Decoupling Amplitude and Mean Stress Effects in Multiaxial Fatigue: A Critical–Integral Approach

ABSTRACT This study presents a novel multiaxial fatigue criterion that decouples the treatment of stress amplitude and mean stress by combining a critical plane–based evaluation of the amplitude with an integral formulation for the mean stress. This critical–integral approach captures both the directional sensitivity of fatigue crack initiation and the distributed influence of stabilizing or destabilizing mean stress fields. The model builds on mesoscopic fatigue concepts by incorporating both shear and normal stress amplitudes and by treating the mean stress as a quasihydrostatic field derived from orientation‐averaged shear and normal components. A comprehensive analysis of 295 multiaxial fatigue tests from the FatLim dataset reveals key shortcomings of established and best performing criteria: (i) The quadratic critical plane (QCP) model fails under compressive mean normal stresses combined with alternating shear due to its coplanar formulation; (ii) integral models such as Böhme–Papuga (BP) overpredict damage in biaxial and triaxial stress states due to their integral treatment of stress amplitudes. The proposed model overcomes both limitations and achieves the highest response accuracy across the dataset. A final case study on Hertzian contact stresses in case‐hardened rollers highlights the practical advantages of the formulation, particularly for subsurface fatigue prediction under residual stress fields.