A life prediction model for welded joints under multiaxial variable amplitude loading histories

This paper describes a simple damage model for fatigue life predictions of welded joints under nonproportional, constant, and variable amplitude loading histories. This model, an extension of Sonsino’s effective equivalent stress amplitude method, consists of four material parameters accounting for the severity of nonproportional loading paths, the material’s susceptibility to nonproportional hardening, the material’s fatigue life under shear versus normal stresses, and the mean stress effect. These four parameters can be obtained by fatigue testing for S–N curves under bending only, torsion only, and 90° out-of-phase loading. This paper investigates the validity of the fatigue damage model by comparing the analytical and the published experimental results for various welded joint configurations subjected to multiaxial constant amplitude loads. This paper also describes a procedure to predict fatigue lives of welded joints under nonproportional variable amplitude loading histories based on the linear cumulative damage rule, the proposed equivalent stress amplitude and the Wang–Brown reversal counting technique.