Abstract:
A reactive armor module for protecting a target from an incoming projectile, and comprising at least one armor cassette formed of a front base plate and a rear base plate sandwiching between them at least one layer of energetic material, the front base plate and the rear base plate being adapted, upon impact of the projectile with the energetic material, to be propelled in opposite directions; the armor module further comprising at least one non-energetic auxiliary plate spaced from the armor cassette and positioned essentially along the expected trajectory of either the front or the rear base plate, such that when propelled, the velocity of a base plate facing the auxiliary plate is reduced upon collision with the auxiliary plate.

Description:
FIELD OF THE INVENTION 
     This invention relates to armor modules fitted for attaching to the outside of a body liable to be exposed to attack by projectiles, e.g. shaped-charged warheads, kinetic energy projectiles and the like. Examples of bodies protectable by armor models in accordance with the present invention are, for example, land vehicles such as battle tanks, armored personnel carriers, armored fighting vehicles, armored, self-propelled guns; marine and navy crafts, static structures and enclosures such as buildings, above-ground portions of bunkers, containers of various nature, for the storage of fuel, chemicals, ammunitions, etc. all of which are collectively referred to herein after as a ‘target’. 
     BACKGROUND OF THE INVENTION 
     Reactive armor cassette modules are known in the art for forming an armor adapted to protect a body from an incoming projectile, and are especially effective against hollow charges. Hollow charges usually comprise an explosive charge set behind a liner which is adapted to transform the liner into a powerful and directional jet adapted to penetrate the body to be protected. 
     A standard reactive armor cassette module usually comprises two plates having sandwiched between them an explosive material, usually referred to as Explosive Reactive Armor (ERA). The explosive material is adapted to explode upon impact of the directional jet therewith, and thereby propel the two plates in essentially opposite directions. The cassette modules are often positioned on the body to be protected at an angle to the expected impact direction of the projectile, whereby upon propulsion of the plates and their subsequent movement, the jet is dispersed upon the plate, whereby its penetration capability is greatly reduced. 
     In order to increase the efficiency of a reactive armor, a plurality of cassettes in a variety of configurations may be used. The armor cassette modules may be spaced apart to cover a greater area of the body to be protected, be angled to each other and even be compactly packed within an armor module. 
     For example, U.S. Pat. No. 7,080,587 discloses an armor module comprising a rigid casing having a front face, a top face and a bottom face, and a plurality of multi-layer planner cassettes fixedly mounted within the casing. Each cassette has a top base plate and a bottom base plate, sandwiching between them at least a one other layer. The top base plate of an uppermost cassette constitutes the top face of the casing, and a bottom base plate of a lowermost cassette constitutes the bottom face of the casing. 
     U.S. Pat. No. 4,741,244 discloses an armor for Protection of land vehicles such as tanks, armored cars or the like against shaped charge projectiles. Protection is achieved by a cover member having suspended therefrom on the side that faces the substrate at least one explosive insert comprising an explosive layer sandwiched between two metal layers, such that when the element is mounted on the substrate the explosive insert remains distanced therefrom. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention there is provided a reactive armor module adapted to protect a target from an incoming projectile, and comprising an armor cassette formed of a first base plate and a second base plate sandwiching between them at least one layer of energetic material, said first base plate and said second base plate being adapted, upon impact of said projectile with said explosive, to be propelled in opposite directions, said armor module further comprising at least one non-energetic auxiliary plate spaced from said armor cassette and positioned essentially along the expected trajectory of either said first or said second base plate, such that when propelled, the velocity of either said first and/or said second base plate is adapted to be reduced upon collision with said auxiliary plate. 
     The layer of energetic material sandwiched between said first and said second plate may be of either an explosive or non-explosive material. 
     The reactive armor module may comprise a plurality of armor cassettes, each having a construction similar to the above described armor cassette, said cassettes may be spaced apart from each other. For example, a reactive armor module may comprise two cassettes. 
     Said reactive armor module may comprise a number of auxiliary plates, positioned in the front or in the rear of the base plates, ‘front’ and ‘rear’ being defined with respect to the expected direction of said incoming projectile. 
     According to a specific design, said armor module comprises two auxiliary plates, one being spaced from said front base plate, and another being spaced from said rear base plate, i.e. said cassette being sandwiched between said auxiliary plates. 
     A longitudinal dimension ‘L’ of the armor cassette, a distance ‘d’ between the auxiliary plate and the respective base plate of about 5-20% ‘L’ was found to provide improved results. For example, if the longitudinal dimension of said base plate is 300 mm, said auxiliary plate may be spaced at a distance of 15 mm therefrom. 
