Composite materials are a combination of two or more materials that result in properties superior to the individual components. They consist of a reinforcement phase, such as fibers, embedded within a binder or matrix phase. Composites offer advantages like high strength and stiffness with low weight. Common applications include aerospace, automotive, sports equipment and construction. The two main categories of composites are polymer matrix composites and metal matrix composites. Fiber reinforced polymers are the most widely used type and consist of fibers, such as glass, carbon or aramid, embedded in a polymer matrix.

1. Composite materials – Introduction
Definition: any combination of two or more different
materials at the macroscopic level.
OR
Two inherently different materials that when
combined together produce a material with
properties that exceed the constituent materials.
 Reinforcement phase (e.g., Fibers)
 Binder phase (e.g., compliant matrix)
Advantages
 High strength and stiffness
 Low weight ratio
 Material can be designed in addition to the structure

2. Applications
 Straw in clay construction by Egyptians
 Aerospace industry
 Sporting goods
 Automotive
 Construction

3. Types of Composites
Matrix
phase/Reinforc
ement Phase
Metal Ceramic Polymer
Metal Powder metallurgy
parts – combining
immiscible metals
Cermets (ceramic-
metal composite)
Brake pads
Ceramic Cermets, TiC, TiCN
Cemented carbides –
used in tools
Fiber-reinforced
metals
SiC reinforced
Al2O3
Tool materials
Fiberglass
Polymer Kevlar fibers in an
epoxy matrix
Elemental
(Carbon,
Boron, etc.)
Fiber reinforced
metals
Auto parts
aerospace
Rubber with
carbon (tires)
Boron, Carbon
reinforced plastics
MMC’s CMC’s PMC’s
Metal Matrix Composites Ceramic Matrix Comp’s. Polymer Matrix Comp’s

4. Costs of composite manufacture
Material costs -- higher for composites
 Constituent materials (e.g., fibers and resin)
 Processing costs -- embedding fibers in matrix
 not required for metals Carbon fibers order of magnitude
higher than aluminum
Design costs -- lower for composites
 Can reduce the number of parts in a complex
assembly by designing the material in combination
with the structure
Increased performance must justify higher
material costs

5. Types of Composite Materials
There are five basic types of composite materials:
Fiber, particle, flake, laminar or layered and filled
composites.

6. A. Fiber Composites
In fiber composites, the fibers reinforce along the line of
their length. Reinforcement may be mainly 1-D, 2-D or 3-D.
Figure shows the three basic types of fiber orientation.
1-D gives maximum strength in
one direction.
2-D gives strength in two
directions.
Isotropic gives strength equally
in all directions.

7. Composite strength depends on following factors:
Inherent fiber strength,
Fiber length, Number of
flaws
Fiber shape
The bonding of the
fiber (equally stress
distribution)
Voids
Moisture (coupling
agents)

8. B. Particle Composites
Particles usually reinforce a composite equally in all directions
(called isotropic). Plastics, cermets and metals are examples of
particles.
Particles used to strengthen a matrix do not do so in the same
way as fibers. For one thing, particles are not directional like
fibers. Spread at random through out a matrix, particles tend to
reinforce in all directions equally.
 Cermets
(1) Oxide–Based cermets
(e.g. Combination of Al2O3 with Cr)
(2) Carbide–Based Cermets
(e.g. Tungsten–carbide, titanium–carbide)
 Metal–plastic particle composites
(e.g. Aluminum, iron & steel, copper particles)
 Metal–in–metal Particle Composites and
Dispersion Hardened Alloys
(e.g. Ceramic–oxide particles)

9. C. Flake Composites - 1
Flakes, because of their shape, usually
reinforce in 2-D. Two common flake
materials are glass and mica. (Also
aluminum is used as metal flakes)

10. C. Flake Composites -2
A flake composite consists of thin, flat flakes
held together by a binder or placed in a
matrix. Almost all flake composite matrixes
are plastic resins. The most important flake
materials are:
1. Aluminum
2. Mica
3. Glass

11. C. Flake Composites -3
Basically, flakes will provide:
Uniform mechanical properties in the plane of
the flakes
Higher strength
Higher flexural modulus
Higher dielectric strength and heat resistance
Better resistance to penetration by liquids and
vapor
Lower cost

12. D. Laminar Composites - 1
Laminar composites involve two or more
layers of the same or different materials. The
layers can be arranged in different directions
to give strength where needed. Speedboat
hulls are among the very many products of
this kind.

