Molecular dynamics simulation of amorphous polyethylene (PE) under cyclic tensile-compressive loading below the glass transition temperature

摘要

The intensive applications of polymer in many engineering composites have imposed an urgent need on the understanding of the mechanical behavior and deformation mechanism of the polymer under cyclic loading. This paper presents the results of a numerical study on the behavior of amorphous polyethylene (PE) subjected to cyclic tensile and compressive loads using molecular dynamics (MD) simulations, based on a united-atom approach. The effects of polymer chain length, the number of chains and strain rates are studied at first. Hysteresis loops, as well as visco-elastoplastic of PE under cyclic loading predicted by MD simulations are qualitatively in agreement with previous experiments. Three distinct hysteresis loops observed in successive loading-unloading reveal the contribution of elasticity, viscosity and plasticity under different loading strains, respectively. The rubber-like recovery behavior of PE at low temperature is attributed to that the mobility of molecular chains is constrained at low temperature. Energy analysis shows that the van der Waals energy and dihedral angle energy are considered to be the primary factors that affects the cyclic behavior of PE.