Effects of Transverse Compression on the Structure and Axial Properties of Polyethylene: A Molecular Simulation Study

Abstract

In this paper, the effects of transverse pressure on the structure and axial tensile properties of polyethylene (PE) crystals have been studied using all-atom molecular dynamics (MD) simulations. In the MD simulations, the inter-atomic interaction is modeled by the modified adaptive intermolecular reactive bond order (AIREBO-M) force field. Hugoniot equation of state of the PE crystal is developed using isotropic compression simulations. To investigate the transverse pressure effects, both the pristine and defective crystals (i.e., crystal with chain ends, equivalent to fibril) are subjected to axial tensile loading at different levels of transverse pressure from 0.0 to 20 GPa, and the tensile properties are predicted as functions of transverse pressure. Simulation results show that the transverse pressure significantly affects the tensile properties of PE especially for the fibril models by intensifying the inter-molecular interactions and changing the damage modes from chain end slippage to chain scission. At the highest level of transverse pressure, the improvement in modulus is predicted to increase by 50% for both pristine and defective crystal. Tensile strength is predicted to increase by 44% and 290% for the pristine and defective crystals, respectively These predictions provide insight into the response of UHMWPE subjected to high velocity impact where strain rates and transverse pressure loading are orders of magnitude greater than quasi-static loading at ambient pressure conditions.