Modeling of crack generation and growth under rolling contact fatigue in martensite steels

Novel systems have employed to clarify the substance crack generation and growth mechanisms unde rolling contact fatigue (RCF) for martensite steels. Advantages to characterize detecting inclusions and crack in the specimen interior by high-frequency ultrasonic test, local strain distribution by electron backscattering diffraction (EBSD), finite element modeling of crack initiation at inclusion and 3D structure of initial cracks by FIB-SEM have been studied. The cracks around inclusions in bearing steel may be generated in the early stage before 10^4 cycles, even though the flaking occurs in the high cycle range. The initial cracks in low carbon martensite steel have heen detected at the strain gradient regime by serial sectioning EBSD analysis. The cracks have been successfully visualized in three-dimensional. A computing model for RCF has been developed and suggested the crack initiation at inclusion under mode I stress. Furthermore, an aduanced RCF life prediction using on stress intensity factor ΔKII' has been developed for bearing steels. A relationship between ΔKII' and fatigue life has been evaluated. Although data were scatted in longer life range, their lower limit can give a critical size of initial cracks or inclusions for crack propagation