Composite material blade including external reinforcing elements

Abstract

Composite material blade comprising external reinforcing elements The invention relates to a blade (30) comprising a flange (31), a joining portion (32) and an aerodynamic profile (33), the blade (30) comprising two skins (21, 22) present on the surface of the aerodynamic profile (33), the two skins (21, 22) also forming a portion of the joining portion (32) and a portion of the flange (31), the distance between the two skins (21, 22) in the joining portion (32) decreasing from the boundary between the aerodynamic profile (33) and the joining portion (32) until reaching a minimum distance, the blade (30) further comprising at least one external reinforcing element (51, 52) superimposed on one of the skins (21, 22) at the joining portion (32) and the flange (31) so as to ensure continuity of the outer surface of the blade (30). Figure for the abstract: Fig. 7

Description

Title of the invention: Blade made of composite material comprising external reinforcing elements Technical field

[0001] The present invention relates to a reinforcing element for a composite blade of a turbomachine or propeller engine. The composite blade may for example be a fan blade, called a "fan blade", or an outlet guide vane, called an "OGV" for "outlet guide vane". Prior art

[0002] It is known to produce blades from composite material comprising skins forming a flange from which a hollow aerodynamic profile extends. These blades can be attached by their flange to a metal support, the rotation of which can allow rotation of the blade. The fixing system between the flange of the blade and the metal support is conventionally produced by means of bolts.

[0003] The lower part of the blade is subjected to significant mechanical stresses during operation, in particular at the flange and at the junction between the flange and the aerodynamic profile. Indeed, the flange and the junction between the flange and the aerodynamic profile are subjected to an asymmetrical loading, one side being stressed in tension while the other side is stressed in compression.

[0004] In order to strengthen the blade in its lower part, it is possible to increase the thickness of the composite material skins at the flange and the junction between the flange and the aerodynamic profile. However, the thickness of the skins must remain limited at the aerodynamic profile in order to maintain a light blade. Thus, it is necessary to achieve local thickening of the skins in the lower part of the blade while maintaining thin skins at the aerodynamic profile. The production of composite material skins with such a variation in thickness is difficult to implement, particularly when the skins are produced by three-dimensional weaving. Statement of the invention

[0005] The present invention proposes to remedy the aforementioned problems, by proposing a blade reinforced at the flange and at the junction between the flange and the aerodynamic profile, while retaining thin skins of constant thickness.

[0006] To this end, the invention proposes a blade made of composite material comprising, in a radial direction, a flange, a joining part and an aerodynamic profile, the joining part linking the flange to the aerodynamic profile, the blade comprising two skins comprising a fibrous reinforcement densified by a matrix, the two skins being present on the surface of the aerodynamic profile and respectively forming the intrados and the extrados of the blade, the two skins also forming a portion of the junction part and a portion of the flange, the blade being characterized in that the distance between the two skins in the junction part of the blade following a thickness direction perpendicular to the radial direction decreases from the limit between the aerodynamic profile and the junction part until reaching a minimum distance, the blade further comprising at least one first external reinforcing element made of fiber reinforcement densified by the matrix superimposed on one of the skins at least at the junction part and the flange so as to ensure continuity of the external surface of the blade.

[0007] Thus, the presence of external reinforcing elements at the flange and the joining part makes it possible to reinforce the blade at these mechanically critical locations without needing to thicken the skins. It is thus possible to maintain particularly thin skins over the entire height of the blade.

[0008] Furthermore, the blade comprises a so-called neutral surface located between the two skins which undergoes few mechanical stresses. Indeed, the central zone of the blade undergoes fewer stresses in static and vibration, and is less subject to shocks. Thus, by reducing the distance between the two skins, the interface between the skins and the external reinforcement elements moves closer to said neutral surface and is therefore less subject to mechanical stresses. Thus, the risk of detachment of the external reinforcement elements from the blade is more limited.

[0009] Since the external reinforcing elements are distinct from the rest of the blade, it is possible to choose a particular fiber reinforcement for said external reinforcing elements, particularly suited to the stresses experienced at the flange and the joining part. A different fiber reinforcement can be chosen for the skins, suited to the stresses experienced at the aerodynamic profile. Thus, the fiber reinforcement chosen can be adapted according to the different parts of the blade.

[0010] According to a particular embodiment of the invention, the blade further comprises a second external reinforcing element made of fibrous reinforcement densified by the matrix superimposed on the other skin at least at the level of the junction part and the flange so as to ensure continuity of the external surface of the blade.

[0011] According to a particular embodiment of the invention, the minimum distance is zero so that the two skins are in contact.

[0012] Thus, the mechanical stresses undergone by the skins and by the interface between the fibrous reinforcements and the skins at this location are particularly reduced.

[0013] According to another particular embodiment of the invention, the portions of the skins which are in contact in the junction part are linked by fibers.

[0014] Thus, the mechanical properties of the blade are improved, because the two skins are linked to each other.

[0015] According to another particular embodiment of the invention, the external reinforcing elements are produced by three-dimensional weaving.

[0016] The use of three-dimensional weaving makes it possible to improve the mechanical properties of the external reinforcement elements.

[0017] According to another particular embodiment of the invention, a lower reinforcing element is present in the flange and extends in the thickness direction between the two skins.

[0018] The lower reinforcing element makes it possible to improve the hold of the flange, by reducing the stresses at the junction part of the blade and by limiting the opening between the two skins.

