Blade comprising structure made of composite material and associated manufacturing method

Abstract

The invention relates to a blade comprising:-an airfoil (12) having an aerodynamic profile, the airfoil comprising a first fibrous reinforcement obtained by three-dimensional weaving and a first matrix in which the first fibrous reinforcement is embedded, a portion of the airfoil (12) comprising a cavity formed by a debonding of the first fibrous reinforcement,-a blade root, the invention relates to a blade (1) comprising a blade root (2) intended to be connected to a variable pitch mechanism of the blade, and a spar (13) comprising a core (14) made of a composite material and two metal shells (21a, 21b) attached to the core (14) on both sides of the core (14). The core (14) includes a first section extending within the cavity of the airfoil and a second section forming a blade root. Two metal shells (21a, 21b) attached to the core (14) made of composite material extend over said second section and continue over the first section within the cavity of the airfoil (12).

Description

Technical Field

[0001] The present invention relates to a blade comprising a composite material structure and to a related method of manufacturing. Background Art

[0002] The advantage of an unducted fan engine is that the diameter of the fan is not limited by the presence of a duct, making it possible to design an engine with a high bypass ratio, thereby reducing fuel consumption.

[0003] Therefore, in this type of engine, the blades of the fan can have a large span.

[0004] Furthermore, these engines generally include a mechanism capable of modifying the calage angle of the blades in order to adjust the thrust generated by the fan according to the different flight phases.

[0005] However, the design of such blades requires consideration of contradictory constraints.

[0006] On the one hand, the dimensions of these blades must be such as to obtain the best aerodynamic performance (maximizing efficiency and providing thrust while minimizing losses). Improving the aerodynamic performance of the fan tends to increase the bypass ratio (BPR), which manifests itself as an increase in the external diameter and therefore in the span of these blades.

[0007] On the other hand, there is also a need to guarantee resistance to the mechanical stresses that may be exerted on these blades, while limiting their acoustic signature.

[0008] Furthermore, in configurations with unducted fans, the starting of the engine is usually done with a very open pitch. In fact, a very open pitch enables the power to be consumed through torque, which ensures the safety of the machine while guaranteeing a low fan speed.

[0009] However, at very open pitch, the blades are subject to a completely separated turbulent aerodynamic flow, which produces broadband vibration excitation. Especially on blades with a large chord and a large span, the bending forces are strong even at not maximum engine speed.

[0010] In normal operation, during the ground phase and in flight, the pitch is modified (pitch angle is more closed). Therefore, the aerodynamic flow is completely healthy (adheres to the aerodynamic profile). Broadband stresses disappear, rotation speed is higher and bending forces are controlled.

[0011] The blades may be made of metal material. Although metal blades have good mechanical resistance, they have the disadvantage of having a relatively large mass.

[0012] In order to reduce this mass, it is desirable to be able to manufacture the blades in composite materials. However, the strong aerodynamic forces to which the blades are subjected risk damaging the blades and / or the hub in the interface region between the blades and the hub of the fan's rotor at the root of the blades.

[0013] Document WO2022 / 18353 describes a blade comprising an airfoil with an aerodynamic profile and a spar. The spar comprises a composite material core having: a first section inside the airfoil with an aerodynamic profile; and a second section outside the airfoil with an aerodynamic profile so as to form a blade root, the second section extending from the first section. The spar also comprises two metal shells covering a bulge in the composite material blade root.

[0014] The metal shell constitutes a structural reinforcement of the blade root. However, in such a configuration, there is still a risk that the metal shell becomes detached and that the mechanical properties of the system are subsequently suddenly altered. Summary of the invention

[0015] One object of the invention is to design a blade comprising an airfoil with an aerodynamic profile and a blade root in composite material reinforced by a metal shell to prevent the shell from detaching.

[0016] To this end, the present invention provides a blade, the blade comprising:

[0017] an airfoil with an aerodynamic profile, the airfoil comprising a first fiber reinforcement obtained by three-dimensional weaving and a first matrix in which said first fiber reinforcement is embedded, a portion of the airfoil with an aerodynamic profile comprising a cavity formed by a disbond of the first fiber reinforcement,

[0018] - a blade root, the blade root being intended to be connected to a variable pitch mechanism of the blade, and

[0019] a spar comprising a composite core and two metal shells attached to the composite core on both sides of the composite core, the composite core comprising a first section extending within the cavity of the airfoil and a second section forming the blade root,

[0020] Two metal shells attached to the composite core extend over the second section and continue over the first section within the cavity of the aerodynamically profiled airfoil.

[0021] This continuation avoids the transmission of aerodynamic forces from the aerodynamically profiled airfoil to the metal shell through the composite material, which would subject the boundary between the metal shell and the composite material to large shear forces that could cause the shell to detach. The continuation of the metal shell in the cavity ensures the transmission of aerodynamic forces directly to the attachment area through bending forces.

