Patent Publication Number: US-2006016360-A1

Title: Anti-bunker ammunition

Description:
BACKGROUND OF THE INVENTION  
      1. Field of Invention  
      The technical scope of the invention is that of ammunition able to destroy targets heavily protected by a wall, for example of concrete.  
      2. Description of the Related Art  
      It is known, namely by patent U.S. Pat. No. 6,186,072, to define a piece of ammunition incorporating a perforating body whose inertia ensures its passage through thick protective walls. This ammunition encloses an explosive or incendiary charge that is ignited during the perforation or after perforation of the wall.  
      The problem with these pieces of ammunition is that, when the wall to be passed through is of great width (more than one meter), the explosive charge may be disorganized or fractured during its passage. The effectiveness of the explosive ammunition is thus severely reduced.  
      One means to improve the resistance of this ammunition is to thicken the casing surrounding the explosive. However, this increases the mass of the ammunition without necessarily increasing the mass of the front part ensuring the perforation.  
      Furthermore, the volume available for the explosive is reduced and the effectiveness of the splinter cone may be reduced due to the over-fragmentation of the casing.  
      Moreover, these pieces of ammunition incorporate a high mechanical properties steel casing intended to generate splinters. It is not possible for the radius of effectiveness of this splinter charge to be defined reliably and reproducibly since it becomes deformed after passing through a wall.  
     SUMMARY OF THE INVENTION  
      It is the purpose of the invention to propose anti-bunker ammunition that does not suffer from such drawbacks.  
      Thus, the anti-bunker ammunition according to the invention allows the effectiveness of the splinter charge to be controlled whatever the thickness of the wall through which it passes.  
      Thus, the invention relates to an anti-bunker ammunition comprising a penetrating body delimiting an internal cavity closed by a base, ammunition characterized in that the cavity encloses at least one sub-munition, a device to eject said sub-munition as well as a device to eject the base, the sub-munition or munitions and the ejection devices being insulated from at least one of the walls of the internal cavity by a shock-absorbing material.  
      According to a particular embodiment, the sub-munition or munitions comprise an explosive charge placed in a splinter-generating casing.  
      Advantageously, the explosive charge of the sub-munition or munitions may comprise two ignition devices, each device being placed at one end of the splinter-generating casing, the joint ignition of the two devices ensuring the concentration of the splinters.  
      According to another embodiment, the sub-munition may comprise an incendiary heat and/or blast effect charge, or a thermobaric charge.  
      The shock-absorbing means may comprise at least two blocks.  
      The ammunition according to the invention may incorporate control means connected to a fuse ensuring the detection of the passage through a wall, such control means sequentially ensuring the ignition of the base ejection device then that of the sub-munition or munitions ejection device.  
      The ignition of the sub-munition or munitions ejection device will be advantageously commanded after passage through the wall.  
      The perforation body may incorporate a front nose comprising at least one bar crimped in at least one bore.  
      The perforation body may be integral with a propellant.  
      The perforation body may be integral with a guiding/piloting module.  
      The anti-bunker ammunition according to the invention may thus constitute a bomb or an air-to-ground missile. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will become more apparent from the following description of different embodiments, such description being made with reference to the appended drawings, in which:  
       FIG. 1  shows a partial longitudinal section of a piece of ammunition according to the invention,  
       FIG. 2  shows an enlarged longitudinal section of the perforating part of an ammunition according to a first embodiment of the invention,  
       FIG. 3   a  shows an enlarged longitudinal section of the perforating part of an ammunition according to a second embodiment of the invention,  
       FIG. 3   b  is an external side view of this same ammunition,  FIG. 3   c  being a front view of the nose cone of this ammunition,  
       FIG. 4  shows an enlarged longitudinal section of the perforating part of an ammunition according to a third embodiment of the invention,  
       FIGS. 5   a ,  5   b  and  5   c  show three stages in the operation of an ammunition according to the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      With reference to  FIG. 1 , an anti-bunker ammunition  1  according to one embodiment of the invention comprises a front perforating warhead  1   a  which here is integral with a rear part  1   b  comprising a propellant module  2  and an electronic guiding/piloting module  4 .  
      The propellant module  2  is not shown here in detail. It classically encloses a gas-generating propellant charge (not shown), such gases ejected rearwards of the ammunition  1  by a nozzle  3 .  
      The electronic guiding/piloting module  4  is also not shown in detail. It is connected to four rear piloting fins  5  formed into a cross.  
      The ammunition  1  thus constitutes a missile or else an air-to-ground bomb having a piloting capability to a target.  
      The propellant module  2  allows the projectile to be given a minimal velocity required for impact on a target, such velocity ensuring the perforation of the target. This module may thus be ignited only a few tens of meters before impact. For a concrete target of a thickness wider than one meter, an impact velocity great than or equal to 300 m/s will be required.  
      In the event of the ammunition  1  being a missile, the propellant module  2  may incorporate a cruise propellant stage which will ensure the required range is reached for the missile.  
      According to the range of the missile in question, the cruise propellant may itself ensure the impact velocity required or else may be coupled with a perforating propellant supplying the minimal velocity required on impact.  
