anodes must be more reactive than the metal they are protecting so are usually made
of zinc, aluminium or magnesium. They are used on boat hulls to prevent the steel hull from corroding. Impressed
current protection systems (ICCP) use a current to reverse the standard electrical flow associated with corrosion.
By reversing the current flow, the structure becomes cathodic. It is used in pipelines and long structures where
sacrificial anodes would be ineffective.
Recyclability of Materials
Recycling is often defined as the series of activities including collection, separation and processing, by which
products or other materials are recovered from the solid waste stream for use as raw materials in the
manufacture of new products.
Steel
About 95% of steels used in bridges can be recovered and recycled. The manufacture of steel from scrap is much
more energy-efficient than from iron ore. Recycled steel can be used in place of virgin iron thus reducing iron ore
extracted from mines. Structural members from decommissioned bridges as well as steel reinforcing recovered
from concrete can easily be recycled into new steel. Steelmaking technologies such as the basic oxygen furnace
and electric arc furnace contribute to high rates of steel reusability.
Concrete
Recycled concrete is weaker than the original material due to its exposure to the elements. For this reason,
reclaimed concrete aggregate is mostly reassigned as rubble for drainage instead of being reconstituted as
aggregate for new concrete. Concrete slabs are fed into a crushed and an electromagnet used to remove the steel
reinforcing rod. A series of graded screens sort the aggregate according to its size.
Engineering Studies – Page 67
Timber
Timber is normally treated during its lifetime so is not normally suitable for recycling. Some structural members
may be suitable for reuse. Wood can also be recycled. Large chips can be used for garden mulch and smaller chips
may be used for reconstituted wood materials such as hardboard and fibreboard.
Asphalt
Waste products from incinerated plants are being used to replace aggregates as the supply or rock and gravel
becomes limited.
Glass
Recycled glass, or cullet, is now used to make new glass. Cullet preserves the countryside by reducing quarrying
and reduces energy and emission because cullet melts more easily. Glass is now commonly made from batches
containing up to 95% cullet.
ENGINEERING COMMUNICATION
Australian Standards
Engineering drawing to a specific standard provides a commonality of language across a variety of fields. The
Australian Standard (AS1100) is one such standard. The standard covers both engineering and architectural
designs and provides strict guidelines to assist when developing and reading drawings.
Computer-Aided Design
Computer-aided design (CAD) packages offer many opportunities and advantages for fast remote communication
and collaboration, particularly if each of the contributors is scattered around the state and the site location is also
remote. Through the use of CAD software, adjustments can be made without the need for manual redrafting.
Closer scrutiny is available through electronic zoom features and hard copies may be produced on paper for nonelectronic viewing.
Finite Element Analysis
Finite element analysis (FEA) is a computer modelling practice whereby a virtual model or design may be
stressed and analysed. Elements of the design may possess properties such as thickness, coefficient of thermal
expansion or Young’s Modulus.
Life Cycle Analysis
Life cycle analysis (LEA) is a tool to support the decision making for designers, engineers and manufacturers
when assessing the impact a product or process has on the environment. Specifically, the process involves the
consideration of all stages of product development including extraction of raw materials, production, packaging,
use, maintenance and ultimately, disposal.
Engineering Studies – Page 68
Threads
Threaded features such as bolts and nuts are drawn to specific AS 1100 standards. When dealing with threads,
the size details are normally given as:
MD × P
M stands for metric to indicate that it is a metric thread. D is the diameter of the thread in millimetres and the
P is the pitch of the thread. Hence, a thread described as M12 × 1.5 has a diameter of 12 mm and a pitch of 1.5
mm. The pitch is the total width of the thread on both sides of the bolt. Hence, the thread depth is equal to half
the pitch.
For a bolt, the distance across the flats is defined as 1.6D and the distance across the points is defined as 1.8D.
The depth of the bolt head is 0.7D. The thread depth is 0.5P or 0.1D.
For a nut, the distance across the flats is 1.6D and the distance across the points is 1.8D. For a standard hex nut,
the depth of the head is 0.8D. For a lock nut, the depth of the head is 0.5D.
For a washer, the diameter is 2D and the depth is 2 mm.
Counter Bores and Counter Sinks
Counter bores are used in engineering to allow a bolt head to be recessed below the face of an object. This is done
by creating a larger diameter hole at the top of an existing hole through an object. Counter sinking alloys a
recessed screw head.
Engineering Studies – Page 69
The Engineering Report
An engineering report should include:
 A title page, which gives the title of the report and you or your group’s name.
 A synopsis, which gives a summary of the content and aim of the report.
 An introduction that gives the subject, purpose and parameters of the report.
 A description of the methodology used.
 An overview of the results including figures, graphs and diagrams.
 A conclusion that gives the judgement made from the evidence found during the investigation.
 A recommendation if necessary based on the findings of the report.
 Acknowledgements of sources and people involved in the investigation.
 References.
 Appendices for additional information.
Engineering Studies – Page 70
ENGINEERING STUDIES
HSC Module 2: Personal and Public Transport
HISTORICAL AND SOCIETAL INFLUENCES
Historical Development of the Bicycle
The invention of the bicycle is credited to Frenchman le Comte de Sivrac who introduced his machine, the
célérifére at the Jardin du Palais Royale in Paris in 1791. He put wheels on what had been a rocking horse. It was
renamed the velocipede or dandy horse In 1816, Baron Karl von Drais von Sauerbron improved the original
velocipede by fitting a steerable front wheel, armrests, a padded seat and a primitive rear wheel brake. His
machine was called the draisienne, but was still propelled by walking it along the ground. In 1821, Lewis
Compertz designed a rack and pinion system so the arms could be used to assist the feet pushing along the
ground.
A Scotish blacksmith, Kirkpatrick Macmillan, developed a pedal drive in 1839. He used a pair of hanging stirrup
pedals, attached to long arms that connected to cranks on the rear wheel. Gearing was determined by the size of
the rear wheel. Macmillan’s machine weighed over 30 kg. Rear wheel drive was not to become popular on bikes
for a long time. In 1861, Monsieur Brunel took his draisienne for repairs to a coach maker, Pierre Michaux.
Michaux’s son suggested fitting cranks with pedals to the front wheel to that it could be pedalled. Michaux opened
a factory and produced these bicycles.
The speed of bicycles has motivated new designs. The velocipede moved very slowly with one rotation of the
wheel for each rotation of the pedal. Before gears, the solution was to make the front wheel larger. The penny
farthing bicycle had a large front wheel and a small rear wheel. Although difficult to ride, they were the fastest
thing on two wheels until the chain driven bicycle.
Attempts to make the front wheel smaller were defeated by a lack of feasible solution at the time. A reliable
bicycle chain was a major invention needed to develop a safe successor to the old ordinary (penny farthing).
James Starley produced a chain driven bicycle for Rover in 1885. He used a geared chain drive, wheels of equal
sizes, direct steering, inclined forks and the diamond-shaped frame. Initially, there was resistance to his design,
but these bicycles were a vast improvement and when John Boyd Dunlop invented the pneumatic bicycle tyre in
1888, they became easier and more comfortable to ride at speed.
By the late 1800s, the bicycle had ceased to be a novel status symbol and was becoming a cheap and practical
form of personal transportation. Mass product of the bicycle began in 1914. Through the 1900s, the bicycle frame
did not change dramatically. The frame angles were altered and different alloys were used to reduce weight.
Originally, aluminium alloy frames were used. Now, cheaper bicycles use mild steel and aluminium alloys and
more expensive bicycles use carbon fibre reinforced polymers.
By the 1990s, the mountain bicycle had demanded wider range gearing than the simple ten speed derailleur
system expanded to rear clusters and front derailleurs. Derailleur gear systems are more efficient than hub gears
but require more maintenance. Brakes have improved with cast aluminium alloys now allowing dual pivot
calliper brakes. Some bicycles now use disc brakes.
Modern Bicycles
Mountain bikes typically have smaller wheels than road bicycles and thicker tires with a tread. Such tyres are not
ideal for riding because of the high rolling resistance. Mountain bikes typically use aluminium alloy frames except
for those in competitive and professional applications which are made of carbon fibre reinforced composite
materials. Road bicycles typically use aluminium frames for entry level bikes and carbon fibre reinforced polymer
moulded frames for more expensive models. They have a larger diameter but narrower wheels and tyres.
Moulton bicycles used small wheels and high pressure tyres and suspension. They provided a rougher ride but
were very popular in the 1960s. Folding bicycles used the small wheel concept of the Moulton bicycle. Recumbent
bicycles were designed to better support the human body by requiring less weight to be supported by the arms.
Engineering Studies – Page 71
Train Development
From the 1300s, trains were horse powered and consisted of many wagons on track hauled up out of mines using
pit ponies. Originally the rails were timber but iron rails were introduced in 1728 in England. In 1803, the first
public railway was opened for hauling freight from Wandsworth to Croydon in Southern England. This was
followed in 1806 by the first passenger line with a horse-drawn train in South Wales. The first railway in Australia
was in Tasmania and was propelled by convicts who ran alongside the train.
In 1803, the first steam locomotive was constructed by Richard Trevithick for the Coalbrookdale Ironworks.
Trevithick’s locomotive used high-pressure steam and provided more power than a horse, but it was too heavy
and was abandoned. In 1812, the first locomotives to conduct regular work were designed by John Blenkinsop
for a colliery in Yorkshire. The wheels and tracks had interlocking teeth as Blenkinsop felt that otherwise the
trains would not have sufficient traction. In 1814, George Stephenson invented a locomotive which was the first
step in his work of developing railways. Stephenson envisaged a railway system across the whole of England. His
locomotive, Locomotion, was designed with his son, Robert. It was capable of speeds of up to 25 km/h.
Stephenson’s Rocket was a famous locomotive which had an innovative boiler design consisting of 25 tubes which
passed water through the firebox, more efficiently creating steam. Rocket could pull a 14 tonne train at 46 km/h.
Mechanical brakes were difficult to use, but in 1869, George Westinghouse patented an air brake design that was
widely used. The brakes were held off by the application of air from the engine. In 1876, Anatole Mallet invented
the compound steam engine. Instead of the steam being given off, it was first used in a small cylinder, then used
in a larger cylinder, so it was used twice. Following compounding, there was superheating which was adopted in
Germany in 1898 which reduced the moisture content of the steam and hence increased the efficiency.
The standard steam locomotive has between two and ten driving wheels with many smaller wheels to distribute
the load and allow the locomotive to negotiate curves more easily. The locomotives were often equipped with
tenders to carry water and coal. However, this design meant that most of the weight was not above the driven
wheels. The Garret and the Shay designs attempted to avoid this. The Garret locomotive had three articulated
parts with the boiler in the middle and tenders in front and behind. There were driving wheels on the tenders
which gave less chance of wheel slip. Shays were locomotives in which the boiler was offset to one side to allow
for a set of vertical pistons on the other side. These pistons moved up and down and were connected to a
crankshaft that ran along the right side of the locomotive. Pinions on the crankshaft engaged with bevel gears on
every wheel. The crankshaft had to have universal and sliding joints to allow the bogie to turn. Shays had a very
low maximum speed. Four Shays were used on private railway lines in NSW.
Gauge refers to the distance between the tracks. By the 1830s, Railway gauge was a contested topic. Standard
gauge, or 4 ft. 8 ½ in. gauge, was used in NSW, but Victoria utilised 5 ft. 2 in. broad gauge and Queensland used
3 ft. 6 in. gauge. This was resolved by adopting standard gauge in the 1900s.
The first real challenge to the dominance of the steam locomotive was the electric train. They didn’t need to
produce the power on board and were quieter, but they required the construction of more infrastructure, either
overhead catenary or third rail electrification. In NSW, the electricity is provided by overhead copper catenary.
The trains contact this with a pantograph.
The diesel locomotive was the true successor to the steam train. Electric trains ran alongside steam trains in the
cities but could not service outlying areas. The first diesel train rain in 1912 in Germany. A diesel-electric engine
uses a diesel engine to drive a turbine which generates electricity for electric motors at the wheels. A dieselhydraulic system uses the diesel power generated to directly power the motor and wheels. By the 1960s, in NSW
diesel trains were becoming more widespread and replaced the steam engine. Diesel electric trains are
extensively used for long distances. Most diesel locomotives in NSW now are diesel-electric. The NSW Train Link
Xplorers and Endeavours are diesel-hydraulic multiple units.
Effects of Engineering Innovations in Transport on People’s Lives
Bicycles have had many effects on people’s lives:
 The pedal-powered velocipede improved the usability of bicycles.
 The penny farthing allowed for faster bicycle transportation.
 The Rover Safety bicycle allowed safer, faster transportation.
 Freewheeling hubs made bicycles safer to use because the pedals did not continuously rotate with the
wheels.
Engineering Studies – Page 72
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Recumbent bicycles allowed for better comfort but they were outlawed from racing.
Lightweight aluminium alloys and reliable derailleur gears improved the design by making it more
efficient.
After World War II, the interest in cycles declined as cars became cheaper.
The Suez oil crisis in the 1950s forces many people back onto bicycles.
The mountain bike sparked a cycling craze in Europe and suited the image of the Swinging Sixties.
The BMX allowed for off-road racing.
Trains have had many effects on people’s lives:
 The steam train allowed for a more powerful and efficient form of transportation than horse and cart.
 Railways were developed worldwide in the early-1900s which allowed people to travel across countries
for the first time.
 Electric trains reduced pollution in cities compared to steam engines.
 Trains were an important tool in World War I and II for moving supplies and troops.
 The diesel train produced less pollution and had greater reliability. It also only required one man to
operate rather than two.
 The increase in electric rail networks further improved air quality.
 High-speed trains greatly cut transport times.
Effects of Engineering Innovation on Transport and Society
The history of transport is closely related to the development of modern society. As transportation increased in
capacity and efficiency, the barriers to trade and communication between villages were reduced. Improvements
in the reliability of transport allowed England to transport convicts to Australia and permitted the migration of
countless refugees around the world during times of economic and civil distress.
Construction and Processing Materials
Many materials have been used in the construction of bicycles over time:
 Timber was used in early bicycles because of a lack of suitable alternative materials.
 Iron was initially used as a tyre on wooden wheels.
 Steel was used for cycle frames from the 1870s because it offered good strength and relatively low weight.
Steel frames were joined by brazing with lugs. The lug was a small joint piece onto which the tubes slid.
 Alloy steels such as manganese-molybdenum steels offer better strength-to-weight ratio and resistance
to wear.
 Stainless steel is not typically used for frame construction except in Moulton bikes. Now it is offered in
the form of martensitic aging stainless steel which offers extremely high stress values.
 Aluminium alloys are used because they are more lightweight and have better strength properties than
steels. They are normally TIG or MIG welded.
 Titanium alloys are now used in gear componentry.
 Carbon fibre reinforced polymers are being used as an alternative to aluminium alloy. It has a good
strength-to-weight ratio and the frame can be moulded.
 Solid rubber tyres were replaced with pneumatic tyres which provided better ride quality.
 Polymers are used extensively in bicycles where flexibility is an advantage.
Bicycles
The bicycle frame needs to provide a balance of stiffness, flexibility and strength. Increased frame stiffness allows
the efficient transfer of energy by the rider to the wheel, but decreases the ride comfort. Spring suspension
systems are now commonly included in bicycle designs to counteract this. General purpose bicycles are often
made from a chrome-moly grade steel, while specialised bicycles can be obtained in aluminium, titanium or
carbon fibre-reinforced polymers. Mountain bikes require frames with high strength to absorb large and
repeated shock loads. The properties of the materials required for bicycle frames include:
 stiffness
 formability
 fatigue strength
 corrosion resistance
 high strength-to-weight ratio
 weldability or other appropriate joining method.
Engineering Studies – Page 73
The wheels of bicycles generally consist of steel rims with cold drawn carbon steel, stainless steel or aluminium
spokes. Solid disc carbon composite and ceramic wheels are also available but are restricted to velodrome use
where wind resistance during turning is not an issue.
Motor Vehicle
Traditionally, the engine block has been made from a flake graphite grey cast iron. However, the high weight of
cast iron has led to increasing use of lighter materials such as cast aluminium, often with iron inserts.
Development work continues on lighter materials. Grey cast iron is still used extensively in diesel engines due to
its superior vibrational dampening properties. Compacted graphite iron is also used in some instances. The
properties of the materials used for engine blocks include:
 castability
 lightweight
 machinability
 impact resistance
 dimensional stability
 thermal conductivity
 vibrational dampening
 high temperature strength.
Pistons are generally manufactured from aluminium although cast iron pistons are sometimes used. The
properties of the materials used for pistons include:
 lightweight
 machinability
 impact resistance
 thermal conductivity
 dimensional stability
 high temperature strength.
Crankshafts have previously been made from cast iron but are today principally forge from alloy steel and heattreated to an appropriate strength. The properties of the materials used include:
 machinability
 tensile strength
 fatigue strength
 dimensional stability.
Body panels were originally made from wood. Aluminium body panels over a wooden frame were used for a
period until steel was introduced. Steel is used due to its high formability. The properties of the materials used
include:
 toughness
 weldability
 formability
 good surface finish
 corrosion resistance
 strength-to-weight ratio
 ability to be easily recycled.
