Abstract:
A lightweight armor system may comprise multiple reinforcement materials layered within a single metal matrix casting. These reinforcement materials may comprise ceramics, metals, or other composites with microstructures that may be porous, dense, fibrous or particulate. Various geometries of flat plates, and combinations of reinforcement materials may be utilized. These reinforcement materials are infiltrated with liquid metal, the liquid metal solidifies within the material layers of open porosity forming a dense hermetic metal matrix composite armor in the desired product shape geometry. The metal infiltration process allows for metal to penetrate throughout the overall structure extending from one layer to the next, thereby binding the layers together and integrating the structure.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/005,127 filed 3 Dec. 2007. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to lightweight armor systems in general and more specifically to an integrated, hybrid ceramic tile panel system comprising dense ceramic plate layers combined with metal and/or metal matrix composite (MMC) enveloping structures which include metal rich posts for energy absorption and for attachment of the composite structure to a backing plate. 
     BACKGROUND OF THE INVENTION 
     Many different kinds of lightweight armor systems are known and are currently being used in a wide range of applications, including, for example, aircraft, light armored vehicles, and body armor systems, wherein it is desirable to provide protection against bullets and other projectiles. While early armor systems tended to rely on a single layer of a hard and brittle material, such as a ceramic material, it was soon realized that the effectiveness of the armor system could be improved considerably if the ceramic material were affixed to or “backed up” with an energy absorbing material, such as high strength Kevlar fibers. The presence of an energy absorbing backup layer functions to catch the fragments of an incoming projectile but without significantly reducing the spallation of the ceramic caused by impact of the projectile. 
     Testing has demonstrated that such multi-layer armor systems tend to stop projectiles at higher velocities than do the ceramic materials when utilized without the backup layer. While such multi-layer armoring systems are being used with some degree of success, they are not without their problems. For example, difficulties are often encountered in creating a multi-hit capability armor with multi-layered material structure having both sufficient mechanical strength and ballistic shock resistance as well as sufficient bond strength at the layer interfaces. 
     Partly in an effort to solve the foregoing problems, armor systems have been developed in which a “graded” ceramic material having a gradually increasing dynamic tensile strength and energy absorbing capacity is sandwiched between the impact layer and the backup layer. An example of such an armor system is disclosed in U.S. Pat. No. 3,633,520 issued to Stiglich and entitled “Gradient Armor System”. 
     The armor system disclosed in the foregoing patent comprises a ceramic impact layer that is backed by an energy absorbing ceramic matrix having a gradient of fine metallic particles dispersed therein in an amount from about 0% commencing at the front or impact surface of the armor system to about 0.5 to 50% by volume at the backup material. 
     While the foregoing type of armor system was promising in terms of performance, it has been discovered by the present inventors that a dense ceramic armored tile system intimately encapsulated in solid metal and/or metal matrix composites and including cast-in energy absorbing post structures reduces “spallation” caused by projectile impact and has not yet been presented in the art. 
     SUMMARY OF THE INVENTION 
     The armor tile system according to the present invention comprises one or more dense ceramic plates encapsulated in solid metal and/or metal matrix composites (MMC) and includes cast-in integrated energy absorbing post structures extending outward from the tile(s). The enveloping aluminum or MMC may contain “reinforcing bars” of strong metal alloy wires to create a re-bar reinforced ductile aluminum or MMC skin, or various configurations of rods or metal sheets, which acts to dissipate energy upon projectile impact while maintaining the structural integrity surrounding the impact zone. 
     Each individual hybrid tile may comprise a structure of dense ceramic plate(s) and the hybrid tile can be bonded to an aluminum backing plate via extending post structures by methods known in the art such as welding, adhesive bonding, or mechanical swaging. Various arrays of dense ceramic plates, including a single dense plate or a plurality of dense plates may be utilized (1×1, 2×2, 4×4, 2×8, etc) within a hybrid tile and multiple tiles may be mounted to a backing plate depending on the area to be protected. 
