Explosively formed penetrator

Explosively formed penetrator

An explosively formed penetrator (EFP), is a type of petard also known as an explosively formed projectile, a self-forging warhead, or a self-forging fragment, is a special type of shaped charge designed to penetrate armour effectively at stand-off distances. They are also used extensively in the oil and gas industry. They were first developed during WWII.

Difference from conventional shaped charges

A conventional shaped charge generally has a conical metal liner that projects a hypervelocity jet of metal able to penetrate to great depths into steel armour; however, in travel over some distance the jet breaks up along its length into particles that drift out of alignment, greatly diminishing its effectiveness at a distance.

An EFP eight inches in diameter threw a seven-pound copper slug at Mach 6, or 2,000 meters per second. (A .50-caliber bullet, among the most devastating projectiles on the battlefield, weighs less than two ounces and has a muzzle velocity of 900 meters per second.). Washington Post

An EFP, on the other hand, has a liner in the shape of a shallow dish.The force of the blast molds the liner into any of a number of configurations, depending on how the plate is formed and how the explosive is detonated. Sophisticated EFP warheads have multiple detonators that can be fired in different arrangements causing different types of waveform in the explosive, resulting in either a long-rod penetrator, an aerodynamic slug projectile or multiple high-velocity fragments. A less sophisticated approach for changing the formation of an EFP is the use of wire-mesh in front of the liner: with the mesh in place the liner will fragment into multiple penetrators.

In addition to single-penetrator EFPs (also called single EFPs or SEFPs), there are EFP warheads whose liners are designed to produce more than one penetrator; these are known as multiple EFPs, or MEFPs. The liner of an MEFP generally comprises a number of dimples that intersect each other at sharp angles. Upon detonation the liner fragments along these intersections to form up to dozens of small, generally spheroidal projectiles, producing an effect similar to that of a shotgun. The pattern of impacts on target can be finely controlled based on the design of the liner and the manner in which the explosive charge is detonated.

The (single) EFP generally remains intact and is therefore able to penetrate armour at long range, delivering a wide spray of fragments of liner material and vehicle armour backspall into the vehicle's interior, injuring its crew and damaging other systems.

As a rule of thumb, an EFP will perforate a thickness of armour equal to only about the diameter of its charge, whereas a typical shaped charge will go through six or more diameters.

EFPs have been adopted as warheads in a number of weapon systems, including the CBU-97 and BLU-108 air bombs (with the Skeet submunition), the M303 Special Operations Forces demolition kit, the M2/M4 Selectable Lightweight Attack Munition (SLAM), the SADARM submunition, the Low Cost Autonomous Attack System and the TOW-2B anti-tank missile.

Use in improvised explosive devices

EFPs have been used in improvised explosive devices against armoured cars, for example in the 1989 assassination of the German banker Alfred Herrhausen (attributed to the Red Army Faction), and by the Hezbollah in the 2006 Israel-Lebanon conflict. A recent development is their widespread introduction in IEDs by insurgents in Iraq.

The charges are generally cylindrical, fabricated from commonly available metal pipe, with the forward end closed by a Concave copper or steel disk-shaped liner to create a shaped charge. Explosive is loaded behind the metal liner to fill the pipe. Upon detonation, the explosive projects the liner to form a projectile at a speed well over 1 km/s, depending on the design and type of explosive used.

Because they use explosives to form a solid copper penetrator instead of using an explosive blast or metal fragments, these charges are extremely dangerous, even to the new generation of MRAPs (which are made to withstand an anti-tank mine), and many tanks.

Often mounted on crash barriers at window level, they are placed along roadsides at choke points where vehicles must slow down, such as intersections and junctions. This gives the operator time to judge the moment to fire, when the vehicle is moving more slowly.

Detonation is controlled by cable, radio control, or remote arming with a passive infrared sensor. EFPs can be deployed singly, in pairs, or in arrays, depending on the tactical situation.

References

  • Fundamentals of Shaped Charges, W.P. Walters, J.A. Zukas, John Wiley & Sons Inc., June 1989, ISBN 0-471-62172-2
  • Tactical Missile Warheads, Joseph Carleone (ed.), Progress in Astronautics and Aeronautics Series (V-155), Published by AIAA, 1993, ISBN 1-56347-067-5

See also

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