Explosively Formed Projectile from Stepped Casing Shaped Charge: Formation Mechanism of Canted Fins

Canted fins can significantly improve the flight stability and the on-target accuracy of Explosively Formed Projectiles (EFP). The current work uses the effective charge theory to derive the formation of periodic tails from shaped charge with stepped casing by considering the detonation impulse. According to the established model, the distribution of velocity along the circumference of the liner increases linearly with the square root of the casing thickness. There are two stages in the formation of canted fins influenced by the stepped casing: (1) the distribution of velocity along the circumference of the liner upon initiation, and (2) the torsion and folding of the liner edge during deformation. Numerical simulation was carried out with LS-DYNA for shaped charge (56 mm in diameter) with regular and stepped casing. The expansion of the casing and the deformation of the liner with velocity distribution at initial times were compared between the regular and the stepped casing. The distribution regularities and the final velocity of the canted fin EFP from the simulation agree well the established velocity distribution model. Soft recovery experiments were also carried out to prove the feasibility of using shaped charge with stepped casing.