Composites: A Definition
A composite material is defined as a material made by combining two or more materials to give a unique combination of properties, one of which is made up of stiff, long fibres and the other, a binder or 'matrix' which holds the fibres in place.
According to Jartiz 1965, “Composites are multifunctional material systems that provide characteristics not obtainable from any discrete material. They are cohesive structures made by physically combining two or more compatible materials, different in composition and characteristics and sometimes in form.”
This definition is can be contradicted as it allows to any mixture of materials to be classified as a composite without specifying the laws which should distinguish it from other very banal, meaningless mixtures.
Beghezan (1966) defined as “The composites are compound materials which differ from alloys by the fact that the individual components retain their characteristics but are so incorporated together as such to take advantage only of their attributes and not of their short comings, in order to obtain improved materials.”
Kelly (1967) stated that “the composites should not be regarded simple as a combination of two materials. In the broader significance; the combination has its own distinctive properties. In terms of strength, resistance to heat or some other desirable quality, it is better than either of the components alone or radically different from either of them.”
Composites Constituents
Most composites consist of a bulk material referred as the “matrix” and a “reinforcement” of some kind. The reinforcement is added primarily to increase the strength and stiffness of the matrix.
Importance of Matrix in a Composite
A matrix material of composites is required to perform the following functions:
- 1.
To bind together the fires of the reinforcement by the virtue of its cohesive and adhesive characteristics.
- 2.
To protect the fibres from environment and handling.
- 3.
To disperse the fibres to maintain the desired fibre orientation and spacing.
- 4.
To transfer stresses on the fibres by adhesion or friction across the fibre-matrix interface when the composite is under load thus to avoid propagation of cracks and subsequent failure of composites.
- 5.
To be chemically and thermally compatible with the reinforcing fibres.
- 6.
To be compatible with the manufacturing methods which are available to fabricate the desired composite components (Mathews et al. 1994).