Failure mechanisms in polymeric materials

Abstract

Polymers differ from other molecules by virtue of their size. They are macromolecules, whose total molecular weight (or relative molar mass) may reach millions. As we shall see, this has important consequences for their response to mechanical stress or strain. In particular, whereas most materials (including polymers) which exhibit any degree of ductility may show a shear response, an alternative mode of deformation is also open to polymeric materials and to them alone, the mechanism known as crazing. In order to understand toughening and failure mechanisms in polymers, one therefore has first to look at the nature of the polymer chains. Only a brief overview of salient facts will be presented here to introduce the key factors and terminology. The interested reader is referred to other texts (e.g. Refs 1–3) for a broader picture.