The origin of fatigue life scatter was quantitatively analyzed by fatigue test of specimens containing small drill holes with various sizes. The size of the holes ranged from 40 µm to 400 µm. In several specimens, three holes with different sizes were introduced to investigate the behavior of crack growth from holes which were observed at the cycle Nf of fatigue failure from the largest hole. The dependency of fatigue life and its scatter on defect size and stress level was analyzed by the model explained in the 1st report and the factors which cause the scatter of fatigue life for other materials such as cast irons and AM materials were discussed by comparing the fatigue data and the predictions.
