Fundamental Investigations of Fretting Fatigue : Part 4, The Effect of Mean Stress

Abstract

A series of investigations is proceeding to clarify the phenomena of fretting fatigue. In the present paper, the effects of mean stresses on the initiation of minute fatigue cracks in superficial layer and on their propagation to complete fracture, under controlled conditions of fretting slip amplitude, are investigated using the fretting fatigue testing machine described in the previous paper. Annealed specimens and induction hardened specimens made of carbon steel are employed in the experiment. The following are the main results obtained. (1) The range of alternating stress amplitude at which no fatigue cracks initiate is not affected by the mean stresses, but is a constant value depending on the materials. The fatigue limit can be raised by induction hardening. (2) A fatigue limit against propagation of minute cracks (maximum alternating stress amplitude at which the minute fatigue cracks do not propagate) is cosiderably affected by the mean stresses, and it decreases with the increase of mean stress.