Study On The Mechanism Of Penetration Into Concrete Of Nose Headed Projectile

The penetration ability of the earth penetrating weapon is an important content of theworld military researchers. The shape of the projectile head is an important factor whichimpacts the penetration ability. Thus, it is of great significance to study the penetration ofirregular nose head projectile into the target. The characteristics and the regulars of theirregular nose head projectile are investigated by the experiments, theoretical analyses, andnumerical calculations when the projectiles penetrate the concrete targets at a velocity of400～600m/s.(1) Two kinds of irregular nose head projectiles and a normal ogive nose projectile areall designed for the penetration tests of the semi-infinite concrete target. By using the testtechnology of the gas gun, the tests of the penetration into semi-infinite concrete target at amiddle or low velocity are carried out. The crater damage range and the penetration depthof the target are observed, so are the abrasion, deformation, and the mass loss of theprojectiles. The penetration damage of the normal ogive nose projectile and that of theirregular nose head ones are compared. During the period when the impact velocity is400m/s, the penetration depths of the irregular nose head projectiles are larger than that of thenormal one. During the period when the impact velocity is600m/s, the penetration depthsof the three are almost the same. There are all abrasions obviously on the head of the threeprojectiles, and the degree of the abrasion on the projectile decreases with the distance fromthe top of the warhead. There is almost none abrasion at the end. The abrasions of theirregular nose head projectiles are both smaller than that of the normal one, and it decreaseswith the growth of the length of the small cylindrical-nose-tip.(2) Based on the p-equation of the porous material, the dynamic cavity expansiontheory of the concrete is proposed. The relationship of the pressure-volumetric strain of theconcrete material is described by employing the p-state equation, the tensile failure of theconcrete material is described by the maximum tensile stress failure criterion, and thestrength characteristics of the concrete material is described by the Mohr-Coulomb yieldcriterion. Thus, the dynamic cavity expansion theory of the concrete is proposed. Thenumerical calculations show that, the expanding velocities of the crack zone and thecomminute zone have nonlinear growths with the growth of the cavity expansion velocity. When the expansion velocity exceeds the critical value (300m/s), the expanding velocity ofthe comminute zone would exceed that of the crack zone, thus, the crack zone disappears.The cavity expansion pressure with the crack zone is lower than that without the crack zone.Based on the theory of fracture mechanics, the maximum expansion velocity of the brittlefracture is calculated, and it agrees with both the rest result and the calculated result ofcavity expansion theory well.(3) The resistance model of the penetration of the irregular nose head projectile intothe concrete is established. Based on the dynamic cavity expansion theory of the concrete,the penetration process of the irregular nose head projectile is divided into three period, thepenetration of the small cylindrical-nose-tip, the crater of the main warhead, and thecomplete penetration of the main warhead. The parameters of penetration depth, penetrationresistance, displacement, velocity, and etc. of the three periods are all calculated. Then, thecalculated parameters are compared with the test results of the penetration of the irregularnose head projectile into the semi-infinite concrete, and they are in good agreement.Therefore, the accuracy and the feasibility of the resistance model of the penetration of theirregular nose head projectile into the semi-infinite concrete are validated.(4) The smoothed particle hydrodynamics (SPH) is adopted for the numericalsimulation of the penetration concrete target. According to the problem that the Lagrangeerosion algorithm can’t describe the motion boundary problem of crack formationaccurately, based on the SPH method of AUTODYN program, both the JH2model and theCrack Softening model are employed to describe the compression failure and the tensilefailure of the concrete material, to simulate the penetration concrete target of the irregularnose head projectile, and to calculate the regular pattern of the penetration of the irregularnose head projectile into the concrete target. The penetration depths of the irregular nosehead projectiles are both larger than that of the ogive nose one. The penetration velocity andthe diameter of the cylindrical-nose-tip of the irregular nose head projectile both have greatimpacts on the penetration depth. The lower the penetration velocity is, the drag reductioneffect of the irregular nose head projectile is more obvious. The smaller the diameter of thecylindrical-nose-tip of the irregular nose head projectile is, the penetration resistance of thewarhead is smaller. Meanwhile, the formation, expansion, and the damage of the crack when penetrating the concrete are calculated, which are consistent with the tests. Thecombination of SPH method, JH2model, and Crack Softening model could offer gooddescriptions of the formation of the crack, the expanded motion boundary, and the problemof the penetration of the irregular nose head projectile into concrete.(5) The mechanisms of the irregular nose head projectile how to decrease theresistance of penetration and how to increase the depth of penetration are presented. Thetests, theoretical analyses, and numerical simulations show the mechanisms of them that:when the penetration velocity of the projectile is lower than that of the crack propagation,the pre-penetration of the small cylindrical-nose-tip could produce the crack zone whichwould decrease the resistance of the warhead of the projectile, improve the penetrationefficiency of the projectile, and increase the penetration depth of the irregular nose headprojectile.