Fatigue assessment of smooth metallic specimens using a simplified multiaxial criterion based on a critical plane approach

In the present paper, a high-cycle critical plane-based multiaxial fatigue criterion is employed to evaluate the multiaxial fatigue strength of smooth metallic specimens subjected to biaxial cyclic loading. According to such a criterion, the critical plane orientation is correlated to the weighted mean 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 modified 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 high-cyle fatigue strength results for smooth metallic specimens, subjected to in-phase or out-of-phase biaxial loading with different loading ratios and mean stress values, are analysed by employing the C-S criterion, its modified version, and other criteria available in the literature.