2015 年 64 巻 8 号 p. 668-674
The evaluation of fatigue limit is important in designing products. The fatigue limit estimation based on dissipated energy has been getting considerable attentions. In this method, the temperature change due to irreversible energy dissipation is measured by infrared thermography for various levels of stress amplitude. It is known that the dissipated energy increases with increasing stress levels, and a certain stress level, where the change in dissipated energy shows the sharp increase, coincides with the fatigue limit of the material. In this study, the dissipated energy measurement was applied to the estimation of the crack initiation location. The fatigue limit estimation was carried out for the specimen that had multiple notches. The estimated fatigue limit showed similar value at each notch and that gave close agreement with the fatigue limit obtained from conventional fatigue tests. On the other hand, the magnitude and change of dissipated energy at each notch were different. In experiments of fatigue limit estimation, the notch, where the maximum value of dissipated energy was measured, was different from the notch where the maximum sum of principal stress was measured. To investigate the location of the crack initiation, the same specimen was carried out in the constant stress amplitude fatigue test. It was found that the notch where the largest dissipated energy was observed coincided with the crack initiated notch. Therefore, it was considered that the location of crack initiation could be estimated at the early period of fatigue by using the dissipated energy measurement.