Abstract:
A fragmentation warhead includes a cylindrical fragmenting body, a pair of concentric cylindrical liners within, made of plastic, and an explosive charge disposed within the innermost liner. In one embodiment, one liner provides various “legs” of liner material and the other liner provides various open receptacle areas, into which such legs may come to rest when the liners are slid together and/or rotated relative to one another. Various recessed and/or raised areas of liner material can thus be randomly created by such adjustments, which lead to select fragmentation of the warhead upon detonation.

Description:
RELATION TO OTHER APPLICATIONS 
     This application is a Continuation-in-Part of U.S. patent application Ser. No. 12/709,534 filed on Feb. 22, 2010 now U.S. Pat. No. 8,272,330 by the like inventors, and is commonly assigned. 
    
    
     U.S. GOVERNMENT INTEREST 
     The inventions described herein may be made, used, or licensed by or for the U.S. Government for U.S. Government purposes. 
    
    
     BACKGROUND OF INVENTION 
     Warhead fragmentation effectiveness is determined by the number, mass, shape, and velocity of the fragments. By using a controlled fragmentation design, warhead fragmentation can generally be achieved quickly and cost effectively. Exemplary controlled fragmentation techniques are described in U.S. Pat. Nos. 3,491,694; 4,312,274; 4,745,864; 5,131,329; and 5,337,673. 
     In general, conventional designs use “cutter” liners that form fragments by generating a complex pattern of high-velocity “penetrators” for fragmenting the shell. Although these conventional fragmentation designs have proven to be useful, it would be desirable to present additional functional, cost and safety improvements that minimize the warhead weight, reduce manufacture expenses, and advance current United States Insensitive Munition (IM) requirements. 
     What is therefore needed is a controlled fragmentation technique through the use of patterned liners which introduce shear stress into the warhead body and creates the desired fragmentation patterns. Fragment size, fragment numbers, and patterns thereof may be influenced through novel liner configurations. The need for such a controlled fragmentation technique has heretofore remained unsatisfied. 
     SUMMARY OF INVENTION 
     The present invention satisfies these needs, and presents a munition or warhead such as a projectile, and an associated method for generating controlled fragmentation patterns. According to the present invention, warhead fragmentation is achieved more efficiently and more cost effectively than conventional techniques, through the use of a relatively inexpensively formed plastic liner with a predetermined pattern of recessed areas and a plastic liner with a predetermined pattern of raised areas, sized to fit within the recessed areas, and capable of being moved about relatively and locked that way before detonation, to create varying levels of overall liner thickness in select regions, that is experienced during a detonation. The more thin regions will more likely lead to larger fragments ultimately, than will the more thick regions, as will be appreciated from the discussion here after. The liners could also be made of steel, tungsten, tantalum, or other materials. 
     According to one embodiment of the present invention, the warhead includes two movable liners that are disposed inside the warhead body which include predetermined patterns that are created with areas of different overall thicknesses presented to the exploding core, such allowing the detonation shock wave to correspondingly propagate into the fragmenting case through various effective thicknesses of liner material. The liner recessed and raised areas, and combinations thereof by physical positioning can, by varying thicknesses in regions, create contours of localized transitional regions with high-gradients of pressures, velocities, strains, and strain-rates acting as stress and strain concentration factors. Unstable thermoplastic shear (adiabatic shear) eventually transfers the entire burden of localized strain, to a finite number of shear planes leading to ultimately to an outer shell break-up and formation of fragments. 
     As a result, the explosion produces a complex pattern of shear planes in the warhead body, causing the case break-up and formation of fragments with various, predetermined sizes. This design is distinguishable from existing fragmentation liner technologies that attempt to score or cut the warhead body. 
