Abstract:
The precursor-follow through kinetic energy explosively formed penetrator assembly greatly enhances target penetration. It is formed of two sections: an initial precursor penetrator followed by a penetrator encapsulating a reactive material. The target will initially be perforated by the precursor penetrator with the second follow through penetrator containing a reactive material causing internal damage through a secondary reaction.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to U.S. patent application, Ser. No. 09/641,957 entitled “Segmented Kinetic Energy Explosively Formed Penetrator Assembly”, by Richard Fong, filed on Aug. 21, 2000, and which is incorporated herein by reference in its entirety. 
    
    
     GOVERNMENTAL INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States for governmental purposes. 
    
    
     FIELD OF THE INVENTION 
     This invention generally relates to the field of ballistics, and it particularly relates to explosively formed projectiles (EFP). More specifically, this invention relates to a precursor-follow through kinetic energy explosively formed penetrator, to achieve greater penetration. 
     BACKGROUND OF THE INVENTION 
     The concept of using explosive energy to deform a metal plate into a coherent penetrator while simultaneously accelerating it to extremely high velocities offers a unique method of employing a kinetic energy penetrator without the use of a large gun. A typical explosively formed projectile (EFP) is comprised of a metallic liner, a case, an explosive section, and an initiation train. Very often there is also a retaining ring to position and hold the liner-explosive subassembly in place. EFP warheads are normally designed to produce a single massive, high velocity penetrator. After detonation, the explosive products create enormous pressures that accelerate the liner while simultaneously reshaping it into a rod or some other desired shape. The EFP then hits the target at a high speed, delivering a significantly high mechanical power. 
     Two major applications have evolved for explosively formed projectiles or warheads, namely, long-standoff sensor-fuzed submunitions and medium-standoff, close-overflight missiles. The former application, which is the more traditional one, requires the formation of a single-piece EFP capable of flying in a stable fashion to the target. This refinement has led to the flared EFP rod and, more recently, to the finned EFP rod designs. 
     For the medium or short-standoff applications, a new type of EFP was developed. The need for an aerodynamic shape is not necessary for these applications because of the short distance the EFP must travel, hence, the length of the rod was increased and the flared tail was eliminated from the design. In fact, some of these rods are purposely stretched beyond their breaking point and fracture into several pieces resulting in greater total length. 
     An EFP warhead configuration may be comprised of a steel case, a high-explosive charge, and a metallic liner. Explosively formed penetrator (EFP) warheads have been designed to project a single massive high velocity penetrator to attack the top of armored vehicles. Such armor perforation capability needs further improvement to counter new generations of harder armored vehicles, without resorting to a larger caliber weapon system. In developing a warhead configuration that meets system constraints and also meets performance requirements, several parameters in the warhead configuration must be redesigned to achieve an optimum configuration. Several warhead configurations have been developed to accommodate varying system constraints. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to satisfactorily address the foregoing need and to form a new a precursor-follow through kinetic energy explosively formed penetrator (EFP) assembly, for greatly enhancing penetration. 
     The foregoing and other objects and features of the present invention are realized by forming the EFP assembly into two sections: an initial precursor penetrator followed by a penetrator encapsulating a reactive material. This will greatly enhance the lethality of the warhead against certain targets, and particularly targets consisting of multi layers or multi compartments. These targets will initially be perforated by the precursor penetrator with the second follow through penetrator containing a reactive material causing internal damage through a secondary reaction. Potential targets include tanks, light armored vehicles, ships, submarines, ballistic missiles, aircraft and bunkers. 
     The EFP warhead or assembly of the present invention is comprised of the following major components: a copper liner, a reactive material, an explosive billet or charge, a backplate, an aluminum housing, and a detonator assembly for initiating the explosive billet. When the explosive billet is initiated by the detonator assembly, it causes the liner to be accelerated forward with the outer edges folding forward to form or mold the reactive material in a desired aerodynamic shape. The forward folding penetrator then separates into two sections, a precursor and a follow through penetrator. The precursor impacts and penetrates the target with the follow through penetrator containing a reactive material entering the target and causing a secondary reaction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features of the present invention and the manner of attaining them, will become apparent, and the invention itself will be best understood, by reference to the following description and the accompanying drawings, wherein: 
     FIG. 1 is a schematic, exploded, cross-sectional, side elevational view of a precursor-follow through kinetic energy explosively formed penetrator (EFP) assembly according to the present invention; 
     FIG. 2 is a schematic, cross-sectional, side elevational view of the EFP assembly of FIG. 1, shown assembled; and 
     FIG. 3 is a view of a two-stage penetrator that form part of the EFP assembly of FIGS. 1 and 2, shown in flight toward a target, after it has been fired. 
    
