Abstract
A method to estimate the fatigue crack initiation life of notched specimens from the S-N curve of smooth specimens had been proposed in the previous papers by the present authors. In the method, the local stress and strain were calculated through the relationships of cyclic stress-strain and Kσ-Kε, where Kσ and Kε are the stress and strain concentration factors respectively, based on the assumption that the damage in local material by local stress was just the same as the damage in material of smooth specimen by nominal stress, provided that the local stress of the notched specimen was equal to the nominal stress of the smooth one. From the test results, the applicability of the method was shown to be good for carbon steels (S35C, S15C) in reversed stress.
In order to confirm its applicability to high strength steel, fatigue tests were executed on the notched specimens of an alloy steel (SCM435). The influence of mean stress on fatigue crack initiation life of notched specimens was also investigated on both SCM435 and S15C steels. The results showed that the fatigue life prediction method proposed by the authors was valid to SCM435 and that the influence of mean stress was insignificant.
