Effect of stress ratio on long life fatigue behavior of high carbon chromium bearing steel under axial loading

Abstract

Effect of the stress ratio on fatigue properties of a bearing steel (JIS:SUJ2) in the long life regime was experimentally examined under axial loading. As a result, the duplex S– N characteristics given by superposition of S– N curves for surface-induced fracture and interior inclusion-induced fracture were obtained similar to the corresponding results in rotating bending. Fish-eye marks were necessarily observed on the fracture surfaces failed in the latter fracture mode and an inclusion was found at the center of the fish-eye. The fatigue fracture of this steel in the long life regime occurred through three different processes of: (1) formation of the characteristic area of Fine Granular Area (FGA), (2) crack propagation to form the fish-eye and (3)rapid crack propagation to cause the catastrophic fracture. The effect of the stress ratio on the FGA size was confirmed and, this effect was well explained by the stress intensity factor at front of the FGA.