    
     Similar numerals refer to similar elements in the drawings. It should be understood that the sizes of the different components in the figures are not necessarily in exact proportion or to scale, and are shown for visual clarity and for the purpose of explanation. 
     DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 and 2 illustrate an exemplary embodiment of a precursor-follow through kinetic energy explosively formed penetrator (EFP) assembly  10  according to the present invention. The EFP assembly  10  generally includes a backplate  12 , a housing  14 , an explosive billet  16 , a liner  20 , and a reactive material  70 . These components are assembled along a central axis  30 . 
     The backplate  12  and the housing  14  provide a protective casing for the explosive billet  16  and the liner  20 . In addition, the mass of the housing  14  provides confinement for the explosive billet  16 . The addition of mass around the explosive billet  16  and the liner  20  increases the duration of the explosive impulse and hence the total energy delivered to the liner  20 . The material of choice for the backplate  12  and the housing  14  is typically steel because of its relative low cost, high strength, and density. However, other materials, such as aluminum can alternatively be used, as long as the mass is sufficient to provide the necessary confinement. 
     The density and the physical dimensions of the explosive billet  16  are also of major importance, as they affect the deformation of the liner  20 . 
     With reference to FIGS. 1 and 2, the liner is generally curved and dome (or bell) shaped. The liner  20  has a generally circular peripheral rim or edge  60  and a concave surface  65 . The liner  20  is placed inside the housing  14  against the explosive billet  16  such that the concave surface  65  of the liner  20  is curved toward the backplate  12 . The rim  60  of the liner  20  abuts against and is secured to the inner surface of the housing  14 . The material of choice for the liner  20  is iron, tantalum, copper, or material of like composition, or of metallic materials such as silver, tungsten, or depleted uranium, or of other materials as described herein. The liner  20  might be 0.100 inch thick if of copper, or 0.120 inch thick if of Tantalum. 
     The reactive material  70  partly fills the liner  20  so that it is formed by the liner  20  into a desired shape, subsequent to firing. The reactive material  70  might be 0.120 inch thick and 1.5 inches in diameter, and made of reactive material such as aluminum or teflon, which upon impact, give a higher burst of energy. The speed of impact could be 2 Kilometers per second if liner  20  was made of Tantalum, or 2.7 Kilometers per second if the liner was made of Copper. A recess may be provided in the housing  14  to receive an additional liner  26 , which could be done by machining or other physical alterations. The liners  20  and  26  could be mounted together physically, in the explosive billet&#39;s end, by a retaining ring around the liner end of the explosive billet, or even held together by glue or some bonding material, with or without a retaining ring. Although the liners are shown here as tapered, concave shaped, lens-like, they could also in practice be made as disc-shaped, of uniform thickness, with round circumference. 
     In FIG. 1, section  12  forms a backplate placed flush to a hollow cylindrical housing  14  which has an inside diameter that could be 3 to 6 inches. The cylindrical shaped explosive (billet)  16  could be made of LX-14, OCTOL, or Hand packed C-4, or some other solid explosive, and it can be machined to fit snugly within the inside of the housing, as well as to have a countersunk recess in its forward end, to receive snug placement of a liner or liners, as may be needed. The detonator is physically positioned between back plate  12  and the back end of explosive  16 . Ordinarily a shock wave is propagated because of the explosive burning of the billet, in the form of ever expanding hemispheres that are concentric at the detonation point (if there is a single point of detonation). However, with spaced apart, judiciously placed multiple points of detonation, the shock wave front could be more nearly like a plurality of plane waves, propagating straight forward down the housing towards the liner(s), and being nearly plane perpendicular to the central axis of the housing. With plane waves rather than hemispherical type, e.g., it improves the chances to impart as much pressure as possible to the liner(s) to deform and propel same. The detonator could be made of RDX, PETN, RXN, for example, and could be arranged in many detonation configurations, such as by a high voltage detonator into an explosive train, or by a standard Army blasting cap, a line detonator across the back end of the explosive billet, or even plural line detonators that intersect at near equal angles through the center of the back end of the explosive billet. Electrical wires may be run out between the back plate and back end of the explosive billet, if needed. There is a detonation delay of for instance, 15 microseconds, causing perhaps a 5 Kilobar shock wave to propagate down the explosive until it reaches the area of the liner(s). With more powerful explosives or perhaps with multiple simultaneous detonations of the explosive, a 6 Kilobar shock wave might be generated. 
     With reference to FIG. 3, when the detonator assembly  35  is fired from a gun (not shown), and the detonator assembly  35  initiates the explosive billet  16 , the liner  20  is accelerated forward with its outer edges  60  folding forward to form or mold the reactive material  70  in a desired aerodynamic shape. Both the expelled liner  20  and the reactive material  70  enveloped by the liner  20  form a two-stage projectile  77 . 
     During flight, and as it approaches the target, the reactive material  70  perforates the concave surface  65  of the liner  20  and escapes from the liner  20  through a hole  99 , separating the projectile  77  into two sections or penetrators: a precursor penetrator  20  (previously the liner  20 ) and a follow through penetrator  70  (previously the reactive material  70 ). The precursor penetrator  20  travel along a common trajectory. 
     As the precursor penetrator  20  reaches and impacts and penetrates the target at impact point  90 , and creates a crater therein. The follow through penetrator  70  containing the reactive material enters the target at the crater site and causes a secondary reaction. 
     In one embodiment, the erosion time of the precursor penetrator  20  is equal to the delay time between the precursor penetrator  20  and the follow through penetrator  70 . This delay time can be on the order of milliseconds, but it is a function of several parameters, including velocity, penetrator diameter, length, etc. 
     It should be understood that the geometry and dimensions of the components described herein may be modified within the scope of the invention and are not intended to be the exclusive; rather, they can be modified within the scope of the invention. Other modifications may be made when implementing the invention for a particular application.