Avoiding fiber axial compression fatigue in the design and use of tension members

Fiber axial compression fatigue is a unique form of damage which can occur in ropes, cables and other tension members. It can occur during cyclic tension loading, when some fibers go into compression as overall tension on the rope is relaxed. It can also occur under other circumstances, such as when the rope is bent or rotated. In most forms of fatigue, the mechanism is progressive, meaning it increases in intensity as fatigue damage develops. A familiar example is crack propagation fatigue during tension cyclic loading of metals. But the mechanism in fiber axial compression fatigue is regressive, meaning it decreases in intensity as fatigue damage develops. Axial compression fatigue only takes place in those fibers which become slack and go into compression. As this occurs when tension on the rope is relaxed, further axial compression fatigue is arrested because additional fibers do not become slack after those initially slack fibers fail. Thus axial compression fatigue usually does not progress to complete failure of the rope. However, if a significant number of fibers fail due to axial compression fatigue, tension in the remaining fibers increases, and the overall rope strength decreases. Fiber axial compression fatigue can therefore increases the tendency for a rope or cable to fail due to other causes, including the more common forms of fatigue.