      In the event of the ammunition being a bomb and if the total mass of the bomb is sufficient to ensure the minimal velocity required on impact, the propellant module may be omitted.  
      Lastly, for certain bombs dropped at low altitudes it is possible not to provide for a guiding/piloting module.  
      The propellant  2  and guiding/piloting  4  modules are not the object of the present invention and will therefore not be described in any further detail hereafter.  
      The ammunition  1  comprises a perforating warhead  1   a  comprising a penetrating body  6  having a solid front nose  6   a  prolonged by a cylindrical rear part  6   b  delimiting an internal cavity  7  closed by a base  8 .  
      According to the invention, the internal cavity  7  encloses a sub-munition  31  and an ejection device  9  for said sub-munition  31 .  
      This ejection device  9  comprises an igniter  10  and a gas-generating pyrotechnic charge  11 . A piston  12  is also placed between the sub-munition  31  and the pyrotechnic charge  11 .  
      The internal cavity  7  also encloses an ejection device  13  for the base  8 .  
      This device  13  also incorporates an igniter  14  and a gas-generating pyrotechnic charge  15 .  
      The two igniters  15  and  10  are connected by wire links  16  to control means  17  placed inside the internal cavity  7 , between the front nose  6   a  and the sub-munition ejection device  9 .  
      This control means is itself connected to a fuse  18  designed so as to be able to detect the passage through a wall. Such fuses are well known to the Expert. Reference may be made, for example, to U.S. Pat. No. 5,255,608 which describes such a fuse.  
      The control means  17  and fuse  18  may constitute a single electronic circuit comprising an appropriately programmed microprocessor.  
      According to another characteristic of the invention, the sub-munition  31  and ejection devices  9  and  13  are insulated from the walls of the internal cavity  7  by shock-absorbing means  19 . Thus, the sub-munition  31  and the ejection devices  9 ,  13  are not perturbed by the perforation body  6  impacting on the target.  
      The shock-absorbing means  19  will be constituted, for example, by an elastomer material such as RTV 630. This material will be installed, for example, by casting inside the internal cavity  7  before the sub-munition  31  and ejection devices  9  and  13  are installed. Appropriate tooling will allow a volume to be left free during the casting operation for the subsequent installation of the sub-munition and ejection devices.  
      Thus, the shock-absorbing material will adhere to the walls of the perforation body  6  without adhering to the sub-munition  31  which may thus be ejected without any difficulty.  
      The operation of the ammunition according to the invention will now be described with reference to  FIGS. 5   a  to  5   c.    
       FIG. 5   a  shows the arrival of the ammunition  1  to impact on a target  20  made of concrete whose thickness E is more than one meter and which covers and internal cavity  21 .  
      The impact velocity V of the perforation body  6  is greater than or equal to 300 m/s. This velocity, depending on the case, results either from the inertia of the fall (non-propelled bomb), or from the thrust of a propellant (propelled bomb or missile).  
       FIG. 5   b  shows the first instants following the impact of the ammunition  1  on the target  20 .  
      During the impact on the target, the control means  17  firstly cause the ejection device  13  of the base  8  to be ignited.  
      This ejection of the base may also ensure the ejection of the rear part  1   b  of the ammunition (not shown here).  
      When the target  20  is being perforated, the sub-munition  31  is insulated from the mechanical stresses to which the perforation body  6  is submitted thanks to the shock-absorbing material  19 .  
       FIG. 5   c  shows the target  20  bearing a hole made by the passage of the perforation body  6 .  
      The fuse  18  detects the entry into the cavity  21  and by means of the control means  17  ignites the device  9  ensuring the ejection of the sub-munition  31 .  
      The control means  17  also ensure the ignition of the sub-munition  31  after a pre-programmed delay corresponding to the time required to eject the sub-munition  31  from the body  6 .  
      The sub-munition  31 , which is not deformed by passing through the target  20 , may thus exert its action inside the cavity  21 .  
       FIG. 2  shows in greater detail an embodiment of a perforating warhead. According to this embodiment, the sub-munition  31  is a splinter-generating sub-munition which comprises an explosive charge  22  placed in a splinter-generating casing  23 .  
      Splinter-generating casings are well known to the Expert. Reference may be made, for example, to patents FR2807156, U.S. Pat. No. 5,544,589 and EP918206 which describe such casings.  
      The casing  23  here is a cylindrical casing stopped at each end by a lid  24 . Each lid carries an ignition device  25  which will advantageously incorporate a pyrotechnic delay ensuring the ignition of the explosive charge  22  after the ejection of the sub-munition from the body  6 .  
      The ignition devices  25  are both connected to the control means  17 . Thus, since each device is placed at a different end of the casing  23 , the joint ignition of the two devices ensures a concentration of the splinters in a median plane substantially perpendicular to the axis of the cylindrical casing  23 .  
      In accordance with this embodiment, the front nose  6   a  of the perforation body  6  is made as a single block of a material having high mechanical properties, that is to say a material whose limit of elasticity is greater than or equal to 1200 Mega Pascals. For example, 35NCD16 type steel may be used.  
