Patent Publication Number: US-2016231094-A1

Title: Internal reinforcement and confinement structure for warheads

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of -pending U.S. patent application Ser. No. 13/672,762 filed on Nov. 9, 2012 by inventor Michael A. Minnicino II titled “Warhead” which is related to and claims priority from co-pending U.S. Provisional Patent Application No. 61/562,732 filed on Nov. 22, 2011 by inventor Michael A. Minnicino II titled “Reinforcement of Dense High-Explosives for Gun-Launch Applications” which are all hereby incorporated herein by reference in their entirety including all attachments, appendices and figures filed with U.S. Provisional Patent Application No. 61/562,732 and U.S. patent application Ser. No. 13/672,762. 
    
    
     GOVERNMENT INTEREST 
     The invention described herein may be manufactured, used, and licensed by or for the United States Government. 
    
    
     BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     The present invention relates generally to items requiring structural support and geometric alignment when encapsulated in weak or compliant materials and, more particularly, to warheads subjected to large axial and rotational accelerations during gun launch. 
     II. Description of Related Art 
     Many types of warheads are gun launched, for example a warhead can be fired in a predetermined axial direction and elevation by a gun toward a target. A low collateral damage munition, where the munition&#39;s warhead has a significantly reduced lethality footprint compared to traditional warheads, is desirable in many of today&#39;s conflict environments. Warheads can be subject to large axial accelerations during gun launch. 
     Modern low collateral damage munition designs typically feature either a thin metallic or a polymer composite warhead outer shell, oftentimes in conjunction with a high-density high explosive fill material. The use of the thin metallic or polymer composite warhead outer shell and/or dense high explosives, however, creates significant design, performance, and safety issues during gun launch. 
     For example, in order to safely fire the gun, the warhead outer shell, regardless if it is a overly thin metal or polymer composite material, must exhibit sufficient structural integrity to withstand not only the gun launch loads incurred when the munition is fired, but also those gun launch loads in conjunction with the pressure resulting from the inertial loading of the high-density high explosive fill due to the Poisson effect. 
     However, simply increasing the strength of the warhead outer shell alone creates additional problems. If the burst strength of the outer shell is too large, the explosive blast at the target is largely contained within the warhead thus reducing its effectiveness. Specifically, the performance of the low collateral damage warhead in the vincinity of the target is strongly influenced by the burst strength of the warhead outer shell. Conversely, if the burst strength is too weak, the munition structurally fails in bore during the gun launch due to the loading created by the Poisson effect and a serious safety hazard results. Consequently, the goal is to design the outer shell strength of the warhead such that the warhead maintains its structural integrity during launch, but fails in the vicinity of the target during the explosive blast. 
     One previously known approach for warhead design has been to use thick plates or baffles aligned in a direction perpendicular to the direction of the gun launch axis that are then supported within the warhead either by the warhead outer shell or secondary structure, i.e. centered column support, at spaced axial intervals and the spaces between the baffles are then filled with high-density high explosive. The baffles support the dense high explosive during gun launch and reduce the loading due to the Poisson effect. In this fashion, the (typically planar) surfaces of the baffles are normal to the detonation wave created during the explosive blast. As such, these baffles may disadvantageously reduce the detonation propagation from one high explosive volume to the neighboring high explosive volume across the baffle support structure. In addition to the concern of detonation propagation, a primary disadvantage of this approach, however, is that the overall amount of explosive is reduced, thus reducing the overall effectiveness of the warhead. Addtionally, the supporting baffle structure is likely to unintentionally add significant lethality to the low collateral warhead. 
     SUMMARY OF THE PRESENT INVENTION 
     The present invention provides a warhead design of the type that is gun launched which overcomes the above mentioned disadvantages of the previously known warheads. 
     In brief, the warhead of the present invention provides a support structure having a plurality of walls which extend in a direction parallel to the axial launch direction of the warhead. These walls form a plurality of axially elongated chambers that are spaced apart but laterally adjacent each other. Support structures described herein may be used to provide supplemental internal support in explosive structures and/or maintain geometric alignment of encapsulated explosive fill. 
     Embodiments of the present invention do not require multipoint detonation. Desirably, each chamber has a cross section greater than the critical detonation cross section area required for stable, sustainable detonation. The cross section area and critical cross section area are measured perpendicular to the axial launch axis. 
     In certain preferred embodiments of the invention, the support structure is a honeycomb so that each elongated chamber is hexagonal in cross-sectional shape. Preferably, each hexagonal elongated chamber has a cross section greater than the critical detonation cross section for the particular explosive fill contained within the hexagonal elongated chamber. The structure itself is constructed of any suitable structural material, such as a polyamide or aluminum or an aluminum alloy. The entire structure is then substantially filled with a dense high explosive to form the warhead. 
     In operation, the structure supports the dense high explosive against deformation during launch and thus maintains the integrity of the warhead. The structure does this through a combination of load transfer between the dense high explosive and the support structure and confinement of the high explosive by the support structure. Upon detonation, the detonation wave, which travels in a direction parallel to the walls of the support structure and therefore the support structure does not disturb the detonation process in contrast to the baffle support described previously. The effective result of the support structure is that the warhead is structurally capable of surviving gun launch while also efficiently delivering the warhead payload to the target while simultaneously minimizing collateral damage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       A better understanding of the present invention will be had upon reference to the following detailed description when read in conjunction with the accompanying drawing, wherein like reference characters refer to like parts throughout the several views, and in which: 
         FIG. 1  is a side view illustrating a warhead; 
         FIG. 2  is a fragmentary elevational view illustrating the support structure for the warhead; and 
         FIG. 3  is a side view illustrating the support structure during an explosive fill of the support structure. 
     
