Atomic Simulation Of Defectes Affecting Dynamic Deformation And Spallation Of Magnesium Metal

The study of dynamic deformation and damage evolution of materials under extreme conditions has extremely important value and significance in both engineering mechanics and practical life.Typical hexagonal close-packed(HCP)structure magnesium(Mg)metals have high specific strength and light weight properties.In practical engineering materials,there are various unavoidable defects,and there are relatively few reports on the effects of defects on the dynamic deformation and spallation behavior of magnesium metal under shock compression.Therefore,the influence of vacancies and grain boundaries on the shock wave propagation,plastic deformation and spallation of magnesium metals under shock conditions were studied by using the non-equilibrium molecular dynamics(NEMD)method combined with the FS potential function.The effect of vacancies on the dynamic response of single crystal magnesium is closely related to the direction of shock loading.For shock along the [0001] direction,the vacancies significantly reduce the shock wave velocity and increase the spall damage.For shock along the [10-10] orientation,vacancy defects not only provide the nucleation sites for compression-induced plasticity,but also significantly reduce the spall damage.The degree of spall damage is related to two competing mechanism induced by plasticity: energy absorption and stress attenuation.Through the evolution of microstructure,it is found that the void evolution during the spallation process is mainly based on the emission mechanism of dislocations,{11-22}<11-23> pyramidal dislocations and {1-100}<11-20> prismatic dislocations mainly contribute to the nucleation of the void along the [0001] and [10-10] shock directions,respectively.Furthermore,the spall strength generally decreases with the increase of the shock strength,and the vacancies further reduce the spall strength.The dynamic response of magnesium bicrystals is obviously affected by the grain boundary characteristics,that is,in the shock compression stage,the inelastic deformation caused by the elastic shock wave occurs on both sides of the {10-12}CTB,but only on one side of the ITB region.Basal dislocation slip is easily activated when elastic shock wave passes through CTB,resulting in shock wave attenuation.The ITB undergoes grain boundary migration driven by elastic shock waves.Unlike CTB,due to the high mobility of ITB,spallation tends to occur inside the grain rather than in the ITB.Compared with single-crystal Mg,the existence of grain boundary structure significantly lowers the tensile stress threshold for void nucleation.