Charge with conical liner.
Some details of the power of shaped charges and how they function.
Detonation of the booster within the main charge starts an explosive wave which causes the metal cone to collapse - the forces are such that the strength of the material (copper, steel, DU, whatever) is negligible, and the metal behaves as a fluid. The cone separates into two parts: the outer surface, adjacent to the explosive charge, collapses into a relatively slow moving slug travelling at 500-1000 m/s; the inner surface forms a jet travelling along the main axis of the cone at very high velocity, 2,000-10,000 m/s*. It is the jet that penetrates the target.
There are two main phases in the penetration: first the jet formation, the efficacy of which is dependent on having an optimum stand off distance between the target material and the cone; and second the forcing aside of the target material by the very high pressures of the high speed jet in excess of 250,000 atmospheres*. With these pressures the target material becomes almost irrelevant hardened steel armour is no better than mild steel. The penetration of the target can be viewed akin to how a water stream washes mud out of a mud bank, although not a perfect analogy as the metal jet not does erode metal out of the target, except for a very small amount at the front surface. The hole is caused by radial plastic flow of the target material.
If the shaped charge fires too close to or too distant from a target surface, the jet velocity at impact is much reduced from its maximum. Maximum velocity, and thereby penetrative effect, is achieved by standing the charge off the target a certain distance this is clearly seen in the cavity in front of the conical liner in sectioned munitions.
The jet hole is typically of small diameter, around 5-6mm, although holes bigger than this are found due to directional wobble of the jet. The slug following the jet often hits the target off-axis from the penetration and splatters fairly harmlessly against the armour. Obviously the jet is far from harmless for the crew within the target.
Ultimately the power of the jet falls off and it collapses. Use of higher density materials such as tungsten and DU allow greater penetration compared with copper or steel, by maintaining the energy of the jet for longer.
EFP, as a derivation of the shaped charge effect, uses the slug rather than jet for attacking armour. One reason for the initial development of EFP (as in SADARM) was top-attack of armoured vehicles, where armour plating is much thinner than on the front and sides. It also lent itself to off road anti-vehicle mines, as noted at the beginning of this thread. The principle of EFP is shown in the following:
[ame="http://www.youtube.com/watch?v=PqO15oyWueE"]http://www.youtube.com/watch?v=PqO15oyWueE[/ame]
* Source: Journal of Applied Physics, Volume 19, June 1948. Jet velocities and pressures in current munitions are even higher than when calculated and measured in this pioneering work.
