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The shaped charge warhead is a very effective means of defeating targets of many types. The model described is part of QUINETIQ’s JET Suite of software for the design and assessment of such charges. ATJETSuite is a subset of QUINETIC's JETSuite software.
First, some background on the shaped charge warhead may be useful for the general reader. In its most common configuration a shaped charge consists of a cylindrical tubular casing containing a hollow metal liner which is mounted so that its axis of symmetry is coincident with that of the casing. The liner shape is most commonly conical or has the form of a truncated cone, although other geometries, for example hemispheres or trumpets, can be used. The base of the liner is at the end of the cylinder facing the target. Explosive is packed within the casing and around the outside of the liner.
When the explosive is detonated at the end of the cylinder furthest away from the target, a detonation front sweeps the liner causing it to collapse as a result of the very high pressures in the gaseous detonation products. The collapse of the liner produces a hypervelocity jet, the tip of which can reach speeds of 8-12 km/s, while the rear moves more slowly at of the order of 1 km/s. An even slower moving slug is also formed, which can be moving forwards or backwards depending on the charge design, but usually travels forwards very slowly at of the order of 100 m/s.
The hypervelocity jet is used to penetrate targets in both military and civil applications. The figure below shows the formation process. The collapse process is captured in a snapshot at one time t. The figure also shows the corresponding state of the liner when the element just about to be projected at that time t reaches the axis at a later time.
Present-day military applications exploiting the penetrative capability of the jet include:
No matter what the configuration, the shaped charge warhead offers a low-mass means of delivering a highly controllable directed penetrative jet to a target. The increasing demand for this capability in munitions ensures a continuing role for it in modern warfare. Continuing research and development of the JET Suite recognizes this role.
JETFORM performs the theoretical prediction of the formation of the shaped charge jet, in its unbroken state, from charge properties. The program includes an algorithm determining which portions of the jet are formed in a coherent state, an important feature for designers. Unlike other shaped charge formation programs, it uses a novel time-based approach that has both allowed high accuracy and enabled the detailed investigation of asymmetries.
Various methods are used to initiate the explosive and shape the form of the detonation wave. For example, a track plate or barrier is sometimes used to reduce the angle between the detonation wave front and the liner by forcing the front to originate or appear to originate from the periphery of the charge. This has the benefit of increasing the speed of the jet. It is important to ensure that all such initiation methods ensure the symmetry of the front and that the charge geometry is symmetric, if a good quality straight jet is to be obtained.
A shaped charge warhead is typically comprised of a liner, casing, and explosive, as shown in the figure below. The liner is most commonly a hollow cone made from a dense, ductile metal (e.g. copper), with the apex of the cone pointing away from the intended target. The casing is usually cylindrical in shape, and fabricated from metal (typically steel).
The liner is fastened to the cylinder via common joining techniques (threading, staking, etc.) and the cavity inside the casing behind the liner is filled with explosive.
Initiation of the explosive takes place at the opposite end of the warhead from the liner. A detonation wave travels rapidly away from the point of initiation toward the liner.
The liner collapses inward in response to the high pressures of the detonation, causing the liner material to compress rapidly along its internal axis of symmetry. The collapse forms two distinct metal segments, a jet and a slug. The leading edge of the "jet" (the tip) moves at speeds around 10 km/sec, while its tail travels at 1-2 km/sec. The slug moves more slowly, typically having a speed of 0.5 km/sec. The jet, by virtue of its density and high velocity, is capable of penetrating either military or geophysical targets of interest.
The collapse of the liner can be analytically modeled (two dimensionally) as two fluid streams impinging on one another. If the collapse is assumed to be symmetric, the liner collapse can be further simplified to the impingement of a single stream striking a rigid wall.
The flow is depicted in the figure above, in a reference frame moving along with point "S". The point "S" is the so-called "stagnation point", chosen for its unique reference with respect to other points in the jet. At the stagnation point, there is no liner material motion relative to this point.
As the liner material collapses toward S, the material in the flow stream splits into two portions. Material to the right of S, outside the stagnation zone, forms the jet, while material to the left of S forms the slug. If the jet is formed with a tip velocity lower than its "critical sound speed", the jet tip is a narrow, focused, cohesive mass of metal and the tip is considered "coherent".
If the jet tip velocity is above the bulk sonic velocity for the jet material throughout its whole section, the jet is "overdriven", resulting in radial dispersal of the jet tip. The radial dispersal of the jet tip causes the jet to be "incoherent" and lower penetration results due to jet break up and radial velocity components of the jet (jet particles do not strike a consistent point on the target).
The velocity of the material comprising the jet is highest at the tip and decreases linearly along its length. This velocity gradient along the jet causes it to continue to stretch until some break-up criteria is satisfied, and the jet sequentially segments into individual particles.
| © 2002 Arrow Tech Associates |