     One of the advantages of the present embodiment compared to existing technologies is the cost effectiveness of the manufacturing process of the present design, in that it is faster and more economical to fabricate and to pattern plastic liners as opposed to notching or cutting a steel warhead body itself. Another advantage of the present invention is that the use of plastic material reduces the overall weight of the warhead compared with use of other materials. Fortuitously, the use of plastic is also a great safety feature. An unwanted ignition of the explosive due to the heat of launch would normally be catastrophic as well as fratricidal, but here the plastic liners in this invention are mounted to cover the explosive inside the casing body. In the event of unwanted heat/ignition, the plastic (which is also low melt temperature material), would melt to seal the explosive which adds to safety. Moreover the (melted) plastic would also flow and could push out overflows that are usually provided in these rounds. Because of the plastic, neither sudden pressure nor heat/ignition inside the round would therefore be as catastrophic. Therefore, choice of low-melt temperature plastic as liner materials in this invention, adds safety to the round. This benefit is favorable, consistent with current Insensitive Munition (IM) requirements in minimizing accidental ammunition explosion due to fire hazards. 
     OBJECTS OF THE INVENTION 
     It is an object of the present invention to provide means for generating fragments upon detonation of a warhead, with a relatively less expensive to manufacture structure of plastic liner components, and; 
     It is a further object of the present invention to provide a fragmentation warhead which generates fragments upon detonation wherein the size and shape of such fragments may be selected through liner design, and; 
     It is a still further object of the present invention to provide a fragmentation warhead which generates fragments upon detonation wherein the size and shape of such fragments may be selected prior to detonation by manually dialing in a change to positioning of liner components within said warhead, and; 
     It is a yet another object of the present invention to provide a fragmentation warhead of increased safety and sensitivity against unwanted fratricide of other warheads by reason of melting properties of the plastic materials within the warhead providing protection there against. 
     These and other objects, features and advantages of the invention will become more apparent in view of the within detailed descriptions of the invention and in light of the following drawings, in which: 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a cutaway isometric view of a fragmenting warhead assembly according to this invention; 
         FIG. 2  shows an isometric view of inner liner  200  according to the invention with a grid system of recessed areas  202 , that is internal to the fragmenting warhead of  FIG. 1 ; 
         FIG. 3  shows an isometric view, inside of the fragmenting warhead, of an outer sleeve liner  300  (with its inner surface grid system of raised tabs  302 ), that is sized to fit in tight assembly to grip (around) liner  200  of  FIG. 2 . 
         FIG. 4A  shows positioning of the sleeves of  FIG. 1  to favor development of large fragmentation. 
         FIG. 4B  shows positioning of the sleeves to favor development of smaller size fragmentation. 
         FIG. 5  shows an embodiment having sleeve liners different from  FIG. 1  and positioning of these (different type) sleeve liners to favor development of smaller size fragmentation. 
         FIG. 6  shows an embodiment having sleeve liners different from  FIG. 1 , and positioning of these (different type) sleeve liners to favor development of larger size fragmentation. 
         FIG. 6A  illustrates in shaded form the positioning shown in the  FIG. 6  sleeves embodiment, to favor development of larger size fragmentation. 
         FIG. 6B  illustrates in shaded form the positioning shown in the  FIG. 5  sleeves embodiment that favors development of smaller size fragmentation and  FIG. 6C  shows another embodiment of a sleeve system  693 ,  694 ,  695  having tabs  696  and slots  697 , wherein the sections are shown arranged in one possible layout that will favor development of smaller sized fragmentation. 
