Material Inclusion Factors for Lundberg-Palmgren-Based RCF Life Equations

Material inclusions in the form of hydrogen embrittlement, carbides, etc., are by-products of manufacturing processes and commonly present in bearing steel. The objective of this study was to develop a life equation for rolling contact fatigue phenomenon that accounts for the effects of inclusions. The life equation was developed using the fatigue results previously obtained using the damage model (Jalalahmadi and Sadeghi, Journal of Tribology vol. 132, 2010). Four modifying factors counting for effects of the stiffness, size, depth, and number of the inclusions are used to modify the life equation. These modifying coefficients are extracted from the simulations obtained from the Voronoi Finite element (FE) model and the Lundberg-Palmgren-based fatigue criterion (Jalalahmadi and Sadeghi, Journal of Tribology vol. 131, 2009). These simulations predict Weibull slopes and L10 lives that are in good agreement with the previous theoretical and experimental results. It is seen that as inclusions become larger or shallower, they cause a larger decrease in the fatigue lives and their scatter. Also, introduction of more inclusions to the material significantly reduces the fatigue lives and their Weibull slopes.