Vehicle frames were originally made from wood, but wood could not be formed into curves which restricted the
design options. Now, low carbon alloy-steel frames are used as well as aluminium frames. Aluminium is difficult
to weld, so usually has to be riveted or glued. The properties of the materials required for vehicle frames include:
 stiffness
 weldability
 fatigue strength
 corrosion resistance
 ability to be easily recycled.
Annealed glass was originally provided as an enclosure from the weather. Henry Ford introduced laminated glass
windscreens as a safety feature in 1927 which consisted of a polymer interlayer bonded between two sheets of
annealed glass so that the glass stays together when fractured. Laminated glass windscreens are now standard
Engineering Studies – Page 74
in all vehicles. Tempered glass, or toughened glass, was introduced in the 1950s and shatters into small rounded
pieces (dice). The fracture pattern obscures vision, however, so it cannot be used in windscreens. Tempered
laminated glass is also beginning to be used for security. The properties of the materials used include:
 rigidity
 transparency
 optical clarity
 thermal stability.
Early wheels were constructed from wire spokes. This was later changed to a solid disc which resisted flexing
during cornering. Fabricated steel, cast aluminium or magnesium alloy is used. The properties of the materials
required for wheels include:
 castability
 formability
 machinability
 fatigue strength
 impact resistance.
Early tyres used zinc oxide as a reinforcing agent. This was changed to carbon later. Tyres originally had no tread,
but this was later added to increase handling. Construction techniques such as cross-ply and radial-ply were
progressively introduced. The properties of materials used for types include:
 traction
 UV resistance
 wear resistance
 resistance to photochemical attack
 absorption of shocks and road vibrations.
Environmental Effects of Transport Systems
Cycling is often looked at as one of the solutions to environmental problems. Cycling, as a form of transport, is
one of the most efficient ways to travel and is non-polluting.
Trains have had negative impacts on the environment. The construction of railways has resulted in tree felling
and levelling of land. Many railway lines also cut tunnels and cuttings through the landscape. Steam trains caused
excessive pollution with an efficiency of only 5 – 10%. Oil fired steam engines produced even more pollution
Electric trains also cause pollution, but the pollution is released away from cities where air quality is normally a
problem. Diesel trains are more efficient than steam engines but still pollute the atmosphere. For passenger and
freight transport, trains are more environmentally friendly than road vehicles. Railway lines are narrower and
can haul many people and carriages with a single engine.
Environmental Implications from the Use of Materials in Transport
Forests have been affected by large scale transport developments. Timber was used for railway sleepers and as
a fuel source for some steam locomotives. Such uses resulted in the clearing of large areas of forest.
Steel has been used as a transport material since 1856. Steelworks such as those at Port Kembla affect the local
atmosphere and air quality and produce large amounts of pollutants. The mining operations of iron ore usually
consist of open cut mines which damage the local environment and destroy habitats for fauna. Coal and limestone
are also required for the fuelling of the blast furnaces to produce the iron.
Aluminium is refined from bauxite ore which is also mined in an open cut manner. Aluminium is refined using
electrolysis which uses power from coal-fired power stations. Aluminium refining also produces fluorine gas,
which is an atmospheric pollutant.
Polymer usage in transport systems has increased since World War II. To protect the environment, the use of
polymers must be backed up by the recycling of old equipment, as polymers greatly contribute to landfill.
Engineering Studies – Page 75
ENGINEERING MECHANICS
Mechanical Advantage
The mechanical advantage of a machine is a measure of how it helps the user.
load
effort
𝐿
𝑀𝐴 =
𝐸
mechanical advantage =
The higher the mechanical advantage, the lower the effort must be for a given load. If the mechanical advantage
is less than one, then there is a mechanical disadvantage, which means that the effort is greater than the load.
Velocity Ratio
The velocity ratio is the ratio of the distance that the effort moves to the distance that the load moves in a
mechanical system.
velocity ratio =
𝑉𝑅 =
distanceeffort
distanceload
𝑑𝐸
𝑑𝐿
The higher the velocity ratio, the greater the distance that the user must move. Velocity ratio is not affected by
losses in the system. If a machine is perfectly efficient, then the velocity ratio will equal the mechanical advantage.
However, the lower the velocity ratio, the greater the effort that is required.
Efficiency
An ideal machine is 100% efficient. This means that all energy inputted is used by the machine. However, this is
never the case. There is always some energy loss that results in the efficiency being less than 100%. The velocity
ratio is always the same irrespective of efficiency, since there is no change in the distances the effort and the load
move. The mechanical advantage of a machine will always be less than its efficiency ratio.
efficiency =
𝜂=
mechanical advantage
velocity ratio
𝑀𝐴
𝑉𝑅
Consider the bicycle shown on the right. The
tractive force at the wheel and the force on the
pedals have been determined experimentally.
𝐿
𝐸
73
=
425
𝑀𝐴 =
= 0.1718
Engineering Studies – Page 76
Before calculating the velocity ratio, it needs to be considered that the bicycle’s gearing effects how many times
the rear wheel rotates for one revolution of the pedals.
𝑉𝑅 =
=
𝑑𝐸
𝑑𝐿
𝑑
𝐷 × 𝑁𝑟𝑒𝑣
𝜋 × 3402
4
=
𝜋 × 6702 46
× 16
4
= 0.1765
Now the efficiency can be calculated.
𝑀𝐴
𝑉𝑅
0.1718
=
0.1765
𝜂=
= 97%
If the drive system were properly maintained, then the efficiency would be 97%.
Pulleys
Pulleys are an adaptation of the wheel. They are used to transmit power, change the direction of a force and
provide assistance through mechanical advantage. Single pulleys offer no mechanical advantage, but change the
direction of the effort relative to the load. In all pulley systems, the mechanical advantage and velocity ratio are
dependent on the number of cables present within the system. In a fixed two-pulley system, the mechanical
advantage, assuming 100% efficiency, is 2, as there are two cables supporting the load instead of just one.
Wedge
A wedge is similar to an inclined plane. The effort is not applied to move the load up an incline, but rather applied
in the direction to reach a maximum depth of penetration. A wedge may be used as a device for holding, such as
a door stop, or separating, such as an axe. The mechanical advantage of a wedge is the depth of penetration
attained for the amount of separation achieved.
tan 𝜃 =
𝐸
𝐿
where 𝜃 is the angle made with the horizontal.
Static Friction
Static friction refers to objects that are either not moving or are on the point of moving. Friction hampers
efficiency but is necessary for transport systems to function. The coefficient of friction is the ratio of the frictional
force to the normal reaction.
frictional force
normal reaction force
𝐹𝐹
𝜇=
𝑁
coefficient of friction =
Engineering Studies – Page 77
The normal reaction is the perpendicular reaction provided by the surface on which the object is resting. In some
cases, the applied forces will tend to lessen or increase the normal reaction.
The frictional force is the force resisting the tendency towards motion between surfaces. The higher the
coefficient of friction, the higher the frictional force will be. The frictional force is given by:
𝐹𝐹 = 𝜇𝑁
The coefficient of friction is found to vary if changes occur in:
 plastic or elastic deformation
 surface films, such as water or oil
 temperature and surface roughness.
The following rules apply to friction:
 The coefficient of friction is independent of the area of contact.
 Friction cannot exceed a certain value for two surfaces.
 Frictional forces always act opposite to the direction in which a body tends to move.
 The coefficient of kinetic friction (𝜇𝑘 ) is always less than the coefficient of static friction (𝜇𝑠 ).
Limiting Friction
Limiting friction is the frictional resistance that exists just as motion is about to occur. Static frictional resistance
increases up to a maximum at the point of limiting friction. After this point, the frictional resistance decreases
and moving surfaces exhibit kinetic friction.
Angle of Static Friction
If the frictional force and the normal reaction force are combined into a single force, then the angle that this force
makes with the normal force is given by:
tan 𝜙 = 𝜇
Angle of Repose
If an object is placed on a flat surface with no net force acting on it, it will not move. If the surface is raised at an
angle to become an inclined plane, the weight force will have two components: one acting down the plane
(𝑊 sin 𝜃) and one acting perpendicular to the plane (𝑊 cos 𝜃). As the angle increases, 𝑊 sin 𝜃 will increase and
𝑊 cos 𝜃 will decrease. At the point where 𝑊 sin 𝜃 is larger than the frictional force opposing motion, the object
will slide down the plane. At the point of limiting friction, 𝐹𝐹 , 𝐹𝐹 = 𝑊 sin 𝜃 and 𝑁 = 𝑊 cos 𝜃.
Work
Energy and work are related concepts. Work, in engineering terms, occurs when a force causes motion. Work is
given by:
work = force × displacement
𝑊 = 𝐹𝑠
The unit for work is the joule (J). One joule is equivalent to one newton moved a distance of one metre. Positive
work occurs when work is done in the direction of the applied force. Negative work occurs when work is done in
the opposite direction to the applied force. If the force is applied at an angle, on the component of the force in the
direction of motion is affecting the work done.
Engineering Studies – Page 78
Energy
There are three types of energy of interest to the course.
Potential Energy
Potential energy is the potential to do work and is stored energy. Potential energy is a measure of the ability of
an object to do work from its position. For example, if a brick is lifted off the ground, it has the potential to do
work.
potential energy = mass × acceleration due to gravity × height
𝑃𝐸 = 𝑚𝑔ℎ
Kinetic Energy
Kinetic energy is the energy that a body possesses as a result of its motion. If a body has any velocity, then it will
possess an amount of kinetic energy. Small variations in velocity have a greater effect on kinetic energy than
small variations of mass. Kinetic energy is the amount of energy required to stop an object.
1
× mass × (velocity)2
2
1
𝐾𝐸 = 𝑚𝑣 2
2
kinetic energy =
Kinetic and potential energy are closely linked. For any object:
initial potential energy + initial kinetic energy + work done = final potential energy + final kinetic energy
𝐾𝐸𝑖 + 𝑃𝐸𝑖 + 𝑊 = 𝐾𝐸𝑓 + 𝑃𝐸𝑓
Calculating Power
If a 12 kg bicycle and an 80 kg rider are at the top of a 20 metre high hill and it is 300 metres to the bottom and
the combined resistance to motion is 40 N, determine the velocity of the bicycle after it coasts to the bottom of
the hill.
𝐾𝐸𝑖 + 𝑃𝐸𝑖 ± 𝑊 = 𝐾𝐸𝑓 + 𝑃𝐸𝑓
1
0 + 𝑚𝑔ℎ − 𝐹𝑠 = 𝑚𝑣 2 + 0
2
1
0 + 92 × 10 × 20 − 40 × 300 = × 92𝑣 2 + 0
2
6400
𝑣=√
46
≈ 11.8 ms−1
≈ 42.5 km h−1
Engineering Studies – Page 79
Car Crashes and Crumple Zones
The work-energy principle also allows for the calculation of the forces involved during car crashes. It should be
noted that the energy lost due to sound and heat energy is ignored.
Calculating Crumple Zones
A car of mass 1000 kg was travelling at a speed of 72 km/h when it hit a tree. Crumpling of the bonnet allowed
the car to stop in a distance of 0.4 m. Determine the force on the car.
𝑚𝑢2
2𝑠
1000 × 202
=−
2 × 0.4
= −500 kN
𝐹=−
The force is 500 kN in the opposite direction.
Loss of Kinetic Energy
When a vehicle is moving, it has kinetic energy. The brakes must do negative work to retard the vehicle. Friction
brakes convert kinetic energy into heat energy. Cars use engine braking where the motor resists the motion of
the car when the accelerator is released. Trucks and buses may use magnetic compression braking to slow a
vehicle. All these methods decrease the kinetic energy. When braking, trains can use the electric motors at the
wheels as generators to produce power. Electric cars can feature a similar system.
Power
Power is the rate at which work is done. The unit for power is the watt (W) which is equal to a rate of one joule
per second.
work
time
𝑊
𝑃=
𝑡
power =
This can also be expressed as:
power = force × velocity
𝑃=
𝑊 𝐹𝑠
=
= 𝐹𝑣
𝑡
𝑡
Torque
Torque is the turning moment that the motor produces. The higher the torque, the greater the turning moment.
Torque is a measure of the forces that a given engine can develop and use in moving a load.
torque = force × perpendicular distance
𝜏 = 𝐹𝑑
Power and Torque
Power figures are regularly quoted in transportation publications as an indicator of how effective a motor is. This
figure is only one indicator of how a motor performs. Another is the torque figure which indicates the turning
moment of the motor. The power alone does not determine how fast a vehicle will move. A lighter, less powerful
car may have a better ratio of power to weight than a heavy car and hence perform better. A higher torque figure
means that a vehicle climbs and pulls loads will. The power figure for a motor is the power at the crankshaft.
After the gearbox, differential and drive shafts, the usable power is less than 50% of this.
Engineering Studies – Page 80
Calculating Power with Losses
A bicycle and rider of mass 92 kg are ascending a hill of grade 1 in 30. Determine the total power the rider
needs to expend to maintain a velocity of 20 km/h if the total resistance to motion is 30 N.
Summing forces parallel to the incline:
ΣF ↗+ = 0
0 = 𝐹𝑇 − 𝑚𝑔 sin 𝜃 − 𝐹𝑅
𝐹𝑇 = 𝑚𝑔 sin 𝜃 + 𝐹𝑅
= 92 × 10 × sin 1.91° + 30
= 60.65 N
𝑃 = 𝐹𝑣
= 60.65 × 5.56
= 336.9 W
ENGINEERING MATERIALS
Hardness Tests
Hardness Test
Brinell
Vickers
Rockwell
Shore Scleroscope
Operation
A hardened steel ball is forced into an object under a specified load. The diameter of the
ball is dependent on the thickness of the test piece. The hardness number is determined
by measuring the depth and surface area of the impression and using a formula which
also incorporates the applied load.
A small square pyramid is forced into a test piece under a specified load. The hardness
number is derived from a formula that contains the load and area of the indentation.
A diamond cone is formed into a test piece under specified load conditions. There are
different scales displayed on a dial which indicate the hardness of the material being
tested.
This test involves a small striker in a tube. The tube is placed over the item and the
striker dropped. The height that the striker rebounds is a measure of the hardness. Soft
items will absorb more of the energy of the falling striker.
Impact Tests
Impact tests determine the notch toughness of a material. Tough materials will not break under a concentrated
load as easily as brittle materials. The test piece has a small V notch placed in it to concentrate the stress and
promote crack propagation.
Hardness Test
Izod/Charpy
Hounsfield
Operation
A large pendulum is raised to a specific height to give it potential energy. Upon release,
it loses potential energy and gains kinetic energy. At the bottom of the swing, it will
strike the test piece and some kinetic energy will be absorbed in breaking it. After
passing the test piece, the pendulum will swing up in height, gaining potential energy.
The height reached is recorded and used to calculate the energy absorbed. In an Izod
test, the bar is placed vertically. In a Charpy test, the bar is held horizontally.
Two smaller pendulums, one solid, the other hollow, swing through and hit the test
piece. The result is double the impact. The energy required is read from a scale on the
pendulum pivot.
Engineering Studies – Page 81
Ferrous Materials
Engineering materials are often classified as ferrous or non-ferrous. Ferrous materials have iron as their primary
constituent. Iron exists as a face-centred cubic or body-centred cubic. The face-centred cubic is often referred to
as austenite and the body-centred cubic as ferrite. The form in which it is found depends on the temperature and
the influence of alloy additions. At room temperature, unalloyed iron is BCC.
Carbon additions up to about 2.2% are classified as steel. Above 2.2% is classified as cast iron. General
categorisation of steel is made by carbon content. At room temperature, iron will only maintain about 0.02 wt%
carbon in solution. Above this, carbon and iron combine to form cementite, iron carbide or Fe3 C. At carbon levels
below 0.83 wt% cementite and ferrite exist together in a lamellar form called pearlite. Steel containing 0.83 wt%
carbon is called eutectoid steel and is fully pearlitic. At carbon contents over 0.83 wt%, iron carbide is
increasingly found as rivers of cementite in the structure.
Heat Treatment of Ferrous Materials
The properties of steels can be altered by the way they are cooled following heating. Heat treatment is most often
performed:
 for stress relief
 before a manufacturing process, to make the metal easier to form
 after a manufacturing process to achieve the final desired strength and hardness
 between manufacturing processes to relieve the effects of strain hardening and to prepare the material
for further deformation.
The most important considerations for heat treatment are:
 the time at temperature
 the uniformity of heating and cooling
 heating or cooling rate
 requirements for atmosphere control
 temperature at which heat treatment was performed
Process Annealing
Process annealing involves heating a steel with less than 0.3% carbon content to a temperature below the
austenite range, usually about 600°C. This relieves stress from distorted grains caused by cold working or
deformation. The ferrite grains will reform as unstressed grains, while the pearlite grains remain in the deformed
state.
Full Annealing
Full annealing involves heating a eutectoid or hypoeutectoid steel into the austenite range at a temperature of
about 900°C. The steel is then cooled very slowly in a furnace which produces large, soft grains. All grains will be
unstressed. Annealing removes the hardness of a material. It is commonly used after casting, forging and rolling
operations to reduce internal stresses and increase ductility. It leads to reduced hardness by means of successive
stages of recovery, recrystallisation and grain growth. The removal of stresses and the generation of new grain
growth results in:
 a softer material
 a homogeneous microstructure
 improved machinability and formability
 a tougher and more ductile material
 removal of residual stresses.
