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(11) | EP 0 636 849 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Armour tile |
| (57) An armour tile that can be used in an appliqué armour system and includes a generally
flat ceramic component of relatively low tensile strength and an impedance match enhancing
sheet component of greater tensile strength than the ceramic component is described.
The sheet component overlies the major surface opposite the impact surface and the
side surfaces of the ceramic component. |
[0002] It is frequently desirable to enhance the survivability of various structures, including fixed and movable structures, and depending on particular applications, survivability enhancement structure may be placed on internal or external surfaces, or both, of the structure whose survivability it is desired to enhance.
[0003] In particular applications, survivability enhancement structures are applied to external surfaces of a vehicle or other structure. Armoured vehicles, for example are designed to provide ballistic protection commensurate with a specific threat. In connection with such vehicles and other structures, the ability to readily vary the ballistic protection configuration or to quickly repair damaged armour as a function of particular threats to which the vehicle or other structure may be exposed may enhance survivability. Appliqué armour, that is, supplemental armour applied on top of the basic armour designed into the vehicle or other structure, has been proposed to enhance survivability. It has been proposed to attach such appliqué armour to the basic armour by adhesive bonding, by mechanical bolting, and by mechanical attachment. US Patent 4 928 575 describes a system employing separable fastener structure for attaching appliqué armour to basic armour.
[0004] Such separable fastener structure arrangements have effective force dissipation characteristics and maintain attachment at effective levels even as the survivability enhancement structure is subjected to large shear forces (for example, upon ballistic impact and shattering of an adjacent tile or flexing of an armour sheet member). Such systems enable easy installation of auxiliary armour structure, as well as easy removal and reapplication to facilitate future armour revisions and upgrades. Easy replacement of damaged armour members in the field is possible. The structural integrity of the attachment system withstands normal system shocks, vibrations, brush loads, etc. However, the compliantly mounted ceramic armour tiles tend to require greater thicknesses (and accordingly, increased weight) to provide armour effectiveness comparable to rigidly mounted appliqué armour of the same material.
[0005] US Patent No: 5 191 166, the disclosure of which is hereby incorporated by reference, describes an appliqué armour system that includes a plurality of ceramic armour tiles that have thin sheets of metal or polymer material that are adhered to supporting surfaces of the ceramic and support a compliant separable fastener. The thin sheet serves to reduce impedance mismatch between air and the ceramic armour material, allowing greater transmission of a shock wave generated by a projectile with reduced stress at the ceramic boundary.
[0006] In accordance with one aspect of the invention, an armour tile for use in an appliqué armour system includes a generally flat ceramic component and an impedance match enhancing sheet component of material such as metal or polymer material that is adhered to the surface of the ceramic component remote from the anticipated direction of attack and extends around and overlies the sides of the ceramic component. The ceramic component preferably has a thickness at least ten times the thickness of the impedance match enhancing sheet component. Having the sheet component extend around the side surfaces extends the impedance mismatch correction around the edges, something that is particularly important for projectiles hitting closer to the edge of a tile than the centre. In addition, the portions of the sheet component that extend around side surfaces of the ceramic component act to deflect debris from the breaking tile away from adjacent tiles.
[0007] In particular embodiments a plurality of such armour tiles with impedance match enhancing sheet members extending to side surfaces each have compliant separable fastener components and are assembled together to provide an appliqué armour system.
[0008] Preferably, the separable fastener component on the armour tile cooperates with a second type of separable fastener component, one of the fastener components having a multiplicity of hooking elements and the other separable fastener component having complementary structure for releasable interengagement with the hooking elements. Preferably each hooking element includes a flexible stem portion and a head portion, the head portion including a laterally projecting inclines deflecting portion and a latch surface located between the deflecting surface portion and the stem portion for engaging a portion of the cooperating fastener structure in fastening relation. While the hook-type fastener elements may be of a variety of materials, including metals, in particular embodiments, the base portion and hook elements are of a thermoplastic polymeric material such as nylon, polypropylene or the like, and the base portion of that fastener structure is bonded with an epoxy adhesive or the like on the surface to which it is secured. In particular embodiments, the cooperating fastener structure includes a multiplicity of loop elements which may be formed from nylon fibres, metal wire or the like, the loops being releasably interengageable with the projecting hooking elements of the other fastener structure. Depending on the particular application, either the loop element structure or the hooking element structure may be on the composite armour member with the cooperating releasable fastener structure on the structure whose survivability is to be enhanced. The engaged hook and loop fasteners space the composite armor member at least about one millimeter from the support surface on which the composite armor member is mounted.
