A Modified Johnson–Cook Constitutive Model for Characterizing the Hardening Behavior of Typical Magnesium Alloys under Tension at Different Strain Rates: Experiment and Simulation

The mechanical behavior of AZ31B magnesium alloy was studied through uniaxial tensile tests at strain rates of 0.001, 1, 100, and 1000/s. The results show that an increase in the strain rate results in a gradual increase in the flow stress. Considering that the original Johnson–Cook (J–C) model cannot adequately describe the flow stress of AZ31 magnesium alloy at different strain rates, a rate-dependent modified Johnson–Cook (M-J–C) model was proposed, and the coefficients were calibrated according to the experimental results. The calibration and validation show that the M-J–C model has a high accuracy in characterizing the flow stress of AZ31B magnesium alloy and can well predict the hardening curve of ZK60 and AM60 magnesium alloys at different strain rates in the literature. In addition, the variation in the fracture strain with different strain rates was characterized. The fractography was studied to reveal the mechanism of underlying fracture. The proposed M-J–C constitutive model combined with a failure criterion was developed and coded into LS-DYNA through the user subroutine UMAT. The comparison between the simulation and the experiment shows that the developed subroutine is accurate enough to simulate the plastic and fracture behaviors of AZ31B magnesium alloy at different strain rates.