Fibrous assembly having improved weaving for a belted mechanical part

Abstract

The invention relates to a fibrous assembly (200) intended to form the reinforcement of a part (100) made of composite material, the fibrous assembly (200) comprising a fibrous core preform (210) produced by three-dimensional weaving, at least one opening (231) which is adjacent to the fibrous core preform (210) and is intended to be passed through by a shaft in order to produce a connection, and a fibrous belt preform (220) surrounding the fibrous core preform (210) and said at least one opening (231), the fibrous core preform (210) comprising a central portion (211) in which the warp threads (211c) or weft threads have a first shrinkage and at least one flexible portion (212), present between the fibrous belt preform (220) and the central portion (211) and extending from the opening (231), in which the warp threads (212c) or weft threads have a second shrinkage which is greater than the first shrinkage.

Description

Description Title of the invention: Fibrous assembly with an improved weave for a belted mechanical part Technical Field

[0001] The present invention relates to a part made of composite material intended to be articulated with one or more other parts at its ends, in particular a connecting rod, a brake bar or a landing gear lever. Previous technique

[0002] Figure 1 shows a landing gear comprising two struts 1 and 1', respectively called the main strut and the lateral strut. These struts are articulated to the landing gear leg 4 and the landing gear frame 5. Each strut 1 and 1' is formed of two connecting rods, as illustrated in Figure 2. Thus, strut 1 comprises an upper connecting rod 3 and a lower connecting rod 2. The connecting rods of a strut are articulated to each other and to other landing gear components at their ends by means of pivot pins. Such connecting rods are subjected to significant mechanical stresses during operation, primarily compression and tension, oriented along the longitudinal axis of the component.

[0003] These connecting rods were traditionally made from steel, aluminum, or titanium alloys. To reduce their weight, they can now be made from composite materials. Indeed, manufacturing connecting rods from composite materials allows for lighter rods than metal ones while maintaining good mechanical properties. Composite connecting rods are therefore easier to operate during landing gear movement and help reduce the aircraft's mass, thus lowering fuel consumption.

[0004] Documents FR 2 887 601 A1 and FR 3 017 819 describe such connecting rods made of composite material, comprising a core surrounded by a belt, the fibrous reinforcements of the core and the belt being produced by three-dimensional weaving and then co- injected. Figure 3 illustrates an example of a connecting rod made of composite material according to the prior art comprising a web A, a ring B located in the extension of the web A and allowing articulation with another part and a belt C surrounding the web A and the ring B.

[0005] It was observed that, during operation and under significant stress, cracks F could appear on the connecting rod at the interface between the web A and the belt C, said cracks generally extending from the ring B, as illustrated in Figure 3. Description of the invention

[0006] It was observed that these cracks could be caused by a high concentration of stress at the interface between the web, the belt, and the ring orifice under significant loads. Indeed, it was found that the fibrous reinforcements of the web and the belt did not deform in the same way, thus generating significant shear stresses at the web-belt interface, as well as opening and closing stresses. These stresses at the web-belt interface are caused, for example, by the difference in fiber orientation between the web and the belt near the interface, and by the different coefficients of thermal expansion on either side of the interface. Furthermore, it was observed that these cracks could be exacerbated by residual manufacturing stresses.These residual stresses appear particularly during the cooling of the part during its manufacturing process.

[0007] The invention therefore aims to prevent the formation of cracks at the interface between the core and the belt, or at least to increase the tensile or compressive load supported by the part in order to delay the appearance of cracks.

[0008] To this end, the invention proposes a fibrous assembly intended to form the fibrous reinforcement of a mechanical part made of composite material, the fibrous assembly comprising a fibrous core preform having a three-dimensional weave extending along a longitudinal direction and at least one orifice extending along a thickness direction perpendicular to the longitudinal direction, said assembly at least one orifice being adjacent to the core fiber preform along the longitudinal direction and intended to be traversed by an axis to make a connection with another part, the fiber assembly further comprising a belt fiber preform surrounding the core fiber preform and said at least one orifice, the fiber assembly being characterized in that the core fiber preform comprises a central portion in which the warp yarns, or respectively the weft yarns, have a first bend and at least one flexible portion present between the belt fiber preform and the central portion and extending from the orifice along the longitudinal direction over a determined distance, the warp yarns, or respectively the weft yarns, of said at least one flexible portion having a second bend greater than the first bend.

