On the consideration of normal and shear stress interaction in multiaxial fatigue damage analysis

Abstract Due to the abundance of engineering components subjected to complex multiaxial loading histories, being able to accurately estimate fatigue damage under multiaxial stress states is a fundamental step in many fatigue life analyses. In this respect, the Fatemi-Socie (FS) critical plane damage parameter has been shown to provide satisfactory fatigue life correlations for a variety of materials and loading conditions. In this parameter, shear strain amplitude has a primary influence on fatigue damage and the maximum normal stress on the maximum shear plane has a secondary, but important, influence. Additionally, in order to preserve the unitless feature of strain, the maximum normal stress is normalized by the material yield strength. However, in examining some data from literature it was found that, in certain situations, the FS parameter can result in better fatigue life predictions if the maximum normal stress is normalized by the shear stress range on the maximum shear plane instead. These data include uniaxial loadings with large tensile mean stress, and some combined axial-torsion load paths with different normal-shear stress interactions. This modification to the FS parameter was investigated by using fatigue data from literature for 7075-T651 aluminum alloy and a ductile cast iron, as well as additional data from 2024-T3 aluminum alloy fatigue tests performed in this study.