Patent Publication Number: US-9851187-B2

Title: Shock mitigation assembly for a penetrating weapon

Description:
FIELD OF THE INVENTION 
     The present invention is related to a weapon system called a penetrator that is used to destroy hard targets, which typically are armored vehicles and at least one thing associated with a reinforced structure, buried underground, or combination. The present invention is also related to systems launched by gun firing. More particularly, the present invention is related to a method of shock mitigation for electronic components of a penetrating weapon, gun fired system, or combination and an assembly for mitigating shock for those electronic components. 
     BACKGROUND 
     A penetrating weapon system is designed to destroy hard targets, which typically are armored vehicles and at least one thing associated with a reinforced structure, buried underground, or combination. The penetrating system includes one or more explosive charges, and a fuze or portion of a fuze for detonating each charge. A fuze also may be an electronic safe and arm device (ESAD), electronic safe, arm, and fire (ESAF), warhead initiation module, or other electronics for initiating ordnance. Each fuze includes one or more electronic devices for controlling one or more electro-explosive devices. Each electro-explosive device initiates an explosive train which may include a charge, warhead, or combination. 
     The penetrating system, in the form of a bomb, shell, missile, or other munition, guided or unguided, has at least one charge called a penetrator or follow-through warhead. The penetrating system may have a second charge, such as a shaped-charge warhead. After proximity or impact to a surface, the shaped-charge warhead detonates and bores a passage for the follow-through warhead. Then the follow-through warhead penetrates and detonates to destroy the target, whether it is an armored ship or land vehicle, a reinforced building structure, a buried bunker, etc. Without the shaped charge warhead, the penetrator impacts a surface, penetrates, and detonates to destroy the target. 
     Systems launched by a gun may contain one or more explosive charges, electronics, and one or more electro-explosive initiators. Gun firing can apply setback acceleration and shock, balloting shock, and set forward acceleration and shock to the electronics and electro-explosive initiators. 
     The electronic device, electro-explosive device, or combination can be damaged and prevented from functioning properly due to mechanical shock from gun firing, as the penetrator impacts the structure, penetrates, slaps a structure, or from pyrotechnic shock from detonation of an explosive charge. Prior attempts to mitigate shock and thereby protect electronic components in a penetrator have included placing a plurality of glass beads between an electronics housing and an electronic device, placing a potting material between the housing and the electronic device, and mounting the electronic device in a metal cup and holding the cup in a metal housing with a metal cover. 
     SUMMARY 
     The present invention provides a means to protect an electronic device in an explosive weapon from shock and acceleration from gun firing and the shock of impact and shock from detonating an explosive so that the electronic device can still control detonation of an explosive. 
     More particularly, the present invention includes a shock mitigation assembly for a weapon having an explosive charge, where the shock mitigation assembly consists of a support with an internal spiral flange, an electronics package with an external spiral flange, and hyperelastic material between the support and the electronics package. Hyperelastic material is omitted from the explosive train interface between the fuze and an explosive charge for reliable initiation of the explosive charge, to facilitate venting to control explosive initiation from cook-off, or a combination thereof. 
     Paraphrasing the claims, the present invention also provides a shock mitigation assembly for an explosive weapon having an explosive charge that includes (a) an electronic device having an electronic circuit that is connectable to an electro-explosive device to control detonation of the explosive charge, (b) a weight attached to the electronic device to mitigate high frequency shock forces and to form an electronic subassembly that includes the electronic device and the weight, (c) a housing enclosing the electronic subassembly within an enclosed volume, and (d) a hyperelastic material between the housing and the electronic subassembly, where the hyperelastic material has a modulus of elasticity that has elastic characteristics with shock or temperature, or a combination of shock and temperature. 
     In the shock mitigation assembly, the electronic device may include a circuit card assembly that includes an electronic circuit, and the weight may be secured to the circuit card assembly. 
     The shock mitigation assembly may further include a fuze, connectable to an explosive to initiate detonation in response to a signal from the electronic circuit. The fuze may be mounted to the electronic device and incorporated into the electronic subassembly. 
     In the shock mitigation assembly, the weight may be attached to the electronic device with one or more of an adhesive, a potting material, one or more screws, bolts, rivets, weld, or a combination thereof. 
     The housing may include a casing and a cover secured to the casing, the casing and the cover cooperating to define the enclosed volume. The casing and the cover may include corresponding features that mate with one another and prevent separation of the cover from the casing, with a hyperelastic material filling a gap between the cover and the casing. The corresponding features may include facing threaded portions of the casing and the cover. 
