COMPOSITES
Classification of composites
The composite materials are shortened as composites. They are formed by combining two or more different materials to make better use of their virtues and by minimizing their deficiencies. Each material retains its physical or chemical properties separate and distinct within the finished product.
Composition
The composites are made from two main constituent materials.
1. Strong load carrying material known as reinforcement or reinforcing fibres.
2. Weaker material known as matrix.
1. Reinforcing fibres
Following are the functions of reinforcing fibres:
(i) It provides strength and rigidity.
(ii) It helps to support structural load.
There are three most common types of reinforcing fibres.
(i) Glass fibres
(ii) Carbon fibres
(iii) Aramid fibres
Glass fibers are the heaviest having greatest flexibility and the lowest cost. Aramid has moderate stiffness and cost.
Carbon is moderate to high in cost, slightly heavier than aramid but lighter than glass fibres. Carbon is the strongest.
2. Matrix
Following are the functions of matrix.
(i) It works as a binder
(ii) It maintains the position and orientation of the reinforcement.
(iii) It balances the loads between the reinforcement.
(iv) It protects the reinforcement degradation.
(v) It provides shape and form to the structure.
The most common type of matrix is thermosetting resins.
Epoxy resins are the most widely used thermo setting resins in advanced composites. Others resins used as matrix are polyester, vinyl ester, phenolic, bismaleimade, epoxy no volar.
Examples:
Composites natural
Wood - Cellulose fibres plus polysaccharide.
Bones, teeth and mollusc shells = Hard ceramic + organic polymer
Man made composites
1. Mud + straw
2. Bricks made up straw + mud
3. Plywood
4. Concrete, plastic, MMC, CMC
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