Torque cycle fatigue of wire ropes
Running ropes have a limited service life. Material fatigue is caused by oscillating bending stress as the rope runs over sheaves and by pulsating tension-tension stress during service. Oscillating bending stress and fluctuating tension-tension stress may occur simultaneously too. Depending on the application, one of these forms of loading is predominant. In applications with friction winders and high lifting heights such as occur in the mining industry, the rope opens and closes itself in a cyclic manner while running through the shaft. These torque stresses also lead to material fatigue. Beyond a certain shaft depth material fatigue is caused mainly by the torsional stress. The service life of ropes stressed by pulsating or oscillating torque has been hardly explored until now. In the following, torque tests will be reported and an equation for describing the expected service life will be introduced.
Author: U. Briem