Gill Sans Bold
Engineering Studies
Preliminary Course
Stage 6
Landscape products
ES/S6 – Prelim 41081
P0021820
Acknowledgments
This publication is copyright Learning Materials Production, Open Training and Education Network –
Distance Education, NSW Department of Education and Training, however it may contain material from
other sources which is not owned by Learning Materials Production. Learning Materials Production
would like to acknowledge the following people and organisations whose material has been used.
Board of Studies, NSW
All reasonable efforts have been made to obtain copyright permissions. All claims will be settled in
good faith.
Materials development:
Neil Falkner
Revised version:
Jeff Appleby, Brian Jobson and Stephen Russell
Coordination:
Jeff Appleby and Nicola Pegum
Content review:
Flyn Henry, Brian Jopson, Mike Mcphee
Illustrations:
Tom Brown, David Evans
DTP:
Nick Loutkovsky, Carolina Barbieri
Copyright in this material is reserved to the Crown in the right of the State of New South Wales.
Reproduction or transmittal in whole, or in part, other than in accordance with provisions of the
Copyright Act, is prohibited without the written authority of Learning Materials Production.
© Learning Materials Production, Open Training and Education Network – Distance Education,
NSW Department of Education and Training, 1999. 51 Wentworth Rd. Strathfield NSW 2135.
Revised 2003
Module contents
Subject overview ................................................................................ iii
Module overview................................................................................ vii
Module components.......................................................................... vii
Module outcomes .................................................................... viii
Indicative time ........................................................................... ix
Resource requirements...............................................................x
Icons
................................................................................................ xi
Glossary............................................................................................. xiii
Directive terms.................................................................................. xix
Part 1: Landscape products –
developments ................................................................. 1–21
Part 2: Landscape products –
materials ........................................................................... 1–27
Part 3: Landscape products –
mechanics ........................................................................ 1–53
Part 4: Landscape products –
machines and communication ...................................... 1–29
Part 5: Landscape products –
engineering report........................................................... 1–28
Bibliography........................................................................................29
Module evaluation .............................................................................31
i
ii
Subject overview
Stage 6 Engineering Studies Preliminary Course and HSC Course each
have five modules.
Engineering Studies Preliminary Course
Household appliances examines common appliances
found in the home. Simple appliances are analysed
to identify materials and their applications.
Electrical principles, researching methods and
techniques to communicate technical information are
introduced. The first student engineering report is
completed undertaking an investigation of materials
used in a household appliance.
Landscape products investigates engineering
principles by focusing on common products, such as
lawnmowers and clothes hoists. The historical
development of these types of products demonstrates
the effect materials development and technological
advancements have on the design of products.
Engineering techniques of force analysis are
described. Orthogonal drawing methods are
explained. An engineering report is completed that
analyses lawnmower components.
Braking systems uses braking components and
systems to describe engineering principles. The
historical changes in materials and design are
investigated. The relationship between internal
structure of iron and steel and the resulting
engineering properties of those materials is detailed.
Hydraulic principles are described and examples
provided in braking systems. Orthogonal drawing
techniques are further developed. An engineering
report is completed that requires an analysis of a
braking system component.
iii
Bio-engineering examines both engineering
principles and also the scope of the bio-engineering
profession. Careers and current issues in this field
are explored. Engineers as managers and ethical
issues confronted by the bio-engineer are
considered. An engineering report is completed that
investigates a current bio- engineered product and
describes the related issues that the bio-engineer
would need to consider before, during and after this
product development.
Irrigation systems is the elective topic for the
preliminary modules. The historical development of
irrigation systems is described and the impact of
these systems on society discussed. Hydraulic
analysis of irrigation systems is explained. The
effect on irrigation product range that has occurred
with the introduction of is detailed. An engineering
report on an irrigation system is completed.
iv
HSC Engineering Studies modules
Civil structures is the first of the HSC course modules.
Engineering principles as they relate to civil structures
such as bridges and buildings are described. The historical
influences of engineering, the impact of engineering
innovation, and environmental implications are discussed
with reference to bridges. Mechanical analysis of bridges
is used to introduce concepts of truss analysis and
stress/strain. Material properties and application are
explained with reference to a variety of civil structures.
Technical communication skills described in this module
include assembly drawing. The engineering report asks the
student to compare two engineering solutions to solve the
same engineering situation.
Personal and public transport uses bicycles, motor
vehicles and trains as examples to explain engineering
concepts. The historical development of cars is used to
demonstrate the developing material list available for the
engineer. The impact on society of these developments is
discussed. The mechanical analysis of mechanisms
involves the effect of friction. Energy and power
relationships are explained. Methods of testing materials,
and methods of modifying material properties are
examined. A series of industrial manufacturing processes
are described. Electrical concepts such as power
distribution and AC motors are detailed in this module.
Students are introduced to the use of freehand technical
sketches.
Lifting devices investigates the social impact that these
devices from complex cranes to simple car jacks have had
on our society. The mechanical concepts are explained,
including the hydraulic concepts often used in lifting
apparatus. The industrial processes used to form metals
and the processes used to control physical properties are
explained. Electrical requirements for many devices are
detailed. The technical rules for sectioned orthogonal
drawings are demonstrated. The engineering report is
based on a comparison of two lifting devices.
v
Aeronautical engineering is the first focus engineering
module in the HSC course. The scope of the aeronautical
engineering profession is investigated. Career
opportunities are considered, as well as ethical issues
related to the profession. Technologies unique to this
engineering field are described. The mechanical analysis
topics include aeronautical flight principles and fluid
mechanics. Materials, and material processes concentrate
on those most associated with the aeronautical engineer.
The corrosion process is explained and preventative
techniques listed. Communicating technical information
using both freehand and computer aided drawing are
required. The engineering report is based on the
aeronautical profession, current projects and issues.
Telecommunications engineering is the final focus module
in the HSC course. This field of engineering, its history
and impact on society are discussed. Ethical issues and
current technologies are described. The materials section
concentrates on specialised testing, copper and its alloys,
semiconductors and fibre optics. Electronic systems such
as analogue and digital are explained and an overview of a
variety of other technologies in this field are described.
Analysis, related to telecommunication products, is used to
reinforce mechanical concepts. Communicating technical
information using both freehand and computer aided
drawing is required. The engineering report is based on
the telecommunication profession, current projects and
issues.
Figure 0.1 Modules
vi
Module overview
The shaping of landscapes from public parks to domestic gardens
involves the use of engineered products.
Landscape products could include tools, such as wheelbarrows and
shovels, powered machinery such as lawnmowers and trimmers,
structures such as fences and wall or equipment such as clothes lines,
flagpoles and garden seats.
This module however, will focus on products such the lawn mower and
rotary clothes hoist tracing their development, investigating materials,
analysing the mechanics and examining drawing techniques relevant to
these landscape products.
Module components
Each module contains three components, the preliminary pages, the
teaching/learning section and additional resources.
•
The preliminary pages include:
–
module contents
–
subject overview
–
module overview
–
icons
–
glossary
–
directive terms.
Figure 0.2 Preliminary pages
vii
•
The teaching/learning parts may
include:
–
part contents
–
introduction
–
teaching/learning text and tasks
–
exercises
–
check list.
Figure 0.3 Teaching/learning section
•
The additional information may
include:
–
module appendix
–
bibliography
–
module evaluation.
Additional
resources
Figure 0.4 Additional materials
Support materials such as audiotapes, video cassettes and computer disks
will sometimes accompany a module.
Module outcomes
At the end of this module, you should be working towards being able to:
viii
•
identify the scope of engineering and recognise current innovations
(P1.1)
•
explain the relationship between properties, uses and applications of
materials in engineering (P2.1)
•
use mathematical, scientific and graphical methods to solve problems
of engineering practice (P3.1)
•
apply graphics as a communication tool (3.3)
•
describe developments in technology and their impact on engineering
products (P4.1)
•
describe the influence of technological change on engineering and its
effects on people (4.2)
•
identify the social, environmental and cultural implications of
technological change in engineering (4.3)
•
demonstrate the ability to work both individually and in teams (5.1).
Extract from Stage 6 Engineering Studies Syllabus, © Board of Studies, NSW, 1999.
Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.
Indicative time
The Preliminary course is 120 hours (indicative time) and the HSC
course is 120 hours (indicative time).
The following table shows the approximate amount of time you should
spend on this module.
Preliminary modules
Percentage of time
Approximate
number of hours
Household appliances
20%
24 hr
Landscape products
20%
24 hr
Braking systems
20%
24 hr
Bio-engineering
20%
24 hr
Elective: Irrigation systems
20%
24 hr
HSC modules
Percentage of time
Approximate
number of hours
Civil structures
20%
24 hr
Personal and public transport
20%
24 hr
Lifting devices
20%
24 hr
Aeronautical engineering
20%
24 hr
Telecommunications engineering
20%
24 hr
There are five parts in Landscape products. Each part will require about
four to five hours of work. You should aim to complete the module
within 20 to 25 hours.
ix
Resource requirements
During this module you will need to access a range of resources
including:
•
technical drawing equipment
–
drawing board
–
T-square
–
set squares (30∞–60∞, 45∞)
–
protractor
–
pencils
–
plastic eraser
–
pair of compasses
•
calculator
•
rule
•
protractor
•
spring balance
•
rope or strong string
•
bar magnets
•
copper sheet or wire.
You need access to textbooks covering the topics on engineering
mechanics, engineering materials and engineering drawing.
Contact your library to obtain these resources.
x
Icons
As you work through this module you will see symbols known as icons.
The purpose of these icons is to gain your attention and to indicate
particular types of tasks you need to complete in this module.
The list below shows the icons and outlines the types of tasks for Stage 6
Engineering studies.
Computer
This icon indicates tasks such as researching using an
electronic database or calculating using a spreadsheet.
Danger
This icon indicates tasks which may present a danger and
to proceed with care.
Discuss
This icon indicates tasks such as discussing a point or
debating an issue.
Examine
This icon indicates tasks such as reading an article or
watching a video.
Hands on
This icon indicates tasks such as collecting data or
conducting experiments.
Respond
This icon indicates the need to write a response or draw
an object.
Think
This icon indicates tasks such, as reflecting on your
experience or picturing yourself in a situation.
xi
Return
This icon indicates exercises for you to return to your
teacher when you have completed the part. (OTEN OLP
students will need to refer to their Learner's Guide for
instructions on which exercises to return).
xii
Glossary
As you work through the module you will encounter a range of terms that
have specific meanings. The first time a term occurs in the text it will
appear in bold.
The list below explains the terms you will encounter in this module.
acceleration
when the force system is not balanced, the resultant
force will change the velocity of the object. The
rate at which this velocity changes is called its
acceleration.
annealing
a heat treatment process that reduces the internal
stress in a material and leaves the material in its
softest manufacturing condition
AS1100
Australian Standards: the rules that need to be
followed when drawing
bearing
a part in a machine that is designed to reduce the
frictional forces between two adjoining parts that
move relative to one another
CD-ROM
Compact Disk Read Only Memory – a computer
disk that stores information
clutch
a mechanism that disengages the power of the
engine to the blade of the mower, allowing the
engine to continue running without the cutting
blades of the mower rotating
collinear
Forces are in one line
composite
material
they contain two or more different substances,
which are combined to form a homogeneous
product
concurrent
passing through the same point eg. Lines that cross
each other
xiii
coplanar
Forces are in the same plane
couple
Two equal and opposite forces which create a
turning effect
cowling
a protective covering
crown and pinion
A gear mechanism found in the hills hoist clothes
line, a turning ‘crown’ cog meshes with a pinion
rod. When the crown rotates, the pinion is moved.
This mechanism forms the hoist.
dimension
a label placed on a drawing that indicates a size
drip feed
lubrication
a lubrication system for the engine that drips oil for
lubrication
ductility
the ability of a material to be shaped without
fracturing
Normally used to describe how a material can be
stretched into a wire form without fracture
xiv
effort
the force applied to overcome the resistance
elastic
deformation
temporary deformation, the material will return to
its original shape when the distorting force has been
removed
equilibrium
a state in which all forces are balanced
equilibrant
the one force that will balance all the other forces.
The opposite sense to the resultant
fatigue
is the tendency of a metal to break when subjected
to repeated cyclic stressing
force
a push or a pull, technically defined as the
interaction between bodies
friction
the force that tends to reduce movement between
two surfaces in contact with one another
front view
the view in an orthogonal drawing that shows the
details of the front face of the object
fulcrum
a pivot point that allows a body to freely rotate
about it
galvanised
a process used to coat a base material (normally
steel) with a thin coating of zinc alloy, a corrosion
resistant metal
gravitational
attraction
the Earth’s pull on a body towards its centre
hardness
is the ability of a material to resist scratching,
abrasion, indentation or penetration
high carbon steel
steel containing between 0.6% carbon and 0.9%
carbon. This steel is heat treatable, and is hard with
low ductility, (brittle) high tensile strength, and has
poor machinability qualities
hoist
a lifting mechanism
homogeneous
continuos structure, containing one form of evenly
distributed grains or phases
housing
a covering that often is used to support the other
components
laser
light amplification by stimulated emission of
radiation. A device for producing a high intensity
beam of radiation of a frequency within or close to
the range of visible light
load
the force that is the resistance
load arm
the distance the load is from the fulcrum
magnitude
quantity, size
mains electricity
electricity supply by power generating authorities
for domestic and industrial purposes
mechanism
a piece of machinery
medium carbon
steel
steel containing between 0.3% carbon and 0.6%
carbon. This steel is tough, heat treatable, hard,
and has good machinability qualities
orthogonal
a type of technical drawing which is used to show
accurate detail of an object in two dimensions
patent
a registration of a design or concept that gives the
owner some legal protection against the design
being used by other manufactures
xv
pawl
a pivoted bar arranged to catch in the teeth of a
ratchet wheel to prevent movement backwards or to
impart motion
perpendicular
a direction at 90°
phase
a physically distinct, mechanically separable and
chemical homogeneous portion of a material
point of
concurrency
the position at which the vectors cross
plastic
deformation
permanent change in shape
polymer material
a hydrogen/carbon based material with a chain
molecular structure, commonly called ‘plastics’
prototype
an initial version of a product, used to test the
design
resultant
the one force that could replace all the other forces,
or the result of all the other forces
rotary mower
a mower that uses a spinning blade that is mounted
to a vertical shaft
scalar
a quantity that can be defined by magnitude (size)
only
screw jack
a simple lifting device that uses a screw to lift a
load
scythe
a curved blade on a handle which can be used to cut
grass
service
applications
this describes the applications suitable for a
material when used in a product
side view
the view in an orthogonal drawing that shows the
details of the side face of the object
splash lubrication a system that uses the action of the internal engine
components to splash the lubricating oil to the
moving parts
strong
xvi
the ability of a material to withstand high forces
without failure
tempering
a heat treatment process that reduces the internal
stress in a material and leaves the material less
brittle but also less hard
tensile testing
exerted a stretching force on a material and plotting
the extension as the force is increased
top view
the view in an orthogonal drawing that shows the
details of the top face of the object
toughness
is the ability of a material to absorb energy when
being deformed and thus resist deformation and
failure
transmissibility
used to describe the fact that a force can be
transferred anywhere along its line of action and
retain the same effect
upper critical
temperature
the temperature at which a material needs to be
heated in order for internal re-crystallisation to
occur, abbreviated to UCT
uniform resource
locator
a unique address for word wide web sites,
abbreviated to URL
velocity
a quantity that described the distance travelled in a
given time. The unit for velocity is metres per
second. Velocity is a vector, quantity.
xvii
xviii
Directive terms
The list below explains key words you will encounter in assessment tasks
and examination questions.
account
account for: state reasons for, report on;
give an account of: narrate a series of events or
transactions
analyse
identify components and the relationship between
them, draw out and relate implications
apply
use, utilise, employ in a particular situation
appreciate
make a judgement about the value of
assess
make a judgement of value, quality, outcomes,
results or size
calculate
ascertain/determine from given facts, figures or
information
clarify
make clear or plain
classify
arrange or include in classes/categories
compare
show how things are similar or different
construct
make, build, put together items or arguments
contrast
show how things are different or opposite
critically
(analyse/evaluate)
add a degree or level of accuracy depth, knowledge
and understanding, logic, questioning, reflection
and quality to (analysis/evaluation)
deduce
draw conclusions
define
state meaning and identify essential qualities
demonstrate
show by example
xix
describe
provide characteristics and features
discuss
identify issues and provide points for and/or against
distinguish
recognise or note/indicate as being distinct or
different from; to note differences between
evaluate
make a judgement based on criteria; determine the
value of
examine
inquire into
explain
relate cause and effect; make the relationships
between things evident; provide why and/or how
extract
choose relevant and/or appropriate details
extrapolate
infer from what is known
identify
recognise and name
interpret
draw meaning from
investigate
plan, inquire into and draw conclusions about
justify
support an argument or conclusion
outline
sketch in general terms; indicate the main
features of
predict
suggest what may happen based on available
information
propose
put forward (for example a point of view, idea,
argument, suggestion) for consideration or action
recall
present remembered ideas, facts or experiences
recommend
provide reasons in favour
recount
retell a series of events
summarise
express, concisely, the relevant details
synthesise
putting together various elements to make a whole
Extract from The New Higher School Certificate Assessment Support Document,
© Board of Studies, NSW, 1999.
Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.
xx
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Landscape products
Part 1: Landscape products –
developments
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Part 1 contents
Introduction............................................................................................2
What will you learn?.................................................................... 2
Landscape products............................................................................ 3
Development of the lawnmower.................................................. 4
Exercises ........................................................................................... 15
Progress check................................................................................... 19
Exercise check sheet......................................................................... 21
Part 1: Landscape products – developments
1
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Introduction
In Part 1 you will trace the development of a landscape product, the
lawnmower, and investigate innovation in design and materials as well as
discuss the social impact of technological change.
What will you learn?
You will learn about:
•
historical and societal influences
–
the historical development of landscape products
–
the effect of engineering innovation on people’s lives.
You will learn to:
•
discuss the social implications of technological change in engineering
as applied to landscape products.
Extract from Stage 6 Engineering Studies Syllabus, © Board of Studies, NSW, 1999.
Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.
2
Landscape products
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Landscape products
Landscape products range from small hand held garden equipment found
around the home, such as the shovel and wheelbarrow, to power driven
devices used on large scale projects, for example, chainsaws and
compactors, as well as construction materials for such purposes as
retaining walls and open area furniture, such as benches.
The development of landscape products parallels technological change. In
engineering, design changes are often associated with materials
development.
Are there new needs that encourage new products?
Do developments in one area spur developments in another?
You will probably find the answer to both these questions is yes.
As you read through the material, consider the reasons for the changes
mentioned. The last two centuries are notable not only for change, but
the rapid rate at which it occurred.
Lawn mowing products will be used to illustrate the development in
landscape products.
Initially lawns were grazing areas around the manors of the gentry and
were seen as a status symbol – evidence of wealth. Public parks did not
become established as recreational areas until late in the nineteenth
century. With the population movement to the cities as a result of the
industrial revolution, housing became more congested, and the ability to
use livestock to keep the lawn cut became impractical.
Initially the land associated with detached and semidetached housing was
used for growing vegetables and flowers. Lawns did not become popular
in a domestic setting until after World War I, as they were easier to
maintain than vegetable and flowers plots.
The maintenance of lawns has developed into an obsessive activity for
many in our modern society.
Part 1: Landscape products – developments
3
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As mentioned previously, initially lawns were maintained by the grazing
of livestock but as this became less practical there was a move to develop
mechanical methods of cutting the grass. Slashing with a scythe was the
initial method used. A scythe is a sharp blade on the end of a long
handle. The blade of the scythe needed to hit the grass with enough force
to cut it. This required a very sharp blade and sufficient blade velocity.
A skilled worker was able to trim grass to produce an even length lawn.
Figure 1.1 Scythe
This was a slow process and was best carried out at the beginning of the day
when the grass was damp and more rigid. The scythe was limited to smaller
areas but as the size of lawns increased, there was a need to improve cutting
efficiency. To this end the first lawnmowers were developed.
Development of the lawnmower
In less than two hundred years the machinery that is used to prepare a
lawn has evolved from simple hand implements to solar powered devices.
In the 1830s Edwin Budding developed one of the earliest mechanical
devices that we know as a lawnmower. As a result of work in the textile
industry, Budding knew that a shearing motion between two blades with
the grass trapped between them would produce a more efficient cut. This
concept was patented and the device was manufactured in partnership
with John Ferrabee.
The Budding model had a large cylindrical roller driving, through a series
of gears, the blades. Construction was essentially cast iron, which
accounted for its significant weight, but it was declared as a success by
the foreman at Regents Park Zoological Gardens who confirmed that this
machine does as much work as six or eight men with scythes and brooms,
without leaving marks behind.
4
Landscape products
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It was not until the early 1840s that the prospect of using a wider cutting
face powered by a small horse met with success. Alexander Shanks
initially constructed a 27 inch (700mm) wide lawnmower and registered a
42 inch (1100 mm) machine in 1842. These machines were scaled up
versions of the hand propelled type. To prevent the pony damaging the
lawn it was often required to wear leather boots to prevent its hooves
digging into the lawn.
Theoretically one person could operate such a mower, in practice this
remained a two-person operation with one maneuvering the lawnmower
whilst the other guided the horse. In latter and larger versions the
lawnmower operator was able to sit on a seat mounted above the cutters
and multiple sets of cutters were joined together to form a gang
lawnmower. A grass catcher box was an optional extra.
Horse drawn mowers were used extensively until the 1930s and can still
be seen being used in many third world countries.
It was not until the mid 1850s that the first structural changes occurred.
When the first of Buddings’ patients began to expire, the gears were
replaced with chain drives.
However, another major change was the introduction of the sidewheel
machines. These lawnmowers did not have the heavy rear metal roller but
utilised cast iron wheels mounted on the side of the cutting blades. This
drastically reduced the weight of the machines and made them less expensive
to manufacture. Initially this concept was developed in England but it was
the Americans that raised the popularity of this type of lawnmower.
Figure 1.2 Sidewheel lawnmower
Courtesy: Mowers Ark Taren Point.
© LMP
Part 1: Landscape products – developments
5
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Motorised lawnmowers
It was some 60 years after the development of the Buddings lawnmower
that the addition of a motor occurred.
Steam power
Today it may seem unbelievable that a lawnmower was at one time
powered by a steam engine, but it was actually developed. Steam power
was the principle form of locomotion at the turn of the century and was
therefore a practical choice of propulsion.
Steam lawnmowers were developed and used between 1894 and 1902.
They were large and very heavy; some machines weighed in excess of one
tonne and would travel at a walking pace. It had limited applications
because of its size.
Petrol power
Petrol powered machines began to appear around 1902. Ransomes, a British
engineering company, who still make lawnmowers, produced a 42 inch
machine powered by a six horsepower water-cooled, four-stroke motor.
Figure 1.3 An early style petrol lawnmower
Courtesy: Mowers Ark Taren Point.
© LMP
6
Landscape products
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The basic configuration of lawnmowers changed little until after World
War I. At this time there were developments in construction materials
and a wider use of fabricated steel components, along with the
introduction of the air-cooled, four-stroke motors. These developments
resulted in a lighter and more maneuverable lawnmower.
Electric power
Electrical motors were also tried in the early 1900s and remained popular
for many years; some bowling clubs still use variations of the electrical
powered lawnmowers.
Ransomes produced the ‘Electra’ in 16 inch and 20 inch variations.
These models were very successful and featured a revolutionary cable
pole arrangement that attempted to keep the power lead away from the
cutters. The electrical mowers were in most instances a version of the
petrol machines.
Figure 1.4 Old style electric lawnmower
Courtesy: Mowers Ark Taren Point.
© LMP
Part 1: Landscape products – developments
7
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Rotary lawnmower
The development of the rotary lawnmower was the first radical
movement away from the roller type lawnmowers. In the rotary
lawnmower the blades were attached to a vertically revolving shaft.
The earliest successful version of the rotary lawnmower was the
Rotoscythe, developed in 1933 by Power Specialities of Maidenhead,
Berkshire and was manufactured until the 1950s.
A more common model of the rotary lawnmower is the product
developed by Mervyn Victa Richhardson. In 1952 he launched the now
famous Victa lawnmower. The earliest version was known as the Peach
tin. This mower had no guards and was powered by an imported air cool
motor, an example can be seen on the Victa web site. Subsequent models
featured guards over the revolving base plate and blades, an extremely
reliable, locally produced powerful two-stroke, air-cooled motor, folding
handle bars and eventually a catcher. An early production Victa
lawnmower is shown in figure 1.5.
If you have access to the Internet visit the following website and select
about victa to find out ‘About development of the victa’
(www.victa.com.au> (accessed 22.08.03)
Figure 1.5 Early production Victa lawn mower
Courtesy: Mowers Ark Taren Point.
© LMP
8
Landscape products
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The replacement of many of the components with plastic molding further
lightened the product thereby achieving greater maneuverability. Such a
lawnmower is shown in figure 1.6.
Figure 1.6 Modern lawnmower
Courtesy: Mowers Ark Taren Point.
© LMP
Turn to the exercise section and complete exercises 1.1 and 1.2.
Part 1: Landscape products – developments
9
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Other innovations
The rotary hover lawnmower
By using the lightweight nature of plastics and the power of modern
electric motors the lawnmowers were able to hover, thus eliminating the
need for wheels as the mass of the machine is supported on a cushion of
air. This made it quite maneuverable, making it popular when mowing
undulating and sloping surfaces. Examples of this type of lawnmower
have been made by Flymo since 1966 and can be seen in figure 1.7.
Figure 1.7 Flymo lawnmower
Courtesy: Mowers Ark Taren Point.
© LMP
Line trimmers, brushcutters and vacuum/blowers
Line trimmers and brushcutters use a lightweight motor, either electric or
petrol, to transfer the rotary motion through a flexible shaft to a cutting
head.
Brushcutters typically have a disc to provide a cutting action and are
used for clearing scrub and thin out gnarled bushes, as well as for general
mowing jobs.
Line trimmers use a heavy monofilament nylon line that cuts grass where
lawnmowers have difficulty reaching, along walls, the side of the house,
around trees and under and between bushes. They can additionally be
used to cut small areas of grass.
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Figure 1.8 Line trimmer
Courtesy: Mowers Ark Taren Point.
© LMP
Vacuum and/or blowers use a similar petrol or electric to power a strong
fan that can be used to suck up the leaves and grass cuttings or blow them
away. An example of a modern blower is shown in figure 1.9.
Figure 1.9 Petrol powered blower
Courtesy: Mowers Ark Taren Point.
© LMP
Automatic lawnmower
An automatic lawnmower can be powered by either a rechargeable
battery or solar power and is environmentally sound as it collects its
energy either from the mains electrical supply or directly from the sun
through solar panels. This type of lawnmower works continuously and
automatically as it has collision sensors, which guide it around obstacles
such as garden furniture, rocks and trees. An example is shown in figure
1.10.
Part 1: Landscape products – developments
11
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Solar lawnmower
Automatic lawnmower
Figure 1.10 Husqvarna solar and automatic lawnmowers
© http://international.husqvarna.com/
Modern ride on lawnmower
Historically ride on lawnmowers that were used to mow large expanses of
grass were pulled by horses. Steam power was tried in the early 1900s
but the mass of these machines limited their usability. Mechanical
tractors, both petrol and diesel powered, replaced the horse but the
cutters were still set as a ‘gang’ where multiple sets of side wheel mowers
were arranged together to increase the cutting width.
Many modern ride on mowers still use petrol or diesel power along with
slashers – like a very large rotary blade. However, there has been a trend
towards small ride on mowers amongst the owners of large blocks of land
and by professional trades people which use a rotary cutting action.
Figure 1.11 Modern small ride on mower
Courtesy: Mowers Ark Taren Point.
© LMP
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Turn to the exercise section and complete exercise 1.3.
Social implications
Social implications associated with technological developments in the
field of landscape engineering include the impact on the natural
environment and individual health and safety.
It has been reported that with the persistent use of pesticides there have
been numerous instances of short and long-term poisoning, cancer and
disease in people and wildlife. The excessive use of fertilisers has caused
water pollution and the use of lawnmowers and landscaping machinery
use significant amounts of petrol and produce high levels of air and noise
pollution.
In the early 1990s in the United States $25 billion a year was spent on
lawn care products, of which:
•
$5 250 million was spent on fossil fuel derived fertilisers
•
$700 million was spent on 28 million kgs of poisonous synthetic
pesticides
•
2 610 million litres of petrol was used to run lawnmowers in the US
every year
•
it is estimated hat 44% of domestic water consumption in California
is used for lawns.
Lawns, do we really need them?
Turn to the exercise section and complete exercise 1.4 to 1.6.
Part 1: Landscape products – developments
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Exercises
Exercise 1.1
a
Name in chronological order three technological developments in the
evolution of the lawnmower.
b
Describe, in terms of materials, power source or design changes, the
features that distinguish each technological development.
Development 1:
_____________________
Description:
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
Development 2:
_____________________
Description:
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
Development 3:
_____________________
Description:
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
Part 1: Landscape products – developments
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Exercise 1.2
Choose a landscape product, other than the lawnmower, and outline its
historical development.
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
Exercise 1.3
a
Select one innovation developed and applied to a landscape product,
other than the lawnmower.
_______________________________________________________
b
Describe the impact this innovation had on the landscape product.
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
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Exercise 1.4
a
State two major disadvantage of a steam engine lawnmower over a
petrol engine mower.
i
___________________________________________________
___________________________________________________
ii
___________________________________________________
___________________________________________________
b
Developments, to allow for better safety, are continually being made.
Outline two safety developments that have been made for the
operator’s safety, with particular reference to rotary lawnmowers
since the first Victa prototype – the peach tin lawnmower.
i
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
ii
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
Exercise 1.5
a
Select one landscape product, other than the lawnmower.
_______________________________________________________
b
Describe the impact this product has had on society.
You might consider how different society might be without this
product.
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
Part 1: Landscape products – developments
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Exercise 1.6
a
Identify one other landscape product, other than the lawnmower.
_______________________________________________________
b
List the three technological developments over the life of this
product.
i
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
ii
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
iii
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
b
State two effects this product has had on society – the natural
environment and people’s lives.
i
___________________________________________________
___________________________________________________
___________________________________________________
ii
___________________________________________________
___________________________________________________
___________________________________________________
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Progress check
In this part you traced the development of lawnmowers and investigated
developments in other landscape products and the impact such
innovations have had on society.
✓
❏
Disagree – revise your work
✓
❏
Uncertain – contact your teacher
Uncertain
Agree – well done
Disagree
✓
❏
Agree
Take a few moments to reflect on your learning then tick the box which
best represents your level of achievement.
I have learnt about
•
historical and societal influences
– the historical development of landscape products
– the effect of engineering innovation on people’s lives.
I have learnt to
•
discuss the social implications of technological change
in engineering as applied to landscape products.
Extract from Stage 6 Engineering Studies Syllabus, © Board of Studies, NSW, 1999.
Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.
In the next part you will examine the types of materials used in landscape
products, such as the lawnmower and rotary clothes hoist.
Part 1: Landscape products – developments
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Exercise cover sheet
Exercises 1.1 to 1.6
Name: ______________________
Check!
Have you have completed the following exercises?
❐ Exercise 1.1
❐ Exercise 1.2
❐ Exercise 1.3
❐ Exercise 1.4
❐ Exercise 1.5
❐ Exercise 1.6
If you study Stage 6 Engineering Studies through a Distance Education
Centre/School (DEC) you will need to return the exercise pages with your
responses.
Return the exercise pages with the Title Page cover attached. Do not
return all the notes, they should be filed for future reference.
If you study Stage 6 Engineering Studies through the OTEN Open
Learning Program (OLP) refer to the Learner’s Guide to determine which
exercises you need to return to your teacher along with the Mark Record
Slip.
Part 1: Landscape products – developments
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Landscape products
Part 2: Landscape products –
materials
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Part 2 contents
Introduction ........................................................................................... 2
What will you learn?.................................................................... 2
Engineering materials .......................................................................... 3
Engineering properties.............................................................. 3
Modification of materials............................................................. 5
Composite materials ................................................................ 10
Recyclability of products .......................................................... 12
Materials in landscape products................................................ 14
Exercises............................................................................................ 17
Progress check................................................................................... 25
Exercise cover sheet ........................................................................ 27
Part 2: Landscape products – materials
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Introduction
In this part you will investigate the materials used in landscape products,
such as the lawnmower and clothes hoist.
What will you learn?
You will learn about:
•
engineering materials
–
•
engineering applications of materials
recyclability of materials.
You will learn to:
•
conduct simple test aimed at improving materials’ properties through
work hardening, heat treatment and composites
•
analyse the properties, uses and appropriateness of materials for
landscape products
•
explain the benefits of recycling materials.
Extract from Stage 6 Engineering Studies Syllabus, © Board of Studies, NSW, 1999.
Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.
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Engineering materials
Why do engineers choose particular materials for specific applications?
As you have seen in Household appliances, this question is not
necessarily simple to answer. There are numerous and sometimes
conflicting choices to be made. If fact, engineering is about making
choices. There is rarely one correct solution, more likely there are
multiple options, the choice of the best solution depends on what criteria
are used when making the choice.
Engineering properties
Engineering properties are the physical properties that can be
experimentally determined for all materials. They allow the engineer to
predict how the material will react under various conditions. Typical
properties include:
•
hardness
•
ductility
•
flexibility
•
electrical conductivity
•
heat conductivity
•
melting point
•
wear resistance
•
toughness
•
corrosion resistance.
The best solution may be determined by the properties of the material.
