FR3095202A1 - Oxide bush for oxide / oxide composites - Google Patents

Abstract

The present invention relates to a fiber preform of a composite material with a ceramic matrix of the oxide / oxide type comprising at least one monolithic bush (100) composed of an oxide, characterized in that the surface of the sleeve in contact with the fiber preform (S1) comprises at least one shoulder (14) sandwiched between fibers (15) of the fiber preform (101). Figure for the abstract: Fig. 1.

Description

Oxide bushing for oxide/oxide composite materials

The present invention falls within the technical field of parts made of composite materials with a ceramic matrix of the oxide/oxide type and more particularly of means for assembling such parts.

Composite materials with a ceramic matrix of the oxide/oxide type have a very high microporosity which gives them good heat dissipation properties for a relatively low weight. They are suitable for applications for turbomachine parts, in particular for parts at the nozzle outlet. Nevertheless, their high microporosity is associated with low mechanical strength, particularly in terms of resistance to matting or compressive strength. It is therefore necessary, when assembling such parts, to work with low tightening torques to generate few stresses and not locally damage the composites. It is also necessary to provide a large number of fixing points, which weighs down the entire structure, and is therefore not desirable for an aeronautical application. In addition, composite materials are difficult to machine once formed. Thus, the means of fixing by bolted or riveted connections which require the drilling of a part made of composite material do not provide complete satisfaction when it comes to assembling parts made of composite materials.

There remains a need for a product making it possible to fix parts made of composite materials with a ceramic matrix of the oxide/oxide type which is devoid of the aforementioned limitations.

The present invention aims precisely to meet this need.

In one embodiment, the invention relates to a fibrous preform of a composite material with a ceramic matrix of the oxide/oxide type comprising at least one monolithic sleeve composed of an oxide, characterized in that the surface of the sleeve in contact with the fiber preform includes at least one shoulder sandwiched between fibers of the fiber preform.

The sleeve composed of an oxide, makes it possible to locally increase the mechanical properties of the composite material with a ceramic matrix of the oxide/oxide type, obtained after densification of the preform and in particular its resistance to caulking or compression.

Indeed, monolithic oxides have excellent resistance to compression or matting. This makes it possible to achieve tightening torques at the level of the sockets that are inaccessible with only the oxide matrix.

In addition, the shoulder(s) provided on the surface of the sleeve in contact with the fiber preform allow, after densification of the preform, excellent mechanical strength of the sleeve in the composite material part.

In one embodiment, the sleeve is made by additive manufacturing. Such an embodiment represents an economical means of manufacturing a sleeve whose dimensions, in particular the geometry of the shoulder(s), can be perfectly controlled.

In one embodiment, the surface of the sleeve in contact with the fiber preform comprises a circular shoulder.

Such a shoulder is arranged to be easily sandwiched between fibers of the fibrous preform during the establishment of a sleeve. In addition, once the preform has been densified, the shoulder inserted into the composite material part ensures strong cohesion between the sleeve and the composite material part.

Embodiments of the invention are not limited to a single circular shoulder. The sleeve may in fact comprise two or more than two circular shoulders. In such embodiments, fibers of the first part can be inserted between each of the different shoulders, which further strengthens the cohesion between the sleeve and the fiber preform.

In another embodiment, the surface of the sleeve in contact with the fiber preform comprises a plurality of helical shoulders. Such shoulders provide increased hold of the sockets in the direction transverse to the socket, but also when the socket is under shear stress, for example when tightening a screw in the socket.

In one embodiment, the socket has a tapered first end so that it is adapted to receive a tapered head screw. Such an embodiment makes it possible to use a screw with a conical head without requiring prior machining either of the screw or of the fiber preform.

In one embodiment, the socket has a second flat end, so that it is adapted to receive a nut. Such an embodiment makes it possible to use a nut without requiring prior machining either of the nut or of the fiber preform.

In one embodiment, the sleeve has a tapered first end and a flat second end. This embodiment makes it possible to obtain a sleeve allowing the fixing of the part by means of a conical head screw and a nut without requiring prior machining.

In one embodiment, the sleeve is composed of a material with a chemical composition close to the oxide matrix of the composite material, or even identical to the oxide matrix of the composite material.

