Numerical study on the optimum design of explosively formed projectile

Explosively Formed Projectile (EFP) is a self-forging shape charged structure having very high penetration ability compared to conventional kinetic energy projectile. The penetration capability of an EFP is strongly dependent on various design parameters. The present research is an effort to study the effect of liner thickness, explosive type and length to diameter ratio of charge (L/D) on the formation of EFP and its effectiveness is studied in terms of penetration subjected to ballistic impact and penetration of Rolled Homogeneous Armor (RHA) target. The study is carried out by performing a number of simulations by using explicit finite element (FE) hydrocode ANSYS/Autodyn. Under the explosive loading the liner collapses severally without breakage and forms a high-speed projectile. In all the simulations, the explosive is modeled using Euler processor to best predict the large material flow and venting of explosive gases whereas the liner and casing are numerically discretized using Lagrange processor. The interaction of explosive gases with casing and liner is modeled through Euler-Lagrange coupling technique available in ANSYS/Autodyn. It was originated that for same EFP design only by varying the liner thickness from 6 to 4 mm gives an increased velocity of the developed high-speed projectile without losing structural integrity. The developed high-speed projectile velocity is further enhanced by using more powerful charge types having a higher velocity of detonation (VOD). Three different charge types are analyzed for EFP performance and it was found that HMX based charge gives a significant increase in projectile velocity and henceforth penetration in RHA target. Finally, by increasing the length-diameter ratio of EFP system from 0.75-1.1 either the high-speed projectile or the long stretchy projectile can be formed. The field tests were conducted for selected EFP configurations for validation of calculated results. It was found through simulations that by decreasing the thickness of liner the 40 % increase in EFP velocity and 31 % increase in penetration depth in RHA can be achieved. In addition to this using HMX based charges for length-charge diameter ratio of 1.0, the 21 % increase in EFP velocity and 35 % increase in penetration depth in RHA was estimated. This research provides EFP designers to get an optimum high-speed projectile by incorporating different geometrical parameters.