Normalising
Normalising involves heating a steel up into the austenite region well above the upper critical temperature. When
the structure is all austenite, it is then cooled in still air. The process takes less time than full annealing and
produces a finer grained structure which is a stronger steel.
Hardening
If a steel is heated until it is austenite in structure and then quenched rapidly, the transformation from face
centred cubic (FCC) austenite to body centred cubic (BCC) ferrite is not given enough time to fully occur, and
steel becomes trapped as a body centred tetragonal (BCT) martensite. The new structure is very hard, but brittle.
Engineering Studies – Page 82
Martensite will form in any steel with a carbon composition of greater than 0.03%. Low carbon martensite is soft
and does not become really hard until the carbon composition is in the range of 0.4 to 0.8%.
Air Hardening
If a steel has nickel or chromium added, then it will have air hardening properties. This means that if it is heated
to red hot and cooled in still air, martensite will form. Usually molybdenum is also added to reduce brittleness.
Tempering
If a steel is hardened, it becomes brittle. If hardness and toughness are both required, then a hardened steel
should be tempered. This involves heating to about 400°C and then cooling. A lower tempering temperature will
produce higher hardness and lower toughness, whilst a higher temperature will create less hardness but higher
toughness. Tempered steels are much harder than annealed or normalised steels.
Microstructural Changes
Annealed steels tent to be soft with moderate strength due to the coarse grain structure. Normalised steels have
higher strength because they have a finer grain structure. By hardening a steel, the grain structure is highly
stressed and has an acicular appearance. Tempered steels tend to have a very fine structure of carbide particles
in a ferrite matrix which gives toughness and moderate hardness.
Bainite has a structure consisting of very fine cementite particles in a ferrite matrix. Bainite is similar to pearlite
but consists of tiny particles of cementite instead of layers. Bainite is formed by austempering where an austenitic
steel is quenched at about 400°C and held there until that temperature exists throughout the steel. Then, it is
quenched to room temperature. The resulting structure is similar in performance to tempered martensite.
Surface Hardening
In some cases, it is desirable to have a hardwearing surface but the toughness of a soft core. There are a number
of processes that harden only the surface but leave the core soft.
Case Hardening
Case hardening involves heating and soaking the steel in a carbon rich atmosphere or medium. The carbon
diffuses into the structure at the surface, increasing the carbon content and hence the hardness of the material.
Any heat treatment of the steel is more challenging due to the different surface and carbon content, so the steel
is usually normalised or hardened.
Nitriding
Nitriding is a surface hardening process where a special alloy steel is heated in a furnace with a gaseous nitrogen
present from the decomposition of a material such as ammonia. The nitriding is performed at 500°C for between
40 and 100 hours and the gaseous nitrogen reacts with aluminium, chromium or vanadium in the steel. Nitriding
offers high hardness in the core and produces a corrosion resistant surface finish.
Flame Hardening
This process takes a suitable carbon composition greater than 0.4% and applies a flame to a localised area and
then quenches it. This process results in a localised area being hardened. The process is mechanised with the
flame holder and water jet being the one assembly, with the water jet trailing the flame holder.
Induction Hardening
An induction coil increases the temperature in the steel to the desired range for heat treatment. The current is
turned off and then the surface is quenched with water to harden it.
Changes in Properties
There are three ways that the properties of steels can be altered. Steels are greatly affected by the addition of
carbon. This is because carbon and iron form an interstitial solid solution. Properties can be further changed by
heat treatment. The allotropic nature of iron means that by varying the rate of cooling, different properties can
be induced in the steel. The hardening and tempering of steel cannot be repeated with most other alloys.
Properties of steel can also be altered by alloying. The addition of alloying elements bring about improved
properties without the detrimental effects of high carbon contents.
Engineering Studies – Page 83
Plastic Deformation
The majority of plastic working techniques employ compression rather than tensile methods due to the larger
reductions possible. Hot working operations are undertaken at a temperature above the recrystallisation
temperature. Advantages of hot working include:
 large reductions are possible
 improvement in the mechanical properties through grain refinement
 reduction of internal defects such as porosity
 favourable directionality of grain flow.
Cold working operations are undertaken at a temperature where recovery and recrystallisation do not occur.
Advantages of cold working include:
 increased strength
 increased hardness
 improved surface finish and tolerances.
Manufacturing Processes for Ferrous Metals
Forging
Forging is the shaping of a metal through the use of force. Forging may be carried out above the recrystallisation
temperature (hot forging) or below it (cold forging). Forging may draw out a metal while reducing its crosssectional area (drawing) or reduce its length while increasing its cross-sectional area (upsetting), or it may force
the metal into dies to take the required shape, such as in drop forging. The macrostructure of a forged material
consists of grain flow around the shape. This results in no planes of weakness which increases the strength of the
finished article.
Rolling
Rolling can be done above or below the recrystallisation temperature (hot rolling) or below it (cold rolling). The
recrystallisation temperature is the temperature above which deformed (stressed) grains in the metal will
renucleate and grow into annealed grains. Unstressed grains will not renucleate but will grow. Hot rolling is used
extensively in the production of sheets, strips, bars and rods of metal. Ingots of the required metal are passed
through successive rollers which deform the structure. Above the recrystallisation temperature, the stressed
grains reform. The advantages of hot rolling are:
 less strain on the machinery when compared to cold rolling
 an unstressed finished product.
The disadvantages of hot rolling are:
 the products are not as dimensionally accurate
 the metal forms an oxide layer over the finished product.
Cold rolling is performed below the recrystallisation temperature, so the final structure consists of elongated
coarse grains. The advantages of cold rolling are:
 a harder final product that is more dimensionally accurate
 a more presentable product because of the lack of oxides.
The disadvantages of cold rolling are:
 heavier machinery is involved
 cold rolling puts more wear on the machinery.
Ingot Casting
Many metals are not cast in their final shape. Often they are cast in ingots that may be shaped by rolling or forging.
Ingot casting involves pouring a molten metal into a large tapered metal mould. Upon solidification, the mould is
lifted away and the ingot is ready for shipment. Ingot casting was used extensively but has now been replaced by
more mechanised methods of continuous casting.
Continuous Casting
Continuous casting allows for the rapid production of simple cross-section products like bars and strips. The
molten metal is poured into a water-cooled ingot with a sliding base. Once the bottom of the ingot has solidified,
the base moves down which allows the metal above it to solidify. The resulting long metal string is cut to the
Engineering Studies – Page 84
required length. This method of casting is used in large plants because of its rapid speed and cost effectiveness
on large runs.
Sand Casting
Sand with the addition of a binder (green sand) is packed around a pattern of the finished product in a mould
that is in two hales. The pattern is removed and the mould reformed. Molten metal is poured into the cavity. Once
the metal solidifies, the sand is removed and reconstituted to be reused. The process can be automated and it
used extensively in automobiles. The advantages of sand casting are that it is cheap and the castings have a good
final grain structure. The disadvantages are that the final surface finish is poor and every product requires a new
mould to be produced.
Shell Moulding
This is a close relative of sand casting and utilises sand as a molten material in a different way. In shell moulding,
a heated pattern plate is placed over a dump box. At the bottom of the dump box is a mixture of sand and
thermosetting resin. The dump box is inverted and the sand and resin mix drops over the heated pattern plate.
The heat from the pattern plate partially sets over the resin, holding the sand together. The half mould and
pattern plate are then heated at 315°C to ensure the resin fully cured. The cured half is then ejected off the pattern
by small ejector pins. Two half moulds are then placed together. They may be bolted or screwed together. Finally,
the mould is placed in a box to receive the molten charge. Upon solidification, the metal is removed.
Engineering Studies – Page 85
Centrifugal Casting
This method relies on centrifugal force to spin the metal to the outsides of the mould to create a hollow cylinder.
This type of casting is useful for creating pipes. Piston rings for cars can be made this way.
Permanent Mould Casting (Die Casting)
Permanent mould casting involves the use of a permanent mould which is not remade each time. Gravity die
casting uses a permanent metal mould into which molten metal is poured by gravity. Since the mould cannot be
broken to remove the cast item, the mould mast be separable. The advantages of gravity die casting on long
production runs are that it is less costly than sand casting and the final product has a better surface finish.
Pressure die casting is similar, but the molten metal is force in under pressure. The result if a denser casting and
has good surface finish. Pressure die casting is primarily used with alloys that have a low melting point. If ferrous
metals are to be cast using this method, it is necessary to use graphite dies.
Investment Casting (Lost Wax Casting)
A pattern of the item is made from wax and a refractory ceramic is poured over the wax and allowed to set. Once
set, the wax is melted and drained leaving a cavity that is a perfect replica of the item to be cast. Molten metal is
poured into the ceramic cast and allowed to solidify, then the cast is broken away. This is very costly for large
production runs but the final cast has very good surface finish and is dimensionally accurate.
The Full Mould Process
The full mould process is similar to investment casting and is used for prototypes. An expendable pattern for the
item to be cast is made from polystyrene and placed in a box surrounded by sand and thermosetting resin. The
molten metal is then poured into the foam runner and this melts the foam. Since only 2% of the foam is solid,
then this solid simply melts into the sand and binds it together. The air passes through the sand and does not
contaminate the casting.
Extrusion
Extrusion may be likened to squeezing toothpaste from a tube. The molten metal is forced through a die at the
end of the tube by a ram. Direct extrusion (left) occurs when the ram pushes from the opposite side to the die.
Indirect extrusion (right) occurs when the ram pushes from the same side as the die. Indirect extrusion is
normally used in the extrusion of alloys with lower ductility but direct extrusion is cheaper, so is used where
possible.
Impact Extrusion
Impact extrusion is a cold working process. Impact extrusion uses a hammer impact to extrude a shape. The
punch goes into a die and the material blank is forced from the die around the punch. Cans and short tubes are
often made using this method.
Powder Forming
Metal powder forming or powder metallurgy is a process that involves powdering a metal by mechanical or
chemical disintegration and then mixing with dry lubricants to the required mix. The mixture is then pressed
into a mould to the required shape and compacted to give the item strength to be handled. It is then sintered in
a non-oxidising environment to allow atoms to diffuse between the grains. Powder forming is used to produce
products with porous metals, complex articles, products that are difficult to machine or composites. Powder
forming alloys many articles to be produced that would otherwise have been difficult.
Engineering Studies – Page 86
Materials produced by powder metallurgy are often:
 hard materials such as cutting tools and wear resistant parts
 metals with very high melting points
 composite materials
 porous materials
Welding
When materials are welded together, there are some changes in the structure of the parent material. The area
around the weld is called the heat affected zone and this is the area in which the heat of the welding process may
cause some changes in the grain structure of the material.
If the plate is cold rolled before welding, then the heat affected zone will cause equiaxed grains to form. While
mild steel is very easily welded, it will also suffer from grain growth near the weld which will soften the cold
rolled plate. Higher carbon steels and alloy steels are more challenging to weld and may need to be slow cooled
to stop martensite forming.
Welding Method
Type of
Process
Spot welding
pressure
Butt welding
pressure
Seam welding
pressure
Oxy-acetylene
welding
fusion
Bronze welding
fusion/
alloying
Electric arc
welding
fusion
Metal inert gas
welding
fusion
Tungsten inert
gas welding
fusion
Plasma arc
welding
fusion
Method
Electric current melts metal sheets under pressure
and joins in ‘spots’.
Metal is butted together at the ends and a current is
melts the metals, joining them together.
Metal is moved through rotating wheels that pass an
electric current through the metal, melting it.
Metal is melted by an oxy-acetylene flame and a
filler material is added.
A flame heat the parent metal, and bronze filler
material is added to the joint. The parent metal is
not melted.
Metal is melted by an electrode, which is the filler
material. When the arc is struck, the electrode melts
into the joint. The electrode is covered in flux to
prevent oxidation of the parent metal.
MIG replaces the electrode with a continuous feed
wire for quicker welding. The flux is replaced by an
inert gas.
Uses
Joining sheet metal
Joining tubes
Manufacturing and
joining pipes
Joining small metal
parts
Used instead of oxyacetylene for lower
strength applications
Joining steel used in
thick sections in small
run applications
More automated than
electric arc welding
Joining aluminium and
TIG replaces the continuous feed wire with a
stainless steels in thick
tungsten electrode filler rod.
sections
A gas, such as argon, is passed through an electric
arc, which ionises the electrons and positive ions. Specialty use only
The ions recombine to form a flame.
Engineering Studies – Page 87
Non Ferrous Metals and Alloys
Aluminium and its Alloys
Aluminium is one of the most common metals in the Earth’s crust. In nature, it exists as an aluminium ore, bauxite.
Because of its reactivity, it is never found as pure aluminium and forms from electrolytic refining from its ore.
Aluminium is highly reactive, has relatively low strength, is ductile and is easily fabricated. It is more difficult to
weld than ferrous alloys and costs more than mild steel. Aluminium does, however, have a good strength-toweight ratio, corrosion resistance and electrical conductivity. Aluminium is used for overhead electrical wiring,
the manufacture of cooking pots and pans and for cooking foil. Most engineering applications use aluminium
alloys.
Aluminium alloys are classified as either wrought alloys or casting alloys. Casting alloys are used for casting only,
while wrought alloys are used for mechanical working. Beyond the wrought classification, there are heat
treatable and non-heat treatable alloys.
Aluminium alloys are numbered such that the first number relates to the family of alloys and the remaining
numbers, shown as 𝑥𝑥𝑥 for the purposes of description, describe the varying composition of alloying elements
within the family.
Non-heat treatable alloys of aluminium include:
 1𝑥𝑥𝑥 is primarily pure aluminium with small amounts of iron and silicon. It is used for sheet metal work.
 3𝑥𝑥𝑥 is an alloy with manganese which provides solid solution strengthening. It is used for pressure
vessels, chemical equipment and sheet metal work.
 5𝑥𝑥𝑥 is an alloy with magnesium added. 5052 with approximately 2.5% manganese and 0.2% chromium
is the most important industrial alloy in this family.
Heat treatable alloys of aluminium include:
 2𝑥𝑥𝑥 in which the primary alloying element is copper and contains duralumin. It is primarily used for
aircraft structures because of high tensile strength properties.
 6𝑥𝑥𝑥 contains magnesium and silicon, strengthened by precipitation hardening. They offer good
corrosion resistance and strength.
 7𝑥𝑥𝑥 contain zinc with magnesium and copper. The alloy is strengthened through precipitation
hardening. Alloy elements allow denser precipitates and produce a stronger alloy.
Casting alloys are divided into heat treatable and non-heat treatable alloys. Most aluminium alloys are cast. Most
casting alloys contain silicon which lowers the melting point of the alloy and improves its fluidity. Aluminium/
silicon/manganese/iron alloys are used in the transport industry in the manufacture of cars.
Casting alloys of aluminium include:
 1𝑥𝑥. 𝑥 with 99% aluminium or greater.
 2𝑥𝑥. 𝑥 contain copper.
 3𝑥𝑥. 𝑥 contain silicon with copper and/or magnesium.
 4𝑥𝑥. 𝑥 contain silicon.
 5𝑥𝑥. 𝑥 contain magnesium.
 7𝑥𝑥. 𝑥 contain zinc.
 8𝑥𝑥. 𝑥 contain tin.
 9𝑥𝑥. 𝑥 contain other elements.
Aluminium lithium alloys are used in bicycles because they offer better fatigue life and aluminium alloy tubing.
Such an alloy is important in the competitive world of cyclins. It was first used in aviation fields and is used in
some aircraft applications.
Copper
Copper is the third most used metal. Copper finds extensive use in electrical industries as its conductivity is
second only to silver. It is far more cost effective than silver.
Engineering Studies – Page 88
Brass
Brass is an alloy of copper and zinc. Commercial brasses rarely contain more than 40% zinc, as beyond this level,
the alloy becomes brittle and is of little use. There are many different types of brass:
 cartridge brass contains 30% zinc and is ductile. It is used in the production of cartridges for bullets and
has higher ductility than copper from which it is mainly composed.
 standard brass contains 25% zinc and is a good quality, cold working alloy used where the ductility of
cartridge brass is not required.
 Muntz metal contains 40% zinc and is contains two phases. It is usually hot-worked to shape and is used
in the manufacture of rods and bars.
 naval brass contains 37% zinc and 1% tin, with the tin adding to the corrosion resistance in seawater.
 high tensile brass, also called manganese bronze, is a copper (58%), zinc (36%) alloy with small additions
of manganese, aluminium, lead, iron and tin. These improve the tensile strength over other brasses at the
expense of ductility. It is used for stampings and marine applications.
Bronze
Bronze relates to tin bronze which is an alloy of copper and tin. Tin bronzes usually contain tin within the range
of 3 to 18%. There are many different types of tin bronze:
 low tin bronze contains only 4% tin and demonstrates good elasticity and corrosion resistance. It is used
in springs.
 high tin bronze with large amounts of tin is used in heavy load applications such as slewing turntables
and on large cranes.
 admiralty gunmetal is a bronze with 10% tin and 2% zinc, with some nickel. The zinc makes the alloy
more fluid in the liquid state so it is better suited to casting. It is used for pumps and valves, especially in
marine applications.
 leaded gunmetal has 5% tin, 5% zinc and 5% lead which reduces ductility for pressure vessels.
 phosphor bronzes have phosphorus added and so tend to have higher tensile strength and corrosion
resistance than standard tin bronzes.
