Structure-mechanical property relationships in engineering polymers

An overview is given of recent work in our laboratory aimed at exploring structure-mechanical property relationships in engineering polymers. This has involved both model systems and systems with direct relevance to practical industrial problems. However, the emphasis has always been on characterization in terms of intrinsic materials parameters and investigation of the underlying microdeformation mechanisms. Particular effort has gone into extending the range of test conditions over which fracture mechanics parameters such as K-IC or G(IC) may be determined rigorously using simple geometries, up to and beyond speeds characteristic of impact tests. Alternative concepts such as the essential work of fracture have also been introduced in cases where linear elastic fracture mechanics fails to provide an adequate appreciation of the intrinsic behaviour of relatively ductile polymers. At the same time, microscopical techniques have been developed that give access to detailed information on the nature and extent of mechanically induced damage in specimens with different geometries, including bulk fracture specimens. In certain systems, this has made it possible to establish quantitative links between macroscopic fracture properties and microscopic parameters such as the number of covalent bonds crossing unit area of the crack plane.