[0009] Thus, a greater degree of flexibility in the flexible portion compared to the central portion makes the flexible portion less stiff than the central portion. Consequently, the core fiber preform retains a certain stiffness thanks to its central portion, allowing it to adequately withstand compressive forces. The flexible portion softens the area of ​​the core fiber preform most susceptible to cracking, thereby improving the distribution of compressive and tensile loads at the interface between the core fiber preform and the belt fiber preform. Indeed, during operation, the core preform and the belt preform each have their own mechanical function and are subjected to different mechanical stresses to ensure the proper functioning of the component.This solution improves the transmission of forces between the web preform and the belt preform, and significantly limits stress concentrations at the interface between the web and belt preforms. The crack resistance of the final part, whose fiber reinforcement is formed by the entire fiber structure, is thus greatly improved without reducing the overall mechanical properties of said part.

[0010] According to a particular embodiment of the invention, the central portion and said at least one flexible portion are linked together by a common weave in the fibrous core preform.

[0011] This solution does not require the addition of any extra material or separate fiber portion. This allows for cost reduction and maintains ease of manufacturing. Since the specific weaving of the core fiber preform is carried out conventionally on a loom with minimal human intervention, the risk of defects or errors is reduced, while maintaining good repeatability.

[0012] According to another particular embodiment of the invention, the central portion and said at least one flexible portion each comprise an independent woven structure in the fibrous core preform.

[0013] The fibrous belt preform can be positioned in contact with the flexible portion(s) of the fibrous core preform. A third element can be interposed between the fibrous belt preform and the fibrous core preform without departing from the scope of the invention.

[0014] According to a particular embodiment of the invention, the flexible portion extends along the longitudinal direction from the orifice over a distance between 80% and 220% of a reference distance extending between the axis of the orifice and the point on the external surface of the belt preform closest to said axis.

[0015] Indeed, it has been observed that the risk of cracking is limited to an area close to the opening. Therefore, it is unnecessary to unnecessarily extend the flexible section, which could reduce the overall stiffness of the part.

[0016] According to another particular embodiment of the invention, the flexible portion extends along a transverse direction perpendicular to the thickness direction and to the longitudinal direction between the belt preform and the central portion of the core preform over a distance between 4% and 40% of a reference distance extending between the axis of the orifice and the point on the external surface of the belt preform closest to said axis.

[0017] The wider the flexible portion, the more it will dampen stresses at the interface between the web and the belt. However, an excessively wide flexible portion impairs the mechanical performance of the part, particularly when subjected to compressive loading. The overall stiffness of The part is also reduced in size. Such a range of values ​​for the width of the flexible portion thus ensures very satisfactory protection against cracking at the interface between the core preform and the belt preform without significantly reducing the overall mechanical performance of the part.

[0018] According to a particular embodiment of the invention, the weave structure of the fibrous reinforcement of the fibrous core preform is an interlock type weave.

[0019] Thus, the central portion and the flexible portion(s) have the same weave structure.

[0020] Indeed, the implementation of the solution is facilitated with an interlock-type reinforcement. An interlock reinforcement notably facilitates the transition between the central portion and the flexible portion(s) of the fibrous core preform. The interlock reinforcement can also allow for localized plastic deformation near the orifice, and, if necessary, near the ring.

[0021] According to a particular embodiment of the invention, the weave structure of the flexible portion(s) differs from the weave structure of the central portion. In this case, the weave structure of the flexible portion(s) may be an interlock weave, or the weave structure of the central portion may be an interlock weave.

[0022] According to a particular embodiment of the invention, the flexible portion is a first flexible portion, the core preform further comprising a second flexible portion present between the fibrous belt preform and the central portion and extending from the orifice along the longitudinal direction over a determined distance, the first flexible portion and the second flexible portion being located on either side of the central portion, the warp threads of said second flexible portion having a third setting greater than the first setting.

[0023] By using at least two flexible portions on either side of the central portion, crack resistance is improved on both sides of the opening.

