Experimental study on stable growth of crack and craze damage in HIPS under tension at room temperature

This study focuses on investigating the stable damage and crack growth process of high impact polystyrene (HIPS) by using the damage mechanics approach and the moire method. Under excessive tensile loading, HIPS will be damaged due to multiple crazing that causes volume dilatation. A damage variable is defined by the dilatation of the representative volume element to characterize the craze-damage. The relationship between the dilatation and the total strain has been determined experimentally. A specimen with a sharp initial discontinuity is tested under tensile force to study the damage and crack growth process. It is observed that an elliptical damage zone is formed in front of the crack tip. The crack propagation is stabilized by the damage zone. Moire fringe patterns show that the deformation within the damage zone is non-uniform. A dynamic configuration of deformation, which comprises the elastic zone, the transition zone, the damage processing zone, and the residual damage zone, has been established. The non-linear strain and stress fields inside the transition zone and the damage processing zone are analyzed. The experimental result also shows that a critical plastic strain criterion may be used to predict the stable growth of macrocracks for HIPS.