An Introduction to Composite Materials

The elastic behaviour of long and short fibre composites is described in Chapters 4–6. This involves considering the stresses in individual plies of a laminate (under an external load) and stress distributions within and around short fibres. This information is now used to explore how a composite material suffers microstructural damage, potentially leading to ultimate failure of some sort. There are two distinct aspects to these (highly important) characteristics. First, there is the onset and development of microstructural damage (mainly cracking of various types) as a function of applied load. Second, there are the processes that cause absorption of energy within a composite material as it undergoes such failure and fracture. The latter determine the toughness of the material and are treated on a fracture mechanics basis in Chapter 9. In the present chapter, attention is concentrated on predicting how applied stresses create stress distributions within the composite and how these lead to damage and failure. The treatment is largely oriented towards long fibre composites (particularly laminates), and also towards polymer-based composites, although most of the principles apply equally to discontinuous reinforcement and other types of matrix.