Abstract:
A fragmentation warhead with a flexible liner enables increased control of the warhead&#39;s fragmentation pattern. The flexible liner is fixed to a rigid portion of the warhead housing. Explosive material is contained in the housing. A fluid is disposed between the explosive material and the flexible liner to function as a shock transition material. The fluid is contiguous with and bears on an inner surface of the flexible liner. A plurality of rigid fragments or a plurality of explosively formed projectile (EFP) liners are fixed to an outer surface of the flexible liner opposite the fluid. Initiation of the explosive material propels the fragments or EFP liners in directions that may be varied by varying the shape of the flexible liner.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of priority of U.S. provisional patent application Ser. No. 61/824,554 filed on May 17, 2013, which is incorporated by reference herein. 
    
    
     STATEMENT OF GOVERNMENT INTEREST 
     The inventions described herein may be manufactured, used and licensed by or for the United States Government. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates in general to munitions and in particular to fragmentation warheads. 
     The fragmentation effects of a warhead can be delivered by a variety of known techniques. In some cases, unintended collateral damage may be caused by warhead fragments. A need exists for an apparatus and method to direct or channel the fragmentation effects of a warhead to a targeted area, while simultaneously eliminating excess fragmentation and collateral damage. 
     SUMMARY OF INVENTION 
     One aspect of the invention is a fragmentation warhead with a central longitudinal axis and a housing. The housing includes a portion formed of a flexible liner and a portion formed of a rigid material. A high explosive material is disposed in the housing. A fluid is disposed between the high explosive material and the flexible liner. The fluid is contiguous with and bears on an inner surface of the flexible liner. A plurality of rigid fragments or a plurality of explosively formed projectile liners are fixed to an outer surface of the flexible liner opposite the fluid. 
     The fluid may be an energetic material. The fluid and the high explosive material may be the same viscous material. 
     In one embodiment, the rigid material portion of the housing may be generally in the shape of a hollow right circular cylinder having one open end and a central longitudinal axis. The flexible liner may be fixed to the perimeter of the one open end. The rigid material portion may include a telescoping portion that moves the flexible liner between concave, neutral, and convex positions. The flexible liner may be symmetric about the central longitudinal axis of the warhead. 
     In another embodiment, the rigid material portion of the housing may include a pair of opposed end plates and the flexible liner may be fixed to and extend between the pair of opposed end plates to form a side wall of the housing. The side wall of the housing may be movable between concave, neutral, and convex positions by altering a volume of the fluid in the housing. 
     A framework in the form of a grid may be disposed between the side wall and the high explosive material. The grid may include a plurality of longitudinal members extending between the pair of opposed end plates and a plurality of circumferential members extending around the side wall. The side wall may be fixed to the plurality of longitudinal members and the plurality of circumferential members to form an individually movable sub-curvature for each opening in the grid. The sub-curvatures may be movable between concave, neutral, and convex positions by altering the volume of the fluid in the housing. 
     Another aspect of the invention is a method that includes providing a warhead having a flexible liner and adjusting a shape of the flexible liner to thereby alter a fragmentation pattern of the warhead. 
     The step of adjusting may include adjusting the shape of the flexible liner between concave, neutral, and convex positions. 
     In one embodiment, the step of adjusting includes adjusting the shape of the flexible liner by altering a volume fluid in the warhead. 
     In another embodiment, the step of adjusting includes translating a telescoping portion of the housing of the warhead. 
     The invention will be better understood, and further objects, features and advantages of the invention will become more apparent from the following description, taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, which are not necessarily to scale, like or corresponding parts are denoted by like or corresponding reference numerals. 
         FIG. 1A  is a top view of an embodiment of an end-fired warhead with a flexible liner. 
         FIG. 1B  is a sectional elevation view along the line  1 B- 1 B of the warhead of  FIG. 1A , with the flexible liner in a neutral position. 
         FIG. 2  is a sectional elevation view of the warhead of  FIG. 1A  with the flexible liner in a convex or divergent position. 
         FIG. 3  is a sectional elevation view of the warhead of  FIG. 1A  with the flexible liner in a concave or convergent position. 
         FIG. 4  is a sectional elevation view of the warhead of  FIG. 1A  with the flexible liner in a more concave position than in  FIG. 3 . 
         FIG. 5A  is a top view of an embodiment of a side-fired warhead with a flexible liner. 
         FIG. 5B  is a sectional view along the line  5 B- 5 B of the warhead of  FIG. 5A  with the flexible liner in a concave or convergent position. 
         FIG. 6  is a sectional view of the warhead of  FIG. 5A  with the flexible liner in a convex or divergent position. 
         FIG. 7A  is a sectional view of an embodiment of a side-fired warhead having a flexible liner and an internal grid. 
