OSL - Lightweight carbon fibre mirrors

In general, composite materials consist of strong fibres surrounded by a weaker matrix material, which serves to distribute the fibres and transmit the load. One of the simplest forms of composite material is plywood, where wood is layered in different directions to create a more durable structure. These days commonly used fibre materials include glass, carbon, boron and silicon carbide. The matrix can be polymer, ceramic or metallic.

The principal advantages of composite materials are:

Low weight, which leads to fuel saving (for use in space or in aircraft) and cost reduction
Good fatigue resistance, which leads to enhanced lifetime
Good corrosion resistance means saving on maintenance cost
Low thermal expansion coefficient

A composite plate, or laminate, is made up of a number of layers, or plies, each with fibres running through it in a given direction. Because of this directionality, a ply's behaviour is only isotropic along its material axes (i.e. orthotropic). By stacking the plies in a symmetrical and balanced sequence, the directional properties of each ply can be combined to give a laminate that displays quasi-isotropic behaviour.

The endless possible combinations of fibre and matrix materials, as well as the many laminate configurations and stacking sequences make that composites are very difficult to compare like for like. Finite element analsyis (FEA) is therefore a very valuable tool in predicting a material's behaviour.