Structure-mechanical property relationships in engineering polymers

An overview is given of recent work in our laboratory aimed at exploring st ructure-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 characteriza tion in terms of intrinsic materials parameters and investigation of the un derlying microdeformation mechanisms. Particular effort has gone into exten ding 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 concep ts such as the essential work of fracture have also been introduced in case s where linear elastic fracture mechanics fails to provide an adequate appr eciation 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 dama ge in specimens with different geometries, including bulk fracture specimen s. In certain systems, this has made it possible to establish quantitative links between macroscopic fracture properties and microscopic parameters su ch as the number of covalent bonds crossing unit area of the crack plane.