Strain rate effects on the axial tensile behavior of crystalline polyethylene: Insights from molecular dynamics simulations

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During a transverse impact, ultra-high molecular weight polyethylene fibers within the laminates experience axial tension over a range of high strain rate loading. We employed molecular dynamics simulations to explore the influence of strain rate on the axial tensile behavior of polyethylene crystals, both with and without chain end defects. When the strain rate increased from 1010 s−1 to 1013 s−1, polyethylene crystals without chain ends showed an approximate 60% increase in strength. This increase can be attributed to the fact that higher strain rates impede the relaxation of individual polymer chains, compelling them to store more energy. Furthermore, our results revealed that the strength of crystals with short chains improved more than sevenfold when the strain rate increased from 1010 s−1 to 1013 s−1. This substantial strength increase can be mainly attributed to the transition of the failure mode from chain end sliding to chain scission at multiple locations along each chain. This transition occurs when the loading velocity surpasses the maximum speed at which chains can slide. Additionally, our simulations find that the effect of strain rate on the modulus and strength of crystals initiates at relatively lower strain rates as the molecular weight increases.