An engineer will look at properties in terms of manufacturing properties
and service properties.
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Manufacturing properties
Manufacturing properties are the properties that relate to how the
material can be formed. Manufacturing techniques suitable for metals,
polymers, ceramics and composites are well established, although
constantly developing.
Manufacturing properties can be a determining factor when a material
choice is made. While a wheelbarrow tray can be made from a steel or
polymer, the manufacturer with a million dollar factory set up to press
sheet metal parts is going to consider the manufacturing equipment
available as a significant selection criteria.
The manufacturing process can dramatically alter the characteristics of a
material.
Service properties
Service properties are those properties possessed by the material that
will be put to use in the product.
List the service properties that you might expect would be required
from a wheelbarrow tray.
__________________________________________________________
__________________________________________________________
__________________________________________________________
Did you answer?
• High strength to weight ratio
• Impact resistant
• Resistant to chemical attack.
When considering the required service properties for a wheelbarrow tray
it is necessary to examine the possible uses that a wheelbarrow may be
used for. These include the use on a building site where it is required to
transport sand and concrete mix, whereas a landscaper may use it for
moving heavy rocks, plants, garden rubbish as well as soil, and
construction materials. For these reasons the wheelbarrow tray needs to
be robust.
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Modification of materials
The manufacturing process can significantly alter the properties of a material.
Elastic and plastic deformation
When a force is applied to a metal it will bend or deform. As the force is
removed the material will return to its original shape. This change of
shape is known as elastic deformation, a little bit like an elastic band that
stretches when a force is applied and returns to its original shape when the
force is removed. If more force is applied to the metal it will bend further
and when the force is removed it may retain its new shape. This is known
as plastic deformation.
Obtain a thin strip of metal (copper works well) and place it on a desk
so that half of it hangs over the edge. Gently apply force to it so that it
bends. Release the force and note that it returns to its original shape.
Keep repeating this experiment with increasing amounts of force until
plastic deformation occurs.
Did you note that there was a degree of spring back, when the force was
removed, after plastic deformation occurs?
To fully understand the mechanism that is occurring it is necessary to look
at the movement of the atoms in the material. Atoms are held in position
by metallic bonds. The atoms are in ordered arrays forming crystals.
metallic ion
sea of
delocalised
electrons
three-dimensional
representation
Figure 2.1
Ordered array of atoms in a metal crystal
In figure 2.2 the atoms are in a non-stressed condition but when a force is
applied the crystal lattice is distorted.
Part 2: Landscape products – materials
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Non-stressed
Distorted crystal lattice
caused by a shearing force
Figure 2.2 Stressed and non-stressed crystal lattice
When the force is removed the crystal returns to its original position. This
is what happens in elastic deformation.
In figure 2.3, as the force is increased the stress that is built up in the
lattice causes a row of atoms slide over the top of another row.
Slip plane
Figure 2.3
Plastic deformation whereby a row of atoms slip over another
If the force is then removed the atoms do not return to their original
positions but remain in their new position. This is known as plastic
deformation This method of deformation in metallic structures is known
as slip.
Work hardening of metals
The movement of a row of atoms over another is a simple concept and
the theoretical force required to cause this displacement can be calculated
given that the bond strength between the atoms is known. In practice
considerably less force is needed to cause deformation. This discrepancy
was found to be in the order of 105. This is a significant discrepancy and
can be explained by the existence of crystal imperfections. This resulted
in the differences between observed and theoretical values and led to the
theory of dislocations. This theory proposed that the presence of a
dislocation or an imperfection in the crystal lattice meant that when a
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force was applied to the crystal, instead of breaking all of the bonds in a
slip plane only one bond at a time need be broken. Thus less force was
required to cause plastic deformation. Figure 2.4 shows the presence of a
dislocation at the center of the crystal.
Shear plane
Dislocation
(incomplete row
of atoms)
Non-stressed metal crystal
Figure 2.4 Non stressed metal lattice showing a dislocation.
If a shearing force is applied to the crystal then as the crystal deforms
plastic deformation can proceed by the breaking of only one bond at a
time. This can be seen in figure 2.5.
Figure 2.5 Movement of a dislocation
The dislocation is free to continue across the length of the crystal and will
stop at, the point at which two crystals (metallic grains) meet, known as a
grain boundary.
Figure 2.6 Three metallic grains with dislocations apparent in each
It has been observed that when a metal is worked or deformed more force
is required as the amount of deformation increases. This is known as work
hardening and can be explained in terms of the movement of dislocations
through the metal.
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In the first instance only small quantities of force are required to cause
plastic deformation as the dislocations begin to move in the crystal, but as
more deformation takes place many of the dislocations become locked or
stuck at the grain boundaries. This results in more force being needed to
produce more deformation.
Figure 2.7
Dislocations moving to and becoming locked at grain boundaries
Use the piece of copper from the previous task and continue to bend it
backward and forward, note your observations.
__________________________________________________________
__________________________________________________________
__________________________________________________________
Did you answer?
The metal surface became hotter and the force required became greater to
bend the metal. In practical applications it is possible for the metal to break
under severe conditions of work hardening.
It is necessary under sever conditions of deformation for the metal to be
heat treated to redistribute the dislocations and soften the metal. This
process is known as annealing.
Turn to the exercise sheet and complete exercise 2.1.
Heat treatment
Heat treatment is carried out on metals so as to alter their properties.
All heat treatments involve:
8
•
heating the metal to a particular temperature
•
holding the metal at that temperature so that it is heated throughout,
this is known as soaking
•
cooling the metal at a particular rate.
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A majority of heat treatment processes are carried out on ferrous metals
particularly steels, and can be broadly grouped as those that soften the
metal and those that harden the metal.
Hardening process
The ability to harden steel depends on the carbon content of the steel and
the cooling rate. Steels with low amounts of carbon are difficult to harden
by simple heat treatments, whereas steel with carbon contents greater
than 0.2% are readily hardened.
To harden steel it is heated to a temperature above 800oC and held there
until the it is soaked. The steel is then cooled quickly. This is done by
placing it in a solution of brine (very salty water), water or oil, this
process is known as quenching. This rapid cooling causes stress to build
up in the steel causing it be become extremely hard. The resulting
substance is known as martensite.
Because of its hardness, martensite is extremely brittle and is usually
subjected to other heating processes in order to increase its toughness.
Softening process
The softening processes that will be examined include annealing,
normalizing and tempering.
Annealing processes are used to soften the metal to some degree by
relieving the internal stresses and producing a uniform grain structure
throughout.
There are two types of annealing, full annealing and process annealing.
Full annealing requires a steel to be heated above a critical temperature.
This temperature will depend on the carbon content of the material. A
0.2% carbon steel would be heated to about 950oC, whilst a 0.8% carbon
steel would be heated to about 750oC. Once soaked at this temperature
the cooling is commenced at a very slow rate, sometimes the heating
furnace is turned off and is allowed to cool over a number of days.
This process is very slow, costly and results in a significant reduction in
the strength of the component. This is not a process that is used often in
an industrial setting.
Process annealing on the other hand is widely used in industry and is
commonly applied to items that have been cold worked so as to soften
them. The specimen is heated to a temperature between 550oC and
650oC, soaked and allowed to air cool. This process is only suitable for
steels having a composition of less than 0.6% carbon.
Part 2: Landscape products – materials
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Normalizing is a similar process to full annealing but at a slightly higher
temperature and the specimen once soaked is allowed to air cool. This
results in a fine grain structure and is used as a stress relieving process for
materials that have been cast or forged.
Tempering is a softening process that is applied to materials that have
been previously hardened by quenching, for example, martensite. These
materials are usually extremely hard and brittle and will fail under minor
impacts. The steel is heated to between 200oC and 450oC, soaked and
allowed to air cool. This process relieves the internal stresses, and results
in a slight decrease in the hardness but a significant increase in the
toughness of the material.
Use the same piece of copper, which now should be work hardened and
heat it until it is very hot and allow it to cool, actually you can quench
it note your observations.
__________________________________________________________
__________________________________________________________
Did you answer?
The metal changed colour and became softer.
Turn to the exercise sheet and complete exercise 2.2.
Composite materials
Many engineering materials have a composite structure, that is they
contain two or more different substances. Composite materials are
normally produced to give extra strength, but many other properties can
be engineered.
A composite material can be one material coated with a different material.
This is common with steel, as steel exposed to the atmosphere will rust.
This can be overcome by covering the steel with a coating. Materials
commonly used are tin (tinplating), zinc (galvanising), chromium (chrome
plating) and painting.
Identify a composite material in any landscape product.
__________________________________________________________
__________________________________________________________
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Did you answer?
A couple of examples include:
• Fiberglass shovel handle
• Plastic coated clothes line.
Concrete is a common composite material consisting of cement, sand and
aggregate, used in the landscaping industry.
Have you wondered why they add steel bars to concrete?
Concrete is a ceramic material and is very strong in compression but has
relatively poor strength in tension. Steel on the other hand is strong in
tension but lacks the compressive strength of a ceramic. If these two
materials are combined then the landscaper can take advantage of both
properties.
Figure 2.8 shows a concrete slab with steel reinforcing in the lower half of
the slab.
Concrete slab
Steel reinforcing
Figure 2.8 Reinforced concrete slab
If the slab is loaded, for example by a car or a truck driving over it, figure
2.9, it can be seen that the upper surface becomes compressed and the
lower surface becomes tensioned as the loading forces tend to bend the
slab.
Compressive load
Tensile load
Figure 2.9 Reinforced slab under load
Turn to the exercise sheet and complete exercise 2.3.
Part 2: Landscape products – materials
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Recycling of products
In Australia today significant volumes of solid waste are being produced
by all sectors of the community. More than 14 million tonnes of waste
solids and 200 000 tonnes of waste fluids are being deposited into landfill
and treatment facilities annually.
In response, the Federal Government has developed a National Waste
Minimisation Strategy to address the problems of waste generation and
landfill disposal.
This strategy is aimed at achieving the following recycling targets by the
year 2000:
•
polymer containers 25%
•
glass 45%
•
aluminium cans 65%
•
steel cans 40%
•
paperboard containers 20%
•
newsprint 40%
•
paper packaging 71%.
Source:
http://www.nohsc.gov.au/OHSInformation/Databases/Practical
GuidanceMaterial/t/003564.htm
Recycling is sometimes defined as the treating of waste so that new
products can be manufactured from them or prepare products for a
second use, often with some adaptation or reconstruction.
Common recycled materials include steel, aluminium, polymers, glass,
paper, cardboard and rubber. Recycling centres are becoming
commonplace and will accept these items for recycling, sometimes free of
charge.
Recycling of steel waste products such as cans, car bodies, and off cuts
are important to the iron and steel industry. Scrap steelyards supply the
waste material back to the industry. The scrap is remelted in a furnace,
cast into ingots and then rolled into rods, bars, sheet materials and other
suitable steel products.
Polymers, particularly thermosoftening polymers, can be recycled by
converting the waste product to granules or powder, which is then
reheated and reprocessed to form new polymer products, often by an
extrusion process. Extrusion is a process that forces a fluid product
through a die to produce the required cross sectional shape of the final
product. A common example of this can be seen when we squeeze
12
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toothpaste out through the round hole in the end of the tube to form a
cylindrical shape. Examples of landscape products produced by this
extrusion process include the manufacture of garden hoses, fuel lines of
lawnmowers, plastic wheelbarrow handles, plastic garden stakes and
drainage pipes.
Recycled concrete is common, not by reforming it, but by using it as fill
in landscaping projects. It can also be used in drainage areas to assist
with the easy movement of water below the surface.
Glass can be crushed into ‘cullet’, which is then melted down to make
new glass products.
Rubber, in particular disposal of old car and truck tyres, has become a
major environmental problem globally. Some are cut up and mixed with
bitumen to form a road surface. Complete tyres can also used for fill,
particularly in retaining walls where different landscaping levels are
required, as in a terrace type effect.
The recycling of rubber tyres is a relatively new and expensive process.
The tyres are processed by cutting and shredding machines to produce
rubber chips, which are then reduced to various sizes of powder in a
grinding machine. The fibre and steel are separated and the rubber
powder is screened. There is a high demand for recycled, ground or
powdered rubber. Uses include tiles and tile adhesives, mixing with
asphalt, sports surfaces, carpet underlay, noise and vibration insulation,
playgrounds and matting.
Part 2: Landscape products – materials
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Materials in landscape products
A wide variety of materials is used in the design and manufacture of
landscape products.
The lawnmower
The application of materials in the manufacture of components for a
common landscape product, the lawnmower, are outlined in the following
table.
14
Material
Product
Reason for selection
Mild Steel
Handle
Easily formed into tubular section,
good strength to weight ratio
Stainless Steel
Throttle Cable
Ductility (can be drawn into wire)
Medium Carbon
Steel
Blade
Toughness, wear resistance, impact
resistance
Polymer
Fuel tank
Corrosion Resistant, resistant to
petrol and oils.
Ceramic
Spark plug
Insulator to high voltage
Polymer
Grass catcher
Lightweight, easily moulded into
complex shapes
Aluminium alloy
Engine block, head
Lightweight, good heat transfer via
cooling fins, good for shell casting
Rubber
Tyres
Wear resistance, quietness on
concrete paths
Nylon
Nyloc nuts (locks nut so
it won’t vibrate loose)
Flexibility
Thermosoftening
polymer
Wheel
Lightweight, easily cast into complex
shapes, appearance, corrosion
resistant.
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The rotary clothes hoist
A rotary clothes hoist is constructed from various materials. As shown in
figure 2.10 each have a practical role to play:
•
galvanised mild steel pipe for the main structure
•
high carbon steel is used in the spring in the gearbox
•
polymer material for gears and nuts that raise and lower the worm
•
nylon bearings and washers, polypropylene for the caps and handle,
and polyester core in the line that the clothes are attached to is
•
aluminium is used as housing for the gearbox and for the worm gear.
The steel is galvabond, or hot dip galvanised, creating a composite
material suitable for outside use. The arm is made from medium carbon
steel that is rolled into tubes and then cut to length. Wire staples are
welded to the arm. to act as guides for the clothesline wire. The arms are
then galvanised coated with zinc to prevent rusting. The stays are made
from galvabond strip, which is rolled into tube, cut to length, flattened,
pierced and bent to shape. The main standard, the post, is made from
high tensile galvabond. The steel is rolled into tubes and cut to length.
The top main standard has a hole drilled into one end and a notch in the
other end. The bottom main standard has two holes drilled, notched one
end, and indents pressed into it. A zinc-plated steel plug is welded into
the end of the standard.
The hoist polymer components are made from polymers Nylon 6,
Akulon and Acetal Delrin. These are moulded in multiple cavity dies.
The cap at the top of the hoist is made from galvabond strip that is
pressed and formed to shape.
Cases, cross and worm gears, are made from aluminium alloy cast to shape.
The pinion is a moulded component from a polymer Acetal Delrin 100
material. The crown wheel is also a moulded component made from
Acetal Delrin 100.
The original Hills Hoists were made from water pipe but it has become
more economical to make the parts from thinner section tube. The
original crown wheel and pinion were made from cast iron.
The following technical drawings identify the component materials used
in the rotary clothes hoist. Codes used include:
•
MSGB – mild steel, galvanised
•
MTGB – high carbon steel, galvanised
•
Z/P – zinc plated.
Part 2: Landscape products – materials
15
16
Figure 2.10
A
Issue
Ref.
Hills Hoist Model 6
„ Hills Industries Limited
Turn to the exercise sheet and complete exercise 2.4 to 2.8.
Landscape products
REVISION
INITIAL ISSUE
TOLERANCES
Unless otherwise stated
NO DEC. ±
1 DEC. PL ±
2 DEC. PL ±
IRG
16.7.99 HOLE DIAM. ±
Drawn Appr. Date ANGLES ±
Date
Approved
Design OK
Checked
Drawn
SCALE
16.7.99
I.R. GUNN
1:1
Material:
© COPYRIGHT 19
99
HILLS INDUSTRIES LIMITED
Name:
✓
DO NOT SCALE
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Drawing No.:
DIMENSIONS IN MILLIMETRES
UNLESS OTHERWISE STATED
FIXED HEAD HOIST SPECIFICATION
OLD STYLE MODEL 6
DRAWN TO
AS1100
No manufacture date on product
Stabliser plug: 1.5mm steel Z/P
Bush supa C reducer: nylon natural
Pinion bearing: nylon black
Pinion tapped: acetal natural
Crown wheel: acetal natural
Conical washer: nylon natural
Retaining washer: 0.4mm MSGB G2 Z275
End caps: polypropylene black
Spring: ø3.5mm spring wire
Supa C cross: alum alloy CB401
Thrust ring: alum alloy CB401
Plain case: alum alloy CB401
Pinion case: alum alloy CB401
Worm: alum alloy CB401
Supa C reducer: alum alloy CB401
Pinion cover: alum alloy CB401
Handle assembly: polypropylene black with ø1/2" CRS shafting grade 2
Other material specs:
Line space: 65.6m
Head diameter: 5.95m
Space requirements 7.1m
Weight: 31kg
Elevation height: 445mm
Saturated washing capacity 50kg
Line Lengths:
Line 1: 548mm total length 2.192m
Line 2: 1140mm total length 4.56m
Line 3: 1740mm total length 6.96m
Line 4: 2341mm total length 9.36m
Line 5: 2940mm total length 11.76m
Line 6: 3541mm total length 14.16mm
Line 7: 4150mm total length 16.6mm
Line spacings:
Line 1 & 2: 425mm
Line 2 & 3: 425mm
Line 3 & 4: 425mm
Line 4 & 5: 425mm
Line 5 & 6: 425mm
Line 6 & 7: 425mm
7 lines
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Exercises
Exercise 2.1
a
Explain how manufacturing properties differ from service properties.
