Study On The Penetration Mechanism Of Grooved-nose Projectile Impact To Concrete Target

Earth penetration weapons(EPW)is an effective way to attack hard and deeply buried targets.The EPW takes advantage of its high kinetic energy and the structure with low penetration resistance,which can penetrate into and destory targets effectively.In order to satisfy the penetration performance of EPW,it is significant to design the projectile structure and investigate the depth of penetration(DOP)of projectile into concrete target.Grooved-nose projectile is one type of new concept EPW,which enhances DOP by its grooved nose structure.Study on the penetration performance of grooved-nose projectile is still at a groping stage.In this dissertation,the mechanism of grooved-nose projectile penetrating into concrete target was studied by theoretical,experimental and numerical methods.The main research contents and conclusions are listed as follows:(1)Study on the localized interaction model for grooved-nose projectile penetrating into semi-infinite concrete targetBased on the localized interaction models(LIMs),an analytical model for projectile with arbitrary nose-shape penetrating into concrete target was developed.Referring to the structure of ogive-nose projectile,U-shape-nose symmetrical grooved projectile and L-shape-nose asymmetrical grooved projectile were proposed.The structural characterization of grooved-nose projectile was defined and the theoretical model was constructed to investigate the DOP for grooved-nose projectile penetrating into concrete target under the framework of LIMs.Moreover,the sharpen effect of U-shape-nose symmetrical grooved projectile and L-shape-nose asymmetrical grooved projectile were analyzed by the theoretical model.The computed results show that grooved-nose projectile has better penetration performance.Compared with L-shape-nose asymmetrical grooved projectile,the U-shape-nose symmetrical grooved projectile enhancethe DOP more dramatically.(2)Numerical study on the grooved-nose projectile penetration into semi-infinite concrete target with stress equivalent FEM subroutineBased on the modelled FEM of projectile and stress equivalent subroutine,simulations were systematically conducted on U-shape-nose symmetrical grooved projectile and L-shape-nose asymmetrical grooved projectile penetrating into concrete targets.The relation of displacement-time and velocity-time were analyzed,as well as the passive rotation angle-time curves and passive rotation angular velocity-time curves of L-shape-nose asymmetrical grooved projectile.The improvement of DOP and penetration process of grooved-nose projectile were analyzed.The numerical results show that DOPs of grooved-nose projectile are obviously deeper than ogive-nose projectiles.The effects of passive rotation during the penetration of L-shape-nose asymmetrical grooved projectile are realized in the numerical simulation.(3)Experimental study on the grooved-nose projectile penetration into semi-infinite concrete targetThe Φ014.5mm and Φ030mm caliber smoothbore gun were utilized to launch the ogive-nose projectile,U-shape-nose symmetrical grooved projectile and L-shape-nose asymmetrical grooved projectile to penetrate into concrete targets.The DOPs,characteristization of targets damages,terminal ballistic trajectory and passive rotation angle of L-shape-nose asymmetrical grooved projectile were obtained through the high-speed camera system and analysis on target damages and recovered projectiles.The advantage on enhancing DOP of grooved-nose projectile was analyzed by the quadratic polynomial curves of experimental DOP-impact velocity relation.The comparison between the results of experiment and theoretical model was conducted to explore the penetration mechanism of grooved-nose projectile.The results show that DOPs of grooved-nose projectile are closely related with the structures of groove nose.The passive rotation was found during penetration of L-shape-nose asymmetrical grooved projectile.The grooved-nose projectile reduces the target resisitance,which contributes to the enhancement of DOP.(4)Study on the target resistance under considering wedge-embedded penetration regimenDepending on the macro characteristics of target damages,the penetration process stage of U-shape-nose symmetrical grooved projectile was developed.Based on wedge-embedded penetration regimen,the stress distribution on the surface of U-shape-nose groove region were analyzed and the stress function was proposed.The penetration model of U-shape-nose groove region were used to investigate the penetration process and influence of characteristic parameters of U-shape-nose symmetrical groove on DOPs.The results show that theoretical prediction of DOPs under considering wedge-embedded penetration regimen and simulation result are consistent well with experimental data of U-shape-nose symmetrical grooved projectile.The main factor of increasing DOP is the variation of failure mode of the target but not merely the sharpening effect.(5)Study on the target resistance of cavity expansion model with tangential shear effectThe simulation of cavity expansion process under radial expansion with tangential shear loading was performed by ANSYS/AUTODYN,to analyze the regularity of cavity stress.Based on the traditional one-dimensional quasi-static cylindrical cavity expansion model,an extended quasi-static cylindrical cavity expansion model was proposed.The relationship between cavity stress and cavity radius was derived and the weakening factor of the shear effect in cavity expansion was definded.The influence of the ratio of radial velocity to tangential angular velocity and the uniaxial compression strength of concrete on the value of cavity stress was investigated.Moreover,characteristic parameters analysis of the L-shape-nose asymmetrical grooved projectile was conducted.The results show that penetration model with tangential shear effect is able to predict DOPs and parameters of passive rotation.The enhancement of DOP is affected by the nose shape and the weakening of concrete strength caused by passive rotation of projectile.