Tech-Info 09.2: What is the bending fatigue strength?

The bending fatigue strength of a wire rope is defined as the number of bending cycles a rope can achieve in fatigue bending test under specified conditions (for example, running over sheaves with a defined diameter and a specified line pull in relation to the rope’s minimum breaking load). The fatigue bending strength of a rope is increased by increasing the D/d ratio (= sheave diameter D: nominal rope diameter d) and by reducing the strand load. The bending fatigue strength of a wire rope can be increased by enlarging the contact area between the wire rope and the sheave and by enlarging the contact areas between the rope elements, for example by a plastic insert between IWRC and the outer strands. Due to the larger contact area between rope and sheave and greater flexibility, 8-strand wire ropes have a higher bending fatigue strength than 6-strand wire ropes of comparable make.