Microstructure-sensitive weighted probability approach for modeling surface to bulk transition of high cycle fatigue failures dominated by primary inclusions

A simulation-based probabilistic strategy is developed to characterize the surface to bulk transition of high cycle fatigue failures dominated by primary inclusions. The probability of fatigue crack initiation in the surface region is calculated by computing the expected number of critical fatigue hot spots in this region. This is done by considering the probability of inclusion-matrix debonding and the fatigue crack initiation potency of partially-debonded inclusions for a given load ratio and stress amplitude. A case study is presented whereby the surface initiation probability is studied in uniaxial strain-controlled cyclic loading simulations of round smooth specimens of the fine grained powder metallurgy (PM) processed Ni-base superalloy IN100. The fatigue crack initiation potency of partially-debonded nonmetallic inclusions is assessed by calculating the Fatemi–Socie (FS) critical plane parameter from generalized plain strain crystal plasticity finite element simulations. Idealized spherical ceramic inclusions with homogeneous linear elastic isotropic material properties are considered to isolate the FS parameter sensitivity to inclusions’ size, stress amplitude, and polycrystalline microstructure realization around the inclusion.