[0022] According to other optional features of the present invention, these features are used alone or in combination when technically feasible:

[0023] the blade root has an axisymmetric shape about a pitch axis of the blade, and the first section has a first thickness, the first thickness being measured in a plane passing through the pitch axis and the intersection between a leading edge line of the airfoil and a flow limiting chord line, the flow limiting chord line being located at the boundary between the airfoil and the root, the first thickness increasing over at least a portion of the first section from the flow limiting chord to the interior of the airfoil;

[0024] - the first section has a second thickness, the second thickness being measured in a second plane perpendicular to the first plane, the second thickness decreasing over said portion of the first section from the flow limit chord to the interior of the airfoil;

[0025] - a first fiber reinforcement comprises weft yarn strands extending from the leading edge to the trailing edge and defining a debonding portion, the debonding portion being defined upstream by a first interlacing portion between the weft yarn strands and downstream by a second interlacing portion between the weft yarn strands;

[0026] - in a plane perpendicular to the pitch axis, the distance measured between a first interlacing and a second interlacing of the weft yarn strands delimiting the debonding portion increases from the blade root to the interior of the airfoil;

[0027] - the blade comprises a workpiece of a rigid porous material, preferably polyurethane foam, attached to a first section of the spar and positioned in a cavity of an airfoil having an aerodynamic profile;

[0028] - the two metal shells attached to the composite core are not joined together and are therefore separate and not in direct contact;

[0029] - a first section of the composite core comprises a facet, each of the two metal shells having a facet positionable in contact with the facet of said first section, so as to define the relative positioning of each of the shells with respect to the core;

[0030] - an airfoil having an aerodynamic profile having a first end connected to a blade root and a second end opposite the first end, and wherein a debonded portion of the first fiber reinforcement forming a cavity extends from a first opening leading to the first end to a second opening leading to a leading edge of the airfoil, a first section of the spar being inserted into the cavity;

[0031] - the first fiber reinforcement is obtained by three-dimensional weaving of carbon fiber strands, and the first matrix comprises an epoxy resin;

[0032] - the composite core of the spar comprises a second fiber reinforcement obtained by three-dimensional weaving and a second matrix in which the second fiber reinforcement is embedded;

[0033] the second fiber reinforcement comprises a plurality of fiber reinforcement layers stacked on top of each other, the plurality of fiber reinforcement layers being arranged in such a way that the stiffness of the fiber reinforcement layers decreases when following the second fiber reinforcement from the inside to the outside of the second fiber reinforcement;

[0034] - the blade root has an axisymmetric shape around a pitch axis of the blade, and the second section has a radial dimension measured along a radial axis perpendicular to the pitch axis, which increases and then decreases continuously when following the second section along the pitch axis while moving away from the first section to form a bulge.

[0035] The present invention also relates to a blade assembly, the blade assembly comprising:

[0036] - a blade as previously described, and

[0037] - an attachment device, the attachment device comprising: a first attachment part, the first attachment part being able to be supported on a portion of the blade root whose radial size continuously increases; a second attachment part, the second attachment part being able to be supported on a portion of the blade root whose radial size continuously decreases; and a third attachment part, the contour of the third attachment part being suitable for cooperating with the contour of the first attachment part to block the first attachment part from translating relative to the third attachment part along the pitch axis, the second attachment part having an orifice, the third attachment part having an orifice intended to face the orifice of the second attachment part so that a blocking member can be inserted into the facing orifice so as to maintain the protuberance in a compressed state between the first attachment part and the second attachment part.

[0038] Another object of the invention is to devise a manufacturing method for a blade comprising an airfoil with an aerodynamic profile and a blade root in composite material reinforced by a metal shell to prevent the shell from detaching.

[0039] To this end, the present invention proposes a method for manufacturing a blade as described above, the method comprising the following consecutive steps:

[0040] - producing a composite spar core comprising a first section and a second section,

[0041] - attaching the two metal shells to the core of the spar so that each of the two metal shells extends over the second section and continues over the first section,

[0042] - producing a fiber blank by three-dimensionally braiding fiber strands, the blank having debonded sections forming cavities,

[0043] - shaping the fiber blank to obtain a preform having an aerodynamic profile, said shaping comprising inserting a first section of the spar into the cavity,

[0044] - Injecting resin into a mould comprising a first fibre blank and a spar to obtain a blade comprising an airfoil with an aerodynamic profile, the airfoil having a first fibre reinforcement densified by a matrix, a first section of the spar extending inside a cavity of the airfoil and a second section of the spar forming a blade root.

[0045] According to other optional features of the present invention, these features are used alone or in combination when technically feasible:

[0046] - the step of shaping the fiber blank is preceded by a step of assembling the spar with a workpiece of rigid porous material, preferably polyurethane foam, so that a first section of the spar is inserted together with the workpiece into the cavity formed by the debonded portion of the fiber blank;

[0047] - the debonded portion of the fiber blank is continued to a second opening in the leading edge line of the airfoil, and the spar is inserted through the opening into the cavity formed by the debonded portion of the fiber blank;

[0048] - the step of producing the core of the spar comprises machining a protuberance with a facet on one end of a first section of the core, and the step of attaching two metal shells to the core comprises positioning each of the two shells against the facet to define the relative positioning of each of the shells with respect to the core. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Other features and advantages of the present invention will be revealed by the following detailed description made with reference to the accompanying drawings, in which:

[0050] - Figure 1 An example of an engine including an unducted fan is schematically shown.

[0051] - Figure 2 A fan blade and an attachment device are schematically shown, which attachment device enables the pitch angle of the fan blade about a pitch axis to be modified.

[0052] - Figure 3A A spar of a blade is schematically shown along a cross section in a first plane including the pitch axis and the intersection between a leading edge line and a flow limiting chord between an aerodynamically profiled airfoil of the blade and the root of the blade.

[0053] - Figure 3BThe spar of the blade is schematically shown in a cross section in a second plane containing the pitch axis and perpendicular to the second plane.

[0054] - Figure 4 The core of the composite material spar is schematically shown in a cross section AA of the spar in a plane perpendicular to the pitch axis.

[0055] - Figure 5 The facets enabling the relative positioning of the metal skin and the composite material core of the spar in the cross section CC of the spar are schematically shown.

[0056] - Figure 6 A method of manufacturing a blade including a spar is shown.

