Composite
Materials
Course content
Navigation material world
Content
• Introduction
• Raw materials
• Material Selection Guide
• Composite Manufacturing Techniques
• Mechanical Behaviour of Composites and test methods
• Micromechanical models of composite behaviour
• Failure analysis and mechanism
• The long term behaviour of composite materials
• Emerging Composites (nanocomposites,biocomposites,
Introduction
• Conventional engineering materials
• What are the composites?
• Classification of composites materials
• Functions of fibres and matrices
• Special features of composites
• Composite processing
• Composite Markets
• Bariers in composite markets
• Questions
Conventional engineering materials
• Metals
• Plastics
• Ceramics
• Composites
Engineering Materials
Metals: conductors of electricity and heat, quite strong but yet deformable (ductile)
Ceramics: compounds between metallic and non-metallic elements, insulators (electricity and heat),
temperature resistant, hard but very brittle
Polymers: compounds of non-metallic elements, large molecule structures, low density, extremely
flexible (very ductile)
Composites: consist of more than one type of material. Composite materials aim to combine the best
characteristics of each of the component materials. Composites are a combination of properties
Semiconductors: Materials with unique electrical properties
Bio-Materials: could also be described as polymers or composites
The evolution of engineering materials
Basic Material Properties
Mechanical Properties
• There a 6 properties typically used to describe a
• materials behavior and capabilities:
• 1. Elasticity
• 2. Strength
• 3. Hardness
• 4. Ductility
• 5. Brittleness
• 6. Toughness
Strength and Elasticity
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Strength means:
- The ability to resist deformation and maintain shape
- Given in terms of the yield strength, σy, or the ultimate tensile
strength, σult
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The ELASTIC Range means:
- The strain, or elongation over a unit length, will behave linearly (as in
y=mx +b) and thus predictable
- The material will return to its original shape once an applied load is
removed
- The stress within the material is less than what is required to create a
plastic behavior (deform or stretch significantly without increasing stress)
Hardness
Hardness means:
The ability to resist indentation, correlated to abrasion and wear
For metals, this is determined with the Rockwell Hardness or Brinell tests that measure indentation/
penetration under a load
STRENGTH and HARDNESS are related!
A high-strength material is typically resistant to
wear and abrasion...tration under a load
Ductility and Brittleness
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Ductility means:
- The ability to deform before ultimate failure
- Ductile materials can be pulled or drawn into pipes, wire, and other
structural shapes
Ductility and Brittleness
Brittleness means:
- The inability to deform before ultimate failure
- The opposite of ductility, brittle materials deform little before
ultimately fracturing
- Brittle materials include glass and cast iron
- Brittleness is the LACK of ductility...
Toughness and Fatigue
• Toughness means:
- The ability to absorb energy
- Material Toughness (slow absorption)
- Not a readily observable property
- Defined by the area under the stress-strain curve
- Impact Toughness (rapid absorption)
- Ability to absorb energy of an impact without fracturing
- Toughness and Ductility/brittleness are related!
- Brittle things are not tough!
Fatigue means:
-The reduction of strength due to the repetitious loading/ unloading
- Fatigue does not always lead to failure
- Failure can occur if the stress surpasses the endurance limit of the material
Why do we have to know the material
properties in the desing process
Properties of Engineering Materials
Strong materials
• How strong (and stiff) can materials be ?
• Why are they not that strong ? ( actually they are very weak )
• What type of defects exist ? (one perfect state exists, but many defect
states exist)
• Can defects be eliminated or controlled ?
• What is the best strategy for strong materials ?
Strong material
Strong materials
• Fibres are stronger along their lengths than the same
material in bulk form.
• Less sensitive to crack
• Options for material design in the form of
composites.
• Low resistance to transverse loads, and there is
therefore a need a surrounding matrix material to
transfer these loads by displacement of the fibers
Bulk form
Fibre form
Strong materials
Two-phase materials (multi-phase materials)
a. group of particles no use (?)
b. bundle of fibres useful
a. particles can be used to strengthen weak materials / dislocation sensitive
materials (typically metals)
b. solid / material is divided into fibres, and held together by matrix:
separates fibres (from large cracks)
transfers loads
protects fibres (from surface defects)
Strong material
Strong material
Metals
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provide the largest design and processing history to the engineers.
Common metals are iron, aluminum, copper, magnesium, zinc, lead, nickel, and titanium
In structural applications, alloys are more frequently used than pure metals.
Alloys offer better properties than pure metals.
cast iron is brittle and easy to corrode, but the addition of less than 1% carbon in iron makes it
tougher,and the addition of chromium makes it corrosion-resistant.
Through the principle of alloying, thousands of new metals are created
Metals are, in general, heavy as compared to plastics and composites.
Only aluminum, magnesium, and beryllium provide densities close to plastics.