[0019] According to another particular embodiment of the invention, the flange of the blade further comprises a reinforcing plate perpendicular to the radial direction maintained in contact with the end of the two skins.

[0020] Such a reinforcing plate makes it possible to have continuity of material at the lower edge of the blade, and in particular continuity of the fibers in the case where the reinforcing plate comprises continuous fibers.

[0021] The present invention also relates to a method of manufacturing a blade made of composite material, the method comprising:

[0022] - shaping a fiber blank into a main fiber blade preform comprising at least two skins so as to form in a radial direction a flange portion, a joining part portion and an aerodynamic profile portion, the distance between the two skins in the joining part portion in a thickness direction perpendicular to the radial direction decreasing from the limit between the aerodynamic profile portion and the joining part portion until reaching a minimum distance,

[0023] - the superposition of a first and a second fibrous preforms of elements external reinforcement respectively on one and the other of the two skins at least at the level of the junction portion and the flange portion so as to obtain a fibrous blade assembly with continuous external surfaces, then

[0024] - co-densification by a matrix of the fiber blade assembly, so as to obtain a composite material blade comprising two external reinforcing elements.

[0025] Such a method makes it possible to obtain the blade as described above with the corresponding advantages. In addition, the co-densification makes it possible to ensure good cohesion of the assembly.

[0026] According to a particular embodiment of the invention, the minimum distance is zero so that the two skins are in contact.

[0027] Thus, the mechanical constraints undergone by the skins and by the interface between the fibrous reinforcements and the skins in this area are particularly reduced.

[0028] According to a particular embodiment of the invention, the method further comprises the bonding of the portions of the skins which are in contact in the joining part portion by fibers.

[0029] Thus, the mechanical properties of the blade are improved, because the two skins are bonded to each other.

[0030] According to a particular embodiment of the invention, the two fiber preforms of external reinforcement elements are produced by three-dimensional weaving.

[0031] The use of three-dimensional weaving makes it possible to improve the mechanical properties of the external reinforcement elements.

[0032] According to a particular embodiment of the invention, the fibrous blade assembly further comprises a lower reinforcing element extending in the thickness direction between the two skins in the flange portion, said lower reinforcing element being co-densified with the rest of the fibrous blade assembly.

[0033] The lower reinforcing element makes it possible to improve the hold of the flange, by reducing the stresses at the junction part of the blade and by limiting the opening between the two skins. Brief description of the drawings

[0034] [Fig-1] [Fig.l] is a schematic perspective view illustrating the weaving of a fiber blank for the manufacture of the main fiber blade preform.

[0035] [Fig.2] [Fig.2] is a schematic front view of the fiber blank of [Fig.l]

[0036] [Fig.3] [Fig.3] is a schematic side view of the fiber blank of figures 1 and 2.

[0037] [Fig.4] [Fig.4] is a diagram detailing the shaping of the fiber blank of Figures 1 to 3 into the main fiber blade preform.

[0038] [Fig.5] [Fig.5] is a schematic sectional view illustrating the superposition of the external reinforcing element fiber preforms on the main blade fiber preform of [Fig.4].

[0039] [Fig.6] [Fig.6] is a schematic sectional view illustrating the positioning of a lower reinforcing element on the assembly comprising the main blade fiber preform and the external reinforcing element fiber preforms.

[0040] [Fig.7] [Fig.7] is a schematic sectional view illustrating the resulting blade. Description of the embodiments

[0041] The invention applies generally to the production of a turbomachine blade made of composite material, including the production of a propeller blade.

[0042] The invention finds an advantageous application for stator blades, called vanes fixed, for example for the rectifier blades. The blade of the invention may be an OGV type distributor blade, for "outlet guide vane" in English, in the case of a ducted engine. The blade of the invention may also be a stator blade of an unducted engine. The blade of the invention may thus be a blade of a UDF type turboprop comprising two unducted and counter-rotating fans, or of a USF type turboprop comprising a single unducted fan and a rectifier. The blade of the invention may be a propeller blade.

[0043] The method of the invention comprises a shaping step making it possible to obtain a main fiber preform comprising at least two skins.

[0044] The main fiber preform can be obtained by shaping a fiber blank 100.

[0045] The fibrous blank 100 can be obtained, as schematically illustrated in [Fig.l], by three-dimensional (3D) weaving carried out in a known manner using a jacquard-type loom on which a bundle of warp threads 101 or strands has been arranged in a plurality of layers of several hundred threads each, the warp threads being linked by weft threads 102. The fibrous blank 100 is preferably woven in a single piece, in order to improve its mechanical characteristics.

[0046] By "three-dimensional weaving" is meant here a weaving method by which at least some of the warp threads bind weft threads over several weft layers. It is considered that a fiber blank produced by three-dimensional weaving may comprise another type of weaving on its surface, for example two-dimensional weaving, in order to improve its surface condition.

[0047] Preferably, the three-dimensional weave used is an "interlock" weave. By "interlock" we mean here a weave weave in which each layer of warp threads links several layers of weft threads with all the threads of the same warp column having the same movement in the plane of the weave.

[0048] Other known types of three-dimensional weaving may be used, such as those described in document WO 2006 / 136755. This document describes in particular the production by weaving in a single piece of fiber reinforcement structures for parts such as blades having a first type of core armor and a second type of skin armor which make it possible to confer both the mechanical and aerodynamic properties expected for this type of part.