         FIG. 7B  is a perspective view of a portion of an internal grid. 
         FIG. 8  is a sectional view of the warhead of  FIG. 7A  showing the sub-curvatures in convex or diverging positions. 
         FIG. 9  is a sectional view of the warhead of  FIG. 7A  showing the sub-curvatures in concave or converging positions. 
         FIG. 10  is a sectional view of the warhead of  FIG. 7A  showing the sub-curvatures in more concave positions than in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION 
     A novel fragmentation warhead has a housing formed in part by a rigid material and in part by a flexible liner. The warhead has a central longitudinal axis. An explosive composition, such as a high explosive material, is disposed in the housing. A fluid is disposed in the housing between the explosive material and the flexible liner. The fluid is contiguous with and bears on an inner surface of the flexible liner. A plurality of rigid fragments are fixed to an outer surface of the flexible liner opposite the fluid. The rigid fragments are propelled at a high velocity by energy produced when the explosive material is initiated. 
     In some embodiments, a plurality of explosively formed projectile (EFP) liners may be used in lieu of the plurality of rigid fragments. That is, a plurality of EFP liners may be fixed to the outer surface of the flexible liner, rather than a plurality of rigid fragments. 
     In some embodiments, the fluid and the explosive material may be the same viscous material. 
     In some other embodiments, the fluid and the high explosive material may be different materials. By way of example only, the fluid may be oil and the explosive material may be a solid material. 
     The configuration or shape of the flexible liner with the fragments (or EFP liners) fixed thereto may be adjusted or changed prior to reaction of the explosive material. Adjustment of the flexible liner changes the cone angle of the fragment pattern. The fragment pattern may be adjusted in a continuous manner from a diverging pattern to a linear or neutral pattern to a converging pattern. 
     In some embodiments, the fragments may be propelled in directions that are parallel or acutely angled with respect to the central longitudinal axis of the warhead. These embodiments are “end-fired” warheads. In the end-fired warheads, adjustment of the shape of the flexible liner may be enabled by altering the volume of fluid in the warhead or by translating a telescoping portion of the rigid part of the housing. 
     In some other embodiments, the fragments may be propelled in directions that are generally radial with respect to the central longitudinal axis of the warhead. These embodiments are “side-fired” warheads. In the side-fired warheads, adjustment of the shape of the flexible liner may be enabled by altering the volume of fluid in the warhead. 
     The novel warhead may be used in a variety of ways. By way of example only, the warhead may be placed by hand and remotely detonated, or the warhead may be launched from a gun tube. In some embodiments, the flexible liner may be adjusted manually. In other embodiments, the flexible liner may be adjusted by a remotely-operated mechanism. 
       FIGS. 1-4  are views of an embodiment of an end-fired fragmentation warhead.  FIGS. 5-10  are views of embodiments of side-fired fragmentation warheads. 
       FIG. 1A  is a top view of an embodiment of an end-fired warhead  10  with a flexible liner  12  in a neutral position.  FIG. 1B  is a sectional elevation view of the end-fired warhead  10  of  FIG. 1A . Warhead  10  has a central longitudinal axis A. The housing  14  of warhead  10  includes flexible liner  12  and a rigid portion. The flexible liner  12  may be made of, for example, neoprene. The rigid portion includes an end cap  16 , a cylinder  18  fixed to end cap  16 , and a telescoping portion  20 . The rigid portion may be made of, for example, steel. 
     Telescoping portion  20  is translatable with respect to cylinder  18  in the direction of axis A. A sealing ring  38  for sealing fluid may be disposed between telescoping portion  20  and cylinder  18 . The rigid portion of housing  14  is generally in the shape of a hollow right circular cylinder having a central longitudinal axis B and an open end which is closed by flexible liner  12 . The flexible liner  12  is fixed to the perimeter of the telescoping portion  20  and may be symmetric about axes A and B. Axes A and B are coincident. 
     An explosive material, such as a high explosive material  22 , is disposed in housing  14 . A fluid  24  is disposed between high explosive material  22  and flexible liner  12 . Fluid  24  is contiguous with and bears on an inner surface  26  of the flexible liner  12 . Fluid  24  functions as a shock transition material. Fluid  24  may be, for example, oil, such as hydraulic oil. A plurality of rigid fragments  28  are fixed to an outer surface  30  of the flexible liner  12  opposite the fluid  24 . Fragments  28  may be made of, for example, steel or other materials. Fragments  28  may be fixed to liner  12  by, for example, gluing. As mentioned previously, a plurality of mini-EFP liners (not shown) may be used in lieu of fragments  28 . 
     In the embodiment shown, the fluid  24  is separated from explosive  22  by a membrane or plate  32 . However, fluid  24  and explosive  22  may be the same material, for example, a viscous explosive material, in which case membrane  32  is not needed. 