Steel is 4 to 7 times heavier than plastic materials; aluminum is 1.2 to 2 times
heavier than plastics.
Metals generally require several machining operations to obtain the final product.
Metals have high stiffness, strength, thermal stability, and thermal and electrical conductivity.
Due to their higher temperature resistance than plastics,
They can be used for applications with higher service temperature requirements.
Plastics
• The production of plastics on a volume basis has exceeded steel production in
recent decades
• Due to their light weight, easy processability, and corrosion resistance, plastics are
widely used for automobile parts, aerospace components, and consumer goods
• Formed as sheets, rods, bars, powders, pellets, and granules
• They can provide high surface finish and therefore eliminate several machining
operations
• Provides the production of low-cost parts.
• not used for high-temperature applications due to their poor thermal stability.
• Operating temperature for plastics is less than 100°C, Some can take in the range
of 100-200°C .
• Lower melting temperatures than metals and therefore they are easy to process
Ceramics
• Strong covalent bonds and therefore Great thermal stability and high hardness
• The most rigid of all materials.
• They possess almost no ductility and fail in brittle fashion.
• Ceramics have the highest melting points of engineering materials.
• require high-temperature equipment for fabrication.
• Due to their high hardness, ceramics are difficult to machine and therefore require net-shape
forming to final shape
• require expensive cutting tools, such as carbide and diamond tools
Composites
• New century materials
• these materials start capturing the attention of industries with the
introduction of polymeric-based composites.
• Automotive components, sporting goods, aerospace parts, consumer
goods
• composite materials have the potential to replace widely used steel
and aluminum
• Save 60 to 80% in component weight replacing steel components,
20 to 50% weight by replacing aluminum parts.
Composites
"a complex solid material
composed of two or
more materials that
on a macroscopic scale
form a useful material.”
Composite Definition
A composite material is a heterogeneous combination of
two or more materials (reinforcing elements, fillers and
binders), differing in form or composition on a macroscale.
The combination results in a material that maximizes
specific performance properties. The constituents do not
dissolve or merge completely and therefore normally
exhibit an interface between one another.
What are the composites?
• Two or more materials to give a unique combination of properties (Metal Alloys,
Plastic copolymers, minarels and wood).
• the constituent materials are different at the molecular level and are mechanically
separable (fibre reinforced composites).
• bulk form, the constituent materials work together but remain in their original forms.
• final properties of composite materials are better than constituent material
properties.
Wood is a natural composite that consists of cellulose fibers in a matrix
of lignin and hemicellulose
Concrete is an artificial composite that consists of sand,cement, and
stone
More commonly, polymer matrix composites are reinforced with glass
or carbon fibers (e.g. wings of aircraft, tennisracquets)
Particulate composites: matrix material with fillers (e.g. wood plastic
composites)
History of composite materials
(Table of early fibres 1930 – 1960)
1938 natural fibres + polymers:
-- flax asbestos glass
-- phenolic resins
1950 -- fibre geometry and orientation
-- delta-wing for aircraft, made of asbestos / phenolics; competitive with metals (Al)
-- new, high-stiffness, lightweight fibres are needed
1955 search for such fibres:
whiskers (ceramics, inorganics)
special glass fibres
carbon fibres
History of composite materials
1958 metallic composites
-- SiO2 / Al (Rolls Royce, England)
filament winding:
-- motor cases for missile systems,
made of glass fibre / plastics (USA)
1960 principles of fibre reinforcement
1962 fibres in metals:
-- high yield stress, by blocking of dislocations
-- crack tolerance, by weak interfaces
1965 fibre pull-out mechanism:
-- quasi-ductile behaviour
Composite formation
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Cemented carbides (WC with Co binder)
Plastic molding compounds containing fillers
Rubber mixed with carbon black
Wood (a natural composite as distinguished from a
synthesized composite)
Functions of Fibres and Matrices
• The main functions of the fibers in a composite are:
• To carry the load. In a structural composite, 70 to 90% of the
load
is carried by fibers.
• To provide stiffness, strength, thermal stability, and other
structural
properties in the composites.
• To provide electrical conductivity or insulation, depending on
the
• type of fiber used.
Functions of Fibres and Matrices
• To binds the fibers together and transfers the load to the fibers.
It provides rigidity and shape to the structure.
• To isolates the fibers so that individual fibers can act separately.
This stops or slows the propagation of a crack.
• To provides a good surface finish quality and aids in the
production of net-shape or near-net-shape parts.
• To provides protection to reinforcing fibers against chemical
attack and mechanical damage (wear).
• The performance characteristics such as ductility, impact
strength, etc. are also influenced.
