1977 年 26 巻 280 号 p. 50-55
The statistical fatigue property was investigated for 3 steels corresponding to AISI types 4135, 4340 and 403, heat-treated to 7 different strength levels. The fatigue tests were conducted in rotating bending with both smooth and notched specimens, so that 14 cases were studied in total, each using about 120 specimens.
The distribution characteristics in fatigue strength were discussed by examining those in the stress deviations of test data from the mean S-N curve determined by the Probit analysis method, and then the P-S-N curves were obtained for all test conditions. The S-N curves for steels 4135 and 4340 revealed, with smooth specimens, no definite fatigue limit within the test range of cycles (>2×107), especially for materials of higher strength levels, while with notched specimens they exibited ordinal fatigue limits.
The variation in fatigue strength could be fitted by the normal distribution in most cases of smooth specimens, but it became asymmetric with larger scatter in the weaker side in the case of notched specimens. The magnitude of fatigue variations was analysed in relation to the Vickers hardness values and a possibility of predicting the fatigue variation from that of the hardness value was shown.