Fatigue

Summary

Fatigue is the weakening of a material under repeated loading. It leads to failure at stresses well below those that break the material under a single load. Small cracks start at points of stress concentration and grow a little with each cycle until the part breaks. The fatigue life of a material is described by its S–N curve, the number of cycles to failure as a function of the stress amplitude. Fatigue causes a large share of the failures of machines, vehicles and aircraft, so its prediction is a central task of engineering design.