[0024] The second and third soakings can be identical. This simplifies the production of the fibrous bundle. The second soaking and the third layering may be different, in order to have better adaptation to the geometry of the part and the mechanical constraints specific to each area.

[0025] According to a particular embodiment of the invention, the central portion of the core preform opens onto the orifice.

[0026] Thus, the stiffness of the fibrous core preform is improved and the absorption of compressive forces is easier, without increasing the risk of cracks in the flexible portions.

[0027] The invention also relates to a mechanical part made of composite material whose fibrous reinforcement is formed by the fibrous assembly as described above densified by a matrix, the core preform densified by the matrix forming a core and the belt preform densified by the matrix forming a belt surrounding the core and at least one orifice.

[0028] According to a particular embodiment, the part further comprises at least one ring disposed in the orifice and adjacent to the core.

[0029] The invention further relates to a method for manufacturing a fibrous assembly intended to form the fibrous reinforcement of a mechanical part made of composite material, comprising:

[0030] - the production by three-dimensional weaving of a fibrous core preform extending along a longitudinal direction comprising a central portion in which the warp yarns have a first settling and comprising at least one flexible portion present at the edge of the fibrous core preform in which the warp yarns have a second settling greater than the first settling,

[0031] - the production of a fibrous preform for the belt,

[0032] - the arrangement of the fibrous belt preform around the fibrous core preform such that the fibrous belt preform delimits at least one cylindrical orifice extending in a thickness direction perpendicular to the longitudinal direction, said at least one cylindrical orifice being adjacent to the fibrous core preform in the longitudinal direction, and such that said at least one flexible portion of the fibrous core preform is between the fibrous belt preform and the central portion of the fibrous core preform and that the at less a flexible portion extends from the cylindrical orifice along the longitudinal direction over a determined distance.

[0033] The fibrous preform of the belt can be produced by three-dimensional weaving.

[0034] Such a manufacturing process can make it possible to obtain the fibrous assembly as described above.

[0035] The invention also relates to a method for manufacturing a mechanical part comprising:

[0036] - the manufacture of a fibrous assembly according to the process as described above,

[0037] - the densification of the fibrous assembly by a matrix while retaining the cylindrical orifice without matrix, so as to obtain a mechanical part in composite material comprising a core, a cylindrical orifice adjacent to the core, and a belt surrounding the core and the cylindrical orifice.

[0038] Such a manufacturing process can make it possible to obtain the mechanical part as described above. Brief description of the drawings

[0039] [Fig. 1] Figure 1 is a schematic view of a landing gear.

[0040] [Fig. 2] Figure 2 is a schematic view of a strut of the landing gear of Figure 1.

[0041] [Fig. 3] Figure 3 is a partial schematic view of a connecting rod according to the prior art showing cracks.

[0042] [Fig. 4] Figure 4 is a schematic cross-sectional view of a fibrous assembly.

[0043] [Fig. 5] Figure 5 is a schematic weaving plan of the central part of the core fibrous preform of the fibrous assembly of Figure 4.

[0044] [Fig. 6] Figure 6 is a schematic weaving plan of a flexible part of the fibrous core preform of the fibrous assembly of Figure 4.

[0045] [Fig. 7] Figure 7 is a schematic cross-sectional view of a mechanical part obtained by densification of the fibrous assembly of Figure 4. Description of the implementation methods

[0046] Figure 4 illustrates an example of a fiber assembly 200 according to the invention. The fiber assembly 200 is intended to be densified by a matrix. The fiber assembly 200 is intended to form the fibrous reinforcement of a mechanical part made of composite material.

[0047] For example, the fiber assembly according to the invention can be used to form the fiber reinforcement of a connecting rod or lever. The fiber assembly according to the invention can also be used to form the fiber reinforcement of a mechanical part for aeronautical equipment intended for flight. For example, the fiber assembly according to the invention can be used to form the fiber reinforcement of a connecting rod or landing gear lever. The fiber assembly according to the invention can also be used to form the fiber reinforcement of a part comprising only single clevises, as in the example illustrated in Figure 4. Of course, the invention remains within the scope of this application if the fiber assembly is used to form the fiber reinforcement of a part comprising one or more double clevises.

