Impact fracture of polyethylene: A non-linear-elastic thermal decohesion model

Abstract

A model for brittle dynamic and impact fracture of tough polymers has recently been proposed, according to which a crack-tip Dugdale craze fails by melting of a thin layer at each cohesive surface. A plane-stress, linear-elastic formulation accounted for the measured dynamic fracture resistance to within the accuracy of measurement, and for the variation of impact fracture resistance with impact speed, in two pipe-grade polyethylenes; but the predicted impact fracture toughness G c was in error by a factor of up to two. It is shown here that a pseudoelastic formulation, which accounts for non-linearity of the impact load/displacement trace due to craze extension as well as to non-linear elasticity, corrects these shortcomings. Impact fracture behaviour of a medium density and modified high-density polyethylene between −20 and 23°C, which embraces a transition to notch-ductile behaviour, is predicted using stress/strain and thermal property data only.