Modelling of creep behaviour in injection-moulded HDPE

Tensile creep experiments on HDPE with a duration of 8 weeks were performed at a temperature of 23 degrees C. Since the tests were performed 32 weeks after moulding of the specimens, the effect of ageing during creep can be n eglected. The creep strain can be fitted up to 5% using the Leaderman model in terms of true stress and true strain. However, the yielding ar larger s train levels cannot be described with this model. A good fit of the creep d ata, including yield behaviour, is obtained with a model of two processes i n parallel, each having its own time-stress shifting function. Predictions of this model for constant strain rate experiments show good agreement with observations. (C) 2000 Elsevier Science Ltd. All rights reserved.