[0049] The fiber blank 100 extends in a radial direction DR, corresponding to the span direction of the blade to be manufactured, between a lower edge 100a and an upper edge 100b. The fiber blank 100 extends in an axial direction DA, corresponding to the chord direction of the blade to be manufactured, between a first lateral edge 100c and a second lateral edge 100d.

[0050] During weaving, a delinking 106 can be carried out in a well-known manner at the interior of the fibrous blank 100 between two successive layers of warp threads. Thus, the uncoupling 106 extends along a plane parallel to the surface of the fibrous blank 100. The uncoupling 106 thus locally separates a first skin 110 and a second skin 120. The first skin 110 is intended to form the intrados of the blade and the second skin 120 is intended to form the extrados of the blade.

[0051] The disconnection 106 opens onto the lower edge 100a and onto a portion of the lateral edges 100c and 100d adjacent to the lower edge 100a. Thus, the first skin 110 comprises a first portion 111 connected by the lateral edges 100c and 100d to a first portion 121 of the second skin 120, as illustrated in FIGS. 2 and 3. The first skin 110 also comprises a second portion 112 not connected to a second portion 122 of the second skin 120 by the lateral edges 100c and 100d. The first portion 111 of the first skin 110 extends from the upper edge 100b and the second portion 112 of the first skin 110 extends from the lower edge 100a. The first portion 121 of the second skin 120 extends from the upper edge 100b and the second portion 122 of the second skin 120 extends from the lower edge 100a.

[0052] Once the weaving is finished, the non-woven threads present around the fibrous blank 100 are cut to extract said blank, as illustrated in [Fig.2]. The uncoupling 106 thus forms a single internal housing 160a in the fibrous blank 100, accessible via the lower edge 100a.

[0053] The obtained fiber blank 100 is then shaped so as to obtain a main fiber blade preform 200.

[0054] The main fiber preform 200 may comprise a plurality of threads of various types, in particular ceramic, glass or carbon threads or a mixture of such threads. Preferably, the main fiber preform 200 may be made from carbon fibers. Generally, the main fiber preform 200 may also be made from fibers made of the following materials: alumina, mullite, silica, silicon carbide, an aluminosilicate, a borosilicate, carbon, or a mixture of several of these materials. The main fiber preform 200 may be made by three-dimensional weaving.

[0055] As illustrated in [Fig.4], the fiber blank 100 is shaped to obtain the main fiber preform 200. The main blade fiber preform 200 comprises a first skin 210 obtained by shaping the first skin 110 of the fiber blank 100 and a second skin 220 obtained by shaping the second skin 120 of the fiber blank 100. The shaping is carried out so as to obtain a main fiber preform 200 comprising, in the radial direction DR, a flange portion 201, a joining part portion 202 and an aerodynamic profile portion 203.

[0056] The flange portion 201 is intended to form a part of the fibrous reinforcement of the flange. of the blade. The joining part portion 202 is intended to form a part of the fiber reinforcement of the joining part of the blade. The aerodynamic profile portion 203 is intended to form the fiber reinforcement of the aerodynamic profile of the blade.

[0057] The joining part portion 202 connects the flange portion 201 to the aerodynamic profile portion 203. The flange portion 201 comprises two parts 201a and 201b extending on either side of the aerodynamic profile portion 203 in a thickness direction DE perpendicular to the axial DA and radial DR directions.

[0058] The distance between the first and second skins 210 and 220 is defined along the thickness direction DE. The distance between the first and second skins 210 and 220 may be adapted, for example by introducing a shaping element inside the uncoupling 106. The shaping element may for example be a foam. The shaping element may be made of a fugitive material which will be eliminated, so that the shaping element is not present in the final blade.

[0059] In the joining part portion 202 of the main fiber preform 200, the distance between the first and second skins 210 and 220 decreases from the boundary between the aerodynamic profile portion 203 and the joining part portion 202 along the radial direction DR until reaching a minimum distance.

[0060] In the airfoil portion 203 of the main fiber preform 200, the distance between the first and second skins 210 and 220 may vary. In particular, the distance between the first and second skins 210 and 220 in the airfoil portion 203 may start to decrease along the radial direction DR up to the boundary between the airfoil portion 203 and the joining portion portion 202. Thus, the distance between the first and second skins 210 and 220 may decrease continuously from the airfoil portion 203 to the joining portion portion 202.

[0061] The reduction in the distance between the first and second skins 210 and 220 can be achieved asymmetrically.

[0062] [Fig.4] illustrates a surface N extending along the radial direction DR and along the axial direction DA. The surface N corresponds to a neutral surface of the final blade subjected to low mechanical stresses. Thus, the surface N corresponds to a surface of the final blade which will be lightly loaded mechanically, undergoing few static and vibratory stresses, and subjected to little shock.

[0063] By reducing the distance between the first and second skins 210 and 220, said skins 210 and 220 are brought closer to the surface N. Consequently, the skins 210 and 220 in the final blade will be subjected to lower mechanical stresses at the junction portion of the blade. However, the junction portion of the blade is a part of the blade that is particularly subjected to mechanical stresses, particularly in tension and compression. Therefore, a reduction in the mechanical stresses on the skins in the junction part of the blade allows for thinner skins.

[0064] The minimum distance may be located at the boundary between the joining part portion 202 and the flange portion 201 of the main fiber preform 200. On the contrary, the distance between the first and second skins 210 and 220 may increase from the minimum distance along the radial direction DR to the boundary between the joining part portion 202 and the flange portion 201 of the main fiber preform 200, in order to allow the formation of the flange portion 201. In particular, the distance between the first and second skins 210 and 220 may increase from the minimum distance along the radial direction DR to the lower end of the main fiber preform 200.