[0057] - Figure 7 The steps of inserting a spar into an airfoil of a blade are schematically shown. DETAILED DESCRIPTION

[0058] Description of the blade

[0059] exist Figure 1 In the diagram, the engine 1 shown is an "open rotor" type engine in what is currently defined as a "propeller" configuration (i.e., the fan is placed at the rear of the power generator and the air inlet is located at Figure 1 center right).

[0060] The engine comprises an unducted fan 3 and a nacelle 2 intended to be attached to the fuselage of an aircraft. The fan 3 comprises two counter-rotating fan rotors 4 and 5. In other words, when the engine 1 is running, the rotors 4 and 5 are driven to rotate in opposite directions relative to the nacelle 2 about the same axis of rotation X (which axis of rotation coincides with the main axis of the engine).

[0061] exist Figure 1 In the example shown, the engine 1 is an engine of the "Open Rotor" type in a "pusher" configuration with counter-rotating fan rotors. However, the invention is not limited to this configuration. The invention is also applicable to engines of the "Open Rotor" type in a "puller" configuration (i.e. the fan is placed upstream of the power generator, with the air inlet being located in front of, between or just behind the two fan rotors).

[0062] Furthermore, the invention is also applicable to engines having different architectures, such as an architecture comprising a fan rotor with movable blades and a fan stator with fixed blades, or an architecture comprising a single fan rotor.

[0063] The invention is applicable to turboprop type architectures (comprising a single fan rotor).

[0064] exist Figure 1 In , each fan rotor 4, 5 comprises a hub 6 mounted to rotate relative to the nacelle 2, and a plurality of blades 7 attached to the hub 6. The blades extend substantially radially relative to the axis of rotation X of the hub.

[0065] like Figure 2 As shown, the fan 3 also includes an actuation mechanism 8 that enables the pitch angles of the blades of the rotor to be collectively modified in order to adapt the performance of the engine to different flight phases. To this end, each blade 7 comprises a blade root 9 and an airfoil 12 having an aerodynamic profile. The blade root 9 is mounted to rotate relative to the hub 6 about the pitch axis Y. More precisely, the blade root 9 is mounted to rotate in an attachment device 10 by means of a ball 11 or other rolling element, the attachment device 10 being arranged in the hub 6.

[0066] The airfoil 12 has an aerodynamic profile and has a first end connected to the blade root and a second end opposite the first end. When the engine is running, the part of the airfoil 12 with the aerodynamic profile is intended to extend in the air flow of the engine to generate lift. On the other hand, the blade root 9 is intended to extend outside the air flow.

[0067] The airfoil 12 with an aerodynamic profile has a composite material structure including a first fiber reinforcement obtained by three-dimensionally weaving strands and a first matrix in which the first fiber reinforcement is embedded. The first fiber reinforcement is obtained, for example, by three-dimensionally weaving carbon fiber strands, and the first matrix may include epoxy resin.

[0068] The first fiber reinforcement comprises a disbond defining a cavity within the aerodynamically profiled airfoil 12. The cavity opens into a first opening 25 at a first end of the aerodynamically profiled airfoil 12. The cavity preferably extends from this first opening 25 to a second opening 24 that opens into the leading edge of the airfoil.

[0069] Reference Figure 4 The first fiber reinforcement may include a first group of weft yarn strands 26 extending from a leading edge to a trailing edge of an airfoil having an aerodynamic profile, and the first group of weft yarn strands 26 define a debonding portion upstream by a first interlacing portion 26a between the weft yarns of the first group of weft yarn strands, and a debonding portion downstream by a second interlacing portion 26b.

[0070] The first fiber reinforcement may also include a second group of weft strands 27 extending from the leading edge to the trailing edge in the skin of the aerodynamically profiled airfoil (i.e., the second group of weft strands are the strands closest to the outer surface of the aerodynamically profiled airfoil 12), but without or with only a few local interlacing portions in the low thickness areas of the preform, so as to give the shape of the airfoil. In particular, the second group of weft strands 27 constitute a reinforcement that resists deformation of the airfoil when the resin used to form the first matrix is ​​injected. Finally, a third group of weft strands 28 may also extend from the leading edge to the trailing edge. The weft output of this third group 28 provides a rapid change in the thickness of the airfoil 12.

[0071] The fan blade 7 also includes Figure 3A and Figure 3B A spar 13 is shown. The spar itself comprises a core 14 of composite material.

[0072] The composite core 14 comprises a first section extending within the cavity of the airfoil and a second section forming the blade root 9 .

[0073] The first section of the core enables the forces to which the aerodynamically profiled airfoil 12 is subjected to be transmitted to the blade root 9. The shape of the first section of the core is chosen to ensure that the airfoil 12 remains on the root 9.

[0074] A first plane is defined which passes through the pitch axis Y and the intersection between the leading edge line of the airfoil and the flow limiting chord line, the flow limiting chord line being located at the boundary between the airfoil 12 and the root 9, the spar 13 being located at the boundary between the airfoil 12 and the root 9. Figure 3A As shown in the first plane of Figure 3A As can be seen in FIG. 1 , the first section has a first thickness, the first thickness being measured in a first plane, the first thickness preferably increasing over at least a portion 15 of the first section from the flow limit chord to the interior of the airfoil.

[0075] Mutually, the distance measured between the first interlacing 26a and the second interlacing 26b of two weft yarn strands of the first fiber reinforcement (the first interlacing 26a and the second interlacing 26b delimiting the disbonding portion) increases from the first opening of the cavity at the flow limit chord to the interior of the airfoil in the same first plane, so that the weft yarn strand 26 most closely surrounds the first section of the core of the spar 13.

[0076] The first section may be attached in the cavity directly by the resin constituting the first matrix or by an adhesive film.

