Anti-bullet Mechanism And Shell-like Structure Design Of B₄C/Al Gradient Armor

High strength and toughness,light density and high efficiency are the development trend of protective armor.B₄C ceramics with low density and high hardness are widely used in the field of military protection.Toughening is the key problem in the application of B₄C ceramics.Ceramic/metal laminated structure is the most common toughening method.However,the large gap between ceramic and metal interface properties leads to impedance mismatch and easy spalling failure.Gradient armor can solve this problem.However,the research on the properties of B₄C/Al composites in China are not comprehensive,which restricts the development of B₄C/Al gradient armor.In addition,the preparation process of B₄C/Al gradient armor needs to be improved,and the research on ballistic mechanism and structural design is also scarce.Therefore,the material properties,ballistic mechanism,structural design and preparation process optimization of the B₄C/Al gradient armor were studied in this paper.The main research contents and conclusions are as follows:（1）B₄C/Al composites with different volume fractions were prepared by spark plasma sintering.The relationship between sintering temperature,holding time and the properties of composites such as Vickers hardness,flexural strength and fracture toughness was studied.The optimal sintering process of composites was explored.Finally,the cross-section morphology of composites was analyzed by scanning electron microscopy.The results showed that moderate sintering temperature and holding time are beneficial to the densification of B₄C/Al composites,and the sintering temperature of B₄C/Al composites increases with the increase of B₄C content.In addition,after process optimization,the sintering preparation of composites with high B₄C content（more than 40%）was realized.The B₄C particles in the composites were evenly distributed without obvious pores,and the mechanical properties were superior,which met the requirements of B₄C/Al gradient armor for material layer properties.（2）The constitutive models of B₄C/Al composites with different volume fractions were determined according to the bending curve.The material parameters were predicted by the law of mixture.Combined with the bullet-target test,Hopkinson bar and internal stress wave finite element model,the influence of gradient structure on the ballistic performance and stress wave of protective armor were studied,and the ballistic mechanism of B₄C/Al gradient armor was revealed.The simulation results showed that compared with the laminated armor,the B₄C/Al gradient armor had higher impact toughness,longer anti-penetration time and continuous consumption of bullet energy.In addition,there was no obvious difference between the performance of the gradient armor layers,the spallation phenomenon was released,and the multiple hit performance and stress wave absorption capacity of the protective armor were improved.（3）The influence mechanism of different layers,gradient distribution index and shell-like structure on the ballistic performance of gradient armor under the penetration of bullets were studied from residual velocity and acceleration of bullets,energy consumption and consumption efficiency,and armor penetration resistance,optimizing the design of gradient armor structure.The simulation results showed that the B₄C/Al shell-like gradient armor with 6 layers and 0.6distribution index had slight difference in interface performance,and had well impact toughness and instantaneous rupture resistance.In addition,the probability of crack deflection between armor layers was increased by the shell-like structure,meanwhile,the effective time of anti-penetration of gradient armor was prolonged,and the anti-elastic performance of armor was improved.（4）Based on the study of the properties of single-layer homogeneous B₄C/Al composites and the mechanism and structure of gradient armor,the preparation process of B₄C/Al shell-like gradient armor was developed,and the B₄C/Al shell-like gradient armor with better impact resistance was prepared by the spark plasma sintering.The microstructure,interlayer bonding and mechanical properties of the prepared samples were tested and analyzed by scanning electron microscopy and Vickers hardness tester.Finally,the impact resistance of double-layer armor,gradient armor and shell-like gradient armor was verified by drop hammer impact test.The test results showed that the impact resistance of B₄C/Al protective armor was enhanced by the structural of gradient and shell-like,which was consistent with the simulation results.