[0065] Preferably, the reduction in the distance between the first and second skins 210 and 220 is done symmetrically between the first skin 210 and the second skin 220.

[0066] The minimum distance may be zero. Thus, in the joining part portion 202, the first skin 210 of the main fiber preform 200 comprises a portion in contact with a portion of the second skin 220 of the main fiber preform 200. Said portions of the first skin 210 and of the second skin 220 in contact are called “contact portions”. The contact portions of the first and second skins 210 and 220 may be bonded together, for example by sewing with fibers. Said bonding fibers are preferably of the same nature as the fibers of the first and second skins 210 and 220. The contact portions of the first and second skins 210 and 220 may also be unbonded.

[0067] The reduction in the distance between the first and second skins 210 and 220 may create a first outer hollow 202a at the first skin 210 relative to the aerodynamic profile portion 203 and a second outer hollow 202b at the second skin 220 relative to the aerodynamic profile portion 203. The first outer hollow 202a extends in the thickness direction DE between the first skin 210 and an imaginary surface extending the outer surface of the first skin 210 belonging to the aerodynamic profile portion 203 to the flange portion 201. Similarly, the second outer hollow 202b extends in the thickness direction DE between the second skin 220 and a imaginary surface extending the outer surface of the second skin 220 belonging to the aerodynamic profile portion 203 to the flange portion 201.

[0068] In the case where the reduction in the distance between the first and second skins 210 and 220 starts from the aerodynamic profile portion 203, it can be considered that the first outer hollow 202a also includes the narrower part of the aerodynamic profile portion 203 directly positioned near the joining part portion 202, if this corresponds to a continuous hollow. Similarly, in the case where the di reduction of the distance between the first and second skins 210 and 220 starts from the aerodynamic profile portion 203, it can be considered that the second outer hollow 202b also includes the narrower part of the aerodynamic profile portion 203 directly positioned near the joining part portion 202, if this corresponds to a continuous hollow.

[0069] Increasing the distance between the first and second skins 210 and 220 after the minimum distance to obtain the flange portion 201 creates a lower space 201c between the first and second skins 210 and 220 in the lower part of the blade. This lower space extends in the thickness direction DE between the first skin 210 and the second skin 220, and extends in the radial direction DR from the minimum distance between the skins 210 and 220 to the lower end of the main preform 200.

[0070] When the fiber blank 100 is obtained as described above, the main fiber preform 200 is obtained by folding the second parts 112 and 122 of the first and second skins 110 and 120 outwardly, so that the second parts 112 and 122 of the first and second skins 110 and 120 extend oppositely along the thickness direction DE, as illustrated in [Fig. 4]. Furthermore, at least one of the first and second skins 110 and 120 is shaped so as to change the distance between them along the thickness direction DE at the joining part portion 202, in accordance with what is described above. Preferably, the first skin 110 and the second skin 120 are shaped so as to modify the distance between them along the thickness direction DE at the joining part portion 202, in accordance with what is described above.

[0071] The method of the invention comprises a step of superimposing at least one external reinforcing element fiber preform 510 or 520 on the main fiber preform 200, as illustrated in [Fig. 5]. Preferably, as illustrated in [Fig. 5], two external reinforcing element fiber preforms 510 and 520 are superimposed on the main fiber preform 200. Thus, the remainder of the description will describe the case of two external reinforcing elements. Those skilled in the art will easily understand that the characteristics indicated below can easily be applied to the case of a single reinforcing element.

[0072] The superposition step can be carried out simultaneously with the preceding shaping step. In particular, the arrangement of the two external reinforcing element fiber preforms 510 and 520 on the main fiber preform 200 can be carried out so as to deform the main fiber preform 200 so as to obtain the adequate variation in distance between the two skins 210 and 220 along the thickness direction DE at the level of the joining part portion 202.

[0073] The fiber preforms of external reinforcing elements 510 and 520 are preferably made by three-dimensional weaving. The fiber preforms of external reinforcing elements 510 and 520 are preferably made with the same fibers. Thus, the fiber preforms of external reinforcing elements 510 and 520 are preferably made with fibers of the same size and made from the same material.

[0074] In order to facilitate the implementation of the method of the invention and to reduce its cost, the first external reinforcing element fiber preform 510 may be identical to the second external reinforcing element fiber preform 520.

[0075] The fiber preforms of external reinforcing elements 510 and 520 may each comprise a plurality of threads of various types, in particular ceramic, glass or carbon threads or a mixture of such threads. Preferably, they may be made from carbon fibers. Generally, they may also be made from fibers made of the following materials: alumina, mullite, silica, silicon carbide, an aluminosilicate, a borosilicate, carbon, or a mixture of several of these materials.

[0076] In particular, the fiber preforms of external reinforcing elements 510 and 520 can be obtained from flat fiber blanks, which are curved to obtain the fiber preforms of external reinforcing elements 510 and 520. Such flat fiber blanks can be produced in a well-known manner using a jacquard-type loom. Each flat fiber blank then has a thickness which decreases at one of its ends.

[0077] The external reinforcing fiber preforms 510 and 520 are arranged in contact with the main fiber preform 200.

