Composite Materials (Concise Notes for Semester Exam)

Difference between alloy and composite?

Alloy :- is solid solution of two or more constituent where physical significance of each constituent is not generally possible but it constituent has effect on overall properties.

Composite :- is material with two or more constituent where physical significance of each is clearly possible but it can student has effect on overall properties of materials.

Definition of composite materials.

A material that satisfies the following condition is a composite material.

1. It is manufactured.

2. It consists of two or more physically and/or chemically distinct suitably arranged or distributed phase with an interface separating them.

3. It has characteristic that are not depicted by any of the components in isolation.

What is solid solutions?

A solid solution forms when the solute atoms are added to the host material, the crystal structure is maintained and no new structures are formed.

Example of composite materials.

1. Natural occuring composites are:-

Wood, Bones, Granite etc

2. Man made composites are:-

Concrete, Plywood, Fiberglass etc

Factors on which composite strength depends:-

1. Inherited fibre strength

2. Fibre length

3. Number of flaws

4. Fibre shape

5. Bonding and interface

6. Voids

7. Moisture

8. Orientation

Classification of composite on the basis of reinforcement

Composites can be broadly divided into  particle reinforced,fibre reinforced and structural.

Further, particle reinforced composites can be divided into large particle and dispersion strengthened.

Fibre reinforced composite can be divided into continuous and discontinuous fibres.

Structural can be divided into laminates and sandwich panels.

Classification on the basis of matrices.

Composites can be divided into metal matrix composites, ceramic Matrix composites and polymer Matrix composites.

Advantages of composites.

1. High strength to weight ratio.

2. High stiffness.

3. Resistant to wear.

4. Higher damping properties.

5. Electrical conductivity can be increase or decrease.

6. Thermal conductivity.

7. Temperature resistant.

8. Acoustic insulation.

9. Aesthetics.

10. Resistant to corrosion.

11. High creep resistance.

12. Impact load and vibration can we modify according to needs.

13. Dimensional change due to temperature change can be much less.

14. Design freedom.

15. A number of manufacturing advantages.

Limitations and disadvantages of composites

1. Anisotropy - (Different material property in different direction)

2. Nonhomogeneous.

3. Costly.

4. Difficult to fabricate.

5. Sensitive to temperature.

6. Sensitive to moisture.

7. Repair of composites can be difficult.

8. Wide range of variability.

9. Operating temperature can be an issue for polymer matrix.

10. Inspection and testing are typically more complex.

11. Lack of design standards.

12. Only few mass production process are available.

Cost of composite manufacture

1. Material costs - Material cost is higher for composites than their constituent materials. It also includes the processing cost of composite.

2. Design costs - it is generally lower for composites. One can reduce the number of parts in a complex assembly by designing the material in combination with structures.

Increase performance of the components must justify the higher cost of composites.

It is observed that most material have tensile strength several times greater as fibres than in bulks. This is because in fibres materials have less flaws, hence less defects. Matrix provides the bulk save to the composite and protect the fibre from damages.

Applications of composite materials

1. Automotive sector - Composites are very heavily used in automotive sector due to its light weight, wear resistance, rust resistance and aesthetics.

2. Aerospace sector  - In aerospace industry, we need things lighter so composite is preferred. It is used to make nose of aircraft nose,studs,cowlings fairings, flaps and many things. It is widely used in rockets and missiles.

3. Satellites - It is used to make frame and structural part of the satellites.

4. Sports - composites are used to make tennis racket, bikes, badminton rackets, boats, hockey sticks, golf balls and golf stick and parts of motorcycles.

5. Transportation - Composites are also used in transportation industry. Metro, railway coaches, bridges and ships and boats.

Applications of composites can also be visualising in infrastructures, biomedical, consumer goods, agriculture equipments, computers,healthcare industry and Marine industries.