Effect of loading condition on very high cycle fatigue behavior in a high strength steel

Very high cycle fatigue tests were conducted under rotating bending and axial loading using a high carbon chromium steel, JIS SUJ2, in order to evaluate the effect of loading condition on subsurface fracture with a fish-eye. In very high cycle region where subsurface crack was generated at a non-metallic inclusion, the fatigue lives under axial loading were shorter than those under rotating bending. This was attributed to the maximum size of non-metallic inclusions included in the control volume, because the sizes of non-metallic inclusions that acted as fracture origin were larger under axial loading than under rotating bending. Under both loading conditions, the Kmax values for crack initiation from non-metallic inclusion decreased with increasing fatigue life and were almost similar irrespective of loading condition, while the threshold K values where the transition from the granular area to the flat area in fish-eye took place depended on the size of the granular area. The transition condition was similar under both loading conditions.