Shaped Charge - History
Charles Edward Munroe was the inventor of "The Monroe Effect" in explosives in 1885. He noted that a high explosive with a cavity facing a target left an indentation. The earliest known reference to the effect appears to be 1792, and there is some indication that mining engineers may have exploited the phenomenon over 150 years ago. The Monroe Effect was rediscovered by Von Neumann in 1911, but no practical applications were developed.
Shaped charges were first developed after World War I to penetrate tanks and other armored equipment. A cylindrical charge that lies flat against the armour and is being initiated in one end gives a directed detonation effect so that a hole is created at the point of contact is Generation I. If that charge is equipped with a conical hole the force of the explosion will be channeled further and increases the chances for a penetration it is Generation II. The most common type of hollow charge munitions is the jet creating hollow charge, also called Hollow Charge Generation III. The other type of hollow charge munition is the projectile creating munition. It is referred to as Genetration IV. Gen I and Gen II (developed during the WW II) are predecessors to Gen III and IV but they are no longer in use in any munitions.
The "shaped charge" was introduced to warfare as an anti-tank device in World War II after its re-discovery in the late 1930s. In 1935, Henry Mohaupt, a chemical engineer [and a machine gunner in the Swiss Army] established a laboratory in Zurich to develop an effective anti-tank weapon that could be used by infantry soldiers. Henry Mohaupt was the inventor of the lined shaped charge. Other accounts mention earlier work by R.W. Wood of the John Hopkins University Physics Department as the discoverer of the metal liner principle. After the war started, Mohaupt came to the United States, and in October 1940 he took over direction of the bazooka project.
In January, 1945, Ramsey C. Armstrong founded Well Explosives Company, Inc. in Fort Worth, Texas. He decided to pursue perforating technology related to the bazooka, an anti-tank device based on the shaped charge concept. Armstrong contacted Mohaupt in Washington, DC, where he was then working for the Navy, and in October of 1946, Mohaupt and his wife made the long drive from Washington to Fort Worth.
The Beehive Charge was a six in diameter shaped charge demolition/sabotage device devised by the UK in October 1941.
The RPG-43 Ruchnaya Protivotankovaya Granata ("Hand Anti-Tank Grenade") Model 1943 was Russia's first shaped charge grenade for anti-tank purposes. It replaced the RPG-40 which was an ordinary stick grenade with an oversized high explosive head. It had an impact fuze with a 95mm diameter warhead containing 612g of TNT which could penetrate 75mm of armor.
In 1965 a Russian scientist proposed that a shaped charge originally developed for piercing thick steel armor be adapted to the task of accelerating shock waves. The resulting device, looking little like a wind tunnel, is called a Voitenko compressor. The Voitenko compressor initially separates a test gas from a shaped charge with a malleable steel plate. When the shaped charge detonates, most of its energy is focused on the steel plate, driving it forward and pushing the test gas ahead of it. Ames translated this idea into a self-destroying shock tube. A 66-pound shaped charge accelerated the gas in a 3-cm glass-walled tube 2 meters in length. The velocity of the resulting shock wave was a phenomenal 220 000 feet per second. The apparatus exposed to the detonation was, of course, completely destroyed, but not before useful data were extracted.
The US Army Ballistic Research Laboratory, an ARL predecessor organization, made several important contributions to the development of shaped-charge technology. BRL scientists delineated the penetration mechanics of the stretching, high-velocity jet of metal that is formed by the warhead, thus making it possible to design relatively light, inexpensive weapons to defend against tanks. Guided missiles, such as Shillelagh, TOW, Dragon, and Hellfire, exploited the high penetration capability of such warheads with accurate fire at long range. Further contributions included the demonstration of tandem shaped-charge warheads and the application of advanced liner material technology that increased jet velocity and ductility and provided enhanced lethality within existing weapon system envelopes.
Early work on shaped charges showed that a range of alternative constructions, including modifying the angle of the liner or varying its thickness, would result in a faster and longer metal jet. These research and development efforts to maximize penetration capabilities were based largely on trial and error. It was not until the 1970s that modeling codes could predict with any accuracy how a shaped charge would behave. While the concept of a metal surface being squeezed forward may seem relatively straightforward, the physics of shaped charges is very complex and even today is not completely understood.
In early 1997, Lawrence Livermore successfully tested a shaped charge that penetrated 3.4 meters of high-strength armor steel. The largest diameter precision shaped charge ever built produced a jet of molybdenum that traveled several meters through the air before making its way through successive blocks of steel.
A shaped charge, by design, focuses all of its energy on a single line, making it very accurate and controllable. When size is added to that accuracy, the effect can be dramatic. The success of this demonstration by Lawrence Livermore at the Nevada Test Site's Big Explosives Experimental Facility would not have been possible without the combination of reliable hydrodynamic codes and diagnostic tools that verify one another.
X-radiography produces shadowgraphs that provide experienced researchers with information about the jet's velocity, density, and mass distribution. The rotating-mirror framing camera, a kind of motion picture camera, can shoot millions of frames in a second. A typical shaped-charge jet-formation experiment lasts less than 30 microseconds, and the framing camera is usually set to record an image about once every microsecond. The exposure time for the framing camera may be anywhere from 100 to 200 nanoseconds, or billionths of a second. The newest tool is the image-converter (IC) camera, which was developed at Livermore in the mid-1980s. A pulsed ruby laser is synchronized with the IC camera frames to provide illumination of the shaped charge. The electronic image tube that acts as the shutter for each image frame converts the photons of laser light reflected by the shaped charge to photoelectrons. These photoelectrons are accelerated by a high-voltage pulse onto a phosphor, where they are reconverted to photons that are then transmitted to the film. With exposure times of just 15 to 20 nanoseconds (up to ten times shorter than those of the framing camera) and a band-pass filter mounted on the camera to exclude extraneous light, the IC camera has supplied the first truly high-resolution images of the formation and early flight of a shaped-charge jet.
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