Abstract:
Disclosed is an ammunition cartridge case that includes a sleeve, a base fixedly attached to the sleeve and a fiber reinforced polymer composite annulus that is at least partially within the base. In certain embodiments, the sleeve and the base are formed partly or entirely from a metal, for example steel or stainless steel. The base has a central aperture that affords for the annulus ring to fit within. The annulus is dimensioned such that it fits securely within the central aperture of the base and has a center aperture wherein a primer can be located. The annulus ring contains a volume of composite fibers ranging from 10 to 90 volume percent. The annulus isolates the primer from the cartridge case and thereby prevents galvanic corrosion between the primer and case. In addition, a metallic foil can be present between the annulus and the cartridge case in order to assure proper securement of the annulus therewithin.

Description:
GOVERNMENT INTEREST 
     The invention described herein may be manufactured, used, and licensed by or for the United States Government. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to an ammunition cartridge cases, lightweight metallic ammunition cartridge cases, lightweight metal ammunition cartridge cases and lightweight steel ammunition cartridge cases. 
     BACKGROUND OF THE INVENTION 
     Ammunition cartridge cases serve many purposes by providing the ability to combine a projectile, a primer and a propellant into one complete system. This complete system allows for a cartridge to be placed within a weapon and fired such that the projectile exits a barrel of the weapon at a high rate of speed in an attempt to strike a desired target. During combustion of the cartridge, the cartridge case obturates a chamber of the weapon as a result of pressure exerted thereon by gunpowder combustion gases while providing a finite volume for the controlled ignition of the gunpowder to take place. After firing of the ammunition, the cartridge case has served its purpose and is typically discarded, recycled, or reloaded. 
     While primer and gunpowder serve critical roles in conveying the projectile toward a desired target, the cartridge packaging does not directly progress the projectile toward the target and as such cartridge modification would minimally affect the overall system performance. Thus, if a lightweight cartridge case could be engineered, such that the system provided the same functionality, but with a lighter weight, an overall system performance increase could be obtained. For example, a soldier or individual could carry additional ammunition at the same basic load or carry an equal amount of ammunition with a reduced weight burden. Similar benefits could be demonstrated on larger mobile platforms, such as aircraft, where weight-limiting factors also exist. 
     Small caliber ammunition cartridge cases typically consist of brass that has been formed through a series of cold working and annealing steps. This process results in a graded microstructure that produces higher hardness and strength near the base of the cartridge and a graded hardness and strength along the length of the sleeve sidewalls. The base of the cartridge is substantially thicker than the remainder of the cartridge, as it serves to hold the primer in place, as well as allow for extraction of the cartridge case from the weapon after firing. Thus the base area possesses the highest mass of the entire cartridge. Weight savings of the ammunition can be obtained by substituting steel for brass. However, to achieve larger reductions in weight for the ammunition, additional changes are needed. Therefore, an ammunition cartridge case with greater weight savings compared to traditional brass cartridge cases is desired. 
     SUMMARY OF THE INVENTION 
     Disclosed is an ammunition cartridge case that includes a sleeve, a base fixedly attached to the sleeve and a fiber reinforced polymer composite annulus at least partially within the base. The base has a central aperture that affords for the annulus to fit within. In certain desirable embodiments, the sleeve and the base are made of a metal or a metallic material. In certain more desirable embodiments, the sleeve and the base are made of steel. In still more desirable embodiments, the sleeve and the base are made of a stainless steel. 
     In some instances, the steel base is integral with the steel sleeve and the steel base has an extractor groove. The fiber reinforced polymer composite annulus is dimensioned such that it can be placed securely within the central aperture of the steel base and has a center aperture wherein a primer can be located. The annulus ring may contain a volume of composite fibers ranging from 10 to 90 volume percent. The annulus isolates the primer from the steel cartridge case and thereby prevents galvanic corrosion between the primer and case. In addition, a metallic foil can be present between the annulus and the steel cartridge case in order to assure proper securement of the annulus therewithin. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a longitudinal cross-sectional view of an embodiment of an inventive cartridge case where all longitudinal cross-sectional views are symmetric; and 
         FIG. 2  is an exploded longitudinal cross-sectional view of the base region shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is a lightweight cartridge case having a base with a fiber reinforced polymer composite annul us therewithin. As such, the present invention has utility as a cartridge case for ammunition. 