     The armor tile system of the present invention is created utilizing a molten metal infiltration process. First, a mold cavity comprising elongated holes machined into its base is provided. Next, one or more dense ceramic plates are placed within the mold cavity resting on one or more spacers that separate the bottom surface of the ceramic plates(s) from the base of the mold cavity to create a space therebetween. The spacers may be a dense or porous ceramic, or metal or combinations thereof. 
     The dense ceramic plates are further positioned within the mold cavity to create a controlled space between adjacent plates via alignment spacers positioned between adjacent plates to keep the plates from shifting during metal infiltration. The alignment spacers can be a soft metal or hard ceramic, porous or dense material. The dense ceramic plates and spacers include ceramics which may include open porosity only at the material surface and that are devoid of open interconnected porosity within the interior of the materials. 
     A mold typically contains one or more ceramic plates however various geometries of flat plates, and combinations of dense layers may be utilized. The mold may further contain metal “rebar” wire or various configurations of rods or metal sheets, placed around the edges of the mold cavity, over the surface of the ceramic plates, and between the plates, to create a reinforced ductile aluminum or MMC skin. 
     A second set of spacers are next placed on the ceramic plates top surface to create a space between the mold cavity cover and the ceramic plates top surface. A plurality of ceramic plates and spacers may also be stacked according to the shape of the mold cavity and desired ballistic resistance. The mold cavity is next infiltrated under pressure with molten metal allowing for metal to penetrate into any open porosity of the dense ceramic plate layer surfaces and spacer open porosity and through or around areas within the mold cavity that contain open spaces, thereby binding the layers together, and encapsulating the dense ceramic plates and spacers into an integrated tile panel. 
     The elongated holes in the mold cavity base are also filled with liquid metal that once solidified then form integrated cast-in post structures. These posts may be metal rich or contain other dense or porous ceramic or metal inserts and are provided for energy absorption and attachment of the composite tile structure to a backing plate. 
     The mold chamber is fabricated to create the final shape or closely approximate that desired of the final product. The hybrid armor tile is next demolded and comprises a hybrid structure of metal matrix composite and ceramic plates with an encapsulating aluminum rich skin and/or metal matrix composite (MMC) enveloping structure. Integrated cast in metal rich post structures are provided for both 1.) energy absorption and 2.) attachment of the composite tile structure to a backing plate. The length, diameter, draft angle and spacing of the posts are variable to meet a desired ballistic threat and blast over-pressure. 
     A fraction of the posts may be used to attach the composite tile structure to the backing plate, and may be recessed within the backing plate or affixed to the surface of the backing plate. The other fraction of posts being shorter and with post ends either contacting the backing plate, or raised above the backing plate. The attachment posts have a length to allow a separation between the backing plate and the hybrid tile body. The posts help absorb shock and the space between the hybrid tile and backing plate help to deflect an overpressure blast wave. 
     Additionally, a rubber or adhesive material may be present between the post ends and backing plate and as a filler placed between adjacent posts to further enhance ballistic or blast energy absorption by attenuating shock waves after projectile impact or blast over-pressure. 
     The dense layers can include an infinite combination of dense material types and geometries. These dense layers may comprise inorganic material systems such as ceramics, metals, carbon/graphite materials, or composites with dense microstructures. Other dense layers include ceramic structures containing interior voids or hollow regions (which are not connected to the surface). The geometries can be in the form of flat plates of varying thickness, compound curved shapes, spheres, cylinders, and of multiple sequences and combinations of the dense materials. 
     The dense layers are wetted with liquid metal which chemically bonds and/or mechanically infiltrates any open surface porosity and then solidifies and binds the layers together to create a coherent integral structure. The dense layers can be selected according to their denseness and fraction of void volume at the material surface that are to be infiltrated with liquid metal. The selection of different dense material types allows the designer to vary thermal expansion coefficients throughout the structure to create varying stress states for increased effectiveness of the armor tile system. The selection of different material types may also be based on hardness, strength, toughness, and weight attributes of the individual material types desirable for projectile impact protection. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is best understood from the following detailed description when read in connection with the accompanying drawings, which illustrate an embodiment of the present invention: 
         FIG. 1  is a top view of the mold cavity  15  utilized in the production of the armor system of the present invention, illustrating the machined holes for the fabrication of the armor tile post structures. 
