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A shaped charge, commonly also hollow charge if shaped with a cavity, is an explosive charge shaped to focus the effect of the explosive's energy. Different types of shaped charges are used for various purposes such as cutting and forming metal, initiating , penetrating armor, or perforating wells in the oil and gas industry.
A typical modern shaped charge, with a metal liner on the charge cavity, can penetrate armor steel to a depth of seven or more times the diameter of the charge (charge diameters, CD), though depths of 10 CD and above have been achieved. Contrary to a misconception, possibly resulting from the acronym HEAT (high-explosive anti-tank), the shaped charge does not depend in any way on heating or melting for its effectiveness; that is, the jet from a shaped charge does not melt its way through armor, as its effect is purely kinetic energy in nature; however, the process creates significant heat and often has a significant secondary incendiary effect after penetration.
The addition of a liner increases the effect of the explosion by providing a heavy mass that is ejected from the cone.
The first true hollow charge effect was achieved in 1883, by (1845–1905), chief of the nitrocellulose factory of Wolff & Co. in Walsrode, Germany.Kennedy (1990), pp. 5, 66.See:
By 1886, Gustav Bloem of Düsseldorf, Germany, had filed for hemispherical cavity metal detonators to concentrate the effect of the explosion in an axial direction. The Munroe effect is named after Charles E. Munroe, who discovered it in 1888. As a civilian chemist working at the U.S. Naval Torpedo Station at Newport, Rhode Island, he noticed that when a block of explosive guncotton with the manufacturer's name stamped into it was detonated next to a metal plate, the lettering was cut into the plate. Conversely, if letters were raised in relief above the surface of the explosive, then the letters on the plate would also be raised above its surface.See:
In 1894, Munroe constructed his first crude shaped charge:C.E. Munroe (1894) Executive Document No. 20, 53rd U.S. Congress, 1st Session, Washington, D.C.Charles E. Munroe (1900) "The applications of explosives," Appleton's Popular Science Monthly, vol. 56, pp. 300–312, 444–455. A description of Munroe's first shaped-charge experiment appears on p. 453.
Among the experiments made ... was one upon a safe twenty-nine inches cube, with walls four inches and three quarters thick, made up of plates of iron and steel ... When a hollow charge of dynamite nine pounds and a half in weight and untamped was detonated on it, a hole three inches in diameter was blown clear through the wall ... The hollow cartridge was made by tying the sticks of dynamite around a tin can, the open mouth of the latter being placed downward.Munroe (1900), p. 453.
Although Munroe's experiment with the shaped charge was widely publicized in 1900 in Popular Science Monthly, the importance of the tin can "liner" of the hollow charge remained unrecognized for another 44 years.Kennedy (1990), p. 6. Part of that 1900 article was reprinted in the February 1945 issue of Popular Science, "It makes steel flow like mud", Popular Science, February 1945, pp. 65–69 describing how shaped-charge warheads worked. It was this article that at last revealed to the general public how the United States Army bazooka actually worked against armored vehicles during WWII.
In 1910, Egon Neumann of Germany discovered that a block of trinitrotoluene, which would normally dent a steel plate, punched a hole through it if the explosive had a conical indentation. (1989). 9780471621720, John Wiley & Sons inc.. ISBN 9780471621720 The military usefulness of Munroe's and Neumann's work was unappreciated for a long time. Between the world wars, academics in several countries Myron Yakovlevich Sukharevskii (Мирон Яковлевич Сухаревский) in the Soviet Union,М. Сухаревский M. (1925) Техника и Снабжение Красной Армии (Technology and Equipment of the Red Army), no. 170, pp. 13–18; (1926) Война и Техника (War and Technology), no. 253, pp. 18–24. William H. Payment and Donald Whitley Woodhead in Britain, See also: and Robert Williams Wood in the U.S. recognized that projectiles could form during explosions.