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b
Outline the difference between elastic and plastic deformation.
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c
Identify and describe one method by which plastic deformation can
proceed.
_______________________________________________________
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_______________________________________________________
_______________________________________________________
_______________________________________________________
d
Identify another method by which plastic deformation can proceed by
researching the process further.
_______________________________________________________
_______________________________________________________
Part 2: Landscape products – materials
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Exercise 2.2
a
Outline what you understand by the term work hardening.
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b
Identify and describe three softening heat treatment processes.
i
___________________________________________________
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___________________________________________________
ii
___________________________________________________
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iii
___________________________________________________
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Exercise 2.3
a
Identify four composite materials.
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b Discuss the advantages of composite materials?
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Exercise 2.4
The materials used in landscape products have changed over the years.
Identify two landscape products and:
a
state the name of the product
b
identify one material used in the original design and one material that
is used in the current model
c
outline two reasons why this change has occurred.
i
a
Product 1____________________________________________
b
Old material__________________________________________
New material_________________________________________
c
Reason 1
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
Reason 2
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
ii
a
Product 2____________________________________________
b
Old material__________________________________________
New material_________________________________________
c
Reason 1
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
Reason 2
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
Part 2: Landscape products – materials
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Exercise 2.5
Complete the following table by listing a suitable material for each clothes
line component, stating a manufacturing and an in-service properties.
Clothes line
components
Material
Manufacturing
property
In-service
property
Top cap
Standard
(post)
Pinion
gearing
Spring
Exercise 2.6
Consider the recycling of a landscape product – a petrol engine
lawnmower.
a
Describe how three materials could be recycled.
i
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ii
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iii
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b
Identify and evaluate two recycling programs.
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Exercise 2.7
The steel, as supplied, is not hard enough for a particular lawnmower
component. The manufacturer designs a process whereby the component
is repeatedly pressed into a changed shape. The component is then
tested and found to be of a suitable hardness.
a
What is this process called?
W ______________________
H
_____________________
Another component of the lawnmower requires substantial hardness.
The manufacture decides to heat the component to a red-hot temperature,
then quench the component in a bath of oil.
b
What is this heat treatment process called?
_______________________________________________________
The manufacturer finds that the process just described causes the
component to become brittle. The component is re-heated to 650ºC, then
allowed to cool slowly in a controlled atmosphere.
c
What is this process called?
_______________________________________________________
The manufacturer experiments with the process to see the effect when the
component is reheated to 300ºC.
d
What would this heat treatment process be called?
_______________________________________________________
e
What heat treatment process would the manufacturer use to obtain a
uniform structure throughout the component and to reduce the
stresses that have been created in the component during the
manufacturing process? The component is allowed to air cool.
_______________________________________________________
_______________________________________________________
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Exercise 2.8
a
Conduct a simple test on a piece of sheet material (copper is the best
metal to use) by hammering it to form a cupped shape.
i
What property change happens to the copper after you have
hammered it several times?
___________________________________________________
ii
Does the force required to change its shape decrease or increase?
___________________________________________________
A heat treatment process can change the coppers property back
to its original state.
Heat the copper up to a dull red, and then allow it to cool. Do
this by placing it on the kitchen-stove hot plate. After heating,
allow the copper to completely cool. The cooling rate of the
copper is not important.
iii What is this heat treatment process called?
___________________________________________________
iv
What can you notice about the ease of deforming the copper
after this heat treatment process?
___________________________________________________
b
Hold a piece of steel in a vice (or pair of pliers), bend it backwards
and forwards.
Why does the steel eventually break?
_______________________________________________________
c
Steel is commonly coated with different products.
Find examples of coated steel products, such as a tin can or the
upright pole of a rotary clothes line. Locate a scratch in the surface
coating that has exposed the steel.
What term is used to describe what has happened to the steel when
exposed to the atmosphere?
_______________________________________________________
Part 2: Landscape products – materials
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Progress check
In this part you examined a range of materials used in landscaping
products the modification of materials and recycling aspects.
✓
❏
Disagree – revise your work
✓
❏
Uncertain – contact your teacher
Uncertain
Agree – well done
Disagree
✓
❏
Agree
Take a few moments to reflect on your learning then tick the box which
best represents your level of achievement.
I have learnt about
•
engineering materials
– engineering applications of materials
•
recyclability of materials.
I have learnt to
•
conduct simple test aimed at improving materials’
properties through work hardening, heat treatment and
composites
•
analyse the properties, uses and appropriateness of
materials for landscape products
•
explain the benefits of recycling materials.
Extract from Stage Engineering Studies Syllabus, © Board of Studies, NSW, 1999.
Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.
In the next part you will analyse the mechanics involved in landscape
products.
Part 2: Landscape products – materials
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Exercise cover sheet
Exercises 2.1 to 2.8
Name: ______________________
Check!
Have you have completed the following exercises?
❐ Exercise 2.1
❐ Exercise 2.2
❐ Exercise 2.3
❐ Exercise 2.4
❐ Exercise 2.5
❐
Exercise 2.6
❐
Exercise 2.7
❐
Exercise 2.8
If you study Stage 6 Engineering Studies through a Distance Education
Centre/School (DECs) you will need to return the exercise pages with
your responses.
Return the exercise pages with the Title Page cover attached. Do not
return all the notes, they should be filed for future reference.
If you study Stage 6 Engineering Studies through the OTEN Open
Learning Program (OLP) refer to the Learner's Guide to determine which
exercises you need to return to your teacher along with the Mark Record
Slip.
Part 2: Landscape products – materials
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Landscape products
Part 3: Landscape products –
mechanics
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Part 3 contents
Introduction ........................................................................................... 3
What will you learn?.................................................................... 3
Engineering mechanics........................................................................ 3
Equilibrium................................................................................ 3
Force Review ............................................................................ 4
Static equilibrium ..................................................................... 12
Moments of force .................................................................... 27
Force/couple systems ............................................................. 34
Exercises............................................................................................ 37
Progress check................................................................................... 51
Exercise cover sheet ........................................................................ 53
Part 3: Landscape products – mechanics
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Introduction
In this part you will analyse the mechanical forces involved in landscape
products.
What will you learn?
You will learn about:
•
mechanical analysis of force systems
–
equilibrium
–
the nature and types of force
–
addition of vectors, space and free body diagrams
–
resultants and equilibrium, transmissibility of forces
–
3 force rule for equilibrium
–
moments of a force
–
force/couple systems.
You will learn to:
•
apply mathematical and/or graphical methods to solve mechanical
problems related to landscape products
•
investigate and interpret the concept of equilibrium in the mechanics
of landscape products.
Extract from Stage 6 Engineering Studies Syllabus, © Board of Studies, NSW, 1999.
Refer to <http//ww.boardofstudies.nsw.edu.au> for original and current documents.
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Engineering mechanics
Force and force systems are engineering concepts that have applications
to all static objects. In the study of statics it is essential that a sound
understanding of the principles of equilibrium be understood.
Equilibrium
Equilibrium is the term used to describe a system where a body is at
‘rest’. The force system is balanced and no change is occurring.
The body will remain at rest (static equilibrium) or will continue moving
in a straight line with uniform velocity (dynamic equilibrium) unless it is
acted upon by another force.
If the forces that are acting on the body are not balanced then there will be
a net force, this will cause the object to accelerate, Newtons Second Law.
Conditions for equilibrium
1
A single force system cannot be in equilibrium. It will always result
in acceleration.
Force
Figure 3.1 Single (1) force acting on a body
2
A two-force system is only in equilibrium when the forces have the
same magnitude (size of the force) and act in opposite directions
along the same line of action.
Figure 3.2 Two (2) forces acting on a body
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A three-force system may be in equilibrium if the lines of action of the
three forces pass through a common point, that is, they are concurrent,
and the sum of the horizontal and vertical components are zero.
Figure 3.3 Three (3) forces acting on a body – concurrent system
From this, it can be predicted that if a body is in equilibrium and there are
three forces acting, then they should be concurrent. This is commonly
known as the 3 force rule for equilibrium.
Force review
Force concepts are the foundation knowledge for many topics that you
will study during the engineering course. Let us review some content
from earlier work including:
•
definition of a force
•
resultants and equilibrants
•
addition and subtraction of vectors.
A force is defined as the interaction between bodies. All bodies (objects)
can be subjected to systems of forces. Such systems will either maintain
the body’s equilibrium or cause its state of rest or motion to change.
If a single force is applied to a stationary body, the body will move, in
fact it will accelerate. This is an example of an unbalanced force system.
If two or more forces are applied to a body, the body may or may not
accelerate.
In any equilibrium situation, all the forces acting on the body balance one
another – there is no net force.
Additionally, force was described as having a push or pull effect on a
body. For example, a pulling force could easily replace a pushing force.
They would both have the same effect as long as they had the same
magnitude, line of action and sense.
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In figure 3.4 a 100 kN force is pushing a garden rock to the right, however
in figure 3.5 a similar force is attempting to pull the rock to the right.
Both of these forces will have the same effect on the rock if they have the
same magnitude, line of action and sense.
Line of transmissability
Figure 3.4
Rock being pushed
Line of transmissability
Figure 3.5
Rock being pulled
This is known as the Principle of transmissibility of a force.
Other common terms that you will become familiar with include:
•
collinear – the forces are in one line
•
coplanar – the forces are in one plane
•
concurrent – the forces are acting at one point.
It is important for successful analysis of engineering situations to be able
to distinguish between a resultant and an equilibrant. The terms are often
incorrectly interchanged.
A resultant is the net effect of all the forces combined. If two forces act
upon an object, the resultant is the combined effect of those two forces.
The resultant is a single force that could replace the two forces and
achieve the same effect.
An equilibrant, is the single force that can balance a system. A balanced
system is in equilibrium.
What force would need to be added to the force system to achieve
equilibrium?
To answer this question, you will identify all the acting forces, add them
together to calculate the total resultant force, then determine the
equilibrant force required to balance this resultant force.
It can be seen that the equilibrant has exactly the same magnitude as the
resultant, but opposite in sense.
For example, if a resultant is 100 N to the right, then the equilibrant is
100 N to the left.
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Addition and subtraction of vectors
Addition of vectors can be done either by the graphical method or the
analytical method.
Graphical construction involves accurately drawing vectors to scale
whereas mathematical analysis is done by calculations. Vectors can be
resolved into components at right angles to each other (–x, –y or h, v) by
simple trigonometry.
Regardless of method, the objective of adding vectors is to obtain the
resultant.
Graphical solutions – force systems
When solving problems involving forces, it is convenient to use various
diagrams to assist with a graphical solution, such as:
1
space diagram –
a pictorial representation of the problem. The forces drawn on this
diagram are not drawn to scale, but the spaces, their angles and
distances between their lines of action are drawn to scale.
2
free body diagram (FBD) –
a diagrammatic sketch of the forces, known and unknown, involved
in the problem. The forces have been isolated from the space
diagram. Again, the forces need not be drawn to scale.
3
force diagram or vector diagram –
a graphical solution of the problem is drawn accurately to scale. The
scale used should be shown. This can also be used to assist in an
analytical solution.
Worked example 1
Problem: find the resultant of the two forces acting at point 0 in figure
3.6.
Force 1 is 40 N Æ
Force 2 is 50 N
65º
Graphical methods
The simplest graphical method of vector addition is the force polygon
method, where the vectors are added ‘tip-to-tail’. Consider the two
forces in worked example 1.
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50 N
q = 65∞
0
40 N
Figure 3.6 Two (2) forces
Solution: construct a vector diagram.
Figure 3.7 shows how the resultant of the two forces can be determined.
R
0
=
80
N
f = 40∞
50 N
q = 65∞
scale 1 mm = 1 N
40 N
Figure 3.7 Solution – Vector diagram
1
The 40 N force was drawn (40 mm horizontal to the right).
2
The 50 N force was then drawn (at 65º upwards to the right) attached
to the tip of the 40 N force.
3
The starting point (the origin point) was then connected to the
finishing point.
4
This resultant force was measured (76 mm) and the angle off the
horizontal was measured as 40º.
The resultant is therefore a 76 N force upward to the right at 40o.
In any graphical solution, the magnitude of the resultant is determined by
measurement using a rule and the known scale of the diagram. The
direction is measured with a protractor. The degree of accuracy is
increased when larger scales are used.
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Analytical method
The analytical method makes use of trigonometry to resolve the vectors
into –x and –y components, then ‘reassemble’ them to obtain the
resultant.
50 N
65∞
40 N
Figure 3.8 Two (2) forces and their components
Step 1
Determine the horizontal components of both forces.
40 N
æ ææÆ
The 40 N Æ force is ‘all’ horizontal, so the effect is 40 N Æ. If
you use the convention that forces to the right ( Æ) will be
considered positive, you therefore have + 40 N.
The 50 N force has both a vertical and horizontal
component. The horizontal component (H) is
determined by:
50 N
V
H
65∞
H
Figure 3.9
H
50
= 50cos65
= 50 ¥ 0.422
= 21 N Æ
Cos 65∞ =
50 N force and its horizontal component
As the convention is horizontal forces to the right are positive,
you have + 21 N.
To find the total horizontal forces (FT), you now add the two
horizontal components (H1 and H2):
FT = H1 + H 2
= 40 + 21
= 61 N Æ
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Step 2
Determine the vertical components of both forces.
The 40 N Æ has zero vertical component.
The second force is 50 N
65º.
The vertical component of the 50 N force is
determined by:
50 N
V
V
50
= 50sin65
= 50 ¥ 0.9
Sin 65∞ =
V
= 45.3 N ≠
65∞
H
Figure 3.10
50 N force and its vertical component
If you use the convention the vertical forces up are positive, you
have + 45.3 N.
To find the total vertical forces (FT), you now add the two
vertical components.
FT = V1 + V2
= 0 + 45.3
= 45.3 N ≠
Sometimes this is easier to see in table form.
Force
Horizontal component
Fx
Vertical component
F1
40
0
F2
50cos65 = 21
50sin65 = 45.3
R (Total)
61
45.3
Step 3
Fy
You have now determined the total vertical and total horizontal
effect created by the two original forces. The following diagram
graphically represents this.
Part 3: Landscape products – mechanics
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R=?
45 N
?
61 N
Figure 3.11
Two (2) forces and their components
To determine the resultant (R) of these two components, you
use Pythagoras theorem and trigonometry.
Step 4
Use Pythagoras theorem to find the resultant magnitude:
R2 =
H2 + V2
2
+ V2
\ R =
H
R =
61
R =
5746
2
+ 452
= 75.8 N
Step 5
Use trigonometry to find the angle (direction) that the resultant
is acting:
45
61
= 0.7377
\ q = 36.4∞
Tan q =
75.8 N
45 N
61 N
Figure 3.12
Step 6
Two (2) forces and their components
Consolidate all the data into one final statement.
The resultant of the two forces is 75.8 N at
36.4.
Having seen the graphical and analytical solutions, which method do you think is
generally faster?
What method would you choose if there are many more forces acting on the
system Considering that the sample was a two force system?
Did you notice that the graphical and analytical solutions to example 1 and 2 were
different?
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This is acceptable. A larger graphical scale would improve the accuracy
of the result. Worked examples 3 and 4 show a graphical, then an
analytical solution to a three force system.
Worked example 2
Determine the resultant of the three-force system.
F1 =
F2 = 4 kN
5 kN
20∞
F3 = 3 kN
Figure 3.13 Three (3) forces system
Graphical method
The convention is to add vectors ‘tip-to-tail’, anti-clockwise from the +x
axis:
20o).
Step 1
Draw to scale force 1 (5 kN = 50 mm
Step 2
Draw to scale force 2 (4 kN = 40 mm¨).
Step 3
Draw to scale force 3 (3 kN = 30 mm Ø ).
Step 4
Draw a line between the origin point and the last arrowhead.
This is the resultant.
4 kN
3 kN
118∞
5 kN
R
Figure 3.14 Adding vectors graphically
Step 5
Measure the resultants length 15 mm– convert this to a
magnitude 1.5 kN).
Step 6
Use a protractor to measure the angle of the resultant (62º).
