Investigations On The Penetration Of Semi-infinite Metal Target By Two Types Of Heterogeneous Long Rod Penetrators

On one hand,design and optimization of new structure long rod and its material parameters are one of the effective methods to improve the penetration performance.On the other hand,with the appearance of the new generation of combat platforms,the launch speed of weapons and ammunition will increase to 1800-3500 m/s.Hence,it is of important engineering application significance to systematic investigate on the damage mechanism,failure mode and penetration performance of new structure long rod penetrate into semi-infinite metal target with striking velocity ranges from low to hypervelocity.Meanwhile,the researches of penetration process are also of important academic significance,for which involve armor-piercing mechanics,terminal ballistics,high-pressure physics and fracture mechanics,etc.The design and fabricate of jacketed and axial heterogeneous long rods,the damage mode,failure mechanism and penetration performance of these projectiles under penetration process,as well as the establishment of theoretical model were investigated comprehensively in this paper.The research work and conclusions are described mainly as follows:Firstly,the damage mode,failure mechanism and penetration performance of jacketed long rods penetration into semi-infinite 4340 steel target are investigated.For the deficiencies of research on jacketed long rods,mainly concentrated incident velocity around 1.6km/s and 2.5km/s and the jacket materials tested in the experimental are less,the incident velocity was extended to 0.9-3.3km/s and two types of jacketed long rods with two kinds of new jacket material(1060 aluminum and TC4 titanium alloy jacket,93 W core)were investigated.Series of ballistic experiments as well as numerical simulation were carried out to analyze the damage mode and failure mechanism of the jacketed long rod and homogeneous tungsten alloy long rod,and the effects of incident velocity,incident kinetic energy and material properties(thickness,density and strength)of the jacket on the penetration performance of the projectiles were discussed.The results show that the 93 W homogeneous long rods always present typical ?mushroom head? damage;and the two kinds of jacketed long rods presented ?co-erosion? damage mode at all test velocities,except for the 93W/1060 Al jacketed long rod at an incident velocity of 936 m/s.Specially,the damage mode of the 93W/1060 Al with incident velocity of 936 m/s turns from?bi-erosion? at early penetration stage to ?co-erosion? at late penetration stage.When the incident velocity is less than 1.65 km/s,the penetration performance of the jacketed long rod is significantly smaller than that of the 93 W homogeneous long rod with the same shape,and slightly lower than the 93 W core projectile.When the incident velocity is larger than 2.0 km/s,the penetration performance of the jacketed long rod is the same as the 93 W homogeneous long rod and better than the 93 W core projectile.However,the penetration performance of the jacketed rod is significantly better than that of the two kinds of 93 W long rods,when the incident kinetic energy of the projectile is the same.In addition,the influence of the thickness and density of the jacket on the penetration performance of jacketed rod is small,and the strength of the jacket has a significant influence;the smaller the strength of the jacket,the better the penetration performance of the projectile.Secondly,the design and fabricate of the axial heterogeneous long rod as well as the quasi-static and dynamic mechanical properties of the projectile materials were investigated.Based on the theory of the homogeneous long rod penetrates into the semi-infinite target,the structure and the materials used to fabricate the axial heterogeneous long rod were determined.The axial heterogeneous long rod was composited by several layers of materials(40Cr Ni Mo A steel,Q490 steel and Q235 steel)with different strength,and the strength decreases in turn from the head to the tail.To fabricate the axial heterogeneous long rod,the explosive welding method was used.Finally,the quasi-static and dynamic mechanical properties of the axial heterogeneous long rod materials after explosive welding and the target material were experimentally tested,and the Johnson-Cook constitutive model parameters of these materials were obtained.Thirdly,the penetration of axial heterogeneous long rods into semi-infinite 6061-T651 aluminum alloy target was investigated.The axial heterogeneous long rods with three kinds of head shapes were used,and it was compared with the Q235 steel homogeneous long rod.Series of ballistic experiments and numerial simulations were carried out in a large speed range(0.7-3.2km/s),and good agreement between them was obtained.The damage mode and failure mechanism of the axial heterogeneous long rods and Q235 steel homogeneous long rods were analyzed,as well as the effects of incident velocity,nose shape and projectile structure on the penetration performance of the projectile were discussed,by combining experimental and numerical results.The results show that the Q235 homogeneous long rod presented typical erosive penetration at all test velocities,and large ?mushroom head? was shaped during penetration process;while,the axial heterogeneous long rods exhibit three kinds of damage modes in sequence with the increase of the incident velocity,namely deformation non-erosive penetration,deformation and erosive penetration,and erosive penetration.The incident velocity has a great effect on the penetration performance of the axial heterogeneous long rod,especially in the middle and low velocity sections(700-1150m/s),its change will cause significant changes in the damage mode and failure mechanism of the projectile.In the experimental test velocity range,the axial heterogeneous long rod with truncated ogival nose has the best penetration performance,while that with spherical nose is the lowest.It shows that a sharper nose shape will be benefite in improving the penetration performance of the axial heterogeneous long rod.The penetrating performance of the axial heterogeneous long rod is significantly improved compared with the Q235 steel homogeneous long rod,as that of the axial heterogeneous long rod with truncated ogival nose is 35%-510% better than the Q235 steel homogeneous long rod.At the same time,it is the same as that of the homogeneous long rod with higher strength,at high incident velocity(>2000 m/s)range.It can be concluded that the proposed composite projectile structure in the present paper is advantageous for improving the penetration performance of the projectile.Finally,the theoretical models used to predict the crater diameter and penetration depth of the jacketed long rods and axial heterogeneous long rods penetration into semi-infinite metal targets was discussed.For jacketed long rod,the existing theoretical model used to predict the diameter of crater is compared and verified by combining experimental and numerical results.It is found that the theoretical model taken the strength and density of the jacket and core into account can predict the crater diameter better.Then,the theoretical model used to predict penetration depth of the jacketed rod was modified,in which the concept of the effective cross-setional area of the jacket is proposed,which makes the equivalent strength and density of the jacket more close to the strength and density of the homogeneous long rod.And,the penetration depth of the jacketed long rods predicted by the modified penetration model is in good agreement with the experimental data in large speed range(0.9-3.3km/s).In addition,the penetration depth model of the homogeneous long rod is applied to the axially heterogeneous long rod projectile,and the predicted penetration depth curves agree well with the experimental data.And,the change trend of the penetration depth of the axially heterogeneous long rod under different failure mode with the incident velocity is more accurately reflected.