Bending Fatigue


Fatigue damage is a typical phenomenon which is not caused by a single event, but by repeated bending, tension and rotational stresses: since the working life of wire ropes generally involves repeated passages over drum and sheaves, this damage has to be carefully considered during operations.


The first factor to be considered with respect to fatigue damage is the working load: taking a safety factor of five as a reference point, relative service life of rope operating in the same system with different loads is shown in the first figure.

Fatigue damage occurs gradually, and becomes evident when it reaches a point where it has caused a high number of broken wires and consequent wire elongation, which rapidly increase to reach wire rope discard criteria.

The typical trend of fatigue growth is shown in the second graph: it is clear that there is a rapid increase in the curve slope after a certain threshold, and this is strongly affected by working load. 







Fatigue: Progressive and localised damage due to cyclic stress.