[0077] When the fan rotates, the blades 7 are subjected to centrifugal forces directed in a radial direction relative to the axis of rotation of the fan, which tend to separate the aerodynamically profiled airfoil 12 from the spar 13. The anchoring of the airfoil 12 on the spar 13 is provided by the adhesive or resin and by the shrinkage of the connecting cross section of the first section and the cavity from the inside of the airfoil to the flow limit chord. Thus, even in the event of a rupture of the interface between the spar 13 and the resin or adhesive film, the shrinkage of the cross section ensures that the aerodynamically profiled airfoil 12 remains on the spar 13.

[0078] In addition, if Figure 3B As can be seen in FIG. 1 , the first section of the core has a second thickness, measured in a second plane including the pitch axis Y and perpendicular to the first plane, which decreases in a portion 15 of the first section from the flow limit chord to the interior of the airfoil.

[0079] As in Figure 3A or Figure 3B As can be seen in the figure, the second section of the core consists of two parts. The first part or attachment part 16 of the second section of the core is attached to the inside of the attachment device 10 and provides the function of attaching the blade to the hub. The second part, called strut 17, forms the connection between the attachment part 16 located inside the attachment device 10 and the first section of the core located inside the airfoil.

[0080] The strut 17 provides a transfer of aerodynamic forces from the first section of the core to the attachment area. A first dimension of the strut 17 measured in a first plane increases when moving from the attachment area to the airfoil. Conversely, when moving in the same direction, a second dimension of the strut 17 measured in a second plane decreases to reach the dimension imposed by the aerodynamically profiled airfoil 12 at the limit of the flow. In the first plane, the cross section of the strut 17 increases from the attachment area to the aerodynamically profiled airfoil 12, which enables the strut 17 to provide better force transfer.

[0081] The first part 16 of the second section is intended to be inserted into the variable pitch attachment device 10 of the blade 7. When following the first part of the second section along the pitch axis Y while moving away from the first section, the radial dimension of the first part 16 measured along a radial axis perpendicular to the pitch axis Y increases continuously, thereby defining a first frustoconical surface called "upper bearing surface". Then, the radial dimension decreases continuously, thereby defining a second frustoconical surface called "lower bearing surface". This evolution of radial dimensions corresponds to the ridge 16a. In other words, the first part has the shape of a bulb.

[0082] When the first portion 16 is inserted into the attachment device 10 and the blade 7 rotates, the upper bearing surface ensures that the blade 7 is retained under the influence of centrifugal forces, ensuring the absorption of tension forces that are substantially radial relative to the axis X. The upper bearing surface also ensures the absorption of tangential bending forces exerted circumferentially relative to the axis X on the aerodynamically profiled airfoil 12, which bending forces are generated by the vortices of the air caused by the airfoil.

[0083] The lower bearing surface enables a preload to be applied during assembly of the blade root 9 into the attachment device 10 , ie the blade root is pressed between the upper and lower bearing surfaces.

[0084] The first part 16 of the second section may also include a pitch member 16b extending from the lower bearing surface. The pitch member 16b does not have an axisymmetry around the pitch axis Y, so that the pitch member 16b enables the pitch of the blade 7 to be controlled, in particular in the event of excessive torque, such as during bird ingestion. The pitch member 16b then intervenes as an integral safety member.

[0085] The variable pitch attachment device 10 comprises a first segmented attachment member 18 which can be supported on a portion of the blade root 9 of continuously increasing radial dimension.

[0086] The attachment device 10 also comprises a second attachment member 19 , referred to as an inner rolling ring, which can be supported on a portion of the blade root 9 of continuously decreasing radial dimensions.

[0087] Finally, the attachment device 10 comprises a third attachment member 20 . The profile of the third attachment member 20 can cooperate with the profile of the first attachment member 18 to block translation of the first attachment member 18 along the pitch axis Y relative to the third attachment member 20 .

[0088] The second attachment part 19 has an aperture 29. The third attachment part 20 has an aperture 30 which is intended to be arranged facing the aperture 29 of the second attachment part 19 so that a blocking member, such as a screw, can be inserted into the facing apertures 29, 30 to keep the protuberance 16a in a compressed state between the first attachment part 18 and the second attachment part 19.

[0089] The composite material core 14 of the spar 13 comprises a second fiber reinforcement obtained by three-dimensional weaving and a second matrix in which the second fiber reinforcement is embedded.

[0090] The second fiber reinforcement may be three-dimensionally woven and have a debonding portion defining a central cavity into which a workpiece (for example polyurethane foam) is inserted. The workpiece enables the desired shape and thickness of the spar to be obtained.

[0091] Alternatively, the second fiber reinforcement may comprise a plurality of fiber reinforcement layers stacked on top of each other. According to this embodiment, each fiber reinforcement layer extends over the entire length of the core, the thickness of each layer varying over said length. Thus, the thickness variations of each layer add up so that the desired core shape can be obtained, in particular with the desired ridges.

[0092] Still alternatively, the second fiber reinforcement may comprise a fiber reinforcement layer having a width substantially equal to the length of the spar, the fiber reinforcement layer being wound upon itself.The variation in thickness of the fiber reinforcement layer over its width enables the desired shape of the spar to be obtained.

[0093] The stiffness or Young's modulus of the second fiber reinforcement may vary in different regions of the second fiber reinforcement. Thus, the stiffness of the second fiber reinforcement may advantageously decrease when following the second fiber reinforcement from the interior of the second fiber reinforcement to the exterior of the second fiber reinforcement.

[0094] As an example, if the fiber reinforcement layer does not have the same stiffness over its entire length, a stiffness variation between the core and the skin of the second fiber reinforcement may be obtained in the case of a fiber reinforcement layer wound upon itself.

