Bullet-resisting Armor

Abstract

Laminar plates having an outer layer of hard, polycrystalline, sintered cmic backed by an aluminum alloy layer resist the passage of bullets and like projectiles as well as much heavier steel armor or heavier armor having a similar ceramic outer layer over a steel base. An intermediate rubber layer permits a reduction in the thickness of the aluminum layer and a corresponding reduction in overall weight at equal protection. Armored vests in which small laminar plates are held in pockets in overlapping relationship are a prime field of application.

Description

This invention relates to the protection of the human body against bullets and like projectiles, and particularly to light, bullet-resisting armor plates and to clothing including armor plates.

Armored vests in common use heretofore include a flexible base of sheet material, such as woven fabric, and are provided with multiple pockets and like receptacles each of which contains a plate of high-strength steel. Because of the weight of the metal, the steel plates more recently have been replaced in some instances by glass-fiber reinforced plastic. However, neither the plastic plates nor steel plates of tolerable weight can stop a high-velocity projectile, such as that of a large-caliber pistol, at reasonably close range. The reinforced plastic plates are pierced by the projectile without sufficiently reducing its kinetic energy, and the steel plates, even if they can slow or stop the projectile, are deformed or disrupted sufficiently so as themselves to injure the bearer of the protective garment.

It has now been found that a facing layer of hard, crystalline, non-metallic material absorbes enough of the shock of an impinging projectile to permit a substantial reduction in the weight of an underlying metal layer, and the use of light-weight aluminum alloys where high-strength steel was considered indispensible heretofore for equal protection.

A bullet or other projectile hitting the facing layer causes the same to crack, and the kinetic energy of the projectile is consumed to a large extent in overcoming the forces of cohesion which bond the crystals of the facing layer to each other. A shock wave travels in the crystalline material transversely to the direction of impact at the speed of sound in the material while the crack formed by the initial impact is propagated at a much slower rate. The advancing shock wave thus proceeds in a still continuous, coherent portion of the layer, and its energy is dissipated relatively rapidly. The metallic backing layer may be deformed at the point of impact to form a bulge not of sufficient magnitude in most instances to cause injury to the wearer of the vest. Even a thin layer of rubber or other elastomeric material interposed between the facing and backing layers has been found to distribute the stresses more widely on the metallic backing layer so as materially to reduce the height of the bulge formed upon impact of a projectile under otherwise identical conditions.

The laminar plates of the invention, when replacing steel inserts, permit the protection afforded by a conventional armored vest to be increased greatly at equal weight, or the weight to be reduced sharply at equal protection. They are employed to advantage wherever else strong armor of light weight is of importance as in the seat armor of military and police helicopters.

Exemplary embodiments of the invention are being described hereinbelow with reference to the appended drawing in which:

FIG. 1 shows a laminar plate of the invention in fragmentary cross section on a greatly enlarged scale;

FIG. 2 shows a first armor plate of the invention in elevational section;

FIg. 3 illustrates another armor plate in a view corresponding to that of FIG. 2;

FIG. 4 is a plan view of yet another armor plate; and

FIG. 5 is a perspective view of an armored vest equipped with armor plates of the type illustrated in FIGS. 1 to 4.

Referring now to the drawing in detail, and initially to FIG. 1, there is seen a laminar plate having a coherent outer layer 1 of polycrystalline, sintered aluminum oxide fired to a pore volume of less than 2 percent. A rubber layer 2 separates the ceramic outer layer from a sheet 3 of high-strength aluminum alloy containing zinc and magnesium as the principal alloying elements, such as Type AA 7075, but other strong aluminum alloys may be employed to advantage.

The thickness of the three layers may be chosen according to the type of projectile against which protection is being sought and to the range from which the projectile is expected to be fired. For use in armored vests, the ceramic layer may typically have a thickness of 1.5 to 2.5 mm, the rubber layer need not be thicker than 1 mm, and the aluminum alloy backing may be 3 to 4 mm thick. It is as effective as a layer of high-strength steel having half its thickness, and therefore approximately 50 percent greater weight, and the combined layers 1, 2, 3 provide protection equal to that of a steel plate several times their combined weight.

The manner in which the several layers of the plate are secured to each other is without significant influence on the protection afforded. Adhesives of many known types may be employed, but we are not aware of a commercially available adhesive whose bond strength is sufficient to offer measureable resistance to the stresses generated in the plate by a high-speed projectile. It is also possible to coat the ceramic and metal layers 1, 3 with known materials which permit the rubber layer 2 to be vulcanized to both other layers. The improvement, if any, achieved thereby is not commensurate with the increased cost.

