Patent Grant
7681485
An embodiment of the invention relates to a transparent ballistic resistant structure, namely, one that has a multi-layered or laminated structure composed of an intermediate or middle panel made of transparent ceramic tiles, sandwiched by glass panels. Other embodiments are also described.
All law enforcement, peacekeeping and military communities are often faced with the need to observe potentially hostile environments through protective shielding of some configuration. Transport vehicles such as aircraft, vehicles or vessels often suffer in adequate protection from ballistic and fragmentation threats through the windshields and surrounding windows and/or view ports. Protection of all vehicles in the combat theater has become a seriously realized requirement over the past few years due to urban deployments where typical ballistic stand-off distances are no longer afforded, and improvised explosive devices are becoming more prevalent. Some of the personal protection applications of transparent armor would be protective visors, guard shack glazings, transport vehicle, vessel and aircraft applications, currency transport vehicles, medical, communications and scientific research and development transparency applications.
The current existing transparent armor systems are typically comprised of several layers of either of the following materials: glass, polycarbonate or acrylic, adhered together by polyvinyl butylral (PVB) or urethane adhesive interlayers. The resulting armor structure can have multiple layers of the same material, or it may use a combination of any of the three depending upon the primary and any other secondary threat considerations. The four most utilized transparent ballistic and fragmentation resistant armor materials are as follows.
Bullet resistive glass laminates are relatively heavy and thick, and are manufactured with multiple layers of annealed glass, and polyvinyl butylral (PVB) interlayers from 0.015 inches to 0.120 inches thick. They can pass ballistic and fragmentation ratings and are generically not required to eliminate spall. Anti-spalling components have to be added to the existing already thick glazing, on the rear or protected side. Once attacked, the glass unit will become cracked and partial glass loss to either side will be noticed depending upon whether no spalling or low spalling is specified. Spalling is the exit of glass toward the protected or safe side during an attack, regardless of projectile penetration/access. Typical no-spalling materials utilized are polycarbonate sheet attached to the safe side of the transparent armor system, or a two part film composite manufactured from a 7 to 10 mil thick polyethylene terephthalate (PET) facing film with a 15 or 30 mil (thousandths of an inch) thick polyvinyl butylral (PVB) primary adhesive attached to the safe side of the transparent armor system.
Acrylics are lightweight synthetic materials with excellent optical clarity and a high degree of break resistance. They do offer limited ballistic resistance. However, acrylic glazing materials are highly combustible thermoplastics, and as such, support flames and emit toxic fumes when burned. They are also extremely susceptible to a loss of clarity through scratching, gouging and ultraviolet (UV) exposure. Acrylics once attacked exhibit large cracking and loss of the acrylic material especially during ballistic and heavy fragmentation attacks.
Polycarbonates are lightweight synthetic materials with many times the break resistance of equal thicknesses of plate glass with excellent optical clarity. Similar to acrylics, polycarbonates are susceptible to a lesser degree to scratching, gouging and yellowing from ultraviolet exposure. They too are not fire resistant and emit toxic fumes when burned, but are much more difficult to ignite, and generally have the capability to self-extinguish once flame is removed. Polycarbonates once attacked may show signs of slight delamination between layers directly surrounding a ballistic/fragmentation attack, and will encapsulate the bullet, depending upon composition and speed.
Glass-clad polycarbonates are composite glazings made by sandwiching a polycarbonate sheet between laminations of glass and PVB or urethanes; or by laminating a polycarbonate sheet to the backside of laminated glass as an anti-spall shield.
More recently, transparent ceramics (also referred to in some circles as glass-ceramics) have been showing significant ballistic performance capabilities at substantially reduced weights and overall thicknesses over the conventional glass/plastic systems. Polymeric material advancements, such as improvements in the optical properties of polyurethanes, have shown promise in their combined use with ceramics for further reductions in the overall weight of the finished transparent systems.
Both current and future requirements of military and peacekeeping organizations will involve regular combat actions in urban hostile environments, where single vehicles or supply convoys are at much at risk as organized troop formations. This brings with it the realization that all military and security personnel are at risk. There is also a need for reduced logistical burden in the theatre of operation, such that there is a continued strive for transportation systems that possess reduced weight and operational costs, with increased maneuverability and payload capability. This can be made possible by reducing the weight burden of the armor components. Preferably, such armor components should also not be overly thick, and should have the capability to withstand multiple repeat hits.
The embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment of the invention in this disclosure are not necessarily to the same embodiment, and they mean at least one.
In accordance with an embodiment of the invention, a laminated, transparent (at least in the visible spectrum) ballistic resistant structure is described that has an intermediate or middle layer of transparent ceramic tiles. The tiles are spread across respective, transparent layers that are bonded to opposite sides of the intermediate layer. A transparent adhesive, whose index of refraction is selected to match that of the transparent layers, for improved overall transparency of the structure, may be used to bond the different layers together, front to back. In addition, another adhesive, also with a matching index of refraction, is used to bond the tiles to one another, within and across the intermediate layer. At least three different embodiments of the such a structure will be described below.
Some of the advantages that may be available in the embodiments of the invention described below are as follows: First, ballistic protection is available in two classes, namely 7.62 mm caliber, and HMG 12.7 mm and 14.5 mm. In addition, fragmentation protection may be provided by each of the embodiments, at up to 25 mm caliber. Such combination protection is provided with reduced weight and thickness, as compared to conventional security glazings. In addition, an improvement in multiple repeat hit capabilities has also been observed relative to conventional designs. Such ballistic performance has been obtained with reduced distortion and obscurity of the viewing area around the impact locations, thus permitting continued unobstructed visibility even after a projectile impact. Selection of materials that make up the different layers also provide for compatibility with night vision equipment (in addition to, of course, transparency in the visible frequencies). Overall light transparency has also proved to be not only obtainable, but may also be improved relative to conventional multilayer glass security glazings.
Any reference here to “transparent” is intended to mean at least visually transparent, that is transparent in the visible frequencies of the electromagnetic spectrum. A typical window glass, for example, is transparent in the visible frequencies, while a radome (used to house rotating radar units) is transparent to radar frequencies and may not be required to be transparent in any visible frequencies.
Any reference here to “ballistic resistant” is intended to mean at least having the ability to defeat a bullet fired from a gun, in accordance with any one, or all, of the Level III threats listed below (which may be as defined in National Institute of Justice (NIJ) 0108.01 or in Mil-Std-662F. Use of the term “ballistic” here does not preclude the ability to provide fragmentation protection, such as defined in Mil-P-46593A (e.g., calibers 0.22, 0.3, 0.5, and 20 mm.). Additional definitions for Level IV and higher threats are also given below.
The resulting ballistic resistant structure is rigid, obtained in one case by the lamination of what are separately formed and essentially solid layers. Each layer is sufficiently transparent in the visible spectrum so as to provide a needed overall transparency requirement for the structure. This transparency may be defined in terms of light transmission characteristics, and haze, for the overall structure. Even when looking into the structure at a diagonal (rather than perpendicular or head-on), the structure is likely to not cause too much distortion, provided the tiles are polished and the adhesive layers are correctly selected and applied. The composition of the different layers to promote transparency, as well as, of course, to provide for ballistic resistance, are described below.
In a preferred embodiment of the invention, the intermediate layer is sandwiched by what are essentially glass layers. Glass may be viewed as an amorphous solid with the structure of a liquid. Typically, glass has been super cooled at a rate too high to allow crystals to form. It may also be defined as an inorganic product of fusion that has cooled to rigid condition without crystallization. Glass typically contains at least 50 percent silica, which is known as a glass former. Certain properties of glass may be modified by the addition of oxides of aluminum, sodium, calcium, barium, boron, magnesium, titanium, lithium, lead, and potassium. Depending upon their function, these oxides are considered intermediates (modifiers). For practical purposes, the behavior of glass is regarded as perfectly inelastic and brittle. The hardness of typical glass may be approximately 350 HK to 500 HK (Knoop Hardness). Glass with lower iron content is more transparent, however, it is not as strong (and thus perhaps requiring a greater thickness).
Although glass is considered amorphous, transparent ceramics (also referred to here as glass ceramics) have a high crystalline component to their microstructure. In forming glass, crystallization is to be prevented, whereas in the processing of transparent ceramics, crystallization of desired phases and crystal morphologies is to be promoted. Transparent ceramics may contain large proportions of several oxides, and their properties may be a combination of those of glass and ceramics. Hardness of some, typical transparent ceramics may range from 520 HK to 650 HK, but can be much higher (as mentioned below). The properties of transparent ceramics may be changed by modifying the composition of the material and by using heat treatment. The optical properties of the material can be controlled by using various formulations and by controlling the structure, for example, to impart different degrees of transparency and different colors. As an example, single crystal sapphire (single crystal aluminum oxide) is considered highly transparent. In fact, the glass panels used in the different embodiments of the invention are likely to exhibit lower transparency as compared to the transparent ceramic and adhesive layers used.
