Bending fatigue in high-strength fibre ropes

Abstract

Bending fatigue tests on parallel lay (Parafil) ropes of the aramid fibre Kevlar 49, and helically laid ropes of Kevlar 29 and high-modulus polyethylene (HMPE) are reported. The Parafil ropes were subjected to three different regimes: free bending-tension tests intended to produce failures at the mouth of a termination, sheave bending through 45° under varying axial load, and sheave bending through 180° at constant axial load. The Kevlar 29 and HMPE ropes were tested over a 180° sheave. Full descriptions of the various procedures are given, and more than 20 separate results presented. Although the free bending-tension tests were intended to produce failures at the mouth of the termination, most failures occured elsewhere: one test was stopped after one million cycles. The 45° sheave bending tests produced lifetimes of about 4000 cycles when tested at up to 50% of the static breaking strengh. The 180° sheave bending test gave lives of 157 cycles at 25% of the static breaking load (SBL) for the Parafil ropes, and 100 to 400 cycles at about 40% SBL for the helically laid Kevlar 29 ropes. The HMPE rope gave nearly 6000 cycles at a load of 40% SBL.