Fatigue crack growth in polyurethane foam

The growth of fatigue cracks in compact tension specimens of rigid polyurethane foam has been studied at room temperature under conditions of constant load-amplitude cycling. The growth of the cracks at the frequencies employed (0.2 Hz) is found to be reasonably reproducible and the growth rate can be related to the cyclic stress intensity range in the conventional way. The rate of growth of the cracks is also found to depend on the mean stress level and an attempt has been made to separate out the effects of stress-intensity range, K, and the maximum stress intensity in each cycle, K_max, by combining the data obtained under a variety of loading conditions.