Inter-molecular interactions in ultrahigh molecular weight polyethylene single crystals

Abstract

This paper investigates the inter-molecular interactions during tensile loading in ultrahigh molecular weight polyethylene (UHWMPE) single crystals at the atomistic scale. Molecular dynamics (MD) simulations of velocity controlled chain pullout are employed to study inter-molecular load transfer mechanisms. The transfer of tensile load is governed by van der Waals forces that dominate the inter-molecular shear interactions. The tensile stress build up occurs over a length of approximately 40c, where c is the lattice constant along the chain axis. Atomistic MD models incorporate the influence of surrounding neighboring atoms. Therefore, a nonlocal shear lag continuum model is developed for the first time to bridge length scales by extending the classical shear lag model of stress transfer in composites. The nonlocal model predictions correlate better with the MD results compared to the classical shear lag formulation. Combining the MD and shear lag model results, a bilinear mode II cohesive traction-separation behavior is identified to describe the inter-molecular interactions of the continuum with interface stiffness (2.38 GPa/nm), peak traction (0.14 GPa) and mode II fracture toughness (17 mJ/m2).