Studies On Local Impact Responses Of High-speed Projectile Penetrating Into Concrete Target

Concrete, which is a mixture of cement grout, sand, water and quartz aggregates(gravel), has been used extensively as a construction material in all aspects of our everyday life. This heterogeneous material suffers certain limitations. Variation of any of these components will lead to a change in the mechanical properties. Despite Concrete is well known for its high compressive strength as compared to metals, low tensile strength has long been recognized as a shortcoming of concrete. Therefore, the mechanical properties of antipenetration into concrete and the dynamic damage constitutive relationship must be taken into consideration, when high-speed projectile penetrating into concrete target is studied. In the process of high-speed projectile penetrating into concrete target, projectile body will bring about elastic deformation, plastic deformation, abrasion and instability, buckling and other destructions; while penetration, plugging and shearing, scabbing and spalling, radial cracking, perforation and other local impact responses will be generated on concrete target. It is not easy to capture and observe these physical processes and phenomena exactly by modern testing technologies. Nevertheless, to build high-speed penetration model of concrete by means of numerical modeling can obtain time history curve and calculation nephogram of every physical variable in penetration process. What’s more, it also can substantially make up for the deficiency of experiment measurement and theoretical analysis.As for local impact effects on concrete target, subsistent empirical formulae are collected and verified on the basis of the low-speed impact tests or fitting analysis. However, due to the limitation of experimental conditions and other factors, high-speed penetration test and data is scarce; and there is no appropriate empirical formula that can reflect the structural response characteristics of projectile high-speed penetration into concrete well. On the other hand, in a hydrocode simulation, the rationality of constitutive model and the accuracy of input parameters is a true representation of dynamic damage behavior of material and a basic requirement to obtain correct calculation results. Hence, this paper intends to investigate the influence of various constitutive models, penetration velocity and target thickness on local impact responses behavior of concrete by LS-DYNA, and major research work include the following three aspects:First, verification of CSCM( The Continuous Surface Cap Model) constitutive model. The inputting parameters of the models can be gathered by comprehensive literature and relative experimental data; in the meantime, the relationship between various parameters and physical quantities can also be established. By comparing with the experiments of Hanchak et al, the accuracy and rationality of the inputting parameters can be verified, which indicate that CSCM model is valid and practicable in the local response simulation of highspeed projectile penetrating into concrete target. Based on the constitutive model, digital visibility graphs of the penetration process of 30 MPa plain concrete will be presented. And the damage patterns of all stages in the course of local responses of high-speed projectile penetrating into concrete are able to be reflected primely.Second, comparison of penetration model between CSCM and HJC pattern. This paper discusses the influence of CSCM pattern and HJC pattern on destruction pattern of concrete target, mainly from plugging and shearing in the top surface, scabbing in the bottom surface and perforation. The results prove that compared with HJC pattern, CSCM pattern is capable of simulating the local impact response of concrete penetration more precisely.Third, influence factors of concrete penetration. On the basis of CSCM model, numerical simulation of 30 MPa plain concrete penetration is carried out in this paper. And it analyses qualitatively the impact velocity and the thickness of concrete target on the local impact response of high speed penetrating into concrete. Besides, the paper also presents quantificationally the effects of penetration velocity and target thickness on crater diameter, the depth of anterior crater, missile velocity, acceleration and force-displacement curve. The results show that the tunnel diameter of concrete target is approximately one to one point five times as long as the diameter of projectile, and with the velocity decreasing, all the diameter of anterior crater and posterior crater is decreased when the target thickness is the same. However, as for the concrete perforation response, when the penetration velocity is the same, with concrete target thickness increasing, the structural response becomes more obvious, damage region enlarged gradually, and projectile acceleration fluctuated remarkably. This implies that the thicker target thickness is, the more difficult it is for projectile to penetrate concrete.