Aluminium bronze is a copper alloy in which the primary alloying element is aluminium, up to 11%. Aluminium
bronzes contain good corrosion resistance and good tensile strength. Their corrosion resistance sees them used
extensively in marine and chemical applications. Casting them is difficult because of the oxidation of the
aluminium. Aluminium bronze is hardenable through heat treatment.
Nickel
High nickel alloys exhibit exceptional corrosion resistance and elevated temperature strength. Many of the
physical properties of nickel such as melting point and modulus elasticity are similar to those of steel. Some nickel
alloys are called superalloys. This group of metal alloys all feature high temperature strength and resistance to
thermal shock. Superalloys have an FCC structure. Most superalloys have significant chromium additions which
forms an adherent oxide layer that restricts access of oxygen to the alloy surface, further impeding oxidation.
Magnesium Alloys
Magnesium is similar to aluminium. It is very reactive and combines with oxygen rapidly. Magnesium is used in
applications where lightweight materials are needed. Pure aluminium has poor ductility and tensile strength so
is usually alloyed with aluminium, zinc or manganese.
Structure/Property Relationship
The microstructure has a large impact on the properties of many nonferrous alloys. In many cases, a second
harder phase is often present which reduces ductility such as in Muntz metal.
Engineering Studies – Page 89
Heat Treatment of Nonferrous Alloys
Annealing
Annealing is performed to relieve internal stress. Each alloy has an optimum annealing temperature.
Precipitation Hardening
Precipitation hardening is performed on duralumin and other aluminium alloys. The aluminium alloy, after being
cast or hot worked, is a mixture of a primary phase (𝛼) and a secondary phase (𝛽) usually at the grain boundaries.
The alloy is heated to 530°C until the 𝛽-phase dissolves to produce a homogenous single phase alloy. The alloy is
then quenched to room temperature which results in equiaxed grains of 𝛼-phase. As the material ages, the
trapped 𝛽-phase precipitates out on the stress planes. This process is called natural aging. It is possible to
acceleration precipitation hardening by artificial aging. When aluminium bronze is quenched, it forms a
microstructure similar to the martensite in steels. It is named 𝛽 martensite and can be tempered.
Ceramics
Ceramics offer good properties that make them desirable for transport applications. Research has been
conducted into manufacturing petrol and diesel motors from ceramic materials to improve thermal efficiency.
Since ceramics can withstand higher temperatures than metal alloys, they could conceivably run at higher
operating temperatures without cooling systems. Modern ceramics such as partially stabilised alumina and
zirconia do not possess the brittleness normally associated with ceramics such as porcelain and china. They are
strong enough to withstand forces and shock waves in the internal combustion engine. Ceramics are now also
used for high performance disc brakes because of their improved performance at elevated temperatures.
Ceramics can also be used for insulation in applications where resistance to heat is required.
Ceramics are used as an insulating material in the spark plugs of cars. Spark plugs carry large voltages but are
also subjected to high temperatures which makes polymers unsuitable as an insulator. Alumina is used as an
insulator between the threaded metal body and the inner copper electrode. This stops the spark being earthed
by contact between the metal thread of the spark plug and the engine block. Ceramic insulators are also used to
support power lines. Glazed porcelain is typically used for this. The glaze is slightly conductive which prevents
the build-up of dust and dirt on the ceramic which would encourage arcing.
Glass
Glass is an inorganic fusion that has failed to crystallise upon cooling. Glasses are an amorphous material, which
means that they have no crystalline structure. The structure of glass does not allow for deformation. When glass
is deformed, it is unable to dissipate the applied forces through a slip/dislocation mechanism. Once the internal
bond resistance is exceeded, the structure fractures. The speed of fracture is very rapid.
Borosilicate Glass
Borosilicate glass contains up to 20% boron and silica. This gives the glass good chemical resistance and low
thermal expansion. Borosilicate glasses such as Pyrex™ are extensively used in electrical insulation, gauge glasses
for laboratory ware and in domestic cooking and ovenware.
High Silica Glass
High silica glass is refined from borosilicate glass and is nearly entirely made of silica (SiO2). These glasses are
clear and are used in situations where they experience high temperatures such as rocket nose cones and space
vehicle windows.
Soda Lime Glass
Soda lime glass is the most common form of glass and contains large amounts of soda (Na2 O) and lime (CaO). The
presence of the soda prevents devitrification (crystallisation) but makes the glass water-soluble. The addition of
lime alleviates this. Soda lime glasses soften at about 850°C and are easily formed to shape when hot. Soda lime
glass is used for window and plate glass, bottles, tableware, electric light bulbs and windscreens.
Lead Glass
Lead glasses contain up to 40% lead which lowers the softening temperature. They have a high refractive index
which makes them optically clearer. They are used extensively for optical glass such as in thermometer tubes
and table wear known as crystal.
Engineering Studies – Page 90
Heat Treatment of Glass
Glass is rarely used in its normal condition for transport devices. Normal glass is too brittle for these applications.
As a consequence, glass is typically laminated and toughened.
Thermoplastic Polymers (Thermosoftening Polymers)
Thermoplastic polymers soften on the application of heat. They can be remelted and reformed. Thermoplastics
have long linear chain structures with the chains formed by strong covalent bonds. Weak secondary forces (van
der Waal’s forces) hold the chains together. As a consequence, they are normally flexible and transparent. They
strength under tensile load as there is little resistance to straightening the chains. Examples of thermoplastic
polymers include polyethylene, polystyrene, polytetrafluoroethylene (PTFE), polymethymethacrylate (acrylic),
polypropylene, polyvinyl chloride (PVC) and acrylonitrile butadiene styrene (ABS).
Thermosetting Polymers
Thermosetting polymers undergo a chemical change when heat is applied. The change is not reversible so these
polymers do not soften when reheated. Thermosetting polymers consist of network structures with covalent
bonds along the chains and across the chains. They tend to be more rigid because of this structure. When under
tension, they resist deformation. Epoxy resins, silicone, polyurethane and polyester resins are examples of
thermosetting polymers.
Rubber
Rubber is a natural polymer. In synthetic form it has wide use in transport. The tyres for cars and cycles use a
modified rubber called vulcanised rubber. Rubber is a natural linear polymer that is too flexible for use in a tyre.
By adding about 5% sulfur to the rubber mix and heating it to 150°C, cross linking is achieved. The vulcanised
rubber is more rigid, but still flexible.
Engineering Textiles
Engineering textiles are polymer resins that are drawn into threads and then woven into cloth-like sheets.
Polyester is a synthetic fibre that is strong and resilient. It is also hydrophobic (resistant to water absorption). It
is used in helium airships and in the manufacture of some tyres. Nylon is used as a dry lubricant. It is now being
replaced by PTFE in most applications. It is resistant to acids, bases and oil. Aramid fibres are extensively used
in engineering. Nomex™ and Kevlar™ are the best known examples. These aromatic polyamide polymers are
strengthened by a backbone of benzene rings. They have good strength qualities but are limited to low
temperature applications. They are used in aircraft and bulletproof vests. Olefins are polyethylene or
polypropylene fibres shaped into sheets. They are waterproof and are used in the manufacture of collapsible
shelters and buildings. PTFE, commonly known as Teflon™ is fire resistant and impervious to water vapour. They
are used for filters in engines.
Manufacturing Processes for Polymers
Blow Moulding
Blow moulding is used to shape thermoplastics. A polymer tube is lowered into a mould and air forces the tube
into the shape of the mould. It is used to make plastic bottles and containers.
Extrusion
Polymers can be extruded in much the same manner as metals. Polymer granules are melted and the molten
material forced through a die. This process is only suitable for thermosoftening polymers. Polymer tubing is
manufactured using this method. The outer covering of bicycle cables is coated with plastic in this way.
Thermoforming
Thermoforming is used in the manufacture of thermoplastic containers. Heated thermoplastic sheets are placed
over dies to produce the required shape. The forming can be done by using matching dies, a vacuum or pressure.
Engineering Studies – Page 91
Calendaring
Calendaring involves pouring a thermoplastic into a cavity between two rollers. The plastic is then squeezed
through the rollers. The rollers can be embossed with patterns or they may be smooth. Tiles, films and curtains
are made this way.
Rotational Moulding
Rotational moulding involves pouring the polymer into a mould which is then rotated. The centrifugal force
propels the polymer to the walls of the contained, forming a hollow article.
Injection Moulding
Injection moulding is the most common forming procedure for polymers. Molten polymer is injected into a cavity
in the shape of the finished article. When the polymer sets, the item is ejected and the procedure repeats. Injection
moulding lends itself to mass production. Many items are injection moulded and these can be identified by a
small notch protruding from the item and a split line.
ENGINEERING ELECTRICITY AND ELECTRONICS
Power Generation
In Australia, electricity is generated by:
 coal burning power stations which use the heat generated from burning coal to produce steam which
drives a steam turbine. The turbine is connected to a generator that produces electricity as it spins.
 hydroelectric systems offer electricity without atmospheric pollution by utilising the potential and
kinetic energy of water flowing through turbines.
 wind power systems involve a turbine turned by the force of wind.
Nuclear power is not used in Australia. Nuclear fission power does not contribute to global warming. Only a small
amount of nuclear fuel is required to produce huge amounts of heat. It is non-polluting to the atmosphere but it
presents other problems. The byproducts of nuclear power generation are often contaminated for thousands of
years. Accidents at Three Mile Island and Chernobyl occurred due to human error and one at Fukoshima occurred
due to a large natural even overwhelming a failsafe mechanism.
Power Distribution
In recent years, many smaller power stations have been closed and replaced by larger ones in more remote
locations. This means that the distribution and carriage of electrical energy is very important. The power lines
used to carry electricity are steel-cored aluminium. The steel core provides the strength to let the wire support
itself and the aluminium provides the electrical conductivity. These cables are not being made with a carbon and
glass fibre reinforced polymer composite. Although aluminium has only 60% of the conductivity as does copper,
its vastly lower density means that per kilogram it is a better conductor. When copper conductors are used in the
railways, more poles are required to support the weight.
To reduce resistive losses in the aluminium cable, power is transmitted at very high voltages such as 500 kV.
Power loss is proportional to the voltage and the current squared. Raising the voltage reduces the current for the
same amount of power and thus reduces the resistive losses in the cable.
Engineering Studies – Page 92
AC and DC Circuits
Alternating current (AC) and direct current (DC) differ considerably. DC current has a constant potential. AC has
a constantly variable voltage. In Australia, the AC mains varies from 0 to +240 V to 0 to −240 V to 0 ever 0.02
seconds (50 Hz).
Rectification
Half wave rectification occurs when one diode is used. This
eliminates the current flowing the opposite way, so blocks half the
waveform. Full wave rectification can be achieved with four diodes.
This will allow the sine wave to pass, but will have all the waves on
the positive side. The final waveform is varying DC.
The varying DC can be smoothed by a capacitor to achieve a better
waveform. The capacitor stores energy that can be used when the
waveform reduces in voltage. The result is a nearly flat waveform
with the capacitor smoothing out the troughs.
Equivalent DC Voltage
The equivalent DC voltage of an AC current is
1
√2
times the peak AC voltage.
Electric Motors in Transport Systems
Many years ago, DC motors were used in trains, partly because it was difficult to control AC motors when the
generation driven by a diesel engine produced DC. Now, AC induction motors are used in diesel-electric trains.
DC Motors
Shunt wound motors are rarely used in locomotives. They have a constant speed but low starting torque and are
therefore not suitable for stopping and starting. Series wound motors offer excellent torque at low speeds and
will operate at high speeds under light load. Compound motors have good starting torque but will not run away
under no load.
AC Motors
AC motors used in trains are usually induction motors. These have no brushes or commutators which increases
their lifetimes. They rely on the frequency of the electricity and magnetic induction for their power. Their
function is aided by generators being replaced by alternators in diesel-electric motors. Alternators produce AC.
In the Channel Tunnel, locomotives are powered by single phase AC, which is rectified to DC for a control circuit,
then back to AC for the motors. The Sydney Trains M Sets, H Sets and A Sets use three phase induction motors.
The train uses an inverter to generate AC from the 1500 V DC supply. Pulse width modulation (PWM) is used to
control the motors.
Pulse Width Modulation
Pulse width modulation is a method of controlling electric motors. Instead of varying the voltage or current, the
supply is effectively switched on and off rapidly to replicate an average on time.
Control Technology
Control technology is the use of some type of mechanism or circuit to control the operation of an item. The simple
float arm in a toilet controls the water delivery. This is an example of control technology. In transport, one of the
earliest control devices was the governor on steam engines. Centrifugal force caused the arms to rise which
controlled the throttle system which maintained the engine at a constant speed. Cars have electronic cut-outs
that sense the speed of the crankshaft and cut the ignition if the engine revs to fast.
Engineering Studies – Page 93
ENGINEERING COMMUNICATION
Sectioning
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

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
Half section means half the sectioned view is sectioned, while full section means the section covers the
whole of the view.
Features like ribs are not sectioned to avoid confusion.
Bolts, nuts, studs and shafts are not sectioned.
Hatching lines are thin dark lines.
Hatching lines are 45° unless one side of the shape is at that angle.
If different parts are sectioned but are adjacent, first use the opposite 45° orientation, then use other
common angles such as 30° or 60°.
Hidden detail should not be shown on the sectioned view.
Engineering Studies – Page 94
ENGINEERING STUDIES
HSC Module 3: Aeronautical Engineering
SCOPE OF THE PROFESSION
Nature and Scope of the Aeronautical Engineering Profession
Aeronautical engineers are responsible for the design and development of new aircraft. They are also employed
in modifying and improving existing designs. The aeronautical engineer is required to take a set of requirements
and develop an aircraft that can perform according to the design specifications. Aeronautical engineers can work
closely with aerospace engineers, who are concerned with space flight and its requirements.
Current Projects and Innovations
Aeronautical engineers are constantly engaged in the design of new aircraft to improve air travel and defence.
Aeronautical engineers work with materials engineers to reduce the weight of aircraft. For many years, fighter
jets have used composite materials to reduce weight which can improve the range or allow for a greater weapon
load. In civil aviation, one of the most recent developments has been the Airbus A380. Its development depended
on larger power, increased lift and reduced weight. Another recent development has been the Boeing 787
Dreamliner, which is the first commercial passenger aircraft with carbon fibre composite fuselage.
Health and Safety
Aeronautical engineers are exposed to the risks of the profession and the area in which they are employed. They
may be exposed to machinery while overseeing manufacture or other safety risks when doing fieldwork. If the
engineer only works in the design office, then the risk to health and safety is minimised greatly.
Career Prospects
Although a vast country such as Australia has a vast need for aircraft, its requirements have never been able to
sustain an indigenous aircraft industry. During and after World War II, Australia had a strong aircraft industry
with the Commonwealth Aircraft Corporation (CAC) producing the Wirraway and Boomerang fighters and the
Woomera bomber. The greatest employer of aeronautical engineers are the Defence Forces. They have great
needs for engineers to deal with modifications and upgrades to the aircraft used.
Unique Technologies to the Profession
The successful development of the turbine has been a technology has stayed unique to the aircraft and the
aeronautical engineer. Many material technologies remain unique to the profession also, such as aircraft alloys.
Generally, there are four key material properties looked for in aeronautical engineering: strength to weight ratio,
formability, durability and corrosion resistance. However, materials used in aircraft manufacture must be stable
at high temperatures. In this aspect, titanium and nickel superalloys like Nimonic find extensive use. Extensive
use of composite materials and adhesive technologies have been developed in this field. Composites offer good
specific strengths and can be readily joined by adhesives.
Legal and Ethical Considerations
Ethics means the morality or treatment of moral questions or honourable actions in any situation. Professional
ethics should always govern the actions of the engineer. New developments continually raise the issue of
intellectual property. To protect these, engineers can patent them. Patenting involves registering a design so that
it is legally recognised as being owned by a particular person or company. If a design is patented, it is not ethical
for another company to copy that design. Some designs may be used under license by other companies. Patents
need not be granted on a finished product; they may be granted on an idea or a series of annotated sketches and
descriptions. While there are patents to protect a new development, some people have claimed patents hamper
development. IK Brunel claimed that patents had the potential to slow nineteenth century engineering, as new
developments could not be utilised by others. Patents eventually expire, although they can be renewed. Once this
occurs, anyone is free to use that design without compensation to the original patentee. While most people
comply with registered patents, some use unethical methods to obtain and copy registered designs. This is called
industrial espionage.
Engineers as Managers
Engineers may be the managers of the design process on a project such that they oversee a number of other
engineers working on the process. In a larger project, a hierarchical structure is established with different
engineers managing different aspects. Engineers can also manage companies because they have a valuable skill
set and common sense which often transfers well to the boardroom. It is important that engineering companies
Engineering Studies – Page 95
have a balance of engineers on the management team to ensure that the company does not lose its way in terms
of aircraft requirements.
Relations with the Community
Aeronautical engineers have a good relationship with the community. Through their designs, they provide people
with safe, fast transport. In recent years, aeronautical engineers have produced commercial aircraft that are
quieter than previously, through the development of turbo fan engines which produce around 10% of the noise
of turbojets. Even disarmament groups rarely vent their anger at aeronautical engineers for their development
of fighter planes. This is because they correctly see that it is the choice of governments to decide how to use these
devices, not the engineers.
