Passive defence system against hollow charged weapons   

FIELD OF THE INVENTION

The present invention relates to a defence barrier against hollow charge warheads, the barrier comprising a plurality of sealed, demountable elements filled with pressurised fluid and being provided side by side to form the barrier.

BACKGROUND OF THE INVENTION

When a shaped hollow charge warhead detonates upon collision with a target, the energy is concentrated to the center of the hollow space in front of the charge. A powerful jet of the explosion gases hits the target with a tremendous speed and penetrating pressure. The effect can be increased by putting a metal liner to the surface of the hollow. When the explosion occurs, the liner metal is formed into a plasma jet burning its way through the target.

For armoured vehicles, a number of related defence mechanisms have been developed. One if the method includes an explosive layer sandwiched between two metal layers, for example as disclosed in U.S. Pat. No. 5,637,824 by Benyami and in references therein.

In contrast to explosive defence mechanisms, passive mechanisms without explosive have been considered as well. German patent DE 3122367, discloses a passive armour for vehicles against hollow charge weapons, where sections are provided between two armour pates, the sections being filled with a liquid, especially water or fuel, or a solid, porous material, such as concrete, in order to provide shock wave reflection upon collision with a hollow charges warhead trying to burn its way through the armour. This passive armour in this disclosure has the disadvantage that a hit part of the armour is not easily repaired and implies a weakened part of the armour until a repair garage is reached by the vehicle. Especially in connection with strategic multi-hit attacks on the same area of the armour, this system is disadvantageous

A general approach for a defence mechanisms in connection with missiles is disclosed in GB 101836 by Murray, where a ship comprises a number of hollow removable sections to enclose part of the hull, the sections being armoured outside and forming vertical columns and horizontal rows, each section comprising a series of springs and compressed air supplied from a supply on the ship. The spring mechanism does not have any practical defence effect on attacks with hollow charge weapons, which indicates that this system is not envisaged for this kind of weapons. Though no pressure level is disclosed, the envisaged pressure level is unlikely to have any effect on hollow charge warheads as well.

From DE 1 902 856 another solution is known, where a barrier consists of an amour plate covered by elements filled with a pressurised fluid or an explosive charge. These elements are fixed side by side with external fixation means. The external fikation means will easily be damaged during an attack and therefore replacement of damaged elements is made difficult, further the amour plate is constructed with a number of projecting ribs, which also easily will be damaged and leading to a situation where the elements can not be replaced.

It is the object of the invention to provide passive defence means against hollow charged weapons, especially a defence barrier for vehicles, which is efficient, flexible and easy to repair.

This object is achieved by a defence barrier against hollow charge warheads, the barrier comprising a plurality of sealed, demountable elements filled with pressurised fluid and being provided side by side to form the barrier. The pressure of the fluid is above 100 bars, preferably above 500 bars or even above 1000 bars.

The high pressure of the fluid in the elements according to the invention implies a very short reaction time against the plasma jet of a penetrating hollow charge warhead, which is necessary, as the penetration of the plasma jet from the warhead occurs in a time frame of less than milliseconds. This is in contrast to the disclosure of German patent DE 3122367, where a certain delay occurs due to the built up and reflection of a shock wave.

Preferably, the fluid is liquid. The high pressure and the rather small change of volume during pressure changes imply an almost immediate resistance against the plasma jet of the warhead, when it enters an element. The resistance reduces the power of the plasma jet considerably and, as soon as the highly directional and narrow plasma jet has been disturbed, the warhead loses most of its penetration power. When used in connection with an armour shield behind the element, this disturbance prevents the warhead from traversing the shield stopping the warhead from performing further damage to the object to protect.

The object to protect may be a vehicle, such as a tank, a ship or other objects. Due to the system according to the invention with demountable elements, any object can—in principle—be surrounded by a wall barrier made up of such elements. This is especially so, if the elements have a relatively small size such that they are suited to be placed side by side even on curved surfaces. The elements may be constructed such that each element is fastened to an armoured surface. I a preferred embodiment of the invention, the elements may be constructed for mutual assembly into groups of elements which are then fastened in groups to a surface, grid, or other means. Such a group of elements can be arranged side by side, over and under and of cause in combinations thereof. It is thus possible to have one group of elements covering a certain area and in multiple layers. Such a group of elements can easily and quickly be changed in case of damage.