Part 3: Landscape products – mechanics
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62∞
Figure 3.15 Direction and sense indication
Analytical method
The analytical solution is best presented in the table, noting that x and y
components have a positive or a negative sense:
Force
Horizontal component
Fx
Vertical component
Fy
F1
5 cos 20° =
F2
- 4.0
0.0
F3
0.0
- 3.0
R (Total)
0.7
- 1.3
R
4.7
5 sin 20° =
1.7
= (0.7) 2 + (-1.3) 2
= 1.5 kN
-1.3
0.7
= 1.9
Tan q =
\
q = 620
62∞
Static equilibrium
The whole discipline of ‘statics’ concerns itself with the unique condition
of a system of forces having a zero resultant. Commonly referred to as
‘balance of forces’, this condition of no net force on a body means that it
will not move under that system of forces – it will be in a state of static
equilibrium.
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Equilibrium
If a body is in equilibrium under the action of a system of coplanar forces,
then the resultant of those forces is zero.
This condition has two important consequences for the graphical and
analytical methods for dealing with forces. The first is that a zero
resultant can only be produced if the vector polygon closes onto itself
and returns to the origin as all the forces are added. The second is that,
just as the vector sum of all the forces is zero, so too the sum of all the x
components and the sum of all the y components.
SF = 0
then
SFx = 0
and
SFy = 0
These principles enable you to solve a wide range of problems.
Worked example 3
Consider a body on a string, which is in equilibrium under the action of
three forces, a horizontal force (F), its weight (W) and the tension in the
string (T).
cieling
q
T
F
T
W
mass
F
scale 1 m = 1 N
W
Figure 3.16
Space diagram
Figure 3.17 Force diagram
The fact that the three vectors add to form a closed triangle tells us the
system is in equilibrium or if we knew that the system was in equilibrium
then we could predict the size of the force pulling the block to the left.
Part 3: Landscape products – mechanics
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Using figure 3.16, the suspended body has a mass of 4 kg and the string is
at an angle of 45º.
If the system is in equilibrium what would be the tension in the string?
We need to convert the 4 kg to a force.
(where g is the gravitational factor whose value is 10)
W
= mg
W
= 4 ¥ 10 = 40 N
A scaled vector diagram shown in figure 3.17 can now be drawn and used
to determine the force and tension.
F
= 40 N Ø
T
= 57 N
The angle of each force is measured using a protractor.
The principle that three forces in equilibrium form a closed triangle, and
that three or more such forces form a polygon, can be extended to any
system of coplanar forces.
Worked example 4
A lawnmower is to be lifted up a retaining wall. The retaining wall is at
an angle of 75º to the horizontal and the mass of the mower is 40 kg.
During the lift, the mower is held stationary in the position shown in
figure 3.18 by a force, FH, acting along the handle.
FH
handle
mower
45∞
wall
mg
FW
75∞
ground
Figure 3.18 Mower being pulled up retaining wall
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Fo
rc
e
in
ha
nd
le
Applying the graphical method, using the three-force rule, determine the
magnitude of the force FH (note that the reaction at the wall will be at 90º
to the wall – this is known as the normal reaction).
45∞
Reac 15∞
tion a
t wa
mg
ll
Figure 3.19 Free Body Diagram
Graphical method
Solution: Draw a vector diagram
Step 1
Draw 400 N to scale (mg = 40 kg x 10 = 40 N Ø ).
Step 2
Draw an arrowhead, representing the 400 N force vertically
down.
Step 3
Draw the direction of FW (the reaction at the wall) from the end
position of the 400 N force.
Step 4
Draw the direction of FH (the force in the handle) from the
starting position of the vector diagram.
Step 5
A three force vector diagram is created by adding the arrow
heads to FW and FH.
Step 6
As the system is in equilibrium, the arrow heads must start from
and lead back to the original point, forming a closed force
polygon.
Part 3: Landscape products – mechanics
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45∞
FH
400 N
scale 5 N = 1 mm
FW
15∞
Figure 3.20 Vector diagram
Step 7 Measure FH (77 mm) and FW (59 mm).
Step 8 Using the scale, the final answer can be stated:
FH = 445 N
45º
FW = 330 N 15º
Worked example 5
At another time the lawnmower is being lifted up a small step, 100 mm
high.
Determine the effort required in the handle if the lawnmower is balancing
at the top of the step.
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handle
mower
45∞
wall
mg
100 mm
A
ground
Figure 3.21 Lawnmower balancing at the top of the step
From figure 3.21 it is easy to see the lines of action for the weight force of
the lawnmower and the direction for the reaction in the handle but the
reaction between the wheel and the step is no longer at a normal to the
step face.
fo
rc
e
in
ha
nd
le
From the principle of equilibrium, if a three-force system is in equilibrium
then the lines of action of the forces must be concurrent – they must go
through the same point. So, the reactive force must pass through the
point A, as this is the only point of contact between the wheel and the
step, and the intersection of the lines of force for the reaction at the
handle and the weight force at the rear wheels as seen in figure 3.22.
mg
A
Line of action
for reaction at
top of step
Figure 3.22 Free body diagram
Part 3: Landscape products – mechanics
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Once this line of action is determined then it is simply a three-force
system that can be solved graphically.
Graphical method
re
ac
tio
na
ts
tep
fo
rc
e
in
ha
nd
le
mg
Figure 3.23 Vector diagram
From figure 3.23 it can be determined that the force in the handle is 340 N.
Turn to the exercise sheet and complete exercises 3.1 and 3.2.
Worked example 6
Two workers are trying to move a large rock along a predetermined path,
by pulling on ropes attached to the rock. The ropes are attached to the
rock as shown in figure 3.23.
30°
path
40°
Figure 3.24 Space Diagram
Determine the minimum force that each worker needs to apply before the
rock will move in the desired direction if the force resisting motion is
1000 N.
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F1
30∞
1000 N
40∞
F2
Figure 3.25 Free body diagram
Graphical method
Start with drawing the 1000 N force at an appropriate scale (the arrow
head pointing to the left), then from one end draw a line at 30o to the
horizontal. From the other end draw a line at 40o to the horizontal. Since
the system is in equilibrium then this determines the direction of the
arrowheads, shown in figure 3.25.
F1
F2
30∞
40∞
Scale 1mm = 20 N
1000 N
Figure 3.26 Vector diagram
From figure 3.26 it can be determined that:
F1=34mm or 680 N and
F2 = 27mm or 540 N
This is a straight forward example but the analytical solution may be
more challenging.
Analytical solution
Firstly, analyse the components of the forces.
Force
Horizontal component
Fx
Vertical component
F1
F1 cos 30
F1 sin 30
F2
F2 cos 40
– F2 sin 40
resistance
– 1000
0
Part 3: Landscape products – mechanics
Fy
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As the resultant force is to follow the –x path only, then the sum of three
forces in the –y direction must equal zero.
At the point just before moving the system is in equilibrium, so the
standard conditions of equilibrium must apply.
So
SFx
1000
=
0
=
–1000 + F1cos 30 + F2cos 40
=
F1cos 30 + F2cos 40
If you are not confident with the manipulation of the trig functions then
turn them into values as soon as possible.
=
0.866F1 + 0.766 F2
What do we do when there are two unknowns?
Lets try the vertical reaction
S Fy
=
0
=
F1sin 30 – F2sin 40
=
0.5F1 – 0.643F2
Again two unknowns, but it is possible to get F1 or F2 as the subject of
the formula.
0.643F2
=
0.5F1
F2
=
0.5F1/ 0.643
=
0.777F1
This will allow you to substitute in to the above formula and eliminate
one of the unknowns. For example:
from 1000
=
0.866F1 + 0.766 F2
The F2 value can be substituted with 0.777F1
1000
F1
20
=
0.866F1 + 0.766 x 0.777F1
=
0.866F1 + 0.595F1
=
1.461F1
=
1000/1.461
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F1
=
684.5 N
since
F2
=
0.777F1
then
F2
=
0.777 x 684.5
=
531.8 N
Therefore F1 is 684.5 N upward to the right at 30o to the horizontal
and F2 is 531 N down to the right at 40o to the horizontal.
Worked example 7
Consider a pot plant supported by two unequal strings as shown in figure
3.27.
60∞
30∞
Figure 3.27 Space diagram
In this example, the two unequal length strings support a 5 kg pot plant.
Determine the tension in the two supporting strings
T1 30∞
60∞
T2
W = 50 N
Figure 3.28 Free body diagram – Three (3) force system
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Graphical method
To solve this problem graphically it is necessary work through the following
steps.
Step 1 Select a suitable scale for the vector diagram (say, 10 mm = 10
N).
Step 2 Draw the vertical weight force vector (50 mm).
Step 3
Draw lines from the tip and tail of the weight vector in the
directions of the two tension vectors (T1 and T2).
Step 4 Where those lines meet is the third point of the vector
triangle.
Step 5
Add arrow heads (to create a ‘circuit’ of arrow heads).
Step 6 Measure the tension vectors and use the scale to determine their
actual values.
60∞
T1
W = 50 N
30∞
T2
Figure 3.29 Vector diagram
The values determined in this manner are:
T1
= 44 N
T2
= 26 N
Analytical solution
From resolution of the forces the following table can be developed.
Force
22
Horizontal component
Fx
Vertical component
T1
– T1 cos 60
T1 sin 60
T2
T2 cos 30
T2 sin 30
W
0
– 50
Fy
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From the conditions of equilibrium:
SFx
=
0
=
–T1 cos 60 + T2cos 30
=
–0.5T1 + 0.866T2
0.5T1
=
0.866T2
T1
=
0.866T2/ 0.5
=
1.732 T2
=
0
=
T1sin 60 + T2sin 30 –50
=
0.866T1 + 0.5T2 – 50
=
0.866T1 + 0.5T2
S Fy
50
Two unknown values but from the sum of the horizontal forces
T1 = 1.732 T2
this value is substituted into the sum of the vertical forces then:
50
T2
=
0.866 x 1.732T2 + 0.5T2
=
1.499T2 + 0.5T2
=
2T2
=
25 N
As T2 = 25 then by substituting into one of the above equations
containing T1 we can determine T1.
So
T1
=
1.732 T2
=
1.732 x 25
=
43.3 N
Therefore the force in T1 is 43.3 N upward
The force in T2 is 25 N upward
at 30o.
at 60o.
The mathematical resultants are in close agreement with those obtained
by the graphical method, but it is obvious that while the calculation
method is more accurate, it is considerably more time consuming.
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Note that the directions of the tension forces are apparent from the
geometry of the physical system, which is logical as the tension forces
must act in the directions of the strings.
It is clearly demonstrated that the determination of the forces is often
faster and easier to see with a graphical solution rather than an analytical
or mathematical solution.
Turn to the exercise sheet and complete exercises 3.3.
Worked example 8
A 2.5 m long ladder stands against a smooth wall (this means that there is
no friction between the ladder and the wall so the reaction at the wall is
perpendicular or normal to the wall) and on rough ground. The ladder
rests 2.35 m up the wall.
2.5
2.35 m
Determine the reaction at the wall and the ground.
m
250 N
Figure 3.30 Ladder resting against a wall
From figure 3.30 we can see that the weight force will act vertically down
and the reaction at the wall must act horizontally so the reaction at the
ground must pass through the point of contact at the ground and the
intersection of the weight force and the reaction at the wall.
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Explain why the reaction at the ground must pass through the intersection of the
reaction at the wall and the weight-force.
__________________________________________________________
__________________________________________________________
Did you answer?
If the ladder is not going to fall down it must be in equilibrium therefore the
three force system is concurrent (a condition of equilibrium).
RWall
250 N
RGround
Weight force
of ladder
Figure 3.31 Free body diagram
Knowing the direction of the three forces it is now possible to construct
the force polygon to determine the missing forces. Remember that this
must be drawn accurately.
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RGround = 254 N
250 N
RWall = 47.5 N
Figure 3.32 Vector Diagram
Measure the lengths of the vectors and determine the reactions at the
ground and the wall.
RG = 254N 80o
RW = 47.5 N
Turn to the exercise sheet and complete exercises 3.4.
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Moments of a force
Up until this stage, all force calculations have been made concerning single
forces, or several forces all acting at one point.
F1
F2
F3
Figure 3.33 Concurrent forces
Another type of force analysis considers the effect when forces are not all
acting at one point, rather they are acting at a distance from a point and
are nonconcurrent.
A force will move or tend to move a body situated on its line of action in
the direction of the force as stated by Newton’s Second Law and the
Principle of transmissibility.
A force can also tend to rotate a body. The tendency of a force to rotate
a body about a point is known as its turning effect, or moment. Another
name sometimes used is torque.
The value of the moment is the product of the magnitude of the force and
the perpendicular, or shortest distance, from the turning point to the line
of action of the force.
The perpendicular distance is called the moment arm.
moment arm
90∞
force
P
Figure 3.34 Force causing moment about P
The moment of Force about P is
Moment = Force x distance
If point P lies on the line of action of the force, then the moment arm is
zero and the value of the moment is zero.
The units of moments are newton-metre (Nm).
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This gives rise to the third condition of equilibrium, which is the sum of
the moments must equal zero as well.
So
SFx = 0
SFy = 0
and SM = 0 for the object to be in equilibrium
Worked example 9
Determine the effect of a 100 N force acting at 2.5 m from the pivot
point.
2.5 m
P
100 N
Figure 3.35 Example of a force and distance
The moment or turning effect of the 100 N force about P is:
M
= F ¥ d
= 100 ¥ 2.5
= 250 Nm
Position and magnification of the force
A moment involves the product of the two quantities force and distance –
there are many combinations that produce the same moment value.
To illustrate this, the force required to lift the rock would get smaller as
the distance from the pivot increases as shown in figures 3.34 and 3.35.
50 N force
rock
crowbar
200
Figure 3.36 Rock on lever – force close to pivot
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M
= F ¥ d
= 50 ¥ 0.2
= 10 Nm
force = 5 N
rock
crowbar
2000
Figure 3.37 Rock on Lever – force away from pivot
M
= F ¥ d
= 5 ¥ 2
= 10 Nm
Note that the moment created is the same as in both situations (10 Nm).
The moment of a force is a vector quantity and so must have a direction.
The directions used for moments are either clockwise or anti-clockwise.
To distinguish between these directions, a convention is used. Moments
that are anti-clockwise are usually assumed as positive and clockwise
moments are assumed as negative.
There are several accepted ways for indicating moment directions.
They are:
+ 10 Nm
or
Figure 3.38 10 Nm (anti clockwise)
– 10 Nm
Figure 3.39 10 Nm (clockwise)
Worked example 10
Determine the force, F, required to balance the force system shown. Such
an example could be when determining the load to be lifted in a wheel
barrow.
F
5
100 N
5
Figure 3.40 Force system
Part 3: Landscape products – mechanics
29
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Analytical solution
As there are two forces each will have a turning effect about the pivot
point.
F
5
100
10
and
Figure 3.41 Forces causing a turning effect
Calculate moments created by each force about the pivot point.
SM
=
0
=
(F1 x d1) + (F2 x d2)
=
(–F x 5) + (100 x 10)
=
–5 F + 1000
5F
=
1000
F
=
200 N
The positive value for F means that the original assumption that F was
going downwards was correct.
Worked example 11
Determine the force (F) required to balance the force system shown.
50 N
F
10
P
5
20 N
5
Figure 3.42 A beam being loaded with three forces
Analytical solution
In this example there are three forces that will have a turning effect about
the pivot point.
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F
50
10
P
P
5
20
P
10
Figure 3.43 Forces causing a turning effect
Calculate the moments created by each force about the pivot point.
SM
=
0
=
(F1 x d1) + (F2 x d2) + (F3 x d3)
=
(F x 10) + (–50 x 5) + (20 x 10)
=
10F – 250 + 200
=
10F – 50
–10F
=
–50
10F
=
50
F
=
5N
Worked example 12
As we have seen previously not all forces are vertical or perpendicular to
a reference plane. In figure 3.44 you can see that there is an inclined force
at the end of the lever.
Determine the force (F) to balance the inclined 100 N force.
F1
100 N
2
6
45∞
Figure 3.44 A beam with an inclined force being balanced by force F
Analytical solution
As before when looking at inclined forces we break the force up into it
vertical and horizontal components.
Part 3: Landscape products – mechanics
31
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Force
Horizontal component
Fx
Vertical component
F
0
–F
100N
–100cos45
–100sin45
Fy
There appear to be three forces but do they all have a turning effect?
Lets see.
F1
100 sin 45∞
100 cos 45∞
Figure 3.45 Forces causing a turning effect
A moment is created by a force is determined by multiplying the force by
the distance to the pivot point (M = F x d), if the distance is zero, then
no moment will be created. If the force creates no moment, it can be
eliminated from the calculations.
The third force in figure 3.45 goes through the pivot point therefore there
is no distance so the moment so created is zero and the turning effect of
this force can be dismissed.
SM
=
0
=
(F1 x d1) + (F2 x d2)
=
(F x 2) – (100sin45)
=
2F – 70.71
2F
=
70.71
F
=
35.4 N
Indicate another method to solve this problem.
