A critical plane-based multiaxial fatigue life prediction method considering the material sensitivity and the shear stress

The material sensitivity coefficient of Fatemi-Socie model (FS model) is proved to be not a constant for different materials and the effect of the shear stress on fatigue life is not considered. In this condition, a new multiaxial fatigue prediction model considering the shear stress and material sensitivity is established based on the critical plane method in this paper. Firstly, the material plane with the maximum shear strain amplitude is defined as the critical plane and a calculating method to determine the location of critical plane is presented. Secondly, a calculating method of material sensitivity coefficient k' is proposed considering the effects of both the stress and strain on the critical plane by investigating the relationship between material sensitivity coefficient and the multiaxial fatigue life. Besides, the effect of the normal strain amplitude on the critical plane is considered because it has a certain impact on multiaxial fatigue life. Finally, four materials, including 45 steel, 316 L stainless steel, GH4169 alloy, and 7075-T651 aluminum alloy, are adopted to verify the feasibility and correctness of the proposed model under the proportional and non-proportional loading condition by comparing the equivalent strain model, the maximum shear strain model, the SWT model, KBM model, and FS model with the experimental result. The comparison results show that the prediction life of the proposed model is only second to the KBM model under multiaxial proportional loadings, but the prediction capability is superior to the other five models and the majority of the prediction results are within the scatter band with factor 3 under non-proportional loadings.