Textiles: weaving – Fabrics – Drier felts
Reexamination Certificate
1998-12-23
2002-07-16
Calvert, John J. (Department: 3765)
Textiles: weaving
Fabrics
Drier felts
Reexamination Certificate
active
06418973
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to ceramic composites and, in particular, to integrally woven ceramic composite structures used in insulation.
2. Description of the Related Art
In certain high temperature operating environments, such as exterior surfaces of space reentry vehicles and combustion chambers and nozzles in jet engines, rocket engines, and power generators, for example, thermal barriers are necessary to protect supporting structures and equipment. A combustion chamber liner, for example, must be mounted on a strong surrounding structure, typically metal, which must be kept relatively cool and protected from heat, both radiant and conductive. Ceramic materials have utility as thermal barriers because of their high temperature stability. Moreover, since thermal barrier components typically comprise large panels or shell structures that are difficult to fabricate from monolithic ceramics, fiber reinforced ceramic composites are preferred.
In extremely high heat flux environments, such as in rocket engines, the thermal barrier material must also be actively cooled by some mechanism, such as an internally circulating fluid, because the operating temperatures exceed the capabilities of the exposed ceramic materials. All non-ablative rocket nozzles are currently designed in this manner, using high conductivity metals with internal channels for flow of coolant (usually high pressure fuel). The high conductivity is needed to maintain the temperature of the hot surface below the melting point of the metal. If ceramic composites could be used instead of than metals for such structures, large improvements in engine performance would result from: (I) reduced weight; and (ii) reduced heat flux absorbed at the hot surface because of the higher temperature capability of the ceramic. However conventional ceramic composite fabrication methods cannot produce structures capable of satisfying the combined requirements of high pressure containment and high heat flux management.
State-of-the-art ceramic composites are built up to the required thickness using stacked layers of fiber fabrics that are subsequently infiltrated with a ceramic matrix. Unfortunately, such layered composites are not suited to the formation of the structures needed for actively cooled panels because of their susceptibility to delamination of the layers, leading to catastrophic failure.
A preferred approach for forming such panels would be to begin with an integrally woven 3-dimensional fiber preform of the desired shape, with reinforcing fibers in walls and face sheets surrounding internal cavities aligned everywhere predominantly parallel to the stresses expected in use, and to infiltrate the preform with the desired ceramic matrix. Several methods are known for forming integrally woven structures consisting of face sheets connected by walls aligned along the weft direction during weaving. These walls form internal channels which could be used for coolant flow. However, such weft channel structures have several shortcomings for actively cooled structures: (1) the packing density of fiber yarns aligned around the circumference of weft channels (as needed for pressure containment) is inherently limited by the weaving process, so that thicker walls are required to achieve pressure containment, which defeats satisfaction of the heat flux requirements for high performance rocket nozzle and other applications; (2) low packing densities of fibers around channels makes it difficult to achieve hermetic containment of pressurized cooling fluids; (3) the channel lengths in weft channel structures cannot exceed the width of the loom, imposing severe restrictions to structural designs and increasing the difficulty of the weaving process; and (4) weft channel structures are not easily modified to incorporate connecting structures such as manifolds as part of the woven structure at the ends of the channels or elsewhere.
In some systems, passive thermal insulation systems as opposed to active for reentry vehicles is used. One such system includes space vehicle tiles. The passive thermal insulation systems typically comprise very low density ceramic materials bonded to the metal skin of the vehicle. Because of their low density, such materials are very fragile and susceptible to damage from contact with other objects. It would be desirable to provide such low density materials with an outer protective coating of dense tough ceramic composite material that is not susceptible to debonding, or to sandwich it between front and back faces of tough ceramic composite.
State-of-the-art passive thermal protection panels are built up to the required thickness by bonding a low density core of thermally insulating ceramic or other material to a protective skin or thin relatively dense composite sheet consisting of a fibers infiltrated with a ceramic matrix. Unfortunately, such sandwich structures are not durable as thermal barrier panels because of their susceptibility to delamination of the protective skin, leading to catastrophic failure.
A preferred approach for forming such panels would be to begin with an integrally woven 3-dimensional fiber preform of the desired shape, consisting of face sheets connected by walls or struts, the woven reinforcing fibers in the face sheets and walls or struts being infiltrated with a ceramic matrix, and the spaces between the face sheets and walls or struts being infiltrated with a low density insulation material. Several methods are known for forming integrally woven structures consisting of face sheets connected by walls aligned along the weft direction during weaving. These walls form internal channels which could be used for insertion of passive insulation. However, existing channel structures have the severe shortcoming that access to the space between the front and back skins of the structure for inserting passive insulation materials is limited to the ends of the channels—this is not suitable for the processing methods needed for certain preferred insulation materials.
SUMMARY OF THE INVENTION
The present invention comprises an integrally woven 3-dimensional ceramic composite structure with internal channels aligned in the warp weaving direction. The composite includes a multilayer fabric woven from yarns of fibers such as carbon, silicon carbide, silicon nitride, aluminum oxide, mullite, glass, yttrium aluminum garnet (YAG), polyethylene, and other fibrous materials. At least upper and lower layers (or skins) of the composite comprise woven warp and weft yams. The layers may form planes or curved surfaces or tubular structures that can be woven tightly for internal fluid pressure containment. The layers are joined or connected by integrally woven warp and weft yarns forming walls or rows of connecting columns so as to form interior channels in conjunction with the skins.
Weaving processes and designs are chosen in such a way that much higher packing densities of fibers are achieved around the perimeter of each channel to improve the ability of the channels to contain pressure without undue increase in the thickness of either the skins or the walls or columns that form the channel structure.
The woven yarns of the composite material are infiltrated or impregnated with a curing agent that may be in the form of fibers, particulates, powders, vapors, or liquids. The curing agent comprises a material, such as a curable polymer in uncured form or a ceramic precursor, for example, that can be cured by exposure to heat or light (such as infrared or ultraviolet radiation), for example, to form a rigid matrix for the infiltrated fiber yarns. A polymer agent optionally may include ceramic particles so that treatment at higher temperatures will sinter the ceramic particles into a ceramic matrix around the woven yarns and eliminate the polymer or convert it into a ceramic. Ceramic matrix material can also be added after either curing or initial heat treatment by chemical vapor infiltration (CVI) or infiltration of a liquid precursor followed by heat treatm
Berbon Min Z.
Cox Brian N.
Davis Janet B.
Marshall David B.
Boeing North American Inc.
Calvert John J.
Muromoto Jr. Robert H.
Stout Donald E.
Stout, Uxa Buyan & Mullins, LLP
LandOfFree
Integrally woven ceramic composites does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Integrally woven ceramic composites, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Integrally woven ceramic composites will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2863060