Explosively formed penetrator

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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 designed to penetrate armour effectively at stand-off distances. They are also used extensively in the oil and gas industry[1]. They were first developed during WWII.[2]

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[edit] Difference from conventional shaped charges

Formation of an EFP warhead. USAF Research Laboratory.

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, 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.[3] 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.[4]

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.[5]

As a rule of thumb, an EFP will perforate a thickness of armour steel equal to half the diameter of its charge for a copper or iron liner[6], and armour steel equal to the diameter of its charge for a tantalum liner, whereas a typical shaped charge will go through six or more diameters.

The penetration is proportional to the specific weight of the liner metal, tantalum 16654 kg/m3, copper 8960 kg/m3, iron 7874 kg/m3.
Tantalum is preferable if the delivery system have limitations in size like the SADARM which is delivered with a howitzer (artillery cannon). For other weapon systems where the size doesn't matter, a copper liner and double the calibre is used.

Also worth noting is that extensive research is going on in the grayzone between jetting charges and EFPs, which combines the advantages of both types, resulting in very long stretched rod EFPs for short to medium distance (because not aerostable) with improved penetration capability.

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.

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 [7]

[edit] Use in improvised explosive devices

Improvised Explosive Device in Iraq. The concave copper shape on top is an explosively formed penetrator.

EFPs have been used in improvised explosive devices against armoured cars, for example[8] in the 1989 assassination of the German banker Alfred Herrhausen (attributed to the Red Army Faction)[9][10], and by the Hezbollah in the 2006 Israel-Lebanon conflict[11]. A recent development is their widespread introduction in IEDs by insurgents in Iraq.[12]

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.[13]

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.[14]

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

[edit] Simplified Improvised Multiple Explosively Formed Penetrators (SIM-EFP)

At close standoff distance there is no need for the cone-tailed projectiles' aerodynamic stability, which means that the liner can be simplified.

The SIM-EFP is a construction that fits in between the military linear cutting charge (see Shaped charge) and the platter charge (see Improvised explosive device). And the main difference is how much the rectangular liner plate is bent.

SIM-EFPs are built from simple cut and bent steel bars, side by side, with explosives attached. And upon explosion it creates multiple projectiles spread out alongside the vehicles length, which makes it more probable that the enemy troops inside the vehicle are hit. And also allows for longer timing errors, and makes it easier to hit fast moving vehicles.

The SIM-EFP is a modified version of the platter charge, but the projectiles are better optimized for armour penetration instead of demolition, and spread out perfectly for effective killing of armoured vehicles. (Optimized for long projectiles instead of a broad flat projectile.)

The simplified EFP design also makes it easier for small groups of motivated individuals to build big EFPs that can penetrate a heavy battle tank or stationary high-value targets of virtually any sort.

Other examples of non circular EFPs are U.S. patents 6606951[15] and 4649828[16].

[edit] See also

[edit] References

  1. ^ http://www.globalsecurity.org/military/systems/munitions/bullets2-shaped-charge.htm
  2. ^ Military.com article on the evolution of hand-held anti-tank technology http://www.military.com/soldiertech/0,14632,Soldiertech_EFP,,00.html
  3. ^ U.S. Air Force Research Laboratory description of an EFP http://www.afrlhorizons.com/Briefs/Dec04/MN0407.html
  4. ^ U.S. Patent 5540156: Selectable effects EFP warhead http://www.google.com/patents?id=VHUgAAAAEBAJ&dq=5540156
  5. ^ DoD Directive 2000.19E, "Joint Improvised Explosive Device Defeat Organization (JIEDDO)", February 14, 2006 http://www.dtic.mil/whs/directives/corres/html/200019.htm
  6. ^ ng.pdf, on the web, US military testing of SOFDK
  7. ^ http://www.washingtonpost.com/wp-dyn/content/article/2007/09/30/AR2007093001675_5.html
  8. ^ Stratfor, "The Imminent Spread of EFPs", April 11, 2007 http://www.stratfor.com/products/premium/read_article.php?id=287118&selected=Stratfor+Weekly
  9. ^ http://www.williambowles.info/articles/app_e.pdf
  10. ^ http://blog.wired.com/defense/2008/07/the-assassinati.html
  11. ^ http://ipsnews.net/news.asp?idnews=39810
  12. ^ Salon, "Surge of danger for US troops", January 22, 2007 http://www.salon.com/news/feature/2007/01/22/ieds/print.html
  13. ^ USA Today,"As explosives in Iraq get deadlier, makers of armored vehicles alter plans", August 2, 2007 http://www.usatoday.com/news/military/2007-08-01-force-protection-mraps_N.htm
  14. ^ The Telegraph, "The precision-made mine that has killed 17 British troops", June 25, 2006 http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2006/06/25/wirq225.xml&sSheet=/news/2006/06/25/ixnews.html
  15. ^ http://www.google.com/patents/pdf/Bounding_anti_tank_anti_vehicle_weapon.pdf?id=oOoMAAAAEBAJ&output=pdf&sig=ACfU3U3WM4xBQ5f0d23uQdUeF1unjyGE9Q
  16. ^ http://www.google.com/patents/pdf/Explosively_forged_penetrator_warhead.pdf?id=Uyw6AAAAEBAJ&output=pdf&sig=ACfU3U3aUKsDPXUSxwjmUwkWpex_mpvRPA
  • 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

[edit] External links

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