Abstract:
An explosive fragmentation munition having a longitudinal axis which includes a cylindrical shell portion having a thickness and an interior; a rounded shell portion having a thickness and an interior, the rounded shell portion being disposed at a front end of the cylindrical shell portion; an explosive disposed in the interiors of the cylindrical shell portion and the rounded shell portion; wherein the thickness of the rounded shell portion equals the thickness of the cylindrical shell portion where the rounded shell portion joins the cylindrical shell portion, and wherein the thickness of the rounded shell portion increases in a forward direction along the longitudinal axis.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of application Ser. No. 10/249,479 as originally filed on Apr. 14, 2003, now abandoned by Vladimir Gold et al. for “Explosive Fragmentation Munition”, which itself claims the benefit under 35USC119(e) of U.S. Provisional Application No. 60/320,027 filed Mar. 20, 2003, the entire file wrapper contents of which applications are hereby incorporated by reference herein as though fully set forth at length. 

   FEDERAL RESEARCH STATEMENT 
   [The inventions described herein may be manufactured, used and licensed by or for the U.S. Government for U.S. Government purposes.] 
   BACKGROUND OF INVENTION 
   The invention relates in general to explosive fragmentation munitions and, in particular, to an explosive fragmentation munition with improved fragment distribution. 
   The principal rationale for the airburst fragmentation warhead technology is to optimize the efficiency of the fragment spray dispersion pattern by detonating the round in the air at location near the target. The technical feasibility of the airburst warhead technology is largely due to recent advances in the state-of-the-art electronics that make possible fabrication of miniaturized fuzes with improved “intelligence” and reliability, enabling the round to assess its position at the predetermined location within approximately +5 meters from the target. In addition, the onboard “intelligence” of the fuze will enable the munition to function in a number of modes, including the airburst mode, the point impact mode, and the delayed initiation mode. A brief description of the novel Airburst Explosive Fragmentation Shell with Superior Anterior Fragment Distribution presented here is as follows. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     In the drawings, which are not necessarily to scale, like or corresponding parts are denoted by like or corresponding reference numerals. 
       FIG. 1A  shows an idealized geometry for the airburst explosive fragmentation shell; it shows an idealized cylindrical fragmenting shell  11  of uniform thickness t, and including explosive  10  within;  FIG. 1B  shows the fragment spray pattern  12  of such idealized cylindrical shell device;  FIG. 1C  shows the fragment spray pattern cross-sectionally viewed, of a cylindrical shell device  14  of wall thickness t but front ogive portion having thickness t A  at its tip and thicknesses tapering down to t at the walls of the cylinder, and having explosive  13  within such shell device. 
       FIGS. 2A–2C  show  FIG. 2  shows the fragmenting shell ( 21 ,  23 ), having explosive  20  within, but with a fragmenting anterior liner  22  surrounding a pusher liner  24 ; a closeup of the shell ogive is shown in  FIG. 3C ; a side view of the shell; and then shell  25  with pusher liner  27 , and a fragmenting anterior liner  28 . 
       FIGS. 3A–3D  results of analyses of fragmentation patterns of two viable embodiments of the invention: baseline fragmenting shell of  FIG. 2A  in  FIGS. 3A and 3B ; and a Composite fragmenting shell  FIG. 2C , in  FIGS. 3C and 3D . The two images  FIGS. 3A ,  3 C represent computed images of these two munitions after the explosives are detonated and the metal shells are about to break up ejecting a spray of fragments into the air;  FIGS. 3B and 3D  respectively are polar graphs showing results of idealized analyses of the probability of incapacitation in the area of the explosive burst. The spray pattern  41 ,  43  of bat wings  31 ,  33  is shown in the graph of  FIG. 3B . The spray pattern  45  is shown in  FIG. 3D , representing the effect of particles formed as  35  in  FIG. 3C . As shown in the graphs, the lethal area of the munition of  FIG. 2C  is more than four times that of the baseline munition of  FIG. 2A , predominantly due to the Super Anterior Fragment distribution pattern thereof  35  filling the entire front space between the two bat-wings ( 31 ,  33 ) with fragments. 
