Most composites have strong, stiff fibres in a matrix which is weaker and less stiff. The objective is usually to make a component which is strong and stiff, often with a low density. Commercial material commonly has glass or carbon fibres in matrices based on thermosetting polymers, such as epoxyor polyester resins.

Sometimes, thermoplastic polymers may be preferred, since they are mouldable after initial production.


There are further classes of composite in which the matrix is a metal or aceramic. For the most part, these are still in a developmental stage, with problems of high manufacturing costs yet to be overcome. Furthermore, in these composites the reasons for adding the fibres (or, in some cases, particles) are often rather complex; for example, improvements may be sought in creep, wear, fracture toughness, thermal stability, etc. This software package covers simple mechanics concepts of stiffness and strength, which, while applicable to all composites, are often more relevant to fibre-reinforced polymers.

  Load Transfer in Composite Material

The concept of load sharing between the matrix and the reinforcing constituent (fibre) is central to an understanding of the mechanical behaviour of a composite. An external load (force) applied to a composite is partly borne by the matrix and partly by the reinforcement. The load carried by the matrix across a section of the composite is given by the product of the average stress in the matrix and its sectional area.

Transverse Stiffness

The stiffness and strength of the composite are expected to be much lower in this case, since the (weak) matrix is not shielded from carrying stress to the same degree as for axial loading. Prediction of the transverse stiffness of a composite from the elastic properties of the constituents is far more difficult than the axial value. The conventional approach is to assume that the system can again be represented by the "slab model".

What happens with Short Fibres?


Short fibres can offer advantages of economy and ease of processing. When the fibres are not long, the equal strain condition no longer holds under axial loading, since the stress in the fibres tends to fall off towards their ends. This means that the average stress in the matrix must be higher than for the long fibre case.



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