     It would be readily appreciated that the term ‘plate’ used herein is not restricted and applies for a variety of thicknesses which may range from about 2 to about 10 mm. 
     According to a specific design variation, the auxiliary plate is positioned substantially parallel to the base plate, such that, when propelled by said explosive, said base plate is designed to collide with said auxiliary plate and have a maximal contact area. 
     The base plates and the auxiliary plate may be made of a variety of materials. The materials may be chosen such that the collision between either of said base plates and said auxiliary plate is either of plastic or elastic nature. For example, while the base plates may be made of steel, said at least one auxiliary plate may be made both of metallic materials such as soft steel, Aluminum or Titanium and non-metallic materials including Aramid (Kevlar®), HDPE (Dynema®), Zylon® and ceramic materials. 
     In case ceramic material, and/or any form of ballistic fibers are used for the production of said auxiliary plate, said auxiliary plate may further provide protection against light firearm threats such as automatic machine gun, rifles etc. 
     The explosive layer between said first base plate and second base plate may be a sheet of energetic (reactive) material as known per se, adapted to explode upon impact of said projectile therewith. 
     The armor may be directly mounted onto the target to be protected and may be positioned thereon in a slanted orientation with respect to the expected direction of said incoming projectile. A slanted orientation may provide for greater efficiency of the armor as known per se. a plurality of armor modules may be mounted onto the target body allowing better coverage and overlap so as to provide improved protection thereof. 
     By a particular design of the invention, the armor cassette is confined within a casing having at least two walls to form an armor module adapted to be mounted onto the target body to be protected. Said walls may be made of a variety of materials, e.g. steel, metal etc. The walls of the armor module may be so designed as to allow mounting of a plurality of similar armor modules onto said target in a tessellated form, e.g. a top wall of one module extending adjacent or flush against a bottom wall of an adjacent module. 
     According to a specific design variation, the armor module comprises a casing formed with two side walls and the cassette and the auxiliary plate extend between said side walls. The extremities of said auxiliary plate are attached to the side walls of said casing, thereby increasing structural strength of the armor module. More particularly, said extremities may be inserted into pre-formed punctures/slots/ apertures in said side walls and then soldered or otherwise attached thereto. In addition, said auxiliary plate and said casing may be made of the same material, which provides for a more simplified production. According to another specific design, said auxiliary plate may be constituted a part of said casing. 
     The armor module may comprise one or more armor cassettes and corresponding auxiliary plates disposed therein, and the cassettes may be inclined with respect to each other so as to provide protection against various expected directions of an incoming projectile. 
     In operation, when an incoming projectile, for example a hollow charge, impacts the armor module, the jet formed by the hollow charge may likely initiate explosion of the energetic material sandwiched between the first and second base plates. The explosion of the energetic material then propels the first and second base plates very rapidly in opposite directions, normal to the surface of the plates, the first base plate moving outwards of the target to be protected and the second base plate moving inwards. The energetic material thus allows quick reaction to the impact of the jet, and causing its disruption. 
     The first base plate and/or the second base plate may plastically collide with an associated stationary auxiliary plate. Such collision will result in mutual movement of the auxiliary plate with the base plate colliding with it, in essentially the same direction, however at a reduced mutual speed. Said reduced mutual speed may be determined based on the initial velocity of said base plate and the masses of both said base and auxiliary plate. 
     Alternatively, said collision may be of fully or partially elastic nature, whereby said auxiliary plate is adapted to gain movement upon collision of said base plate therewith, whereby said the velocity of said base plate is consequently reduced. The velocity of movement of said auxiliary plate, and the reduced velocity of said base plate may be determined by the initial velocity of said base plate and the mass ratio between said base plate and said auxiliary plate. 
     When directional jets are concerned, it is known that the leading end of the directional jet usually travels with a greater speed than that of the trailing end of the directional jet. For example, the velocities of the leading and trailing ends may be 5 Km/s and 1 Km/s respectively. Thus, when designing armor panels, although a very short time interval is desired for reaction to the impact of said leading end, it is not desired for the plates to move too quickly, thus being unable to absorb and scatter the trailing end of said directional jet. 
     Thus, it would be appreciated, that by controlling the number of auxiliary plates used in one reactive armor module, the material from which they are made and additional design parameters such as mass, distance, thickness etc. it is possible to manipulate said armor module to provide, upon impact of a directional jet therewith, an array of moving plates the velocity and orientation of which correspond to the various velocities of the directional jet from leading to trailing end. 
