Stress-relaxation-informed thermo-metallurgical-mechanical modeling of residual stress and distortion for LDED of TA15 alloy

Residual stress and distortion in laser-directed energy deposition (LDED) are critical issues affecting dimensional accuracy and component reliability. Currently, thermo-mechanical-based (TMB) models are widely used for residual stress and distortion prediction in LDED. Nevertheless, TMB models generally neglect the coupled effects of solid-state phase transformation (SSPT) and stress relaxation. In particular, stress relaxation induced by repeated thermal cycling remains insufficiently captured, limiting the fidelity and accuracy of residual stress prediction. To address this issue, a stress-relaxation-informed thermo-metallurgical-mechanical (TMM-SR) model was developed for LDED of TA15 alloy based on a previously validated thermal and SSPT framework. A calibrated hyperbolic-sine constitutive model was introduced to incorporate high-temperature stress relaxation into the SSPT-based mechanical framework, enabling simultaneous consideration of SSPT and stress relaxation. A two-stage deposition experiment combining DIC-based in situ monitoring and ex situ residual stress measurements was conducted for validation. The results demonstrate that the proposed TMM-SR model significantly improves the prediction accuracy of residual stress and distortion compared with conventional TMB models, providing deeper insights into their evolution mechanisms during LDED.