[0048] The fiber assembly 200 comprises at least one core fiber preform 210 and at least one belt fiber preform 220. In the example illustrated in Figure 4, the fiber assembly 200 comprises a single core fiber preform 210 and a single belt fiber preform 220. It is, of course, still within the scope of the invention if the fiber assembly 200 comprises several core fiber preforms 210 and / or several belt fiber preforms 220. For example, if a connecting rod with a double clevis is to be made, the fiber assembly could comprise two core fiber preforms and one or two belt fiber preforms.

[0049] The fibrous assembly 200 includes at least one orifice 231 delimited by the core fiber preform 210 and the belt fiber preform 220. In the example illustrated in Figure 4, the fibrous assembly 200 further includes a second orifice 231 delimited by the core fiber preform 210 and the belt fiber preform 220. The belt fiber preform 220 surrounds the preform The fibrous core 210 and the orifice(s) 231 and 232. The invention remains within the scope of this invention even if the fibrous assembly 200 comprises a single orifice or more than two orifices. For example, in the manufacture of a connecting rod with double clevises, the fibrous assembly may comprise four orifices.

[0050] The first orifice 231 is delimited by an internal surface. The second orifice 232 is delimited by an internal surface. Both orifices 231 and 232 are through orifices. The axis of orifice 231 extends along a first direction D Esaid thickness. All the orifices of the fibrous assembly can extend in the same direction. The orifices 231, 232 preferably have a cylindrical shape, for example a cylindrical shape of revolution.

[0051] The fibrous core preform 210 extends along a second direction D T said transverse between a first longitudinal edge 210a and a second longitudinal edge 210b opposite the first longitudinal edge 210a. The second direction D T is perpendicular to the first direction D EThe core fiber preform 210 further comprises at least one first curved edge 210c. The first curved edge 210c connects the first longitudinal edge 210a to the second longitudinal edge 210b. The first curved edge 210c partially delimits the first orifice 231. Thus, a portion of the internal surface of the first orifice 231 is defined by the first curved edge 210c of the core fiber preform 210. The core fiber preform 210 extends along a third direction D L said longitudinal from the first curved edge 210c. The third direction D L is perpendicular to the first direction D E and in the second direction D TIn the example illustrated in Figure 4, the core fiber preform 210 includes a second curved edge 210d opposite the first curved edge 210c, which connects the first longitudinal edge 210a to the second longitudinal edge 210b. The second curved edge 210d partially delimits the second opening 232. Thus, a portion of the internal surface of the second opening 232 is defined by the second curved edge 210d of the core fiber preform 210. The core fiber preform 210 thus extends along the third direction D L between the first curved edge 210c and the second curved edge 210d.

[0052] The fibrous preform of the belt 220 includes a closed internal surface 220a. The belt 220 includes a closed external surface 220b opposite the closed internal surface 220a. The closed internal surface 220a of the fibrous belt preform 220 is in contact with the longitudinal edges 210a and 210b of the fibrous core preform 210. The closed internal surface 220a of the fibrous belt preform 220 partially delimits the first opening 231. Thus, a portion of the internal surface of the first opening 231 is defined by the closed internal surface 220a of the fibrous belt preform 220. Consequently, the internal surface of the first opening 231 is formed on one side by the closed internal surface 220a of the fibrous belt preform 220 and on the other side by the first curved edge 210c of the fibrous core preform 210. The closed internal surface 220a of the fibrous belt preform 220 partially delimits the second opening 232. Thus, a portion of the surface The internal surface of the second orifice 232 is defined by the closed internal surface 220a of the fibrous belt preform 220.Therefore, the internal surface of the second orifice 232 is formed on the one hand by the closed internal surface 220a of the fibrous belt preform 220 and on the other hand by the second curved edge 210d of the fibrous core preform 210.

[0053] Each orifice 231, 232 of the fibrous assembly 200 is associated with a reference distance d R i, d R2 The reference distance of R i, d R2 corresponds to the distance extending between the axis of the orifice and the point on the external surface 220b of the belt preform 220 closest to said axis.

[0054] The 220 belt fiber preform can be produced by weaving. In particular, the 220 belt fiber preform can be produced by three-dimensional weaving. By "three-dimensional weaving," we mean a weaving method in which at least some of the warp yarns interlock with weft yarns over several weft layers. A reversal of the roles between warp and weft is possible. The 220 belt fiber preform can be produced in a well-known manner using a Jacquard loom. Preferably, the 220 belt fiber preform is made of carbon fibers.