     According to one such example of an armor module, said armor module comprises two auxiliary plates. Thus, activation of the energetic material may result in four moving plates, each having a different velocity which provides for an encounter of the plates with various portions of various velocities of the directional jet. However, this is achieved, compared to an armor module having two reactive armor cassettes, with the use of only one armor cassette module, allowing a substantial reduction ob about 30% in the overall weight of the armor module. 
     In particular, another important advantage of the present invention is noticed when a reactive armor module is mounted on a body to be protected such that said at least one auxiliary plate is positioned between said armor cassette and a hull of said body to be protected. In this case, a predetermined distance is formed between said rear base plate and the hull of said body to be protected. According to the present invention, due to the reduction of the velocity of the moving base and/or auxiliary plate, the time required to displace along said predetermined distance is prolonged, effectively increasing the contact time between said moving plate and said directional jet, providing for better use of said distance. 
     In the event several armor cassettes are used in a single module, an explosion in one of the reactive cassettes, and subsequent propulsion of the base plates may cause one of the base plate to impact an adjacent cassette armor. This may cause a chain reaction or ‘domino’ effect in which each cassette armor is activated by a propelled base plate or at least displaced or deformed thereby. This effect is usually referred to in the art as ‘sympathetic detonation’. In order to prevent the ‘sympathetic detonation’, a shock absorbing layer may be coupled to the armor cassettes, such that a propelled base plate encounters said layer prior to impact with said adjacent cassette armor, the shock absorbing layer being adapted to reduce the kinetic energy of said propelled base plate. The shock absorbing layer may in the form of a one or more layers of elastic material, which in turn may be reinforced. 
     The following advantages may arise from the above described invention:
         overall increase of about 20% in the effectiveness of the armor module compared to a standard design;   considerable reduction of weight of about 30% compared to a standard design;   an increase in the survivability of the target to be protected both due to efficiency of the armor module and due to reduced amount of overall energetic material;   reduced assembly time due to a simpler design;   cost efficient due to the reduction in the amount and variety of materials, both of the base plates and the energetic material;       

     The above described reactive armor module and armor module may typically be mounted on a passive armor of the target body to be protected. Thus, among other advantages of the present invention is the fact that the weight of such a passive armor may be increased due to the reduction in the overall weight of the reactive armor. Increasing the weight of said passive armor subsequently increases it&#39;s effectiveness, allowing it to better withstand explosions and impact of Improvised Explosive Devices (IED). 
     According to another aspect of the present invention there is provided an armor module adapted to protect a target from an incoming projectile, said armor module comprising at least one armor module cassette confined between two side walls of a casing, said module comprising an armor cassette formed of a first base plate and a second base plate with at least one layer sandwiched of energetic material therebetween, said first base plate and said second base plate being adapted, upon impact of said projectile with said explosive to be propelled thereby at a predetermined velocity and in opposite directions, said armor module further comprising at least one non-energetic auxiliary plate spaced from said armor cassette and positioned essentially along the expected trajectory of either said first or said second base plate, such that when propelled, the velocity of either said first and/or said second base plate is adapted to be reduced due to collision with said auxiliary plate. 
     The present invention calls also for a method for protection a target body against projectiles, the method comprising the following steps: 
     fitting the body on an outside thereof with at least one armor module for protection against said projectiles and shaped-charged warheads, said armor module comprises at least one armor module cassette confined between two side walls of a casing, said module comprising an armor cassette formed of a first base plate and a second base plate with at least one layer sandwiched of energetic material therebetween, said first base plate and said second base plate being adapted, upon impact of said projectile with said explosive to be propelled thereby at a predetermined velocity and in opposite directions, said armor module further comprising at least one non-energetic auxiliary plate spaced from said armor cassette and positioned essentially along the expected trajectory of either said first or said second base plate, such that when propelled, the velocity of either said first and/or said second base plate is adapted to be reduced due to collision with said auxiliary plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to understand the invention and to see how it may be carried out in practice, several embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which: 
         FIG. 1A  is a schematic cross section view of a prior art armor module; 
         FIG. 1B  is an enlargement of detail ‘A’ of  FIG. 1A ; 
         FIG. 2A  is a schematic isometric view of an armor module according to the present invention; 
         FIG. 2B  is a schematic cross section view of the armor module shown in  FIG. 2A ; 
         FIG. 2C  is an enlargement of detail ‘B’ of  FIG. 2B ; 
         FIG. 2D  is a schematic cross-sectional view of a portion of the armor module according to another exemplary embodiment of the present application; 
         FIGS. 3A to 3C  are schematic illustrations of an armor cassette according to one example of the present invention during impact of a directional jet thereon, in which the auxiliary plate is positioned behind the armor cassette; 
         FIGS. 3D to 3F  are schematic illustrations of an armor cassette according to another example of the present invention during impact of a directional jet thereon, in which the auxiliary plate is positioned in front of the armor cassette; 
         FIG. 4  is a scheme of Velocity vs. Time of base plates used in an armor cassette according to the present invention; 
         FIGS. 5A and 5B  schematically illustrate a side wall of a target body fitted with a prior art armor assembly, and an armor assembly according to the present invention, respectively, both of which fitted also with a passive armor plate; and 
         FIG. 6  is a diagram showing a comparison of weight distribution between an armor known in the art and an armor according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       FIGS. 1A and 1B  show a standard armor module as known in the art, generally designated  1 , and comprising a casing  2  and two armor elements  3 . The armor module  1  is attached onto a target body to be protected  5 , schematically illustrated here in phantom lines. 
