Macroscopic criterion for craze initiation in polystyrene

Abstract

Macroscopic failure of polystyrene has been investigated under pure shear and simple tension by isochronal static tests in air at room temperature. A number of crazes were clearly observed under both stress states. The craze initiation identified under pure shear provides an obvious counterevidence to the current criteria, which involve explicitly the dilatational stress term as a requisite for craze initiation. A criterion expressed by a product form of the maximum principal stress and the maximum principal shear stress with an isotropic stress term was examined. The proposed criterion was marked to predict a priori a peculiar feature that the craze initiation never takes place under biaxial compression. A theoretical ratio of critical stress for craze initiation under pure shear to that under simple tension coincided with the experimental result.