It is preferred, therefore, to hold the three layers in their superposed relationship by mechanical means as illustrated, by way of example, in FIGS. 2 and 3 from which the rubber layer has been omitted for the sake of simplicity.

The laminar plate illustrated in FIG. 2 includes a square, backing sheet 4 of high-strength steel having an integral raised rim 5 which extends about the entire circumference of the sheet 4 and conformingly envelops the edges of a thin sheet element 6 of sintered aluminum oxide of the type described with reference to FIG. 1. The outer face of the plate 6 is flush with the raised rim 5, and a sheet-steel cover 7, too thin to offer relevant resistance to a bullet, is fastened to the steel rim 5 by soldering or spot-welding in a manner conventional in itself and not shown.

The ceramic element 6 is preferably inserted into the shallow trough formed by the sheet 4 and its rim 5 at elevated temperature, and it is dimensioned to provide a close fit at that temperature. After cooling of the assembly, the greater thermal contraction of the metal as compared to that of the ceramic material causes the edges of the latter to be confined by the rim 5 under compressive stress. This has been found to impede crack propagation in the brittle ceramic layer. Under conditions in which an unconfined aluminum oxide sheet is completely shattered by a projectile, the same sheet may remain intact over a sufficient portion of its surface area to stop a second projectile hitting at some distance from the point of impact of the first projectile.

The cover plate is made unnecessary in the laminar assembly shown in FIG. 3 which has been found particularly useful with a metallic backing layer of aluminum alloy softer than the high-strength steel mentioned with reference to FIG. 2.

The laminar plate of FIG. 3 was prepared by first shaping an aluminum alloy blank under pressure into a square trough having a bottom wall 8 and a side wall 9, inserting a ceramic element 10 into the trough, and thereafter bending the free edge 11 of the side wall at right angles inward of the trough to form a flange which retains the ceramic element 10.

Aluminum oxide elements prepared by sintering green blanks of compacted very fine powder provide a convenient combination of low cost, high strength and hardness, and relatively light weight. However, other crystalline, non-metallic materials having a hardness value of at least 8 on the Mohs scale, may be substituted for the alumina where their specific properties are of advantage, or where they may be more readily available. Chromium sesquioxide forms even harder, sintered plates than alumina. Other eminently suitable materials include the carbides of titanium, silicon, and boron. Zirconium oxide and tungsten carbide plates are readily sintered to the high density of not more than 10 percent, and preferably less than 2 percent pore volume, required to achieve the necessary hardness and cohesion, but are too heavy for many applications. Sapphire plates of the necessary thickness and having a width and length of approximately 2 inches each, as is convenient in armored vests, are available and excellently suited for the purpose of the invention, but economically unattractive at this time.

Even better protection against shattering of an entire ceramic layer in a laminar plate of the invention by the impact of a single projectile is achieved by subdividing the nonmetallic layer and interposing metal strips or ribs between the edges of the ceramic portions, as is hown in FIG. 4.

The integral aluminum alloy structure seen in FIG. 4 includes an obscured bottom wall, a side wall of which only flanges 12, analogous to the flanges 11 in FIG. 3, are seen, and two ribs 13 projecting upward from the bottom wall. The ribs divide the initially formed aluminum alloy trough into four equal compartments respectively receiving ceramic sheet elements 14 under compressive stress as explained with reference to FIG. 2. After insertion of the ceramic plates 14, the flanges 12 were formed and the tops of the ribs 13 were simultaneously upset in an analogous manner.

Each of the ceramic sheet elements 14 conceals a conextensive sheet of rubber which separate the adjacent surfaces of the ceramic sheet element 14 and of the non-illustrated bottom wall in a manner evident from FIG. 1. If a composite armor plate of the invention as shown in FIG. 3 and having overall dimensions of approximately 50 mm .times. 50 mm .times. 7 mm is hit by a bullet at some distance from the center of one of the ceramic sheet elements 14, only a portion of that element may disintegrate, leaving the remainder of that element and the other three elements available for protecting the wearer of a vest armored by means of such composite armor plate. A central hit may shatter an entire ceramic element, but leave the other three intact. Under the same conditions, damage to one or more of the other ceramic elements is unavoidable in the absence of the rubber layer.

