FIELD OF THE INVENTION
This invention relates to ballistic armor and, in particular, to such armor comprising ceramic bodies.
BACKGROUND OF THE INVENTION
It is known in the art to provide composite armor plates with a plurality of juxtaposed ceramic bodies such as tiles, cylinders, or spheres in order to protect against impacting ballistic threats.
U.S. Pat. No. 3,616,115 discloses a composite armor plate comprising successive layers of small discrete ceramic blocks encapsulated within a metal matrix by solid-state diffusion bonding. The ceramic blocks are maintained under compression in order to increase the amount of energy required by an impacting projectile to shatter the blocks.
U.S. Pat. No. 5,361,678 discloses composite armor comprising ceramic spheres embedded in a metal matrix. The spheres are fully coated with a binder and ceramic particles in order to insulate them from thermal shock waves produced by the molten matrix during the embedding stage, as well as to enhance the ballistic performance of the armor.
U.S. Pat. No. 6,112,635 discloses a composite armor plate for absorbing and dissipating kinetic energy from a high velocity, armor-piercing projectile, the plate comprising a single layer of ceramic cylinders arranged in a plurality of adjacent rows. The cylinders are in direct contact with each other and are bound by a solidified material.
SUMMARY OF THE INVENTION
The present invention suggests ballistic armor for providing ballistic protection from an impacting projectile threat, the armor comprising a plurality of composite armor units, each comprising a ceramic body having a cylindrical body portion with two end faces, one of which is adapted to face said threat, and a non-ceramic belt member assembled with said ceramic body so that said member contiguously surrounds said cylindrical body portion without covering said one end face.
Preferably, each composite armor unit according to the present invention is bound to other such units by a binding material to form the armor. The armor preferably further comprises a backing layer as is known in the art for trapping fragments of the armor ejected by the impact of the projectile threat.
The cylindrical body portion of the ceramic body, from which the composite armor unit of the present invention is assembled, may have different cross-sectional shapes such as e.g. circular, polygonal, or the like.
The end faces of the ceramic body may be flat, and one may thereby constitute a base for the body portion. As additional examples, the end faces may be convex, bulging away from the body portion, or they may be concave, dipping into said portion. Various such designs may enhance the ballistic performance of the armor or yield other advantages. The two end faces may not necessarily be of the same design.
The ceramic body of the composite armor unit according to the present invention may be made of any known armor ceramic material, such as Alumina, Silicon Carbide, Silicon Nitride, Boron Carbide, or any other refractory material such as ceramic glass and the like. A ceramic material containing reinforcing fibers, as known in the art, may also be used.
The belt member, assembled with the ceramic body in accordance with present invention, has an outer perimeter, and an inner perimeter defining a hollow region to receive and adjoiningly surround the ceramic body to fit about its cylindrical portion. The inner perimeter of the belt member is designed to conform to the shape of said cylindrical body portion to enable the member to closely hug the body after assembly. The outer perimeter of the belt member may be of any design and its dimensions and/or shape may vary along the height of the belt member.
The belt member according to the present invention advantageously allows for a variety of possible shapes and sizes for its outer perimeter. For example, the outer perimeter of the belt member may be circular, elliptical, rectangular, otherwise polygonal, or may have an irregular shape but it is preferable that it have a simple geometry to facilitate its manufacture. Such possibilities allow the composite armor unit and the ballistic armor of the present invention to be suited to a wide range of needs. For example, the belt member may have a hexagonal outer perimeter to allow the unit with which it is assembled to be contiguous with neighboring units in the armor, thereby eliminating the interstices between the units and increasing ballistic immunity to smaller projectile threats. As another example, in order to reduce weight of the unit, and therefore the armor, the belt member may have recesses, such as holes or depressions, formed therein or may have a thickness which varies along its height. In addition, the belt member may not necessarily extend along the entire height of the cylindrical body portion of the ceramic body with which it is assembled, but rather may, for example, have a ring-like shape to simply adjoin the perimeter of the body at a certain height. The above two design possibilities may both be embodied together in the belt member when in the form of a spiral, for example. The spiral belt member may extend along the majority of the ceramic body with which it is assembled, with a space separating successive turns of the spiral. In this way, the spiral design of the belt member serves to reduce the weight of the unit without sacrificing its ballistic performance.
The belt member of the present invention may be made of a variety of materials so long as the belt member possesses a minimal amount of tensile strength, which is at least about 3 kg/mm2. Possible materials include but are not limited to metal alloys such as Aluminum, Titanium and Steel alloys, composites TM such as glass, carbon and aramids, Kevlar™, high strength plastics such as Nylon, polycarbonates, and polyamids, High Density Poly-Ethylene (HDPE) within various resins, carbon fibers and the like. The various resins may include simple fabric, winded fabrics, or mats reinforcement resins.
