The influence of twist on tension-tension fatigue of wire ropes

The lifetime prediction of wire ropes subjected to tension-tension loading (T-T loading) and twist due to height-stress is an issue specifically related to ropes suspended over large differences in height (for example offshore mooring lines, mine hoisting ropes and ropes in aerial ropeways). When suspended over a huge difference in height wire ropes are subject to a higher tensile stress at the upper end than at the lower end due to their own weight. Though terminated and non-rotating at both ends the tension-tension loaded wire rope undergoes different conditions of twist along its free length. In the past, test programs for determination of the T-T fatigue life of wire ropes had their focus on “perfect lab conditions”. Though it obviously occurs in reality, any form of twisting of the rope was explicitly excluded in laboratory tension-tension testing. Thus, up to date the influence of twist on the tension-tension fatigue life of wire ropes is mostly unknown. Currently, the Institute of Mechanical Handling and Logistics (IFT) of Stuttgart University investigates this issue for the first time by means of an extensive experimental test program funded by the German Research Foundation (DFG). The intention is to quantify the influence of twist on the tension-tension fatigue life and to get a deeper understanding of the interaction of the predominant failure mechanisms. The work described in this article is part of a research program still in progress. The authors expect to make additions and slight revisions to statements, data, graphs and conclusions presented in this paper after all experiments have been performed, all data has been gathered and all analyses have been undertaken.

Author(s): B. Ernst and K.-H. Wehking