Penetration Mechanism Of Ogive-nose Projectiles Into Reinforced Concrete Target

The research of kinetic energy(KE)projectiles penetrating plain or reinforced con-crete targets was an hot research area in the past 20 years.With the targets being solidify and underground,the design requirements of KE projectiles are becoming higher.In order to destroy these targets,KE projectiles need more energy.With the increasing velocity of KE projectiles,it is necessary to understand the mechanism of the projectile.penetrating at high velocity.The research has been conducted systematically on the pen-etration mechanism at high velocity by combining the theoretical analysis,experimental study and simulation method.The main research contents and conclusion are listed as follows:(1)Based on the cap model,a new dynamic spherical cavity-expansion model with a general equation of state and yield criterion describing the mechanical response of con-crete has been developed to obtain the general dynamic response expressions of concrete.Yield softening properties of concrete under high pressure are considered in the proposed cavity expansion model by introducing the Drucker-Prager cap model.The relationship of cavity-expansion velocity and radial stress is obtained,which is the key issues in es-tablishing the predicting model of depth of penetration.In order to validate the proposal model,penetration tests are conducted herein by the sub-caliber launching method,in which ?60mm and ?125mm caliber ogival projectiles have been launched by artillery and the velocity of the projectiles are in the range of 800-1400m/s.The depths of penetration at different impact velocity have been obtained in the tests,which has been used in com-paring with the result of the proposal predict model.The calculated results show that the resistance equations of high velocity stage derived using Mohr-Coulomb yield criterion with shear saturation and Tresca criterion are great different from those derived using the cap model.The predictions obtained from the cap model are in good agreement with experimental data.The depth of penetration and the acceleration data in The SNL tests were used to compare with the proposal model,it shows that this model have good calcu-lation accuracy when the impact velocities are at relatively low value(200-500m/s).Based on proposal model,comparative analysis was conducted to understand the influence on penetration caused by CRH,mass,strength of concrete and density of concrete.(2)Combining the SPH meshless method,RHT concrete model and P-? equation of state,numerical simulation technique method has been used to study concrete failure mode during penetration process of ogival projectiles impact finite thickness concrete targets.Damage evolution process has been studied in the three kinds of failure mode which are cratering,spalling and perforation.Particularly,perforation tests which are?60mm ogival projectile perforating medium thickness concrete target(thickness is at the range of 10D-30D)at the speed of 650 m/s and 1100 m/s have been conducted here to focus on the issue of the effect of the thickness of concrete target on the residual velocity under the same impact velocity,revealing the mechanism of ogival projectile perforating medium thickness concrete target.Based on research results of penetration resistance in second chapter,attenuation function which express the penetration resistance varying with the position of rear surface has been structured to modify the penetration resistance function in second chapter,through derivating the spherical cavity-expansion model which considering the free surface effect.A predict model of calculating the limit perforation velocity and residual velocity has been established.the accuracy and applicability of proposal model has been verified by comparing with existing models.(3)Terminal ballistic test about 60mm caliber ogival projectile normal penetrating reinforced concrete target with different reinforcement ratio has been conducted in this chapter.In order to understand the effect of reinforcement ratio on penetration,the?105mm caliber smoothbore gun are utilized to launch ogival projectile to penetrate into reinforced concrete target with three kinds of reinforcement ratio(0.5%,1.0%and 2.0%).Through the macroscopic and microscopic analysis of reinforced concrete block taken from the test.On the basis of the spherical cavity expansion model,considering the resistance of the projectile due to direct impact with reinforced,the projectile penetrating reinforced concrete engineering analytical model is established.Analysis of the forms of resistance reinforced posed on projectile when the collision of projectile and reinforced located at the intersection node,the grid center point,the midpoint of a single reinforced and any other location point.The engineering analytical model studied in this paper is compared to experiments,indicating that the model is effective and practical.Under specific mesh size conditions,as the reinforcement ratio increases the resistance effect of reinforced on projectile becomes more obvious,the influence of bar diameter is less than the interlayer spacing of the steel mesh when reinforcement ratio is invariant.(4)The samples for metallographic analysis are gain from 60mm and 125mm projec-tiles at three typical locations along the depth from projectile surface by Wire Electrical cutting method.Based on the analysis on microstructure images,the microstructure formation of two types projectiles surface layers after penetration is proposed.The evo-lution of nose shape of projectiles after penetration was studied by using 3D scanning technique.Based on Jones penetration model considering mass loss effect,An iteration method is set up in this paper which considering both the mass loss and nose blunting effect.A correction factor is proposal in this study which considering the hardness of aggregate,hardness of projectile and strength of projectile material based on the numer-ical analysis on the penetration experiment.The result calculated by this model is more accurate when the correction factor is introduced.3D scanning technology has been used to scan the surface of the projectile after test to obtain the shape of the projectile's surface profile after erosion,analyze the evolution rule of the nose shape of the projectile,and comparatively analyze the influence of the evolution rule on penetration.(5)The relationship between the penetration resistance and the velocity of penetra-tor in the process of projectile penetrating meso-scale concrete model is studied in this paper using the particle flow discrete element method.Concrete aggregates,whose sizes distribute according to the grading curve are randomly generated and placed according to the Monte Carlo method.In order to get the same effective mechanical properties as the macro-scale model,the parameters of the micro-scale model is determined by apply-ing the parameter inversion technique to the uniaxial compression,splitting tensile,and biaxial compression tests using the particle flow discrete element micromechanical model.The influence of the aggregate,transition layer and mortar 3 phase material microscopic parameters on concrete response with respect to uniaxial compression strength as well as resistance stress on projectile with flat and conical nose are analyzed.The compar-ison of the numerical result of resistance stress calculated by the particle flow discrete element micromechanical model with the analytical result based on the cavity expansion theory shows that discrete element model has a good applicability and accuracy.Based on the analysis of simulation results,correction formula on penetration resistance which considering the maximum aggregate diameter and projectile diameter is proposal herein to analysis the effect of different projectile diameter and mmaximum aggregate diameter on penetration.