Our latest paper, "Molecular dynamics study of axial tensile response of crystalline ultra-high molecular weight polyethylene under different loading conditions," is accessible freely for 50 days from this link:
https://doi.org/10.1016/j.polymer.2024.127564
Our MD simulations reveal that temperature has a significant effect on the strength of UHMWPE fibers. We found that crystals begin to melt around 475 K, resulting in a total loss of strength. For a 20 nm long chain with an initial strength of 3.3 GPa, applying transverse compression above 5 GPa or a strain rate exceeding 10^12 s-1 shifts the failure mode from chain end sliding to chain scission, increasing strength by over fivefold.
We also observed that increasing molecular weight can enhance strength up to 7.2 GPa, an improvement of approximately 120%. However, the presence of chain ends changes the failure mode from bond breaking to chain sliding, leading to a significant 61% drop in strength (from 18.3 GPa to 7.2 GPa). While our simulations predict UHMWPE fiber strength at 300 K to range between 7.2 GPa and 18.3 GPa, experimental results show strength around 3.5 GPa. This discrepancy is mainly due to microstructural defects, such as voids, wavy chains, amorphous regions, and interphases within the fibrils.
This study marks the beginning of our efforts to use MD simulations to model a single UHMWPE fibril, incorporating its complex microstructural features and interfaces, to enable more accurate multiscale finite element modeling.