Improved distortion prediction in additive manufacturing using an experimental-based stress relaxation model

In additive manufacturing(AM), numerous thermal cycles make stress relaxation a significant factor in affecting the material mechanical response. However, the traditional material constitutive model cannot describe repeated annealing behavior. Here, we propose an improved constitutive model based on a serial of stress relaxation experiments, which can descript the temperature and time-dependent stress relaxation behavior during AM. By using the proposed relaxation model, the prediction accuracy is significantly improved due to the recovery of inelastic strain during multilayer deposition. The results are validated by both in-situ and final distortion measurements. The influence mechanism of the relaxation behavior on material mechanical response is explained by the three-bar model in thermo-elastic-plastic theory. The relaxation behavior during the whole AM process is clarified. The stress behavior is found to have a limited effect when merely depositing several layers; nevertheless, it becomes a prominent impact when depositing multiple layers. The proposed model can enhance modeling accuracy both in AM and in multilayer welding.