Arrangement of two parts by means of a mechanical anchoring element, one of which is made of composite material

Description

Background of the invention

[0001] The invention relates to the general field of assembly between two parts of a structure in which one of the parts is made of composite material with a fibrous reinforcement obtained from a fibrous preform produced by three-dimensional weaving and densified by a matrix.

[0002] The invention relates to the assembly between a metal foil and a leading edge of a turbojet blade made of composite material, and the assembly between a shell and a structural core forming a turboprop propeller blade spar made of composite material.

[0003] It is known to produce a turbojet blade from a composite material using a fiber reinforcement obtained from a fiber preform produced by three-dimensional weaving and densified by a matrix. Compared to other known techniques for manufacturing a blade from a composite material, the production of a fiber preform by three-dimensional weaving has many advantages, such as in particular that of not having to resort to inserts or any other added element. Reference may be made to document EP 1,526,285 which describes a method for manufacturing such a fan blade.

[0004] Furthermore, it is known to provide the leading edge of such a composite material turbojet blade with a metal foil (or reinforcement) in order to protect the composite blade from abrasion / erosion and upon impact with a foreign body. This is particularly the case for the fan blades of a turbojet engine which are exposed to ingestion by a bird, hail, ice, etc.

[0005] Typically, the metal foil, which is produced by mechanical processes such as stamping, forming or electroforming for example, is bonded to the leading edge of the composite material blade by means of a bead of glue. This operation can be carried out in a mold ensuring the bonding of the metal foil or in an oven to obtain crosslinking of the bead of glue applied where appropriate to the foil.

[0006] Such an assembly of the metal foil on the leading edge of a composite material blade has many disadvantages. In particular, when the blade undergoes deformations in the direction of the chord or its length, the local buckling of the assembly significantly stresses the glue bead in traction and tearing, which can induce detachment of the wings of the metal foil. However, once these wings are detached, the inertia of the metal foil under the effect of centrifugal force ejects it outwards.

[0007] Local reinforcement of the foil can then be a solution to limit the propagation of the detachment but the solutions envisaged, such as drilling and machining the blade and the foil to pass through a mechanical link, generates an additional operation and locally damages the blade. In addition, the foil position zones must ensure a high level of aerodynamics which requires that the foil assembly means matches the shape of the foil as perfectly as possible. However, with fan blades having increasingly complex shapes, this constraint becomes difficult to respect with the assembly solutions of the prior art.

[0008] Document US 6,431,837 discloses a sewn composite fan blade. Document FR 2963055 discloses a rotor blade made of composite material comprising a connecting yoke. EP 1 681 440 discloses a blade made of composite material. Subject matter and summary of the invention

[0009] There is therefore a need to be able to have an assembly which does not have the aforementioned drawbacks.

[0010] According to the invention, this object is achieved by means of an assembly according to claim 1.

[0011] The invention is remarkable in that the mechanical anchoring element that is inserted inside the composite material part makes it possible to significantly increase the bonding surface between the two parts. In this way, the assembly between the two parts can be considerably reinforced. In particular, in the case of an assembly between a metal foil and the leading edge of a composite material blade, it is possible to adapt the position of the mechanical anchoring element according to the shear stress levels of the blade. Finally, this assembly is remarkable in that it does not require drilling of the composite material part, the mechanical anchoring element being simply inserted between the fibers of the composite material part. Any degradation of the composite material part can thus be avoided.

[0012] The mechanical anchoring element is inserted into a debonding zone created during the weaving of the fiber preform to create the fiber reinforcement of the composite material part.

[0013] Furthermore, the mechanical anchoring element is inserted at the level of the debonding zone of the fiber preform prior to a step of injecting said fiber preform with a resin. In other words, the mechanical anchoring is carried out on a fiber preform (of the composite material part) which is not injected, the preform and the other part then being placed in an injection mold to undergo a co-injection of resin.

[0014] According to one embodiment, the composite material part is a turbojet blade and the other part is a metal foil assembled on a leading edge of said blade.

[0015] In this embodiment, the mechanical anchoring element may comprise several metal rods, some of which are secured to the wings of the foil and one of which is secured to the central part of the foil, all of these rods extending in a direction transverse to the blade inside the latter.

[0016] Alternatively, the mechanical anchoring element may comprise at least one beam which extends between two wings of the metal foil and which passes right through the blade in the direction of its thickness.

[0017] According to another embodiment, the composite material part is a structural core of a turboprop propeller blade forming a spar and the other part is a shell positioned around the core of the propeller blade, said shell being made of composite material.

[0018] In this embodiment, the mechanical anchoring element may comprise at least one lug secured to an inner face of the shell and inserted inside the core of the propeller blade.

