Classifying by matrix systems

All classes of materials can be suitable as matrix material. In this section, we briefly introduce the different matrix systems. A more detailed discussion can be found at the end of the chapter in section 9.4, after the mechanical behaviour of composites has been discussed. 

Polymer matrix composites (PMC) are used to increase the rather low stiffness or strength of polymers by adding stiffer or stronger fibres. If thermoplastics are used as matrix material, short fibres can be added to the granulate material that is subsequently softened by heating and processed, for example in injection moulding. If thermoset resins (duromers) are used, the fibres can be placed into the liquid resin before curing. 

There are a large number of possible fibre materials that can be used in reinforced polymers. The most common are glass, carbon, aramid, and polyethylene. 

One disadvantage is that metal matrix composites have to be processed at markedly larger temperature. This not only increases the requirements on tools used during processing, but also on the fibres which have to withstand 

In ceramic matrix composites (CMC), the fibres mainly serve to increase the fracture toughness. Because one important property of the fibres is their small defect size, it is possible to use the same material for fibre and matrix. The advantage of this is that the elastic properties of fibre and matrix are identical, avoiding the formation of stress concentrations, and that the coefficient of thermal expansion is also the same, so no residual stresses are generated during cooling. Chemical reactions do not occur as well. Possible fibre materials are mainly ceramics. 

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