Design modifications to increase fatigue life of fiber ropes

This paper describes a two-phase program on cyclic bend-over-sheave (CBOS) fatigue testing of 40 mm diameter fiber ropes. A test method that simulates heavy marine CBOS applications proved to be a repeatable measure of fatigue resistance. Cycles-to-failure data are presented for ropes made from high-strength fibers of high modulus polyethylene (HMPE), liquid crystal polyester (LCP), and LCP/HMPE blends. A method for pathological examination of fatigue-damaged braided ropes is described, and a map of observed interior damage is presented. The results of the first phase of fatigue testing, coupled with observations from the post-mortem examinations, suggested possible damage mechanisms. Fatigue life in the second phase of testing was increased by more than 100%, by modifying rope designs so as to preclude or delay failure modes observed in the first phase.