[0019] The invention also relates to a turbojet blade, a turboprop propeller blade and a turbomachine comprising at least one assembly as defined above. Brief description of the drawings

[0020] Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate exemplary embodiments thereof which are not in any limiting nature. In the figures: THE Figures 1 and 2 are views of an assembly between a metal foil and a blade made of composite material outside the invention, respectively in perspective and in cross-section; figure 3is a schematic view showing an example of a decoupling zone to allow the passage of the anchoring element of the Figures 1 and 2 ; there figure 4 is a cross-sectional view of an assembly between a metal foil and a blade made of composite material according to one embodiment of the invention; Figure 5 is a cross-sectional view of an assembly between a metal foil and a blade made of composite material according to another embodiment of the invention; and the figure 6 is a longitudinal sectional view of an assembly between a structural core of a turboprop propeller blade and a shell according to yet another embodiment of the invention. Detailed description of the invention

[0021] The invention applies to any assembly according to claim 1 between two parts of a structure in which one of the two parts is made of composite material with a fibrous reinforcement obtained from a fibrous preform produced by three-dimensional weaving and densified by a matrix (the other part being for example metallic or made of a composite material different from that used for the part with fibrous preform produced by three-dimensional weaving).

[0022] As shown in the Figures 4 and 5 , the invention applies in particular to the assembly between a metal foil 2 and a blade 4 made of composite material of a gas turbine engine.

[0023] The blade 4 comprises a blade 4a which is made of composite material with a fiber reinforcement obtained from a fiber preform made by three-dimensional weaving and densified by a matrix. An example of a three-dimensional weaving pattern of a fiber preform 4b for the production of such a blade is shown in the figure 3 .

[0024] Reference may be made to document EP 1,526,285 which describes an example of the production of such a fiber preform by three-dimensional weaving. After shaping, the fiber preform thus produced is placed in an injection mold. The deposition of the matrix in the fiber preform is carried out by maintaining the preform in the mold at least until the preform is rigidified (or consolidated).

[0025] The matrix is of a nature chosen according to the intended application, for example an organic matrix obtained in particular from a polymer matrix precursor resin such as an epoxy, bismaleimide or polyimide resin, or a carbon matrix or a ceramic matrix. In the case of an organic matrix, the fiber preform is impregnated with a composition containing the matrix precursor resin, before shaping in a tool, or after shaping, the impregnation being carried out in the latter case for example by infusion or by an RTM ("Resin Transfer Molding") type process.In the case of a carbon or ceramic matrix, densification may be achieved by chemical vapor infiltration, or CVI ("Chemical Vapor Infiltration") or by impregnation with a liquid composition containing a carbon or ceramic precursor resin and thermal pyrolysis or ceramization treatment of the precursor, these processes being well known per se.

[0026] In a manner known per se, the blade 4a of the vane extends longitudinally between two longitudinal ends 6 and laterally between a leading edge 8 and a trailing edge 10.

[0027] The metal foil 2, which has the function in particular of protecting the composite blading of the blade 4a from abrasion / erosion and during the impact of a foreign body, is assembled on the leading edge 8 of the blade of the vane by means of a mechanical anchoring element.

[0028] In the figures 1 to 3, the mechanical anchoring element comprises one or more metal rods 12 which are integral with the metal foil 2 and which extend in a direction transverse to the blade 4a inside the latter (i.e. from the leading edge 8 towards the trailing edge 10 of the blade).

[0029] More precisely, as shown in the figure 3 , each metal rod 12 is preferably inserted at the level of a delinking zone 13 which is provided during the weaving of the fiber preform 4b for the production of the fiber reinforcement of the blade. Such a delinking zone 13 is typically obtained by locally omitting to link adjacent layers of wires together and thus makes it possible to obtain two portions of preform which are delinked from each other so as to be able to insert a metal rod 12 for the mechanical anchoring of the metal foil 2 on the blade.

[0030] Advantageously, the metal rod 12 is placed in the debonding zone 14 of the fiber preform 4b prior to the step of injecting said fiber preform with a resin (i.e. prior to placing the preform in the injection mold so that the fiber preform 4b and the metal rod 12 undergo a co-injection of resin).

[0031] As indicated previously, the mechanical anchoring element may comprise one or more metal rods 12 which are integral with the metal foil 2. For example, several metal rods may be positioned at different heights of the blade 4a of the vane.

[0032] Likewise, as depicted on the Figures 2 and 3 , these metal rods 12 can be integral with a central part 2a of the metal foil 2 connecting together the wings 2b of said foil (intended to be positioned against a lateral face of the blade).

[0033] In a variant illustrated by the figure 4 , the mechanical anchoring element of the metal foil 2 on the leading edge 8 of the blade 4a of the vane comprises several metal rods 12', some of which are integral with the wings 2b of the foil and one of which is integral with the central part 2a of the foil, all of these rods 12' extending in a direction transverse to the blade 4a inside the latter.

