S45C調質材の二段多重変動荷重下の回転曲げ疲労寿命評価

抄録

In order to design a rotating shaft, it is necessary to investigate the fatigue characteristics under the variable amplitude loading by using a rotating bending fatigue machine. However, the stress amplitude cannot be changed frequently in a commercial rotating bending fatigue machine. Therefore, the automatic loading apparatus was manufactured in order to perform the fatigue test under the repeated two-step variable amplitude loading by using the commercial rotating bending fatigue machine. In this apparatus, the load was changed by loading or unloading the weight using air pressure. The high stress amplitude and the low stress amplitude were alternately applied to the specimen in the rotating bending fatigue test under repeated two-step variable amplitude loading. Rotating bending fatigue tests were performed using heat-treated 0.45%C steel specimens. Before the fatigue tests, the performance test of the automatic loading apparatus was conducted and it was found that the apparatus was available for fatigue tests. Next, the fatigue tests under the repeated two-step variable amplitude loading were carried out based on the results in the Hi-Lo two-step loading fatigue test and then the cumulative fatigue was investigated. The total fatigue lives to failure of low stress amplitude under the repeated two-step variable amplitude loading are almost same as lives under the Hi-Lo two-step loading, but they have the longer lives as the low stress amplitudes decrease. Finally, the life prediction method for the specimens subjected to repeated two-step variable amplitude loading was proposed. The results estimated based on the proposed method were in good agreement with the experimental ones.