Time-temperature-stress equivalence and its application to nonlinear viscoelastic materials

Stress-dependence of the intrinsic time of viscoelastic materials is investigated. The influence of stress level on the intrinsic time is considered to be similar to that of temperature, pressure, solvent concentration, damage and physical aging. The time-temperature-stress equivalence principle is proposed, by employing which, the creep curves at different temperatures and stress levels can be shifted into a master curve at reference temperature and stress level. Thus the long-term creep behavior of viscoelastic materials at a lower temperature and stress can be predicted from the short-term one at a higher temperature and stress. As an example, the nonlinear creep behavior of high-density polyethylene (HDPE) at room temperature is studied using the time-temperature-stress equivalence principle presented. Project supported by the National Natural Science Foundation of China (No. 19632030, 50003005) and by the Education committee of Human Province (No. 99C122).