In 1932 Franz Rudolf Thomanek, a student of physics at Vienna's Technische Hochschule, conceived an anti-tank round that was based on the hollow charge effect. When the Austrian government showed no interest in pursuing the idea, Thomanek moved to Berlin's Technische Hochschule, where he continued his studies under the ballistics expert Carl Julius Cranz.For a biography of Carl Julius Cranz (1858–1945), see: There in 1935, he and Hellmuth von Huttern developed a prototype anti-tank round. Although the weapon's performance proved disappointing, Thomanek continued his developmental work, collaborating with Hubert Schardin at the Waffeninstitut der Luftwaffe (Air Force Weapons Institute) in Braunschweig.Helmut W. Malnig (2006) "Professor Thomanek und die Entwicklung der Präzisions-Hohlladung" (Professor Thomanek and the development of the precision hollow charge), Truppendienst, no. 289. Available on-line at: Bundesheer (Federal Army (of Austria))
By 1937, Schardin believed that hollow-charge effects were due to the interactions of shock waves. It was during the testing of this idea that, on February 4, 1938, Thomanek conceived the shaped-charge explosive (or Hohlladungs-Auskleidungseffekt (hollow-charge liner effect)).Kennedy (1990), p. 9. (It was Gustav Adolf Thomer who in 1938 first visualized, by flash radiography, the metallic jet produced by a shaped-charge explosion.See:
) Meanwhile, Henry Mohaupt, a chemical engineer in Switzerland, had independently developed a shaped-charge munition in 1935, which was demonstrated to the Swiss, French, British, and U.S. militaries.See:
During World War II, shaped-charge munitions were developed by Germany (Panzerschreck, Panzerfaust, Panzerwurfmine, Mistel), Britain (No. 68 AT grenade, PIAT, Beehive cratering charge), the Soviet Union (RPG-43, RPG-6), the U.S. (M9 rifle grenade, bazooka),Donald R. Kennedy, " History of the Shaped Charge Effect: The First 100 Years ", D.R. Kennedy and Associates, Inc., Mountain View, California, 1983 and Italy ( Effetto Pronto Speciale shells for various artillery pieces). The development of shaped charges revolutionized anti-tank warfare. Tanks faced a serious vulnerability from a weapon that could be carried by an or aircraft.
One of the earliest uses of shaped charges was by German glider-borne troops against the Belgian Fort Eben-Emael in 1940. These demolition charges – developed by Dr. Wuelfken of the German Ordnance Office – were unlined explosive charges and did not produce a metal jet like the modern HEAT warheads.
Due to the lack of metal liner they shook the turrets but they did not destroy them, and other airborne troops were forced to climb on the turrets and smash the gun barrels. (1988). 9780853688792, Arms and Armour. ISBN 9780853688792
The use of add-on spaced armor skirts on armored vehicles may have the opposite effect and actually increase the penetration of some shaped-charge warheads. Due to constraints in the length of the projectile/missile, the built-in stand-off on many warheads is less than the optimum distance. In such cases, the skirting effectively increases the distance between the armor and the target, and the warhead detonates closer to its optimum standoff.WILEY-VCH Verlag GmbH, D-69451 Weinheim (1999) - Propellants, Explosives, Pyrotechnics 24 - Effectiveness Factors for Explosive Reactive Armour Systems - page 71 Skirting should not be confused with cage armor which is primarily used to damage the fusing system of RPG-7 projectiles, but can also cause a HEAT projectile to pitch up or down on impact, lengthening the penetration path for the shaped charge's penetration stream. If the nose probe strikes one of the cage armor slats, the warhead will function as normal.
Shaped charges are used most extensively in the petroleum and natural gas industries, in particular in the completion of oil and gas wells, in which they are detonated to perforate the metal casing of the well at intervals to admit the influx of oil and gas. Another use in the industry is to put out oil and gas fires by depriving the fire of oxygen.
A shaped charge was used on the Hayabusa2 mission on asteroid 162173 Ryugu. The spacecraft dropped the explosive device onto the asteroid and detonated it with the spacecraft behind cover. The detonation dug a crater about 10 meters wide, to provide access to a pristine sample of the asteroid.
The resulting collision forms and projects a high-velocity jet of metal particles forward along the axis. Most of the jet material originates from the innermost part of the liner, a layer of about 10% to 20% of the thickness. The rest of the liner forms a slower-moving slug of material, which, because of its appearance, is sometimes called a "carrot".
Because of the variation along the liner in its collapse velocity, the jet's velocity also varies along its length, decreasing from the front. This variation in jet velocity stretches it and eventually leads to its break-up into particles. Over time, the particles tend to fall out of alignment, which reduces the depth of penetration at long standoffs.
At the apex of the cone, which forms the very front of the jet, the liner does not have time to be fully accelerated before it forms its part of the jet. This results in a small part of the jet being projected at a lower velocity than the jet formed later behind it. As a result, the initial parts of the jet coalesce to form a pronounced wider tip portion.
