Predicting failure from the initiation stage of slow crack growth in polyethylene

Abstract

The crack opening displacement against time was measured in linear polyethylene as a function of stress, notch depth, and temperature for three-point bending under plane strain conditions. The experimental conditions were accurately controlled so that the scatter in the rate of damage was within ±20%. Microscopic observations showed that the shape of the damaged zone was triangular for stresses less than one-half the yield point and that the length was predictable from measurements of the crack opening displacement. The initial rate of damage prior to crack growth was constant up to crack opening displacement = 15 to 25Μm. The entire shape of the crack opening displacement-time curve and the time to complete failure could be predicted from the initial damage rate. A theory based on the observed microcrazing is presented which explains the dependence of damage rate on stress intensity and microstructural parameters.