Abstract:
A fragmentation warhead includes a cylindrical body, a pair of concentric cylindrical liners made of plastic, and an explosive charge disposed within the innermost liner. The innermost liner includes patterns formed thereon of recessed areas and solid liner elements. The outermost liner&#39;s interior surface includes patterns formed thereon of raised areas and solid liner elements. The outermost cylindrical liner is arranged to be adjustable relative to the innermost liner through rotation or translation. The explosive charge is disposed adjacent to the interior of the innermost cylindrical liner. Upon detonation of the explosive charge and because of the random dampening and temporal delay in transmitting the detonation energy through various locations of the randomly aligned cylindrical liners, the warhead body is caused to shear and break into fragments with different sizes. It can be understood that adjustment of the outermost cylindrical liner can be used to influence the size of fragments ultimately generated when the warhead breaks apart through detonation.

Description:
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 relatively inexpensively formed plastic liners with a predetermined pattern of recessed areas, plastic liners with a predetermined pattern of raised areas, and plastic liners with a predetermined pattern of cutouts. According to the present invention, the “shear” and “stamp” liner recessed areas, raised areas, and cutouts, respectively can 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 a shell break-up and formation of fragments. 
     According to one embodiment of the present invention, the warhead includes liners that are disposed inside the warhead body (one of which liner may be manually positioned from outside the warhead) 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. 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. An 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 cover(s) 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 therefore 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 
         FIGS. 1 and 1A  show a cutaway isometric view of a fragmenting warhead assembly according to this invention; 
         FIG. 2  shows an isometric view of the stationary liner  200  in one embodiment of the invention with a grid system of open gapped areas, that is internal to the fragmenting warhead of  FIG. 1 ; 
         FIG. 2A  shows an isometric view of the stationary liner  200  in another embodiment of the invention with a grid system of solid areas, and also of recessed areas, that is internal to the fragmenting warhead of  FIG. 1A ; 
         FIG. 3  shows an isometric view of an adjustable liner  300  with its grid system of open gaps, that in one embodiment of the invention is internal to the fragmenting warhead of  FIG. 1 , and in relatively tight assembly with an inner liner such as  FIG. 2 ; 
         FIG. 3A  shows an isometric view of another type of adjustable liner  300  (with its inner surface grid system of raised square bumps), that in another embodiment of the invention can be made internal to a fragmenting warhead, and in tight assembly with an inner liner such as  FIG. 2A ; 
         FIGS. 4A through 4C  illustrate the effect of randomly possibly lining up open gaps of liner  300  of  FIG. 1  directly over recessed areas in liner  200  of  FIG. 2A , and in various other random positions of liner  300  with respect to liner  200 ; 
         FIG. 5  illustrates the effect of lining up recessed areas of the liner of  FIG. 2  through various ways of moving liner  300  of  FIG. 1  relative thereto. 
         FIG. 5A  illustrates the effect of lining up recessed areas of the liner of  FIG. 2A  through various ways of moving liner  300  of  FIG. 1A  relative thereto. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1 ,  1 A illustrate 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 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 (stationary) liner  200 . As further illustrated in more detail hereunder, a pattern of the liner  200  has recessed areas  202  and non-recessed areas  203 , while the outer (adjustable) liner  300  has rectangular holes therein. The recessed areas and rectangular holes could be formed by any conventional method such as by stamping or by 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. The patterns described herein comprise openings, gaps, or cutouts (collectively referred to herein as gaps) that are interposed among a plurality of patterned liner solid areas. Upon detonation of the explosive charge  104  of the warhead  100 , in the areas of liner recessed areas, 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, non-recessed areas, 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 non-recessed areas, whether or not lined up under a cutout area in outer liner  300 , can “stamp out” a pattern of localized transitional regions so as to cause the warhead body  102  to shear and break into fragments with controlled sizes. The thinnest liner material presented to the explosion would be a recessed area  202  lined up under a rectangular hole in  300 . Twice as much material would be a non-recessed area  203  lined up under a rectangular hole in  300  and three times as much material would be a non-recessed area  203  not lined up under a rectangular hole in  300 . 