___________________________________________________________
___________________________________________________________
Did you answer?
As there are three forces acting, this problem could be answered graphically
using the principles of concurrent forces.
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Two unknown forces
When a force system has two unknowns, it is possible to eliminate one of
the unknowns by using its point of application as the point about which
to take moments. This means that the force passes through the position
where moments are being taken. Therefore, the moment arm length is
zero, so the moment is zero.
These systems are common in landscaping where a beam is supported by
two supports.
Worked example 13
Determine the force required at position RR and RL in order to create
equilibrium.
100 N
6
RL
4
RR
Figure 3.46 A beam is supported at each end
The conditions of equilibrium are:
SM = 0
SFx = 0
SFy = 0
The terminology RR and RL are commonly used when analysing problems
where there are reactions at supports. The term RR refers to the reaction
at the right hand support and RL refers to the reaction at the left support.
In this example we will initially take the moments at the point where RL
meets the beam.
The pivot at RL, thus eliminates that force from the calculations as there
is no distance from the pivot point to the force so the moment is zero.
Part 3: Landscape products – mechanics
33
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+
S MR L = 0
=
=
(F ¥ d) + (F ¥ d)
( ± 100 ¥ 6) + (R R
¥ 10 )
= ± 600 + 10R R
600 = 10R R
R R = 60 N ≠
Because a force system in equilibrium must have all forces balanced,
S F ≠must equal S F Ø, that is, SFy = 0.
We can therefore calculate that:
± Ø
FV
= F1 + F2 + F3
=
RL
(R )
L
+ ( ±100) + ( 60)
= 40 N ≠
We have now determined that the 100 N force vertically downwards,
located in the position indicated, can be balanced by a 40 N force at RL
and a 60 N force at RR. Both the 40 N and 60 N forces must act upwards
to balance the 100 N force acting downwards.
Force/couple systems
A couple consists of two separate forces, equal in magnitude, acting
parallel to each other but having opposite senses.
60
10 N
10 N
TAP HANDLE
Figure 3.47 A force couple system
The distance (d) is called the couple arm.
A single force exerting a moment on an object would cause it to change
position. The effect of a couple is purely rotational because the resultant
of the forces is zero.
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A couple has a moment or turning effect equal to the product of the
magnitude of one of the forces and the perpendicular distance between the
forces.
In figure 3.46 the value of the force couple created would be:
+
M
= F ¥ d
= 10 ¥ 0.06
= 0.6 Nm
Couples can be active, as in the above example where both forces are
intended to cause rotation as in figure 3.46.
Couples can be reactive which result from the application of a force and
oppose the twisting effect that the applied force creates, as in figure 3.47.
A pot plant is hanging on a bracket that is bolted to the wall. The pot
plant has a mass and will create a turning effect at the wall.
Figure 3.48 Pot plant supported by a wall bracket
As the system is in equilibrium there must be both a turning effect and a
force opposing that generated by the plant.
This is shown in figure 3.48 where a force and couple are positioned so as
to maintain equilibrium.
Part 3: Landscape products – mechanics
35
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Force to oppose the
weight of the plant.
Couple system must
oppose the turning
effect caused by the
weight of the plant.
Force due to the
mass of the plant.
Figure 3.49 Force couple system
Turn to the exercise sheet and complete exercises 3.5 to 3.7.
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Exercises
Exercise 3.1
a
Explain why a single force system cannot be in equilibrium.
_______________________________________________________
_______________________________________________________
_______________________________________________________
b
Outline the principle of transmissibility.
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
c
Explain how equilibriants differ from resultants.
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
d
Differentiate between space diagrams, free body diagrams and force
diagrams.
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
_______________________________________________________
Part 3: Landscape products – mechanics
37
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Exercise 3.2
A garden roller of mass of 60 kg is to be moved up and over a step. The
roller diameter is 500 mm and the step is 150 mm high.
Determine the effort required to roll the roller over the step using the
handle inclined at 30∞. The reaction at the top of the step will be directed
towards the centre of the axle.
Ø 500
EH
150
30∞
Figure 3.50 Garden roller placed near a step
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Exercise 3.2 continued
Part 3: Landscape products – mechanics
39
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Exercise 3.3
Two workmen are using a block and tackle to unload a large plant from
the back of a truck.
Determine the tension in the ropes if the plant has a mass of 150 kg.
Check your answer graphically.
50°
30°
Figure 3.51 Two men unloading a plant
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Exercise 3.3 continued
Part 3: Landscape products – mechanics
41
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Exercise 3.4
A gardener (mass 70 kg) is standing near the top of a 5 m ladder pruning
the branch of a tree.
5m
Determine graphically, the reaction at the top of the ladder and at the
ground.
Centre
of mass
Figure 3.52 A worker pruning a tree
Ignore the mass of the ladder and assume a smooth surface between the
tree and the ladder.
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Exercise 3.4 continued
Part 3: Landscape products – mechanics
43
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Exercise 3.5
The shape and size details of a lawnmower are given below. The
lawnmower has a mass of 40 kg, and the centre of gravity is situated
150 mm to the left of the rear wheels.
90
0
Calculate the reaction forces required at both the front and rear wheels
if the system is in equilibrium.
45°
400
Figure 3.53 Mower with dimensions
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Exercise 3.5 continued
Part 3: Landscape products – mechanics
45
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Exercise 3.6
The figure 3.50 shows two hanging pot plant holders suspended from a 1
metre horizontal bar. The bar is attached to an overhead beam by a chain.
Assuming the system to be balanced, find the resulting tension force
acting in the chain and the position the chain must be attached to the bar
using moments.
?
6 kg
4 kg
Figure 3.54 Pot plants suspended on a 1 metre bar
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Exercise 3.6 continued
Part 3: Landscape products – mechanics
47
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Exercise 3.7
A wheelbarrow, with its load, has a combined mass of 120Kgs is shown
below.
Determine:
a
the reaction at the ground, both at the wheel (R2) and the stand (R1)
b
the effort required at the handles to just lift the rear stands clear of
the ground.
Centre of mass (120 kg)
Effort
R1
600
R2
400
500
Figure 3.55 Loaded wheelbarrow
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Exercise 3.7 continued
Part 3: Landscape products – mechanics
49
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50
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Progress check
In this part you learnt to apply mathematical and/or graphical methods to
solve mechanical problems related to landscape products.
✓
❏
Disagree – revise your work
✓
❏
Uncertain – contact your teacher
Uncertain
Agree – well done
Disagree
✓
❏
Agree
Take a few moments to reflect on your learning then tick the box which
best represents your level of achievement.
I have learnt about
•
mechanical analysis of force systems
– the nature and types of force
– addition of vectors, space and freebody diagrams
– resultants and equilibrium, transmissibility of forces
– 3 force rule for equilibrium
– moments of a force
– force/couple systems
– equilibrium …
I have learnt to
•
apply mathematical and/or graphical methods to solve
mechanical problems related to landscape products
•
investigate and interpret the concept of equilibrium in
the mechanics of landscape products.
Extract from Stage 6 Engineering Studies Syllabus, © Board of Studies, NSW, 1999.
Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.
In the next part you will examine the conventions that govern technical
drawing techniques in engineering illustrate landscape products such as
lawnmowers and rotary clothes hoists.
Part 3: Landscape products – mechanics
51
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52
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Exercise cover sheet
Exercises 3.1 to 3.7
Name: ______________________
Check!
Have you have completed the following exercises?
❐ Exercise 3.1
❐ Exercise 3.2
❐ Exercise 3.3
❐ Exercise 3.4
❐ Exercise 3.5
❐ Exercise 3.6
❐ Exercise 3.7
If you study Stage 6 Engineering Studies through a Distance Education
Centre/School (DEC) you will need to return the exercise pages with your
responses.
Return the exercise pages with the Title Page cover attached. Do not
return all the notes, they should be filed for future reference.
If you study Stage 6 Engineering Studies through the OTEN Open
Learning Program (OLP) refer to the Learner's Guide to determine which
exercises you need to return to your teacher along with the Mark Record
Slip.
Part 3: Landscape products – mechanics
53
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Landscape products
Part 4: Landscape products –
machines and communication
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Part 4 contents
Introduction ........................................................................................... 2
What will you learn?.................................................................... 2
Simple machines................................................................................. 3
Levers ...................................................................................... 3
Inclined planes.......................................................................... 4
Wheel and axle.......................................................................... 4
Combined mechanisms ............................................................. 5
Pulleys ..................................................................................... 6
Engineering drawing............................................................................ 8
Drawing practices – some basic rules .......................................... 8
Computer aided drawing .......................................................... 17
Exercises ........................................................................................... 21
Progress check................................................................................... 27
Exercise cover sheet ........................................................................ 29
Part 4: Communication landscape products
1
Introduction
In this part you will examine technical drawing techniques. The basics of
orthogonal projection are discussed, and specific details of the AS 1100
drawing standards are described. You will have an opportunity to
demonstrate some of your skills.
What will you learn?
You will learn about:
•
simple mechanisms
–
inclined plane, lever, screws, wheel and axle, pulley gears
•
orthogonal drawings
•
Australian Standards AS 1100
•
dimensioning
•
materials lists
•
introduction to computer assisted drawing (CAD).
You will learn to:
•
examine and analyse the function of simple mechanisms
•
produce orthogonal assembly drawings applying appropriate
Australian Standard (AS 1100).
Extract from Stage 6 Engineering Studies Syllabus, © Board of Studies, NSW, 1999.
Refer to <http//ww.boardofstudies.nsw.edu.au> for original and current documents.
2
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Simple machines
Most landscape products rely on a system of simple mechanisms to
achieve the result required.
A mechanism, is a device for doing work in overcoming a resistance,
known as a load, by applying a force known as an effort.
Mechanisms may be used to help do work with less effort, or with
greater speed, or by applying the effort at a more convenient position.
Levers
In part three of Landscape products we looked at simple applications of
levers to perform tasks.
We saw how the length of a lever and the positioning of the pivot point,
also known as a fulcrum, affected the effort required to lift a rock in figure
3.35. If you have ever opened a can of paint, the task is almost
impossible with your fingers, but with the aid of a screwdriver relatively
simple.
Load
Effort
Fulcrum
Figure 4.1 Application of a lever
It is assumed that a lever is very strong and will not bend. Additionally
in most situations the lever has no mass, therefore there is no weight force
associated with the lever. In practice this is not true, but makes the
calculations a little simpler.
Part 4: Communication landscape products
3
A lever allows the user to magnify the size of the effort. This is known
as mechanical advantage and will be discussed in greater detail in
Bio-engineering.
Inclined plane
It is easy to think of an inclined plane as a ramp. When trying to raise a
mass up a particular height it is usually easier to slide or wheel the mass
up a ramp rather than lift it directly up. This can be observed when
unloading or loading a crate from a truck or carrying bricks up a scaffold.
Figure 4.2
Examples of inclined planes
The screw thread can be considered to be an inclined plane that is placed
around a shaft. The pitch of the thread can be considered as the angle of
incline. There are many types of screw threads and they can be used for
transmitting motion or power and for fastening surfaces or parts together.
Wheel and axle
After the lever, the wheel was probably the next machine to be used.
Many believe that the wheel is the single most important innovation ever
developed.
In its simplest application it may have been a log placed under a heavy
mass. The resultant rolling motion required less force than trying to slide
the mass. This rolling action reduces the friction between the surfaces.
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Figure 4.3 Simple application of wheels
The application of wheels to aid movement is commonplace and can be
seen regularly. Perhaps you have used a skateboard to move a heavy pot
plant.
Combined mechanisms
Simple machines often use a combination of the levers, inclined planes
and wheel and axle. The wheelbarrow is a combination of the wheel and
the lever as is the windlass, which uses a combination of wheel and axle.
Typical examples of a windlass include winches used for lifting water,
tensioning sheets and halyards on boats and for winching boats onto
trailers.
Figure 4.4 Winching devices
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5
Pulleys
Other devices that are used for pulling, or winching, are pulleys. The
simplest pulley system is passing a rope over a wheel and axle system as
seen in figure 4.5.
Figure 4.5 Simple pulley system
This system does not have any mechanical advantage – the force applied
by the operator is equal to the mass of the motor. It is possible to
position a number of pulleys in such a way that they will have a
mechanical advantage. The operator will be able to lift greater masses with
less effort. Some arrangements of pulleys are shown in figure 4.6.
L
E
E
E
L
L
Figure 4.6 Examples of pulley systems that have mechanical advantage
Pulleys and belts are used for the transmission of power. They are often
used in conjunction with electric motors as shown in figure 4.7. The
spindle speed of an electric motor is not always suited to the speed of the
device being driven. By combining different sized pulleys it is possible to
change the effective speed of the driven device.
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Figure 4.7 Pulley drives
To overcome the problem with belt slippage, because of greater loads, it
is possible to replace the belt with a chain drive. This system is used in
bicycles and motorbikes. An alternative solution is to use a gear drive as
shown in figure 4.8, like that used in a car or truck gearbox. Such drives
do not allow for any slippage in the drive mechanism and are extremely
robust.
Figure 4.8
Gear drives
Part 4: Communication landscape products
7
Engineering drawing
Technical drawing is the engineer’s way of communicating information.
You are familiar with the process of freehand representation of objects
using both orthogonal and pictorial style of drawings. You will be
examining some technical rules for construction of an engineering drawing.
Standards Australia sets down these standards in Australian standards
(AS1100), these rules vary little from country to country.
Drawing practices – some of the
basic rules
Engineering drawings are understood throughout the world. When you
learn the rules, you have learnt an international language!
Linework
If all lines on a drawing board are of equal thickness, the drawing may be
confusing and difficult to interpret. If the outlines of the object are drawn
using thick lines, and the projection and dimension lines are drawn using
thin lines, the outline of the object becomes the visible feature and the
drawing is more readily interpreted. Therefore, the Australian Standard
Association defines variation in the thickness of each type of line. Some
of these Standards are shown in figure 4.9.
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Line style
Example
Continuous – thick
Common application
All visible outlines
General details
Existing buildings
Landscaping in site plans
Continuous – thin
Dimension lines
Projection lines
Intersection lines and
leaders
Hatching
Fold lines
Continuous – thin, freehand
Break lines
Dash – thin
Hidden outlines
Chain – thin
Centre lines and axes of
solids
Path lines
Chain – thick at ends & at
change of direction
Cutting planes
Figure 4.9 Line standards
Note: all lines are drawn dark. To achieve lines of varying thickness
it is a good idea to use a 0.5 mm and a 0.3 mm pencil.
Orthogonal projection
Orthogonal projection is a method of drawing the exact shape of an object
when viewed from a given direction. It generally converts a threedimensional pictorial drawing (3D) into a series of two-dimensional (2D)
views.
Each ‘face’, that is the side of the object, is considered in turn and drawn
in a position relative to the other views. When drawing an orthogonal
projection, the object is normally projected vertically or horizontally onto
planes of projection.
Part 4: Communication landscape products
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When a vertical and horizontal plane intersect, four 90∞ angles, or
quadrants, are formed. In each quadrant the object can be viewed and
projected onto the planes horizontally or vertically.
Vertical
plane (VP)
Horizontalal
plane (HP)
2nd angle
X
1st angle
3rd angle
4th angle
Figure 4.10 Four quadrants about VP and HP
As the horizontal plane is rotated to form a flat surface, the second and
fourth quadrants are closed, hence the object is drawn in the first or third
quadrant.
1st
3rd
Figure 4.11 Rotation of a plane
Third angle projection
Australia has standardised drawing practice and third angle projection is
now the accepted method of projection.
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B
3rd
C
A
Figure 4.12 Projection of views onto planes
Views are named from the direction in which they are viewed – front
view, top view, left side view, right side view and bottom view.
Top
B view
F
Rear
view
D
C
Left side view
Right side
view
E Bottom
view
A
Front
view
Figure 4.13 Direction of views
Only those views that are actually required to describe the object are
drawn, for example; front, top and side view, depending from which side
the object was viewed.
Part 4: Communication landscape products
11
B
D
C
A
Figure 4.14 Rotation of views onto one plane
L
B
W
C
D
L
D
D
W
A
D
Figure 4.15 Relative views of solid
Method of construction
The following construction procedure is suggested when drawing an
orthogonal drawing from a pictorial drawing.
1
The pictorial drawing should have an arrow pointing to it. This
indicates where the front view is viewed as shown in figure 4.16.
Front
Figure 4.16 Pictorial drawing showing arrow for front view
2
12
The front view is drawn to length as well the height
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3
The top view is always positioned directly above the front view.
The length of the top view is projected from the front view. The top
view will also show the width of the object.
4
A space should be left between the two views, normally a minimum
of 20 mm would be used.
5
On either side of the front view, a side view would be shown. The
side view is placed on the same horizontal base line as used for the
front view. The height is projected from the front view. The righthand side view is placed to the right side of the front view, the lefthand view on the left. The side view will also show the width of the
object. This is normally projected from the top view via a 45∞ line
drawn from the top of the front view.
