Damage of a large-scale reinforced concrete wall caused by an explosively formed projectile(EFP)

To quickly break through a reinforced concrete wall and meet the damage range requirements of rescuers entering the building,the combined damage characteristics of the reinforced concrete wall caused by EFP penetration and explosion shock wave were studied.Based on LS-DYNA finite element software and RHT model with modified parameters,a 3D large-scale numerical model was established for simulation analysis,and the rationality of the material model parameters and numerical simulation algorithm were verified.On this basis,the combined damage effect of EFP penetration and explosion shock wave on reinforced concrete wall was studied,the effect of steel bars on the penetration of EFP was highlighted,and the effect of impact positions on the damage of the reinforced concrete wall was also examined.The results reveal that the designed shaped charge can form a crater with a large diameter and high depth on the reinforced concrete wall.The average crater diameter is greater than 67 cm(5.58 times of charge diameter),and crater depth is greater than 22 cm(1.83 times of charge diameter).The failure of the reinforced concrete wall is mainly caused by EFP penetration.When only EFP penetration is considered,the average diameter and depth of the crater are 54.0 cm(4.50 times of charge diameter)and 23.7 cm(1.98 times of charge diameter),respectively.The effect of explosion shock wave on crater depth is not significant,resulting in a slight increase in crater depth.The average crater depth is 24.5 cm(2.04 times of charge diameter)when the explosion shock wave is considered.The effect of explosion shock wave on the crater diameter is obvious,which can aggravate the damage range of the crater,and the effect gradually decreases with the increase of standoff distance.Compared with the results for a plain concrete wall,the crater diameter and crater depth of the reinforced concrete wall are reduced by 5.94%and 9.96%,respectively.Compared to the case in which the steel bar is not hit,when the EFP hit one steel bar and the intersection of two steel bars,the crater diameter decreases by 1.36%and 5.45%respectively,the crater depth decreases by 4.92%and 14.02%respectively.The EFP will be split by steel bar during the penetration process,resulting in an irregular trajectory.

STUDY ON EFP PENETRATION SIMULATION LAW

This paper analyses the geometrical analogue rules of explosively formed projectile (EFP) penetrating armours with the help of similarity theory, and establishes EFP penetrating armour simulation law. Based on the simulation law established here, prototype experiments and model experiments with the simulation ratio of 1.33 are designed, and the penetrating armour experiments with 45 # carbon steel plates are separately conducted. By means of data processing of experimental results, it is concluded that EFP penetrating armour simulation law established is tenable.

Optimized design of biconical liner by orthogonal method

A biconical liner was optimized to improve its penetration ability. Its formation and pene- tration mechanism was studied through numerical simulation and experiments. And the influence of different liner geometry sizes on the jet performance was analyzed using the orthogonal method. The liner formed the high-speed jet with an explosively formed projectile. The small angle 2a remarkably influenced the jet speed which was inversely proportional to 2a. And the liner thickness t＇ and large angle 2β had highly significant effect on the projectile speed. The liner was optimized at t＇ = 0. 14 cm, 2α = 50°, 2β = 135°, N = 0. 4 or 0. 5, when its jet speed respectively is at 6 613 m/s and 6 839 m/s and projectile speed is at 2 247 m/s and 2 095 m/s, steel target penetration is at 8. 24 cm and 8. 31 cm, and aperture is in 2.12 cm and 2.08 cm. The results show that target is penetrated by the high-speed jet and high-speed projectile resulting into double damages. The penetration ability is improved greatly.

Analytical Calculation Model for Mach Wave Parameters

When a wave shaper is embedded in a liner,Mach wave will emerge above the liner,which affects the head shape of an explosively formed projectile.Mach wave parameters,including radius and pressure need to be determined to effectively match Mach wave with the liner,so that a good head shape can be obtained.An analytical calculation model for Mach wave parameter is presented based on three-shock theory,and the theoretical values agree well with the experimental ones.The analysis shows that when the radius of the wave shaper is constant,the radius of the Mach wave increases,whereas the pressure decreases while increasing the distance between the liner and the wave shaper.When the distance between the liner and the wave shaper is constant,the radius of the Mach wave increases,whereas the pressure decreases when decreasing the radius of the wave shaper.