Currently, there are three transparent crystalline ceramics that have substantial promise for improved transparent armor applications. One is magnesium aluminate spinel (MgAl2O4), commonly referred to as “Spinel”, aluminum oxynitride (AL23O27N5), commonly referred to as “ALON™”, and single crystal aluminum oxide (AL2O3), commonly referred to as “Sapphire”. The table below provides some relevant physical and mechanical properties of several glasses and transparent ceramics that may be used in different embodiments of the invention.
The currently preferred material for the tiles is sapphire. A typical hardness of single crystal sapphire is approximately 1,300 HK. It is a transparent ceramic that possesses a rhombohedral crystal structure. From a production and application perspective, sapphire is currently a mature transparent ceramic. However, it is relatively high in cost due to the needed high processing temperatures and machining and polishing steps. Sapphire exhibits high strength, but its clarity and transparency are still highly dependent on the surface finish.
Referring now to
In the embodiment of
The intermediate layer 103 may consist of a single, rigid panel made of transparent ceramic tiles 106_1, 106_2, . . . . The term “tile” as used here is not limited to a square or rectangular piece, but also encompasses polygons more generally, as well as disks. All of the edges of each interior tile, i.e. not located at the boundary of the overall structure, should be sufficiently polished, to impart greater transparency to the overall structure. In the first embodiment, the tiles 106 are transparent ceramic squares, whereas in the second and third embodiments they are disks. In the first embodiment, the transparent ceramic tiles 106 are preferably made essentially of sapphire. Each tile 106, referring now to
To make the mosaic structure easier to manufacture consistently, each of the tiles 106 should have essentially the same dimensions. In the first embodiment depicted in
When the layer 103 consists of a single layer of tiles 106 that are arranged in a planar, mosaic pattern as shown, the thickness of each tile 106 may be 5 mm to 10 mm for protecting against Level III ballistic threats, 7 mm to 12 mm for Level IV threats, 11 mm to 20 mm for Level V threats, 13 mm to 16 mm for 12.7 mm caliber ballistic threats, and 16 mm to 20 mm for defeating 14.5 mm caliber ballistic threats. These thickness recommendations are based on experimental results of tested ballistic resistant structures in accordance with the first embodiment, as summarized below. The thickness can vary, depending upon the number of backing layers in the third layer 104 (behind the transparent ceramic intermediate layer 103). This aspect, of using multiple backing layers in the third layer 104, is also applicable to the second and third embodiments of the invention.
Returning to
The last layer of the structure, at the rear, is an anti-spalling layer 108. This layer 108 may consist of a single sheet of polycarbonate that has a thickness of 0.125 to 0.5 inch, depending upon the threat level to be defeated, the required multiple hit capability, and secondary threat requirements such as forced entry or explosive blast mitigation. The anti-spalling layer 108 serves to preclude any glazing entry to the safe side of the installation. The anti-spalling layer 108 may be bonded to the back face of the layer 104, by a further adhesive layer 111 that is designed to bond the material of the anti-spalling layer 108 to, for example, a backing ply of glass.
The following configurations of the first embodiment have been tested and have passed the noted threat levels (all thicknesses are in millimeters):
Suitable descriptions of the different threat levels tested above are as follows. Note that the bullet types and velocities may be in accordance with NIJ Standard 0101.04 Performance Requirements, or other typical U.S. military standard specifications.
The table above shows a configuration of the first embodiment that can defeat all of the above-listed Level III threats, with three glass backing plies (glass #3, #4, and #5). An edge view of such a structure is depicted in
In yet another configuration of the first embodiment that was tested, all of the above-listed Level IV threats were defeated when the layer 104 had four back-to-back glass backing plies (glass #3, #4, #5, and #6). The first embodiment was also able to defeat all of the above-specified Level V threats, also using a structure having four glass backing plies in layer 104. However, in that case, the ceramic layer #2 (an example of the intermediate layer 103 with just a single layer of transparent ceramic tiles) had its tile thickness increased to 11 mm and 14 mm.
