The impact fatigue properties of iron and steel

When a specimen or component is subjected to repeated impacts it may develop a crack or cracks and eventually fracture. It is then said to have failed by impact fatigue. The strain-rate involved in impact fatigue is about 103 s−1 which is substantially higher than the strain-rate usually used in a conventional fatigue or tensile test. Because of this, an iron or steel specimen undergoing impact fatigue has an unusually high ultimate tensile strength and ductile–brittle transition temperature. This can explain some of the main features of impact fatigue behavior such as the high endurance relative to conventional fatigue for a given stress level, and the tendency to exhibit cleavage rather than a ductile fracture mode. Impact fatigue characteristics may be enhanced by surface hardening techniques such as carburizing, nitriding and steel shot bombardment. The effects of corrosive environments on impact fatigue have not yet been explored.