The Work-Hardened Surface Layer and the Crossing of the S-N Curves

抄録

The work-hardened surface layer induced by machinig is generally thought to improve the fatigue strength in metallic materials. However, at high stress levels, the specimen B with thin work-hardened layers by turning has proved to have a lower fatigue strength than the specimen A whose surface layers are removed electrolytically, namely the S-N curves of the specimens A and B cross each other, in the rotating bending and the constant strain torsional fatigue tests, using the structural steels S30C and S35C. However, the torsionally pro-strained specimens with deep work-hardened layer have proved to have a higher fatigue strength at all stress levels than the virgin specimens. These results are well explained by applying the concept in the formula for the axial strain cycling by S.S. Manson, to the constant stress fatigue behavior.