This embodiment makes it possible to propose a sleeve whose temperature behavior is close to that of the part obtained after densification of the preform. In particular, having similar coefficients of thermal expansion between the part made of ceramic material and the sleeve makes it possible to prevent stresses from appearing between the sleeve and the part made of ceramic material during thermal stress.

For example, the sleeve can be made of alumina, mullite, silica, zirconia, aluminosilicate or aluminophosphate, or a mixture of these components.

The invention also relates to a part made of composite material with a ceramic matrix of the oxide/oxide type comprising at least one fibrous preform as described above, densified by a ceramic matrix of the oxide/oxide type.

The invention also relates to a method for preparing a part made of a composite material as described above comprising a step of inserting at least one sleeve as described above during the draping of a fibrous preform of a composite material with a ceramic matrix of the oxide/oxide type, and a step of densifying the fiber preform.

Figure 1 schematically describes a fiber preform comprising a sleeve,

Figure 2 is a photograph of a socket according to a first embodiment,

Figure 3 is a photograph of a socket according to a second embodiment.

The invention is now described by means of the figures, present for illustrative purposes, and should not be interpreted as limiting the scope of the present invention.

FIG. 1 schematically represents a fibrous preform 101 comprising a monolithic sleeve 100 according to one embodiment of the invention. The surface of the sleeve in contact with the fiber preform S1 comprises a shoulder 14 sandwiched between fibers 15 of the fiber preform.

The fibrous preform 101 can be made by stacking strata or plies obtained by two-dimensional (2D) weaving. The preform can also be made directly in one piece by three-dimensional (3D) weaving. By “two-dimensional weaving”, we mean here a classic weaving mode by which each weft thread passes from one side to the other of threads of a single warp layer or vice versa. By “three-dimensional weaving” or “3D weaving”, we mean here a weaving for which warp yarns cross several layers of weft yarns, or weft yarns cross several layers of warp yarns.

The fibrous preform 101 can also be produced by sheets of unidirectional fibers (UD), which can be obtained by automatic placement of the fibers (AFP for “Automated Fiber Placement” according to the English expression), or by filament winding.

The fibrous preform 101 can be made from fibers consisting of the following materials: alumina, mullite, silica, an aluminosilicate, a borosilicate, silicon carbide, carbon, or a mixture of several of these materials.

The fibrous preform comprises at least one sleeve 100 forming an opening 16 in the fibrous preform 101 and having mechanical properties superior to those of the fibrous preform 101.

This sleeve 411 makes it possible locally to provide sufficient mechanical strength to allow assembly by means of fastening which stress the part in caulking or in compression, such as bolted or riveted connections.

In the embodiment shown, the sleeve 100 has a cylindrical part 10 defining an opening 16 which allows the passage of a fixing element, for example a screw or a rivet, not shown. The cylindrical part 10 of the sleeve 100 preferably has a shear strength greater than that of the composite material with a ceramic matrix of the oxide/oxide type.

In the embodiment shown, the internal surface of the cylindrical part 10 of the sleeve 100 is smooth. In an alternative embodiment not shown, the cylindrical part 10 of the sleeve 100 can be threaded. This embodiment allows better mechanical strength in the case where a screw is used as a fixing means.

As shown in Figure 1, the sleeve 100 may have a first end provided with a flange 11 having an internal face 12 conical. Such a collar 11 allows the use of screws with standard conical heads without requiring prior machining either of the screw or of the fiber preform.

In addition, the presence of a flange 11 makes it possible to increase the contact surface S2 between the sleeve 100 and the fiber preform. This increase in the contact surface makes it possible to better distribute the matting or compression force on the ceramic matrix of the part obtained after densification of the fiber preform, and thus to increase the resistance to matting and shearing at the level of the sleeve.

In another embodiment, not shown, the sleeve may have a flat first end to accommodate the screws with flat heads or a cylindrical collar to accommodate the screws with cylindrical heads.

As shown in Figure 1, the sleeve may have a second end 13 flat, so that it ensures optimum contact with a nut.

In one embodiment, the sleeve has a conical first end 11, and a flat second end 13, so that it is adapted to receive a conical head screw and a nut.