Most of the jet travels at hypersonic speed. The tip moves at 7 to 14 km/s, the jet tail at a lower velocity (1 to 3 km/s), and the slug at a still lower velocity (less than 1 km/s). The exact velocities depend on the charge's configuration and confinement, explosive type, materials used, and the explosive-initiation mode. At typical velocities, the penetration process generates such enormous pressures that it may be considered hydrodynamic; to a good approximation, the jet and armor may be treated as inviscid flow, compressible fluids (see, for example,Garrett Birkhoff, D.P. MacDougall, E.M. Pugh, and G.I. Taylor, "[14]," J. Appl. Phys., vol. 19, pp. 563–582, 1948.), with their material strengths ignored.
A recent technique using magnetic diffusion analysis showed that the temperature of the outer 50% by volume of a copper jet tip while in flight was between 1100K and 1200K, much closer to the melting point of copper (1358 K) than previously assumed. (1998). 9780471621720, CMCPress. ISBN 9780471621720 This temperature is consistent with a hydrodynamic calculation that simulated the entire experiment. In comparison, two-color radiometry measurements from the late 1970s indicate lower temperatures for various shaped-charge liner material, cone construction and type of explosive filler.
A Comp-B loaded shaped charge with a copper liner and pointed cone apex had a jet tip temperature ranging from 668 K to 863 K over a five shot sampling. Octol-loaded charges with a rounded cone apex generally had higher surface temperatures with an average of 810 K, and the temperature of a tin-lead liner with Comp-B fill averaged 842 K. While the tin-lead jet was determined to be liquid, the copper jets are well below the melting point of copper. However, these temperatures are not completely consistent with evidence that soft recovered copper jet particles show signs of melting at the core while the outer portion remains solid and cannot be equated with bulk temperature.
The location of the charge relative to its target is critical for optimum penetration for two reasons. If the charge is detonated too close there is not enough time for the jet to fully develop. But the jet disintegrates and disperses after a relatively short distance, usually well under two meters. At such standoffs, it breaks into particles which tend to tumble and drift off the axis of penetration, so that the successive particles tend to widen rather than deepen the hole. At very long standoffs, velocity is lost to air drag, further degrading penetration.
The key to the effectiveness of the hollow charge is its diameter. As the penetration continues through the target, the width of the hole decreases leading to a characteristic "fist to finger" action, where the size of the eventual "finger" is based on the size of the original "fist". In general, shaped charges can penetrate a steel plate as thick as 150% to 700% Jane's Ammunition Handbook 1994, pp. 140–141, addresses the reported ≈700 mm penetration of the Swedish 106 3A-HEAT-T and Austrian RAT 700 HEAT projectiles for the 106 mm M40A1 recoilless rifle. of their diameter, depending on the charge quality. The figure is for basic steel plate, not for the composite armor, reactive armor, or other types of modern armor.
Liners have been made from many materials, including various metals and glass. The deepest penetrations are achieved with a dense, ductile metal, and a very common choice has been copper. For some modern anti-armor weapons, molybdenum and pseudo-alloys of copper-tungsten (9:1, thus density is ≈18 Mg/m3) have been adopted. Nearly every common metallic element has been tried, including aluminum, tungsten, tantalum, depleted uranium, lead, tin, cadmium, cobalt, magnesium, titanium, zinc, zirconium, molybdenum, beryllium, nickel, silver, and even gold and platinum. The selection of the material depends on the target to be penetrated; for example, aluminum has been found advantageous for concrete targets.
In early antitank weapons, copper was used as a liner material. Later, in the 1970s, it was found tantalum is superior to copper, due to its much higher density and very high ductility at high strain rates. Other high-density metals and alloys tend to have drawbacks in terms of price, toxicity, radioactivity, or lack of ductility.Alan M. Russell and Kok Loong Lee, Structure-Property Relations in Nonferrous Metals (Hoboken, New Jersey: John Wiley & Sons, 2005), p. 218.
For the deepest penetrations, pure metals yield the best results, because they display the greatest ductility, which delays the breakup of the jet into particles as it stretches. In charges for oil well completion, however, it is essential that a solid slug or "carrot" not be formed, since it would plug the hole just penetrated and interfere with the influx of oil. In the petroleum industry, therefore, liners are generally fabricated by powder metallurgy, often of which, if sintering, yield jets that are composed mainly of dispersed fine metal particles.