       FIG. 4  is a schematic sectional view of another embodiment of a munition according to the invention. 
       FIG. 5  is a front view of the munition of  FIG. 4 . 
       FIG. 6  is a schematic sectional view of another embodiment of a munition according to the invention. 
   

   DETAILED DESCRIPTION 
   Examples of possible idealized geometries for the airburst explosive fragmenting shell are shown in  FIG. 1 . Upon initiation of the high explosive charge, rapid expansion of high-pressure high-velocity detonation products results in high-strain, high-strain-rate dilation of the metal shell encapsulating the explosive, which eventually ruptures generating a “spray” of high-velocity fragments moving with trajectories at angles Θ with the z-axis. Accordingly, the principal lethality parameter of the explosive fragmenting shell is the number of fragments as a function of the angle Θ, which determines the statistical probability of incapacitation of the target and, ultimately, the overall efficiency of the munition. Assuming that the changes in the trajectories of the fragments due to the air resistance are negligible, the angular distribution of the fragment spray is a function of the initial geometry of the fragmenting shell&#39;s surface, the strength, the density, and the thickness thereof. 
   For example, in the case of an idealized cylindrical shell of uniform thickness t,  FIG. 1  ( a ), the available shell mass at the ends is relatively small, and, therefore, only a small number of fragments will be ejected into the anterior region of the munition target space. Thus, since the bulk of the fragment spray is ejected predominantly in the direction normal to the z-axis, the effectiveness of cylindrical airburst shells is relatively low. On the other hand, in the case of an idealized spherical shell of the same mass,  FIG. 1  ( b ), the fragment spray distribution pattern at the quasi-static burst conditions is nearly perfect, but, unfortunately, the concept is impractical for gun-launched munition applications, mostly because of the projectile design constraints including payload-to-gun caliber ratio, and projectile stability. In addition, high terminal projectile velocities tend to degrade the penetration capability of fragments ejected from the posterior portion of the shell, thereby reducing the warhead lethal area by approximately a factor of two compared to that at quasi-static burst conditions. 
   An alternate approach for a solution to the problem is shown in  FIG. 1  ( c ) whereas the ogive front portion of the shell is thickened and rounded. Thickening and rounding the front portion of the shell enables generating a fixed number of fragments per unit length of the shell and per unit angle Θ of the target space, which integrates the best features of the two idealized geometries of  FIGS. 1  ( a ) and  1  ( b ) and maximizes warhead lethality. As shown in  FIGS. 2 and 3 , the embodiment of a munition of  FIG. 1  ( c ) can be further extended to that of a Composite Fragmenting Shell, enabling even greater lethality than that of the single material approach. 
   The Composite Fragmenting Shell embodiment of the munition is shown in  FIGS. 2(   b ) and  2 ( c ). As shown in the figures, the cylindrical portion of the fragmenting shell encapsulates the explosive from the sides and generates fragment spray in the direction normal to the z-axis, while the front portion serves as a “pusher” to transfer the momentum to the Anterior Fragmenting Liner that projects fragments to the front. In order to optimize preferred fragment size distribution, the Anterior Liner could be comprised of two or more layers of liners stacked to each other. Since in order to generate an approximately fixed number of fragments per unit length of the shell requires significant amount of the shell mass in the front, the Anterior Liner has to be fabricated from a high-density material. Accordingly, a material of choice for the Fragmenting Anterior Liner is tungsten, mostly because of the high density and strength properties. However, the Anterior Liner could also be made from a variety of high-density metals and metal alloys including tantalum, lead, and depleted uranium. The Anterior Liner could be fabricated with surface patterns of scores to produce preferred fragment sizes, or could be comprised of preformed high-density fragments imbedded in a different matrix material. 
