Creep life assessment craze damage evolution of polyethylene methacrylate

Tests have been conducted to investigate the influence of temperature, stress, and crazing for polyethylene methacrylate (PMMA) creep life. Creep life decreases with stress in a logarithmic relation, and rupture strains increase with decreasing stress. To assess the creep life of PMMA, the Larson–Miller parameter is first introduced to correlate stress and temperature with rupture time. The important role of crazing in polymer material damage, especially, the craze density and craze growth rate in the stable creep stage, is demonstrated. The craze initiation time is related to the tensile strength and to the stress and temperature at the elastic limit, and the craze initiation time can be predicted by an empirical model subsequently presented in this paper. Based on the connection between craze growth and creep rupture time, thereafter, a modified Monkman–Grant model is presented to predict creep life. The curve of craze density over creep time has the same two distinct stages as the curve of strain over time. In the final sections, a critical assessment of creep damage is also presented to provide a convenient method to predict residual life using only craze density.