Influence of material constitutive models on thermomechanical behaviors in the laser powder bed fusion of Ti-6Al-4V

A transient three-dimensional thermomechanical model was developed to examine the evolution of thermal and mechanical fields in the laser powder bed fusion of Ti-6Al-4V alloy, particularly with respect to the development of plastic strain. A primary focus was to evaluate the influence of material constitutive models on predicted mechanical behaviors. Johnson-Cook (JC) constitutive material models were chosen to account for the contribution of strain, strain rate, and temperature on material responses. Three different modifications of the JC models were applied to assess the sensitivity of rate hardening and temperature-dependent strain hardening on mechanical prediction. Numerical results revealed that predicted stress and strain fields were highly sensitive to the rate-dependent term but minimally affected by the temperature-dependent strain hardening. The maximum differences in average stresses and plastic strains were 23% and 13% when comparing results between the JC model and the JC model without strain rate hardening, respectively. Moreover, it was found that strain rate hardening mostly occurred at intermediate temperatures, ≈ 1000 – 1600 K, during the continuous cooling phase. Finally, the present study emphasizes the importance of material constitutive models on mechanical behavior in laser powder bed fusion as well as providing insight for further exploration of process parameter optimization.