Simulation and Analysis of Collision Between Rigid Projectile and Unreinforced Concrete Target

Simulation and analysis of bullet (projectile) impact to structures is one of the needed subjects in retrofit of structures. To study the penetration phenomenon in structures, the affecting parameters should be indentified and this identification leads to prediction of penetration depth and then, to minimizing it. One of the main affecting parameters on the final penetration depth is the type and amount of energy dissipation during the penetration process. Generally, energy dissipation occurs in three steps of penetration process including impact, tunnel and exit steps in three different forms. In the first step, i.e. the projectile impact on concrete target, the compressive strength of concrete is the affecting parameter on energy absorption. However, the shear-frictional strength and concrete tensile strength are respectively the main affecting parameters in the second and third steps. In this paper, the affecting parameters on energy dissipation during these three steps are studied and it will examine that the energy dissipation during the tunnel (shear-frictional between projectile and concrete) is lower than that of the two other steps because of the geometrical shape of projectile head. In other words, the main portion of energy dissipation during the penetration phenomenon occurs when the projectile clashes the front surface and when it exits the back face of slab. Considering the above results, it can be said that to increase the strength and efficiency in penetration phenomenon, an applicable and inexpensive method is to implement a specific thickness of multilayer concrete with small clearance between the layers. The energy dissipation of this assembly is higher than that of a single layer concrete of the same thickness and thus, the penetration depth will be reduced.