1989 年 38 巻 434 号 p. 1268-1274
Statistical fatigue tests on nodular cast iron in rotating bending were carried out by using a number of specimens, and P-S-N characteristics were discussed quantitatively. Fracture surfaces were observed by SEM, with special attention given to the crack initiation site and the effect of graphite morphology on the fatigue life. The main conclusions are summarized as follows;
(1) No significant difference was found in the S-N properties among different blocks cast under the same conditions. It was also confirmed that the S-N property is independent of the location within a block from which the specimen was cut.
(2) Fatigue life distribution was well represented by a three-parameter Weibull distribution modified by the saturated probability of failure. Based on the stress dependence of parameters in the distribution, statistical fatigue property was successfully determined.
(3) Fatigue crack initiation was governed by graphite morphology in the surface layer of the specimen. A correlation was found between fatigue life and the square root of the projected area of the graphite section in the longitudinal direction of the specimen.