         FIG. 1A  is a cross-section of  FIG. 1  illustrating the varying depth machined holes  15 A and  15 C. 
         FIG. 2  illustrates the spacers  20  placed within the mold cavity of  FIG. 1 . 
         FIG. 3  illustrates the mold cavity  15  of  FIG. 2  containing dense ceramic plate inserts  25  stacked on the first set of spacers and a second set of spacers  20 A placed on the ceramic plate  25 . 
         FIG. 3A  illustrates mold cavity cover  16  for the mold cavity  15  of  FIG. 3 . 
         FIG. 3B  illustrates the mold cavity  15  of  FIG. 3  with rebar reinforcements  3 B 1  placed therein. 
         FIG. 3C  is a cross-section of  FIG. 3B . 
         FIG. 4  illustrates a cross-sectional view of the mold cavity  15  prior to molten metal infiltration illustrating a mold cavity cover  16 , a layer of spacers  20 , a layer of dense ceramic plates  25 , a second layer of spacers  20 A, and a mold cavity base  15 B with machined post cavities  15 A and  15 C therein. 
         FIGS. 4A and 4B  illustrates alternative dimensioned spacers  20  and  20 A incorporated in a demolded tile panel  60  after metal infiltration. 
         FIG. 5  illustrates a cross-sectional view of the mold cavity of  FIG. 4  after molten metal infiltration denoting the molten metal as “x”. 
         FIG. 6  illustrates a perspective view of four individual demolded tile panel  60  placed adjacent to one another. 
         FIG. 6A  illustrates a sectional view of a demolded hybrid tile panel  60 . 
       FIG.  6 A 1  illustrates a sectional view of an alternative embodiment of spacer  20  and post  6 B of tile panel  60  after metal infiltration. 
         FIG. 6B  illustrates a detail view of an example of an aluminum rich rib  6 C used for bonding demolded tile panel  60  together. 
         FIG. 7  illustrates the demolded tile panel  60  secured to a backing plate  7 . 
         FIG. 7A  is an enlarged view of the aluminum plate contact points of  FIG. 7  at  6 A and  6 B. 
         FIG. 7B  is a perspective view of four demolded tile panel  60  and backing plate  7 . 
         FIG. 7C  is a perspective view of the tile panel  60  of  FIG. 6  mounted to backing plate  7 . 
         FIG. 8  is a cross section of a mold cavity  15  prior to molten metal infiltration including a plurality of ceramic tiles  25  and spacers  20 . 
         FIG. 9  illustrates a cross section of the mold cavity  15  prior to metal infiltration including a layer of dense ceramic plates  125 . 
         FIG. 10  illustrates a sectional view of the demolded ceramic tile panel  60  after metal infiltration of the mold cavity  15  of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A hybrid tile armor system  10  of the present invention is illustrated in  FIGS. 6 through 10 . The system is constructed in accordance with a process heretofore described and as illustrated in  FIGS. 1 through 5 . First a mold cavity  15  is prepared and is typically made from a die suitable for molten metal infiltration casting with the dimensions defined to produce a hybrid tile armor system. 
     The dimensions of the mold cavity may be flat or include compound curves required for applications such as personal body armor. Mold cavity  15  includes a plurality of openings  15 A milled into mold  15  bottom surface  15 B which are subsequently filled with molten metal during the infiltration casting process to form posts  6 A and  6 B (see  FIG. 5 ) which are integral to and part of containment layer  25 B 1  and extend outward from spacers  20  and ceramic plates  25  (see  FIG. 5 ) that are placed within the mold cavity  15 . 
     Referring to  FIG. 1A , openings  15 A within mold  15  bottom surface  15 B may be a fixed length ranging from about 0.020 inches to about 0.5 inches or more but may also include a plurality of longer openings  15 C (to form posts  6 B) to facilitate bonding of the hybrid armor tile panel  60  to a backing plate  7  as illustrated in  FIG. 7 . It is also contemplated that the length of openings  15 A may be varied throughout the mold cavity  15  according to a particular application requiring either specific length posts for energy absorption requirements or for mounting requirements. 