In the first embodiment shown in
Turning now to the second embodiment of the invention,
Positioned above or in front of the lower sub-layer is the upper sub-layer, composed of tiles 106_37, . . . 106_61. The latter are also arranged in a mosaic-like pattern, similar to the lower sub-layer, except that the position of the upper sub-layer is offset relative to the lower sub-layer. This allows each tile in the upper sub-layer to be aligned so as to close off a respective gap in the lower sub-layer, where this gap is between two abutting tiles of the lower sub-layer. For example, the gap 502 (delineated within dotted lines) that is formed as a result of the tiles 106_1, 106_2, 106_7, and 106_8 abutting each other is aligned with tile 106_37. This arrangement of the sub-layers is retained in position preferably by just a single layer of adhesive material that bonds the front face of lower layer to the back face of the upper layer. The adhesive material also preferably fills the gaps between abutting tiles of the upper sub-layer (i.e., the gaps between the tiles 106_37, . . . 106_61). The adhesive material should also be used to fill-in the gaps in the lower sub-layer (between tiles 106_1, . . . 106_36). This aspect is depicted by reference 409 in
The thickness of the adhesive layer used to fill-in the gaps of each sub-layer in this embodiment is thus greater than the relatively thin film that is used in the first embodiment (to abut the straight edges of the square tiles together). Also, given the stacking and overlapping condition of the disks in the second embodiment, a relatively thicker adhesive layer may also be needed, to bond the face areas of the transparent ceramic sub-layers to each other. In addition to adhering the transparent ceramic disks in place, the thicker adhesive layer is believed to help in buffering a back face signature deformation due to a ballistic of fragmentation impact. The deformation would appear behind the rear most transparent ceramic sub-layer (in this case composed of tiles 106_1, . . . 106_36) and might include premature cracking, chipping, or nicking of the transparent ceramic which could possibly result in disk dislodgment or turning.
Regarding the adhesives, these may be pourable, or they may be in the form of rolled stock or flat sheets, or they may be injected into a mold such as using a vertical resin transfer molding (VRTM) process. For example, to make the intermediate layer 103, a sufficient amount of adhesive may be poured into a containment area in which the tiles 106 are then laid out. Care should be taken to avoid the formation of air bubbles in the subsequently cured adhesive layers. The curing process may involve simply elapsed time, a UV energy application, and/or a heat and pressure process (e.g., an autoclaving process). One of ordinary skill, once informed by the disclosure here, will readily recognize several different ways of making the intermediate layer 103, and the multi-layer structure as a whole.
Referring now to
Viewed another way, the third embodiment has an arrangement of tiles 106, where each tile is a transparent ceramic disk, in which the tiles are arranged in overlapping rows, such that in the interior of a row, a tile overlaps its predecessor in that row and is overlapped by its successor in that row. In addition, a subsequent row overlaps its predecessor and is overlapped by its successor. For example, referring again to
As was mentioned above, the tiles 106 of the third embodiment are preferably transparent ceramic disks that have non-uniform thickness. For instance, each disk may have a flat side and an opposite, dome-shaped side. When used in the third embodiment, a dome-shaped side or face of each tile should face the threat side of the structure. Each of the tiles 106 preferably has substantially the same dimensions in order to facilitate the manufacture of the intermediate layer 103. Note that as an alternative, the non-uniform thickness may be obtained by having both sides substantially dome-shaped, such as shown in
Regardless of the profile of each tile, it is instructive to compare the edge views of the different embodiments of the invention. In the first embodiment, depicted in
To maintain the arrangement of the tiles 106 in the intermediate layer 103 of the third embodiment, the entire volume of that layer, except for the tiles 106, may be filled with a volume 609 of adhesive material (that may be selected from the list given above). This material should be selected to have an index of refraction that will match that of the tiles 106, to improve transparency of the overall structure. As in the first and second embodiments, the intermediate layer 103 of the third embodiment may be sandwiched between the first layer 102 and the third layer 104. Each of these latter layers may have a respective, rigid panel made of glass whose area is large enough so that the panel is co-extensive, at its periphery, with the layer 103 (as shown in
Based upon experimental and simulated results of subjecting the different embodiments of the invention to the various ballistic threat levels defined above, the following characteristics of the transparent ceramic tiles are desirable.
