A novel energy-based equivalent damage parameter for multiaxial fatigue life prediction

Energy-based damage parameters are widely used, due to their availability, in the prediction of multiaxial fatigue life, usually by integrating the product of stress and strain range into a single scalar quantity. However, in most engineering applications, stress and the strain histories cannot be known simultaneously. Although incremental plasticity methods can be used to estimate the response from measured or specifically designed loads, these processes are too complicated to be employed. In this paper, a novel energy-based Equivalent Damage Parameter (EDP) based on uniaxial fatigue data is proposed to predict the fatigue life under multiaxial fatigue loadings. In this way, the augmentation of uniaxial tensile elastoplastic work can be estimated thanks to the non-proportional (NP) hardening factor F_NP and the energy-based material constant α_w. Moreover, the contributions to total elastoplastic work from different loading components can be separated and quantified by using the Moment Of Inertia (MOI) method and weighting factor ξ introduced as a parameter. The efficiency of the proposed parameter is validated by reasonable correlations with the experimental fatigue data of 316L steel tubular specimens subjected to various proportional or NP loadings.