         FIGS. 7A-7C  and  FIGS. 8A-8B  attempt to show conceptually how the physical structures in  FIGS. 1-3 ,  4 A- 4 B,  5 - 6 , and  6 A- 6 C can be variously moved about to influence development of smaller sized vs. larger sized fragments. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an exemplary warhead, projectile, munition, explosively formed projectile, or shaped charge liner, etc., (referenced herein as warhead  100 ), utilizing liners  200  and  300  that are selectively patterned to effect control of fragmentation of a warhead body  102  according to the present invention. The warhead  100  generally comprises the fragmenting warhead body  102  that houses the liners, an explosive or explosive charge  104 , back plates (not shown), and an initiation mechanism assembly (not shown). The warhead liners generally take the cylindrical shape of the warhead body  102 . The explosive charge  104  comprises, for example, LX-14, OCTOL, hand packed C-4, or any other solid explosive, that can be machined, cast, or hand-packed to fit snugly within the inside of inner liner  200 . As further illustrated in  FIG. 2 ,  3 , and in more detail hereunder, a pattern of the liner  200  has recessed areas  202  while the outer liner  300  has rectangular tabs  302  meant to fit therein and be able to be slid up and down there within. In the embodiment shown, the layout of the tabs and recessed areas are all symmetrical and equidistant, in the sense that the position of each tab within its respective recessed area is the same for all tabs, i.e., if one tab is midway inside a recessed area, all tabs will be so positioned within their respective recessed areas. If one tab were at the end inside a recessed area, then all tabs will be likewise so positioned within their respective recessed areas, e.g. However, it is possible to vary the size, the shape, and the positioning of the tabs and recessed areas so they are not all identical, symmetrical, equidistant, or even of the same geometric shapes, thicknesses or depths, wherever advantages could be realized thereby. The recessed areas could be formed by a conventional method such as stamping or stereo lithography. The liners could be made of any suitable low-melt temperature material such as HDPE (High Density Poly Ethylene), or Accura SI 40 stereo lithographic material mimicking Nylon 6:6. Liner thickness could be approximately a fraction of a millimeter to several millimeters. It will be appreciated that the liners are made of a low melt-temperature plastic material to facilitate heat-induced melt out, further enhancing ammunition resistance to fire hazards wherein, in the event of unwanted heat or pressures of launch, the liner plastic melts and flows acting to seal the explosive from catastrophic fratricide, and further the melted plastic also tends to flow to exit the warhead to eliminate pressure within the body. While plastic has been described as a liner material, numerous other materials might be used such as steel, copper, tungsten, aluminum or titanium, e.g., which might be employed based on actual warhead application and type of explosive fill. Upon detonation of the explosive charge  104  of the warhead  100 , in the areas of liner recessed areas  202  that are not blocked by tabs  302 , the momentum of the shock wave propagating through the explosive  104  is transmitted more readily to analogous sections of the interior of the warhead body  102  by breaking through, as compared to breaking through the thicker areas that are blocked by a tab  302 , and then to those analogous sections of the interior of the warhead body  102 . 
     The time delay between the moments when the shock waves arrive is determined by the differences between the detonation velocity of the explosive  104  and the shock wave propagation speed of liner material, in various thicknesses of the liner material, respectively. It can be appreciated that this generates a high gradient of pressures, velocities, and strains between parts of the liners, acting as stress and strain “concentration factors”. Unstable thermoplastic shear (adiabatic shear) eventually transfers the entire burden of localized strain to a finite number of shear planes leading to the warhead body  102  break-up and formation of fragments. As a result, a predetermined pattern of liner recessed areas or tabs can “stamp out” a pattern of localized transitional regions so as to cause the warhead body  102  to shear and break into fragments, accordingly, with controlled sizes. The thinnest liner material presented to the explosion would be a recessed area  202  alone. As an example, twice as much material in thickness would be seen in an explosion, where a tab  302  fills part of that recessed area. 
     The thickness of a liner in various locations and type of explosive help determine the fragment results. A selectively controlled pattern of recessed areas can comprise sections of equal size or, alternatively, sections ranging in size from a relatively large size to smaller sections. The larger size of such sections is selected for more heavily armored targets, while the smaller size of such sections is applicable for lightly armored or soft targets. Consequently, the pattern efficiently enables variable and selective lethality of the warhead  100  that can range from maximum lethality for more heavily armored targets to a maximum lethality for lightly armored or soft targets. 