     The shock mitigation assembly may further include a shock mitigation plate between the electronic subassembly and the cover. The shock mitigation plate may include a sheet of polyimide, epoxy fiberglass board, other shock dampening material, or combination thereof. 
     The present invention further provides a penetrating weapon having an outer casing enclosing a primary explosive and a secondary explosive, first and second fuzes coupled to respective ones of the primary explosive and the secondary explosive, and a shock mitigation assembly as described above, where the electronic circuit is connected to the first and second fuzes to selectively control detonation of the primary and secondary explosives. 
     The present invention further provides a shock mitigation assembly for an explosive weapon having an explosive charge that includes an electronics package having (a) an electronic subassembly including an electronic device having an electronic circuit that is connectable to an electro-explosive device to control detonation of the explosive charge, and (b) a casing enclosing the electronic subassembly within an enclosed volume. The casing has an external spiral flange configured to overlap with an internal spiral flange of a support, and a hyperelastic material fills a space between the casing and the support. The hyperelastic material has a modulus of elasticity that has elastic characteristics with shock or temperature, or a combination of shock and temperature. 
     The electronic subassembly may further include a weight attached to the electronic device to mitigate high frequency shock forces. 
     The electronic device may include a circuit card assembly that includes an electronic circuit, and the weight may be secured to the circuit card assembly. 
     The shock mitigation assembly may further include a hyperelastic material between the casing and the electronic subassembly. 
     The shock mitigation assembly may include a fuze, connectable to an explosive to initiate detonation in response to a signal from the electronic circuit, mounted to the electronic device and incorporated into the electronic subassembly. 
     The present invention also includes a penetrating weapon having an outer casing enclosing a primary explosive and a secondary explosive, and first and second fuzes coupled to respective ones of the primary explosive and the secondary explosive, and the shock mitigation assembly as described above, where the electronic circuit is connected to the first and second fuzes to selectively control detonation of the primary and secondary explosives. 
     The foregoing and other features of the invention are hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail one or more illustrative embodiments of the invention. These embodiments, however, are but a few of the various ways in which the principles of the invention can be employed. Other objects, advantages and features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a weapon system such as a missile, incorporating a protective assembly provided by the invention. 
         FIG. 2  is a schematic cross-sectional view of a protective assembly provided by the invention. 
         FIG. 3  is a schematic cross-sectional view of an exemplary protective assembly provided by the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention provides a shock mitigation assembly to mitigate shock to an electronics package from the external support for the electronics package (i.e. external shock mitigation), and also provides a shock mitigation assembly to mitigate shock to an electronic device from the housing that encloses the electronic device (i.e. internal shock mitigation). Features that enable external shock mitigation, and features that enable internal shock mitigation, may be used separately or together to mitigate shock to relatively fragile electronic components of an explosive weapon, such as a penetrator or gun fired system, through a combination of structural mass and application of a hyperelastic material. 
     A hyperelastic material differs from an elastic material in that a hyperelastic material maintains elastic characteristics to protect electronics and initiators during shock or temperature, or a combination of shock and temperature. The temperature can include the operating temperature range of a weapon, such as from −54 C (or lower) to 71 C (or higher). In contrast, an elastic material hardens during shock or temperature, or a combination of shock and temperature, preventing an elastic material from protecting electronics and initiators during shock or temperature, or a combination of shock and temperature. 
     Shock is a sudden and often violent force, a force applied in a short time. The electronic components may need to be protected from shock, acceleration, and deceleration from gun firing, impact shock, penetration shock, and pyrotechnic shock. Impact shock can occur as the weapon impacts a hard media, such as the ground or a wall or other structure. Penetration shock can occur as the momentum of the weapon moves it through the media after impact. And pyrotechnic shock can occur due to the detonation of an explosive, including an explosive charge in the weapon itself. Impact, penetration, and pyrotechnic shock also include rebound shock from impact, penetration, pyrotechnic shock, or a combination. As a result, impact shock, penetration shock, structure slap shock, and/or pyrotechnic shock may prevent proper functioning of a penetrator by damaging electronic components in the penetrator, gun fired system, or a combination. 
     Turning now to the drawings, and initially to  FIG. 1 , an exemplary penetrator  10  has an outer casing  12  that encloses multiple charges. Two explosive charges are shown, including a primary charge  14 , such as a shaped-charge, and a secondary charge or follow-through charge  16 . Each charge  14  and  16  is controlled by a respective fuze  24  or  26 . At least one of the fuzes  24  or  26  may be controlled by signals from an umbilical connector  18 , the weapon subsystem controller  20 , or a combination. 
