Anisotropic mechanical response of UHMWPE crystals under hydrostatic pressure and elevated temperature: a molecular dynamics study

Abstract

This study presents an atomistic investigation of the pressure- and temperature-dependent behavior of ultra-high molecular weight polyethylene (UHMWPE) crystals under multiaxial loading. Using molecular dynamics, we evaluate the anisotropic stress–strain responses under tension, compression, and shear along the three principal crystallographic directions. The results reveal pronounced anisotropy driven by chain orientation and direction-specific deformation mechanisms, including covalent bond stretching, chain buckling, and interchain slip. Hydrostatic pressure enhances both modulus and strength in most configurations, apart from axial tension along the chain direction, where covalent interactions give high strength but limited pressure sensitivity. At 400 K, relevant to elevated-temperature processing and consolidation, stiffness and strength fall in the transverse directions, which are governed by interchain van der Waals interactions, with the a-direction tensile strength dropping by over 50%. We report direction-resolved pressure-coefficient sets for twelve loading modes at 300 K over 0–6 GPa, with a 400 K cross-section for four modes. The chain-direction modulus exceeds the softest transverse modulus by about a factor of 60, and the transverse tensile and compressive moduli fall by roughly 27%–49% as temperature increases from 300 to 400 K.