Fatigue behaviour of closed-cell polyurethane rigid foams

This paper investigates the compression-compression fatigue behaviour of polyurethane rigid (PUR) foams of three relative densities (RDs): 0.0854, 0.1239 and 0.2564 respectively. Preliminary tensile and compression tests were performed in order to obtain the stress–strain characteristics of the investigated materials and to determine the yield stresses in compression, required for the establishment of the relative stress levels used in the fatigue tests. It was observed that the failure mechanism during fatigue consisted in the collapse of a region of the specimens, which was characterized by a sudden increase in strain. In consequence, stress–strain cycles were recorded at various cycle intervals in order to narrow the degradation cycle interval. The resulting compression-compression fatigue curves show a similar behaviour between the RDs of 0.0854 and 0.1239 (with the latter exhibiting the best fatigue strength of the three investigated RDs), that can be described by a single trend line for each, while the foam at 0.2564 RD showed the lowest fatigue strength, the curve being characterized by two regions.