Effects of different loading methods in molecular dynamics on deformation behavior of polymer crystals

Thermoplastics have a crystal structure. It has been pointed out that the crystalline structure affects viscoelastic behavior in crystalline polymers, which must be taken into account in MD simulations. In this study the crystalline lamellar structure of Polyethylene (PE) was reproduced via molecular dynamics. To investigate the mechanical behavior and deformation behavior of the lamellar structure of PE, deformation was applied to the model under a constant tensile rate and constant tensile load as tensile and creep analyses, respectively. A tensile analysis indicated localized cracking, and a creep analysis revealed molecular-chain undulation along the tensile direction. To clarify the reason for the difference in deformation distribution between tensile and creep analyses, the potential energy during tensile loading was examined. In the tensile analysis, all the potential energies increased at the start of tension development and decreased rapidly at the break. As revealed in the creep analysis, the bond stretching and bond angle potential energies did not change when deformation started at a strain of approximately 0.20. These results indicated that the deformation behavior depended on the loading configuration, such as tensile and creep loading, and that deformation behaviors vary because of differences in displacement distribution and potential energy.