[0078] The first external reinforcing fiber preform 510 is arranged in contact with the first skin 210 in the joining part portion 202 and in the flange portion 201. The first external reinforcing fiber preform 510 is arranged so as to cover the joining part portion 202 and the flange portion 201. Preferably, the first external reinforcing fiber preform 510 covers the first skin 210 completely at the joining part portion 202 and the flange portion 201. However, it is not outside the scope of the invention if the first external reinforcing fiber preform 510 covers only a part of the flange portion 201.

[0079] The first external reinforcing fiber preform 510 comprises an inner surface and an outer surface. The inner surface of the first external reinforcing fiber preform 510 is in contact with the first skin 210 at the junction portion 202 and the flange portion 201. The outer surface of the first external reinforcing fiber preform 510 is located in the extension of the aerodynamic profile portion 203. Thus, the outer surface of the first skin 210 at the aerodynamic profile 203 is extended by the outer surface of the first external reinforcing preform 510 at the flange portion 201. joining portion 202 so as to ensure continuity of the outer surface. Thus, the first external reinforcing fiber preform 510 fills the first external hollow 202a.

[0080] The second external reinforcing fiber preform 520 is arranged in contact with the second skin 220 in the joining part portion 202 and in the flange portion 201. The second external reinforcing fiber preform 520 is arranged so as to cover the joining part portion 202 and the flange portion 201. Preferably, the second external reinforcing fiber preform 520 covers the second skin 220 completely at the joining part portion 202 and the flange portion 201. However, it is not outside the scope of the invention if the second external reinforcing fiber preform 520 covers only a part of the flange portion 201.

[0081] The second external reinforcing fiber preform 520 comprises an inner surface and an outer surface. The inner surface of the second external reinforcing fiber preform 520 is in contact with the second skin 220 at the junction portion 202 and the flange portion 201. The outer surface of the second external reinforcing fiber preform 520 is located in the extension of the aerodynamic profile portion 203. Thus, the outer surface of the second skin 220 at the aerodynamic profile 203 is extended by the outer surface of the second external reinforcing preform 520 at the junction portion 202 so as to ensure continuity of the outer surface. Thus, the second external reinforcing fiber preform 520 fills the second outer hollow 202b.

[0082] According to a particular embodiment of the invention illustrated in [Fig.6], a lower reinforcing element 700 may be arranged in contact with the main fiber preform 200. The lower reinforcing element 700 is arranged in the lower space 201c. The lower reinforcing element 700 fills the lower space 201c.

[0083] The lower reinforcing element 700 may be a fibrous reinforcement. In this case, the lower reinforcing element may be made by weaving, in particular by three-dimensional weaving. The lower reinforcing element 700 will then be co-densified with the fibrous preforms of reinforcing elements 510 and 520 and with the main fibrous preform 200 by the same matrix. The lower reinforcing element 700 may also be made with short fibers dispersed in a matrix. The lower reinforcing element 700 may also be made of other materials, for example metal.

[0084] According to a particular embodiment of the invention illustrated in [Fig.6], a reinforcing plate 800 can be arranged in contact with the main fiber preform 200. The reinforcing plate 800 extends along the thickness direction DE and perpendicular to the radial direction DR. The reinforcing plate 800 is arranged in contact of the two parts 201a and 201b of the flange portion 201 of the main fiber preform 200. Thus, the reinforcing plate 800 covers the lower part of the main fiber preform 200.

[0085] The reinforcing plate 800 may be a fibrous reinforcement. In this case, the reinforcing plate 800 may be made by weaving, in particular by three-dimensional weaving. The reinforcing plate 800 will then be co-densified with the fibrous preforms of reinforcing elements 510 and 520 and with the main fibrous preform 200 by the same matrix. The reinforcing plate 800 may also be made with short fibers dispersed in a matrix. The reinforcing plate 800 may also be made of other materials, for example metal.

[0086] The reinforcing plate 800 may have homogeneous mechanical properties along the thickness direction DE and along the direction perpendicular to the thickness direction DE and to the radial direction DR. On the contrary, the reinforcing plate 800 may also comprise different mechanical properties in some of its portions, for example in order to reinforce the mechanical properties in certain directions.

[0087] A fibrous blade assembly 300 is thus obtained as illustrated in [Fig.5] or 6, comprising, in the radial direction DR, a fibrous flange preform 301, a fibrous junction part preform 302 and a fibrous aerodynamic profile preform 303.

[0088] The flange fiber preform 301 is intended to form the fiber reinforcement of the flange of the blade. The joining portion fiber preform 302 is intended to form the fiber reinforcement of the joining portion of the blade. The aerodynamic profile fiber preform 303 is intended to form the fiber reinforcement of the aerodynamic profile of the blade.

[0089] The flange fiber preform 301 is formed by the flange portion 201 of the main fiber preform 200 and by a portion of the external reinforcing element fiber preforms 510 and 520. Optionally, the flange fiber preform 301 may comprise the lower reinforcing element or at least a portion of the lower reinforcing element. Optionally, the flange fiber preform 301 may comprise the reinforcing plate 800. The joining portion fiber preform 302 is formed by the joining portion portion 202 of the main fiber preform 200 and by a portion of the external reinforcing element fiber preforms 510 and 520. The airfoil fiber preform 303 is formed by the airfoil portion 203 of the main fiber preform 200.

[0090] The surface N illustrated in Figures 5 and 6 corresponds to a neutral surface of the final blade subjected to low mechanical stresses. Thus, the surface N corresponds to a surface of the final blade which will be lightly loaded mechanically, undergoing little static and vibratory constraints, and little subject to shocks.

