A pragmatic approach to predict fatigue strength concerning the short crack behavior in VHCF

Abstract

Unlike LCF (low cycle Fatigue) and HCF (high cycle fatigue), VHCF (very high cycle fatigue) failures of high-strength steel are mostly caused by internal nonmetallic inclusions. In view of fact that more than 90% of VHCF life is consumed in the process of crack propagation from inclusion to GBF (granular bright facet) boundary, the SIF (stress intensity factor) KGBF at the periphery of GBF could be regarded as a material constant independent of fatigue life, which could be also considered as the macro threshold SIF controlling the internal small-long crack growth. Therefore, based on experimental research and theoretical analysis, the threshold crack growth stress model was derived from the change of SIF considering the effect of local stress and crack configuration. This model diagramed the relationship between the threshold stress and defect size (including inclusions and cracks) and could be used for fatigue strength prediction. Finally, the validity of the threshold stress-defect size diagram was proved by the VHCF test data of other five kinds of high-strength steels.