Improving Yarn-on-Yarn Abrasion Test Geometry for High Modulus Fibers
Test methods ASTM D6611 and CI 1503 were developed to measure yarn-on-yarn abrasion resistance directly, e.g. to evaluate the effectiveness of marine grade finishes in low modulus commodity fibers such as nylon and polyester. However, similar yarn-on-yarn abrasion data from high modulus fibers have not correlated well with CBOS life across a variety of rope constructions. Aramid, LCP, and HMPE fibers break at relatively low fatigue cycles when tested under tensions typical of high cycle rope service. In this study, first order analysis of the standard geometry of the ASTM/CI methods demonstrates that fibers are subjected to severe bending in addition to abrasion. The recommended yarn-to-yarn contact angle of 34 degrees can result in effective D:d ratios of less than 4:1 and a double-bend on each fatigue cycle. Experimental evidence suggests contact angles should instead be limited to less than 12 degrees to limit non-abrasive damage mechanisms. Effects of other test parameters, such as number of fiber wraps, were also studied. A general solution for the 3-pulley yarn-on-yarn test geometry is presented as an Appendix.
Author(s): F. Sloan, K. Ikehata