Multiaxial fatigue assessment using a simplified critical plane-based criterion

In the present paper, a simplified critical plane-based criterion is employed to evaluate the multiaxial high-cycle fatigue strength of smooth metallic specimens. According to such a criterion, the critical plane orientation is correlated to the weighted average directions of the principal stresses, and the multiaxial fatigue strength is assessed through an equivalent stress expressed by a quadratic combination of the shear stress amplitude and the amplitude of an equivalent normal stress acting on the critical plane. The criterion is a simplified version of the original Carpinteri–Spagnoli (C–S) criterion. The proposed modifications are related to: the weighting procedure of the principal stress axes; the definition of the equivalent normal stress by taking into account the mean normal stress effect; the expression of the quadratic combination of stresses. Several experimental results related to the high-cycle fatigue strength for smooth metallic specimens, subjected to in-phase or out-of-phase biaxial loading with different mean stress values and various ratios of the stress amplitudes, are analysed by employing the C–S criterion, its simplified version, and other criteria available in the literature.