Statistical fatigue tests in the very high cycle regime were carried out for the high carbon chromium bearing steel (JIS: SUJ2) in rotating bending as a common research project. Duplex S–N characteristics consisting of different S–N curves for the surface-initiated fracture and the interior-initiated fracture were clearly confirmed. Only the surface-initiated fracture took place at high stress levels, whereas only the interior-initiated fracture occurred at low stress levels. However, at medium levels of the applied stress, both fracture modes were mixed with a certain ratio of each fracture mode depending on the stress level. By applying the concept of the mixed-mode Weibull distribution, the statistical fatigue property was analyzed through the stress dependence of Weibull parameters and the occurrence probability of each fracture mode. It was finally found that the analytical results thus obtained were in good agreement with the statistical aspect of the experimental fatigue data.