     The primary charge  14  typically is initiated (detonated) before, upon, or after impact with a media to bore a hole in the media for further passage of the secondary charge  16 . The impact, penetration, and initiation of the primary charge  14  or other part of the system applies impact shock, penetration shock, and pyrotechnic shock to fuzes  24  and  26 . 
     The present invention provides at least one of external and internal shock mitigation to reduce the effects of gun firing, impact, penetration, and pyrotechnic shock on the fragile electronic components of the electronics package, electro-explosive initiator, or a combination thereof. 
     An exemplary shock mitigation assembly  30  with external shock mitigation features is shown in  FIG. 2 . The shock mitigation assembly  30  includes an electronics package  40  having a casing  34  with an external spiral flange  52  that cooperates with a support  32  with an internal spiral flange  54  to support the electronics package  40  relative to the support  32 . A hyperelastic material  50  fills a gap between the support  32  and the electronics package  40 . As noted above, a hyperelastic material has a modulus of elasticity that remains elastic with shock or temperature, or a combination of shock and temperature. An exemplary hyperelastic material includes silicone. The support  32  may be part of the outer casing  12  ( FIG. 1 ) of a penetrator, a gun fired system, an electronics well, an electronics housing, or a combination. 
     The electronics package  40  includes a housing composed of the casing  34  and a cover  36 . The cover  36  closes an opening in the casing  34 , and cooperates with the casing  34  to define an enclosed volume  38 . The cover  36  may be attached to the casing  34  with a threaded interface, screws, welding, or a combination thereof. 
     External shock mitigation is provided by a) the hyperelastic material  50  between the support  32  and the casing  34  and b) the mass of the electronics package  40 . One or more, and two o-rings  35  and  37  in the illustrated embodiment, or other means of retaining the hyperelastic material  50  may be employed to retain the hyperelastic material  50  in the space between the casing  34  and the support  32  before the hyperelastic material  50  is cured. In the case of the overlapping spiral flanges  52  and  54  on the casing  34  and support  32 , rotation of the casing  34  relative to the support  32  is required to remove the electronics package  40  from the casing  34 . The spiral flanges  52  and  54  must extend a sufficient distance to be long enough to support the electronics package  40  with or without the hyperelastic material  50 . Yet sufficient space is retained between the spiral flanges  52  and  54  for the hyperelastic material  50  to fill the gap between the support  32  and the casing  34 . 
     The electronics package  40  further includes a controller or other electronic device with an electronic circuit, on one or more printed wiring boards, for example, enclosed in the casing  34 . Thus the electronics package  40  includes a circuit card assembly  42  with an electronic circuit integrated into a semiconductor or otherwise mounted to a circuit board. The circuit card assembly  42  is enclosed in the enclosed volume  38  in the casing  34 . 
     The shock mitigation assembly  30  also may include an explosive initiator (initiator  25  or  27  in  FIG. 1 ) or a connector for attaching the circuit card assembly  42  or other electronics package to an explosive initiator (such as initiator  25  or  27  in  FIG. 1 ). The electronics package  40  may be the fuze  26 . A similar electronics package may be the fuze  24 . 
     In the illustrated shock mitigation assembly  30 , a weight  44  is connected to the circuit card assembly  42  to add mass to what is typically a relatively lightweight device. The weight  44  typically is made of a dense material, such as metal, to minimize the volume taken up by the weight  44 . The weight  44  can be attached with any means of attachment, including mechanical fasteners, potting, an adhesive, etc., including combinations thereof. 
     The combination of the circuit card assembly  42  (or other electronic device) and the weight  44  forms a subassembly, which can be referred to as the electronic subassembly  46 . Adding the weight  44  to the circuit card assembly  42  mechanically mitigates impact shock, penetration shock, and pyrotechnic shock by attenuating high frequency shock levels and frequencies. The frequency can be reduced according to the following relationship: frequency equals the square root of the modulus of the shock-carrying media divided by the combined mass of the electronic subassembly  46 . 
     The illustrated electronic subassembly  46  also is separated from the inside surfaces of the housing (spaced from both the casing  34  and the cover  36 ) by a hyperelastic material  50  to provide internal shock mitigation. Providing the hyperelastic material  50  between the support  32  and the electronics package  40  reduces shock coupling between the support  32  and the electronic subassembly  46  to provide external shock mitigation and reduce shock damage to the electronic devices, such as a circuit card assembly  42 . And providing the hyperelastic material  50  inside the electronics package  40 , in the enclosed volume  38  provided by the casing and the cover  36 , around the electronic subassembly  46 , reduces shock coupling between the casing  34  and the cover  36  and the electronic subassembly  46  to provide internal shock mitigation and reduce shock damage to the circuit card assembly  42  and other electronic devices associated with the electronics package  40 . 
