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TECHNICAL FIELD

The present invention relates to reactive or "dynamic" protective armour arrangements for protection against obliquely impinging hollow explos ve charge jets. The armour arrangement comprises two mutually spaced metal plates, which can be penetrated by an imping ng hollow explosive charge jet to form a hole n the plates, and

10 further comprises an intermediate layer of non-explosive material located between the plates.

BACKGROUND PRIOR ART

One such reactive armour arrangement is known from U.S.

15 Patent Specifica ion No. 4,368,660. Incorporated between the plates of this known arrangement is an explosi e substance which will detonate when a hollow charge jet or like projectile impinges on the reactive armour arrange¬ ment, the subsequent detonation pressure causing the two

20 plates to move away from each other and therewith greatly degrade the hollow charge jet.

The plates of such protective armour arrangement, however, need to be relatively large in order to function effec-

25 tively, and consequently commensurately large quantit es of explosive must be used in order to achieve the effect desired. One drawback in t is regard is that the explosive forces generated by such large quantities of explosi e are liable to result in damage to the object protected by the

30 arrangement (e.g. an armoured vehicle or tank).

SUMMARY OF THE INVENTION

The object of the present invention is therefore to pro¬ vide a reactive armour arrangement of the aforesaid kind

35 which does not require the use of an explosive charge to fulfill its protective function.

This object is achieved with a reactive armour arrangement having the inventive features set forth in the charac¬ terizing clause of the following Claim 1.

Further developments of the invention are set forth in the depending claims.

The invention is based on the discovery that the intrinsic energy of the hollow explosive charge jet in itself can be used to create Shockwaves of different pressures in the plates and in an interlayer of the reactive armour arrangement. The pressure differentials created result in two counter-directional forces which tend to move the plates away from one another, n a manner which causes fresh plate material to be moved progressively into the path of the hollow explosive charge jet, thereby reducing the energy of the jet.

Compressible materials such as, e.g. rubber, or gases, e.g air, cannot be used to form the interlayer since almost all of the energy present in the Shockwaves is dissipated in dislodging or punching material from the plates. The interlayer material should therefore be incompressible and possess a high dynamic mechanical strength.

The physical explanation of the Shockwave effect is that practically total reflection of a Shockwave takes place when the Shockwave moves from a medium of relatively high density to a medium of lower density. Thus, in the case of the inventive protective arrangement, an impinging hollow charge jet will initiate in the outer plate a first shock- wave which is reflected towards the thinner interlayer, this procedure being repeated some microseconds later behind the tip of the jet or thorn in the nner plate. This results in two forces wh ch act n mutually opposite directions and which tend to draw the plates apart. It has been found, in accordance ith the invention, that an

optimal Shockwave effect s obtained when the interlayer comprises an incompressible material and has a density which is at most 1/3 of the density of the plates.

The hollow charge jet will create in the protecti e armour arrangement a hole wh ch s nversely proportional to the flow stress of the outer material and which is greater than the diamater of the hollow charge jet. Due to the aforesaid counter-direction forces, the edges around the hole will be lifted to form a bulged or cratei— like surround, such that the plate material around the hole wi ll move progressively into the path of the obliquely impinging jet, thereby causing the jet to penetrate further material with a subsequent decrease in jet energy.

The invention can also be explained in terms of Shockwave pressure. For example, it has been established exper ¬ mentally that when the Shockwave pressure in the plates is p^ pressure units and the Shockwave pressure in the interlayer is p2 pressure units, the optimal outward bulging or lifting of the plate material surrounding the hole is obtained when P- _j p? ⁼ about 7. An acceptable outward lifting of the hole-defining edges is obtained within the range 2 < p.. /p ₂ < 12.

Thus, the energy trans itted from the hollow charge jet to the protective armour arrangement (excluding the pen¬ etration energy) is converted to kinetic energy for movement of the armour plates, which therewith expand at a certain velocity. The rate of expansion increases with the energy content of the jet tip or thorn, but decreases with the mass of the outer plates.

Degradation ceases when the jet no longer touches the protective armour, this loss of contact possibly being due to the fact that the plates have been lifted sufficiently in the region of the hole-defining edges thereof, or because the plates have ceased to expand.

The plates will suitably have a thickness between 2 and 20 mm, preferably between 2 and 10 mm, in order to ensure that the hole-defining edges will be lifted or upwardly bulged, to the extent desired, i.e. to ensure that sufficient plate material is shifted into the path of the hollow charge jet.

The plates are preferably joined together by strips which function as hinges and which concentrate the rate of expansion for the protective armour to the region thereof around the entrance hole. It has been found in practice, however, that the plate material located in the vicinity of the hole w ll tend to lift even when the plates are not connected together with the aid of such strips, thereby indicating that their presence is not absolutely necessary.

