回転曲げ強度と平面曲げ強度の関係に関する一考察

抄録

A rotating bending specimen and three types of flexural bending specimens of SC49 were tested to investigate the relationship between rotating and flexural bending strengths. Tufftrided specimens were also tested to examine the effect of surface treatment on the relationship.
Rotating and flexural bending strengths coincide fairly well with each other, though the hourglass-shaped flexural bending specimen manifests a little bit longer life than any other rotating and flexural bending specimens. The longer life of the hourglass-shaped flexural bending specimen is brought about by the smaller plastic strain range induced.
A slight difference between the lives of the rotating bending and the hourglass-shaped flexural bending specimens, observed even when the test data is arranged with the plastic strain range versus the number of cycles to failure, seems attributable to the shorter period of crack propagation caused by load-amplitude-controlled loading, and the higher probability of failure due to the larger volume of the surface layer exposed to maximum stress in the rotating bending specimen.
The lower strength of the tufftrided rotating bending specimen compared with the tufftrided flexural ones, especially in the life range less than around 10⁵ cycles, seems due to the facts that the tufftrided surface layer is easily affected by the higher temperature caused by the larger volume of heat generation and the smaller area of heat radiation in the rotating bending specimen, and that the strengthening effect of tufftride treatment is smaller in circular specimens than in rectangular ones.