[0095] Also as an example, the stiffness variation can be obtained by superimposing a plurality of fiber reinforcement layers, the layers then being arranged such that the stiffness of the layers decreases when following the second fiber reinforcement from the inside to the outside of the second fiber reinforcement. The stiffness then varies between the different fiber reinforcement layers and within each layer.

[0096] A stiffness variation may also be obtained when the second fibre reinforcement comprises a fibre reinforcement layer, the stiffness of the layer varying over the thickness and / or the width of the layer.

[0097] In addition to the composite core 14, the spar comprises two metal shells 21a, 21b attached to the core 14, for example by mechanical assembly or preferably by gluing. The two metal shells 21a, 21b are positioned like nut shells on both sides of the core 14. The two metal shells 21a, 21b are an impression of the composite core 14, so that the shape of the spar 13 including the metal shells 21a, 21b and the composite core 14 is similar to the shape of the core 14 previously described.

[0098] The two metal shells 21a, 21b extend over the second section of the core 14 and continue over the first section inside the cavity of the aerodynamically profiled airfoil 12. Thus, according to one embodiment, the two metal shells 21a, 21b cover the bulb-shaped 16a attachment portion 16, which is continued by the pitch member 16b, the strut 17 and at least a portion of the first section of the core located inside the cavity. According to a particular embodiment, the two metal shells 21a, 21b continue to the end of the first section of the core 14.

[0099] Thus, at the portion where the metal shells 21a, 21b continue within the cavity, the spar 13 is attached to the aerodynamically profiled airfoil 12 by means of the metal shells 21a, 21b directly by resin or by an adhesive film as previously described.

[0100] The two metal shells 21a, 21b constitute structural reinforcements of the composite core 14. The continuation of the two metal shells in the cavity of the aerodynamically profiled airfoil 12 ensures the transmission of aerodynamic forces from the airfoil 12 more directly than in a configuration in which the shells would extend over the second section of the core but would not continue in the cavity. In fact, the lack of continuation of the metal shells over the first section of the core forces the forces to be transmitted from the airfoil to the shells through the composite material, subjecting the struts 17 to shear forces. The metal shells 21a, 21b extending in the cavity ensure the transmission of aerodynamic forces to the attachment area directly through bending forces.

[0101] Furthermore, the continuation of the shells 21a, 21b inside the aerodynamic profiled airfoil 12 ensures continuity of stiffness and makes it possible to avoid discontinuities in the macroscopic mechanical properties between the attachment area 16, the struts 17 and the aerodynamic profiled airfoil 12 (at least close to the flow air limit). The shells 21a and 21b participate in the transmission of the aerodynamic bending forces and centrifugal tension forces exerted on the aerodynamic profiled airfoil 12 towards the attachment area 16. This avoids having these forces transmitted through the composite material core 14 only in the thinned areas, where the struts 17 or the composite material core 14 have a reduced thickness in the second plane ( Figure 3B ), so in the thinned area these forces are concentrated.

[0102] Finally, in a configuration where the metal shell will extend over the first section of the core but will not continue in the cavity of the airfoil, the end of the metal shell considered when moving towards the airfoil will constitute a free edge that could concentrate stresses. Stress concentrations on the edge could cause the shell to detach. Therefore, the continuation of the metal shell 21a, 21b in the cavity makes it possible to avoid detachment of the shell 21a, 21b and the abrupt changes in mechanical properties that would result from it.

[0103] In order to define the relative positioning of each of the shells 21a, 21b with respect to the composite core 14, each of the two metal shells 21a, 21b may have a facet 22. Figure 5 As shown in more detail in FIG. 2 , the first section of the core further comprises a facet, the facet of each of the two metal shells 21 a , 21 b being positioned in contact with the facet 22 of the first section of the core.

[0104] Preferably, the two metal shells 21a, 21b attached to the composite core 14 are not joined together, i.e. separated from each other without direct contact, so as to allow good attachment of the metal shells 21a, 21b to the composite core 14. In particular, during the attachment by gluing, the aim is not to leave a space between each of the two metal shells 21a, 21b and the composite core 14. If the metal shells 21a, 21b are not correctly arranged against the composite core 14, there is a risk of discontinuities in the mechanical properties, which could lead to internal weakened areas in the blade in the event of an impact, for example during contact with a bird.

[0105] According to one embodiment, when the spar 13 is positioned in the cavity of the aerodynamically profiled airfoil 12, each of the two metal shells 21a, 21b extends around the core 14 from the leading edge to the trailing edge, so that the first of the two metal shells 21a is positioned as a whole toward the pressure side of the airfoil, and the second of the two metal shells 21b is positioned as a whole toward the suction side of the airfoil.

[0106] According to an alternative embodiment, each of the two metal shells 21a, 21b extends around the core 14 from the pressure side to the suction side, so that the first of the two metal shells 21a is positioned entirely at the leading edge of the airfoil and the second of the two metal shells 21b is positioned entirely at the trailing edge of the airfoil.

[0107] The positioning of the metal shells 21a, 21b on the pressure side and the suction side has the advantage of being easier to process, the shape of each of the two metal shells 21a, 21b is relatively flat in this configuration, and the positioning of the metal shells 21a, 21b at the leading edge and the trailing edge provides a better response of the shells 21a, 21b to bending forces.

[0108] In addition to the aerodynamically profiled airfoil 12 and the spar 13, the blade may also comprise a workpiece 23 of rigid porous material. The workpiece 23 is then attached to the spar comprising the metal shell and positioned in the cavity of the airfoil formed by the debonding. Thus, according to this embodiment, the dimensions of the cavity enable the introduction of the foam and the spar 13 into the cavity.