While natural rubber is adequate and convenient as an intermediate layer in the armor plates of the invention, it may be replaced by other elastomeric materials without reducing the effectiveness of the armor. The several types of synthetic rubber and elastomeric resin compositions not normally embraced by the term "synthetic rubber" may be used successfully.

The number of individual ceramic sheet elements in a composite armor plate of the invention may be chosen to suit specific circumstances. The single-element plates of FIGS. 2 and 3 are usually sufficient in armored vests, but composite plates of the same overall dimensions having two or more ceramic sheet elements spacedly juxtaposed in a common plane in a manner evident from FIG. 4 offer greater protection against multiple shots from automatic weapons. Composite armor plates employed under the seat and back cushions and along the sides of a helicopter pilot's seat may contain a multiplicity of individual ceramic sheet elements. The metal and ceramic components employed in a helicopter seat should generally be thicker than has been described above with reference to laminar plates for an armored vest.

Such a vest is shown in FIG. 5. It has an outer layer 15 of flexible cloth which forms the base structure of the vest. Its inner lining 16 carries rows of flat pockets 17 each of which overlaps the edges of all contiguously adjacent pockets. Each pocket serves as receptacle for a laminar plate 18 identical with any one of the devices shown in FIGS. 2 to 4, the overlap being sufficient that the edge portion of each ceramic layer in each plate 18 is aligned with the edge portion of the adjacent ceramic layer in a direction perpendicular to the outer face of the laminar structure on the ceramic layer, all ceramic layers facing in a common direction outward of the vest and away from the wearer and the associated metallic layers.

It should be understood, of course, that the foregoing disclosure relates only to preferred embodiments of the invention, and that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of the disclosure which do not constitute departures from the spirit and scope of the invention set forth in the appended claims.

Claims

What is claimed is:

1. A protective garment comprising:

a. a flexible base of sheet material;

b. a plurality of receptacles on said base; and

c. a bullet-resisting laminar plate member in each receptacle, each plate member including

1. a first coherent layer of crystalline, non-metallic material having a hardness value of at least 8 on the Mohs scale,

2. a second layer of metal backing said first layer, the first layers of said plate members facing in a common direction outward of said garment and away from the associated second layers, and

3. a third layer of elastomeric material interposed between said first and second layers.

2. A garment as set forth in claim 1, wherein said first layer has a circumferential edge portion, and said plate member further includes a metallic rim portion confining said edge portion in a direction transverse to said common direction.

3. A garment as set forth in claim 1, wherein said inorganic material is polycrystalline and selected from the group consisting of aluminum oxide, chromium oxide, titanium carbide, silicon carbide, and boron carbide, the crystals of said material being integrally bonded to each other,and pores in said first layer amounting to less than ten percent of the apparent volume of said first layer.

4. A garment as set forth in claim 1, wherein said plate member further includes at least one other layer of said material spacedly juxtaposed to said first layer on said third layer, and at least one metallic rib projecting from said second layer and separating said first layer and said at least one other layer from each other, said at least one rib and said rim portion confining said first layer and said at least one other layer in all directions perpendicular to said common direction.

5. A garment as set forth in claim 2, wherein said edge portion of the first layer in each plate member is aligned in said common direction with the edge portion of the first layer in another one of said plate members.

6. A bullet-resisting, substantially planar, laminar plate member comprising:

a. a backing layer of aluminum alloy;

b. a shock-absorbing layer having a hardness value of at least 8 on the Mohs scale and essentially consisting of crystalline inorganic material, said shock absorbing layer being superposed on said backing layer; and

c. a stress-distributing layer of elastomeric material interposed between said backing layer and said shock-absorbing layer.

7. A plate member as set forth in claim 6, further comprising a metallic rim projecting from said backing layer and enveloping said shock-absorbing layer and said stress-distributing layer, said shock absorbing layer including a plurality of spacedly juxtaposed pieces of said inorganic material having respective edge portions, and an elongated body of metal interposed between said edge portions and separating said pieces.

8. A plate member as set forth in claim 7, wherein said elongated body essentially consists of alumin alloy.

9. A plate member as set forth in claim 6, wherein said layer of elastomeric material is not thicker than 1 millimeter.

10. A garment as set forth in claim 1, wherein said second layer essentially consists of an aluminum alloy, and said third layer is not thicker than 1 millimeter.