Rolling Contact Fatigue Damage Mechanisms Under Non‐Proportional Cyclic Compression–Torsion Loading: A Modified Multiaxial Fatigue Model for Bearing Steel

Bearings typically undergo rolling contact fatigue (RCF) failure during service, characterized by extensive spalling, which poses significant challenges for capturing crack initiation behavior and elucidating the underlying mechanism. Thus, the stress field under RCF was simulated and utilized as an applied load in 90° out‐of‐phase non‐proportional compression–torsion fatigue tests in this work, enabling the crack initiation characterization. A modified multiaxial fatigue prediction model was developed with a quadratic relationship between the shear stress amplitude and equivalent normal stress on the critical plane, which was determined by introducing a material parameter to quantify the different effects of the amplitude and mean normal stress on fatigue damage. Based on the quantitative relationship demonstrated by the material parameters, the contribution of mean normal stress to fatigue damage is 0.32 times that of the amplitude. The equivalent normal stress on the critical plane is tensile, elucidating that bearings actually experience tension–torsion fatigue failure under RCF, although it manifests as compression–torsion fatigue macroscopically.