[0109] The rigid porous material is preferably polyurethane foam. Alternatively, the rigid porous material may be a previous weather-resistant aluminum honeycomb material.

[0110] The workpiece 23 makes it possible to provide the aerodynamically profiled airfoil 12 of the blade 7 with the desired thickness and shape, while using a material that is lighter than the other elements of the blade.

[0111] Method for manufacturing a blade

[0112] The invention also relates to a method for manufacturing a blade 7 as described above, comprising an airfoil 12 having an aerodynamic profile and a spar 13, the spar 13 itself comprising a composite material core 14 and two metal shells 21a, 21b. Figure 6 , the method for manufacturing a blade 7 comprises the following consecutive steps:

[0113] - producing 101 a spar core 14 of composite material comprising a first section and a second section,

[0114] - attaching 102 the two metal shells 21a, 21b to the core 14 of the spar so that each of the two metal shells 21a, 21b extends over the second section and continues over the first section,

[0115] - producing 103 a fiber blank by three-dimensionally braiding fiber strands, the blank having debonded portions forming cavities,

[0116] - shaping 104 the fiber blank to obtain a preform having an aerodynamic profile, the shaping comprising inserting a first section of the spar 13 into the cavity,

[0117] - Injecting 105 a resin into the mould comprising the first fibre blank and the spar 13 to obtain a blade 7 comprising an aerodynamically profiled airfoil 12 having a first fibre reinforcement densified by a matrix, a first section of the spar 13 extending inside a cavity of the airfoil 12 and a second section of the spar 13 forming the blade root 9.

[0118] Production of composite core 14 of spar 13 101

[0119] The production 101 of the composite core 14 comprises preparing a second fiber reinforcement and then injecting a second matrix to impregnate the second fiber reinforcement.

[0120] According to a preferred embodiment, the second fiber reinforcement is prepared by three-dimensionally weaving the weft yarn strands and by creating disbonds around the insert of the workpiece during weaving, so that the workpiece itself is in the cavity of the second fiber reinforcement. This embodiment has the advantage of being able to well control the thickness of the spar core. Weaving makes it possible to arrange a good interweaving of the fibers to obtain the desired mechanical properties of the second fiber reinforcement in the resin.

[0121] The workpiece may be a previously processed polyurethane foam. As an alternative to foam, nomex, paper or aluminum honeycomb materials may be used. The weft yarns used may be carbon fibers. Alternatively, glass fibers or aramid fibers may be used.

[0122] Optionally, the second fiber reinforcement is woven so that the stiffness of the second fiber reinforcement varies over the width and / or thickness of the fiber reinforcement. Advantageously, the second fiber reinforcement is woven so that the stiffness decreases when following the second fiber reinforcement from the interior of the second fiber reinforcement to the exterior of the second fiber reinforcement.

[0123] The second fiber reinforcement is then positioned in a rigid and strong mold. The mold provides the second fiber reinforcement with a shape in which the second fiber reinforcement will be fixed. A liquid resin is then injected into the mold at a relatively low pressure according to a method known to those skilled in the art as "resin transfer molding (abbreviated to RTM)".

[0124] The method makes it possible to obtain a composite part having a good surface condition over its entire surface.

[0125] Preferably, an epoxy resin having sufficient fluidity for good impregnation is injected. Epoxy resins provide good mechanical properties, in particular good material-cohesion properties. Alternatively, any other thermosetting resin may be used, or even a thermoplastic resin of variant embodiments known to those skilled in the art.

[0126] Finally, the ends of the core 14 secured by the resin may be machined to define facets 22 which will serve as dimensional references for the relative positioning of the two metal shells 21 a , 21 b .

[0127] Alternatively, the second fiber reinforcement can be produced by stacking a plurality of fiber reinforcement layers, each layer being prepared by three-dimensionally weaving weft yarn strands. The stack of these layers is then impregnated with resin. Excess fibers in the length direction are cut off. Finally, the assembly can be slightly processed to obtain the final shape of the part. Therefore, it is preferred to complete a single injection of resin in the second fiber reinforcement comprising a stack of different fiber reinforcement layers, because a single injection of resin enables the assembly to be obtained to be more uniform than the assembly that can be obtained by superposition of multiple layers previously impregnated with resin in different injection steps.

[0128] Alternatively still, the second fiber reinforcement may be prepared by winding one or more fiber reinforcement layers. The fiber reinforcement layer wound upon itself is then positioned in the mold and injected with resin.

[0129] Alternatively, the fiber reinforcement layers may be woven so as to reduce the thickness of the second fiber reinforcement when following the second fiber reinforcement from the interior of the second fiber reinforcement to the exterior of the second fiber reinforcement.

[0130] Alternatively and in a non-limiting manner, a bidirectional braid, a unidirectional braid, or an interwoven composite braid may be used.

[0131] Attachment 102 of the two metal shells 21a, 21b to the core 14 of the spar

[0132] In a non-limiting manner, the two metal shells 21a, 21b are made of the following materials: titanium, a titanium alloy (for example ta6v), steel or aluminum.

[0133] The two metal shells 21 a , 21 b are preferably produced by a forging method and can be completed by mechanical and / or chemical processing.

[0134] In the forging method, the selected material is deformed by impact or by passage between two tools (cold or hot) to adopt the desired shape. Compared with molding, the forging method has the advantage of producing a shell 21a, 21b with good metal properties through the organization of the substance and accurate shaping that can limit subsequent processing.

[0135] Chemical or mechanical processing enables to give each of the two metal shells the desired shape and size by removing matter. For example, processing may include forming facets complementary to the facets 22 machined on the composite core 14 so that the metal shells 21a, 21b can be positioned on the core 14.

