Molecular dynamics study of axial tensile response of crystalline ultra-high molecular weight polyethylene under different loading conditions

Through molecular dynamics simulations, we investigated the effects of temperature on the axial tensile behavior of ultra-high molecular weight polyethylene (UHMWPE) crystals, considering the combined effects of transverse compression, strain rate, and molecular weight. The effects of temperature over the range of 100 K to 450 K is shown to reduce the mechanical properties. Existing chain end defects facilitate chain sliding and induce stress concentration in adjacent molecules, thereby reducing the strength and modulus of crystals. Lower molecular weight and higher temperatures promote chain sliding, while higher transverse compression and increased strain rates inhibit chain sliding, resulting in higher properties. Additionally, higher temperatures increase stress concentration due to thermal vibrations, which induce localized high stress conditions within polyethylene chains. The transition of the failure mode from chain sliding to bond breakage occurs at strain rates between 10¹² s⁻¹ and 10¹³ s⁻¹, and is found to be independent of temperature, pressure, and molecular weight. The results are compared to the response of crystals without chain end defects. These insights contribute to a deeper understanding of the behavior of UHMWPE crystals under extreme loading conditions.