Calculations that will be presented below show that one of the main advantages provided by ballistic armor comprising composite armor units according to the present invention, is a much desired geometrical weight reduction per unit area of armor. To maximize this advantage, the average density of the belt member should be less than that of the ceramic material from which the body is made. The average density of the belt member depends not only on the material from which it is made, but also on its design. Providing the belt member with depressions as mentioned above, for example, would serve to reduce its average density.
The geometrical weight reduction enabled by the present invention is achieved by providing each of the composite armor units, from which the armor is composed, with a belt member of such a design as to reduce each unit's average density without decreasing its ballistic effectiveness. Determination of the optimal design of the belt member may be made by computer calculation and simulation or by trial and error, bearing in mind the nature of the expected threat from which ballistic protection is desired, in particular the types, calibers, ranges, and inclinations of the impacting projectiles. In general, the most important parameter to consider in selecting such a design is the maximal thickness t of the belt member.
It is clear from the above that the maximal possible reduction in the average density of the composite armor unit and the ballistic armor of the present invention is dictated by the necessity to keep the ballistic performance of the armor at a high level so that it may protect against the expected impacting projectile threat. Indefinitely increasing the thickness t of the belt member will surely further reduce the weight of the armor but at some point, ballistic performance will also be compromised. It was found that both significant geometrical weight reduction is achieved and high ballistic performance is maintained so long as the thickness t of the belt member does not surpass about 10% of the ceramic body's diameter D.
The minimal reduction of the average density or weight of the body that would still be considered essential is limited by the need to justify the costs of manufacturing a belt member according to the present invention. Thus, while the provision of a belt member having a thickness of 0.01%, for example, of the diameter D of the ceramic body would also render the composite armor unit lighter to some minor extent, this would not constitute an essential reduction in the unit's average density as it is not sufficiently beneficial to justify such a belt member's manufacture. In general, a belt member having a thickness t of at least about 1% of the diameter D would be considered an essential reduction.
The composite armor unit of the present invention employed in ballistic armor provides additional advantages, which increase the armor's ballistic effectiveness. Firstly, the belt member of the present invention confines the cylindrical body on which it is mounted so that upon a projectile's impact on the body, the member radially resists and delays ceramic fracture of the body outwardly towards the member's perimeter and also applies resistance forces, which prevent penetration of the projectile. In addition, the belt member provides separation between the cylindrical bodies, which along with the radial confinement it affords, prevents one body's ceramic fracture due to projectile impact from affecting neighboring bodies. In order to enhance these two advantages, the belt member may be assembled with the body so as to hug the body tightly providing it with inward radial compression, thereby increasing resistance. Both of the above advantages increase the armor's multi-hit capability, allowing it to withstand a plurality of projectile impacts while maintaining high ballistic performance. In certain circumstances, the latter advantages may be crucial to the point of being preferable over a reduction in weight, in which case heavier materials may be used to form the belt members in order to enhance ballistic performance at the expense of geometrical weight gain.
The ballistic armor of the present invention is preferably assembled from a single layer of composite armor units, but may also be formed from a plurality thereof. The composite armor units may or may not be in direct contact with each other. The ballistic armor is preferably in the form of a plate and may be curved to allow it to conform to various surfaces whose ballistic protection is desired. The binding material used to hold the units together may be any known suitable material such as thermoset plastic (e.g. epoxy resin or polyurethane) and thermoplastic material (e.g. polyester, polycarbonate, polyamid). The backing layer of the ballistic armor in accordance with the present invention serves to trap ceramic fragments as well as the residual deformed projectile or fragments thereof, resulting from its impact and penetration. The backing layer may be made of any suitable material known in the art, e.g. aluminum, woven or unidirectional fabric laminates comprising SpectraŽ, DyneemaŽ, Kevlar™, Twaron™, S2 or E glass fibers, HDPE, aramids and the like within various resins. The armor preferably also includes a cover material, such as a frontal spall cover, to cover and seal the front of the armor and to keep the units in place, as well as to minimize outward deflection of the impacting projectile threat, fragments of the threat or the units resulting from impact and/or other frontal debris. The cover material is preferably made from layers of fibers, such as Kevlar™ and fiberglass, saturated within thermoplastic and thermoset resins.
The ballistic armor according to the present invention may further include an intermediate layer, as known in the art, between the composite armor units of the present invention and the backing layer to provide a stand-off distance, enhancing the ballistic effectiveness of the armor. Such an intermediate layer may have any design, such as a cellular honeycomb arrangement, and may be made of any appropriate substance, such as foamed materials. Other components known in the art to be used in composite ballistic armor technology may also be added to the armor of the present invention.