Effect of strain rate on stepwise fatigue and creep slow crack growth in high density polyethylene

The effects of frequency and R-ratio (the ratio of minimum to maximum stres s in the fatigue loading cycle) on the kinetics of step-wise crack propagat ion in fatigue and creep of high density polyethylene (HDPE) was characteri zed. Stepwise crack growth was observed over the entire range of frequency and R-ratio examined. A model relating crack growth rate to stress intensit y factor parameters and applied strain rate was proposed by considering the total crack growth rate to consist of contributions from creep and fatigue loading components. The creep contribution in a fatigue test was calculate d from the sinusoidal loading curve and the known dependence of creep crack growth on stress intensity factor in polyethylene. At a very low frequency of 0.01 Hz, fatigue crack growth rate was found to be completely controlle d by creep processes. Comparison of the frequency and R-ratio tests reveale d that the fatigue loading component depended on strain rate. Therefore, cr ack growth rate could be modeled with a creep contribution that depended on ly on the stress intensity factor parameters and a fatigue contribution tha t depended on strain rate. (C) 2000 Kluwer Academic Publishers.