Projectile spinning effects undergoing normal impact

Abstract

The present research deals with the study of the effects of spinning on a projectile undergoing normal impact using the principle of energy. When the projectile is fired from firearms, some of the energy liberated by the propellant is utilized for engaging the driving band with the rifling of a gun barrel which causes the projectile to spin. The spinning helps the projectile to stabilize in the air. The total energy of the projectile comprises both translational and rotational energies just before the impact of the target. Most of the research studies consider translational energy of the projectile only in impact studies by ignoring other forms of energy such as energy due to spinning velocity of the projectile. In the present study, the effect of spinning is studied considering a 7.62 Armour piercing (AP) projectile, at different impact velocities for a varying target thickness having two different target materials viz. Al 7075-T651 and Mild steel. The residual velocity of the projectile and energy required to penetrate the target has been evaluated by Finite Element Analysis (FEA) using a commercially available FE code known as LS-DYNA. Initially, the model is validated with experimental results available in the literature. Subsequently, the validated model is used for studying the projectile spinning effects. It is observed that at some impact velocities, there is very little variation in residual velocity with spin while considering the variation in energy required to penetrate the target is significant. So, the energy required to penetrate the target with spin and without spin is compared for analysis. Another observation is, that near the ballistic limit velocity, the spin of the projectile made the projectile stuck inside the target with partial perforation. For a particular target with a specific target thickness, there is a velocity range in which the energy required to penetrate the target with spin is less than without spin. Within the considered impact velocities, the velocity ranges for the target of Al 7075-T651 with 12 mm thickness are 818–900 m/s, for 20 mm target thickness these velocities are 818–1000 m/s, and for mild steel target of thickness values of 12 mm and 20 mm it is 640.5 to 900 m/s. For a particular target material with finite thickness, the effect of spin is very less or approximately negligible for a given velocity. For the considered impact velocity condition, in case of mild steel, this velocity is approximately equa to 900 m/s, and for Al 7075-T651, it is between 715.7 and 818 m/s.