[0091] The fibrous preform of the joining portion 302 will be particularly subject to mechanical stresses, in particular in tension and compression. By arranging the contact interface between the fibrous preforms of external reinforcing elements 510 and 520 and the portion of the joining portion 202 of the main preform 200 close to the surface N, the risk of separation in operation between the preforms of external reinforcing elements 510 and 520 and the main preform 200 is reduced. In addition, by bringing the skins 210 and 220 closer to the surface N in the fibrous preform of the joining portion, they are subjected to little mechanical stress. The mechanical stresses in the fibrous preform of the joining portion 302 are mainly supported by the fibrous preforms of external reinforcing elements 510 and 520.Similarly, the mechanical stresses in the flange fiber preform 301 are primarily supported by the external reinforcing element fiber preforms 510 and 520. Thus, the skins 210 and 220 do not need to be thicker at the joining portion or the flange, making them easier to manufacture. The skins 210 and 220 can thus be thin over the entire height of the final blade.

[0092] The blade fibrous assembly 300 is then co-densified by a matrix. Preferably, the blade to be produced is mainly made of organic matrix composite (OMC) material: the blade fibrous assembly 300 is then co-densified by an organic matrix. It is of course not outside the scope of the invention if the blade to be produced is mainly made of ceramic matrix composite (CMC) material. In this case, the blade fibrous assembly 300 is co-densified by a ceramic matrix.

[0093] In a well-known manner, the co-densification of the fiber blade assembly 300 can be carried out by injection.

[0094] The fibrous blade assembly 300 is then placed in an injection tool which comprises a first shell comprising in its center a first imprint corresponding in part to the shape and dimensions of the blade to be produced and a second shell comprising in its center a second imprint corresponding in part to the shape and dimensions of the blade to be produced.

[0095] Once the tooling is closed, the first and second impressions and respectively the first and second shells together define a molding cavity having the shape of the blade to be produced and in which the fiber blade assembly 300 is held.

[0096] The densification of the blade fibrous assembly 300 consists of filling its porosities with the material constituting the matrix. This densification is carried out in a manner known per se according to the liquid process (LC). The liquid process consists of impregnating the blade fibrous assembly 300 with a liquid composition containing a precursor of the matrix material. The precursor usually appears- actually in the form of a polymer, such as a high-performance epoxy resin.

[0097] The transformation of the precursor into a matrix, namely its polymerization, is carried out by heat treatment, generally by heating the injection tooling, after removal of any solvent and crosslinking of the polymer, the fibrous blade assembly 300 still being maintained in the molding cavity having a shape corresponding to that of the part to be produced.

[0098] In the case of the formation of a carbon or ceramic matrix, the heat treatment consists of pyrolyzing the precursor to transform the matrix into a carbon or ceramic matrix depending on the precursor used and the pyrolysis conditions. For example, liquid ceramic precursors, in particular SiC, may be resins of the polycarbosilane (PCS) or polytitanocarbosilane (PTCS) or polysilazane (PSZ) type, while liquid carbon precursors may be resins with a relatively high coke content, such as phenolic resins. Several consecutive cycles, from impregnation to heat treatment, may be carried out to achieve the desired degree of densification.

[0099] According to one aspect of the invention, the densification of the fibrous blade assembly 300 can be carried out by the well-known transfer molding process known as RTM ("Resin Transfer Molding"). According to the RTM process, the fibrous blade assembly 300 is placed in a mold having the external shape of the part to be produced. A thermosetting resin is injected into the internal space of the mold which comprises the fibrous blade assembly 300. A pressure gradient is generally established in this internal space between the place where the resin is injected and the orifices for discharging the latter in order to control and optimize the impregnation of the fibrous blade assembly 300 by the resin.

[0100] According to the RTM method, a resin, for example a thermosetting resin, is injected via the injection port of the first shell into the molding cavity occupied by the fiber blade assembly 300. Before injecting the resin, the molding cavity is placed under vacuum, for example via the port of the second shell which is connected to a vacuum draw duct. This configuration allows the establishment of a pressure gradient between the lower part of the fiber blade assembly 300 where the resin is injected and the upper part of the fiber blade assembly 300 located near the injection port. In this way, the resin injected substantially at the level of the lower part of the fiber blade assembly 300 will gradually impregnate the entire fiber blade assembly 300 by circulating therein to the discharge port through which the surplus is discharged.Of course, the first and second shells of the tooling may include several injection ports and several evacuation ports.

[0101] The resin used may be, for example, an epoxy resin of temperature class 180 °C (maximum temperature supported without loss of characteristics). Resins suitable for RTM processes are well known. They preferably have a low viscosity to facilitate their injection into the fibers. The choice of temperature class and / or the chemical nature of the resin is determined according to the thermomechanical stresses to which the part must be subjected. Once the resin has been injected throughout the reinforcement, it is polymerized by heat treatment in accordance with the RTM process.

[0102] The injection of the resin into the fibrous blade assembly 300 and its transformation into a matrix allows the densification or consolidation of the fibrous blade assembly 300.

[0103] After injection and polymerization, the blade is demolded. Finally, the blade can be trimmed to remove excess resin and holes can be made. A blade 30 is then obtained as illustrated in [Fig.7], made of composite material comprising a first skin 21 and a second skin 22, as well as a first external reinforcing element 51 and possibly a second external reinforcing element 52, and possibly a lower reinforcing element 70 or a reinforcing plate 80, all bound by the same matrix.