The sequence of drawing
To achieve the best results, linework is usually drawn to a set procedure:
1
borderlines and title block
2
centre lines
3
circles, arcs and other curved lines
4
horizontal lines
5
vertical lines
6
inclined lines
7
hidden detail lines
8
cross-hatching – evenly spaced
9
dimension lines and
10 dimensional arrowheads and lettering.
Completion of a drawing
The process of completing a drawing involves firming in. To firm in use a
sharp pencil and:
1
firm in all horizontal lines from top to bottom
2
firm in all vertical lines, right to left
3
firm in all angled lines
4
firm in hidden outlines.
Part 4: Communication landscape products
13
TOP VIEW
FRONT VIEW
RIGHT SIDE VIEW
Figure 4.17 Top, front and side views showing height, length and width
Title blocks and materials lists
All drawing sheets must have a borderline, a title block and, where
necessary, a materials list.
Before starting a drawing exercise, prepare the sheet by drawing a set of
lines with the T-square and set square to form a rectangle, 10 mm in from
the edge of the sheet.
All work must be completed inside this rectangle.
Fasten your sheet to a drawing board.
Title blocks
Title blocks are situated in the bottom right hand comer of the borderline
rectangle. They contain the necessary details of the drawing sheet.
Drawing
No
TITLE
NAME
SCALE
Figure 4.18 standard tile block
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Materials list
A material list provides information about the various components, which
make up a machine part assembly on an orthogonal drawing. Materials
lists are drawn above the title block.
75
15
20
Part
Description
Material
Part No
6
15
Drawing
No
TITLE
NAME
SCALE
Figure 4.19 Standard title block with a materials list included
The various components of parts would be numbered and these numbers
are used to identify each component in the materials list.
Dimensioning technical drawings
The purpose of dimensioning is to indicate to the person reading a
drawing the precise size details of the object represented.
To ensure that drawing details can be universally understood, standards
for dimensioning must be followed. The standards indicated in the
following information are consistent with AS 1100.
General
Each dimension necessary for the complete definition of an object shall
appear once only. There shall be no more dimensions other than are
necessary to define the component.
Dimension details
Each dimension shall consist of a dimension line, or arrow line, which is a
thin line drawn parallel to the measurement direction placed whenever
possible outside the outline of the view. At the ends of the dimension
lines arrow heads are placed touching the projection lines or view outline
Part 4: Communication landscape products
15
as necessary. Arrow heads should be in proportion to the size of the
drawing and be 3 times long as they are wide.
1
3
Figure 4.20 Dimension of an arrow head
Projection lines
Where necessary projection lines are thin full lines projected from points,
lines or surfaces starting l mm clear of the outline and extending 2 mm
past the dimension line. Numerous projection lines can be seen in
figure 4.21.
Size indications
Size indication should be in millimetres (mm) and placed next to the
dimension line.
It is recommended that sizes should be kept upright or so they can be
read from the right side of the page as shown in figure 4.21.
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6
1.5 mm chamfers
25
ø 30
ø 30
20
Drill ø 5
M 30x1.5
30
ø 30
20
40
ø 30
Figure 4.21 Dimensioning examples
Computer aided drawing
One of the most significant changes in the way technical drawings are
made has been the introduction of computer assisted drawing (CAD).
CAD is replacing the traditional drawing boards used in technical drawing.
Technical areas such as engineering, architecture, surveying and boat
building have increased their use of CAD with the advent of powerful
computers into the work place.
Drawing programs are many and varied and their complexity means that
specialist companies have been set up to produce drawings for different
clients. A CAD program could be considered to be a sophisticated
Part 4: Communication landscape products
17
graphical word processing program. It can produce a range of drawings
from simple to the most complex.
The CAD package can produce 2D orthographic drawings. From these,
3D pictorial drawing can be produced and modelled, either as a wire frame
linework model, or with colour shading.
An orthogonal drawing, when expanded to a wire-framed graphics are
often coloured, and then animated, and photographic images allows nontechnical people to either walk through or walk-around the article viewing
it from many different angles. This then allows them to have some input
into the design stage of a product.
The advantage with CAD is the convenience of storing drawings, instant
retrieval of drawings, and the ability to edit both technical and nontechnical information on the drawings. Alternative solutions can be
trialled and viewed, and any necessary corrections can be easily changed.
While CAD normally infers technical drawings, many advertisements are
now computer generated by industrial graphic designers.
CAD packages have included in their program, libraries of many
frequently used items. When drawing house plans, items such as tables,
chairs, sinks, toilets, doors, windows and landscaping options, are stored
in an electronic data bank, retrieved and placed on the drawing as required.
To be useful, CAD must assist the drawer. To enable this to happen,
some very powerful features are built into the program. These include:
•
vector graphics – lines can be stored in memory, and moved around
as a line
•
precision – points can be located accurately either by nominated
coordinates or snapped to a grid
•
layering – particular useful in drawing house plans. One layer
contains only certain information. This is then laid on top of the
basic floor plan. Layers can include such things as the electrical
wiring layout, plumbing requirements etc.
•
erasing – ability to remove part or all of a line
•
filleting – arcs of a given radius can be put into position easily
•
hatching – areas that have been sectioned may be hatched with
selected patterns.
As the information is stored electronically, CAD drawings can be used to
download information to other machines. This is increasing in use, with CAD
enabled software being used to control CNC cutting and shaping machines.
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Practice your CAD skills in order to produce a quality drawing for
your engineering report.
Turn to the exercise sheet and complete exercises 4.1 to 4.4.
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20
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Exercises
Exercise 4.1
a
Take a full set of measurements of a lawnmower wheel.
b
Make a detailed freehand pictorial sketch of the lawnmower wheel.
You may use isometric or oblique styles.
Part 4: Communication landscape products
21
c
22
Draw a freehand orthogonal of the front view and the top view of the
wheel. Draw the wheel to a suitable scale.
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Exercise 4.2
Dimension the orthogonal below by adding ten (10) main dimensions.
Use at least four (4) techniques to indicate technical detail on the drawing.
All sizes can be taken directly form the drawing, which is drawn to a scale
of 2:1.
ORTHOGONAL
PICTORIAL
Figure 4.22 Post holder
Part 4: Communication landscape products
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Exercise 4.3
a
Indicate what the letters CAD stand for.
_______________________________________________________
b
Outline the advantages of storing items in an electronic library.
_______________________________________________________
_______________________________________________________
_______________________________________________________
c
Generate a computer aided drawing using the features of the software
available to you. You do not need CAD software to do this exercise.
Many word processors have a draw facility.
Attach your example to this sheet.
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Exercise 4.4
Freehand sketch the component shown in figure 4.23 as a top and front
view orthogonal drawing. Use full Australian Standards AS 1100. Sizes
not indicated can be estimated from the pictorial if required.
50
3
30
10
50
20
10
75
2 HOLES Ø 8
22
R
F
15
25
Ø 20
O
N
T
Figure 4.23 A bracket
Part 4: Communication landscape products
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26
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Progress check
In this part you examined the function of simple machines, and learnt to
produce orthogonal drawings by applying Australian Standard (AS1100).
✓
❏
Disagree – revise your work
✓
❏
Uncertain – contact your teacher
Uncertain
Agree – well done
Disagree
✓
❏
Agree
Take a few moments to reflect on your learning then tick the box which
best represents your level of achievement.
I have learnt about
•
simple machines
•
•
•
•
•
– inclined plane, lever, screws, wheel and axle, pully
gears
orthogonal drawings
Australian Standards AS 1100
dimensioning
materials lists
introduction to computer assisted drawing (CAD).
I have learnt to
•
examine and analyse the function of simple
•
produce orthogonal assembly drawings applying
appropriate Australian Standard (AS 1100)
Extract from Stage 6 Engineering Studies Syllabus, © Board of Studies, NSW, 1999.
Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.
In the next part you will examine an engineering report on the lawn
mower and produce an engineering report on a landscape product of your
choice.
Part 4: Communication landscape products
27
28
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Exercise cover sheet
Exercises 4.1 to 4.4
Name: _______________________________
Check!
Have you have completed the following exercises?
❐ Exercise 4.1
❐ Exercise 4.2
❐ Exercise 4.3
❐ Exercise 4.4
If you study Stage 6 Engineering Studies through a Distance Education
Centre/School (DEC) you will need to return the exercise pages with your
responses.
Return the exercise pages with the Title Page cover attached. Do not
return all the notes, they should be filed for future reference.
If you study Stage 6 Engineering Studies through the OTEN Open
Learning Program (OLP) refer to the Learner’s Guide to determine which
exercises you need to return to your teacher along with the Mark Record
Slip.
Part 4: Communication landscape products
29
Landscape products
Part 5: Landscape products –
engineering report
Part 5 contents
Introduction ........................................................................................... 2
What you will learn?.................................................................... 2
Engineering report............................................................................... 3
Aim of an engineering report...................................................... 3
Structure of an engineering report.............................................. 4
Developing an engineering report .............................................. 6
Sample Engineering Report....................................................... 9
Exercise.............................................................................................. 23
Progress check................................................................................... 25
Exercise cover sheet ........................................................................ 27
Bibliography ...................................................................................... 29
Module evaluation............................................................................. 31
Part 6: Lifting devices – engineering report
1
Introduction
In this part you will examine the components of an engineering report,
and produce and engineering report on a landscape product of your
choice.
It is advisable to select a piece of equipment that you have access to.
This will allow you to inspect the landscape product and make
observations, take measurements and draw conclusions resulting in a
well-informed report.
What will you learn?
You will learn about:
•
engineering report writing
•
communication
–
research methods including the Internet, CD-ROM…
–
collaborative work practices.
You will learn to:
•
complete an engineering report based on the analysis of one or more
landscape products, incorporating the use of computer software
•
conduct research using computer technologies and other resources
•
work with others and appreciate the value of collaborative working.
Extract from Stage 6 Engineering Studies Syllabus, © Board of Studies, NSW, 1999.
Refer to <http//ww.boardofstudies.nsw.edu.au> for original and current documents.
2
Lifting devices
Engineering report
An engineering report is a formal, considered document which draws
together information gained about a product or filed, through research and
analysis, to arrive at a conclusion or present recommendations based on
investigation.
Engineers do not communicate with words alone. In an engineering
report, technical information is presented using a combination of text,
tables, graphs and diagrams.
An engineering report for an application module involves:
•
outlining the area under investigation
•
collecting and analysing available data
•
drawing conclusions and/or proposing recommendations
•
acknowledging contributions form individuals or groups
•
recording sources of information
•
including any relevant additional support material.
An engineering report for a focus module involves covering additional
aspects such as:
•
examining the nature of the work done by the profession
•
discussing issues related to the field.
Aims of an engineering report
A well structured engineering report aims to:
•
demonstrate effective management, research, analysis and
communication skills related to the content
•
include data relevant to the area under investigation
Part 6: Lifting devices – engineering report
3
•
present information clearly and concisely so that it is easily
understood by the reader through the use of tables, graphs and
diagrams to illustrate mathematical and scientific facts
•
justify the purpose using observations, calculations, or other
evidence, to support a conclusion or recommendations.
•
document contributions and sources of information.
Structure of an engineering report
An engineering report generally includes the following sections:
•
title page
•
abstract
•
introduction
•
analysis
•
result summary
•
conclusions/recommendations
•
acknowledgments
•
bibliography
•
appendices.
Title page
The title page gives the title of the engineering report, identifies the
author and gives the date when the report was completed.
Abstract
The abstract is a concise statement that describes the content of the
engineering report. It covers the scope of the report (what it is about)
and the approaches used to complete the analysis (how the information
was assembled).
The purpose of the abstract is to allow a reader to decide if the
engineering report contains relevant information.
The abstract should be no more than two or three paragraphs – shorter if
possible.
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Lifting devices
Introduction
The introduction provides an overview of the subject, purpose and scope of
the engineering report. It may contain background information regarding the
topic.
It also outlines the sections of the engineering report including why the
investigation was undertaken, what research occurred, how data was collected
and what anaylsis was conducted.
Analysis
The analysis is the body of the engineering report and should show evidence of
research and experimentation. Information about materials and the mechanics
of products should be collected or calculated for all engineering reports. This
section must contain information required to satisfy the aim and purpose of the
report.
Tables and graphs, used to summarise detailed data in a concise form, are
common features of an engineering report.
Result summary
The result summary should present the results concisely and note any
limitations on the investigation.
The results inform and support the conclusions and recommendations.
Conclusions/recommendations
The conclusions/recommendations summarises major points or issues in earlier
sections of the engineering report.
This section requires the author to draw conclusions or make recommendations
based on data collected. If the purpose of the engineering report was to ‘select
the best…..’, then the selection should be stated and the reason for the choice
explained.
Acknowledgments
The acknowledgment section provides the opportunity to credit other people’s
work that has contributed to the engineering report.
Bibliography
The bibliography demonstrates that the report is well researched – all
references need to be included. Bibliographic entries should follow established
guidelines.
Part 6: Lifting devices – engineering report
5
A standard approach for referencing bibliographic entries includes identifying
the name of the author, the year of publication, the title of the work, the name
of the publisher and the place of publication.
For example:
Harford , D. 1982, Old Lawnmowers, Shire Publications Ltd,
Aylesbury Bucks.
This information allows the reader to source the information for confirmation
of the details or conduct further research.
Appendices
The appendices should contain detail that has been separated from the main
body of the engineering report. The information in this section is not essential
but enhances the other data. Examples could be engineering drawings of
products being compared, where the overall dimensions of the product may not
have been part of the report, but may be relevant to some readers.
During the engineering course this section may contain a technical drawing and
could include information collected from organisations.
Developing an engineering report
Research and collaboration are the keys to developing an accurate and
informative engineering report.
Research methods
Sources of information are extensive. Valuable sources of information
include individual input such as user groups and field experts, and
electronic media, such as the Internet and Compact Disc Read-Only
Memory.
Individual input
‘Brainstorming’ is a popular practice to facilitate contributions from
individuals. This technique stimulates the flow of ideas. It is democratic
and builds trust, confidence and creative thinking. The topic is clearly
stated, people are invited to give their responses and ideas are listed
quickly and without discussion.
The rules of ‘brainstorming’ are:
•
6
all participants are free to offer ideas
Lifting devices
•
all ideas accepted and recorded
•
judgments on ideas are suspended
•
developing ideas is encouraged.
It is a simple and effective method that can produce creative solutions to
a problem.
Ideas may be discussed, compared and ranked once the session has
concluded.
Electronic media
A Compact Disc Read-Only Memory (CD-ROM) is an valuable source
for researching information.
The media is a flat, round polymer disc with a reflective metal coating
that stores data such as text, images and sound. Most encyclopedias, as
well as specialised information, are now available on CD-ROM.
A disc can hold about 250 000 pages of information text. Most personal
computers now come equipped with a player, similar to a disc drive.
Information is read from the disc as it spins. A laser aims a concentrated
beam of light at the disc. The laser beam follows the track of pits, the
light reflects off the pits, and a light sensitive device turns it into electric
signals. These signals correspond to a digital code.
Compact discs have a long life because lasers do not wear out or scratch
the CD, so they have advantages over either vinyl records or magnetic
tapes.
Another means of locating information is the use of the Internet – a
network of computers linked right around the world to create the World
Wide Web (WWW).
An Internet service provider (ISP) allows you access to the ‘net’.
Browser software allows you to view resources on the ‘net’.
From your personal computer, provided it has a modem, and is connected
to ‘net’, you can access all sorts of information including:
•
databases on virtually any subject
•
information on organisations, companies and institutions
•
library catalogues
•
text books, magazines, journals and newspapers.
Accessing Internet resources can sometimes be slow because of the
number of people using the system and communication lines.
Part 6: Lifting devices – engineering report
7
The Internet also allows the use of e-mail (electronic mail). This is a
quick way of communicating and requesting information electronically.
Information can also be downloaded to your own computer.
To find information on a particular topic you can use a search engine.
There are many search engines available on the Internet for example
‘Yahoo’, ‘Alta Vista’, ‘Lycos’, ‘vivisimo’ and ‘Ask Geeves’. When
searching, click in the search box and type key words that describe what
you want to find out. Use English words or phrases without special
symbols or punctuation. The engine then searches the net and identifies
the addresses of sites that have information on your request.
You can refine your searches by using special techniques in your request.
•
Capitalise names and titles, such as February.
•
Use double quotation marks or hyphens to group words that are part
of a phrase.
•
Use brackets to find words that appear within 100 words of each
other.
•
Place a plus sign (+) in front of words that must be in the documents
found by the search. Do not put a space between the + and the
word.
•
Put a minus sign (-) in front of words that should not appear in the
documents found by the search. Do not put a space between the and the word.
Collaborative work practices
Few, if any, engineering developments are the work of one person.
Collaborative work practices rely on participation of individuals in a team
and can be highly productive.
Because engineers are managers, they need to develop effective
management styles in order to be successful in their role.
