Explosively formed penetrator
shaped charge designed to penetrate armor effectively
An explosively formed penetrator (EFP) – also known as an explosively formed projectile, a self-forging warhead, or a self-forging fragment – is a special type of shaped charge relying on the Misnay–Schardin effect, designed to penetrate armour effectively, from a much greater standoff range than standard shaped charges, which are more limited by standoff distance. As the name suggests, the effect of the explosive charge is to deform a metal plate into a slug or rod shape and accelerate it toward a target. They were first developed as oil well perforators by American oil companies in the 1930s, and were deployed as weapons in World War II.
Difference from conventional shaped charges
A conventional shaped charge generally has a conical metal liner that is forced by an explosive blast into a hypervelocity jet of superplastic metal able to penetrate thick armour and knock out vehicles. A disadvantage of this arrangement is that the jet of metal loses effectiveness the further it travels, as it breaks up into disconnected particles that drift out of alignment.
An EFP operates on the same general principle, but its liner is designed to form not a jet of particles but a single compact, high-velocity projectile (commonly called the slug), permitting it to penetrate armour at greater distance: up to a hundred meters for a practical device. The liner is usually a thick, heavy plate of ductile metal such as copper, tantalum, iron or mild steel, having a plate/dish shape, or cone-shaped with an internal apex angle greater than 100°. The dish-shaped liner of an EFP can also generate a number of distinct projectile forms, depending on the shape of the plate and how the explosive is detonated. The high-explosive charge, pressed evenly against the convex side of the liner/plate, has approximately the same weight of the liner/plate. The concave side of the liner/plate is aimed at the target.
An EFP's penetration is more strongly affected by the density of its liner metal compared to a conventional shaped charge.
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