ABSTRACT
The failure of engineering components through fracture can have catastrophic consequences and much effort has been put in by materials scientists and engineers in developing materials and designing structures that are resistant to premature failure through fracture. It is possible to classify materials as being either brittle like glass which shatters readily or ductile like pure metals such as copper or aluminium which can be deformed to high strains before they fail. Polymers are found to display both types of behaviour depending upon their structure and the conditions of testing. In fact, the same polymer can sometimes be made either brittle or ductile by changing the temperature or rate of testing. Over the years, some polymers have been advertised as being “unbreakable.” Of course, this is very misleading as every material can only withstand limited stresses. On the other hand, domestic containers made from polymers, such as polypropylene or low-density polyethylene, are remarkably tough and virtually indestructible under normal conditions of use.