HISTORICAL AND SOCIETAL INFLUENCES
The Early Years of Flight
Flight had been postulated for many years. Aerodynamic testing had also been done with unmanned gliders, but
it was not until 1903 that humans successfully flew. Wilbur and Orville Wright built a powered biplane, Flyer I,
which Orville flew successfully. At the same time, the French were working on similar projects to produce a viable
flying machine. Initially, banking was achieved by warping the wings. Harry Farman successfully used ailerons
to bank aircraft. Ailerons are a type of flap mounted on the outboard aft surface of each wing which move up and
hence vary the lift of each wing and allow the plane to bank. Other planes were then developed and by World
War I, the planes no longer resembled gliders. They were rapidly developed as German, French, British and
American air forces continually sparred the air.
Military Jets
In 1938, Englishman Frank Whittle had developed a working turbojet engine which promised great
improvements in speed and rate of climb. Once World War II began, it became a race between the British and the
Germans to produce the first jet fighter. The first flight of a turbojet aircraft was by a German Heinkel He178 on
27 August 1939. The Gloster Meteor was the first operational turbojet fighter, and first flew on 5 March 1943. In
Germany, the first operational jet fighter was the Messerschmitt Me262 Schwalbe which first flew in July 1942.
As the Allies thrust into Germany in the last days of the war, they acquired as much German jet technology as
they could. The Me262 became the basis for many jets. The British had also developed a centrifugal flow turbojet,
while the Germans used an axial flow turbojet. The problem with the centrifugal type was that it was bulkier, and
eventually all jets were designed to use the axial system.
In Britain, de Havilland led the way with the Vampire twin boom jet, but it was the United States that began to
fund fighter jet development. The North American F86 Sabre was an impressive aircraft with swept wings and
great manoeuvrability. In the USSR, the Mikoyan-Gurevich MiG 15 was also being developed. After the Korean
War, jets continued to increase in performance, and by the time of the Vietnam War, a variety of fighter jets
existed that could travel at twice the speed of sound.
In the 1960s, the General Dynamics F-111 utilised variable geometry technology in the wings, called swing wing.
This was to deal with the shockwave of high speed travel which necessitated swept wings due to the shock wave
effect of high speed travel. Swept wings have different aerodynamic characteristics which can reduce lateral
control and performance at low speeds and increase stall speeds. The F-111 countered this by having variable
geometry, or swing wings. These are controlled by the pilot and are swept forwards at take off and partially swept
back in flight. The swing wing technology made the plane more expensive and maintenance intensive. The Saab
AJ37 Viggan solved the problem of reducing take off and landing distances. This was achieved using a delta wing,
which was good for high speed, and forward canards to improve lift and enable good take off performance.
Another option for small airfield capability and operational versatility is vertical take off and landing (VTOL).
Most VTOL aircraft development was completed by the United States, although Britain and Russia have also
manufactured VTOL fighters. The British Aerospace Harrier uses a single turbofan with four outlet nozzles, two
per side, that direct the thrust through a 90 degree arc. When at maximum weight, the Harriers use a ski jump,
so they are a very effective STOL jet, while still having little need for long runways. Initially, the Harrier was
designed for the strike or ground attack role, but the Royal Navy purchased about twenty Sea Harriers prior to
the Falklands War against Argentina.
Engineering Studies – Page 96
Changes in technology have now seen a move towards more manoeuvrable, multirole fighters which can create
great savings because one aircraft can do a multitude of jobs. They still offer good payload and excellent
manoeuvrability, but may also be used for reconnaissance duties. The Eurofighter Typhoon makes extensive use
of composite materials.
Commercial Jets
In 1949, the turbojet was designed to fit into commercial aircraft. The United States was leading the world in
aircraft manufacture and Britain appeared to be languishing. In 1949, the British unveiled the de Havilland
Comet, which was a thirty-six seat aircraft, the design of which included swept winds, a pressurised cabin, four
jets in the wing roots, an aluminium stressed skin airframe and a top speed of about 800 kilometres per hour.
Immediately, American companies claimed that turboprop airliners could match this and that US jets would soon
be there, but airlines were eager for a newer, faster jet airliner.
The Comet entered service in 1952. On 26 October of the same year, a Comet ran off the end of the runway due
to a pilot error in raising the nose too high. In March 1953, over rotation during take off at Karachi airport caused
eleven fatalities. Later, a Comet was lost at an altitude of ten kilometres when it encountered severe turbulence
which caused the tailplane to fail.
On 10 January 1954, a British Overseas Airline Corporation (BOAC) Comet left Rome for London. The plane
exploded mid-air and was never found. Another aircraft exploded in similar circumstances a few months later.
One of the Comets was retrieved from the sea floor and examined. The Comet was tested inside a specially
constructed tank. The wings and fuselage were subjected to pressurisation, flight and undercarriage loads on
continuous cycles for twenty-four hours a day. The fuselage of the Comet ruptured in the test and the fault was
traced to two small fibreglass antenna windows. It appeared that the rivet pattern and design of the windows
promoted the propagation of fatigue cracks during pressurisation cycles. The result was catastrophic fuselage
cracking and explosive decompression. The fault finding cost two million pounds and the Comet was grounded.
Later, de Havilland released the Comet 4, which carried up to eighty-one passengers and became the first
passenger jet to make a regular transatlantic crossing. While the Comet had its many problems solved, Boeing
was putting the finishing touches on the Boeing 707. It also used a four turbojet design, but these were slung
underneath the wings. The 707 could carry more passengers, up to about 180. It was then followed by the
McDonnell Douglas DC-8. Between these two planes, most of the world’s commercial jet passengers were carried.
Passenger jets kept increasing in size. A huge step was taken with the development of the Boeing 747. It was
originally designed as a military transport for the US Air Force. Having lost the military contract, the 747 design
was converted for passenger usage. It was revolutionary in design and featured four high bypass turbofan
engines, advanced wing design and complex high lift devices. The original 747-100 would typically carry about
400 passengers.
While military jets were pushing past Mach 1 and then Mach 2, passenger jets were designed, because of size,
cost and technology, to operate at subsonic speeds. The first supersonic transport to enter service was the Soviet
Tupovlev Tu144. It bore a similarity to the Concorde, but after a crash at an air show, it was withdrawn. The
British Aerospace/Aerospatiale Concorde, which first flew in 1969, remains the only supersonic transport to
remain in regular service. It was revolutionary in utilising substantial military technology to produce fast
commercial transport. It was not until 2000 that there was a devastating crash with the Concorde, which marred
an otherwise good safety record. Debris cut the tyre, causing it to blow, resulting in tyre pieces hitting the
underside of the wing fuel tank. This caused a fuel leak, which ignited. As a result, the Concorde is no longer in
service. It proved that while supersonic passenger travel was possible, it was very costly and not as popular as
larger planes like the 747.
The McDonnell Douglas DC-10 was released shortly after the Boeing 747. It is smaller, and has three engines: one
on each wing, and one in the tail. The third engine was added to meet requirements to operate from existing
runways. This arrangement gives fewer problems with a single engine out, but the DC-10 suffered from early
teething problems and the some crashed due to inadequate maintenance. The DC-10 is still operated and is also
used by the US military as an in-flight tanker.
In the late-1970s, the USSR aircraft company Antonov developed what would be for many years the largest series
production aircraft. The An124 is a four engine body with a heavily constructed fuselage, complete with internal
cranes to cope with loads. It has the ability to lower its nose to reduce the ramp over angle for loads.
Engineering Studies – Page 97
In the 1980s and 1990s, Boeing continued to dominate the commercial aircraft market. McDonnell Douglas is
now owned by Boeing. The biggest development in the commercial jet family recently was the Airbus A380. The
aircraft first flew in 2005 and entered service in 2007. It has a larger capacity than the Boeing 747. Boeing based
much of its corporate plan on the 777 family of planes. These have a new wing design that uses composite
materials and much larger turbofan engines. The great reliability and thrust of modern turbofan engines used on
planes such as the 777 made trijets like the DC-10 obsolete. Now only the largest commercial aircraft need four
jet engines. The latest Boeing design, the 787 Dreamliner has focussed not on size, but on efficiency, by using
lightweight composites.
The Effects of Aeronautical Engineering on People’s Lives and Living Standards
The effect of the aeronautical engineers’ work has been astounding. Prior to the advent of the commercial
passenger aircraft, the trip from Sydney to London took six weeks by ship. It can now be done in twenty-four
hours. In regional Australia, the aircraft has had a great influence. The Royal Flying Doctor Service allows access
to medical facilities that could take days with road transport. Also, many farmers on large outback properties
utilise helicopters and light planes for checking their land, herding animals and crop spraying. Aircraft are also
used for geological surveying and cartographical services.
Aeronautical engineering has:
 made travel more accessible to people who have time constraints on holidays
 made overseas commerce more efficient and less costly in terms of time
 allowed families who live overseas to be brought closer together
 reduced the time of overseas postal and freight services
 for military purposes, developed to a point where they may be used instead of ground troops and with
fewer casualties
 allowed for aeronautical ambulances to get patients to hospitals more quickly
 allowed for easier bushfire fighting, protecting people and properties
 allowed images and information to be gathered more efficiently and quickly
 allowed people to be more easily transported in and out of remote areas
 boosted tourism.
Environmental Impacts of Flight
The ability of humans to fly has had an impact on the environment in a variety of ways.
 Pollution is created by both piston and turbine engines that are now used. Aircraft pollute the
environment with exhaust gases. There have been, however, advances in aircraft fuel technology and
engine flight management aimed at dramatically reducing air pollution from engines. There have also
been cases of fuel dumping, which is a serious form of pollution. Another type of pollution is noise
pollution, which is a contentious issue in urban areas.
 Insect spraying has become much easier and expanded to a large scale through use of both conventional
aircraft and helicopters. The ability of crop dusters to cover a large swathe of land has caused far greater
use of insecticides. These do protect crops, but have a major impact on the food chain. Concentrations of
these poisons increase up the food chain, leading to a concern for the food we consume.
 Destruction through the use of aerial bombing has been on the rise since World War II. The damage
caused to British cities by German forces and German cities by the Allies showed the true potential of the
aircraft in warfare. Allied bombers destroyed German industry which led to its eventual defeat. Saturated
bombing in the Vietnam War led to huge areas of forest being destroyed in an attempt to flush out the
Viet Cong troops.
Environmental concerns associated with aircraft include:
 noise pollution
 climate change
 stratospheric ozone reduction leading to increased surface UV radiation
 local air pollution resulting in decreased air quality caused by aircraft and also by the associated ground
transportation
 changes in tropospheric chemistry for tens to hundreds of kilometres downwind of airports due to
emissions of oxides of nitrogen and increases in ozone.
Engineering Studies – Page 98
Measures to reduce emissions from aircraft may include:
 alternative fuels such as liquid hydrogen
 operational improvements through direct routing of smaller aircraft
 higher load factors and optimisation of aircraft speed
 policies and regulations, including more stringent engine emission certification standards
 intermodal transport networks (substitution of short-haul air travel with rail and coach networks)
 technological improvements such as improved engine and airframe designs resulting in greater fuel
efficiency.
ENGINEERING MECHANICS AND HYDRAULICS
Aircraft Geometry and Terms
Component
Purpose
The fuselage houses the flight crew, passengers and freight. It is pressurised in large
Fuselage
aircraft to allow people to survive at high altitudes where turbine aircraft are most
efficient.
The wings provide most of the lift to support the weight of an aircraft. Different
Wing
shapes are used depending on the role of the aircraft.
Ailerons
Ailerons are the outboard trailing edge sections of the wing used to control roll.
Flaps are the inboard trailing edge sections, used to generate additional lift during
Flaps
low speed manoeuvring and landing.
Horizontal stabiliser The horizontal stabiliser, or tailplane, provides the down force to keep the aircraft
(tailplane)
level and stable.
Elevators are the trailing edge sections of the horizontal stabiliser, used for pitch
Elevators
control.
Some high performance delta wing aircraft have the wing and horizontal stabiliser
Elevons
merge at the back of the wing. Positioned on the outside of a delta wing trailing edge,
the elevons perform the role of both the elevator and the ailerons.
Fin (vertical
Fins, or vertical stabilisers, are used to provide horizontal stability. Together with
stabiliser)
the rudder, they provide yaw rotation.
Rudder
The rudder is the trailing edge section of the fin.
Undercarriage
The undercarriage provides a means of manoeuvring on the ground.
Engineering Studies – Page 99
Simple Level Flight Mechanics
In its simplest form, an aircraft flying at constant velocity in level flight can be considered to have a force
equilibrium of four concurrent forces.
 weight is the gravitational force on the mass of the aircraft
 lift is a force generated by airflow over the wing and the tailplane
 thrust is a forward force caused by the engines
 drag is a force resiting the movement of the aircraft through the air.
When an aircraft is travelling at a constant velocity in level flight, then:
lift = weight
𝐿=𝑊
thrust = drag
𝑇=𝐷
Complex Level Flight Mechanics
There are a number of important factors about level flight:
 the weight force acts through the centre of gravity
 the line of the thrust force is inclined to the direction of flight; the angle of attack (𝛼)
 the aerodynamic forces of lift are generated at the aerodynamic centre of the wind and the tailplane
 the centre of gravity in the aircraft moves during flight because of changes in passenger loading, cargo
and fuel usage which makes analysis more complex.
Σ𝐹𝑉 ↑+ = 0
0 = 𝐿𝑊 − 𝐿 𝑇 + 𝑇 sin 𝛼 − 𝑊
Σ𝐹𝐻 →+ = 0
0 = 𝐷 − 𝑇 cos 𝛼
Σ𝑀𝑐𝑔 ↷+ = 0
0 = 𝐿𝑊 𝑥𝑊 − 𝐿 𝑇 𝑥𝑇 − 𝑇 sin 𝛼 . 𝑑
Most medium sized aircraft have a centre of gravity in front of the lift vector and therefore the lift on the tailplane
must act downwards to maintain trim.
Steady Climb Flight Mechanics
If an aircraft is climbing at a constant angle 𝜃 relative to the horizontal, and realising that the thrust and drag
pass through the centre of gravity, then:
Σ𝐹⊥ ↗+ = 0
0 = 𝐿𝑊 − 𝐿 𝑇 − 𝑊 cos 𝜃
𝐿𝑊 − 𝐿 𝑇 = 𝑊 cos 𝜃
Engineering Studies – Page 100
Σ𝐹∥ ↘+ = 0
0 = 𝐷 − 𝑇 + 𝑊 sin 𝜃
𝑇 − 𝐷 = 𝑊 sin 𝜃
Σ𝑀𝑐𝑔 ↷+ = 0
0 = 𝐿 𝑇 𝑥𝑇 − 𝐿𝑊 𝑥𝑊
𝐿 𝑇 𝑥𝑇 = 𝐿𝑊 𝑥𝑊
By solving simultaneously:
𝑊 sin 𝜃
𝑇−𝐷
=
𝑊 cos 𝜃 𝐿𝑊 − 𝐿 𝑇
tan 𝜃 =
𝑇−𝐷
𝐿
Calculating Steady Climb Mechanics
Calculate the angle of climb for an aircraft with a lift to drag ratio of 15 and a thrust to weight ratio of 0.25.
𝑇−𝐷
𝐿
𝑇 𝐷
= −
𝑊 𝐿
tan 𝜃 =
= 0.25 −
=
(∵ 𝑊 ≈ 𝐿)
1
15
11
60
∴ 𝜃 = tan−1
11
60
≈ 0.181
≈ 10.4°
Engineering Studies – Page 101
Calculating Steady Climb Mechanics
An aircraft has a lift to drag ratio of 15. At an altitude of 1500 m, the engine fails. Will the pilot be able to glide
to an airport 16 km ahead?
𝑇 𝐷
−
𝑊 𝐿
1
=0−
15
tan 𝜃 =
(∵ 𝑊 ≈ 𝐿)
= −0.066
∴ 𝜃 = tan−1 −0.066
≈ 3.814
= 3.8°
The angle of glide = 3.8°
1500
𝑑
1500
𝑑=
tan 3.8°
tan 3.8° =
≈ 22.8 km
Therefore, it can reach the airport 16 km ahead.
Basic Aerodynamics
The basic principle of flight is centred on the aerofoil and the way it behaves as air passes over it. The aerofoil is
the cross-sectional shape that a wing or rotor blade had.
The Classic Theory of Lift
The classic theory of lift has been accepted orthodoxy
among many texts for educators for years. Airflow over
the top surface must accelerate to follow the curved
surface. This produces a region of low pressure above the
aerofoil according to Bernoulli’s principle. The difference
in pressure between the upper and lower surfaces acting
on the aerofoil produces lift. Airflow along the lower
surface of the wing decelerates, creating a region of
slightly higher pressure, thus acting to lift the wing. The
speed at which the air passes over the aerofoil is crucial, as is its angle. These determine the amount of lift. The
angle that the aerofoil makes with the oncoming air is called the angle of attack. The aircraft must be moving to
get relative movement between the air and the wing, so a plane must travel along the runway until the required
take off speed is reached.
