Initiation of crazes in polystyrene

Abstract

The initiation of crazes on surfaces of unoriented polystyrene, free of plastioizers, having controlled micro-roughness, has been studied under different combinations of deviatoric stress and negative pressure, in tension-torsion experiments, at both room temperature and – 20°C. These experiments show that the delay time for craze initiation decreases and the saturation craze density increases with increasing deviatoric stress or negative pressure. Experiments performed on individual polystyrene pellets free of entrapped foreign particles, and having microscopically featureless, smooth surfaces, have established an intrinsic crazing phenomenon distributed throughout the volume. A theoretical, micro-mechanical crazing model is presented which accounts satisfactorily for all the observed features of crazing under a multi-axial state of stress, and predicts the stress level for intrinsic crazing.