   Another rationale for using high-density high-strength metals and metal alloys is the superior penetration efficiency of these materials, enabling generation of larger numbers of lethal fragments per unit fragmenting shell mass and significantly increasing the warhead lethality. In order to avoid premature rupture of the shell and leakage of the detonation products, the end of the Fragmenting Anterior Liner is tapered, smoothly blending with the main fragmenting shell. As shown in  FIG. 3 , a proper taper of the liner is a key factor for maximizing the efficiency of the warhead. 
   Since the round may have to withstand high-G gun-launch loads, a material of choice for the main fragmenting shell is high-strength steel. Since the Anterior Liner rests on the main fragmenting shell, the G-load stresses there are small, and, therefore, the preferred fragmentation mode for the Anterior Liner is controlled fragmentation.  FIG. 3  show an assessment of the effectiveness of two preferred embodiments of the munition by taking into account a complex battlefield scenario including the number and positions of the soldiers, the soldiers posture, the combined effects of the helmet, the body armor as well as unprotected portions of the body, resulting in a prediction of high probability of serious or lethal wounds for the entire body. The input for the lethality analyses included the fragment velocity and mass distribution from continuum analyses, plus projectile terminal ballistic parameters at the given range, including warhead velocity at burst, orientation of warhead, the height of burst, and other factors. As shown in  FIG. 3 , assuming ideal fragmentation (0% losses) of the anterior liner, the expected lethal area of the Composite Fragmenting Shell concept is approximately 4 to 8 times greater that of the  FIG. 1  ( c ) baseline concept. 
     FIG. 4  is a schematic sectional view of another embodiment of a munition  30  according to the invention. Munition  30  is similar to munition  22 , except the rounded shell portion  32  includes two layers  34 ,  36 . The first layer  34  comprises the same material as the cylindrical shell portion  26 . The second layer  36  is disposed on an outer surface of the first layer  34 . The second layer comprises matrix material holding fragments  38  disposed therein. The fragments may be made of a high density, high strength material such as tungsten, tantalum, or depleted uranium that are also suitable for second layer  36 . The fragments  38  may be shaped, for example, as spheres, cubes or other shapes. The second layer  36  is attached to the first layer  34  by, for example, an adhesive or shrink fitting. 
     FIG. 5  is a front view of the munition  30  of  FIG. 4 .  FIG. 5  shows scoring  40  (for example, grooves) in the second layer  38  of the rounded shell portion  32 . The surface pattern of scores helps to produce preferred fragment sizes. 
     FIG. 6  is a schematic sectional view of another embodiment of a munition  50  according to the invention. Munition  50  is similar to munition  30 , except the rounded shell portion  52  includes three layers  54 ,  56 ,  58 . The first layer  54  comprises the same material as the cylindrical shell portion  26 . The second layer  56  is disposed on an outer surface of the first layer  54 . The third layer  58  is disposed on the outer surface of the second layer  56 . The material of the second layer  56  may be the same as or different than the material of the third layer  58 . The material of the second and third layers  56 ,  58  may be, for example, a high density, high strength material such as tungsten, tantalum, or depleted uranium.  FIG. 6  has been drawn with an exaggerated nose area where the widths are out of actual proportion; the purpose is only to better illustrate the various layers in the nose cone, however the nose cone shown in  FIG. 2  is more nearly the actual proportion. 
   Either or both of the second and third layers  56 ,  58  may have fragments disposed therein, in a similar fashion as shown with reference to layer  36  in  FIG. 4 . The second layer  56  is attached to the first layer  54  and the third layer  58  is attached to the second layer  56  by, for example, an adhesive or shrink fitting. Third layer  58  may also be scored, as discussed above with reference to layer  36  of  FIG. 5 . 
   While the invention has been described with reference to certain preferred embodiments, numerous changes, alterations and modifications to the described embodiments are possible without departing from the spirit and scope of the invention as defined in the appended claims, and equivalents thereof.