Lift from Flow Turning Theory
The problem with the classic theory is that it does not fit with lift generation and relies on questionable
assumptions. An alternative theory is that the lift force is created by the action of turning the flow of air. Since
𝐹 = 𝑚𝑎 shows that acceleration is the rate of change of velocity over time, by turning the flow of air, the velocity
changes direction. This changing velocity gives an acceleration which creates the lift force. A related by incorrect
theory is that lift is created by the wing deflecting air. While this theory holds for hypersonic speeds, it is not
quite correct for most aircraft, because it ignores the role of the upper surface of the aerofoil.
Engineering Studies – Page 102
Stalling
Stalling can be a dangerous aspect of flight that is often confused with the engine stopping. When a plane stalls,
it means that the wing no longer produces lift. This can be particularly dangerous at low altitudes when the pilot
does not have enough time to recover the aircraft. In level flight, lift is produced according to the theories above.
However, the wing can stall if the airspeed is reduced below a certain point, or if the angle of attack is increased
beyond a certain point. When the wing stalls, the air flowing over it cannot follow the surface, and hence it breaks
up and causes turbulence. This means a reduction in lift. Stalls may occur during landing as the aircraft has its
nose up and is slowing down, but the aircraft have stall warning devices to warn the pilot of an impending stall.
As a plane lands, the pilot will reduce power and raise the nose of the plane to increase drag. This is desirable,
except that as the airspeed falls, the angle of attack increases, and a stall becomes more likely. To avoid this, flaps
are placed on the plane wings to increase the lift generated at a given angle of attack and airspeed. This allows
the aircraft to produce the required amount of lift at low speed. Flaps also produce additional drag to slow the
plane down.
Slats are sometimes fitted to the leading edge of the winds to channel air over the front of the wing and force the
airflow over the wing. Slats are retractable and fitted to large commercial aircraft to reduce the chance of stalling
when flying at high angles of attack.
Stalling may also occur in manoeuvres when tight turns or steep climbs may cause the airflow over the wing to
separate. Stalling has little to do with the engine. A plane can stall with the engine at full power. This is a danger
with taking off in confined areas where the plane must climb and turn sharply immediately after take off.
Lift to Drag Ratio
The lift to drag ratio is a measure of the amount of lift compared to the drag the plane has. A high lift to drag ratio
is preferable. The lift to drag ratio has a large effect on the range of a commercial aircraft, because a low lift to
drag ratio will mean that the plane uses more fuel. In unpowered aircraft such as gliders, a high lift to drag ratio
will allow a glider to travel further as it descends.
tan(glide angle) =
drag
lift
𝐷
= cot 𝜃
𝐿
Glide Angle
The glide path allows the aircraft to maintain airspeed which, in turn, assists in the creation of lift, thus holding
the aircraft aloft. The shallowest glide angle is obtained when, for the required lift, the drag is at a minimum.
When the lift-to-drag ratio is high, the glide angle is shallow, and the plane will glide a long distance.
Engineering Studies – Page 103
Calculating the Lift to Drag Ratio
A glider and pilot have a combined mass of 850 kg and the glider is descending at an angle of 15° to the horizontal
at a constant velocity. Determine the lift of the glider and then calculate the lift to drag ratio.
cos 15° =
𝐿
𝑊
𝐿 = 𝑊 cos 15°
𝐿 = 8500 cos 15°
≈ 8.2 kN
tan 15° =
𝐷
𝐿
𝐿
= cot 15°
𝐷
= 3.73
Effect of the Angle of Attack
The angle of attack (𝛼) refers to the angle the aerofoil makes with the oncoming air. Higher angles of attack will
create greater lift up to a point. If the angle of attack is too great, stalling may occur and then the lift falls away
sharply. There are three basic methods an aircraft can use to increase the lift force over its wings: increasing the
angle of attack, increasing the camber of the wing, increasing the speed of the aerofoil relative to the airflow over
the wing.
Bernoulli’s Principle
Bernoulli’s principle states that increases in fluid velocity result in lower pressure. When fluid moves through a
piston, at first the piston is moving at velocity 𝑣1 at a distance 𝑦1 from the base. Later, it is moving at velocity 𝑣2
and distance 𝑦2 from the base.
𝑊 = Δ𝑃𝐸 + Δ𝐾𝐸
Bernoulli’s principle states that at any point in the fluid:
1
pressure + density × acceleration due to gravity × height + × density × (velocity)2 = constant
2
1
𝑃 = 𝜌𝑔𝑦 + 𝜌𝑣 2 = 𝑘
2
Venturi Effect
If there is no difference between the height of the pipes, then Bernoulli’s equation simple becomes:
1
𝑃 + 𝜌𝑣 2 = 𝑘
2
Engineering Studies – Page 104
With a Venturi, mass must be conserved, so when a fluid of certain density is flowing at a velocity through a pipe,
when the pipe’s area reduces, only a smaller volume of fluid can flow through, but to keep mass conserved,
velocity must increase. So whenever a flowing fluid reaches a constricted section, the rate of flow increases.
Helicopters
A helicopter is any aircraft that employs rotating wings to provide lift, propulsion and control forces. Helicopters
are able to:
 fly backwards
 rotate in the air
 hover motionless in the air.
The basic principles of lift still apply to the aerofoil cross-sectional shape of the rotors on a helicopter. The
purpose of the tail rotor is to counteract the torque effect and prevent the helicopter from rotating. The main
rotor is powered by an engine connected to the rotor shaft. Vibration forces generated by the helicopter’s rotor
and transmitted to the airframe can result not only in passenger discomfort but also reduce the life of the
airframe components and increase maintenance costs. Engineers have been force to use a variety of dampening
and counteracting techniques to keep vibration at acceptable levels.
Stresses on Aircraft
Numerous forces and structural stresses act on an aircraft when it is in flight. Under flight conditions, any action
by the aircraft that causes acceleration or deceleration places stress on the wings and fuselage. Stresses such as
these are absorbed by the structural components of the wings and transmitted to the fuselage. Stresses induced
into aircraft and their structures include:
 vibration
 wind shear
 take-off and landing stresses
 temperature stresses
 pressure differentials.
Propulsion Systems
Propulsion systems are required on an aircraft to generate thrust. Aircraft either rely on a propeller or a turbine
to provide thrust.
Piston Engines
Flat horizontally opposed piston engines are usually used in small commercial aircraft. The piston engine does
not offer the same performance as a turbine, but they are cost effective for small planes and powerful enough for
most small commercial applications. They work similarly to the piston engine in some motor vehicles, except
that they usually use a carburettor, whereas most new cars use fuel injection systems. To improve the
performance of piston engines, they may be turbocharged or supercharged. Many high performance piston
engine planes use turbochargers. Turbochargers and superchargers both force air into the engine under great
pressure which increases the power. The turbocharger is driven off exhaust gases of the engine, while a
supercharger is belt or gear driven off the crankshaft. Piston engine planes use a dual independent ignition
system running in parallel, which provides more efficient fuel combustion and greater safety. Carburettor planes
also have a special heater in the carburettor to stop fuel icing up.
Turbojet
The turbojet is the original form of the jet engine. The process that occurs within a turbojet is as follows:
1. Inlet – air enters and is compressed slightly.
2. Compressor – sets of turning blades compress the air which causes it to heat up.
3. Combustor/burner – fuel is injected into the combustion chambers, where it is mixed with the
compressed air and burned.
4. Turbine – burnt gases expand through the turbine stages, which are rotated by the gas flow. The turbine
is connected on the same shaft as the compressor and provides the energy to drive the compressor. The
turbine only extracts enough energy to keep the compressor going.
5. Nozzle – the gas is expanded through the nozzle and exits the engine as very hot, very fast gas, providing
the thrust.
Engineering Studies – Page 105
Turboprop
The turboprop has the same operation as the turbojet, except that the turbine is used to power the compressor
and drive the propeller. The majority of the energy of the gas is used to drive the turbine, leaving only a small
amount of exhaust energy to provide the thrust.
Turbofan
The turbofan has the same operation as the turbojet, but with an additional fan state mounted inside the nacelle,
forward of the compressor. An additional turbine stage drives the fan. Although turbofans were used prior to the
Boeing 747, the turbofans fitted to the 747 were the first high bypass turbofans used. They are known as bypass
engines because the majority of the air entering the engine nacelle passes around, not through, the engine. The
fan acts as a ducted propeller producing thrust from the bypass air, while the engine still produces thrust as per
the turbojet. A majority of the net thrust is produced by the fan. The advantages of turbofans is that the bypass
air shields the hot engine core gases, significantly reducing the noise, and moreover, most of the air is lower
velocity bypass air, which also contributes to noise reduction. They are more efficient than turbojets, particularly
at the transonic speeds of the commercial jet airliner.
Ramjet
The ramjet is simple because it has no moving parts. The shape of the engine compresses the air entering. This
compressed and hence heated air has fuel injected and then a flame holder ignites the fuel air mix. The expanding
gases are forced out the nozzle to produce thrust. The ramjet, however, needs to reach high speeds to work,
which makes it useless for take off, landing or low speed manoeuvres.
Scramjet
A scramjet is a supersonic combustion ramjet. All of the preceding jet engines required the air entering the motor
to be slowed to subsonic speeds. A scramjet operates similarly to the ramjet, but the airflow through the scramjet
will be supersonic. This allows scramjets to operate effectively above speeds of Mach 3.
Fluid Mechanics
Fluid mechanics is the study of fluids in motion or at rest. Fluids are both liquids and gases
Pascal’s Principle
Pascal’s principle states that the pressure applied to an enclosed liquid is transmitted undiminished to every
point in the fluid and to the walls of the container. A common use for Pascal’s principle is in sealed hydraulic
systems. In a sealed hydraulic system, pressure must remain constant.
𝐹1 𝐹2
=
𝐴1 𝐴2
In aviation, the two aspects of fluid mechanics considered are:
 the systems of sensors used in the aircraft’s instruments
 the systems of fluid pressure used in an aircraft’s avionics.
Each of the above components of an aircraft’s flight and control systems may be connected or operated by
complex and sophisticated hydraulic networks. Specifically, fluid mechanics applied to the aircraft components
include:
 flight sensors
 de-icing systems
 operating control surfaces
 raising and lowering of the landing gear
 opening and closing doors and hatchways
 shock absorption systems and valve lifter systems.
These networks contain high-pressure fluids capable of withstanding below-freezing temperatures and are aided
by servos and fluid pressure sensors.
Engineering Studies – Page 106
Hydrostatic Pressure
Hydrostatic pressure is the pressure that results from a static fluid. Air pressure is an example of static pressure.
In aerodynamics, hydrostatic pressure is called static pressure. A still gas or fluid will produce a static pressure,
either due to the mass of the fluid acting on the container, or through the random movement of molecules, as in
a gas. If an object is placed in a fluid, the fluid pressure will act upon the entire surface of the object at right angles
to the surface. The pressure may be defined as the force per unit area.
force
area
𝐹
𝑃=
𝐴
pressure =
The cross-sectional size or shape of a container does not affect hydrostatic pressure, but the depth does. The
deeper something is under the surface of a fluid, the greater the pressure exerted on the item. Hydrostatic
pressure can be determined by the depth of the container.
pressure at depth ℎ = pressure at the top + density × acceleration due to gravity × depth from top
𝑃 = 𝑃0 + 𝜌𝑔ℎ
Calculating Pressure
The gauge float in a fuel tank is jammed at the bottom of the tank. The float is 300 mm below the surface of the
diesel and the density of the diesel is 800 kg m−3. What will be the pressure on the float if the pressure at the
surface is 101 kPa?
𝑃 = 𝑃0 + 𝜌𝑔ℎ
= 101 × 103 + 800 × 10 × 0.3
= 103.4 kPa
Dynamic Pressure
Dynamic pressure is the pressure that occurs from a moving fluid. This moving fluid tends to create pressure
because of ordered velocity. With dynamic pressure, the movement is ordered, and the velocity of the fluid and
its density can be used to determine the dynamic pressure.
1
× density × (velocity)2
2
1
𝑃𝐷 = 𝜌𝑣 2
2
dynamic pressure =
Applications of Pressure to Aircraft Components
Hydrostatic and dynamic pressures have a large impact on aircraft structures. Many aircraft are pressurised to
allow them to fly at elevated altitudes. When this occurs, the cabin is pressurised. Therefore, there is a static
pressure difference between the inside and outside which the structure must be able to withstand. When an
aircraft climbs to a height and descends again, pressure in the cabin is increased or decreased. This static
pressure differential stresses the cabin each time, meaning there is the potential for metal fatigue.
All aircraft are subject to dynamic pressure as the aircraft encounters the air in flight. The airframes of supersonic
aircraft are subjected to very large amounts of dynamic pressure because of their high speed. Jet engines are
subjected to large amounts of dynamic pressure through the intake of air and the thrust produced. Many jet
aircraft use reverse thruster vanes which guide the jet thrust forward to air in braking following landing. Such a
device undergoes immense amounts of dynamic pressure, as it is actually changing the momentum and direction
of the fluids, which puts large dynamic pressures on them.
Engineering Studies – Page 107
The Pitot Tube
Aircraft instruments rely on the principles of aerodynamics to convey flight information to the pilot. One of the
simplest examples is the pitot tube. This small tube is placed under the wing or on the nose of the plane to
measure the speed of the aircraft. Its operation is based on difference between static and dynamic pressure.
When the aircraft is flying, air is forced into the tube. Relative to the aircraft, this air has velocity and hence
dynamic pressure. The total pressure is registered by the pitot tube. Around the circumference of the tube there
are a number of orifices that measure static pressure. The respective pressures act on two areas that are
separated by a pressure transducer. A strain gauge is used at the transducer to detect movement in the
transducer to determine the pressure differential. Velocity can then be calculated. By measuring the total and
static pressure, the pitot tube can read the forward airspeed. Pitot tubes need modifications to work with
supersonic aircraft.
The Airspeed Indicator
Many airspeed indicators are actually mechanical devices. In such a device, the total pressure entering the pitot
tube acts on the inside of a diaphragm. The outside of the diaphragm is surrounded by static pressure. The
diaphragm is connected to a linkage that controls the airspeed indicator. The diaphragm positions itself
according to the difference between the dynamic pressure and the static pressure.
The Altimeter
The altimeter is used to measure altitude. It works on the principle of having a small expandable vessel of air
called an aneroid, surrounded by static air pressure. As the aircraft ascends, the static air pressure falls, which
allows the aneroid to expand. This expansion acts on the linkage system which controls the needles on the
altimeter.
The Vertical Airspeed Indicator
A vertical airspeed indicator requires reference to the outside static pressure. Air pressure inside an instrument’s
diaphragm is calibrated at sea level. A diaphragm is used in aircraft instruments to sense this vibration of
pressure and measure height and airspeed. The diaphragm is sealed with sea-level air pressure and is lifted into
a lower pressure zone which causes it to expand. The expansion is measured and displayed on a dial.
ENGINEERING MATERIALS
Specialised Testing of Aircraft Materials
The aircraft requires extensive materials testing to ensure that the airframe is in good order. As a consequence,
a variety of non-destructive tests are used to ensure the airframe is sound.
Magnetic Particle Testing
This process is used to find cracks in a part. The piece of metal is placed across two magnetic poles or a magnetic
field is induced in it, and then it is sprinkled with magnetic powder. The excess powder is removed and the cracks
are revealed by magnetic powder sticking to the area each side of the crack. This occurs because each side of the
crack becomes a magnetic pole. The major limitation of this method is that it only works with magnetic materials,
so it cannot be used for aluminium or titanium alloys.
Gamma Ray Testing
Gamma ray testing is similar to X-ray testing, but uses gamma rays which have greater penetrative abilities. They
are, however, much more dangerous, so safety precautions must be in place before they are used.
Aluminium Alloys
Aluminium and its alloys are used in aircraft because of their desirably low density. When duralumin is age
hardened, it is possible to refrigerate it so that it does not age. This is done so it can be naturally aged in service,
hence receiving the max strength while in service. The properties of aluminium and its alloys include:
 excellent corrosion resistance
 good electrical and heat conductivity
 good machining and welding properties
 lightweight (2.70 g cm−3, steel is 7.87 g cm−3)
 low fatigue strength, especially when precipitation hardened
 crystal structure is FCC, so ductile at all temperatures.
Engineering Studies – Page 108
Aluminium Copper (2𝑥𝑥𝑥)
This range of aluminium copper alloys are the most common family of alloys used in aircraft today. Formerly,
duralumin, 2017, was widely used but 2024 alloys offer higher tensile strengths, so these have largely replaced
it. The 2𝑥𝑥𝑥 series of alloys have better resistance to crack formation and are thus likely to be used on the lower
surfaces of wings and the fuselage, where they are most likely to suffer from tensile loads and fatigue cracking.
They are usually used in clad form due to having poorer corrosion resistance than pure aluminium.
Aluminium Silicon
Aluminium silicon alloys are used for casting. The silicon improves the casting properties of the alloy and they
exhibit good corrosion resistance.
Aluminium Silicon Magnesium (6𝑥𝑥𝑥)
Aluminium silicon magnesium alloys are used in wrought form and as a casting alloy. These are readily heattreatable by precipitation hardening. Although not as strong as the 2𝑥𝑥𝑥 series, they are more easily worked and
offer better corrosion resistance.
Aluminium Zinc Magnesium (7𝑥𝑥𝑥)
Aluminium zinc magnesium alloys are extensively used for various parts of the airframe. These may also have
additions of copper and are more heat treatable than the 2𝑥𝑥𝑥 series, but stress corrosion cracking presents a
problem.