[0136] Before attaching the two metal shells 21a, 21b, the surface of the composite material core 14 is treated. The purpose of the treatment is to obtain a good roughness and improve the surface condition of the composite material by removing dust and grease. The surface treatment of the composite material core 14 may include sandblasting.

[0137] The two metal shells 21a, 21b are then applied around the composite part of the spar 13, possibly by mechanical assembly, for example by screwing (vissage), preferably by gluing. The polymerisation of the adhesive film can be done in an autoclave under vacuum. The prior treatment of the surface of the composite core 14 ensures a good bond.

[0138] In the case where facets have been machined on the composite core 14 and the two metal shells 21a, 21b, each of the two metal shells 21a, 21b is positioned against a facet 22. The facets 22 make it possible to define the relative positioning of the shells 21a, 21b with respect to the core 14.

[0139] Finally, the spar 13 thus assembled may be machined to perfect its final external geometry.

[0140] Production of the first fiber blank 103

[0141] The first fiber blank is produced by three-dimensionally weaving weft yarn strands. The first fiber blank is woven to have a debonded portion forming a cavity extending from the first opening 25 to one end of the first fiber blank at the blade root 9 .

[0142] The debond portion is preferably defined upstream by a first interlaced portion 26a between the weft yarn strands and downstream by a second interlaced portion 26b between the weft yarns. In addition, the distance measured between the first interlaced portion 26a and the second interlaced portion 26b of the weft yarn strands 26 defining the debond portion increases from the first opening to the interior of the cavity over at least a portion of the cavity.

[0143] The cavity may extend to a second opening 24 , for example opening into the leading edge of the airfoil.

[0144] Forming 104 of the first fiber blank and injection 105 of the resin

[0145] Alternatively, the spar 13 may be assembled with a workpiece 23 of rigid cellular material, preferably a previously processed polyurethane foam.

[0146] The spar 13 is assembled with the workpiece 23 by gluing, preferably by using a glue that polymerizes at ambient temperature. If the composite core 14 comprises facets 22 , said facets 22 can be used to position the workpiece 23 correctly.

[0147] The surface of the spar 13 is then prepared by a chemical method or by a dry method, for example by laser or by very light sanding. Treating the surface of the spar 13 makes it possible in particular to obtain a surface condition with good grain size for assembly by gluing.

[0148] The adhesive film may then be deposited on the first section of the spar 13 and possibly on the workpiece 23 if present.

[0149] The first fiber blank is then shaped to obtain a preform having an aerodynamic profile, the preform is retained in the tool and the spar 13 is inserted into the cavity defined by the debonded portion of the first fiber blank so that, at the end of the insertion, the first section is inserted inside the cavity and the second section forming the blade root 9 emerges through the first opening of the cavity. If the spar 13 has previously been assembled with the workpiece 23, the assembly comprising the first section and the workpiece 23 is inserted inside the cavity. The assembly comprising the preform, the spar 13 and optionally the workpiece 23 is arranged before impregnation with resin.

[0150] The assembly of the spar 13 and the workpiece 23 before inserting them into the cavity defined by the debonding portion advantageously enables the relative positioning of the spar 13 and the workpiece 23 to be controlled within the cavity.

[0151] Reference Figure 7 If the debonded portion of the fiber blank is extended to include a second opening 24 in the leading edge line of the airfoil, the spar is inserted into the cavity formed by the debonded portion of the fiber blank through the second opening 24 until the second section forming the blade root 9 emerges through the first opening 25 at the end of the airfoil root. The cross-sectional limitation at the first opening 25 ensures the retention of the first section of the spar 13 and possibly the workpiece 23.

[0152] Liquid resin is then injected into the mould containing the first fibre blank and the spar 13 according to the RTM method, in order to fix the aerodynamically profiled airfoil 12 , the spar 13 and possible workpiece 23 in place when attached.

[0153] A blade 7 is thus obtained comprising an aerodynamically profiled airfoil 12 with a first fiber reinforcement densified by a matrix, a first section of a spar 13 extending inside the cavity of the airfoil 12 and a second section of the spar 13 forming the blade root 9 .

[0154] Finally, a metal protection is added to the leading edge of the blade 7 and / or optionally a de-icing system. The metal protection may comprise a titanium shroud to avoid degradation of the composite material of the blade 7 caused on the one hand by the abrasive effects of sand or ice particles and on the other hand by impact effects such as those resulting from contact with hail or birds. Alternatively, a shroud of a fabric layer may be used.

Claims

1. A blade (7), comprising: an airfoil (12) with an aerodynamic profile, the airfoil comprising a first fiber reinforcement obtained by three-dimensional weaving and a first matrix in which the first fiber reinforcement is embedded, a portion of the airfoil (12) with an aerodynamic profile comprising a cavity formed by a disbonded portion of the first fiber reinforcement, - a blade root (9) intended to be connected to a variable pitch mechanism of the blade, and a spar (13) comprising a composite core (14) and two metal shells (21a, 21b) attached to the composite core (14) on both sides of the composite core (14), the composite core (14) comprising a first section extending inside the cavity of the airfoil and a second section forming the blade root (9), The two metal shells (21a, 21b) attached to the composite core (14) extend over the second section and continue over the first section within the cavity of the aerodynamically profiled airfoil (12).

2. The blade (7) according to claim 1, wherein: The blade root (9) has an axisymmetric shape around a pitch axis (Y) of the blade (7), and the first section has a first thickness, the first thickness being measured in a plane passing through the pitch axis (Y) and the intersection between the leading edge line of the airfoil and a flow limit chord line, the flow limit chord line being located between the airfoil and the root, the first thickness increasing over at least a portion (15) of the first section from the flow limit chord to the inside of the airfoil (12).