[0009] In particular embodiments, the ceramic armour material is selected from boron carbide, silicon carbide, aluminium oxide, titanium diboride and cermets that include such a ceramic material. In particular embodiments, each composite member has opposed planar surfaces, is in the range of one half to five centimeters thick, and is of polygon configuration with perimeter edge surfaces at least about four centimeters long; and the impedance match enhancing sheet member is co-extensive with the ceramic component and has a thickness of less than one millimeter.
[0010] Other features and advantages of the invention will be seen as the following description, by way of example only, of particular embodiments progresses, in conjunction with the drawings, in which:
Fig. 1A is a view of a light armoured vehicle that incorporates survivability enhancement in accordance with the invention, the enlarged views of Figs. 1B and 1C illustrating particular configurations of survivability enhancement systems in accordance with the invention;
Fig. 2 is a sectional diagrammatic view of an enlarged portion of a fastened armour tile of the Figs. 1B and 1C systems;
Fig. 3 is a sectional diagrammatic view of a portion at an edge of the Fig. 2 tile; and
Fig. 4 is a perspective view of an impedance match enhancing sheet component of the Fig. 2 tile.
[0011] Shown in Fig. 1 is a lightweight, high-mobility vehicle 10 that includes hull 12 mounted on a series of driven wheels 14, and turret 16 on hull 12. Hull 12 is constructed of one quarter inch (0.0635cm) thick steel armour plate 18, and has fastener structure 20 on the outer surface of hull 12. Fastener structure 20 may be of the hook type 22 as shown in Fig. 1 or of cooperating loop type 24 shown in Fig. 2. Appliqué armour in the form of an array of composite tiles 26 with cooperating fastener structure 28 secured thereto is compliantly fastened to hull 12 in manner similar to the system shown in U.S. Patent No. 4,928,575, the disclosure of which is expressly incorporated herein. Overlying fastener structure 20 is flexible cover sheet 30 which provides signature reduction (such as modified reflectivity to electromagnetic radiation, infrared radiation, or the like). Cover sheet 30 includes a silicone rubber substrate in which particulate signal reduction material 32 is embedded, sheet 30 having a thickness of about six millimeters. Secured on the inner surface of cover 30 by a suitable adhesive is a fastener structure which includes an array of loop elements 34 of polymeric material, the loops having heights of about three millimeters. Hook elements 22 of fastener structure 20 may be engaged with loop elements 34 of cover 30. One or more layers of armour tiles 26 may be interposed between hull 12 and cover 30, a single layer of armour tile 26 being provided in side region 36 as indicated in Fig. 1B and a double layer of armour tile 26 being provided in front region 38 as indicated in Fig. 1C.
[0012] Each composite tile 26 has a hexagonal configuration that is about ten centimeters across the flats. Adjacent tiles are butted up against each other as tight as possible given the separable fastener attachment mechanism. The tensile strength of the impedance match enhancing material is in the order of ten times the tensile strength of the ceramic armor material
[0013] As indicated in Fig. 2, each tile 26 includes ceramic component 42 of, for example, alumina of one-half to five centimeters thickness, preformed steel sheet member 44 of about 10 mil (0.254mm) thickness that is secured to ceramic component 42 with epoxy adhesive 46; and hook-type fastener structure 22 secured to metal sheet 44 with bonding agent 48. Alternatively, the hook structure could be secured to the member being armoured, and the loop structure could be secured to the tile.