Aluminium Lithium Alloys
The high strength of aluminium lithium alloys and low densities means that they are challenging to use. They are
extensively used in military aircraft and space vehicles. The final version of the external fuel tank of the Space
Shuttle was made of aluminium lithium alloy which saved about 3.4 tonnes of weight.
Alclad
Alclad is duralumin that is clad with pure aluminium. This is done because duralumin is not as corrosion resistant
as pure aluminium. The duralumin substrate and pure aluminium sheet are rolled together and pressure welding
used to join them. The aluminium sheet generally accounts for about 1% of the total thickness of the two.
Nickel and Cobalt-based Alloys
Nickel-chromium-iron, nickel-chromium-cobalt and nickel-chromium-molybdenum-iron alloys are often known
as superalloys for their high temperature strength, creep and corrosion resistance. In gas turbine engines, heat
resistant nickel-based alloys make up the compressor blades and turbine blades. The most widely used
superalloy is N07718, Inconel® 718, which contains 52% nickel. Major advantages include improved weldability
and castability, low cost and ease of manufacture.
Grain size is very important. It influences the yield strength, impact toughness, elongation and creep resistance.
The development processes for the production of turbine blades which must operate at high temperatures has
therefore been designed to reduce the number of grain boundaries, particularly those oriented normal to the
blade axis. Grain size can be influenced in a number of ways. The most fundamental of these is to control the rate
of solidification. Several techniques have been developed to obtain directional growth. One of these, normal
freezing, involves placing the metal in a small crucible and melting it in a furnace. A crystal of the preferred
orientation is placed at one end of the crucible. Heating is then performed such that the charge and part of the
seed crystal is melted. The furnace is slowly moved so that solidification begins from the seed crystal and follows
its orientation.
A method known as crystal pulling or the Czochralski technique can be used to produce crystals of germanium
or silicon and involves touching the surface of the molten charge with a seed crystal attached to a rod. The rod it
then rotated as it is gradually raised from the surface, developing a crystal as it goes.
Titanium
Titanium has a density over one and a half times that of aluminium, but when alloyed with other elements, it is
especially useful in load-bearing applications. A common alloy used in engineering applications is Ti-6Al-4V. This
provides strength, stiffness, ductility and higher temperature resistance than aluminium alloys.
Engineering Studies – Page 109
Thermosetting Polymers
Polymer technology is increasingly important in aircraft as a solution to keeping the weight down. Thermosetting
polymers such as epoxy resins find extensive use as a matrix material for fibre reinforced composite construction
in aircraft.
Compression Moulding
This process takes an unpolymerised preform and compresses it in a mould with heat. The heat and pressure
form the shape and polymerise the polymer. The finished moulding is then ejected. It is used for making plugs,
switches and casters.
Transfer Moulding
Transfer moulding is similar to compression moulding, but instead of polymerisation occurring in the mould, it
happens in the adjacent cavity. The molten polymer is transferred via a sprue to the actual mould. It is used for
moulding thermosets.
Hand Lay Up Moulding
This is where fibres are placed into a mould and the resin is manually applied onto the fibres. First, a gel coat is
applied, then the fibre reinforcement is added in the form of a mat or cloth. The resin is poured in, brushed or
sprayed on and then rollers are used to force the resin to impregnate the fibre mat. In areas where extra thickness
is required, more fibre mat is placed down and the resin rolled into that area again. It is essential that the resin
properly bonds to the fibres. An alternative to lay up moulding is spray up moulding, where a special gun sprays
the resin and continuous strand roving glass fibre is cut to size and sprayed at the same time. It is rolled to remove
air and improve the impregnation of the resin into the fibres.
Vacuum Lay Up Moulding
The vacuum bag autoclave process is usually used with epoxy resin based composites. The material used is
prepreg and is unidirectional carbon fibres within a partially cured epoxy resin. The material is arrange din layers
in the mould and then placed in a bag. A vacuum is applied to the bag which removes any air within the laminates.
The bag is then placed into an autoclave at an appropriate temperature and elevated pressure where curing is
then completed. For epoxy resins, the autoclave will be set to a temperature of about 190°C and 690 kPa.
Composites
Composites are one of the newest and most important areas for aircraft manufacture. Composite materials offer
good specific strength, high resistance to cyclic stresses and weather resistance. Composites may be degraded by
UV light, but making them heavily pigmented reduces this. Composites may be manufactured to be stronger in
one direction than another. A composite may be isotropic (equal strength in all direction) or anisotropic (strength
in one direction).
Glass Fibre Reinforced Polymers
Glass fibre reinforced polymers, or fibreglass, are fine glass fibres embedded in a resin matrix. Polyester, vinyl
ester and epoxy resins are all possible resin materials. The glass fibre provides tensile strength while the resin
provides toughness. Although not quite as strong as other fibres and also heavier, they are a cost effective option
that has found aeronautical use in fibre metal laminates.
Carbon Fibre Reinforced Polymers
This is one of the most important composites in the aeronautical industry. Carbon fibre reinforced composites
are a composite of carbon fibres embedded in a resin matrix. Normally, this is epoxy resin. This combination of
the two components provides desirable strength and toughness properties. Typically, carbon fibre reinforced
polymers consist of 62% by volume carbon fibres. The material is lightweight, has high specific strength
properties and a high modulus of elasticity. Particularly important is the resistance to cyclic stress that carbon
fibre exhibits. It is these properties that make it desirable for aircraft. One disadvantage of carbon fibre reinforced
composites is that it fails like a brittle material with no plastic deformation.
Aramid Fibre
Aramid fibre reinforced composites are very similar to carbon fibre composites, but use Aramid fibres. Aramid,
or Kevlar, offers similar properties to carbon fibre, but is more impact resistant and abrasion resistant. This is
important in some battlefield conditions where shrapnel and debris could shorten the life of a carbon fibre
component due to surface defects.
Engineering Studies – Page 110
Fibre Metal Laminates
These are laminated structures of metal and fibre reinforced composites. The most common is GLARE (Glass
Laminate Aluminium Reinforced Epoxy), which is used in the Airbus A380. Because they are laminated with
metals, they perform more like metal sheeting than fibre reinforced composite sheets, but they offer enhanced
properties to a non-laminated metal sheet. Advantages include improved impact resistance, better fatigue and
corrosion resistance and weight advantages. They can also have their strength properties directional for specific
locations in the fuselage.
Metal Matrix Composites
Much research has been conducted into metal matrix composites. They are similar to fibre metal laminates and
aramid fibre, but the matrix is a metal, not a polymer. An example is boron fibre aluminium, which is a composite
using an aluminium matrix with boron fibres to reinforce it. This improves the tensile strength of the aluminium
alloy. Continuous fibre reinforced metal matrix composites give greater tensile strength but are difficult to make.
The discontinuous fibre reinforced metal matrix uses powder metallurgical techniques. They are capable of
withstanding higher temperatures than composites with epoxy matrices, but they are heavier.
Adhesives
Adhesives are used to join composite aircraft surfaces to the base structure.
Structure/Property Relationships
The structure of fibre reinforced composites has a big impact on their behaviour. This is because the way that
the fibres are arranged will affect how the loads are carried. Unidirectional fibres are fibres that all travel parallel
to one another. These include materials like continuous metal matrix composites. These materials are very
effective at carrying a load parallel to the fibres. They are, however, more likely to suffer separation of the fibres
if bending occurs. Such materials are termed anisotropic, meaning that their properties differ in different
directions. It is possible to arrange shorter fibres in random directions, but this will lower the maximum tensile
strength. Another option is to angle the fibres at 45° to each other. This is similar to plywood and will produce a
material that maximises strength in the desired directions.
Corrosion
Corrosion is a great problem in aircraft design. The frames and skin of aircraft are already highly stressed, so
weakening via corrosion is a major concern. Although composites offer resistance to electrochemical corrosion,
UV light and other weather may degrade them. A large majority of aircraft still use metal airframes and skins, so
corrosion is still a problem.
Pit and Crevice Corrosion
This is a concentration cell that occurs because of different oxygen levels at the top and bottom of a crevice.
Crevice corrosion normally involves a fine gap that traps a fluid at the base. This type of corrosion is a concern,
as metal aircraft are often riveted with fine gaps where the skins join. Moisture forms in these gaps each time the
aircraft crosses the dew point. The dew point is a particular combination of pressure, temperature and moisture
where water precipitates onto a surface. Aircraft always have moisture on them because of:
 condensation on the airframe from temperature changes in the atmosphere
 airborne moisture accumulating
 rain.
Stress Corrosion Cracking
This is a particularly dangerous form of corrosion, where the action of tensile stress and a corrosive environment
cause crack formation. The stresses that cause stress corrosion cracking can be residual stresses or applied. On
their own, neither would cause failure, but the two combined can cause failure to occur. Different alloys are
affected by different environments. Stainless steels are susceptible to stress corrosion cracking in chloride
environments but same in ammonia environments. In stress corrosion cracking, the combined action involved
the tensile stress causing pits or cracks to form and then the corrosion occurring within the tip of the crack, which
causes it to become anodic. Applying cathodic protection will prevent this type of corrosion. Reducing stress
levels or removing the corrosive environment will also reduce this corrosion cracking.
Engineering Studies – Page 111
ENGINEERING STUDIES
HSC Module 4: Telecommunications Engineering
SCOPE OF THE PROFESSION
Nature and Scope of Telecommunications Engineering
Telecommunications engineers are responsible for the design and development of communication equipment
and infrastructure. Telecommunications include telephones (fixed and mobile), satellite systems, television
networks and radio networks.
Health and Safety
Telecommunications engineers oversee the manufacture and installation of broadcast, telephony, satellite and
cable systems. Work safety concerns include ergonomics, lighting, electrical hazards and housekeeping.
Technologies Unique to the Profession
Many technologies required for successful telecommunications are not unique to the profession. The industry is
heavily dependent on semiconductors, but these allow telecommunications engineers to develop unique
technologies like digital television, FM radio and mobile telephones. Satellite technology is almost exclusively
used for telecommunications. The use of satellites has allowed the telecommunication revolution to occur.
HISTORICAL AND SOCIETAL INFLUENCES
Historical Developments
The need for people to communicate with one another quickly over ever-increasing distances was an outcome of
the Industrial Revolution. The spread of railways increased the need to convey timetable information between
centres. The electric telegraph was a solution to the problem and worked by sending electrical impulses of
different lengths along overhead cables to a receiver.
The telegraph had been used for nearly forty years before Alexander Graham Bell invented the telephone. Bell
was working on a machine to allow one to converse with the deaf. Bell used sound waves to make a diaphragm
of thin metal vibrate, and expanded this to send a signal down an electrified line. The telephone has not much
changed since. The first telephones were connected to an exchange, where the call was connected by an operator
to the receiver. As the telephone became more popular, the operated exchange became inadequate. The Stowger
switch allowed for automatic telephone exchanges. Computer based exchanges are now used.
The Radio
The big advantage of the radio is its ability to transmit sound without wires. The telephone depended on
expensive cabling that was slow to install, whereas radio equipment was simple. Guglielmno Marconi is credited
with the invention of the radio. Early radios were installed in lighthouses to report on the progress of shipping.
The innovation of wavelength tuning was necessary because it allowed many different signals to be transmitted
simultaneously without interference.
The Effect of Telecommunications Engineering on People’s Lives
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Australia was linked to Europe and Asia by telegraph in 1871 which allowed more rapid communication
with Britain.
The introduction of the telephone allowed smaller groups of people to communicate more directly.
Telephones expanded the availability of communication and information.
The internet originally used existing telephone lines.
The mobile telephone has revolutionised personal communication by making a person contactable in
most places around the world.
The internet has allowed the dissemination of information instantaneously across the world.
The radio was used to improve the safety of ships and shipping.
Engineering Studies – Page 112
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The sinking of the Titanic made shipping safer, as ships were required to monitor radios continuously.
The radio was a vital link for all people in the outback for communication and news.
It was used in World War II to communicate between units.
Radio is still used in communications such as between trucks and buses.
ENGINEERING MATERIALS
Specialised Testing
To test whether a material is suitable for use in telecommunications, its resistivity must be assessed. A material
with a high resistivity is suitable for use as an insulator, whereas one with a lower resistivity might be used as a
conductor.
Resistance Testing
An ohmmeter is used to measure electrical resistance and opposition to an electric current. The unit of
measurement is the ohm (Ω). Often ohmmeters are incorporated into multimeters. Most ohmmeters are now
digital. Earlier instruments used a galvanometer type display. Most ohmmeters measure the voltage and current,
then apply the resistance formula to calculate the resistance encountered:
𝑉
𝑅=
𝐼
Voltage
A voltmeter is used to measure voltage (potential difference) across a component or circuit. The unit of
measurement is the volt (V). Often voltmeters are incorporated into multimeters. Most voltmeters are now
digital. Earlier instruments used a galvanometer type display. Voltmeters must be connected in parallel across
the component or circuit being tested.
Current
An ammeter is used to measure the current passing through a component or device. The unit of measurement is
the ampere, or amp (A). Often ammeters are incorporated into multimeters. Most ammeters are now digital.
Earlier instruments used a galvanometer type display. Ammeters must be connected in series with the
component or circuit being tested.
Insulation
An insulation resistance test is used to measure the total resistance of a product's insulation by applying a high
voltage. The minimum acceptable test is normally about 100 MΩ. The resistance measured is recorded.
Signal Output and Input
Digital input/output (DIO) devices are used to test and measure digital signals. They generate binary patterns
and communicate with the device under test. A logic analyser with two on/off states samples the digital signal.
They are used to measure:
 clock speed and data rates
 bidirectional control per cycle speeds
 programmable voltage levels
 logic channel states
 multiple device synchronisation.
Conductance and Resistance
Conductance (𝐺) and resistance (𝑅) are quantitative terms. Conductance is inversely related to resistance.
𝐺=
1
𝑅
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Conductivity and Resistivity
Conductivity (𝜎) and resistivity (𝜌) are measures of the ease with which free electrons move through a material
and are inherent properties of a material.
𝜎=
1
𝜌
This is only true when applied to metals.
𝑙
𝑅=𝜌 ( )
𝐴
Resistivity arises from any phenomena that disturbs the motion of electrons, such as collisions with:
 solute atoms, such as impurities
 lattice imperfections, such as cold working
 temperature-induced lattice vibrations.
Copper and its Alloys
Copper is second only to silver in terms of electrical conductivity. However, it is far more cost effective to use
than silver. It can be used in either an alloy form or an unalloyed form. Copper and its alloys are also used because
they are ductile, which allows them to be easily drawn into wires. They are also easily annealed and good for
soldering. The main advantages of copper include:
 high levels of conductivity
 termination to copper conductors by any popular means is straightforward and reliable
 its ductility, malleability and flexibility.
Pure Copper
Industrially electrolytic tough pitch copper (ETP) is the most widely used copper alloy. It has low oxygen levels
and is produced through electrolytic processes, so has very low levels of impurities. A purer form of copper can
also be used called oxygen free high conductivity copper (OFHC). This is sometimes used in environments in
which hydrogen embrittlement affects ETP. Small amounts of impurities can greatly increase the resistivity of a
material.
Copper Beryllium Alloy
Beryllium is a light metal that offers excellent strength-to-weight ratio and stiffness, but is rare and forms a
poisonous oxide. Beryllium is sometimes added in small amounts to copper to form a beryllium copper (Be/Cu)
alloy. It has higher strength than pure copper, but good thermal and electrical conductivity remains. Copper
beryllium alloys are able to be hardened by precipitation hardening. They are solution annealed and quenched
to trap the beryllium rich precipitates in the solution. These alloys have been used for non-sparking tools in
electrical applications.
Copper Cadmium Alloy
Pure annealed copper is a dense material with relatively low strength. These limit the span over which cables
can be strung between support towers. Finer cables are cold drawn, but for heavier cables, solid solution
hardening alloys replace pure copper. Cu/1%Cd has good wear resistance and is used for train catenary. High
transmission voltages reduce resistive power loss.
Copper Zinc Alloy
Copper zinc (Cu/Zn) or brass is often used as a connector in telecommunications. They are harder and stronger
than pure copper and have good corrosion resistance (except in ammonia environments where they tarnish).
Conductors, Insulators and Semiconductors
Different materials vary greatly in their ability to conduct electricity. Their conduction strength depends on the
ease with which electrons are able to move through the crystal lattice. In materials that are good insulators, the
atoms in the lattice are held together by strong covalent bonds in which electron pairs are shared between atoms.
This means that the electrons are held tightly together and are not available to conduct electricity. Metal lattices
consist of an orderly array of positive metal ions and delocalised electrons that move through the lattice to
Engineering Studies – Page 114
maintain stability. These electrons can conduct electricity through the lattice. Delocalised electrons move
randomly between atoms. Under the influence of an electric field, the random motion of the electrons decreases
and begins to have a net motion in a direction opposite to the electric field. This produces an electric current.
