Fatigue properties of a bearing steel (SUJ 2) including long life region were experimentally examined under axial loading and discussed from viewpoints of fractography and fracture mechanics. Thus, the complicated S-N property in the wide life region was well explained as the duplex S-N characteristics superimposed two different S-N curves for surface induced fracture and interior inclusion induced fracture. Fish-eye was formed on the fracture surface of each specimen in the interior inclusion induced fracture. Fine granular area (FGA) was necessarily observed around the inclusion at the center of the fish-eye. Stress intensity factor ranges at FGA, fish-eye and final fracture stage were in good agreement with their corresponding levels in the crack propagation law confirmed by CT specimens.
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Sakai et al. (2001) studied this question.