     An explosive booster  34  may be disposed in explosive  22  and a detonator  36  disposed adjacent booster  34 . By way of example only, detonator  36  may be activated by a wireless electromagnetic signal or a known warhead fuze. 
     Telescoping portion  20  may be translated with respect to cylinder  18  in the direction of axis A to thereby alter the shape or position of flexible liner  12  between concave, neutral, and convex positions. In  FIG. 1B , flexible liner  12  is in a neutral position, that is, liner  12  is planar and horizontal. When explosive  22  initiates, fragments  28  will generally be propelled in directions parallel to axis A. 
     In  FIG. 2  and as compared to  FIG. 1B , telescoping portion  20  has been translated downward with respect to cylinder  18  thereby causing fluid  24  to move liner  12  into a convex or divergent position. When explosive  22  initiates, fragments  28  will generally be propelled in directions that diverge from axis A. 
     In  FIG. 3  and as compared to  FIG. 1B , telescoping portion  20  has been translated upward with respect to cylinder  18  thereby causing liner  12  to assume a concave or convergent shape. When explosive  22  initiates, fragments  28  will generally be propelled in directions that converge toward axis A. 
     In  FIG. 4  and as compared to  FIG. 3 , telescoping portion  20  has been translated further upward with respect to cylinder  18  thereby causing liner  12  to assume a more concave or convergent shape than in  FIG. 3 . When explosive  22  initiates, fragments  28  will generally be propelled in directions that sharply converge toward axis A and may form a focused fragment array (FFA). 
     Telescoping portion  20  may be translated with respect to cylinder  18  by hand or by a machine, using a variety of known techniques and mechanisms. For example, telescoping portion  20  and cylinder  18  may be threadingly engaged and rotated with respect to each other by hand or by well-known mechanisms, such as an electric motor drive. The translating mechanism may be placed in a gun-launched projectile with warhead  10  so that translation of portion  20  may occur after the projectile is loaded in a launching tube or during the flight of the projectile. 
     In the embodiment of warhead  10  shown in  FIGS. 1-4 , the shape of liner  12  is varied by translating telescoping portion  20  with respect to cylinder  18 . In a variation of warhead  10 , telescoping portion  20  and cylinder  18  may form a single unitary side wall without a translating portion. In this variation, the volume of fluid  24  in warhead  10  may be increased or decreased to thereby create the variations in the shape of liner  12  shown in  FIGS. 1B and 2-4 . Fluid  24  may be added by through a fluid fitting (not shown) in the unitary side wall. A pump connected to a reservoir may be used to add or remove fluid  24  from the warhead  10 , depending on the desired configuration of liner  12  (i.e., neutral, convex, concave). The pump may be manually operated, or a pump/motor combination and reservoir may be disposed in a projectile with warhead  10  to enable changes in the shape of liner  12  after the projectile is loaded in a launch tube or while the projectile is in flight. 
       FIG. 5A  is a top view of an embodiment of a side-fired warhead  50  having a central longitudinal axis C.  FIG. 5B  is a sectional view taken along the line  5 B- 5 B of  FIG. 5A  showing the flexible liner  52  in a concave or convergent position. The housing  54  of warhead  50  includes flexible liner  52  and a rigid portion. The rigid portion includes a pair of opposed end plates  56 ,  58 . Flexible liner  52  is fixed to and extends between the opposed end plates  56 ,  58 . Liner  52  forms a side wall of the housing  54 . Preferably, liner  52  extends circumferentially 360 degrees to form the complete side wall of the housing. The flexible liner  52  may be symmetric about axis C. 
     Explosive material  22  is disposed in housing  54 . A fluid  24  is disposed between explosive material  22  and flexible liner  52 . Fluid  24  is contiguous with and bears on an inner surface  62  of the flexible liner  52 . Fluid  24  functions as a shock transition material. Fluid  24  may be, for example, oil, such as hydraulic oil. A plurality of rigid fragments  28  (or mini-REP liners) are fixed to an outer surface  64  of the flexible liner  52  opposite the fluid  24 . Fragments  28  may be made of, for example, steel or other materials 
     In the embodiment of warhead  50  shown, the fluid  24  is separated from explosive  22  by a cylindrical membrane or plate  60 . However, fluid  24  and explosive  22  may be the same material, for example, a viscous explosive material, in which case membrane  60  is not needed. If fluid  24  and explosive  22  are both a viscous energetic material, then an internal supporting structure (not shown) would be needed. 
     An explosive booster  34  may be disposed in explosive  22  and a detonator  36  disposed adjacent booster  34 . By way of example only, detonator  36  may be activated by a wireless electromagnetic signal or a known warhead fuze. 