[0055] The 210 core fiber preform is produced by three-dimensional weaving. The 210 core fiber preform can be produced in a well-known manner using a Jacquard loom. Preferably, the 210 core fiber preform is formed from carbon fibers. The same type of fibers and fibers of the same type can be used. material can be used for core fiber preform 210 and belt fiber preform 220.

[0056] According to a first embodiment of the invention, the core fiber preform 210 is made in a single piece by three-dimensional weaving. Thus, there is continuity of the warp and weft yarns between the main portion and the flexible portion(s). According to a second embodiment of the invention, the core fiber preform is made in several parts, each made by three-dimensional weaving. Thus, the central portion comprises a fibrous structure made by three-dimensional weaving, while the flexible portion(s) are each another fibrous structure made by three-dimensional weaving. The fibrous structure of the central portion is therefore independent of the fibrous structure of the flexible portion(s) within the core fiber preform. Therefore, the warp yarns of the central portion do not extend into the flexible portion(s), and the weft yarns of the central portion do not extend into the flexible portion(s).The central portion and the flexible portion(s) are therefore not linked together by weaving.

[0057] The 210 core fiber preform preferably exhibits an interlock weave. "Interlock weave" here refers to a three-dimensional weave in which each warp layer interlocks several weft layers, with all yarns in the same warp column having the same movement within the weave plane. Only the central portion may exhibit an interlock weave. Alternatively, only the flexible portion(s) may exhibit an interlock weave.

[0058] The central portion may exhibit one type of weave structure, and the flexible portion(s) may exhibit a second type of weave structure different from the first. For example, the weave types could be: interlock, 3D multilayer, or 3D orthogonal.

[0059] The fibrous core preform 210 comprises a central portion 211 and at least one flexible portion 212. In the example illustrated in Figure 4, the fibrous core preform 210 comprises a central portion 211 and four flexible portions 212, 213, 214 and 215. Preferably, the fibrous core preform 210 comprises two flexible portions for each orifice.

[0060] The flexible portion(s) extend from one of the curved edges of the fibrous core preform. The flexible portion(s) extend from the junction between a curved edge and a longitudinal edge. Thus, the flexible portion(s) extend along the longitudinal direction D L from one of the curved edges of the fibrous core preform and extend along the transverse direction D T from one of the longitudinal edges of the core fibrous preform. The central portion of the core fibrous preform extends along the longitudinal direction D Lalong the entire length of the fibrous core preform.

[0061] In the example illustrated in Figure 4, the first flexible portion 212 extends along the longitudinal direction D L from the first curved edge 210c of the fibrous core preform 210 and extends along the transverse direction D T from the first longitudinal edge 210a of the fibrous core preform 210. The second flexible portion 213 extends along the longitudinal direction D L from the first curved edge 210c of the fibrous core preform 210 and extends along the transverse direction D T from the second longitudinal edge 210b of the fibrous core preform 210. The first flexible portion 212 and the second flexible portion 213 are separated by the central portion 211. The first flexible portion 212 and the second flexible portion 213 are arranged on either side of the central portion 211 along the transverse D TIn the example illustrated in Figure 4, the third flexible portion 214 extends along the longitudinal direction D L from the second curved edge 210d of the fibrous core preform 210 and extends along the transverse direction D T from the first longitudinal edge 210a of the fibrous core preform 210. The fourth flexible portion 215 extends along the longitudinal direction D L from the second curved edge 210d of the fibrous core preform 210 and extends along the transverse direction D T from the second longitudinal edge 210b of the fibrous core preform 210. The third flexible portion 214 and the fourth flexible portion 215 are separated by the central portion 211. The third flexible portion 214 and the fourth flexible portion 215 are arranged on either side of the central portion 211 along the transverse D T The central portion 211 extends along the longitudinal direction D Lfrom the first curved edge 210c to the second curved edge 210d. The central portion 211 can extend along the transverse direction D T from the first longitudinal edge 210a to the second longitudinal edge 210b.

