Small crack growth model from low to very high cycle fatigue regime for internal fatigue failure of high strength steel

Fatigue failure of high strength steels mostly originates at nonmetallic inclusions. An optically dark area (ODA) beside the inclusion can be observed in specimens fractured at very high cycle fatigue (VHCF) regime. The present paper proposes fatigue life prediction models from low to VHCF regime. The fatigue life prediction model inside ODA has been constructed in the VHCF regime based on the master curve of the growth of ODA where fatigue failure is caused by cyclic loading assisted by hydrogen trapped by inclusion. The fatigue crack growth law is proposed for a small crack outside ODA within the framework of the area parameter model where the concept of “continuously variable fatigue limit” for small crack is introduced. The life and scatter of fatigue life originating at inclusions can be well evaluated by the proposed models.