     As best seen in  FIG. 1B , each armor elements  3  comprises a first thick armor cassette  5   a  and a second thinner armor cassette  5   b . The thick armor cassette  5   a  comprises an rear steel plate  7   a  and a front steel plate  8   a  sandwiching between them a layer of energetic material  9   a . Between the two plates  7   a  and  8   a , an additional steel plate  11  is positioned along with a rubber layer  13 . The layers of the armor cassette  5   a  are held together using a bolt  15   a  and nut  15   b  assembly. 
     The second, thinner armor cassette  5   b  also comprises two steel plates  7   b ,  8   b  with and energetic material  9   b  sandwiched therebetween. The second armor module  5   b  is thinner than the armor cassette  5   a  due to a thinner layer of energetic material  9  and absence of the additional steel plate  11  is positioned along with a rubber layer  13  provided in armor cassette  5   a.    
     Turning to  FIGS. 2A to 2C , an armor module according to the present invention, generally designated  10  is shown comprising a casing  21  containing two armor cassettes  30  ( FIG. 2B ). Each armor cassette  30  comprises an explosive armor cassette  32  comprising in turn a front steel plate  34  and a rear steel plate  36  sandwiching between them a layer of energetic material  38 , and an auxiliary plate  40  extending behind the rear steel plate  36  and spaced from said explosive armor cassette  32  (i.e. from the rear plate  38 ) at a distance d ( FIG. 2C ). The terms ‘front’ and ‘rear’ used herein are defined with respect to the expected direction of said incoming projectile 
     The casing  21  is formed of a rear wall  22 , two side walls  28 , a front wall  26 , a bottom edge  24 , and top and bottom edges  24  and  25  respectively. The rear wall is in the form of two flanges  22 ′ adapted to be connected to a target body to be protected (not shown), for example by a bolt and but assembly (not shown) through apertures  22 ″ ( FIG. 2A ). The bottom edge  25  is formed of three sections  25   a ,  25   b  and  25   c  angled to each other, and the top edge  24  is formed of three respective parallel sections  24   a ,  24   b  and  24   c . The front wall  26  is formed of two sections  26   a  and  26   b  angled to each other. The design of the casing  20  allows a plurality of such modules  10  to be positioned one above the other in a tessellated manner such that, for example, the section  25   a  of a bottom edge  25  of one module  10  comes in contact with a section  24   a  of the top edge  24  of a downwardly adjacent module (not shown). 
     In accordance with a particular embodiment, the rear steel plate  36  has a longitudinal dimension ‘L’ ( FIG. 2B ) of about 300 mm and the auxiliary steel plate  40  is spaced at a distance ‘d’ of about 15 mm therefrom, which is 5% of the length ‘L’. The auxiliary plate  40  is attached directly to the casing  20  by lateral extensions  42  integral therewith inserted into slots  43  formed in the side walls  28 . In assembly the extensions  42  are inserted into the slots  43  and then welded in place thereby fixing the auxiliary plate  40  firmly to the casing  20 . Such an attachment, i.e. directly to the casing  20 , also provides structural strength to the whole module  10 . 
     With reference to  FIG. 2D , it is appreciated that according to another example of the armor module, the latter can comprise an additional auxiliary plate  40 ′ located on the other side of the armor cassette  30 , i.e. in front of the cassette. 
     Turning to  FIG. 3A , an illustration of a high speed photograph of armor cassette  30  according to the present invention is shown an instance before a jet  60  of a hollow charge strikes the explosion armor cassette  32 . The target body to be protected  5  on which the armor module  30  is mounted is shown in phantom line, being spaced apart at a distance ‘w’ from the armor cassette  32 . 
