Damage evolution in high density polyethylene under tensile, compressive, creep and fatigue loading conditions

Influence of various loading histories on mechanical properties and damage evolution of polyethylene (PE) is quantified through a two-stage test method. The first-stage tests are to introduce damage by subjecting the specimens to different prestrain levels under tensile, compressive, creep and fatigue loading condition. Two months later, the second-stage tests apply monotonic tensile loading at a crosshead speed of 0.01 mm/min to characterize the mechanical properties for specimens that have had damage generated in the first-stage tests. Experimental results suggest that yield stress and loading stiffness decrease and residual plastic strain increases with the increase of prestrain introduced in the first-stage tests. Damage evolution law, based on the degradation of loading stiffness has been established as a function of prestrain and residual plastic strain. Results show that damage variable expressed as a function of prestrain strongly depends on loading conditions applied in the first-stage tests. However, damage evolution described by the relationship between damage variable and plastic strain is found to be independent on the loading condition, suggesting that a unified, plastic strain controlled damage evolution law can be established for PE materials.