Statistical evaluation of duplex S-N characteristics with two competing fracture modes

Very high cycle fatigue property of a bearing steel in axial loading was studied. As a result, this steel exhibits the continuously descending S-N characteristics without the occurrence of traditional fatigue limit, and accompanying with two fracture modes including the surface induced fracture and the interior-induced fracture. Compared with its results in rotating bending, the duplex S-N characteristics in axial loading is not so distinct due to the difference of stress distribution. A new general statistical method based on the mixed Weibull distribution is proposed to evaluate the test data corresponding to these two facture modes. Consequently, the P-S-N curve of steel in axial loading can be better plotted by means of the new statistical method.