A deviatoric tensile-based critical plane model to predict peak/mean normal stress effects in multiaxial fatigue

Abstract

This work aims to improve the modeling of peak/mean normal stress effects on multiaxial fatigue lives, applying a deviatoric strain-life model based on the critical plane approach to predict the initiation of tensile-driven cracks. Based on Kujawski’s deviatoric multiaxial fatigue damage parameter, this model assumes the peak deviatoric stress normal to the crack plane controls these effects. Tensile damage models based on deviatoric parameters can solve the main issue with Smith-Watson-Topper’s pioneer model, which is the prediction of no damage in cyclic compression-compression load histories. A calibration procedure based on Coffin-Manson parameters is presented, without the need for additional data-fitting constants to predict peak/mean stress effects. The calibrated multiaxial model is then compared with other tensile-based models for five structural metallic alloys, involving an extensive dataset with 312 uniaxial, torsion, and tension–torsion tests. It is found that the deviatoric formulation is able to explain the fatigue crack initiation behavior under highly compressive mean stresses, including the challenging case of compression-compression loadings. Under zero or positive mean stresses, this formulation provides similar predictions as the Smith-Watson-Topper model, reproducing the observed peak stress effects. Uniaxial versions of this deviatoric model are also presented and calibrated, showing that the minimum instead of the peak stress controls the damage parameter in uniaxial fatigue tests under highly compressive mean loads.