The de Broglie model of electron orbitals around the nucleus of the atom explained why electrons in the atom
can only have certain, well-defined energy levels. For any particular element, the highest energy level available
for electrons to occupy may or may not be completely filled. Elements that have an incomplete outer shell attempt
to fill it by:
 gaining electrons from other atoms, forming ionic bonds
 giving electrons to other atoms, forming ionic bonds
 sharing electrons with other atoms, forming covalent bonds
When atoms of any type of substance are very close together such as in a solid, their highest energy levels overlap
in a continuous fashion. Regions within these highest energy levels are called bands. The highest energy band is
called the valence band. In a conductor, the valence band is only partly filled. Since there are numerous energy
levels, electrons from the partially filled valence energy level are free to move. This means that, in a metal, the
valence band is also the conduction band. In an insulator, electrons completely fill the valence band, and the gap
between it and the conduction band is so large that electrons cannot move under the influence of an electric field
unless they are given sufficient energy to cross the large energy gap to the conduction band. If the electric field
to an insulator is sufficiently large, even an insulator can conduct.
Band Structures in Semiconductors
In a semiconductor, the gap between the valence band and the conduction band is smaller than that in an
insulator. In many materials, including metals, resistivity increases with temperature. In semiconductors, the
resistivity decreases with increasing temperature. The increased thermal energy causes some electrons to move
to levels in the conduction band from the valence band. Once there, they are free to move under the influence of
an electric field. At absolute zero, all electrons in a semiconductor occupy the valence band and the material acts
as an insulator. As the temperature of the semiconductor material increases, thermal energy allows some
electrons to cross the gap into the conduction band. This leaves the valence band unfilled. This means that holes
have been created in the valence band where the electrons have left. These holes actually act as a positive flow
of current moving in the opposite direction to the electron current flow. Thus, conduction is possible in both the
conduction band as a flow of electrons and in the valence band as a flow of holes. The speed of the electron current
is much greater, because the electrons can flow through the overlapping conduction bands of adjacent atoms, but
the holes must move from one atom to an adjacent atom.
Sometimes, an impurity element called a dopant is added. If that dopant has a different number of valence
electrons than the semiconductor material it replaces, extra energy levels can be formed within the energy gap
between the valence and conduction band. This means it is easier for these materials to conduct, because the
energy difference between the bands for the dopant atoms is less. The number of semiconductor atoms per
dopant atom is usually about 200 000. There are two types of semiconductor materials:
 intrinsic – the semiconducting properties of the material occur naturally. No doping of the crystal
lattice is necessary to enable the material to act as a semiconductor. Examples of this include silicon
and germanium
 extrinsic – the semiconducting properties of the material are manufactured to behave in the required
manner. Generally, this is a material that is a naturally-occurring semiconductor that has its
semiconducting properties modified by the addition of dopant atoms. These are general silicon and
germanium with dopants such as phosphorus or boron. Nearly all modern semiconductors are
extrinsic silicon semiconductors.
Making a Semiconductor
The most widely used semiconductor materials are crystals of elements from Group IV. These elements have four
valence electrons. They fill their valence band by sharing an electron with each of the four adjacent atoms.
Silicon
The conducting properties of silicon can be related to its crystal structure. Silicon crystal forms a diamond-like
lattice where each atom has four nearest neighbours at the vertices of a tetrahedron. This fourfold tetrahedral
coordination uses the four outer electrons of each silicon atom. According to quantum theory, the energy of each
electron in the crystal must lie within well-defined bands. The next highest band above the valence band is the
conduction band. It is separated by an energy gap. Heating the semiconducting material enables some electrons
Engineering Studies – Page 115
to gain enough energy to jump to that band. This mean one bond of the tetrahedron is no longer in place and the
resulting gap is called a hole.
Germanium and Zone Refining
Germanium was the first Group IV element that could be sufficiently purified to behave as a semiconductor.
Germanium is relatively rare in the Earth’s crust and is never found uncombined in nature. Early diodes and
transistors used germanium because suitable industrial techniques were developed to purify germanium to the
ultrapure level required for semiconductors during World War II. Germanium, however, becomes a very good
conductor when it is hot. The conductivity level means that the hot germanium electronic components allow too
much electric current to pass through them.
Advantages of Silicon
Silicon was the other element with semiconducting properties that was predicted to be ideal for the production
of electronic components. Unlike germanium, silicon is very common in the Earth’s crust, but it never appears
free in nature. Almost every grain of sand is made of silica, which is of silicon dioxide, SiO2. Silicon is more difficult
to purify than germanium. However, it is the most useful semiconductor for electronics because it is less affected
by higher temperatures. The first silicon transistors were made in 1957 by Gordon Teale, working for Texas
Instruments. After the production of these first silicon transistors, germanium transistors were largely phased
out of production. From the 1960s onwards, silicon became the material of choice for making solid state devices.
Doping and Band Structure
A pure semiconductor has the right number of electrons to fill the valence band. Semiconductors can conduct
electricity only if electrons are introduced into the conduction band or are removed from the valence band to
create holes. Electrons are the negative charge carriers in the conduction band and the holes in the valence band
act as positive charge carriers.
Extrinsic Semiconductors
There are two extrinsic semiconductor types: 𝑛-type and 𝑝-type. 𝑛-type semiconductors are formed when a
Group V impurity atom such as phosphorus or arsenic is substituted into a silicon crystal lattice. Group V atoms
have five electrons in the valence shell, whereas silicon and germanium have only four. This results in an
additional electron in the lattice, which is promoted to the conduction band. These impurity atoms are called
donor atoms. The extra electrons are mobile and can carry a charge. A semiconductor doped in this way has an
excess of negative charge carriers. 𝑝-type semiconductors are formed similarly to 𝑛-type semiconductors, except
that they use a Group III atom such as boron or gallium. Group III atoms have only three electrons in their valence
band. This means that when such an atom replaces a Group IV atoms, there is one electron short in the tetrahedral
structure. This means that a hole has effectively been incorporated into the crystal lattice without the need to
elevate an electron to the conduction band. When the doping impurity has only three electrons, there is one site
unfilled by electrons. This hole acts as a mobile positive charge carrier when an electric field is applied.
Polymers
Polymers are extensively used in telecommunications They are often used for insulation and casings. The use of
polymers in casings prevents the need to earth them. Manufacturers make extensive use of polymer casings for
mobile and fixed telephones. Polymers offer insulation, shock resistance and also lend themselves to mechanised
production by injection moulding.
Fibre Optics
Fibre optics function around the concept of transmitting electronic information encoded onto a light beam. A
fibre optic system consists of a device to convert electric current into light and a cable to carry the light to a
receiver, where it is converted back to an electric current. Fibre optic cabling is lighter and less expensive than
copper cables. There is also less interference from external sources or induction in the cable.
Single mode fibre optics have a central core diameter of 8 μm and classing up to 125 μm in diameter. The narrow
core means that light passes along a single light ray path. The difference in refractive index prevents light from
escaping the cable sides.
Engineering Studies – Page 116
Multimode fibre optics have a larger inner core diameter. The light reflects off the cladding and is reflected
internally by the cabling. With a larger diameter core, light can take different paths which means that they take
differing times to reach the destination.
Properties of fibre optics include:
 lightweight
 high flexibility
 low dispersion
 low attenuation
 high bandwidth
 resistance to kinks
 unaffected by power surges
 unaffected by electromagnetic interference
 difficult to tap (greater security).
Double Crucible Method
The double crucible method uses two crucibles, one inside the other, both of which empty through a common
orifice. The emerging fibre contains a core from the inner crucible with a sheath originating from the outer
crucible.
Modified Chemical Vapour Deposition
Modified chemical vapour deposition (MCVP) uses a silica base or preform onto which a gas mixture (containing
compounds of silicon, metal halides, oxygen and dopant materials) is deposited. The mixture used determines
the refractive index of the glass. The gases are condensed onto either the outside surface of a rod or the inside
surface of a tubular preform to form the core. The preform is then heated in an oven and glass fibre drawn from
it down to a desired thickness.
ENGINEERING ELECTRICITY AND ELECTRONICS
Analogue and Digital Systems
Analogue electrical systems use a continually varying range of values. Voice is recorded by amplitude (volume)
and frequency (tone). A digital system is either on or off. This signal is interpreted as a binary coded number,
either 1 or 0. Digital data can be converted to binary numbers and these can be transmitted as digital electrical
signals. Digital signals can be more easily compressed than analogue signals, which means an increase in
bandwidth. Bandwidth is a measure of the amount of space available for carrying information.
Noise
Noise consists of anything that reduces or interferes with the clarity of the message. In oral communications,
noise may consist of:
 rapid speech
 a heavy accent
 mispronunciation
 hearing impairment
 general background sound
 use of unfamiliar expressions
 contradictory body language
 humour, sarcasm, etc.
In written communications, noise may consist of:
 poor handwriting
 vision impairment
 punctuation errors
 ambiguous meaning
 use of unfamiliar expressions
 translation errors between languages
 change in the meaning of words over time
Engineering Studies – Page 117
Analogue to Digital Conversions
An analogue signal is continually fluctuating and conveys a lot of information. To take the complex wave and
convert it to a digital signal, it is sampled at regular time intervals. The sampling rate determines how accurately
the waveform is reproduced. Quantisation is also used to approximate the amplitude of the analogue wave to the
nearest whole number.
Advantages of digital signals include:
 high fidelity
 time dependence
 source independence
 signals may be coded, increasing data security through encryption.
Disadvantages of digital signals include:
 higher cost of equipment
 signals may be manipulated and falsified
 password protection of access relies on the password being secure.
Modulation and Demodulation
During early experiments with the transmission of electromagnetic waves, it was found that it was easier at
higher frequencies, which require less power for greater distance. To achieve this, low frequency signals
representing speech or music were imposed onto a high frequency carrier wave. Modulation is the process of
using a carrier wave to transmit information. Once the signal is transmitted, it is necessary to demodulate the
signal back to its original form. Multiplexing is the process of placing multiple signals along a single
communication channel. A multiplexer is used for this.
Channels
Channels often involve physical links such as wires, cables and optical fibres, but may also be invisible links such
as microwave, laser, radio and television.
Multiplexing
Multiplexing is the transmission of multiple signals over a single communications channel. A multiplexer
therefore performs the task of merging several low speed transmissions into one high speed transmission.
Radio Transmission
Electromagnetic wave transmission or radio transmission is essential to the existence of radio stations,
televisions, wireless communication and mobile phones. Waves passing through the ground serve those closest
to the transmitter, but are quickly absorbed by poor conductors like sand and do not travel very far. Airwaves
travel up to a part of the atmosphere called the ionosphere. This area is charged with positive ions and negative
electrons. If the radio waves are of a frequency less than 30 MHz, they are reflected from the ionosphere back to
earth. The power of the transmitter determines how far the wave will travel. For outer space communication, the
frequencies must exceed 30 MHz for it to travel through the ionosphere. Most frequencies used exceed 1 GHz.
Amplitude Modulation
To transmit the signal wave, it must be modulated onto a carrier wave that allows it to be sent far greater
distances. With amplitude modulation (AM), the amplitude is varied to transmit the information. AM is used for
some radio stations and for transmitting the visual signal for televisions. AM has a reduced signal quality because
the noise affects the amplitude of the modulated wave.
Frequency Modulation
This method of modulation is more common now. It involves varying the frequency of the carrier wave but
maintaining the same amplitude. Frequency modulation (FM) is less affected by noise,
Engineering Studies – Page 118
Television Transmission
Television transmission relies on radio waves to transmit information. These radio waves are either very high
frequency (VHF) or ultra high frequency (UHF).
Black and White Television
A camera is used to create a video signal of the situation. A black and white camera uses optics and electronics to
display variations in brightness. The vidicom tube fires electrons at a screen, which varies in resistance
depending on the amount of light present. The beam scans across the image and produces a raster. Once scanned,
it is modulated and sent to the transmitted. Televisions used to use a cathode ray tube (CRT). It worked by firing
electrons from a cathode at an anode placed behind a glass screen. The anode is coated with a phosphor to
luminesce. When electrons strike it, the phosphor glows, creating a bright part. The kinetic energy of the
electrons determines how brightly the phosphor glows. An audio signal is simultaneously transmitted with the
video signal.
Colour Television
The principle behind colour television is the same as black and white, but it uses three electron beams instead of
one. The beams react on red, blue and green phosphors on the screen.
Digital Television
Digital TV uses digital modulation techniques and multiplexing to prepare a signal for transmission. The
advantage is improved resolution and the ability to carry more channels within a given bandwidth. Television
stations can run various programs off one frequency at reduced resolution, then drop back to one station for
movies and large sporting events that require higher resolutions. Another advantage is improved sound quality.
Digital TV also allows the easy combination of video and data systems. Many televisions now have internet
connectivity.
Television Display Technology
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Liquid crystal display (LCD) televisions use a colour liquid crystal display that rely on filtering a white
back light. The backlight shines through millions of LCD shutters arranged in a grid. Modern LCD
televisions use an LED backlight.
Plasma televisions use a plasma display panel for visual display. They use electricity to excite a
mixture of noble gases and mercury in cells which then strike a phosphor, producing the appropriate
colour and light. They produce a better contrast than LCD televisions but generate more heat. They
are only suitable for large displays.
3D TVs use some mechanism to create depth perception in the viewing experience.
Fixed Telephones
The mouthpiece of a telephone is a microphone and the earpiece a speaker. A current is fed down the telephone
line to the exchange and then to the receiver telephone. In the earpiece, the current travels up a coil around a
magnet and causes a diaphragm to vibrate recreating the speech patterns of the caller. Telephones only allow
frequencies from around 400 Hz to 3400 Hz to pass to increase the number of calls that can be multiplexed on a
single line.
Mobile Phones
For mobile phones, a city or area is divided into cells. Each cell has a certain number of frequencies, but because
there are more cells, there can be more phones. The signal from each phone is only weak, so cannot reach
neighbouring cells. When a mobile phone is turned on, it sends a signal to the service provider to inform it that
the telephone is on. The network registers where it is and periodically sends out tracing signals to keep track of
the phone’s position. When someone calls the phone, the call goes to the central system which rings the phone
on a frequency that is not being used currently. Two frequencies are used; one to talk and one to listen. This is
called duplexing.
A cell is a relatively small area that is served by a low-powered transmitter tower. A large city may be made up
of hundreds of cells. The mobile phone is a low power transmitter and receiver.
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Satellite Phones
Satellite phones can be used anywhere and make use of a network of orbiting satellites. They use low earth
orbiting satellites which relay the signal back to a ground base receiving station, which then links the signal to
either a mobile or fixed telephone network.
Transmission Media
Cables
Oxygen free high conductivity copper and electrolytic tough pitch cabling is used in many telecommunications
systems. Telephone lines make use of copper cabling to transmit information. In some applications, they are
being replaced by fibre optics. Twisted pair cables use a pair of wires twisted together which reduces the chance
of induced noise.
Microwave
Microwave transmission is used for transcontinental communications. Microwaves are line-of-sight waves, so
about every 40 km there must be repeater towers. Microwaves are also used in communication satellites.
Coaxial Cables
Coaxial cables use a copper conductor surrounded by a polymer dielectric, around which is a braided copper
cable and a vinyl insulator.
Twisted Pairs
Twisted pair cables consist of two individually insulated copper wires twisted around each other. Twisting of the
wires ensures some mutual shielding from external electromagnetic interference.
Satellite Communication Systems
Satellites are one of the most important new technologies for worldwide communication. There are three types
of satellites used:
 geostationary, or geosynchronous, satellites orbit so that they are always over the same point of the
Earth. Most communications satellites are geosynchronous. They must be at an altitude of about
35 785 km and are usually above the equator. This area is very congested with satellites.
 medium Earth orbits have an altitude of between 2000 km and 35 000 km. The most common
satellites here are for communications and navigation. Most GPS satellites orbit at about 20 000 km.
 low Earth orbit occurs between 160 km and 2000 km. At this altitude are manned craft such as the
ISS.
 asynchronous orbits occur when the satellite passes over parts of the globe at varying times.
 polar orbits are low earth orbits in which satellites pass over the polar caps.
Satellite Functionality
Communications satellites are now active devices. They capture the signal, amplify it and relay it back. They may
also relay it to another satellite that relays it back to ground. A ground station sends a signal in the form of low
frequency microwaves. The satellite receives these microwaves and boosts the signal strength before relaying it
to either another satellite or another ground station.
Satellites are extensively used in broadcasting television signals all over the world. For international telephone
calls, satellite communication is usually used. A landline call in analogue is modulated, multiplexed and converts
to digital. It is then transmitted to the satellite which relays it to the ground station. The signal then travels
through the local network to its destination. There is normally a short delay in the conversation because of the
time it takes for this to happen.
Absorption of Radio Frequency Radiation from a Mobile Phone
At distances within a wavelength from a RF transmitter is a region known as the near field. Since the RF radiation
from a mobile phone has a wavelength of 10 to 30 cm, the user’s head will be within this near field region. The
head disturbs the field and alters the manner in which RFR interacts with tissue. This interaction complicates the
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absorption of RF energy within the head and makes calculations difficult. The specific absorption rate is defined
as the rate at which a mobile phone user absorbs energy from the handset.
Thermal Effects
Thermal effects are biological effects which result from absorbed electromagnetic energy, which elicits a
biological response from the heat it produces. Radiofrequency radiation interacts with matter by causing
molecules to oscillate with the electric field.
Athermal Effects
There is a considerable body of scientific literature which describes effects of RFR in biological systems that
cannot be directly attributed to heating. Low levels of RFR have been demonstrated to cause alteration in animal
behaviour or changes in the functioning of cell membranes. These low level effects, often referred to as athermal
or non-thermal, are controversial and have not shown to have adverse health effects.
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