We investigated compressive deformation of high-density polyethylene (HDPE) over a wide range of strain rates. The compression tests were conducted by using a split-Hopkinson bar apparatus at 103 s-1, a custom-built cam plastometer at 101-100 s-1, and a universal testing machine at 10-1-10-5 s-1. The microscopic deformation mechanism was interpreted by considering the slippage of a single polymer chain, based on the Eyring’s plastic deformation model. The slippage distance ΔD at low strain rates was significantly smaller than the lamellar crystalline thickness, suggesting that local crystalline deformation was dominant. The increase of the strain rate resulted in a significant increase of ΔD beyond the long period, suggesting that the amorphous network embedded in the lamellar alternating structure induced interlamellar deformation. The interlamellar deformation was enhanced for HDPE with high molecular weight presumably owing to the increase of the tie molecules and the tie links as the stress transmitter. Further increase of the strain rates above 101 s-1 reduced ΔD comparable to the lamellar crystalline thickness, suggesting that crystalline deformation was promoted by hardening of the amorphous layer.
MORIYAMA et al. (Thu,) studied this question.