Experimental and numerical investigation on the ballistic resistance of ZK61m magnesium alloy plates struck by blunt and ogival projectiles

In the field of ballistics, Johnson-Cook (JC) plasticity and fracture models have provided a good theoretical basis for the prediction of ballistic performance by capturing the essence of ductile metal fracture. Nevertheless, the JC model cannot accurately reproduce the fracture behaviour of some metals. Many Lode parameter-dependent fracture criteria have effectively improved this deficiency, indicating that the fracture loci of these metals are Lode-dependent, even though the flow stress behaviour is stress state dependent, which cannot be well characterized by the JC plasticity model. In this paper, a series of mechanical tests and parallel numerical simulations of ZK61m magnesium alloy were conducted. The results showed that the flow stress behaviour and fracture loci of the alloy were obviously Lode dependent. Therefore, it seems insufficient to evaluate only the necessity of incorporating Lode parameter into a fracture criterion in predicting ballistic performance of ZK61m magnesium alloy, and more investigations on the influence of Lode parameter on the plasticity behaviour of the material should be carried out. In the present work, ballistic tests were conducted on 5 mm thick ZK61m magnesium alloy plates using blunt and ogival nose shaped projectiles with a nominal diameter of 12.68 mm. The targets failed by shear plugging when impacted by blunt-nosed projectiles, but caused a unique failure pattern under the impact of ogival-nosed projectiles. Lode-dependent plasticity model and fracture criterion were adopted. Better prediction accuracy was observed when Lode parameter is considered in both the plasticity model and fracture criterion simultaneously.