Prediction Model for Low-Cycle Fatigue Life of Cast TiAl Alloys Based on Defect Stress Concentration Effects

Internal defects cause significant fluctuations in the dispersion of low-cycle fatigue life of titanium–aluminum alloy specimens under fully reversed strain control (Rε=−1) at room temperature. To accurately analyze the relationship between internal defects and low-cycle fatigue behavior, this study adopts an energy-based approach to investigate the variation patterns of plastic strain energy density (PSE) during low-cycle fatigue testing of specimens. Research has revealed that the decline process of plastic strain energy dissipation is distinctly divided into two stages, and the low-cycle fatigue life exhibits a pronounced nonlinear relationship with the plastic strain energy dissipation rate (PSEDR) during the first stage. Based on internal defect characteristics obtained from X-ray scans, a defect intensity parameter Kt_micro was proposed to establish a life prediction interval under the influence of internal defects. By correcting the stable plastic strain energy using stress concentration factors, the prediction error of the stable plastic strain energy model was reduced from a 3× error band to a 1.5× error band. The maximum relative error decreased from 132% to 34.30%, significantly narrowing the overall prediction error. Compared with the Mason–Coffin (M-C) model and the stable plastic strain energy model, the prediction accuracy is significantly improved.