       FIG. 3B  illustrates the explosion armor cassette  30  an instance after explosion of the energetic material  38  upon hitting and exiting by the jet  60 . The front plate  34  is propelled at an essentially upward direction of arrow  62  and the rear plate  36  is propelled at an essentially opposite and parallel, downward direction of arrow  64 , both having initial velocities V UP  and V BP  respectively. Displacement and deformation of the plates  34  and  36  disperses and scatters the jet  60 . In  FIG. 3C  the rear plate  36  is further deformed and propelled towards the auxiliary plate  40  which now deforms also and displaces together with the rear plate  36 , whereby the power of the distal end (leading end)  67  of the jet is significantly reduced. 
     As opposed to a standard armor cassette previously described, after exciting the explosive material and propelling the rear plate  36  towards the auxiliary plate  40 , the rear plate  36  together with the auxiliary plate  40  acquire a velocity V B′  whereby V B′ &lt;V B′  and where V B &lt;V U ′ designated by arrow  69  in  FIG. 3C , thus still coming in contact with the slower, trailing end  68  of the jet  60 . 
     It would thus be readily appreciated that an array of auxiliary plates  40  may be employed within the armor module  10 , whereby the velocity of the base plates  34 ,  36  is gradually reduced to correspond to the varying velocity of the jet  60 , providing high efficiency of the armor module  10 . 
     It would also be appreciated, that due to the presence of the auxiliary plate  40 , and subsequent reduction in velocity of the base plate  34 , the time required for the plate  34  to travel from its initial position to the body to be protected  5  lengthens. This lengthening in time is equivalent to an effective contact time with the jet  60 . Thus, according to the present invention, the distance ‘w’ is better utilized compared to an armor module  1  according to the prior art. 
     Turning to  FIGS. 3D to 3F , another example of an armor module is shown in which the auxiliary plate  40  is positioned in front of the armor cassette. According to this example, the trailing end  68  of the jet  60  is eventually contacted by the upper base plate  34  and the auxiliary plate  40 . 
     It would thus be appreciated that a variety of modules  10  according to the present invention may be construed, including ones having auxiliary plates  40  both in front and behind the armor cassette  30 , and any combination thereof including more than two auxiliary plates  40 . 
     Turning to  FIG. 4 , the chart shows the velocities of both the rear plate  36  and the auxiliary plate  40  as a function of time. Practically immediate after the impact (at t=˜1 μs), explosion of the energetic material  38  is initiated by the jet  60  causing initial movement of the rear plate  36  designated by point  91 . As the shock wave of the explosion progresses and the rear plate  36  deforms and displaces ( FIG. 3B ) and acquires an initial velocity V B  of about 1.2 Km/s designated by peak  93 . Upon impact with the auxiliary plate  40  (at t=˜17 μs), designated at point  92 , the speed of the rear plate  36  drops to about 0.35 Km/s (designated at point  95 ) where part of the kinetic energy is transferred to the auxiliary plate  40  which deforms and displaces with the rear plate  36 , whereby the auxiliary plate acquires a velocity V B′  of about 0.85 Km/s designated by peak  94 . The upper plate  31  encounters both the jet  60  and the auxiliary plate, thus its velocity being reduced to V B  of about 0.4 Km/s, designated by point  95 . The speed of the plates  36  and  40  soon near so theses plates move substantially together at reduced speeds. 
     An armor module  10  according to the present invention allows reducing the overall weight of the reactive armor while achieving a similar, if not better result.  FIG. 5A  schematically illustrates a side wall  75  of a target body, e.g. an armored vehicle, fitted with a prior art armor assembly  77  (e.g. of the type illustrated in  FIG. 1A ), with a passive armor plate  79 , made of steel and extending between an outer surface of the target wall  75  and a rear of the armor modules  77 . In  FIG. 5B  there is schematically increasing an armor assembly  81  according to the present invention fitted onto a side wall  75 ′ of a target body. 
     It is noted that owing to the reduction in overall weight of the armor assembly  81 , the steel passive armor plate  83  can be substantially thicker and thus provide improved protection and withstand additional threats, for example, an IED. 
     With further reference to  FIG. 6 , a comparison of the weight distribution of the overall weight of an armor between a corresponding prior art armor module (designated  98  in  FIG. 6 ) and a module according to the present invention (designated  99  in  FIG. 6 ) is shown. It is clear that under the same overall weight, 310 Kg, the module  10  according to the present invention may be equipped with about 5 times more weight, i.e. 175 Kg as opposed to 35 Kg. 
     Those skilled in the art to which this invention pertains will readily appreciate that numerous changes, variations, and modifications can be made without departing from the scope of the invention, mutatis mutandis.