表面硬化材の欠陥起点の疲労寿命の解析

抄録

In surface treatments, compressive residual stress developed near the surface layer is one of the important factors to improve the fatigue crack propagation life as well as the crack initiation life. In this study, the effect of residual stresses induced by case-hardening on the crack propagation life was analyzed. A crack was assumed to initiate from a surface or a subsurface defect, and the location of the defect to give the shortest life was determined. When a crack propagates under the compressive residual stress field, a partial crack surface contact occurs. In the present life evaluation, this effect was considered.
Although the residual stresses are effective to improve the crack propagation life for a surface defect, they bring an undesirable effect for a subsurface defect. The analysis shows an optimum residual stress distribution to give the most desirable effect on the propagation life for both defects.