Analysis of the notch tip damage zone in biaxially oriented polypropylene

The circular notch tip damage zone in biaxially oriented polypropylene has been analyzed using a thickness correction to the elastic stress distribution for a sharp‐notched tension specimen. The size and shape of the damage zone as a function of applied stress followed a critical mean stress criterion, independent of specimen thickness. Also, the damage zone only grew while σ 3 was greater than zero. Close observations of sections through the damage zone revealed that the circular zone, which consisted of many delamination crazes, had a distinctive pattern when viewed across the thickness difection. Large crazes grew into a triangular pattern with smaller crazes in between them. The shape developement of the triangular profile as well as the smaller crazes was explained using a stress‐redistribution argument. The growth path of the delamination crazes in the x‐z plane appeared to be in a direction perpendicular to the direction of σ 3 . © 1994 John Wiley & Sons, Inc.