The invention also relates to a part made of composite material with a ceramic matrix of the oxide/oxide type comprising at least one fibrous preform as described above, densified by a ceramic matrix of the oxide/oxide type.

In one embodiment, illustrated by Figure 2, the sleeve 200 may have several circular shoulders 24.

In another embodiment illustrated in Figure 3, the sleeve may have shoulders 34 of helical shapes. The helical geometry of the shoulders makes it possible to ensure good hold of the sleeve whether the latter is stressed in the vertical direction of its opening 16 or in the direction of a stress by a shear stress, for example during screwing or unscrewing of a fastening means passing through it.

The invention also relates to a part made of composite material with a ceramic matrix of the oxide/oxide type comprising at least one fibrous preform as described above, densified by a ceramic matrix of the oxide/oxide type.

In one embodiment, the ceramic matrix of such a part may be alumina, mullite, silica, zirconia, aluminosilicate or aluminophosphate, or a mixture of these components.

The invention also relates to a process for preparing a composite material comprising a step of inserting at least one sleeve as described above during the draping of a fibrous preform of a composite material with a ceramic matrix of oxide/oxide type, and a step of densification of the fibrous preform.

The draping step may correspond to the stacking of strata or folds described above to form the fibrous preform. Placement of the oxide sleeves at the draping stage ensures that the shoulder of the sleeve is effectively sandwiched between different fibers of the fiber preform. If necessary, it is possible to reposition the sleeve correctly, without having to repeat the entire process.

In one embodiment, the same fibrous preform can comprise several sleeves, so that the composite material part obtained after densification of the preform has several openings.

In one embodiment, the fibers can be pre-impregnated, for example by means of a slip loaded with ceramic oxide particles. Such a pre-impregnation makes it possible to obtain a more homogeneous matrix phase after densification of the fibrous preform.

To obtain a ceramic matrix of the oxide type, the particles can be made of alumina, mullite, silica, zirconia, aluminosilicate or aluminophosphate, or a mixture of these components.

The step of densifying the fibrous preform comprising a sleeve can be carried out by a process known per se.

Of course, the densification process is chosen so that the sleeve made of an oxide is not affected by the densification process.

In one embodiment, the preform densification process is performed by resin transfer molding.

In one embodiment, the slip used for such resin transfer molding may be a slip filled with ceramic oxide particles.

As in the preimpregnation step, the particles composing the slip for resin transfer molding can be alumina, mullite, silica, zirconia, aluminosilicate or aluminophosphate, or a mixture of these components.

In one embodiment, the fibrous preform densification step can be followed by additional steps such as high temperature sintering, or a final machining step.

Claims (8)

Fiber preform of a composite material with a ceramic matrix of the oxide / oxide type comprising at least one monolithic sleeve (100) composed of an oxide, characterized in that the surface of the sleeve in contact with the fiber preform (S1) comprises at least at least one shoulder 14 sandwiched between fibers (15) of the fiber preform. A fiber preform according to claim 1, wherein the sleeve 100 is made by additive manufacturing. Fiber preform according to any one of claims 1 or 2, in which the surface of the sleeve in contact with the fiber preform (S1) comprises a circular shoulder (24). A fiber preform according to any one of claims 1 or 2, wherein the surface of the sleeve in contact with the fiber preform (S1) comprises a plurality of helical shoulders (34). A fiber preform according to any one of claims 1 to 4, wherein the sleeve (100) has a tapered first end 11 and a flat second end (13). A fiber preform according to any one of claims 1 to 5, wherein the sleeve (100) is of alumina, mullite, silica, zirconia, aluminosilicate or aluminophosphate, or a mixture of these components. Part of composite material with a ceramic matrix of oxide / oxide type comprising at least fiber preform (101) according to any one of claims 1 to 6, said preform being densified by a ceramic matrix of oxide / oxide type. A method of manufacturing a composite material part according to claim 7 comprising a step of inserting at least one sleeve (100) according to that of claims 1 to 6 during the layup of a fiber preform (101) d a composite material with a ceramic matrix of the oxide / oxide type, and a step of densifying the fiber preform.