Influence of the loading rate on the fracture resistance of isotactic polypropylene and impact modified isotactic polypropylene

摘要

The fracture behaviour of an isotactic polypropylene and an impact modified isotactic polypropylene containing 15wt% of ethylene-propylene rubber has been investigated at test speeds of between 0.1 mm/s and 14m/s, using compact-tension specimens. The homopolymer displayed a ductile-brittle transition as the test speed was increased, which was associated with a transition from shear deformation to crazing.Deformation of the modified polypropylene was characterized by stable crack tip and,at lower speeds, by the formation of extensive shear lips on the fracture surfaces. An observed increase in the size of the crack tip damage zone with test speed suggested a transition from plane stress to plane strain conditions. This is discussed in terms of a simple model, which takes into account the variation of the sample stress state as the test speed increases.