     The thickness of a liner in various locations and type of explosive help determine the fragment results. A selectively controlled pattern of recessed areas (also here in called “gaps”) can comprise sections of equal size or, alternatively, sections ranging in size from a relatively large size to smaller sections. The larger size of the intact (non-gap) sections is selected for more heavily armored targets, while the smaller size of intact (non-gap) 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.  FIG. 1A  shows a cutaway view of the generally cylindrically shaped warhead  100 . Shown through open end  103  of the warhead  100 , is at the core, an explosive  104 , surrounded by the also generally cylindrically shaped, stationary grid  200 . As was described elsewhere, when explosive  104  detonates, the explosive pattern through open areas in adjustable grid  300  is different than at solid areas in liner  300 . These differences in explosive patterns will ultimately lead to analogous fragments in the fragmenting warhead housing  102 . (The respective sizes of the grids, warhead housing, thicknesses, lengths, and/or diameters are not exactly to scale in these drawings). Adjustable grid  300  is turned around from as currently depicted or slid back and forth in place (or some combination thereof), placed into the open end  103  of the warhead  100  shown in  FIG. 1A , between the inside of housing  102  and surrounding the stationary grid  200 , until knob  306  on grid  300  is flush to the end of warhead  100 . The depth on lip  308  on knob  306  is kept short enough so that diameter of knob  306  generally is equal to outside diameter of warhead  100 . Knob  306  preferably has gradation markings  307  to allow a soldier to dial in desired sizes for the fragments to be formed by the exploding fragmenting warhead housing  102 . (Exact position for marked gradations  307  are learned through extensive trial and error in the manufacturing, testing and prove out processes). It must be noted that adjustable grid  300  may be pulled out or returned, pushed back in, in lateral movements, as well as rotated through the knob, in either clockwise or counter clockwise rotations. As will be further described, all these movements will have an ultimate influence on sizes for the fragments to be formed by an exploding fragmenting warhead housing  102 . Although the overall length  309  of adjustable grid  300  shown here is essentially equal to length  209  to that of stationary grid  200  of  FIG. 2A , the length  309  can be made shorter than length  209 . The effect of shortening  309  so that when the knob  306  is flush to warhead housing end  103  is that adjustable grid  300  cannot reach all the way into the warhead. The innermost length of the stationary grid  200  will not be screened any more by any portion of adjustable grid  300 . The effect of this is the innermost (front end) of warhead  100  will generally produce larger sizes of fragments, than the portion of stationary grid  200  that is still screened by adjustable grid  300 . In  FIGS. 4A-4C , the general effect of positioning the grids might be illustrated. With like square patterns, a stationary grid in  FIG. 4A  is shown with square, mostly open gap areas  202  whereas an adjustable grid is shown here to have mostly closed square areas  303  in like patterns in  FIGS. 4B and 4C . As closed areas  303  in  FIGS. 4B and 4C  hypothetically are slid over open areas  202 , the open areas become blocked into smaller areas  202  shown there in  FIGS. 4B and 4C . These smaller areas  202  will lead to differently sized and shaped fragments of the warhead housing  102  than the fully open areas  202  would have. It will be appreciated that many positions and size gaps may be achieved by rotating and sliding in or out, the adjustable grid  300 .  FIG. 5A  may illustrate how an adjustable grid  300  may be rotated, (directions  504 ,  506 ), or pulled out (direction  505 , e.g.), to achieve various gaps  503 ,  502 , or blocked areas  502 , e.g. It should also be remembered that the formed gaps on the grids  200 ,  300  may also be widely varied to produce different fragment sizes. The shapes of individual gaps can be widely varied (holes, parallelograms, curved shapes, etc.); the size of individual gaps (percentage of liner space as gap vs. solid, e.g.); the patterns of the gaps on the grids (fields of different cutouts as desired); and orientation of the patterns (turned 90 degrees from one another, e.g.) can all be altered to advantage in designing the ultimate warhead fragments. Another variation might be to provide an additional plastic liner, which is fully solid, disposed between the inside of housing  102  and adjustable grid  300 , which can further influence the type, size, and shapes of ultimate fragments of exploding fragmentation warhead housing  102 . 
     In  FIG. 3A , the adjustable grid cylindrical liner  300  is now arranged to be smooth on the outside, but on its inside surface there is a checkerboard pattern of rectangular raised surfaces  302 . The height of the raised surfaces is equal to about a thickness of the liner  300 , so that a raised surface on the liner presents twice the thickness of a non-raised surface. The side of the square raised surface is about equal to one third the side length of a recessed area  202  in the stationary liner of  FIG. 2A . The areas in between the raised surfaces are labeled as  303 . Cylindrical liner  300  is meant to snugly envelop stationary liner  200 , so that the rectangular raised surfaces  302  fit in to the recessed areas  202  in the stationary liner  200  since the height of the raised surfaces  302  is approximately equal to the depth of the recessed areas  202  in the stationary liner  200 . It is possible for the raised surfaces  302  to be moved about within the recessed areas  202  in all directions, since as mentioned, the side of the square raised surface is about equal to one third the side length of a recessed area  202 . The movement may be done by rotating adjustable grid  300  clockwise/counter-clockwise or by pulling out/pushing in of the adjustable grid  300 , as may be desired. Moving about the raised surfaces  302  within the recessed areas  202  of course will influence the fragmentation patterns on warhead housing  102 . An explosion pattern that encounters a raised surface  302  after passing through some part of stationary liner  200  will experience plastic material of three times the thickness of a liner; parts of the explosion that miss the (square) outline of a raised surface  302  will only experience material of two times the thickness of a liner (with air in between stationary liner  200  and adjustable grid liner  300  at those points). 
     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.