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT INVENTION 
     With reference first to  FIG. 1 , an exemplary warhead  10  is shown having both a front end  12  and a base end  14 . The warhead  10  is adapted to be gun launched along a launch axis  16  from a gun toward the target. 
     With reference now to  FIGS. 1 and 3 , the warhead  10  includes a support structure  18  positioned within a tubular and cylindrical outer wall  24  of the warhead  10 . The support structure includes a plurality of chamber (cell) walls  20  which, together, form a plurality of chambers  22  each of which is elongated in the direction of the launch axis  16 . Each chamber  22 , furthermore, is a closed chamber and thus isolated from its adjacent chambers  22  by the chamber (cell) wall  20 . Preferred embodiments of the present invention do not require multipoint detonation. Thus, each chamber or at least a majority of the chambers should have a cross section greater than the critical detonation cross section area required for stable, sustainable detonation of the explosive contained within the chamber. The cross section area and critical cross section area are measured perpendicular to the axial launch axis. 
     In the preferred embodiment of the invention, the support structure is a honeycomb structure that includes a plurality of adjacent but laterally separated, elongated chambers that are hexagonal in cross-sectional shape. Thus, in certain embodiments the chambers are each hexagonal in shape in cross section perpendicular to the axial launch direction. Preferably, each hexagonal elongated chamber has a cross section greater than the critical detonation cross section for the particular explosive fill contained within the hexagonal elongated chamber. For example, the side wall length of each hexagonal chamber should be a minimum of 0.55 centimeters when used with a high explosive with a critical diameter of 1 centimeter. Further, it is recommended that the hexagonal side wall length side be at least 57% of the high explosive critical diameter; this side wall length equates to the area of a circle inscribed by the regular hexagon. In other embodiments, the chambers are each circular, rectangular, square or other polygonal in shape in cross section perpendicular to the axial launch direction. The support structure may be defined as a plurality of adjacent chambers  22  that are longitudinally elongated and parallel to the launch axis  16  of the warhead  10  to provide a plurality of parallel cells defined by intersecting internal walls and arranged in vertical rows. Furthermore, within the interior of the warhead  10 , each sidewall  20  forms a side wall of two different and adjacent chambers  22 . 
     As best shown in  FIG. 1 , the support structure  18  preferably extends along the entire length of the warhead  10  so that each chamber  22  has an axial length relative to the launch axis  16  of the length of the warhead  10 . Any suitable lightweight but stiff and strong structural material, such as a plastic, such as a polyamide, or a metal, such as aluminum, may be used to form the support structure  18 . 
     Although the support structure  18  is illustrated in the drawing as honeycomb in shape in which each interior chamber  22  is hexagonal and substantially identical in size to the other interior chambers  22 , other shapes for the chambers  22  may be utilized. For example, the chambers  22  could alternatively be square or rectangular in shape, or triangular in shape, or a have a polygonal cross sectional shape, for example a parallelogram, without deviation from the spirit or scope of the invention. Although the support structure  18  is illustrated in the drawing as honeycomb in shape in which each interior chamber  22  is of a closed cross-section, i.e. the boundary around the interior chamber forms a complete loop, open cross-sections for the support structure  18  may also be used. 
     Preferably, the cell sidewall length,  , of each chamber (cell)  20  of the support structure  18  is relatively small, yet large enough such that the hexagon section area is greater than the circular area corresponding to the high explosive&#39;s critical diameter. However, the chamber (cell) axial length  20  of the support structure  18  may be varied as required in order to ensure side wall integrity during the launch and/or design criteria relative to the minimization of collateral damage. 
     In order to form the warhead, the support structure  18  is filled using a melt-cast approach where the dense high explosive is heated until liquefied and is poured  26  ( FIG. 3 ) into each chamber  22  and allowed to solidify upon cooling. Preferably, each chamber  22  in the support structure  18  is completely filled with the high explosive using the above mentioned technique. 
     In operation, the support structure  18  supports the high explosive during the gun launch and prevents structural failure of the warhead, and possible shock detonation, during gun launch. Since the support structure  18  is constructed of a lightweight material, it does not detrimentally affect lethality of the warhead and enables low collateral damage warhead designs without compromising weapon effectiveness. 
     A still further advantage of the warhead of the present invention is that the thickness of the sidewalls  20  of the support structure  18  may be very thin walled while still maintaining the structural integrity of the structure  18 . Since the sidewalls  20  of the support structure  18  are thin, the overall support structure  18  thus occupies relatively little payload volume thus maximizing the amount of high explosive that can be contained within the warhead  10 . 
     A still further advantage of the warhead  10  of the present invention is that, since the structure sidewalls  20  extend in the launch direction  16 , the plane of the support structure sidewalls  20  extends in a direction parallel to the detonation wave of the warhead. As such, the support structure  18  advantageously does not interfere with the detonation wave. 
     Having described my invention, many modifications thereto will become apparent to those skilled in the art to which it pertains without deviation from the spirit of the invention as defined by the scope of the appended claims.