Unsintered cold pressed liners, however, are not waterproof and tend to be brittle, which makes them easy to damage during handling. liners, usually zinc-lined copper, can be used; during jet formation the zinc layer vaporizes and a slug is not formed; the disadvantage is an increased cost and dependency of jet formation on the quality of bonding the two layers. Low-melting-point (below 500 °C) solder- or braze-like alloys (e.g., Sn50Pb50, Zn97.6Pb1.6, or pure metals like lead, zinc, or cadmium) can be used; these melt before reaching the well casing, and the molten metal does not obstruct the hole. Other alloys, binary (e.g. Pb88.8Sb11.1, Sn61.9Pd38.1, or Ag71.9Cu28.1), form a metal-matrix composite material with ductile matrix with brittle dendrites; such materials reduce slug formation but are difficult to shape.
A metal-matrix composite with discrete inclusions of low-melting material is another option; the inclusions either melt before the jet reaches the well casing, weakening the material, or serve as crack nucleation sites, and the slug breaks up on impact. The dispersion of the second phase can be achieved also with castable alloys (e.g., copper) with a low-melting-point metal insoluble in copper, such as bismuth, 1–5% lithium, or up to 50% (usually 15–30%) lead; the size of inclusions can be adjusted by thermal treatment. Non-homogeneous distribution of the inclusions can also be achieved. Other additives can modify the alloy properties; tin (4–8%), nickel (up to 30% and often together with tin), up to 8% aluminium, phosphorus (forming brittle phosphides) or 1–5% silicon form brittle inclusions serving as crack initiation sites. Up to 30% zinc can be added to lower the material cost and to form additional brittle phases.
Oxide glass liners produce jets of low density, therefore yielding less penetration depth. Double-layer liners, with one layer of a less dense but pyrophoric metal (e.g. aluminum or magnesium), can be used to enhance incendiary effects following the armor-piercing action; explosive welding can be used for making those, as then the metal-metal interface is homogeneous, does not contain significant amount of , and does not have adverse effects to the formation of the jet."Method of making a bimetallic shaped-charge liner"
The penetration depth is proportional to the maximum length of the jet, which is a product of the jet tip velocity and time to particulation. The jet tip velocity depends on bulk sound velocity in the liner material, the time to particulation is dependent on the ductility of the material. The maximum achievable jet velocity is roughly 2.34 times the sound velocity in the material.Manfred Held. " Liners for shaped charges ", Journal of Battlefield Technology, vol. 4, no. 3, November 2001. The speed can reach 10 km/s, peaking some 40 microseconds after detonation; the cone tip is subjected to acceleration of about 25 million g. The jet tail reaches about 2–5 km/s. The pressure between the jet tip and the target can reach one terapascal. The immense pressure makes the metal flow like a liquid, though x-ray diffraction has shown the metal stays solid; one of the theories explaining this behavior proposes molten core and solid sheath of the jet. The best materials are face-centered cubic metals, as they are the most ductile, but even graphite and zero-ductility ceramic cones show significant penetration.
Another useful design feature is sub-calibration, the use of a liner having a smaller diameter (caliber) than the explosive charge. In an ordinary charge, the explosive near the base of the cone is so thin that it is unable to accelerate the adjacent liner to sufficient velocity to form an effective jet. In a sub-calibrated charge, this part of the device is effectively cut off, resulting in a shorter charge with the same performance.
The EFP is relatively unaffected by first-generation reactive armor and can travel up to perhaps 1000 charge diameters (CD)s before its velocity becomes ineffective at penetrating armor due to aerodynamic drag, or successfully hitting the target becomes a problem. The impact of a ball or slug EFP normally causes a large-diameter but relatively shallow hole, of, at most, a couple of CDs. If the EFP perforates the armor, spalling and extensive behind armor effects (BAE, also called behind armor damage, BAD) will occur.
The BAE is mainly caused by the high-temperature and high-velocity armor and slug fragments being injected into the interior space and the blast overpressure caused by this debris. More modern EFP warhead versions, through the use of advanced initiation modes, can also produce long-rods (stretched slugs), multi-slugs and finned rod/slug projectiles. The long-rods are able to penetrate a much greater depth of armor, at some loss to BAE, multi-slugs are better at defeating light or area targets and the finned projectiles are much more accurate.
