Investigation Of Impact Resistance And Damage Mechanism Of ZK61m Magnesium Alloy

With the increase of energy consumption and environmental pressure,the lightweighting of structures or equipment is getting more and more attention,and the application of lightweight materials is important for saving energy and improving mobility.In recent years,magnesium alloy,as the lightest structural metal,has the advantages of higher specific strength and specific stiffness,and gradually gained wider application in aerospace and other fields.But these equipment or structures will inevitably suffer from hail,flying birds and other impact loads,and may even be subject to terrorist attacks.So reveal the protective performance and damage mechanism of magnesium alloy under impact or explosion load will provide important guidance for the design or reliability analysis of protective structure.In this thesis,a series of mechanical properties tests were conducted on the ZK61 m magnesium alloy to reveal the stress flow behavior and obtain the fracture strain of ZK61 m magnesium alloy under different stress states,and then the impact resistance and damage mechanism of magnesium alloy under ballistic impact loading were investigated by using a combination of experimental and numerical simulations.Among the mechanical properties tests include room temperature quasi-static tensile under different stress state,high temperature tensile and dynamic tensile.The test results show that the stress flow behavior and fracture loci of ZK61 m magnesium alloy depend on Lode parameter,so the Lode parameter is introduced into the modified Johnson-Cook(MJC)plasticity model and the Lode-dependent MohrCoulomb(MMC)fracture criterion is used to characterize this phenomenon.Moreover,to reveal the value of Lode parameters in the numerical simulation of ballistic impact of ZK61 m magnesium alloy targets,5 mm thick ZK61 m magnesium alloy plates were used to perform ballistic test on a one-stage light air cannon,and a finite element(FE)model corresponding to the tests were established by Abaqus FE software for numerical simulation.The results show that shear fracture dominates when the ZK61 m magnesium alloy plates were impacted by blunt or ogival projectiles;the introduction of Lode parameters into both the plasticity model and the fracture criterion can effectively improve the predictive capability and prediction accuracy of the numerical simulation.It is known that ductile metallic materials dissipate less energy than ductile fracture when shear fracture occurs.In order to make full use of the high specific stiffness and specific strength of ZK61 m magnesium alloy,a multilayer target consisting of three layers of metal was designed and tested for ballistic impact.The front and back plates are 2 mm thick TC4 titanium alloy,and the middle layers are equal surface density TC4 titanium alloy,2024 aluminum alloy and Zk61 m magnesium alloy plate respectively.The impact resistance and damage mechanism of the multilayer target were analysed by combining with numerical simulation,and then the configuration of multilayer targets was optimized.The results show that the plastic deformation of the middle and back plates is the main energy dissipation mechanism,and the ballistic resistance of the multilayer target can be effectively improved by reducing the thickness of the front plate and increasing the thickness of the back plate with the same quality and thickness.