      Only the front nose  6   a  is involved in the perforation of the target. The cylindrical part  6   b  does not have to protect the explosive charge  22  of the sub-munition, which is insulated from the shock by the shock-absorbing material  19 .  
      The cylindrical part  6   b  may thus be of reduced thickness (of around 6 to 8 mm). The effectiveness of the splinters generated inside the target is that of the sub-munition  31 .  
       FIGS. 3   a,    3   b  and  3   c  show another embodiment of a perforate warhead  1   a  according to the invention.  
      This embodiment differs from the previous one only in the structure of the front nose  6   a  which here comprises bars  26   a ,  26   b ,  26   c  crimped into bores made in the nose body  6   a.    
      Each bar  26   a ,  26   b , and  26   c  is cylindrical and the axis of its bore is parallel to the axis  27  of the perforating head  1   a.    
      Bars  26   a  and  26   b  are thus spaced in two concentric crowns surrounding axis  27  of the penetration body. One bar  26   c  moreover occupies a bore coaxial with the head  1   a  (see  FIG. 3   b ).  
      Thus, around the axial bar  26   c  there is a first crown or median crown comprising eight bars  26   b  evenly spaced around axis  27  and a second crown or external crown comprising sixteen bars  26   a  evenly space around axis  27 .  
      The diameters of the peripheral bars  26   a  are here less than those of the median bars  26   b.  The diameters of the different bars may be identical or different for reasons of organization of the penetration body. The aim is to obtain the highest global density for the perforating head. The diameters of the bars may be between 10 mm and 30 mm.  
      The ends of the different bars are machined such that they are flush with the external cone profile of the front nose  6   a  (see  FIGS. 3   a  and  3   c ). The bars  26  thus don&#39;t disturb the ammunition&#39;s aerodynamism.  
      The bars are made of a dense material with high mechanical properties. A material will be chosen that has a density greater than or equal to 17 and a limit of elasticity greater than or equal to 1000 Mega Pascals. A tungsten alloy with a high limit of elasticity obtained by sintering may be used. Bars may also be made using depleted uranium or tantalum. The body of the head  6   a  is made of steel.  
      This embodiment allows to easily obtain a front nose  6   a  having a high density. It is indeed easier to make dense bars of a reduced diameter (around 10 mm to 30 mm) than it is to make a front nose of a large diameter (over 150 mm) of such a sintered material.  
      Moreover, it would be tricky to make a body  6  of a perforating head of sintered tungsten comprising a massive front part connected to a thin rear part delimiting a cavity.  
      This embodiment thus enables to make a steel body of adequate mechanical properties ensuring the carrying of the sub-munition and nevertheless incorporating a front part of substantial density conferring the required perforating power.  
      It is naturally possible for a different number or arrangement of the bars to be provided. A single bar may namely be provided, placed in a bore coaxial to the perforating head.  
       FIG. 4  shows another embodiment of a military perforating warhead  1   a  according to the invention.  
      This embodiment differs from the one in  FIG. 3  in the nature of the on-board sub-munition  31 . Here, the sub-munition  31  is a heat and/or blast effect sub-munition incorporating a heat charge  28  placed in a case  29  of a plastic or composite material. The heat charge is ignited by a squib  30  connected to the control means  17 . A delay (for example, pyrotechnic) is placed upstream of the squib  30  such that the ignition of the charge occurs only after the sub-munition  31  has been ejected from the internal cavity  7 .  
      This embodiment also differs from the previous ones in that the shock-absorbing means  19  is divided in three parts: a front block  19   a  surrounding the sub-munition ejection device, a cylindrical median block  19   b  surrounding the sub-munition  31  and a rear block  19   c  surrounding the ejection device  13  of the base  8 .  
      Blocks  19   a ,  19   b  and  19   c  may thus be made individually outside of the ammunition and then installed into the internal cavity  7  during assembly.  
      The median block  19   b  will be bonded to the rear cylindrical part  6   b  of the penetration body  6 . The sub-munition  31  will be slid into the median block  19   b.    
      Different variants are possible without departing from the scope of the invention.  
      It is thus possible to provide a shock-absorbing material formed of several blocks in the embodiments shown in  FIGS. 1, 2  and  3 .  
      It is also possible for only a front  19   a  and rear  19   c  shock-absorbing block to be provided without the median  19   b  block or else for the latter to be replaced by a non-shock-absorbing guiding cylinder.  
      It is possible to equip the embodiments in  FIGS. 1 and 2  with a front nose  6   a  comprising bars placed in bores.  
      It is also possible to provide a sub-munition of a different nature, for example a sub-munition generating a heat effect associated with a reinforced blast effect (level of pressure and temperature held over a longer period of time). These charges are well known to the Expert under the term thermobaric charges.  
      It is lastly possible to provide several sub-munitions arranged inside the internal cavity and ejected together after perforation, for example, bomblets or splinter grenades.  
      The ejection device for the base  8  may be coupled with means to measure the temperature outside of the ammunition. It will thus be possible in the event of a substantial rise in this temperature (for example, further to a fire) to command the ejection of the base  8 . This will ensure the deconfinement of the internal cavity  7  thereby preventing the ammunition from accidentally exploding.