     In the exemplary embodiment described and illustrated herein, the lightweight cartridge case includes a steel sleeve and a steel base. However, it is suggested that the sleeve and/or base can be formed entirely or partially from another metal or another material for example a metallic material. In some instances, the steel base is integral with the steel sleeve and the steel case is formed as one unit. The steel base has a central aperture. Within the central aperture, a fiber reinforced polymer composite annulus is located, the annulus operable to have a primer placed within and to withstand the pressures generated from the firing of the cartridge. An overall weight reduction is obtained based on the lower density of the apertured steel base and fiber reinforced polymer composite annulus relative to a conventional cartridge case. Extending from the steel base and to the steel sleeve is a flash hole that affords for the ignition of a propellant that is within the steel sleeve after the primer has been detonated. The steel sleeve is lighter than a comparable brass sleeve and the fiber reinforced polymer composite annulus is lighter than the steel that would be present if the annulus were not used. As such, a weight savings in a small caliber ammunition cartridge case is afforded relative to a conventional cartridge case of like caliber and powder capacity. 
     Referring now to  FIG. 1 , there is shown generally in  FIG. 1  an embodiment of an inventive steel cartridge case at reference numeral  10 . The cartridge case  10  has a steel body  100 , a steel sleeve  110  terminating in a mouth end  112  and a base end  114 . The mouth end  112  is operable to accept and attach a projectile (not shown) to the body  100 . An interior volume  116  is defined between the mouth end  112  and the base end  114 . The volume  116  affords a locale for gunpowder to be located and stored. 
     Joined to the base end  114  of the steel sleeve  110  is a steel base  120 . At least partially within the base  120  of the steel body  100  is a fiber reinforced polymer composite annulus  140 . At least partially within the annulus  140  is a primer  150 . For illustrative purposes, the primer  150  is depicted as a shell empty of ignition powder. 
     The case body  100  can be formed from a single piece of steel through a series of cold working and annealing steps. In the alternative, the steel sleeve  110  can be formed separate from the steel base  120  and joined by conventional steel forming techniques such as induction welding and the like, and subsequently polished as needed. Alternatively, an inventive case body  100  is readily formed by machining a steel boule. 
     An exploded view of the base  120  region is shown in  FIG. 2 . The base  120  optionally includes an extraction groove  122  which is illustrated for exemplary purposes as a depression or groove around the circumference of the base  120 . The extraction groove  122  affords a surface for an autoloader extractor claw to grab the cartridge case  10  and pull it from a firing chamber of a weapon (not shown). 
     Within the base  120  is a central aperture  125 , said aperture having a sidewall  126  and a top wall  127 . Extending from the central aperture  125  to the interior volume  116  is a flash hole  130 . The central aperture  125  of the base  120  is a void in the steel base  120  and thus affords a net reduction in weight for the steel cartridge case  10  by an amount equal to the difference in weight between the annulus  140  and a like volume of base metal. 
     The annulus  140  has an outer sidewall  142  and an inner sidewall  144 . Between the outer sidewall  142  and the inner sidewall  144  is a fiber-reinforced polymer composite. A top end  146  and a bottom end  148  also bound the fiber-reinforced polymer composite. Preferably the outer sidewall  142  is complementary to sidewall  126 . More preferably, top end  146  sits flush against top wall  127  so as to resist combustion gas escape therebetween. Fibers within the annulus  140  can have a variety of orientations, such as hoop oriented fiber orientations and axially oriented fiber orientations and combinations thereof. In certain embodiments, from about 50 to about 80 number percent of the fibers have a hoop orientation. In other embodiments, from about 20 to about 60 number percent of the fibers have an axial orientation. 