• The failure mode is strongly affected by its compatibility with
fibres
Classification of Composites
• Fibrous composites
Fibres in various forms are inherently much stiffer and stronger than the same material in bulk form
• Laminated composites
consist of layers of at least two different materials that are bonded together
Laminated glass, Bimetals and cladmetals, Plastic-based laminates, Laminated fibrous composites
• Particulate composites
of particles of one or more materials suspended in a matrix of another material
Non-metallic/non-metallic (cement and sand), Metallic/non-metallic( Al powder and PU), Metallic/metallic,
Polymeric/inorganic
Classification of Composites
1. Metal Matrix Composites (MMCs) - mixtures of ceramics and metals,
such as cemented carbides and other cermets
2. Ceramic Matrix Composites (CMCs) - Al2O3 and SiC imbedded with
fibers to improve properties, especially in high temperature
applications
• The least common composite matrix
3. Polymer Matrix Composites (PMCs) - thermosetting resins are widely
used in PMCs
• Examples: epoxy and polyester with fiber reinforcement, and phenolic with
powders
Classification of Composites
Adapted from Fig. 16.2,
Callister & Rethwisch 8e.
Classification: Particle-Reinforced (i)
Particle-reinforced
• Examples:
- Spheroidite matrix:
ferrite (a)
steel
Fiber-reinforced
(ductile)
60 mm
- WC/Co
cemented
carbide
matrix:
cobalt
(ductile,
tough)
:
Structural
particles:
cementite
(Fe C)
3
(brittle)
Adapted from Fig.
10.19, Callister &
Rethwisch 8e. (Fig.
10.19 is copyright
United States Steel
Corporation, 1971.)
particles:
WC
(brittle,
hard)
Adapted from Fig.
16.4, Callister &
Rethwisch 8e. (Fig.
16.4 is courtesy
Carboloy Systems,
Department, General
Electric Company.)
600 mm
- Automobile matrix:
tire rubber rubber
(compliant)
0.75 mm
particles:
carbon
black
(stiff)
Adapted from Fig.
16.5, Callister &
Rethwisch 8e. (Fig.
16.5 is courtesy
Goodyear Tire and
Rubber Company.)
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Classification: Fiber-Reinforced (i)
Particle-reinforced
Fiber-reinforced
Structural
• Fibers very strong in tension
– Provide significant strength improvement to the
composite
– Ex: fiber-glass - continuous glass filaments in a
polymer matrix
• Glass fibers
– strength and stiffness
• Polymer matrix
– holds fibers in place
– protects fiber surfaces
– transfers load to fibers
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Classification: Fiber-Reinforced (ii)
Particle-reinforced
Fiber-reinforced
Structural
• Fiber Types
– Whiskers - thin single crystals - large length to diameter ratios
• graphite, silicon nitride, silicon carbide
• high crystal perfection – extremely strong, strongest known
• very expensive and difficult to disperse
– Fibers
• polycrystalline or amorphous
• generally polymers or ceramics
• Ex: alumina, aramid, E-glass, boron, UHMWPE
– Wires
• metals – steel, molybdenum, tungsten
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Fiber Alignment
Adapted from Fig. 16.8,
Callister & Rethwisch 8e.
aligned
continuous
aligned
random
discontinuous
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Classification: Fiber-Reinforced (iii)
Particle-reinforced
Fiber-reinforced
Structural
• Aligned Continuous fibers
• Examples:
-- Metal: g'(Ni3Al)-a(Mo)
-- Ceramic: Glass w/SiC fibers
by eutectic solidification.
formed by glass slurry
Eglass = 76 GPa; ESiC = 400 GPa.
matrix: a (Mo) (ductile)
(a)
2 mm
fibers: g ’ (Ni3Al) (brittle)
From W. Funk and E. Blank, “Creep
deformation of Ni3Al-Mo in-situ composites",
Metall. Trans. A Vol. 19(4), pp. 987-998,
1988. Used with permission.
(b)
fracture
surface
From F.L. Matthews and R.L.
Rawlings, Composite Materials;
Engineering and Science, Reprint
ed., CRC Press, Boca Raton, FL,
2000. (a) Fig. 4.22, p. 145 (photo by
J. Davies); (b) Fig. 11.20, p. 349
(micrograph by H.S. Kim, P.S.
Rodgers, and R.D. Rawlings). Used
with permission of CRC
Press, Boca Raton, FL.
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Classification: Fiber-Reinforced (iv)
Particle-reinforced
Fiber-reinforced
• Discontinuous fibers, random in 2 dimensions
• Example: Carbon-Carbon
-- fabrication process:
- carbon fibers embedded
in polymer resin matrix,
- polymer resin pyrolyzed
at up to 2500ºC.
-- uses: disk brakes, gas
turbine exhaust flaps,
missile nose cones.