     The density of openings  15 A could range from about 2% to about 40% of the surface area of bottom surface  15 B. It is understood that various arrays of dense ceramic tiles or plates, including a single dense plate or plurality of plates (1×1, 2×2, 4×4, 2×8, etc) may be utilized to form a hybrid tile panel and multiple panels may be mounted to a backing plate to form a larger armor panel structure (see  FIG. 7C ) depending on the area to be protected. It is further understood that the dimensions, shapes and thicknesses of individual tiles may also be varied according to a particular application. 
     Referring to  FIGS. 1A through 3 , a first set of one or more spacers  20 , having a total surface area equal to or less than the dense plates  25  surface area, and from about 0.005 inches to about 0.5 inches thickness, is next set on mold  15  bottom surface  15 B in a location suitable to uniformly raise the bottom surface of dense plates  25  placed on top of spacers  20  above bottom surface  15 B. Typically, the spacers range from about 0.25 inches by 0.25 inches at a minimum but may be larger as required. 
     The spacers  20  also serve as a reinforcement point to enhance stiffness of the hybrid tile armor tile panel  60  system and may also act to anchor posts  6 A and  6 B as illustrated in FIGS.  6 A and  6 A 1 . Spacers  20  may also include a through hole  6 B 1  in selected spacer  20  locations covering openings  15 A (See  FIG. 4 ) whereby the through hole  6 B 1  would extend into opening  15 A providing a solid post structure that extends into spacer  20  and enhances the bond of posts  6 A and  6 B to the tile panel  60 . Referring to FIG.  6 A 1 , a post  6 B is shown with the metal infiltrant extending into a spacer  20  opening or through hole  6 B 1 . 
     These reinforced posts can be selected for either posts  6 A or  6 B according to ballistic threat requirements. Referring to  FIG. 3  and  FIG. 4 , at least one dense ceramic plate  25  is next placed within the mold on top of at least one ceramic spacers  20 , with the bottom surface of ceramic plates  25  resting on spacers  20  top surfaces and raising ceramic plates  25  above mold  15  bottom surface  15 B approximately 0.005 inches to about 0.5 inches. In the embodiment illustrated in  FIG. 3 , the mold cavity  15  and tiles  25  placed therein are rectangular, however, it is understood that any dimensioned mold and tile combination is contemplated by the present invention. 
     The thickness of dense ceramic plates  25  can range from about 0.020 inches to about 2 inches or more. The plates  25  are set in the mold cavity such that space  25 A between adjacent ceramic plates is between about 0.01 to about 0.5 inches and the space between the ceramic plate outer periphery  25 B and the mold cavity internal side surface  25 C is approximately ½ of the space  25 A. The controlled spaces  25 A defined above and the space between the tile outer periphery  25 B and the mold cavity internal side surface  25 C is maintained via alignment spacers positioned between adjacent ceramic plates  25  to keep the plates  25  from shifting during metal infiltration. The alignment spacers can be a soft metal or hard ceramic, porous or dense material. 
     Referring to  FIG. 3B , wire  3 B 1  constructed of Ni, or any other alloy of Ni—Fe, Ti, steel, etc, acting as a “re-bar” reinforcement, may be placed on the top surface of ceramic plates  25  and/or in the space between the ceramic plates  25  outer periphery  25 B and the mold cavity internal side surface  25 C. Referring to  FIG. 3C , wire  3 B 1  may also be placed in open spaces below ceramic plates  25  in a similar manner as illustrated in  FIG. 3B . The thickness of wire  3 B 1  ranges from approximately 0.0005 inches to about 0.5 inches. 
     Other possibilities contemplated for the “rebar” reinforcement may include various configurations of rods, woven fibers or wires, or metal sheets, placed around the edges of the mold cavity, over the surface of the ceramic tiles, and between the tiles, to create a reinforced ductile aluminum or stiff Metal Matrix Composite (MMC) skin. Next, a second set of one or more spacers  20 A are placed upon the top surface of tiles  25 , the spacers  20 A, which may be of different composition and size than spacers  20 , and may be placed directly above and parallel to spacers  20  to aid in the reinforcement, toughness and stiffness of the hybrid tile armor system  60 . 