One particular style is the collegial management style and its
characteristics include:
•
trust and confidence in colleagues in all manners
•
getting ideas and opinions from colleagues and constructively using
them
•
encouraging decision-making throughout the organisation.
Engineering firms encourage worker input into efficiency and
productivity issues. Encouragement awards are offered, and by having
8
Lifting devices
input into the running of an engineering practice, worker’s morale and
levels of motivation are also increased. In addition, some excellent cost
cutting or improved production methods can be established.
Sample engineering report
The following section contains a sample engineering report on a landscape
product – the lawnmower.
The sample engineering report provides a general overview of the
landscape product then focuses on a components – the handle.
You can use the sample engineering report as a guide when presenting
your work.
Part 6: Lifting devices – engineering report
9
Landscape products
Title:
Engineering of domestic lawnmowers
Author/s:
L. Mower
Date:
January 2000
Abstract
This engineering report will examine the engineering of the
domestic lawnmower with a focus on the handle. It will look at the
materials used, examine working forces systems and consider
certain safety aspects and make recommendations for further
development.
Introduction
This Engineering Report will investigate lawnmower handles. The
report aims to:
• identify and distinguish various materials
• investigate and analyse mechanical situations involving the use
of a lawnmower
• communicate technical information and data relating to the
handle design
• evaluate and make recommendations based on the information
collected.
Analysis
Development of the lawnmower
In less than 200 years machinery for maintaining domestic lawns
has evolved from hand tools, such as the scythe, to electronically
controlled devices like the solar powered mower.
A time line, shown in figure 5.1, illustrates many of the
significant developments in the domestic lawn mower.
C1830s
Push blade mower, first
patented by Edwin
Buddings
C1840s
Pony driven lawnmower
C1850s
Chain driven lawnmower
C1860s
Sidewheel mower – the
cutting movement for he
blades was supplied by
the wheels rather than a
roller at the back of the
lawnmower
C1890s
Steam driven mower
C1900s
Four stroke petrol engine
lawnmower, first
manufacture by Ransome
C1930s
Two stroke petrol engine
lawnmower
C1950s
First Victa lawnmower
C2000s
Solar powered lawnmower
Figure 5.1 Time line for the development of lawnmowers
Materials investigation
The materials used for the handles in lawnmowers have changed
significantly over the years.
Date
Machine type
Handle
material
Material
characteristics
1830
Budding
cast iron
this is a dense
material, heavy and
brittle
1860
sidewheel
usually wooden
shaft
lighter than cast iron
but reduced
strength
1900
Ransome
cast iron
cast iron – need for
greater strength due
to the mass of the
machine
2000
modern two or fourstroke lawnmower
extruded steel
tubing
light weight with high
strength/weight ratio
The Buddings and Ransome machines were large and heavy
devices that were not really designed for domestic situations.
They were designed for commercial settings. This meant that
they had to be particularly robust and capable of being used on a
daily basis for extended hours. The handle design reflected this
and was robust. The only readily available material that satisfied
this criterion was cast iron.
The sidewheel lawnmowers were lighter and more suited to a
domestic environment.
Their handles were often timber,
however because of their construction were susceptible t o
breaking. They could readily be replaced it they broke.
Figure 5.2
The wooden shaft and handle added to the lightness of the
lawnmower and could be easily replaced if they were broken
or damaged
Courtesy: Mowers Ark Taren Point.
© LMP
There are a number of sidewheel mowers available today where
the timber handles have been replaced with aluminium tubing.
This tubing while being lightweight is easily damaged and difficult
to replace or repair. Such an example can be seen in figure 5.3.
Figure 5.3
Metal tubing replaced the wooden handle used in previous
models
Courtesy: Mowers Ark Taren Point.
© LMP
Most current rotary lawnmower use steel tubing for the handle.
This material is strong and can be easily formed into a variety of
complex shapes.
Alternative materials that could be used include reinforced
fiberglass and carbon fibre. These materials are have good
strength to weight ratios and can be moulded into complex shapes
but could be expensive to mass-produce.
The handle needs to be strong enough to allow the operator t o
control and maneuver the machine in normal lawn mowing
applications. This requires the handle to have certain ergonomic
adjustments and allow the operator to control the engine should
one be fitted.
In powered lawnmowers it is important that the operator be able
to control the speed of the engine and stop the engine easily.
This was recognised on the earliest of the Victa models, as shown
in figure 5.4, with the throttle control being placed on the handle
within easy reach of the operator.
Figure 5.4
An early production rotary lawnmower
Courtesy: Mowers Ark Taren Point.
© LMP
This practice has continued in modern lawnmowers and the
handle can be used to support the air filter housing. If the air
intake was on the side of the motor it would be breathing
significant amounts of dust and lawn clippings. To counter this
the addition of an air filter was required but if it was placed too
close to the ground it would regularly be clogged up with the
filtered dust and lawn clippings. It should be placed as far as
possible from the cutting surface. This position is on the handle.
The filter is placed in a filter box and connected to the intake of
the carburetor through a flexible hose as shown in figure 5.5.
Figure 5.5 The filter box and the throttle lever
Courtesy: Mowers Ark Taren Point.
© LMP
It is interesting to note that the throttle lever and the filter box
can often be incorporated together in the one unit.
Ergonomic issues
The handle is used to both push the mower forward and can be
used as a lever to lift the wheels (either front or back) off the
ground so as to move it over a step.
The height of the handle should be such that the lawnmower is
easily to manoeuvre.
OHS convention recognises that an
appropriate height for the handle is about elbow height. T o
confirm this, a simple experiment was conducted.
Procedure:
In this experiment the handle of the lawnmower was placed at
three angles and the user asked to push the lawnmower forward, as
shown in figure 5.6.
1
2
Handle length 1190 mm
3
Not to scale
50∞
400
40∞
600
Figure 5.6
Testing of handle positions
A number of users were surveyed as to the most appropriate
position for them. The users were then asked to rank the
positions as:
a acceptable
b good
c uncomfortable.
Results:
The responses were summarised in the following table.
Lawnmower handle position number
1
2
3
Person 1
a
b
c
Person 2
c
b
c
Person 3
c
b
a
This confirms that the height of the handle should be about elbow
height.
It was also noted that when the mower was pushed with the
handle at position 1 the rear wheels tended to lift when a
significant force was applied.
The lawnmower may need to be lifted up steps or over obstacles.
By applying only a downward force, with the handle in position
1, it was impossible to lift the front wheels off the ground. In
position 2 and 3 the front wheel could be lifted, with position 3
being the best.
This can be mathematically determined by calculating the force
required to just lift the front wheel off the ground. To do this, it
is necessary to take the sum of the moments at the rear wheel
(assume the mass of the lawnmower to be 20 kg).
With the handle in position 1 it is not possible to generate a
moment about the rear wheels to lift the front wheels, as the
force passes through the rear wheel, the moment so created is
zero. This is shown in figure 5.7.
Force
Not to scale
mg
F
mg
Figure 5.7 Force analysis with the handle in the vertical position
With the handle at position 2, as shown in figure 5.8, the
following conditions apply:
F
Not to scale
50∞
mg
F
mg
750
300
Figure 5.8 Force analysis with the handle at 50o
SM
=
0
=
F x 750 – 200 x 300
=
750F – 60 000
750F
=
60 000
F
=
80 N
With the handle at position 3, as shown in figure 5.9, the
following conditions apply:
F
Not to scale
mg
40∞
F
mg
910
300
Figure 5.9 Force analysis with the handle at 40o
SM
=
0
=
F x 910 – 200 x 300
=
910F – 60 000
910F
=
60 000
F
=
66 N
The longer the handle lever the easier it is to lift the front and
rear wheels off the ground.
The length of the handle also becomes an issue when storing and
transporting the lawnmower. If the handle remains in a fixed
position then the storage area would be greater than if the handle
was detached or folded down. Without a detachable handle or a
fold down handle it would be nearly impossible to fit the
lawnmower into an average motor vehicle for transporting from
one site to another.
With the fitting of the filter box and the throttle on the handle it
is better to fold the handle rather that have it detachable, as the
air intake and the throttle levers would have to be detached too.
For the most efficient storage, the handle in the folded position
should not significantly extend beyond the base of the
lawnmower.
Figure 5.10 Lawnmower with the handle lowered
Safety issues
Lawnmowers are dangerous machines. Hundreds of people are
injured each year. Danger areas are:
1 Feet – protective footwear must be worn at all times
2 Eyes – protective eyewear must be worn at all times
3 Noise – professional lawnmowers must wear ear muffs or plugs
4 Fire – petrol can and does explode and catch fire; care should
always be taken, and hot mowers should never be refilled with
petrol.
Environmental issues
There are a number of environmental issues that could to be
considered. These include:
•
the steel components need to be protected from corrosion;
this can be achieved by painting or by applying a protective
coating, it is not necessary for aluminium components as they
are resistant to corrosion
•
both the steel and aluminium components can be recycled
•
polymers are formed from chemicals and most do not
naturally breakdown in normal environmental conditions and
are difficult to recycle
•
noise and air pollution, from engine fumes need to be
controlled.
Results summary
The lawn mower contains a wide variety of materials ranging from
steel alloys, aluminium castings and numerous polymers. There has
been an attempt to integrate materials that are strong enough t o
perform the tasks but increase the lightness of the overall product.
The results from the mechanical analysis indicated that the handle
is most efficient in lifting the wheels when the handle is lowest t o
the ground, however this position has considerable implications for
the maneuverability of the lawnmower. The best compromise
appears to be with the handle positioned at an angle of 50 o to the
ground.
For storage purposes it is desirable that the handle is capable of
being folded down. Thereby minimizing storage space but retaining
the control linkages in place so that they do not have to be
reattached, as would be the case if the handle was completely
removed.
Conclusions/recommendations
A release mechanism to lower the handle is a desirable feature. I t
allows less storage space for the mower, and could also have the
advantage of folding when mowing in difficult zones such as under
shrubs.
To cater for the different heights of people it is recommended that
the height of the handle be adjustable.
The mower was found to be most maneuverable when the handle
was at 50° to the ground. In this positioned the hands are at an
optimum height for maneuvering.
A recycling program for old lawn mowers and their parts should be
implemented. Oils should also be recycled.
Acknowledgements
The author wishes to acknowledge the contribution of those people
who assisted in the testing of the lawnmower handles.
Bibliography
Intellectual property Australia <http://www.ipaustralia.gov.au/
patents/ex_victa.shtml> (accessed 13.08.03)
Victa <www.victa.com.au> (accessed 13.08.03)
How Stuff Works: <http://howstuffworks.com/index.htm>
(accessed 13.08.03)
Massachusettes Institute of Technology, Department of Materials
Science & Engineering: <http://www-dmse.mit.edu> (accessed
13.08.03)
Board of Studies: <http://www.boardofstudies.nsw.edu.au> (accessed
13.08.03)
Appendices
Technical drawings
Polymer cam handle
TOP VIEW
Figure 5.11 Top view
FRONT VIEW
Figure 5.12 Front view
polymer handle
plated steel lever
metal clip
air pipe
plated steel washer and bolt
Figure 5.13 Throttle lever
locking bolt
plated steel bracket
cam shaped lever
Figure 5.14 Handle locking mechanism
Exercises
Exercise 5.1
Develop an engineering report which:
•
outlines the history of one landscape product, other than the
lawnmower
•
identifies the materials used in the landscape product and describe the
properties of each and evaluate the use of the materials
•
describes the ergonomic, safety and environmental issues associated
with the landscape product
•
summarises the results of the analysis
•
presents conclusions/recommendations
•
includes an orthogonal sketch of the product and or its components.
Use computer software such as a word processing program or
graphics package to aide in the generation of your engineering
report.
Part 5: Landscape products – engineering report
23
24
Landscape products
Progress check
In this part you examined and engineering report and used investigative
techniques to research and develop your own engineering report.
✓
❏
Disagree – revise your work
✓
❏
Uncertain – contact your teacher
Uncertain
Agree – well done
Disagree
✓
❏
Agree
Take a few moments to reflect on your learning then tick the box which
best represents your level of achievement.
I have learnt about
•
engineering report writing
•
communication
–
research methods including the Internet, CDROM and libraries
–
collaborative work practices.
I have learnt to
•
complete an engineering report based on the analysis
of one or more household appliances, integrating the
use of computer software
•
conduct research using computer technologies and
other resources
•
work with others and appreciate the value of
collaborative working.
Extract from Stage 6 Design and Technology Syllabus, © Board of Studies, NSW, 1999.
Refer to <http://www.boardofstudies.nsw.edu.au> for original and current documents.
Congratulations! You have completed, Landscape products.
Part 5: Landscape products – engineering report
25
26
Landscape products
Exercise cover sheet
Exercises 5.1
Name: ______________________
Check!
Have you have all sections of the report?
❐ Exercise 5.1
•
title page
•
abstract
•
introduction
•
analysis
•
result summary
•
conclusions/recommendations
•
acknowledgments
•
bibliography
•
appendices.
If you study Stage 6 Engineering Studies through a Distance Education
Centre/School (DEC) you will need to return the exercise pages with your
responses.
Return the exercise pages with the Title Page cover attached. Do not
return all the notes, they should be filed for future reference.
If you study Stage 6 Engineering Studies through the OTEN Open
Learning Program (OLP) refer to the Learner’s Guide to determine which
exercises you need to return to your teacher along with the Mark Record
Slip.
Please complete and return the module evaluation that follows.
Part 5: Landscape products – engineering report
27
28
Landscape products
Bibliography
Board of Studies, 1999, The New Higher School Certificate Assessment
Support Document, Board of Studies NSW, Sydney.
Board of Studies. 1999, Stage 6 Engineering Studies Examination, Assessment
and Reporting, Board of Studies NSW, Sydney.
Board of Studies. 1999, Stage 6 Engineering Studies Support Document, Board
of Studies NSW, Sydney.
Board of Studies. 1999, Stage 6 Engineering Studies Syllabus,
Board of Studies NSW, Sydney.
Bolton, W, 1998, Engineering Science, Newnes,
Oxford.
Bolton, W. 1998, Engineering Materials Technology, Butterworth Heinemann,
Oxford.
DeGarmo. E. P, 1979, Materials and Processes in Manufacturing,
Macmillan, New York.
H R Products <http://www.hrproducts.com.au/hr_products.html>
Harford, D. 1982, Old Lawnmowers, Shire Publications Ltd,
Aylesbury Bucks.
Hartmann, R. 1986, Lawnmower, Mosman High School, NSW Department of
Education, Sydney.
Higgins, R. A. 1977, Properties of Engineering Materials, Hodder & Stoughton,
London.
Hull, D. 1996, An Introduction to Composite Materials, Cambridge University
Press, Cambridge.
Institute of Engineers, Australia, 1999, Engineers make it happen CD-ROM,
Western Australia.
Institute of Engineers, Australia, Elegant Solution, Marcom 2000 Videos (13
Episodes) Code SBESO.
Ivanoff, V. 1984, Mechanical Engineering Science, McGraw Hill,
Roseville, NSW.
Johnston. S, Gostelow. P, and Jones. E, 1999, Engineering and Society an
Australian Perspective, Longman, South Melbourne.
29
Massachusettes Institute of Technology, Department of Materials Science &
Engineering <http://www-dmse.mit.edu>
Mullins, R. K. 1974, Engineering Mechanics, Shakespear Head Press,
Sydney.
Mullins, R. K and Cooper, D. A. 1980, Programmed Technical Drawing, Book 2,
Longman Cheshire, Melbourne.
Mullins, R.K and Cooper, D.A. 1982, Programmed Technical Drawing, Book 3,
Longman Cheshire, Melbourne.
Recycling, V C Media Pty Ltd, 1990, VHS, (12 minutes)
Rochford, J. 1989, Engineering Science Drawing and Solutions – A Student’s
Workbook, KJS Publications, Terrigal, NSW.
Rochford, J. 2000, Engineering Studies – A Student’s Workbook, KJS
Publications, Gosford, NSW.
Schlenker, B. R, 1974, Introduction to Materials Science, John Wiley & Sons,
Sydney.
Schlenker, B. R, McKern, D. 1979 Introduction to Engineering Mechanics,
Jacaranda Press, Milton, Queensland.
Standards Association of Australia, 1986, Mechanical Drawing for Trade and Tertiary
Students, Standards Association of Australia, North Sydney.
Standards Association of Australia, 1994, Technical Drawing for Students, HBI,
Standards Association of Australia and Standards New Zealand, North
Sydney.
Standards Association of Australia, 985, Design Standards for Mechanical
Engineering Students, Standards Association of Australia, North Sydney.
Taylor, A.O. and Barry, O.J. 1975, Fundamentals of Engineering Mechanics,
Cheshire, Melbourne.
Van Vlack, L. 1966, Elements of Materials Science, Addison-Wesley, Reading,
Massachusettes.
30
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Learning Materials Production
Training and Education Network – Distance Education
NSW Department of Education and Training