First, there is a minimum tile mass that helps maintain integrity of the tile following impact. This translates into a minimum tile thickness and a minimum tile facial area (e.g., corresponding to a minimum diameter for the second and third embodiments that use disks). Second, with respect to the third embodiment in which disks that have non-uniform thickness and in particular a dome-shaped front face, this dome-shaped surface should be optimized to enhance yaw into the projectile upon impact. Because of the slight tilt of each overlapping disk in the imbricated pattern, a perpendicular projectile impact, that is an impact that is perpendicular to the plane of the disk, is highly unlikely. Accordingly, some of the energy of the projectile is expended in deflection, yawing, and lateral shear loading of the projectile core. If the tiles are discus shaped where both sides are dome-shaped, they collectively help in this process as the system flexes upon impact, which in turn forces the projectile to initiate penetration at an obliquity due to the base of the projectile shifting into the penetration phase. The shifting occurs once if the disks are struck once in their center, or two times if in an overlapped disk region. The discus shape, the tapering of the thickness, and the forming of a non-planar incline surface all work together to render a true zero degree obliquity impact highly unlikely.
Also, the surface area (of the front face) of the tile should be optimized to maintain full contact with the projectile upon impact, regardless of the angle of incidence. For instance, based upon the typical length of a 7.62 mm/.30 caliber military bullet, which is approximately 1.03 inches, a 2 inch diameter (circular) disk, or larger, is preferred so as to be susceptible to less total fracture and localized compression damage to both the impacted disk and those in which it was in contact with.
To improve the success rate in creating gross destruction of the projectile and its core, the radius of the dome-shaped face should also be optimized as a function of the types of projectiles expected and their velocities. For example, to defeat a typical civilian law enforcement 7.62 mm Level III ball ammunition threat, the radius should be about 8.62 inches. For military 7.62 mm Level III threats, the preferred radius is about 10.16 inches. For a typical military Level IV armor piercing hardened steel core threat, the preferred radius is about 6.26 inches. This shows just how much a relatively small dimensional variance can induce a substantial impact on the capability to defeat the projectile (where the discus shaped transparent ceramic tile is used).
It may also be estimated that, for the third embodiment, relatively thinner disks may be used as compared to a conventional, larger area but monolithic (or “flat”) ceramic tile structure. It may be expected that the minimum thickness of the transparent ceramic tiles used in the third embodiment should be at least thirty percent of the thickness of the ceramic layer of an otherwise conventional, monolithic plate construction (for the same specified threat).
Again, for the third embodiment, it may be expected that proportionately, as compared to the monolithic ceramic plate construction, the transparent ceramic disks are at their thickest dimension, approximately twenty-five percent less than the thickness of the equivalent defeating flat ceramic plate (e.g., for a 7.62 mm Level III military threat).
In general, for the first embodiment, tiles from one inch to 4 inches square can be utilized, however the 2 inch tiles are preferred as providing the best overall performance for limiting the amount of cracked and destroyed transparent ceramic material, resulting in a less obscured viewable area. Transparent armor may be designed to resist multiple repeat impacts, because it is important, for instance, for the driver of a vehicle to be able to see through the cracked windshield after impact. The 2 inch tiles also appear to provide a reasonable thickness, and are relatively easy to manufacture and would appear to cost less to produce than larger tiles. The first embodiment is the lowest ballistic performer, however, it is the least costly to produce and is generally the thinnest. The second embodiment is a better ballistic performer, but is more costly to manufacture and is thicker. Finally, the third embodiment appears to be the best ballistic performer, but is the most costly to manufacture, as well as being the thickest.
It has also been found that to increase multiple repeat hit capability in the first embodiment, without undue visual impairment, the transparent armor system should have a further layer of ceramic tiles added (referred to above as multiple sub-layers within the intermediate layer 103).
For the second embodiment where flat, round transparent ceramic tiles were used, once again tiles from one inch to 4 inch diameter can be used, however, the 2 inch flat circular disks appear to have the best compromise for limiting the amount of cracked and destroyed transparent ceramic, resulting in a less obscured viewable area. The third embodiment works best with discus shaped tiles of preferably 2 inches in diameter, although smaller or larger diameter discus shaped tiles can alternatively be used.
The invention is not limited to the specific embodiments described above. For example, in the second embodiment of
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