(b)
(a)
Structural
C fibers:
very stiff
very strong
C matrix:
less stiff
view onto plane less strong
500 mm
fibers lie
in plane
• Other possibilities:
-- Discontinuous, random 3D
-- Discontinuous, aligned
Adapted from F.L. Matthews and R.L. Rawlings,
Composite Materials; Engineering and Science,
Reprint ed., CRC Press, Boca Raton, FL, 2000.
(a) Fig. 4.24(a), p. 151; (b) Fig. 4.24(b) p. 151.
(Courtesy I.J. Davies) Reproduced with
permission of CRC Press, Boca Raton, FL.
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Classification: Structural
Particle-reinforced
Fiber-reinforced
Structural
• Laminates -- stacked and bonded fiber-reinforced sheets
- stacking sequence: e.g., 0º/90º
- benefit: balanced in-plane stiffness
• Sandwich panels
Adapted from
Fig. 16.16,
Callister &
Rethwisch 8e.
-- honeycomb core between two facing sheets
- benefits: low density, large bending stiffness
face sheet
adhesive layer
honeycomb
Adapted from Fig. 16.18,
Callister & Rethwisch 8e.
(Fig. 16.18 is from Engineered Materials
Handbook, Vol. 1, Composites, ASM International, Materials Park, OH, 1987.)
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Composite Benefits
• CMCs: Increased toughness
Force
• PMCs: Increased E/r
10
particle-reinf
E(GPa)
10
ceramics
3
2
PMCs
10
fiber-reinf
metal/
metal alloys
1
un-reinf
0.1
polymers
0.01
0.1 0.3
Bend displacement
• MMCs:
Increased
creep
resistance
3
10 30
Density, r [mg/m3]
10 -4
ess (s-1)
1
6061 Al
10 -6
10 -8
6061 Al
w/SiC
whiskers
10 -10
20 30 50
Adapted from T.G. Nieh, "Creep rupture of a
silicon-carbide reinforced aluminum
composite", Metall. Trans. A Vol. 15(1), pp.
139-146, 1984. Used with permission.
s(MPa)
100 200
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Summary
• Composites types are designated by:
-- the matrix material (CMC, MMC, PMC)
-- the reinforcement (particles, fibers, structural)
• Composite property benefits:
-- MMC: enhanced E, s, creep performance
-- CMC: enhanced KIc
-- PMC: enhanced E/r, sy, TS/r
• Particulate-reinforced:
-- Types: large-particle and dispersion-strengthened
-- Properties are isotropic
• Fiber-reinforced:
-- Types: continuous (aligned)
discontinuous (aligned or random)
-- Properties can be isotropic or anisotropic
• Structural:
-- Laminates and sandwich panels
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Features of Composites
• Capabilities for part integration.
• In-service monitoring or online process monitoring with the help of embedded sensors
• A high specific stiffness (equal stiffness of steel at one fifth the weight and one half weight of
aluminium.
• The specific strength is very high (3-5 times higher than stell and aluminium alloys).
• The fatigue strength is much higher for composite materials.
• high corrosion and chemical resistance
• the coefficient of thermal expansion (CTE) can be made zero
• Production of complex parts and reducing production times.
• Good impact properties ( great thoughness)
• Noise, vibration, and harshness characteristics are better for composite materials than metals.
• Design freedom to meet performance of specifications with changing fibre resin types,
orientation length or processing
• Cost of tooling is lower than metals due to pressure and temperature requirements.
Drawbacks of Composites
• The materials cost for composite materials is very high compared to that of
steel and aluminum. It is almost 5 to 20 times more than aluminum and
steel on a weight basis.
• In the past, composite materials have been used for the fabrication of large
structures at low volüme relatively slow
• The temperature resistance of composite parts depends on the
temperature resistance of the matrix materials.
• Composites absorb moisture, which affects the properties and dimensional
stability of the composites. (Average composites work in the temperature range –40 to +100°C and upper
temperature range 150-200 °C).
• Solvent resistance, chemical resistance, and environmental stress cracking
of composites because of polymer sensitivity
Materials and Fibres
Materials and Fibres
Materials and Fibres
Materials and Fibres
Composite applications
Composite Markets
Composite Markets
Composite Markets
Swedish Navy, Stealth (2005)
Pedestrian bridge in Denmark,
130 feet long (1997)
Composite Markets
Composite Markets
Composite Markets
Questions?
• What are types of engineering materials?
• How can you rank the engineering materials based on density spesific
stiffness and spesific strength?
• What is the definition of composite material?
• Why do we need composites? Compare with traditional materials.
• What are the benefits of using composite materials?
• What is the function of the matrix in a composite material
• What are the functions of the fibres in a composite material
• What is the difference between fibre and particle reinforced composites?
Give an example.
Homework
• Give a report (mak. 5 pages) using of polymer composite
materials for different application fields.