     The volume of fluid  24  in warhead  50  may be increased or decreased to thereby create variations in the shape of liner  52 . Liner  52  is in a concave or convergent configuration in  FIG. 5B . When explosive  22  is initiated, fragments  28  will be propelled generally in directions that converge toward axis D, which is normal to axis C. 
     Adding additional fluid  24  to warhead  50  causes liner  52  to assume a neutral configuration (not shown) wherein liner  52  has a shape of a right circular cylinder centered on axis C. In the neutral configuration of liner  52 , fragments  28  will be propelled in directions parallel to axis D. 
     From the neutral configuration of liner  52 , the addition of more fluid  24  causes liner  52  to assume a convex or divergent configuration shown in  FIG. 6 . When explosive  22  is initiated, fragments  28  will be propelled generally in directions that diverge away from axis D. 
     Fluid  24  may be added through a fluid fitting (not shown) in one of the end plates  56 ,  58 . A pump connected to a reservoir may be used to add or remove fluid  24  from warhead  50 , depending on the desired configuration of liner  52  (i.e., neutral, convex, concave). The pump may be manually operated, or a pump/motor combination and reservoir may be disposed in a projectile with warhead  50  to enable changes in the shape of liner  52  after the projectile is loaded in a launch tube or while the projectile is in flight. 
     Other embodiments of novel side-fired warheads are similar to warhead  50 , but include an internal rigid grid. The flexible liner is fixed to the internal grid to form a plurality of individually deformable “sub-curvatures.”  FIG. 7A  is a sectional view of an embodiment of a side-fired fragmentation warhead  70  with an internal rigid grid. The internal grid  86  alone is shown in a partial perspective view in  FIG. 7B . Warhead  70  includes a housing  74  formed by pair of rigid end plates  76 ,  78  and a flexible liner  72 . Warhead  70  has a central longitudinal axis E. 
     Liner  72  forms the side wall of warhead  70 . Fragments  28  are fixed to an outer surface  84  of liner  72 . Explosive material  22  is disposed in the housing  74 . An explosive booster  34  may be disposed in explosive  22  and a detonator  36  disposed adjacent booster  34 . By way of example only, detonator  36  may be activated by a wireless electromagnetic signal or a known warhead fuze. 
     A framework in the form of an internal grid  86  is disposed between the liner  72  and the explosive material  22 . The grid  86  includes a plurality of longitudinal members  88  that extend between the pair of opposed end plates  76 ,  78  and a plurality of circumferential members  90  that extend circumferentially around the warhead  70 . The circumferential members  90  are fixed to the longitudinal members  88  at their points of intersection. The plurality of longitudinal members  88  may be circumferentially equally spaced. The plurality of circumferential members  90  may be longitudinally equally spaced. The members  88 ,  90  may be made of a metal, for example, steel. 
     Liner  72  is fixed to the plurality of longitudinal members  88  and the plurality of circumferential members  90  to form an individual, flexible sub-curvature  94  for each opening  92  ( FIG. 7B ) in the grid. Not seen in  FIG. 7A  is the fluid  24  (see  FIGS. 8-10 ) disposed between liner  72  and explosive  22 . In  FIG. 7A , the liner  72  is in the neutral position wherein the fragments  28  will be propelled in directions generally parallel to radial axes which are normal to axis E, such as radial axis F. 
       FIG. 8  is a sectional view of the warhead  70  of  FIG. 7A  showing the sub-curvatures  94  in convex or diverging positions. An increase in the volume of fluid  24  in warhead  70  causes the sub-curvatures  94  to move from the neutral positions of  FIG. 7A  to the diverging positions of  FIG. 8 . When explosive  22  in warhead  70  of  FIG. 8  initiates, fragments  28  will be propelled in directions that diverge from radial axes which are normal to axis E, such as radial axes G, H and I. 
       FIG. 9  is a sectional view of the warhead of  FIG. 7A  showing the sub-curvatures  94  in concave or converging positions. A decrease in the volume of fluid  24  in warhead  70  causes the sub-curvatures  94  to move from the neutral positions of  FIG. 7A  to the converging positions of  FIG. 9 . When explosive  22  in warhead  70  of  FIG. 9  initiates, fragments  28  will be propelled in directions that converge toward radial axes which are normal to axis E, such as radial axes J, K and L. 
       FIG. 10  is a sectional view of the warhead  70  of  FIG. 7A  showing the sub-curvatures in more concave positions than in  FIG. 9 . A decrease in the volume of fluid  24  in warhead  70  causes the sub-curvatures  94  to move from the concave positions of  FIG. 9  to the more concave positions of  FIG. 10 . When explosive  22  in warhead  70  of  FIG. 10  initiates, fragments  28  will be propelled in directions that diverge from radial axes which are normal to axis E, such as radial axes J, K and L. 
     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.