The fracture behaviour of uPVC at both ambient and high hydrostatic pressures

Abstract

Fracture measurements have been made using a high pressure technique on three batches of uPVC corresponding to distinct levels of gelation.K _c values correlate with methylene chloride attack in the established manner, but are low in comparison with room pressure values measured at comparable strain rates. This is linked with the presence of stress whitening on the fracture surface at room pressure, its absence at high pressure, and its diminution at room pressure when testing speed is increased, when lowK _c values are also recorded. The results are successfully interpreted in terms of a multiple craze slow crack growth model, in which cracking in the tests at room pressure and slow speed is assumed to start at theK _c measured at high pressure, and slow crack growth follows as the load on the specimen continues to increase until the specimen fails catastrophically. A reasonable choice of parameters then gives a good prediction of the observed collapse loads.