[0062] The flexible portion(s) extend from one of the orifices along the longitudinal direction D L over a distance between 80% and 220% of the reference distance d R i, d R2 associated with the orifice, as defined previously. Thus, the flexible portion(s) do not necessarily extend along the entire length of the fibrous core preform 210. The flexible portion(s) may, however, extend along the entire length of the fibrous core preform 210 in the longitudinal direction D L The width of the flexible portion(s) along the transverse direction D Tcan be between 2 mm and 9 mm, and in particular between 3 mm and 7 mm. The width of the flexible portion(s) along the transverse direction D T can be between 4% and 40% of the reference distance d R i, d R2 The flexible portion(s) can extend over the entire thickness of the fibrous core preform 210 along the thickness direction D E The width of the flexible portion(s) along the transverse direction D T can be constant. The width of the flexible portion(s) along the transverse direction D T can also be variable. In particular, the width of the flexible portion(s) along the transverse direction D T can gradually decrease from the orifice along the longitudinal direction D LIf the flexible portion(s) extend along the entire length of the fibrous core preform 210, the width of the flexible portion(s) along the transverse direction D T can gradually decrease from the openings to a narrow central portion.

[0063] The warp yarns of the central portion have a higher first settling height than the warp yarns of the flexible portions. In one variation, the weft yarns of the central portion have a higher first settling height than the weft yarns of the flexible portions. The central portion and the flexible portion(s) may have the same weave structure, or different weaves. The central portion and the flexible portion(s) may all have an interlock weave. The flexible portions may all have the same settling height, or may have different settling heights.

[0064] Embuvage corresponds to the ratio between the length of the woven yarn over a given distance and said given distance, from which 1 is subtracted:

[0065] [Math 1]

[0067] The greater the sizing, the more flexible the woven portion will be. The less sizing, the stiffer the woven portion will be.

[0068] Figure 5 illustrates an example of a weave plan for the central portion 211 and Figure 6 illustrates an example of a weave plan for one of the flexible portions 212. In this example, the weave structures are of the interlock type.

[0069] The weaving plan of the central portion 211 shown in Figure 5 illustrates warp yarns 211c and weft yarns 211t. Over a distance d, the warp yarns 211c travel a length L211C. The warp yarns 211c of the central portion 211 thus exhibit a first weft E2u c which is calculated as follows:

[0070] [Math 2]

[0072] The warp yarns 211c of the central portion 211 plunge into the weft yarn layers 2 bed at a first mean angle of embouchure 0211 as illustrated in Figure 6. The mean angle of embouchure is defined with respect to the plane of the weft yarn layers 211t.

[0073] The weaving pattern of the flexible portion 212 shown in Figure 6 illustrates warp yarns 212c and weft yarns 212t. Over a distance d, the warp yarns 212c travel a length L2120. The warp yarns 212c of the central portion 212 thus exhibit a second wefting E2i2c which is calculated as follows:

[0074] [Math 3]

[0076] In the flexible portion 212, the warp threads 212c travel a greater length L2i2c than the length L2n ctraversed by the warp threads 211c of the central portion 211 over the same distance d. Thus, the second embuvage E2I 2C is superior to the first E2n imbunage c .

[0077] The warp yarns 212c of the central portion 212 plunge into the weft yarn layers 212t at a second mean angle of embedding o 2i2 as illustrated in Figure 7. The mean angle of embouchure is defined with respect to the plane of the 212t weft yarn layers. The second mean angle of embouchure o 2i2 in the flexible portion 212 is greater than the first average embuvage angle o2n in the central portion 211.

[0078] The warp threads 211c, 212c of the fibrous core preform 210 can extend globally along the longitudinal direction D L .

[0079] To create the fiber assembly 200, the core fiber preform 210 and the belt preform 220 are produced as described previously. Then, the core fiber preform 210 is assembled with the belt fiber preform 220. The assembly is carried out so that the fibrous belt preform 220 surrounds the fibrous core preform 210 and delimits the orifice(s) 231 and 232. The fibrous belt preform 220 is arranged in contact with the flexible portions 212, 213, 214 and 215 of the fibrous core preform 210. The central portion 211 of the core preform 210 opens onto the orifice(s) 231, 232.

