Various sizes of localized zones as mechanisms of effects of strain rates on high‐density polyethylene

Abstract The mechanisms governing the effects of strain rates on high‐density polyethylene (HDPE) remain unclear. This study presents an evaluation of the differences in evolving strain and strain rate fields in HDPE samples under varying strain rates to identify mesoscopic mechanisms influencing these effects. The results reveal that the distributions of strain and strain rate over time vary with different strain rates. A high strain rate inhibits the development of plastic regions and necking propagation, leading to premature fracture without strain hardening. Based on the evolving properties of transverse strain rate distributions, this study proposes a method to define the size of the necking localized zone. Faster strain rates result in smaller localized zones in HDPE samples. The variation in the necking localized zone sizes is a key factor influencing the differences in yield stress, stress at the plateau stage, stress drops during the softening stage, strain involved in the softening phase, final elongation, and other mechanical properties. Additionally, increasing strain rates restrict necking propagation in HDPE samples, and the size of the necking localized zones is identified as the mesoscopic mechanism through which strain rates exert their effects. Our results show that the yield strength increases as a power‐law function of strain rates. These findings suggest that considering the size of the necking localized zones and their impact on necking propagation in theoretical and numerical models is crucial for understanding strain rate effects on HDPE and improving deformation evaluation in practical engineering. Highlights Necking zone size differences drive strain rate effects in HDPE. High strain rate inhibits necking, causing premature fracture in HDPE. A method defines the necking zone via transverse strain distribution. Necking zone size decreases as tension strain rates increase. Yield strength follows a power law function of tension strain rates.