Static Torsion and Torsion Fatigue of UHMW-PE and Aramid Filaments

The effects of pre-tension and torsion angle on the torsion fatigue lifetimes of high performance fibers (HPFs), including three p-aramid fibers (Twaron^® 2000, Kevlar^® 29 and Kevlar 129) and ultra high molecular weight polyethylene fiber (UHMW-PE), were studied by means of a self-made torsion fatigue tester. The torsion fatigue performance of the HPFs were characterized and compared. The fracture-end morphology of these fibers after the fatigue tests was observed by scanning electron microscopy (SEM) to seek to explain the fracture mechanism of the fiber fatigue. The experimental results indicate that there was a linear relationship between the logarithm of the fatigue lifetime and the pre-tension or torsion angle for the high performance p-aramid fibers, and the order of torsional fatigue lifetime for the four fibers was UHMW-PE ≥ Kevlar^® 129 ≥ Kevlar^® 29 ≥ Twaron^® 2000. Furthermore, the torsion-to-rupture test showed that the property of torsion to rupture relies on the twist transfer along the fibers, and the degree of twist transfer (DTT) for the UHMW-PE and aramid fibers was also in the order of UHMW-PE ≥ Kevlar^® 129 ≥ Kevlar^® 29 ≥ Twaron^® 2000.