[0014] As indicated in Fig. 2, hook-type fastener structure 22 includes base portion 50 and an array of hook elements 52, each of which includes flexible stem portion 54, deflection surface 56 and latch surface 58. It will be apparent that other hooking element configurations (arrow, mushroom, or spear shape, for example) may be employed. Hook elements 52 are of about 0.7 millimeter height, and base 50 is of about 0.3 millimeter thickness. Cooperating, separable, loop-type fastener structures 24 are loop elements 60 (of nylon filament, metal wire or the like) (of about 1.5 millimeter height) secured to base sheet 62 (of about 0.5 millimeter thickness) that in turn is secured to plate 18 of hull 12 with bonding agent 64. In attached relation as indicated in Fig. 2, formed steel sheet member 44 is compliantly spaced about three millimeters from plate 18.
[0015] As shown in Fig. 3, ceramic component 42 has mounting surface 72, for mounting on an underlying support, and attack direction surface 74 facing the anticipated attack direction. Sheet member 44 has, in addition to major wall 66, which supports the fastening structure, side walls 68 around all six sides. Sheet member 44 is shown in Fig. 4 before assembling in composite tile 26. Sheet member 44 is made from 12-mil (0.3 mm) thick stainless steel that has been deep drawn, according to techniques well-known in the art, and has a resulting average wall thickness of approximately 10 - 11 mils (0.25 mm). Epoxy 46 provides a bond between edge surfaces 70 of alumina ceramic sheet member 42 and side walls 68 of formed sheet metal member 44. Sheet metal member 44 should be sized with respect to ceramic component 42 to result in a tight fit between the two. Ideally there should be zero clearance between the two. If necessary, formed sheet metal member 44 can be heated to expand it slightly prior to assembly over ceramic component 44.
[0016] The holding force of the survivability enhancement fastener system is a function of the configuration, density and material of the hook elements 52 as well as the size, number and material of the loop elements 60. In a particular embodiment, the fastener structures 20, 28 in attached relation, have a tension restraint of about 50 psi (3.45 x 10⁵N/m² for a total of about 700 pounds (3.11 x 10³N) over the fourteen square inch (90.3cm²) area of an individual tile 22; a shear restraint of approximately 75 psi (5.17 x 10⁵N/m²) or a total of about 1050 pounds (4.67 x 10³N) over the fourteen square inch (90.3cm²) area of a tile 22; and are removable by manual force applied through a parting tool.
[0017] Being very thin (less than one-tenth the thickness of the ceramic component, and, in the particular embodiments, much less than that), sheet metal member 44 improves survivability enhancement performance owing to acoustic, not structural, reasons. In particular, member 44 serves to reduce impedance mismatch between air and the ceramic armour material, allowing greater transmission of a shock wave generated by a projectile with reduced stress at the ceramic boundary. Major wall 66 provides this correction at mounting surface 72 of ceramic component 42, and side walls 68 provide this correction at side surfaces 70 of ceramic component 42. The correction provided by side walls 68 is particularly important for a projectile hitting closer to the edge of a tile than the center. In addition, side walls 68 act to deflect debris breaking away from a tile so that they do not hit adjacent tiles.
[0018] In particular embodiments, the hook fastener structure 22 was of injection molded nylon with an integral base 50 and a hook height of about two thirds millimeter and an overall height of about one millimeter, the fastener structure 22 being secured to an armor member. The loop elements 24 were of 200 denier nylon and had a height of about two millimeters and were secured to base 62 of about one half millimeter thickness that in turn was secured to the formed steel sheet member 44 of the composite tile member 26. Formed steel sheet member 44 was made by deep drawing 12 mil (0.3 mm) thick 304 stainless steel so that it had 0.55'' (1.4 cm) high side walls continuously around the six sides and would receive a 0.55'' (0.3 mm) thick hexagon-shaped ceramic tile that is nominally 4'' (10.2 cm) across the flats Epoxy 46 was applied to mating surfaces of ceramic component 42 and sheet member 44, and the two were adhered to each other.
[0019] In comparative tests between tiles made as just described and plain, unreinforced tiles, 50 calibre, armor-piercing M2 projectiles were shot at the centers of the tiles, and V50 values were determined. The tiles were made of a cermet armor material of silicon carbide, aluminum and alumina of 3.25 grams per cubic centimeter density with separable fastener compliant mounting. The tiles with the impedance matched member 44 extending over the side surfaces had a V50 estimated value of 2577 feet per second (785.4696m/s), while the tiles that did not have the sheet metal member had a V50 value of 2300 (701.04m/s), indicating an 11% improvement for shots at the centres of tiles.
