The role of crazes in the crack growth of polyethylene

Brittle slow crack growth, or stress cracking, is a major concern in many applications of polyethylene materials, including piping used in natural gas distribution. Using a constant tensile load test and removing specimens prior to complete failure, details of the crack tip region can be discerned in both butene and hexene copolymerized polyethylene. In both the presence and absence of an accelerating environment (Igepal CO-630), it was found that crazes formed at the crack tip, although secondary crazes were also evident in the specimens removed from the Igepal. Multiple crack arrest lines were clearly evident, suggesting a stick--slip mechanism under static load. The appearance of the craze zone at the crack tip can be explained through invoking an interlamellar failure model. 16 ref.--AA