ANALYSIS OF THE NONLINEAR CREEP OF HIGH-DENSITY POLYETHYLENE

Short- and long-term tensile creep tests of high-density polyethylene (HDPE) have been performed at different stress levels under an ambient temperature of 20 degrees C. The effects of stress and physical agein g on the creep compliance are studied. The short-term creep data show that the distribution of relaxation times of HDPE is shifted even by a very low stress. Acceleration of creep can be realized by applying hi gh stresses, and a momentary master curve of creep compliance can be c onstructed using the time-stress superposition principle. At low stres ses, though the material exhibits strong non-linearity, the ageing rat e mu is found to be independent of stress. A unified non-linear creep relation is obtained that incorporates the physical ageing effect and predicts the long-term creep behaviour with good agreement with experi ments.