Evaluating size effects on fatigue life of 42CrMo4+QT steel using a statistical S-N model with highly-stressed volume and surface

A statistical S-N model based on the highly-stressed volume/surface concept is proposed for evaluating the size effects on fatigue strength of specimens from 42CrMo4+QT steel. The proposed model extends an existing physically valid model (Castillo et al. 2009) and allows the S-N curve to be extrapolated from small-scale to full-scale components. The model is validated against experimental fatigue data obtained by testing solid and hollow smooth cylindrical specimens under push-pull constant amplitude loadings. After checking that the proposed model agrees with experimental fatigue data, it is possible to apply the model to estimate the S-N curve of specimens of the highly-stressed volume up to 1802 mm3. For this case, an S-N expression is provided that can directly be used in fatigue analysis without the necessity of running a non-linear optimization.