[0020] Similar comparative tests were conducted with projectiles shot at the three way joint at the intersection of three tiles. The tiles with the impedance matched member 44 extending over the side surfaces had a V50 estimated value of 2300 feet per second (701.04m/s), while the tiles that did not have the sheet metal member had a V50 value of 2050 (624.89m/s), indicating an 12% improvement for shots at joints between tiles.
[0021] Composite tiles 26 can also be advantageously used in applications involving impedance mismatch other than those employing separable fasteners. For example, tiles that are permanently mounted on a fibreglass body vehicle or other nonmetal support structure can be provided with an impedance match enhancing formed sheet of a metal or a polymer that is adhered to the mounting surface of the ceramic component, the ceramic component preferably having a thickness at least ten times the thickness of the impedance match enhancing sheet member.
1. An armour tile for use in an appliqué armour system comprising a generally flat ceramic
component of relatively low tensile strength and having a mounting surface for mounting
on an underlying support, an attack direction surface facing the anticipated attack
direction, and side surfaces between said mounting surface and said attack surface
around the perimeter of said ceramic component, and an impedance match enhancing sheet
component of greater tensile strength than said ceramic component, and being secured
thereto; the tile being characterized in that said sheet component has a portion overlying
and secured to said mounting surface, and side walls overlying and secured to respective
said side surfaces.
2. A tile according to Claim 1, further characterized in that said ceramic component
has a thickness of at least ten times the thickness of said sheet component.
3. A tile according to Claims 1 or 2, further characterized in that said ceramic component
has a thickness of at least one-half centimetre and is of polygonal configuration
with perimeter edge surface segments that are at least four centimetres long, and
preferably of hexagonal configuration.
4. A tile according to any preceding claim, further characterized in that the material
of said ceramic component is selected from boron carbide, silicon carbide, aluminium
oxide and titanium diboride and cermets that include such a material.
5. A tile according to any preceding claim, further characterized in that said sheet
component has a thickness of between 5 mils and 15 mils (0.127 and 0.381 mm).
6. A tile according to any preceding claim, further characterized in that said sheet
component is made of single sheet of sheet metal that has been formed, preferably
by a deep draw process.
7. A tile according to any preceding claim, further characterized in that said sheet
component is secured to said ceramic component by adhesive.
8. An appliqué armour system characterized in comprising a plurality of armour tiles
according to any preceding claim; in that a separable fastener component of a first
type is secured to said mounting portion of said sheet component for cooperative engagement
with a separable fastener component of a second type secured to a surface of structure
whose survivability is to be enhanced, one of said separable fastener components having
a multiplicity of hooking elements and the other separable fastener component having
complementary structure for releasable interengagement with said hooking elements
of said one separable fastener component; and in that said armour system has energy
absorbing characteristics and provides progressive energy dissipation of energy resulting
on impact of a ballistic missile on an armour tile.
9. A system according to Claim 8, further characterized in that said separable fastener
structures in attached relation have a shear restraint of at least ten psi (6.89 x
10⁴N/m²), and a tension restraint of at least five psi (3.45 x 10⁴N/m²), and can be
manually released by application of manually applied tension force.
10. A system according to Claims 8 or 9, further characterized in that each said armour
tile has a thickness of at least one centimetre and is of polygonal configuration
with perimeter edge surface segments that are at least four centimetres long.
11. A system according to any of Claims 8, 9 or 10, further characterized in that each
said hooking element includes a stem portion and a head portion that projects laterally
from one side of said stem portion, said head portion including an inclined deflecting
portion and a latch surface located between said inclined deflecting surface portion
and said stem portion for engaging a portion of a cooperating fastener structure in
fastening relationship.
12. A system according to Claim 11, further characterized in that said cooperating fastener
structure includes a multiplicity of loop elements upstanding from a base member.