3. Definition
What is a composite?
• A composite material is made by combining 2 or more
distinct materials to give an unique and better
combination of properties.
• Distinct materials:
- Different at the molecular level (chemically
dissimilar) and mechanically separable.
- In bulk form, the constituent materials work
together but remain in their original forms (separated by a
distinct interface)
• Constituents: Matrix and reinforcing phase
4. Composite Characteristics
Advantages:
• Low density
• High specific stiffness (stiffness-to-density ratio)
• Very high specific strength (strength-to-density ratio).
• Much higher fatigue strength
• High corrosion resistance
• Design flexibility
• Good impact properties
• Noise, vibration, and harshness characteristics are better for
CM than metals
9. Fiber-reinforced composites
• Are the most important composites
• Design goals:
- Low density;
- High specific strength;
- High specific modulus.
• Constituents: - Fibers and matrix
- Agents, coatings.
10. Fibers
• Characteristics:
- Principal constituents;
- Occupy the largest volume fraction;
- Share the major portion of the load acting.
• Design considerations:
- fiber type, fiber volume fraction, fiber length, fiber
orientation.
• Some common fiber types:
- Glass fiber, carbon fiber, aramid fiber, boron fiber,
ceramic fiber, etc.
12. Matrix
• Roles:
- Keep fibers in place;
- Transfer stress between fibers;
- Provide a barrier against an adverse environment
(chemicals, moisture)
- Protect the surface of fibers (by abrasion)
- Minor role in the tensile load-carrying capacity, but major
influence on the compressive, inter-laminar shear, in-
plane shear, buckling, etc.
• Types of matrix:
- Polymer matrix, metal matrix, ceramic matrix
13. Polymer matrix
• Thermoset vs Thermoplastic
• Thermoset (resins):
- Examples: epoxy, polyester, and vinyl ester
- Used as matrix in continuous or long fiber-reinforced
composites
- Molecules are joined by cross-links rigid, 3-D network
structure. Once cross-links are formed, it cannot be melted
by heat.
- Long fabrication time.
(curing)
14. • Thermal plastics:
- Examples: PVC, PS, PP
- Individual molecules are not chemically joined together;
- Held in place by Van der Waals bonds and hydrogen bonds
that can be broken by heat;
- Heat-softened, melted, and reshaped as many times as
desired.
16. Glass fiber-reinforced polymer composites
• Glass is popular as a fiber reinforcement because:
- Easily drawn into high-strength fibers;
- Relatively strong very high specific strength
composites
- Inertness with various plastics
- E-glass, C-glass, S-glass
• High strength but not very stiff and rigid enough for some
applications such as: structure members for airplanes and
bridges
• Limited to services temperatures, below 200C ( t
polyimide resins)
• Applications: automotive and marine bodies, storage
containers, industrial flooring, etc.
17. Carbon fiber-reinforced polymer composites
• Carbon characteristics:
- Very high specific moduli and specific strengths (207-
1035 Gpa);
- Retain characteristics at elevated temperatures, high-
temperature oxidation;
- Not affected by moisture, inert with variety of solvents
19. Disadvantages:
- Much more expensive than PMC
- Reactions between matrix and reinforcement at elevated
temperatures composite degradation surface coating
or modifying the matrix alloy composition.
• Applications:
- Aerospace industry: Aluminum-alloy metal matrix
composites
20. Ceramic-matrix composites
Particulates, fibers or whiskers of one ceramic are
embedded into a matrix of another ceramic.
Improve significantly fracture toughness
Fracture toughness is the ability of a material
containing a crack to resist fracture.
• Applications:
- In high-temperature and severe-stress applications :
Components in automobile and aircraft gas turbine engine
21. Carbon-Carbon composites
• Carbon fiber-reinforced carbon-matrix composites
• Advantages:
- High tensile moduli and tensile strength;
- Retained to temperatures in excess of 2000C;
- Resistance to creep;
- Relatively large fracture toughness;
- Low coefficient of thermal expansion; and high thermal
conductivity
Drawbacks:
- High-temperature oxidation
- Expensive
23. - The hand layup technique
- The industrial manufacturing technique:
+ Compression molding, pultrusion, filament winding,
Resin transfer molding, etc.
+ Curing
+ Prepreg
26. • Automotive industry
- Glass fiber
• Sporting goods industry
• Marine Applications
• Consumer goods
- Short fiber composites
• Construction and civil structures
27. Quiz 1
1/ What is a composite material? Give 3 examples of
composite materials, show the matrix and reinforcing phase
in these examples.
2/ What are the functions of: Matrix, Fibers, Agents and
coatings in composites
3/ List 5 general characteristics of composite materials?
4/ What are 2 main and important differences between
polymer-matrix composites and metal-matrix composite.
