Metal working – Method of mechanical manufacture – Assembling or joining
Reexamination Certificate
2000-10-06
2004-05-18
Dinh, Tien (Department: 3644)
Metal working
Method of mechanical manufacture
Assembling or joining
Reexamination Certificate
active
06735842
ABSTRACT:
TECHNICAL FIELD
The present invention refers to a movable structural component for a thermomechanically stressed assembly made from a fiber reinforced ceramic, particularly for reflyable aerodynes in the aviation and aerospace technique as well as a process for producing the structural component.
TECHNICAL BACKGROUND
Reflyable spacecrafts, like for example the Shuttle Orbiter, require for reentering into the atmosphere a protective shield which is, among other things, heat resistant. The Shuttle Orbiter of the United States of America has for this reason body and control surfaces consisting of metallic material which are covered with tiles from a reinforced fiber isolation. These tiles avoid the consequence that under the influence of the highly heated air, converted to a plasma status by the high air speed, the metallic structural elements become so highly heated as to lose their strength and shape stability and will even be destroyed under the load of the flight. Similar or identical problems result with any thermally highly stressed structural elements to be used in the tool making and engineering industry.
Assemblies, structural elements or structural parts, which are based on subsequently disposed or glued-on isolations exhibit considerable disadvantages as is known in the art.
For example the most highly loaded components of a reflyable spacecraft, which, in particular, are the control flaps and such control surfaces, must be made of extremely temperature resistant metallic alloys, so-called superalloys. These have a high specific gravity. Additionally, there is the weight of the thermal isolation. Very dense isolating materials have to be used, to have sufficient resistance against the influences onto such fairings.
Despite the use of very dense fiber isolations known from the state of the art, a heat shield such as that of the Shuttle Orbiter, requires high repair and replacement work since the deposition by gluing and the low strength of the isolating material often results in damage or even complete destruction under the described application conditions. Additionally, there is the weight of the thermal isolation which affects the total weight of the aerodyne.
OBJECT AND SUMMARY OF THE INVENTION
It is a primary object of the present invention to overcome the mentioned technical and economical problems by providing structural components which allow material and structural elements to inherently have an overall increase of thermal and mechanical loading capacity. In connection with the construction of aerodynes, a considerable reduction in weight of the structural components and the reusability or reflyability thereof is envisaged.
The central aspect of the invention is to construct structural components, particularly for reflyable aerospacecrafts, from a fiber composite ceramic. Thereby, depending on the mechanical and thermal requirements to be addressed to individual elements of the structural components, differently produced materials, so called CMC-materials (Ceramic Matrix Composites), could be used.
The present invention thus provides a movable structural component for a thermomechanically stressed structure, which at least partially is built from a fiber reinforced ceramic. Thereby, the movable structural component comprises at least one structural element formed by a polymer infiltration and pyrolysis process (subsequently referred to as LPI-process) and at least one structural element formed by a gaseous phase infiltration or chemical vapor infiltration process (subsequently referred to as CVI-process).
With the structural components according to the invention, a 40% weight saving as well as a significant reduction of the maintenance costs compared with the state of the art is possible. The reduction of the maintenance costs results in that the structural components according to the invention are mechanically and thermally extremely loadable and thus for example during the entry of the atmosphere are less damaged or destroyed.
In accordance with the invention, fiber reinforced ceramics are considered for use which are based on high temperature resistant fibers. These are, particularly, carbon fibers imbedded within a matrix of silicon carbide (C/SiC ceramic), silicon carbide fibers imbedded within a matrix of silicon carbide (SiC/SiC ceramic) or silicon nitride (SiC/Si
3
N
4
-ceramic), aluminum oxide fibers imbedded within an matrix of aluminum oxide (Al
2
O
3
/Al
2
O
3
-ceramic), mullite fibers imbedded within a mullite ceramic or polyborosilazane fibers (SiBNC) imbedded within a polycarbosilane, polysilazane or silicon carbide matrix. The properties of these ceramic materials reinforced with filaments are mainly known and, for example, described in A. Mühlratzer and H. Köberle in Metall (1991), page 435 cf. These materials, however, may be essentially influenced by the manner of their production and processing, respectively. A discussion of suitable fiber or ceramic materials, respectively, may be also found in “Advanced Materials 2 (1990), no. 9, pages 398-404 and “Journal of European Ceramic Society 12 (1990), pages 27-41”.
In accordance with the present invention, carbon reinforced silicon carbide ceramics (C/SiC ceramics), in particular, are envisaged, which, adapted to the final form of the structural element, are formed either via chemical vapor infiltration (CVI-process) or via (liquid) polymer infiltration and pyrolysis (LPI-process). The material producible according to the CVI-process is particularly suitable for mechanically highly stressed parts. In case of, for example, a control flap of an aerodyne, these are the longitudinal and transversal load bearing implements, the connecting or push-rod, the bearings and the hinges as will be further described in detail. For mechanically or thermally less stressed structural elements, a material produced according to the LPI-process is also suitable.
In accordance with an aspect of the invention, the structural component is characterized in that the at least one structural element formed by the liquid polymer infiltration and pyrolysis process is embodied as the base of the movable structural component. These mostly large sized or volumed bases are, in particular, mechanically less stressed so that they may be produced by the LPI-process.
According to another aspect of the invention, the base is a box-type segment with a bottom wall and side walls integrally formed thereon. This measure allows for a wide variation in the final size of the structural component and an accommodation to the individual purpose of use. Via the integrally formed side walls, individual box-type segments may be coupled to larger structural elements or components, respectively.
In a suitable embodiment of the invention, the bottom wall, of the at least one box-type segment, is an essentially plane surface opposite to the side walls. This embodiment avoids the formation of so-called hot spots and along with it the premature wear of the structural element by thermal and/also or mechanical load.
Further, it is within the scope of the invention that the junction region between the bottom wall and the side walls is chamfered. Also, this embodiment avoids or minimizes the formation of hot spots.
According to another aspect of the invention, the at least one box-type segment of the base is stiffened by reinforcement ribs which are, in particular, integrally disposed on the bottom wall and the side walls. These reinforcement ribs or the like avoid torsions of the structural element or the structural component, respectively, under mechanical stress and allow, in particular, a lightweight construction required for the structural elements or structural components, respectively, like, for example, the control flaps of a reflyable aerodyne. These reinforcement ribs may be arranged transversally, longitudinally or diagonally.
Furthermore, it is within the scope of the invention that the at least one box-type segment of the base has a cover or the like, which is reversibly mountable on the side walls, thereby promoting the stiffening of the segm
Koeberle Hermann
Muehlratzer August
Peetz Kilian
Wildenrotter Karl
Dinh Tien
MAN Technologie AG
Reed Smith LLP
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