Prediction of fatigue limits of surface-hardened steel with regard to mean stresses and residual stresses—A comparison

Hardened parts are used to minimize abrasion at contact surfaces and to extend the lifetime of machine components. Different risks to failure, and therefore, different fatigue limits result from imperfections, notches and surface properties. Two methods for calculating fatigue limits of surface-hardened parts are presented and compared. The first method is based on Weibullʹs weakest-link concept which allows to compute survival probabilities of parts with inhomogeneous material properties, the second method is the concept of local fatigue strength. The essential quantities in both models are the distribution of Vickers hardness, the residual stress state, the surface roughness and – if necessary – the surface oxidation depth. The model parameters have to be determined from reference specimens. Both models are successfully validated by comparing experimental and calculated results established with both smooth and notched specimen under different loading conditions.