[0104] The first skin 21 of the blade 30 is formed by the first skin 210 of the main preform 200 densified by the matrix. The second skin 22 of the blade 30 is formed by the second skin 220 of the main preform 200 densified by the matrix. The first external reinforcing element 51 is formed by the first external reinforcing preform 510 densified by the matrix. The second external reinforcing element 52 is formed by the second external reinforcing preform 520 densified by the matrix. The lower reinforcing element 70 corresponds to the lower reinforcing element 70 described previously, densified or not by the matrix depending on its nature. The reinforcing plate 80 corresponds to the reinforcing plate 800 described previously, densified or not by the matrix depending on its nature.

[0105] The blade 30 thus comprises, along the radial direction DR, a flange 31, a joining part 32 and an aerodynamic profile 33, the joining part 32 connecting the flange 31 to the aerodynamic profile 33.

[0106] The fiber reinforcement of the flange 31 of the blade 30 is formed by the flange portion 201 of the main fiber preform 200 and by a portion of the fiber preforms of external reinforcing elements 510 and 520. If necessary, the flange 31 may comprise the lower reinforcing element or at least a portion of the lower reinforcing element. The fiber reinforcement of the joining portion 32 of the blade 30 is formed by the joining portion portion 202 of the main fiber preform 200 and by a portion of the fiber preforms of external reinforcing elements 510 and 520. The fiber reinforcement of the aerodynamic profile 33 of the blade 30 is formed by the aerodynamic profile portion 203 of the main fiber preform 200.

[0107] In the junction portion 32 of the blade 30, the distance between the first and second skins 21 and 22 decreases from the limit between the aerodynamic profile 33 and the junction portion 32 along the radial direction DR until reaching a minimum distance.

[0108] In the airfoil 33 of the blade 30, the distance between the first and second skins 21 and 22 may vary. In particular, the distance between the first and second skins 21 and 22 in the airfoil 33 may start to decrease along the radial direction DR up to the boundary between the airfoil 33 and the joining portion 32. Thus, the distance between the first and second skins 21 and 22 may decrease continuously from the airfoil 33 to the joining portion 32. The minimum distance may be located at the boundary between the joining portion 32 and the flange 31 of the blade 30. On the contrary, the distance between the first and second skins 21 and 22 may increase from the minimum distance along the radial direction DR up to the boundary between the joining portion 32 and the flange 31 of the blade 30.In particular, the distance between the first and second skins 21 and 22 may increase from the minimum distance along the radial direction DR to the lower end of the blade 30.

[0109] Preferably, the reduction in the distance between the first and second skins 21 and 22 is done symmetrically between the first skin 21 and the second skin 22. The reduction in the distance between the first and second skins 21 and 22 can also be done asymmetrically.

[0110] The minimum distance may be zero. Thus, in the joining portion 32, the first skin 21 comprises a portion in contact with a portion of the second skin 22. Said portions of the first skin 21 and the second skin 22 in contact are called “contact portions”. The contact portions of the first and second skins 21 and 22 may be bonded together, for example by fibers. Said bonding fibers are preferably of the same nature as the fibers of the first and second skins 21 and 22. The contact portions of the first and second skins 21 and 22 may also be unbonded.

[0111] The reduction in the distance between the first and second skins 21 and 22 may create a first external hollow at the level of the first skin 21 relative to the aerodynamic profile portion 33 and a second external hollow at the level of the second skin 22 relative to the aerodynamic profile portion 33. The first external hollow extends in the thickness direction DE between the first skin 21 and an imaginary surface extending the external surface of the first skin 21 belonging to the aerodynamic profile 33 to the flange 31. Similarly, the second external hollow extends in the thickness direction DE between the second skin 22 and a imaginary surface extending the external surface of the second skin 22 belonging to the aerodynamic profile 33 to the flange 31.

[0112] In the case where the reduction in the distance between the first and second skins 21 and 22 begins from the aerodynamic profile 33, it can be considered that the first outer hollow 202a also includes the narrower part of the aerodynamic profile 33 directly positioned near the junction part 32, if this corresponds to a continuous hollow. Similarly, in the case where the reduction in the distance between the first and second skins 21 and 22 begins from the aerodynamic profile 33, it can be considered that the second outer hollow 202b also includes the narrower part of the aerodynamic profile 33 directly positioned near the junction part 32, if this corresponds to a continuous hollow.

[0113] The first external reinforcing element 51 is arranged in contact with the first skin 21 in the junction portion 32 and in the flange 31. The first external reinforcing element 51 is arranged so as to cover the junction portion 32 and the flange 31. Preferably, the first external reinforcing element 51 covers the first skin 21 in its entirety at the junction portion 32 and the flange 31. The first external reinforcing element 51 comprises an inner surface and an outer surface. The inner surface of the first external reinforcing element 51 is in contact with the first skin 21 at the junction portion 32 and the flange 31. The outer surface of the first external reinforcing element 51 is located in the extension of the aerodynamic profile 33.Thus, the outer surface of the first skin 21 at the level of the aerodynamic profile 33 is extended by the outer surface of the first external reinforcing element 51 at the level of the junction part 32 so as to ensure continuity of the outer surface. Thus, the first external reinforcing element 51 fills the first external hollow.