13. D. Laminar Composites - 2
Like all composites laminar composites
aim at combining constituents to produce
properties that neither constituent alone
would have.
In laminar composites outer metal is not
called a matrix but a face. The inner
metal, even if stronger, is not called a
reinforcement. It is called a base.

14. D. Laminar Composites - 3
We can divide laminar composites into three basic types:
Unreinforced–layer composites
(1) All–Metal
(a) Plated and coated metals (electrogalvanized
steel – steel plated with zinc)
(b) Clad metals (aluminum–clad, copper–clad)
(c) Multilayer metal laminates (tungsten, beryllium)
(2) Metal–Nonmetal (metal with plastic, rubber, etc.)
(3) Nonmetal (glass–plastic laminates, etc.)
Reinforced–layer composites (laminae and laminates)
Combined composites (reinforced–plastic laminates
well bonded with steel, aluminum, copper, rubber,
gold, etc.)

15. D. Laminar Composites - 4
A lamina (laminae) is any
arrangement of unidirectional
or woven fibers in a matrix.
Usually this arrangement is
flat, although it may be
curved, as in a shell.
A laminate is a stack of
lamina arranged with their
main reinforcement in at least
two different directions.

16. E. Filled Composites
There are two types of filled composites. In
one, filler materials are added to a normal
composite result in strengthening the
composite and reducing weight. The second
type of filled composite consists of a skeletal
3-D matrix holding a second material. The
most widely used composites of this kind are
sandwich structures and honeycombs.

17. F. Combined Composites
It is possible to combine
several different materials
into a single composite. It is
also possible to combine
several different composites
into a single product. A good
example is a modern ski.
(combination of wood as
natural fiber, and layers as
laminar composites)

18. Forms of Reinforcement Phase
Fibers
 cross-section can be circular, square or hexagonal
 Diameters --> 0.0001” - 0.005 “
 Lengths --> L/D ratio
 100 -- for chopped fiber
 much longer for continuous fiber
Particulate
 small particles that impede dislocation movement
(in metal composites) and strengthens the matrix
 For sizes > 1 mm, strength of particle is involves in
load sharing with matrix
Flakes
 flat platelet form

19. Fiber Reinforcement
The typical composite consists of a matrix holding
reinforcing materials. The reinforcing materials, the
most important is the fibers, supply the basic
strength of the composite. However, reinforcing
materials can contribute much more than strength.
They can conduct heat or resist chemical corrosion.
They can resist or conduct electricity. They may be
chosen for their stiffness (modulus of elasticity) or for
many other properties.

20. Types of Fibers
The fibers are divided into two main groups:
Glass fibers: There are many different kinds of glass,
ranging from ordinary bottle glass to high purity quartz
glass. All of these glasses can be made into fibers.
Each offers its own set of properties.
Advanced fibers: These materials offer high strength
and high stiffness at low weight. Boron, silicon, carbide
and graphite fibers are in this category. So are the
aramids, a group of plastic fibers of the polyamide
(nylon) family.

