A Study of Environmental Stress Cracking in Non-Crystalline Plastics

The primary aim of this project was to investigate the initiation and propagation of brittle fracture in plastics on crazing liquids and to establish a mechanism of solvent crazing. As a background to this the fracture process in air has also been studied. Concurrent studies of mechanical properties and fracture morphology have been undertaken. Craze initiation strains for plastics in liquids were found to alter with temperature in a manner. which correlated with the softening effects of the liquids on the plastics. This indicated a plasticisation mechanism was operative in solvent crazing. The morphological studies suggested that a change in fracture behaviour of polystyrene in organic liquids over a narrow temperature range could be due to a glass-to-rubber transition in the craze material brought about by plasticisation at the craze tip. The research to be described was carried out during the period April 1968 to November 1971 at Yarsley Research Laboratories, Chessington, Surrey under the guidance of Mr. R.J. Loneragan (Royal Armament Research and Development Establishment), Mr. M.A. Crook (Polytechnic of the South Bank) and Mr. L.W. Turner (Yarsley Research Laboratories Ltd.)