[0114] The second external reinforcing element 52 is arranged in contact with the second skin 22 in the junction portion 32 and in the flange 31. The second external reinforcing element 52 is arranged so as to cover the junction portion 32 and the flange 31. Preferably, the second external reinforcing element 52 covers the second skin 22 in its entirety at the junction portion 32 and the flange 31. The second external reinforcing element 52 comprises an inner surface and an outer surface. The inner surface of the second external reinforcing element 52 is in contact with the second skin 22 at the junction portion 32 and the flange 31. The outer surface of the second external reinforcing element 52 is located in the extension of the aerodynamic profile 33.Thus, the outer surface of the second skin 22 at the level of the aerodynamic profile 33 is extended by the outer surface of the second external reinforcing element 52 at the level of the junction portion 32 so as to ensure continuity of the outer surface. Thus, the second external reinforcing element 52 fills the second external hollow.

[0115] The surface N illustrated in [Fig.7] corresponds to a neutral surface of the blade 30 subjected to low mechanical constraints. Thus, the surface N corresponds to a surface of the blade 30 which will be lightly loaded mechanically, undergoing few static and vibratory constraints, and subjected to little shock.

[0116] The junction portion 32 will be particularly subject to mechanical stresses, in particular in traction and compression. By arranging the contact interface between the external reinforcing elements 51 and 52 and the rest of the blade 30 close to the surface N, the risk of the external reinforcing elements 51 and 52 becoming detached during operation is reduced. In addition, by bringing the skins 21 and 22 closer to the surface N in the junction portion 32, they are subject to little mechanical stress. The mechanical stresses in the joining portion 32 are mainly supported by the external reinforcing elements 51 and 52. Similarly, the mechanical stresses in the flange 31 of the blade 30 are mainly supported by the external reinforcing elements 51 and 52. Thus, the skins 21 and 22 do not need to be thicker at the joining portion 32 or the flange 31, which facilitates their manufacture.The skins 21 and 22 can thus be thin over the entire height of the blade 30.

Claims

Claims

1. A blade (30) made of composite material comprising, in a radial direction (DR), a flange (31), a joining portion (32) and an aerodynamic profile (33), the joining portion (32) connecting the flange (31) to the aerodynamic profile (33), the blade (30) comprising two skins (21, 22) comprising a fibrous reinforcement densified by a matrix, the two skins (21, 22) being present on the surface of the aerodynamic profile (33) and respectively forming the intrados and the extrados of the blade (30), the two skins (21, 22) also forming a portion of the joining portion (32) and a portion of the flange (31), the blade (30) being characterized in that the distance between the two skins (21, 22) in the joining portion (32) of the blade (30) in a thickness direction (DE) perpendicular to the radial direction (DR) decreases from the boundary between the aerodynamic profile (33) and the joining part (32) until reaching a minimum distance,the blade (30) further comprising at least one first external reinforcing element (51) made of fibrous reinforcement densified by the matrix superimposed on one of the skins (21) at least at the level of the junction part (32) and the flange (31) so as to ensure continuity of the external surface of the blade (30).,

2. Blade according to claim 1, the blade (30) further comprising a second external reinforcing element (52) made of fibrous reinforcement densified by the matrix superimposed on the other skin (22) at least at the level of the junction part (32) and the flange (31) so as to ensure continuity of the external surface of the blade (30).

3. A blade according to claim 1 or 2, wherein the minimum distance is zero so that the two skins (21, 22) are in contact.

4. A blade according to claim 3, wherein the portions of the skins (21, 22) which are in contact in the joining part (32) are bonded by fibers.

5. Blade according to any one of claims 1 to 4, in which the external reinforcing elements (51, 52) are produced by three-dimensional weaving.

6. Blade according to any one of claims 1 to 5, in which a lower reinforcing element (70) is present in the flange (31) and extends in the thickness direction (DE) between the two skins (21, 22).

7. A blade according to any one of claims 1 to 6, the flange (31) of the blade further comprising a reinforcing plate (80) perpendicular to the radial direction (DR) held in contact with the end of the two skins (21, 22).

8. A method of manufacturing a blade (30) made of composite material, the method comprising: - shaping a fiber blank (100) into a main fiber blade preform (200) comprising at least two skins (210, 220) so as to form, in a radial direction (DR), a flange portion (201), a joining portion (202) and an aerodynamic profile portion (203), the distance between the two skins (210, 220) in the joining portion (202) in a thickness direction (DE) perpendicular to the radial direction (DR) decreasing from the boundary between the aerodynamic profile portion (203) and the joining portion (202) until a minimum distance is reached, - superimposing a first and a second fiber preform of external reinforcing elements (510, 520) respectively on one and the other of the two skins (210,220) at least at the level of the joining part portion (202) and the flange portion (201) so as to obtain a fibrous blade assembly (300) with continuous external surfaces, then - co-densification by a matrix of the fibrous blade assembly (300), so as to obtain a blade (30) made of composite material comprising two external reinforcing elements (51, 52).,

9. Manufacturing method according to claim 8, in which the minimum distance is zero so that the two skins (210, 220) are in contact.

10. A manufacturing method according to claim 9, further comprising bonding the portions of the skins (210, 220) which are in contact in the joining part portion (202) by fibers.

11. Manufacturing method according to any one of claims 8 to 10, in which the two fiber preforms of external reinforcing elements (510, 520) are produced by three-dimensional weaving.

12. A manufacturing method according to any one of claims 8 to 11, wherein the blade fiber assembly (300) further comprises a lower reinforcing element (700) extending in the thickness direction (DE) between the two skins (210, 220) in the flange portion (201), said lower reinforcing element (700) being co-densified with the remainder of the blade fiber assembly (300).

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