Shaped charge
explosive charge shaped to focus the released energy. It is used to cut and form metal, ignite nuclear weapons, and penetrate armour. A modern shaped charge can commonly penetrate about 7 times the diameter of the charge.
An armour-piercing explosion creates a small coin-sized hole in the armour, so the destructive effect mainly comes from shrapnel spalled from the inside of the plating.
Shaped charges are frequently used in anti-tank missiles and mortar shells.
An important nonmilitary use of shaped charges is to cut large pieces of metal in confined areas, especially during rescues.
Design
There are several basically different forms of shaped charge.
Metal-cutting charges are flat triangles of plastic explosive (usually plastique). A blasting cap detonator is placed in the point of the triangle. The triangle is laid down with the wide end wrapped around the material to cut. When the blast reaches the end of the explosive, it is reflected into the metal, cutting it.
A scissors charge is two of the above triangular charges, placed on opposite sides of the metal, on opposite sides of the cutting line.
They must be sized and timed so the blast wave of each arrives at the same time at the cutting line. The opposing blast waves shear the metal.
Differential cones transfer momentum from the explosive to another material, usually a metal such as copper, with a speed of sound different from the speed of the blast in the explosive. The slope of the cone is chosen so that the speed of the blast at the surface of the cone is equal to the speed of sound of the metal on the surface of the cone. The result is usually a dense drop or slug of fluid moving at hypersonic speeds. The slug penetrates armour.
This is also called the Monroe effect, discovered in 1883. This is the basis of High explosive anti-tank weapon.
Differential cones are easy to manufacture. Usually the penetrator cone is swaged to a casing, and the explosive is cast inside the resulting shape.
Explosive lenses are machined (usually) from an alloy of a rigid explosive with a compatible plastic. The surface of the lens is calculated to cause the blast front to go where desired. This is possible because the blast ignition in the explosive almost always moves at a different speed than the shockwave in the explosive reaction products.
The term explosive lens is also used to denote explosive charges in which different portions of the charge are made with different high explosives that have significantly different detonation propagation velocities (such as Composition-B and 6040 Pentolite, or TNT and HMX) in a particular geometric arrangement and are constructed in such a manner that the different detonation speeds will work together to focus the force of the blast in a way that achieves a desired effect.
Some explosive lenses (notably those in nuclear weapons) use two different materials with different speeds of ignition. The illustration represents a cross section through a segment of a polygonal wedge. The wedges are fitted together to form a spherical object. The small intiator (similar to a blasting cap) at the left triggers a semi-spherical wave through the slow speed outer explosive. As the wave is transferred to the precision shaped inner explosive a new spherical wave - centered on the object - is formed. This is the implosive wave used to crush the inner parts to a critical mass. The successful operation of this device depends upon the simultaneous initiation of the wave in each segment, uniformity and precision in the speed of the wave, and correctness and accuracy in the shape of the interface between the two explosives
Linear The explosive charge is covered by a liner, but in the shape of a flat plane.
Platter or the Misznay-Schardin effect, discovered in 1944)- A solid piece of metal, with a quantity of explosives placed on only one side or plane, an idea used in the Claymore mine.
