1988 年 37 巻 413 号 p. 178-184
The effects of notch shape and effective case depth on the rotating bending fatigue limit of induction surface hardened S45C steel were investigated. The results are summarized as follows;
(1) In the case of fracture from the inner part of test specimens, the fatigue limit became higher with increasing stress concentration factor (α) and effective case depth (ECD). The reason is that the applied stress at the inner part decreases with increasing α, and the fracture origin becomes deep with increasing ECD.
(2) In the case of fracture from the surface of test specimens, the fatigue limit decreased with increasing α and ECD. The reason is that the applied stress at the notch root becomes higher with increasing α, and the residual compressive stress at the notch root decreases with increasing ECD. However, when α exceeded a certain value, nonpropagating cracks were recognized and the fatigue limit became almost constant.
(3) From the effects of α and ECD on fatigue limit, it is said that the fatigue limit becomes higher with increasing ECD in the case of α<2, while in the case of α>2, the fatigue limit increases with decreasing ECD and the crack initiation strength increases with increasing ECD.