     Mechanical adjustments to the grids could be translational (in or out) or rotational (but rotational only if the tab  302  widths were made less than the recessed area  202  widths). As will be further described, all these movements will have an ultimate influence on sizes for the fragments to be formed on the exploding fragmenting warhead housing  102 .  FIG. 4A  shows positioning of the sleeves to favor development of large fragmentation. Here, the tabs  302  are positioned roughly in the middle of the recess areas  202  (which situation is illustrated by  FIG. 7B  where tab  720  there is roughly in the middle area of a recess area  700  there).  FIG. 4B  shows positioning of the sleeves to favor development of smaller size fragmentation. Here, the tabs  302  are positioned roughly at one far end of the recess areas  202  (which situation is illustrated by  FIG. 7C  where a tab  720  there is roughly at one far end of a recess area  700  there). 
       FIG. 5  shows positioning of different types of sleeve liners to favor development of smaller size fragmentation, while  FIG. 6  shows positioning of these other type sleeves to favor development of large size fragmentation. Outer liner  508  has a lattice like inside structure of many legs  502  interspersed with open spaces  504  and boxed recessed areas  505 . Tightly fitting inner liner  501  has openings such as  503  which accommodate legs  502  sliding there into when the sleeves are so moved, and also has boxed in recessed areas  507 . By closing the sleeves as shown in  FIG. 6 , a more tight joined structure is created, with maximum of open areas that favor development of large size fragmentation. While the sleeves are pulled apart as in  FIG. 5 , it is more likely that smaller fragments can be formed, this because there are fewer contiguous open areas seen by a detonation. The sleeves can also be rotated to advantage, in helping to form a minimum/maximum of open areas, to aid in forming smaller sized vs. larger sized fragments. Shaded in  FIG. 6A  structure for large fragment formation and shaded in  FIG. 6B  structure for smaller fragment formation, show this effect somewhat more vividly. The  FIGS. 7A-7C  and  8 A- 8 B and accompanying explanation, will help to explain why the (tab  302 +recess  202 ) physical structure in  FIGS. 1A-4B  and the leg ( 502 +opening  503 ) physical structures in  FIGS. 5-6B  can be moved about to influence development of smaller sized vs. larger sized fragments. 
       FIG. 7A  shows a recessed area  700  in a general plane area  710 . Recessed area  700  has a depth of D, a length of L 1 , and a width of W 1 .  FIG. 7B  shows the same recessed area  700  of length L 1 , however it is now blocked in the central area by a solid tab  720 , which tab has a (relatively short) length of L 2 , otherwise with the same depth of D, and same width of W 1 . The presence of tab  720  divides the recess into two smaller recessed areas  701  and  702 . To note, the  FIG. 7A  relatively long (L 1 ) contiguous area is more likely to lead to a larger size fragment, than either of the two smaller recessed areas  701  and  702 . In  FIG. 7C , the tab  720  has been positioned so that it is at one of the extreme ends of recess  700 , leaving an almost as large recessed area  703  (whereas a length of only L 2  of recessed area  700  has been blocked off by the tab). The  FIG. 7C  relatively long contiguous area is likely to lead to a large size fragment, almost as large as the  FIG. 7A  recess. The part of  700  blocked off by the tab is relatively negligible as far as forming a larger sized fragment is concerned. In  FIG. 8A , in an identical sized recessed area as was  700  in  FIG. 7B , a leg  810  now is placed midway in the recessed area to block it in that area. Leg  810  has a width W 2  which is perhaps one third of full width W 1  of the full recessed area  700 . The recessed area has now been reduced to two smaller recessed areas,  801  and  802 . Recessed areas  801  and  802  are likely to only lead to two smaller sized fragments, than the full recessed area  700  which relatively wide and long contiguous area is likely to lead to a larger sized fragment. In  FIG. 8B , leg  810  is placed instead over to one side of the recessed area  700 , leaving a less wide (W 1 -W 2 ) recessed area  800 . Recessed area  800  will still lead to a larger sized fragment because of the still relatively wide contiguous open area of  800 , that is larger than the recessed areas of  801 ,  802 . While the recessed areas and tabs discussed herein have been rectangular in shape, numerous other shapes are possible, such as diamond shape, semi-circular, or triangular shaped, e.g. 
     While the invention has been described with reference to certain 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.