21. Fibers - Glass
Fiberglass properties vary somewhat according to the type of glass
used. However, glass in general has several well–known
properties that contribute to its great usefulness as a reinforcing
agent:
 Tensile strength
 Chemical resistance
 Moisture resistance
 Thermal properties
 Electrical properties
There are four main types of glass used in fiberglass:
 A–glass
 C–glass
 E–glass
 S–glass

22. Fibers - Glass
Most widely used fiber
Uses: piping, tanks, boats, sporting goods
Advantages
 Low cost
 Corrosion resistance
 Low cost relative to other composites:
Disadvantages
 Relatively low strength
 High elongation
 Moderate strength and weight
Types:
 E-Glass - electrical, cheaper
 S-Glass - high strength

23. Fibers - Aramid (kevlar, Twaron)
Uses:
 high performance replacement for glass
fiber
Examples
 Armor, protective clothing, industrial,
sporting goods
Advantages:
 higher strength and lighter than glass
 More ductile than carbon

24. Fibers - Carbon
2nd most widely used fiber
Examples
 aerospace, sporting goods
Advantages
 high stiffness and strength
 Low density
 Intermediate cost
 Properties:
 Standard modulus: 207-240 Gpa
 Intermediate modulus: 240-340 GPa
 High modulus: 340-960 GPa
 Diameter: 5-8 microns, smaller than human hair
 Fibers grouped into tows or yarns of 2-12k fibers

25. Fibers -- Carbon (2)
Types of carbon fiber
 vary in strength with processing
 Trade-off between strength and modulus
Intermediate modulus
 PAN (Polyacrylonitrile)
 fiber precursor heated and stretched to align structure
and remove non-carbon material
High modulus
 made from petroleum pitch precursor at lower
cost
 much lower strength

26. Fibers - Others
Boron
 High stiffness, very high cost
 Large diameter - 200 microns
 Good compressive strength
Polyethylene - trade name: Spectra fiber
 Textile industry
 High strength
 Extremely light weight
 Low range of temperature usage

27. Fibers -- Others (2)
Ceramic Fibers (and matrices)
 Very high temperature applications (e.g.
engine components)
 Silicon carbide fiber - in whisker form.
 Ceramic matrix so temperature resistance
is not compromised
 Infrequent use

28. Fiber Material Properties
Steel: density (Fe) = 7.87 g/cc; TS=0.380 GPa; Modulus=207 GPa
Al: density=2.71 g/cc; TS=0.035 GPa; Modulus=69 GPa

29. Fiber Strength

30. Matrix Materials
Functions of the matrix
 Transmit force between fibers
 arrest cracks from spreading between fibers
 do not carry most of the load
 hold fibers in proper orientation
 protect fibers from environment
 mechanical forces can cause cracks that allow
environment to affect fibers
Demands on matrix
 Interlaminar shear strength
 Toughness
 Moisture/environmental resistance
 Temperature properties
 Cost

31. Matrices - Polymeric
Thermosets
 cure by chemical reaction
 Irreversible
 Examples
 Polyester, vinylester
 Most common, lower cost, solvent resistance
 Epoxy resins
 Superior performance, relatively costly

32. Polyester
Polyesters have good mechanical properties, electrical
properties and chemical resistance. Polyesters are
amenable to multiple fabrication techniques and are low
cost.
Vinyl Esters
Vinyl Esters are similar to polyester in performance.
Vinyl esters have increased resistance to corrosive
environments as well as a high degree of moisture
resistance.
Matrices - Thermosets

33. Epoxy
Epoxies have improved strength and stiffness properties
over polyesters. Epoxies offer excellent corrosion
resistance and resistance to solvents and alkalis. Cure
cycles are usually longer than polyesters, however no
by-products are produced.
Flexibility and improved performance is also achieved
by the utilization of additives and fillers.
Matrices - Thermosets

34. Matrices - Thermoplastics
Formed by heating to elevated temperature
at which softening occurs
 Reversible reaction
 Can be reformed and/or repaired - not common
 Limited in temperature range to 150C
Examples
 Polypropylene
 with nylon or glass
 can be injected-- inexpensive
 Soften layers of combined fiber and resin and
place in a mold -- higher costs

35. Matrices - Others
Metal Matrix Composites - higher
temperature
 e.g., Aluminum with boron or carbon fibers
Ceramic matrix materials - very high
temperature
 Fiber is used to add toughness, not
necessarily higher in strength and stiffness

36. Important Note
Composite properties are less than
that of the fiber because of dilution
by the matrix and the need to orient
fibers in different directions.