Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Noninterengaged fiber-containing paper-free web or sheet...
Reexamination Certificate
2003-01-30
2004-03-23
Dixon, Merrick (Department: 1774)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Noninterengaged fiber-containing paper-free web or sheet...
C428S294100, C428S296400, C428S323000, C428S325000, C428S332000, C428S359000, C428S367000, C428S401000, C428S405000, C428S394000, C428S375000, C428S468000, C428S911000, C428S372000
Reexamination Certificate
active
06709736
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to armored products made of a fiber-reinforced or fiber-bundle-reinforced composite material with a ceramic matrix for partial or complete absorption of at least one impact-like load focussed at a point.
In the following description and in the claims, both individual fibers and fiber bundles that are used for the most part and can have a substantially greater width as well as height, as compared with individual fibers, are referred to together under the term “fibers”.
Fiber-reinforced composite materials with a ceramic matrix have been known for a long time and in general are distinguished by high strength and rigidity with simultaneously low weight. Those properties are maintained even up to high temperatures. The fiber-reinforced composite materials have a high thermal conductivity and at the same time a low thermal expansion and thus an excellent resistance to thermal shocks.
Starting from carbon-fiber-reinforced composite materials with a carbon matrix (CFC), composite materials with SiC as a matrix have been developed to an increasing extent over the last ten years, with carbon fibers (C/SiC) and silicon carbide fibers (SiC/SiC) being used as reinforcing fibers.
A silicon carbide body which is reinforced with short graphite fibers and which has a quasi-ductile breaking behavior, is known from German Published, Non-Prosecuted Patent Application DE 197 10 105 A1. The reinforcing short graphite fibers are surrounded by at least one shell of graphitized carbon obtained by impregnation with impregnating agents, which can be carbonized, and subsequent carbonization. The shell of the fibers is partly converted into silicon carbide during the production of the C/SiC composite material. To that end, the composite body is infiltrated with liquid silicon, wherein the at least partial conversion of the carbon matrix of the carbonized initial product into silicon carbide also takes place.
In the discussion of that prior art, lining materials for reusable space missiles, nozzle linings of jet engines, turbine blades or even friction linings are generally spoken of as possibilities of use for composite materials. The composite materials described in German Published, Non-Prosecuted Patent Application DE 197 10 105 A1 can be used as portions of gas turbines, as components of burners and nozzles, as hot-gas pipes, or even as friction materials for high loads, such as linings for brakes.
A process for producing fiber-reinforced composite ceramics with high temperature fibers which are reaction-bonded with a matrix based on silicon and silicon carbide or a silicon alloy, as described in German Published, Non-Prosecuted Patent Application DE 41 27 693 A1, for example, is known from German Patent DE 197 11 829 C1. Composite bodies of that type are used for the production of mass-produced components, such as brake discs.
The use of ceramics as an armor plating system, because of their light weights, is also known. Ceramics are generally distinguished by high rigidity and hardness. In the case of their use for armor plating, it is essential that the ceramics be able to withstand a plastic deformation under high load. A high tensile strength is required particularly on a rear surface of an armor plate. For that reason, a typical armor plating in which a composite comprising ceramic is used is therefore formed of a ceramic front side which is provided with a fibrous composite or metal substrate as a reinforcement (backing) on its rear side. Usually, those different materials are connected to each other by gluing. Glass, glass-ceramics, or technical ceramics such as oxides, borides or even carbides are used as the ceramic material. In particular, aluminum oxide has distinguished itself because it is also relatively favorable in terms of cost. However, the ability to withstand a plastic deformation is not particularly satisfactory in ceramics. Since ceramics display a brittle breaking behavior, a loading of the ceramic material focussed on a point, for example by a projectile, leads to a continuous cracking in the ceramic material. The ceramic material is therefore destroyed over a large area and thus loses its protective effect. Heretofore, that problem could be remedied only by mounting small ceramic segments having a maximum extent of 3 cm for a very high protection (protected cars) and 10 cm for a simple, for example military, protection, on a backing in a plane perpendicular to an action of the point-focal load. Thus, if a projectile was impacted, always only one ceramic segment would ever be destroyed. However, the production of a composite made up of such ceramic segments is very costly. Thus, ceramics alone have not heretofore been able to be used as a large-surface protective element.
When an armor plate is hit by a projectile, in the case of a conventional ceramic material, a breakage of the ceramic plate itself results because of a reflection of stress waves within the ceramic plate. It is only because a further rear side, for example made of metal, is mounted behind the ceramic plate, that it is possible to prevent the projectile from completely penetrating that armor plate.
In the case of the use of ceramic material for armor plates, it is necessary for the ceramic material to have a hardness which is clearly greater than the material of the projectile, which usually has a Vicker's hardness of approximately 6.5 to 8.0 kN/mm
2
. It would therefore be favorable to use materials having a hardness of more than approximately 9.8 kN/mm
2
. If the ceramic material is too soft, the projectile core penetrates through the ceramic material, because it is not damaged or flattened by the ceramic material.
However, there is also ammunition with a clearly greater hardness, particularly if ammunition having a core of tungsten carbide in a nickel-iron matrix is used. In such a case, the hardness can rise to approximately 11 kN/mm
2
, for example.
A ceramic material made of highly pure aluminum oxide could withstand such a projectile because it has a hardness of more than approximately 16.6 kN/mm
2
. It is likewise possible to use other ceramic materials, for example silicon carbide, as already mentioned above, boron carbide, or even titanium diboride, the hardness of which is clearly greater.
It is likewise known to use zirconia-reinforced aluminum oxide, or titanium borides. However, a hot-press process has to be used during production in order to obtain the optimal properties. In order to do that, the powders from the respective starting material are compacted and heated in a graphite nozzle under an inert gas atmosphere. Due to the complicated production process, the costs of a single armor plate are consequently high.
In view of the price/output ratio, aluminum oxide has heretofore been considered the ceramic material of choice.
In the meantime, first attempts were made to use fiber-reinforced composite materials with a ceramic matrix instead of the conventional ceramics for protection against projectiles. For that purpose, trials were carried out with SiC/SiC composite materials. They displayed limited damage to the material by the impacting projectile, so that the material provides protection against multiple bombardment from an automatic weapon (multiple hits). However, the protective effect against projectiles is very low in comparison with the known ceramics. (see an article by Orsini and Cottenot in the 15th International Symposium on Ballistics, Jerusalem, 1995).
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide armored products made of a fiber-reinforced composite material with a ceramic matrix, which overcome the hereinafore-mentioned disadvantages of the heretofore-known materials and products of this general type and in which the ceramic material has a low specific weight and a good resistance to bombardment and thereby withstands even a repeated bombardment. Furthermore, the material which is sought should to be able to be shaped as a large-surface element through the use of sim
Gruber Udo
Heine Michael
Kienzle Andreas
Nixdorf Reinhard
Dixon Merrick
Greenberg Laurence A.
Mayback Gregory L.
SGL Carbon AG
Stemer Werner H.
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