3. The blade (7) according to claim 2, wherein: The first section has a second thickness, measured in a second plane perpendicular to the first plane, which decreases over the portion (15) of the first section from the flow limit chord to an interior of the airfoil (12).

4. The blade (7) according to any one of claims 1 to 3, wherein: The first fiber reinforcement comprises weft yarn strands (26) extending from the leading edge to the trailing edge and defining the debonding portion, the debonding portion being defined upstream by a first interlacing portion (26a) between the weft yarn strands and downstream by a second interlacing portion (26b) between the weft yarns.

5. The blade (7) according to claim 2 or 3 and 4, wherein: In a plane perpendicular to the pitch axis (Y), the distance measured between a first interlacing portion (26a) and a second interlacing portion (26b) of the weft yarn strands (26) defining the debonding portion increases from the blade root (9) to the interior of the airfoil (12).

6. A blade (7) according to any one of claims 1 to 5, comprising a workpiece (23) of a rigid porous material, preferably polyurethane foam, attached to a first section of the spar (13) and positioned in the cavity of the aerodynamically profiled airfoil (12).

7. The blade (7) according to any one of claims 1 to 6, wherein: The two metal shells (21a, 21b) attached to the composite core (14) are not joined together.

8. The blade (7) according to any one of claims 1 to 7, wherein: A first section of the composite core (14) includes a facet (22), and each of the two metal shells (21a, 21b) has a facet that can be positioned to contact the facet (22) of the first section to define the relative positioning of each of the shells (21a, 21b) relative to the core (14).

9. The blade (7) according to any one of claims 1 to 8, wherein: The aerodynamically profiled airfoil (12) has a first end connected to the blade root (9) and a second end opposite the first end, and wherein a debonded portion of the first reinforcement forming the cavity extends from a first opening leading to the first end to a second opening leading to the leading edge of the airfoil, the first section of the spar being inserted into the cavity.

10. The blade (7) according to any one of claims 1 to 9, wherein: The first fiber reinforcement is obtained by three-dimensionally weaving carbon fiber strands, and the first matrix includes epoxy resin.

11. The blade (7) according to any one of claims 1 to 10, wherein: The composite material core (14) of the spar (13) comprises a second fiber reinforcement obtained by three-dimensional weaving and a second matrix in which the second fiber reinforcement is embedded.

12. The blade (7) according to claim 11, wherein: The second fiber reinforcement comprises a plurality of fiber reinforcement layers stacked on each other, the plurality of fiber reinforcement layers being arranged in such a way that the stiffness of the fiber reinforcement layers decreases when following the second fiber reinforcement from the inside to the outside of the second fiber reinforcement.

13. The blade (7) according to any one of claims 1 to 12, wherein: The blade root (9) has an axisymmetric shape around the pitch axis (Y) of the blade (7), and the second section has a radial dimension measured along a radial axis perpendicular to the pitch axis (Y), and when following the second section along the pitch axis (Y) while moving away from the first section, the radial dimension continuously increases and then continuously decreases to form a ridge (16a).

14. A blade assembly, comprising: - a blade (7) according to claim 13, and - an attachment device (10), comprising: a first attachment part (18) which helps to be supported on the portion of the blade root (9) whose radial dimension continuously increases; a second attachment part (19) which helps to be supported on the portion of the blade root (9) whose radial dimension continuously decreases; and a third attachment part (20) whose profile can cooperate with the profile of the first attachment part (18) to block the first attachment part (18) from translating relative to the third attachment part (20) along the pitch axis (Y), the second attachment part (19) having an orifice (29), the third attachment part (20) having an orifice (30) intended to face the orifice (29) of the second attachment part (19) so that a blocking member can be inserted into the facing orifices (29, 30) so as to maintain the protuberance (16a) in a compressed state between the first attachment part (18) and the second attachment part (19).

15. A method for manufacturing a blade (7) according to any one of claims 1 to 14, comprising the following consecutive steps: - producing (101) a composite material core (14) comprising a first section and a second section, - attaching (102) two metal shells (21a, 21b) to the core of the spar (14) such that each of the two metal shells (21a, 21b) extends over the second section and continues over the first section, - producing (103) a fiber blank by three-dimensionally braiding fiber strands, the blank having debonded portions forming cavities, - shaping (104) the fiber blank to obtain a preform having an aerodynamic profile, said shaping comprising inserting a first section of the spar (13) into the cavity, - Injecting (105) a resin into a mould comprising a first fibre blank and said spar (13) to obtain a blade (7), said blade comprising an airfoil (12) with an aerodynamic profile, said airfoil having a first fibre reinforcement densified by a matrix, a first section of said spar (13) extending within a cavity of said airfoil (12) and a second section of said spar (13) forming said blade root (9).

16. The method according to claim 15, wherein: The step of shaping the fiber blank is preceded by a step of assembling the spar (13) with a workpiece (23) of a rigid porous material, preferably polyurethane foam, so that a first section of the spar (13) is inserted together with the workpiece (23) into the cavity formed by the debonded portion of the fiber blank.

17. The method according to claim 15 or 16, wherein: The debonded portion of the fiber blank continues to a second opening (24) in the leading edge line of the airfoil (12), and the spar is inserted through the opening into a cavity formed by the debonded portion of the fiber blank.

18. The method according to any one of claims 15 to 17, wherein: The step of producing the core (14) of the spar (13) comprises machining a raised portion having a facet (22) on one end of a first section of the core (14), and the step of attaching the two metal shells (21a, 21b) to the core (14) comprises positioning each of the two shells (21a, 21b) against the facet (22) to define the relative positioning of each of the shells (21a, 21b) relative to the core (14).

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