In this paper, a life prediction model associated with maximum principal stress and equivalent shear amplitude based on twin-shear unified yield criterion for multiaxial high-cycle fatigue is proposed. The equivalent shear amplitude is the normalized format of the equivalent shear amplitude based on clusters of yield criteria embodying Tresca and the linearization of Huber-von Mises, extending the application to metallic materials. Simultaneously, the effect of mean stress on multiaxial high-cycle fatigue is considered in the proposed model. As an assessment of the new prediction model, the criterion is compared with experimental data of aluminum alloy LY12CZ and carbon structural steel SM45C published in the relevant literature, which shows that most of the data are located within an error range of less than two times the data and are in good agreement with the experiment. Moreover, the proposed model is also compared with other models, such as McDiarmid, Liu, and Freitas, to validate its competitiveness.

In this work, a fatigue stress equation associated with equivalent life is proposed based on the intrinsic damage dissipation energy. This method can be treated as an optimization towards Walker’s equation owing to the similarity between them. Compared to Walker’s equation, a modification of SWT function, the proposed equation is attached to a material parameter directly correlating with the fatigue strength exponent, which eliminates the need to conduct additional HCF experiments. The analysis of experimental results from the existing literature allowed for the comparative validation of the suggested equation with two existing equations that have wide acceptance and simplicity, namely the Goodman relationship and SWT function, which revealed a better performance of the suggested model. The proposal provides great potential for its simplicity in the evaluation of HCF lifetime under tensional fatigue loading with mean stress, further optimizing towards Walker’s equation.