Study On The Effect Of Projectiles High-velocity Normal Penetrating Into Concrete Targets

With the underground targets lying deeper and deeper, the demand on the performance of projectile penetrating into concrete become more and more important. One of the most important method to increasing depth of penetration (DOP) is increase the projectiles impact velocity. This thesis is mainly focus on the response of projectiles within the impact velocity between 800 and 1200m/s, an evolutional process of projectiles mass loss and its effect on the penetration resistance were studied by experimental, theoretical and numerical method. Main contents in the paper were as follows:1. A series of penetrating experiments into concrete target is carried out withφ25mm ballistic gun. With the method of sub caliber technology, the 67g,12mm projectile could be speed up to the velocity of 1.4km/s. The failure modes of projectiles at higher velocity phase were studied by reducing projectiles diameters and decreasing projectiles materials hardness values. The modes including mass loss, bending, flexuosity, fragmentation, molten state or plural. Further analyses showed projectiles failure was correlated with the load on cross section and the strength of projectiles material. Two kinds of projectiles 35CrMnSiA and T10A penetrating concrete targets were studied. The result showed that T10A projectiles which hardness was higher could resist abrasin but took tension failure and fragmentation due to its low toughness, and the 35CrMnSiA projectiles penetrate ability was more preferable than T10A projectiles'. The failure mode of 35CrMnSiA projectiles was mass loss within the velocity between 800 and 1200m/s, but the modes were bend and fracture except mass loss as the striking velocity increasd. Mass loss mostly occurred in the head but the phenomenon also occurred in the shell body. In the high velocity region the CRH (caliber-radius-head) had little effect on mass loss based on available penetration experimental data.2. The penetration process with mass loss was analyzed.By using rigid projectile penetrating model, DOP computed values were bigger than experimental values and the computed values always increased with impact velocity. To deal with the shortage, abrasion model was built incluing three stages of cratering phase, mass loss penetration phase and remainder rigid projectile penetrate phase.The computed values show a good agreement with experimental values at both high and low velocities. When the mass loss is ignore the model came close to rigid projectile model. The computed results showed that projectiles mass loss was incidental head shape varied with mass loss was the staple. Furthermore, the influence was more obvious in high velocity phase than that in low. The shape of projectiles nose became blunt from ogive. In high velocity phase penetrate resistance curves appeared double-humped waves due to different nose shape effect on projectiles nose shape coefficient.3. The numerical simulation of high velocity projectile penetrating into concrete target has been presented. Method of parameter sensitivity analyses was adopted to study the influence of Holmquist-Johnson-Cook (HJC) model parameters on results. The results showed that seven parameters ofρ, fc', T,μock, B, N and Pcrush had important effect on penetration results and the rest had little effect with given values by referring to classic literature. The plastic kinematic model 30CrMnSiA projcetiles penetrating C35 concrete targets with HJC model was also studied. The agreement between computed data and experimental data shows the two models could be applied to high velocity penetration analyses and the penetration process could be divided into cartering stage, projectiles nose shape factor transformation stage and rigid remainder projectiles stage. Furthermore, the velocity versus time travel curves of high velocity no longer had variation uniformity opposite low velocity, and penetrate resistance and decelerating curves became bimodal curves as a result of serious variation of projectiles head shapes in the high velocity penetration process.4. Steel fiber enhancing concrete targets performance was studied. The enhancement was proved by rigid penetration model calculation and experimental verification. Especially anti-penetrate ability of high strength reactive powder concrete (RPC) targets was enhanced by steel fiber more evidently than that of low strength SFRC. The quasi-static mechanical property test and penetration experiment results showed that steel fibers could arrest crack propagation and strengthen concrete targets anti-penetration ability. In addition, with the icreasing of the steel fiber volume fraction, the carter diameter become smaller and the DOP increasd slowly with increasing impact velocity.