Effect of Detonation Wave Profile on Formation of Explosively Formed Projectile (EFP)

Abstract

Explosively Formed Projectiles (EFPs) are used in numerous modern top attack artillery ammunition systems because of their advantages such as higher effective standoff distance and better behind armour effects (BAE) after target penetration. In an EFP warhead, a hemispherical liner under precise initiation and explosive action gets deformed to a compact and aerodynamic shape of projectile, which has high penetration potential due to high EFP velocity is in the range of 1.5-2.5km/s. In this paper, the effects of detonation initiation methods on the formation of EFPs are studied using an EFP warhead of dia.195mm. Two potential materials OFE copper (ρ=8.93gm/cc) and tantalum (ρ=16.6gm/cc) are used as liner materials for EFP warhead. EFP’s velocity, shape and size are studied using AUTODYN Numerical Nonlinear 3D hydrocode software. An Eulerian-Lagrangian approach has been used with Eulerian description of the explosive and casing parts whereas a Lagrangian description is used for the liner part. The liner material and casing material were modeled with a shock equation of state. The Explosive is modeled with JWL equation of state. Two different initiation detonation methods are chosen for numerical simulation. In single point initiated detonation method, warhead is initiated from the centre of the warhead from the rear end and it has been observed that EFPs velocities are 1.5km/s and 0.97km/s in OFE copper and tantalum liners respectively. In case of peripheral initiated detonation method, which favours better perforation performance because of planar shock wave striking normal to the liner material, EFPs velocities are 1.9km/s and 1.1km/s in OFE copper and tantalum liner material respectively. It was also observed that EFP length is more in case of OFE copper liner material whereas EFP diameter is more in tantalum liner material. Length to diameter (L/D) ratio of EFPs was found to be greater in case of peripheral initiated detonation