Multiaxial Variable‐Amplitude Fatigue Life Prediction via Nonlinear Damage‐Critical Plane Approach

ABSTRACT Structural components are often subjected to multiaxial loading, which significantly accelerates fatigue damage through complex interactions between shear and normal stresses/strains. This paper proposes a novel fatigue life prediction model for multiaxial variable‐amplitude loading, developed by integrating nonlinear continuum damage (NLCD) mechanics with the critical plane approach. The model defines the maximum shear strain on the critical plane as the primary damage parameter, supplemented by a secondary parameter based on a weighted combination of normal strain and stress. For constant‐amplitude loading, the NLCD, AGS, FS, and WFS models show relatively higher accuracy, with 63%, 57%, 57%, and 55% of their life predictions, respectively, falling within a factor of 1.5 error bands. For variable‐amplitude loading, the proposed NLCD model achieves the highest accuracy, with 73% of predictions within the same error bands, outperforming the other methods (52%–67%). These comparative trends are consistently supported by error frequency distributions and Taylor diagrams.