| Magnisium,as the lightest metal among the world,has been applied into aerospace,automobile and other lightweight industries fields for its high strength/weight ratio and specific stiffness However,the tackles from forming process and HCP structure also affect the versatile of Mg,such as relatively low yield strength and poor bulletproof performance,to overcome the short service span,it is important to improve the mechanical properties and bulletproof performance of Mg alloy.Nano-crystalline materials have been paid increasingly attentions for its unique structure and excellent mechanical performance.To date,nano-crystalization techniques can generate a layer of nano grains on the surface of Mg alloy,which can not only improve the mechanical performances,especially for higher strength and hardness but also can extend the utility of Mg alloy.Whereas,it’s hard to analyze the mechanics properties of nanocrystalline structure by either micro or macro experiments.To help with this difficulty,first of all,this article use OM and SEM method to characterize the metalgraphic of gradient micro-structure of AZ31 Mg alloy;the nano-indentor test and tensile was used to test the mechanical properties of it;the simulated annealing algorithm and the reverse algorithm have been developed to inverse the mechanical parameters.At last,this article has also investigated the impacted performance of Mg alloy plate and optimize the structure of gradient micro-crystalline Mg plate to obtain the best bulletproof performance.The major research and main achievements of this article are:1.Based on the nano-indentor test results,the simulated annealing algorithm was embedded into ABAQUS in order to obtain the elasto-plasticity constitutive model,during the 200 th times of iteration,the numerical results can perfectly match with loading/unloading curve.A reverse algorithm was used to calculate elasto-plasticity model of micro-crystalline Mg alloy.2.A molecular dynamic voronoi Mg model was built with the grain size of 20 nm.The strain-stress behaviors under different strain rate have been calculated.Then the Johnson-Cook constitutive model and Johnson-Cook damage evolution constitutive model have been established basing on the simulation results.3.The impact performances of AZ31 B Mg alloy have been simulated under different projectile shape,impact velocity and thickness of the plates by AUTODYN.The simulation results has shown that the energy absorption is the highest when the impact velocity is 500m/s,when the impact velocity reaches 2000 m/s,the energy absorption rate becomes the lowest.As the thickness of target plate growing,the total amount of energy that has been absorbed increase,when the thickness of target plate is between 30 mm to 40 mm,the energy absorption rate increase dramatically.The ogive projectile has the highest penetration rate.4.According to the results of mechanical parameters from the second section of this article,the impact behavior of gradient AZ31 B Mg plate have been calculated with the different thickness of micro-grain-layer and plates.The results show that if the thickness of plate is 30 mm,when the micro-grain-layer is on the backside of impacting,it has the best bullet-proof property.The micro-grain-layer with the thickness of 200 μm has better bullet-proof performance than the thickness of 100 μm.However,the results of 2 mm plate impacting have turned out that when the 200 μm micro-grain-layer is on the impact side of plate,it has better bulletproof performance. |
