EFFECT OF HIGH STRESS ON THE AGING BEHAVIOR OF HIGH-DENSITY POLYETHYLENE

The influence of large applied stress on the tensile creep and stress relaxation properties of high density polyethylene (HDPE), quenched from 100°C and aged for various times at room temperature, has been investigated. From the creep experiments it was concluded that physical ageing effects persisted up to at least an applied stress of 20 MPa when a new sample was used for each creep experiment. However, the effects of the ageing appeared to be partially diminished at the highest stress levels used here. A high stress pulse was found partially to erase previous ageing and reactivate the ageing process. In the stress relaxation tests attention was focused on the internal stress level, σi. It has earlier been observed that σi increases with ageing time. This dependence of the internal stress on ageing time was found to persist up to high deformations. Only at very high initial stresses, well beyond the yield point, was σi unaffected by the ageing time. The influence of physical ageing on the stress relaxation behaviour was also studied for HDPE filled with glass spheres. © 1990.