Improved FS model based on material parameters for multiaxial fatigue life prediction of titanium alloys

In order to overcome the empirical dependence and complexity involved in determining the material parameter k within the Fatemi-Socie (FS) multiaxial fatigue framework, this work proposes a revised formulation of k derived from intrinsic material characteristics. In this study, fatigue experiments on pure titanium and BT9 titanium alloys were carried out under constant-and variable-amplitude conditions, covering axial, torsional, and mixed loading with a 90° phase lag. These datasets were then used to benchmark the predictive capabilities of three approaches: the traditional FS model, the Deng criterion, and a refined FS framework featuring an updated k ' parameter. The comparison highlights that the modified M-FS model not only improves the accuracy of low-cycle multiaxial fatigue life estimations for titanium alloys but also delivers stronger robustness against changes in loading paths and sequence effects. Moreover, the proposed method streamlines parameter determination and provides both theoretical insights and practical guidance for fatigue life evaluation of titanium alloys subjected to complex engineering loadings.