       FIG. 3  shows an exemplary shock mitigation assembly  60 . The illustrated shock mitigation assembly  60  includes a housing  62  having a casing  64  and a cover  66  that cooperates with the casing  64  to define an enclosed volume  68 . The housing  62  may have a flange  90  along its outside diameter for securing the housing  62  to a support, such as a penetrator or gun fired projectile case  12 , with a spanner nut, bolts, or other method. The cover  66  and the casing  64  may have corresponding threads again, with the threads on an outer surface of the cover  66  and an inner surface of the casing  64 , or the cover  66  may be secured to the casing  64  in another way, such as with a spanner nut, screws, welding, or other method. 
     An electronics package having a resistor and other electronic devices on a printed wiring board, such as circuit card assemblies  70  and  71 , is enclosed in the enclosed volume  68  in the housing  62 . The circuit card assemblies  70  and  71  are held in the enclosed volume  68  in the housing  62 , and a weight  74  is attached to the circuit card assemblies  70  and  71  to form an electronic subassembly  76 . Attaching the weight  74  to the circuit card assemblies  70  and  71  over spaced-apart locations reduces flexure of the circuit card assemblies  70  and  71  due to shock forces, which helps to maintain electrical connections through solder joints in the circuit card assemblies  70  and  71  and prevents breakage of an electrical part, solder joint, a board conductor, etc., or a combination thereof, in the circuit card assemblies  70  and  71 . Circuit card assemblies  70  and  71  can be similar to increase a system&#39;s reliability or different to provide more functionality. 
     An electro-explosive initiator or detonator often is mounted to an electronics housing with a spanner nut, which provides no shock mitigation between the housing and the electro-explosive initiator. In the illustrated shock mitigation assembly  60 , however, a pair of electro-explosive initiators  80  and  82  are secured to the circuit card assembly  70 , the weight  74 , or a combination and thereby are integrated into the electronic subassembly  76 . 
     The electronic subassembly  76  is spaced from the walls of the housing  62  (including both the casing  64  and the cover  66 ) by a hyperelastic material  84  once again, to mitigate the shock experienced by the electronic subassembly  76 , protecting both the electro-explosive initiators  80  and  82  and the circuit card assembly  70 . 
     The shock mitigation assembly  60  shown in  FIG. 3  further includes a shock mitigator plate  86  between the electronic subassembly  76  and the housing  62 , particularly between the electronic subassembly  76  and the cover  66 . The shock mitigator plate  86  can be a sheet of polyimide, epoxy fiberglass board, other shock dampening plate material, or a combination. The illustrated shock mitigation assembly  60  may also include a lid  88  that is secured to the weight  74  with threads, welding, screws, an adhesive, or a combination thereof, to add further mass and protection to the electronic subassembly  76 . 
     A shock mitigation assembly provided in accordance with these principles has increased the shock level for survivability of an electronic device by over a factor of three. 
     In summary, a shock mitigation assembly  60  for a penetrating explosive weapon  10  ( FIG. 1 ) having a first explosive charge  14  ( FIG. 1 ) and a second explosive charge  16  ( FIG. 1 ) includes an electronic circuit card  42  ( FIG. 2 ) or  70  ( FIG. 3 ) having an electronic circuit formed therein, a weight  44  ( FIG. 2 ) or  74  ( FIG. 3 ) attached to the circuit card  42  or  70  to form a circuit card subassembly  46  or  76 , a housing  62  enclosing the subassembly  76 , and a hyperelastic material  50  or  84  between the housing  62  and the subassembly  76  for internal shock mitigation. The hyperelastic material  50  or  84  has a modulus of elasticity that remains elastic characteristics with shock, temperature, or a combination of shock and temperature. The housing  62  may include a casing  34  ( FIG. 2 ) or  64  ( FIG. 3 ) and a cover  36  ( FIG. 2 ) or  66  ( FIG. 3 ) with corresponding features that mate with one another and prevent separation of the cover  36  or  66  from the casing  34  or  64 . The casing  34  ( FIG. 2 ) also may have an external spiral flange  52  ( FIG. 2 ) that overlaps an internal spiral flange  54  ( FIG. 2 ) of a support  32  for the casing, with a hyperelastic material  50  between the casing and support for external shock mitigation. 
     Although the invention has been shown and described with respect to a certain preferred embodiment, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components, the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiments of the invention. In addition, while a particular feature of the invention can have been disclosed with respect to only one of the several embodiments, such feature can be combined with one or more other features of the other embodiments as may be desired and advantageous for any given or particular application.