In order to degrade effectively the hollow charge jet, the plates should exhibit high dynamic mechanical strength, a h gh density, and have a high expansion rate. According to one preferred inventive feature the plates have a density greater than 4 " 10 kg/m , and preferably greater than 7 • 10 kg/m . The plates may suitably compr se, e.g., steel and tungsten, which together with, e.g., ethyLene plastic in the interlayer satisfactorily fulfills the aforesaid conditions.

The dynamic yield point or flow stress σ _Q ~ of the inventive plate material should, in accordance with one inventive feature, exceed 60 MN/m .

The interlayer is preferably comprised of a solid or liquid non-explosive material, e.g. rubber, plastic, water, or some other inert substance of low density, although at least 750 kg/m , and low Shockwave pressure in response to a hollow charge jet impact.

The interlayer may alternatively comprise a semi-inert material, i.e. a material which when subjected to high pressure, e.g. a pressure in the order 1-2 GPa, gives rise to partial deflagration (combustion) or detonation. By partial is meant here that deflagration or detonation only takes place in the high pressure regions, i.e. does not propagate from these regions.

Examples of such semi-inert materials are various solutions of formaldehyde or its compounds, e.g. an aqueous solution of formaldehyde or a solution of formaldehyde in water and methanol, or alternatively a formaldehyde tπ ^' mer (trioxane) or various forms of homopolymers or copolymers of po lyoxymethy lene (poly- formaldehyde). Other substances r ch in oxygen or halogens may also be used. Additional "acitivity" is achieved when readily sublimated substances are used, e.g. such as the aforesaid trioxane, or ethylene carbonate.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be descr bed in more detail with reference to the accompanying drawings.

Figure 1 illustrates a preferred embodiment of an inven¬ tive projective armour arrangement in a non-activated state.

Figure 2 illustrates the protecti e armour arrangement of Figure 1 in an act vated state. Figures 3a-d are schematic illustrations of four various stages of penetration of the hollow explosive charge jet into the protective armour arrangement

Figure 4 illustrates from above a protective armour arrangement that has been penetrated by a hollow charge jet.

DESCRIPTION OF A PREFERRED EMBODIMENT

Figures 1 and 2 illustrate schematically a "dynamic" protective armour arrangement which comprises one or more panels structures 3, of which only one is shown and this in cross-section. Each panel structure 3 comprises two mutually parallel plates 4 and 5 which are joined together in spaced apart relationship with the aid of oining strips 6 and 7 located at the edges of respective plates, such that all plates together form a contai ner- 1 i ke structure, the plates being of square configuration for example, and said plates and said strips being made, e.g. of steel. The conta i ner- 1 i ke structure thus formed is filled with an inert substance, e.g. rubber, plastic or water, which forms the aforementioned interlayer.

When the hollow charge projectile 2 detonates, it generates, in a known manner, a hollow charge jet or thorn 9 which bores a hole 10 in the outer plate 4 and a hole 11 in the inner plate 5 of the container-like structure. The resultant Shockwaves are reflected in the plates 4 and 5 in the aforedesc ri bed manner, therewith to lift the plate material around the holes 10 and 11 forming conical or crater-like bulges at the hole-surrounds, as illustrated in Figure 2. The jet or thorn is therewith degraded, as shown at 9a, and will penetrate the target 1 to be extent illustrated by reference 9b in Figure 2. The reference 9c designates the extent to which a hollow charge et would penetrate the target if the target were not protected by the inventive dynamic armour arrangement.

The movement executed by the plates 4 and 5 is illustrated more clearly in Figures 3a-d.

Figure 3a i llustrates a hollow explosive charge jet which impinges obliquely on the outer plate 4 of the protective armour arrangement. Figure 3b shows how the jet wi ll penetrate the pla es 4 and 5, to form a hole 10 in the outer plate 4 a ^* - ^* . z a hole 11 in the inner plate 5. As beforenientic-e: _/ .re hollow explosive charge jet is degraded, as i llustrated at 9a. The Shockwave forces in the plates 4 and 5 create crater-like bulges 12a, 12b in the plate material surrounding the respective holes 10 and 11, cf. Figure 3c.

Because the plate material bulges around the holes 10, 11 in the aforesaid manner, fresh plate material wi ll be progress vely shifted into the path of the jet or thorn 9 as the bulges form. The Length extension 13 in Figures 3d and 4 i llustrates the extension of plate material moved into the path of the jet. The plates material contained in said displaced plate extension is sawn by the hollow charge jet in the manner i llustrated at 14 in Figure 4, said Figure i llustrating schemat cally a fragment of the plate 4 and show the appearance of the hole 10 subsequent to cessation of the hollow charge jet.

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