[0034] In another variant illustrated by the Figure 5 , the mechanical anchoring element of the metal foil 2 on the leading edge 8 of the blade 4a of the vane comprises at least one beam 16 which extends between the two wings 2a of the metal foil 2 and which passes right through the blade 4a in the direction of its thickness.

[0035] Of course, mechanical anchoring elements can have other shapes than those described above, in particular profiled shapes which make it possible to increase the adhesion surface between the two parts to be assembled.

[0036] There figure 6 represents another embodiment of the invention in which the assembly is carried out between a structural core 16 forming a spar of the propeller blade 18 of a turboprop engine which is made of composite material and a shell 20 positioned around the core of the propeller blade, said shell being for example made of composite material.

[0037] In this other embodiment, the structural core 16 forming a spar of the propeller blade 18 is made of composite material with a fibrous reinforcement obtained from a fibrous preform produced by three-dimensional weaving and densified by a matrix.

[0038] Furthermore, the mechanical anchoring element of the shell 20 on the structural core 16 of the propeller blade here comprises at least one lug 22 which is integral with an inner face of the shell and which is inserted inside the core of the propeller blade. For example, this lug 22 can be inserted at the level of a delinking zone formed during the weaving of the fiber preform for the production of the fiber reinforcement of the structural core 16 prior to the step of injecting said fiber preform with a resin. Of course, this lug could conversely be integral with the core of the propeller blade and be inserted inside the shell made of composite material.

[0039] Furthermore, whatever the embodiment, it should be noted that the assembly between the two parts is preferably carried out with the composite material part which is in the state of a non-injected fiber preform, so that the step of injecting the preform makes it possible to ensure bonding between the parts. Alternatively, the two parts could be produced separately from each other, then assembled by means of the mechanical anchoring element and finally bonded together during another operation.

Claims

1. An assembly of two parts (2, 4; 16, 20), one of the parts (4; 16) being made of composite material with fiber reinforcement obtained from a fiber preform made by three-dimensional weaving and densified with a matrix, the assembly including a mechanical anchor element (12; 12'; 14; 22) secured to one of the parts and inserted inside the other part, the mechanical anchor element being inserted in a zone (13) of non-interlinking provided during weaving of the fiber preform (4b) that is to make the fiber reinforcement of the composite material part, with the insertion taking place before a step of injecting a resin into said fiber preform, wherein: (i) the composite material part is an airfoil (4a) of a turbojet blade (4) and the other part is a metal strip (2) for assembling on a leading edge (8) of said airfoil, wherein (a) the mechanical anchor element comprises a plurality of metal rods some of which are secured to the flanges (2b) of the strip and one of which is secured to the central portion (2a) of the strip, all of these rods extending in a direction that is transverse relative to the airfoil into the inside of the airfoil, or (b) the mechanical anchor element comprises at least one crossbar (14) that extends between two flanges (2b) of the metal strip (2) and that passes through the airfoil in its thickness direction; or (ii) the composite material part being a spar-forming structural core (16) of a turboprop propeller blade (18) and the other part being a shell (20) that is positioned around the propeller blade core, said shell being made of composite material.

2. An assembly according to claim 1, wherein the composite material part is an airfoil (4a) of a turbojet blade (4) and the other part is a metal strip (2) for assembling on a leading edge (8) of said airfoil and wherein the mechanical anchor element comprises a plurality of metal rods (12') some of which are secured to the flanges (2b) of the strip and one of which is secured to the central portion (2a) of the strip, all of these rods extending in a direction that is transverse relative to the airfoil into the inside of the airfoil.

3. An assembly according to claim 1, wherein the composite material part is an airfoil (4a) of a turbojet blade (4) and the other part is a metal strip (2) for assembling on a leading edge (8) of said airfoil and wherein the mechanical anchor element comprises at least one crossbar (14) that extends between two flanges (2b) of the metal strip (2) and that passes through the airfoil in its thickness direction.

4. An assembly according to claim 1, wherein the composite material part being a spar-forming structural core (16) of a turboprop propeller blade (18) and the other part being a shell (20) that is positioned around the propeller blade core, said shell being made of composite material, and wherein the mechanical anchor element comprises at least one lug (22) secured to an inside face of the shell (20) and inserted into the inside of the structural core (16) of the propeller blade.

5. An airfoil (4a) of a turbojet blade (4) comprising an assembly according to any one of claims 1 to 3, wherein the composite material part is an airfoil (4a) of a turbojet blade (4) and the other part is a metal strip (2) for assembling on a leading edge (8) of said airfoil.

6. A turboprop propeller blade (18) comprising an assembly according to any one of claims 1 to 4, wherein the composite material part is a spar-forming structural core (16) of a turboprop propeller blade (18) and the other part being a shell (20) that is positioned around the propeller blade core, said shell being made of composite material.

7. A turbine engine including at least one assembly according to any one of claims 1 to 4.