Plastic behavior and improved constitutive model of a laser-solid-formed alloy under the synergistic effects of temperature, strain rate, and stress state

Classical J(2) plasticity theory is the most popular continuum plasticity model. However, this plasticity theory is inapplicable for some metals due to the tension/compression asymmetry behavior. According to our previous study, the tension and compression mechanical response of laser-solid-formed Ti-6Al-4V alloy was significantly different in not only yield stress but also work hardening rate. In this study, effects of temperature and strain rate on the tension/compression asymmetry behavior of laser-solid-formed Ti-6Al-4V alloy were analyzed. Through mechanism discussion, different activations of slip systems and deformation twinning were considered to be the main causes of the tension/compression asymmetry. Finally, an improved constitutive model was developed, considering the synergistic effects of temperature, strain rate, and stress state on the plastic behavior of laser-solid-formed Ti-6Al-4V alloy. The calibrated model can accurately describe the temperature and strain rate dependences of the tension/compression asymmetry behavior. To verify the applicability of the developed constitutive model at different stress state, dynamic shear tests and finite element simulations were conducted at different temperatures. The improved constitutive model was shown to be able to predict the plastic behavior of laser-solid-formed Ti-6Al-4V alloy at different stress states over a wide range of temperatures and strain rates.