     The inventors have found that the alignment of the porous ceramic spacers  20  and  20 A can facilitate abrasive type through hole machining. As illustrated in  FIG. 8 , at least one layer comprising at least one dense ceramic plate  25  may be layered upon each other utilizing at least one layer comprising at least one spacer  20  to create an open space between successive layers prior to metal infiltration. All design features described herein for subject invention apply to an embodiment of subject invention utilizing at least one layer of dense ceramic plates  25  as illustrated in  FIG. 8 . 
     The number of layers is determined by the mold size and desired ballistic resistance. A cross-section of the stacked layers of dense ceramic plates  25  and stacked layers of spacers  20  and  20 A of an embodiment incorporating the principles of subject invention is illustrated in a sealed mold cavity  15  without re-bar reinforcement ( FIG. 4 ) and with re-bar reinforcement ( FIG. 3C ). It is further contemplated that spacer(s)  20  and  20 A may be dimensioned as single material layers covering an entire tile panel surface area ( FIG. 4A ,  4 B) versus single isolated areas as illustrated in  FIG. 3 . Spacer(s)  20  may also comprise distinct spacer layers mirroring each dense ceramic plate  25 . As illustrated in  FIG. 9 , an alternate embodiment without spacers, and comprising at least one layer having at least one dense ceramic plate is also contemplated. This embodiment includes the placement of at least one layer of dense ceramic plates  25  within the mold  15  but without layers of spacers  20 .  FIG. 10  illustrates a sectional view of the demolded hybrid tile panel  60  after metal infiltration of the mold cavity  15  of  FIG. 9 . 
     Dense ceramic plates  25  comprise a microstructure designed without interconnected porosity and having a predetermined fraction of void volume or open structure at its surface, or zero void volume or open structure at its surface. If a void volume is present it is filled and bonded with molten metal subsequent to metal infiltration casting. Dense ceramic plates  25  may be dense ceramic such as aluminum oxide, silicon carbide, boron carbide, silicon nitride, chemical vapor deposit diamond or composites of ceramics. Dense ceramic plates  25  may be a dense metal such as titanium, tungsten, molybdenum, and depleted uranium or alloys. 
     Other suitable dense materials include but are not limited to glass-ceramics, and other inorganic material systems which are compatible with molten metal processing and which can contribute to ballistic resistance of the integrated system. Dense materials such as high strength steels, metal alloys, and ceramic alloys may be used in subject invention. Dense ceramic plates  25  include between 0 and 20% surface porosity with the interior of the dense materials not susceptible to metal infiltration. 
     The dense materials may include “voids” or open spaces within their interior, however, no interconnected porosity is present which would provide a path for metal infiltration from the surface to the interior of dense materials. Spacers  20  and  20 A may be ceramic or metal and in the form of particulates or fiber. Spacers  20  and  20 A may also be in the form of metal sheets, rods, wires and weaves functioning to separate the ceramic tile layers. The ceramic and/or metal particulate or fiber reinforcements within the metal matrix include materials such as aluminum oxide, carbon, graphite, silicon carbide, boron carbide, titanium, tungsten, nickel, molybdenum, copper, aluminum and other anticipated ceramics or metal materials. 
     Spacers  20  and  20 A having an interior open porosity would range between about 30% and about 90% prior to metal infiltration. Referring to  FIG. 3A  and  FIG. 4 , mold cavity cover  16  flat bottom surface  16 A is next placed upon spacers  20 A top surface defining the closed mold cavity and creating a space between mold cover bottom surface  16 A and the top surface of ceramic plates  25  in the areas around spacers  20 A. Spacers  20 A may be removed when wire  3 B 1  on the top surface of ceramic plates  25  is utilized and provides a separation between mold cover bottom surface  16 A and the top surface of ceramic plates  25 . The closed mold cavity is next infiltrated with molten metal. 
