Ballistic response and failure mechanisms of gradient structured Mg alloy

Due to their low density, high specific damping capacity and high shock absorbency, magnesium (Mg) alloys have great potential for development as high-performance lightweight armor materials in industrial applications. However, their applications are still limited owing to low strength, ductility and formability. Gradient structure design has been shown to be a good method for improving the mechanical properties and ballistic resistance of Mg alloy plate. This work aims to thoroughly reveal the root causes of ballistic performance enhancement of gradient structured (GS) Mg alloy armor material through ballistic tests and finite element simulations. Compared with homogeneous Mg alloy plate of the same dimensions, the impact energy absorption of GS plate is increased by about 40%. The enhanced strength and plasticity from the gradient structure design certainly contribute in part to the ballistic resistance. More importantly, the gradient structure results in a transition of failure modes from the typical petal-shaped dehiscence to delamination and shear fracture. Based on detailed finite element analysis, we deeply understand the deformation process and the effect of the gradient structure on the propagation of stress wave during ballistic impacting. The energy absorption by each defeat mechanism is also theoretically calculated to quantitatively interpret their intrinsic effects. Meanwhile, microstructural observations and fracture morphology have demonstrated the appearance of adiabatic shear bands along the boundary of the cylindrical plunger after ballistic perforation of GS plate. Therefore, the failure mode transition caused by gradient structure design must also play a major role in improving the ballistic resistance.