The use of this warhead type is mainly restricted to lightly armored areas of main battle tanks (MBT) such as the top, belly and rear armored areas. It is well suited for the attack of other less heavily protected armored fighting vehicles (AFV) and in the breaching of material targets (buildings, bunkers, bridge supports, etc.). The newer rod projectiles may be effective against the more heavily armored areas of MBTs. Weapons using the EFP principle have already been used in combat; the "Smart bomb" submunitions in the CBU-97 cluster bomb used by the US Air Force and Navy in the 2003 Iraq war employed this principle, and the US Army is reportedly experimenting with precision-guided under Project SADARM (Seek And Destroy ARMor). There are also various other projectile (BONUS, DM 642) and rocket submunitions (Motiv-3M, DM 642) and mines (MIFF, TMRP-6) that use EFP principle. Examples of EFP warheads are US patents 5038683Ernest L.Baker, Pai-Lien Lu, Brian Fuchs and Barry Fishburn(1991)" High explosive assembly for projecting high velocity long rods" and US6606951.Arnold S. Klein (2003) " Bounding Anti-tank/Anti-vehicle weapon"
Usually, the front charge is somewhat smaller than the rear one, as it is intended primarily to disrupt ERA boxes or tiles. Examples of tandem warheads are US patents 7363862Jason C. Gilliam and Darin L.Kielsmeier(2008)" Multi-purpose single initiated tandem warhead" and US 5561261.Klaus Lindstadt and Manfred Klare(1996)" Tandem warhead with a secondary projectile" The US Hellfire antiarmor missile is one of the few that have accomplished the complex engineering feat of having two shaped charges of the same diameter stacked in one warhead. Recently, a Russian arms firm revealed a 125mm tank cannon round with two same diameter shaped charges one behind the other, but with the back one offset so its penetration stream will not interfere with the front shaped charge's penetration stream. The reasoning behind both the Hellfire and the Russian 125 mm munitions having tandem same diameter warheads is not to increase penetration, but to increase the beyond-armour effect.
In a typical Voitenko compressor, a shaped charge accelerates hydrogen gas which in turn accelerates a thin disk up to about 40 km/s.Explosive Accelerators" Voitenko Implosion Gun "I.I. Glass and J.C. Poinssot, " IMPLOSION DRIVEN SHOCK TUBE" A slight modification to the Voitenko compressor concept is a super-compressed detonation,Shuzo Fujiwara (1992) " Explosive Technique for Generation of High Dynamic Pressure "Z.Y. Liu, " Overdriven Detonation of Explosives due to High-Speed Plate Impact " a device that uses a compressible liquid or solid fuel in the steel compression chamber instead of a traditional gas mixture.Zhang, Fan (Medicine Hat, Alberta) Murray, Stephen Burke (Medicine Hat, Alberta), Higgins, Andrew (Montreal, Quebec) (2005) " Super compressed detonation method and device to effect such detonation"Jerry Pentel and Gary G. Fairbanks(1992)" Multiple Stage Munition" A further extension of this technology is the explosive diamond anvil cell,John M. Heberlin(2006)" Enhancement of Solid Explosive Munitions Using Reflective Casings"Frederick J. Mayer(1988)" Materials Processing Using Chemically Driven Spherically Symmetric Implosions"Donald R. Garrett(1972)" Diamond Implosion Apparatus"L.V. Al'tshuler, K.K. Krupnikov, V.N. Panov and R.F. Trunin(1996)" Explosive laboratory devices for shock wave compression studies" utilizing multiple opposed shaped-charge jets projected at a single steel encapsulated fuel,A. A. Giardini and J. E. Tydings(1962)" Diamond Synthesis: Observations On The Mechanism of Formation" such as hydrogen. The fuels used in these devices, along with the secondary combustion reactions and long blast impulse, produce similar conditions to those encountered in fuel-air and thermobaric explosives.Lawrence Livermore National Laboratory (2004) " Going To Extremes "Raymond Jeanloz, Peter M. Celliers, Gilbert W.Collins, Jon H. Eggert, Kanani K.M. Lee, R. Stewart McWilliams, Stephanie Brygoo and Paul Loubeyre (2007) Achieving high-density states through shock-wave loading of precompressed samples"F. Winterberg " Conjectured Metastable Super-Explosives formed under High Pressure for Thermonuclear Ignition"Young K. Bae (2008)" Metastable Innershell Molecular State (MIMS)"
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