Compressive double yielding in high-density polyethylene over a wide range of strain rates

Abstract

We investigated the effects of the strain rate on compressive yielding in high-density polyethylene at the strain rates from 10−5–103 s−1. High strain rates promoted distortion in the crystalline lattice, leading to the martensitic transformation from the orthorhombic to monoclinic phase. We explained the strain-rate dependence of the stress by two Eyring processes assigned to the crystalline and amorphous deformation in the low- and high-strain-rate regions, respectively. The crossover strain rate drastically decreased with increasing molecular weight, which we ascribed to an increased fraction of stress transmitters. We attributed the strain-rate dependence during compression to tie molecules and/or tie links (i.e. the amorphous chains that connect lamellar crystals to each other).