     The fibers can be made from a variety of materials that provide strength to the annulus  140 , illustratively including, but not limited to: glass; carbon; polymeric materials illustratively including but not limited to, poly-paraphenylene terephthalamide an example of which is sold under the tradename KEVLAR, polymetaphenylene isophtalamide an example of which is sold under the tradename NOMEX, poly-paraphenylene terephthalamide copolymer an example of which is sold under the tradename TECHNORA, polyamide imide an example of which is sold under the tradename KERMEL, copolyimide an example of which is sold under the tradename P84, polyurethane, polyepoxy, poly vinyl ester), polyphenol, polybenzoxazole, polyamides, polyethylene, ultra high molecular weight polyethylene for example polyethylenes having a molecular weight of greater than 1 million, and M5 synthetic fibers. In some instances, carbon fibers are used and are selected from short chopped carbon fibers, aligned continuous carbon fibers, woven carbon fibers, non-woven carbon fibers, and combinations thereof. Suggested diameters for fibers within the annulus  140  range from about 0.5 to about 100 microns. In some embodiments, the average fiber diameter ranges from about 1 to about 50 microns, and in other embodiments, the average fiber diameter ranges from about 5 to about 10 microns. 
     A polymer within the annulus  140  provides a matrix and can be selected from thermoplastic polymers and/or thermosetting polymers. In some instances, the annulus  140  is made by pressure-assisted infusion of a flowable polymer into a dry fabric. It is appreciated that pressure-assisted infusion includes vacuum-assisted infusion. In addition, the pressure-assistance or vacuum-assistance infusion can be applied to assist a flowable thermosetting resin, polymerizable thermoplastic prepolymer, or dissolved thermoplastic polymers into the dry fabric. The relative proportion of a chosen polymer as the matrix for the annulus  140  ranges between about 10 volume percent to about 50 volume percent. In some instances, the polymer within the annulus  140  ranges from about 15 volume percent to about 40 volume percent. It is appreciated that an annulus with a lower proportion of polymer provides a harder object whereas a higher proportion of polymer provides a member that is more shapeable. It is also appreciated that the balance of the annulus  140  includes one or more of the fibers mentioned above and/or any other type of fiber that can provide strength to the annulus  140 . 
     The annulus  140  is also readily made from thin sheets containing fiber which are impregnated with a polymer. The relative orientation of the fiber is optionally set within the thin sheet before the polymer is impregnated with a polymer(s) and once secured, the annulus can be cut out of the sheet. Naturally, other methods of manufacture are possible so long as an annulus member having the required chemical, mechanical and physical properties is obtained. 
     The annulus  140  is dimensioned such that the distance between the top end  146  and the bottom end  148  is generally equivalent to the distance between the top wall  127  of the central aperture  125  and a head end  124  of the base  120 . In this manner, the annulus  140  fits generally flush with the head end  124  of the base  120 . The annulus  140  is also dimensioned such that the inner sidewall  144  defines a diameter that affords for the primer  150  to be located therewithin. The annulus  140  is sealed in aperture  125  through friction fit or optionally through resort to a layer of an adhesive  151  and/or optionally a layer of metal foil  153 . Adhesive may be applied between side wall  126  of the base and side wall  142  of the annulus. 
     The primer  150  has a sidewall  152 , a top end  156  and a strike end  158 . The primer  150  is placed within the annulus  140  with the sidewall  152  at least partially in contact with the inner sidewall  144 . In some instances, the aperture  145  of the annulus  140  is dimensioned such that the primer  150  can be press fit therein. Optionally an adhesive  151  serves to secure the primer  150  into the annulus  140 . A distance between the top end  156  and the strike head  158  of the primer  150  is generally equivalent to the distance between the top end  146  and the bottom end  148  of the annulus  140 . In this manner, the primer  150  with the strike head  158  is generally flush with the head end  124  of the base  120 . 
     Advantageously, the annulus  140  being made from a fiber reinforced polymer composite affords for the isolation of the primer  150  from the steel body  100 . The isolation of the primer  150  from the steel case  100  advantageously affords for the prevention of galvanic corrosion between a primer having a dissimilar composition such as a copper or copper alloy surface and the steel case  100 . A metallic foil  153  is optionally located between the annulus  140  and the base  120 . A metallic foil may be located therebetween in order to provide improved adhesion of the annulus  140  inside the base  120 , the foil  153  being made from any metallic material known to those skilled in the art, illustratively including, but not limited to, copper, copper alloys, stainless steel, aluminum, aluminum alloys, titanium and titanium alloys. 
     The foregoing drawing, discussion and description are illustrative of specific embodiments of the present invention, but they are not meant to be limitations upon the practice thereof. Numerous modifications and variations of the invention will be readily apparent to those of skill in the art in view of the teaching presented herein. It is the following claims, including all equivalents, which define the scope of the invention.