Ordnance – Shields – Shape or composition
Reexamination Certificate
2001-12-14
2003-06-24
Jordan, Charles T. (Department: 3644)
Ordnance
Shields
Shape or composition
Reexamination Certificate
active
06581504
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the field of armour and armoured vehicles. More specifically, it concerns a passive armour for protection against shaped charges
BACKGROUND OF THE INVENTION
In the old days, the armours were normally made of a homogeneous metal plate made of steel or other high strength alloyed metal. The effectiveness of these plates depends on their thickness. Theoretically, these plates could defeat most forms of attack provided that the plate is thick enough. However, in practice the thickness is limited by considerations of cost and weight. The mobility of an armoured vehicle is an important aspect of performance, which is reduced by excessive weight.
An armour plate with an improved resistance to impact has been developed by the militaries. Such armour plate is made of steel with a high content of residual austenite. The presence of residual austenite allows a release of the mechanical stresses when the plate is under tension. The impact of a projectile striking on the plate put the same under tension. This tension leads to a decrease of the intrinsic compression stresses, which were preventing the final transformation of the residual austenite present in the microstructure, and thus induces the transformation of the residual austenite. This transformation, which is accompanied by a volume increase of approximately 4%, makes it possible to delay and even to prevent the material from reaching the maximum stresses sustainable before the point of rupture. This effect occurs when the projectiles have a velocity that corresponds to the velocity of a typical ballistic projectile. However, such armour plate has proved to be inefficient when the projectile travels at very high speed typical of shaped charges.
Shaped charges are weapons also known as hollow charge munitions, warheads with shaped-charged munitions, kinetic energy projectiles or lined cavity charges. A shaped charge can pierce a thick armour plate having a thickness as large as 19 inches (48.26 cm). A shaped charge fired on an armoured vehicle can pierce the armour of the same and explode within the vehicle thereby destroying the protected objects or people within the vehicle.
U.S. Pat. No. 6,311,605 gives a description of a shaped charge and of the working of such weapon.
FIG. 1
which substantially corresponds to
FIG. 1
of U.S. Pat. No. 6,311,605 shows a shaped charge in the form of a bomblet
1
at the point in time of striking against the surface
100
of a target protected with an armour. The bomblet
1
consists essentially of a housing
2
, which is filled with an explosive
3
in such a manner that this explosive
3
surrounds a downwardly opening insert
4
, which is constituted of a material, such as copper. The explosive
3
that is through-detonated by means of a fuse
6
presses the insert
4
together at a high rate of speed so that, from the tip region of the insert
4
, there is formed a hollow charge-jet or a jet
5
. The insert
4
is thus deformed by means of the detonation of the explosive
3
into the jet
5
, which moves under a continual stretching effect towards the surface
100
and penetrates into the latter. The peak velocities of the particles, which form the jet
5
, lie hereby between 5 and 10 kilometers per second (km/sec), whereas the diameter of the formed jet
5
lies within the millimeter range. At a complete precision, in homogeneous steel armour there are attained penetrating depths, which lie between 4 to 8 times the largest insert diameter. The mechanical impact detonation is effected, as a rule, in that a detonating needle
7
due to its inertia, upon striking against the object moves in a passageway
8
towards the fuse
6
, and pierces the latter, as a result of which there is detonated the bomblet
1
. The fuse
6
thereby brings the explosive
3
to detonation.
The power capability of the bomblet
1
depends essentially upon the stretching or expansion of the jet
5
. This is achieved in that the originally quasi-homogeneous jet at the point in time of its formation is stretched and thereby is caused to be particularized. A depth effect is then obtained from the addition of the individual power of the individual particle forming the jet
5
, which must penetrate behind each other in an absolutely precise manner. The stretching of the jet
5
takes place continuously, whereby the distance between the particles from the tip in the direction of the bomblet
1
continually reduces. For a desired penetrating power, it is necessary to provide a specific stretching path
9
, which is generally designated as a stand-off. The stand-off
9
is formed by the distance of the lower conical boundary of the insert
4
to the surface
10
. It is known that the optimal piercing speed of the jet is obtained at a stand-off of approximately three times the diameter of the insert
4
. This phenomenon is known in the US as the Munroe effect whereas, in Germany, it is known as the Neuman effect.
FIG. 2
b
shows the path of the jet within the thickness of an armour. It is now generally recognised by the scientific community that the jet of metal in fusion that propagates within the thickness of the armour is subject to an erosion effect whereby the jet gradually wears away by abrasion against the surfaces (
102
) defining the hole made by the same in the armour. This erosion effect is believed to be one of the major causes explaining the stop of the jet. The capacity of a shaped charge to pierce thick armour walls results from the extremely high speed (several thousand meters per second) obtained by the jet.
Many attempts have been made in the prior art to reduce the devastating piercing effect of the shaped charges. Among these attempts, there are the reactive armours provided with explosives. These reactive armours consist of a layer of metal backed by a layer of explosive material. The explosive is detonated by the attack and the metal layer is thus projected into or across the path of the attacking device so as to destroy or degrade its attack mechanism. Examples of such reactive armours are given in U.S. Pat. No. 4,869,152 and U.S. Pat. No. 5,637,824. One important drawback with such reactive armours is the collateral damages often caused to the people or army troops surrounding the armoured vehicle under attack. In such case, the shaped charge that explodes at the outer surface of the armour does not cause damage to the people or objects within the vehicle but to the people outside the same.
Also known in the prior art are the armours adapted to deviate the jet from its course before it strikes against the target surface. An example of such armour is given in U.S. Pat. No. 5,402,704, which discloses an armour system comprising a plurality of inclined plates positioned with respect to an incoming projectile in front of the wall target. Another example is given in U.S. Pat. No. 6,311,605 wherein an arrangement for protection against shaped charges is disclosed. Such arrangement comprises disruptive bodies provided on the surface of the target object. The height, shape and arrangement of the disruptive bodies are dimensioned such that at least one such body, for the disruption of the jet formation of the shaped charge, can penetrate into an internal region of a hollow charge insert or into the so-called stand-off region of the shaped charge. The principle of the arrangement disclosed in U.S. Pat. No. 6,311,605 is predicated on that the formation of a symmetrical jet of a bomblet can be prevented, and thereby the power thereof can be quite significantly reduced.
The so important piercing capacity of a shaped charge on a prior art armour made of steel or other alloyed metal can be explained by the fact that the velocity of the jet at the point of impact on the surface of the armour is such that no plastic deformation of the target material can occur. The material is thus subject to a brittle fracture limited only by the density and the hardness of the target material. Once the crack has been initiated at the surface of the armour, its propagation t
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