An element may contain a single chamber with pressurised fluid but may also contain a plurality of fluid chambers, for example 2, 3, 4, 5, 10 or even more. The number of chambers chosen for an element is a balance between the desired size of an element and the desire for having as small as possible an unprotected area after a strike by a warhead. Thus, for replacement, the number of elements should not be too high, as fewer elements are replaced faster than many. On the other hand, after being struck, at least one chamber is emptied, and a further attack on the same spot may be fatal. Thus, the size of the chamber should be small, albeit large enough to be efficient against the attacking warhead. By providing elements with small chambers, only small areas are exposed undefended for further attacks until replacement. In this connection, it should be emphasized that several attacks may strike the same multi-chamber element, especially, because multi-hit attacks are typical strategies for immobilizing vehicles from the enemy. Also, it should be emphasized that attacks under a skew angle may damage several chambers in a single strike. After such attacks, replacement of only one element or a group of elements may quickly replace multiple chambers that have been damaged under these circumstances.

As an advantageous precaution against the plasma jet, in a further embodiment, the content in the element is fire retardant. Apart from a fluid, the element may comprise a fire retardant, non-gaseous, compressible material. The degree of compressibility may be chosen in dependence of the desired defence action. If the material has a low compressibility, a high pressure is needed to compress the material, which implies that the material reacts faster against the plasma jet upon being hit by a warhead.

Preferably and in contrast to the elements in the above mentioned patent GB 101836, the elements do not have an armour on their side facing a possible warhead attack. Instead, the elements have a wall facing a direction for possible warhead attack which is produced in a material with a material thickness and material strength of the order necessary to withstand the pressure of the pressurised fluid but without being armoured to a degree which substantially hinders the warhead to penetrate the second wall. This embodiment of the invention implies that an efficient defence mechanism is provided with low weight, as an outer, heavy armour is avoided, which makes it especially suitable for light weight military vehicles. This is in contrast to the above cited systems in GB 101836 and DE 3122367. Preferred materials for the elements are light weight materials with a high strength. For example, the material may be chosen among glass and polymer, possibly fibre enforced polymer.

As an efficient defence mechanism against tandem warheads, the invention includes the possibility to arrange multiple layers of elements, such that a tandem warhead with two—or even more—explosive charges will be counteracted upon through multiple layers of elements. Also, multiple layers of elements are useful in case of a multiple-hit strategy, where the counterpart attempts to hit the same region of the barrier multiple times in order to weaken the defence mechanism.

It should be mentioned that the term hollow charge warhead not only covers the typical type of warhead, which is known from industrially produced weapons of this kind, but also covers the latest generation of Improvised Explosive Devices (IED), in which hollow charge plasma jet formation is being implemented.

By the invention, a passive defence barrier against hollow charged weapons has been provided, especially a defence barrier for vehicles, the barrier being efficient, flexible and easy to repair.

The barrier according to the invention can be provided as a single layer of elements or as a double, triple or multilayer of elements. For example, part of the barrier can be provided with a single layer of elements, whereas other part of the barrier may comprise elements arranged in two or more layers on top of each other in order to provide a barrier with high flexibility and adaptation properties. As the elements are demountable, preferably independent of each other, the elements may be arranged in a flexible manner in accordance with the actual needs for protection.

The invention will be explained in more detail with reference to the drawing, where

FIG. 1 is illustrating a system according to the invention with a single layer of elements.

FIG. 2 is illustrating a system according to the invention with a double layer of elements.

DETAILED DESCRIPTION

The drawing illustrates a defence barrier according to the invention. The barrier comprises a support 1, for example an armour shield or a grid in front of an armour shield, in front of which a number of elements, generally denoted 3, according to the invention are positioned. The elements 3 are fastened to the support 1 by first fastener 2. Such fasteners 2 can be used to fasten elements 3d individually or in groups of elements 3a, 3b, 3c. Such groups of elements 3a, 3b, 3c may, in this case be fastened mutually by second fastening means 4.

In case that one or several of the elements 3 are damaged, the elements 3 are easily replaced by demounting the elements 3 by loosening the first fasteners 2. If the elements 3a, 3b, 3c are fastened in groups of elements, an entire group 3a, 3b, 3c may be replaced by loosening its fastener 2 to the support 1. Alternatively, both the first fastener 2 and the second fastener 4 may be loosened and single elements within one group may be replaced.

In case that the object to be protected is of static nature, the elements 3e, 3f, 3g according to the invention need not necessarily be fastened to an armour but may be placed on top of it or on its side by stacking.

FIG. 2 illustrates an alternative embodiment, where two layers 31, 32 of elements 3 are provided. The elements 3 of the second layer 32 are fastened to the elements 3 of the first layer 31 by fasteners 2. The elements 32a of the second layer 32 may be fastened displaced form the elements 3 in the first layer 31, or alternatively, the elements 32b of the second layer 32 may be arranged coaxially with the elements 3 of the first layer 31.