発電用水車ランナ材SCS6の圧縮残留応力を考慮した疲労設計指針の確立

抄録

In this study, in order to establish the accurate evaluation method of fatigue properties of materials with compressive residual stress at surface applied by surface treatments, tension-compression fatigue tests were carried out under various kinds of compressive mean stresses by using ASTM CA6NM stainless cast steel with two control modes. In the case of the load control mode, the lower the mean stress value, the higher the fatigue limit because the setting stress level was loaded simply if the mean stress value beyond the compressive yield limit. In the case of the strain control mode, specimens yielded greatly at the first cycle, then the mean stress didn't change to the tensile side with increasing the loading cycles and continued to load at the same stress level. As the results, the fatigue life decreased remarkably and specimens fractured early in comparison with a case of fatigue tests under the load control mode because shakedown behavior was occurred.