     The Al infiltration process causes aluminum to penetrate throughout the overall structure and into any surface open porosity of dense ceramic plates  25 . Spacers  20  and  20 A may have a predetermined fraction of void volume or open structure throughout the material structure that becomes filled with molten metal or become bonded metallurgically or mechanically to ceramic plates  25  subsequent to metal infiltration casting. 
     The Al infiltrant solidifies within and around the material layers extending from one layer interface to the next, thus binding the layers together and integrating the structure. While molten aluminum is the embodiment illustrated other suitable metal infiltrants include but are not limited to aluminum alloys, copper, titanium and magnesium, and other metal alloys cast from the molten liquid phase. The liquid metal infiltration process is described in U.S. Pat. No. 3,547,180 and incorporated herein by reference for all that it discloses. 
     Referring to  FIG. 4 , a cross section of the stacked dense ceramic plates  25  and spacers  20  and  20 A is illustrated before metal infiltration casting and removal from the closed mold  15  and illustrates the open space around dense material layers of ceramic plates  25  and spacers  20  and  20 A.  FIG. 4  further illustrates open space within cast-in post structures  15 A and  15 C of mold  15 .  FIG. 3C  illustrates the cross section of  FIG. 4  further including the re-bar reinforcement  3 B 1 . Subsequent to metal infiltration, the metal infiltrant  25 B is denoted by the drawing symbol “x”, as illustrated in  FIGS. 4 ,  4 A,  4 B,  5 ,  6 A,  6 A 1 ,  7 ,  7 A, and  10 . 
     Any open surface voids within the dense ceramic plates  25 , if present, and open porosity within spacers  20  and  20 A are filled with aluminum during the Al infiltration process including space  25 A between ceramic plates  25 . As illustrated in  FIG. 5 , mechanical and chemical reactive surface bonding allows the dense ceramic plates  25  to bond at their surfaces at metal infiltrant  25 B points “x”. The metal infiltrant  25 B forms a containment layer  25 B 1  at the periphery of the molds internal cavity upon completion of the Al infiltration process. Referring to  FIGS. 9 and 10  the “X” S denote aluminum penetrating any porosity that may be open at the surface in an otherwise dense (no interconnected porosity) ceramic plate  25 . The aluminum forms a thin skin encapsulating the ceramic plate  25 , which thickness depends on tolerances and consequent gap between ceramic plate  25  and the mold cavity internal surfaces. 
     Referring to  FIG. 6 ,  6 A and  FIG. 7 , after the metal infiltration process is complete the hybrid armor tile panels  60  are removed from the casting mold  15  and may be welded at points  6 C and  6 B to form a 2×2 array of tile panels  60  to enhance the rigidity of the armor panel structure. 
     As illustrated in  FIG. 7 , the backing plate top surface  7 A is spaced away from bottom surface  25 B 2  of hybrid armor tile panels  60  and may be substantially parallel thereto. Tile panel  60  may be welded to a backing plate  7  via elongated posts  6 B being recessed into backing plate  7  through a bore formed therein and posts  6 B welded within the bore. In the embodiment illustrated, the top of posts  6 A would be flush with the top surface of backing plate  7  creating a gap  30  between posts  6 A and  6 B, the gap acting to deflect or disperse ballistic shock and impact and blast over-pressure. Other possibilities include shorter posts  6 A that are raised above the top surface of backing plate  7 . 
     A space  30 A may be created below post  6 B depending on the depth of the bore into backing plate  7  and extent to which post  6 B is inserted into the bore. The backing plate  7  serves as a mounting platform to attach the armor panel to the object requiring protection. The backing plate  7 , in combination with armor tile  60 , may be made of aluminum, steel, titanium, fiber reinforced epoxy, or other metal or composite structures. As illustrated in  FIG. 7B , a plurality of panels  60  may be mounted adjacent each other at a distance from about 0 to about 0.01 inches for optimum ballistic deterrence. 
     A single backing plate  7  may be drilled itself for attachment of the panel  60  and aligned spacers  20  and  20 A may also serve as a drillable medium attachment point.