Stress-strain behavior of high-density polyethylene below the yield point: Effect of unloading rate

The stress-strain behavior of HDPE under uniaxial tensile drawing below the yield point is discussed. Special attention is placed on studying the tensile loading-unloading diagrams at different unloading rates. Experimental data are analyzed in terms of a set of two-phase basic structural mechanical elements, which take into account the plastic flow and structural rearrangements of both hard and soft components. Parameters of these elements are calculated by optimal fitting of theoretical curves to an arbitrary experimental tensile loading-unloading curve measured at a constant strain rate. This approach allows description of a decrease in the residual strain with decreasing unloading rate at fixed model parameters. The physical nature of the observed deformational effects is considered.