Fretting fatigue in several steels and a cast iron

Abstract

Both fretting and plain fatigue tests were carried out on a total of 11 steels and one cast iron, of which six were untreated and six were surface treated. The fretting fatigue strengths of the untreated steels were almost half the plain fatigue strengths and varied with specimen hardness in medium strength steel but became independent of specimen hardness in high strength steel. Surface treatments such as nitriding, carburizing and shot-peening were the most favourable methods for improving fretting fatigue strength because of the formation of a compressive surface layer. Shot-peening was particularly efficient. A fracture mechanics analysis revealed that the frictional forces between the pad and the specimen concentrate at the outer contact boundary of the fretting scar. The stress concentration is a main factor in promoting the fretting fatigue strength.