The post-yield deformation of glassy polymers

Abstract

The science and technology associated with the mechanical properties of thermoplastics still harbour many mysteries. There are numerous different aspects of mechanical properties and their evaluation entails many types of measurement, such as short term modulus and creep, yield behaviour and large deformation after yield, toughness and fracture. In various ways all these measurements are related to each other, but until about 1970 the importance of large strains in determining other mechanical properties, often measured separately, was not generally appreciated. Since that time much progress has been made, though there are still many uncertainties concerning the extent and manner in which different mechanical properties are connected. It is therefore appropriate, in a review of large deformations in glassy polymers, to begin by summarizing briefly the way in which ideas on the interrelations between mechanical properties have developed and why it is that large strains are of particular interest. This is also of importance in efforts to understand the differences responsible for tough and brittle fracture.