[0080] To facilitate the positioning of the fiber belt preform 220 around the fiber core preform 210, one or more positioning elements may be used. The positioning element(s) are arranged against the curved edge(s) 210c, 210d of the fiber core preform 210. The positioning element(s) define the cylindrical opening(s) 231, 232 intended to form the opening(s) 131, 132.

[0081] The resulting fibrous assembly 200 is then densified by a matrix. The core fibrous preform 210 and the belt fibrous preform 220 are thus co- densified. Preferably, the mechanical part is made of an organic matrix composite material, known as an "OMC". For this purpose, the fibrous assembly 200 can be placed in a mold. Densification by the matrix can be achieved by introducing a resin into the fibrous assembly 200, such as an epoxy resin. The resin introduction is followed by cross-linking if it is a thermosetting resin, or by cooling if it is a thermoplastic resin. The matrix can be formed by resin transfer molding, a technique that is well-established. The positioning elements described previously can be retained during densification to prevent the matrix material from filling the opening(s) 231, 232.

[0082] This gives us a mechanical part 100 made of composite material, as illustrated in figure 7, whose fibrous reinforcement is formed by the fibrous assembly 200.

[0083] The mechanical part 100 comprises a core 110 whose fibrous reinforcement is formed by the fibrous core preform 210. The mechanical part 100 comprises a belt 120 whose fibrous reinforcement is formed by the fibrous belt preform 220. The mechanical part 100 comprises at least one opening 131 adjacent to the core 110. In the example illustrated in Figure 7, the mechanical part 100 comprises a first opening 131 and a second opening 132 adjacent to the core 110. The opening(s) 131, 132 are intended to be traversed by a shaft to create a connection with another part. The belt 120 surrounds the core 110 and the opening(s) 131, 132.

[0084] As previously mentioned, the mechanical part can include one or more webs and / or one or more belts. For example, if a connecting rod with a double yoke is desired, the part can include two webs, one or two belts, and two or four holes.

[0085] The core 110 of the mechanical part 100 comprises a central portion 111 whose fibrous reinforcement is formed by the central portion 211 of the fibrous core preform 210. The core 110 of the mechanical part 100 comprises one or more flexible portions 112, 113, 114, 115 whose fibrous reinforcement(s) are formed respectively by the flexible portion(s) 212, 213, 214, 215 of the preform fibrous core 210. The flexible portion(s) 112, 113, 114, 115 of the core 110 are present between the central portion 111 of the core 110 and the belt 120. The flexible portion(s) 112, 113, 114, 115 of the core 110 are arranged in contact with the belt 120.

[0086] The variation of the embuvage between the central portion 111 and the flexible portion(s) 112, 113, 114, 115 of the core 110 allows for many mechanical advantages for the part 100.

[0087] The stiffness of the flexible portion(s) can be between 70% and 85% of the stiffness of the central portion due to increased foaming. Specifically, the stiffness of the flexible portion(s) can be between 75% and 85% of the stiffness of the central portion to maintain optimal rigidity. Stiffness can be measured in gigapascals (GPa) using conventional methods.

[0088] For a conventionally shaped connecting rod with two orifices and for a conventional warp-weft ratio, the addition of flexible portions according to the invention can reduce tensile stresses by up to about 30% at the interface between the belt and the web, and reduce compressive stresses by up to about 7% at the interface between the belt and the web, depending on the loading cases.

[0089] The axis of the orifice 131 of the mechanical part 100 extends along the thickness direction D E The core 110 of the mechanical part 100 extends from the orifice 131 along the longitudinal direction D L In the illustrated example, the web 110 extends lengthwise along the longitudinal direction D L between the first orifice 131 and the second orifice 132. The core 110 extends in width along the transverse direction D TThus, the flexible portions 112, 113, 114, 115 of the core 110 extend from the orifices 131, 132 along the longitudinal direction D L The flexible portions 112, 113, 114, 115 of the core 110 extend along the transverse direction D T between the central portion 111 of the soul 110 and the belt 120.

[0090] The mechanical part 100 may include one or more rings 141, 142. The ring(s) 141, 142 may be added to the orifice(s) 131, 132. Of course, this does not depart from the scope of the invention if the rings 141, 142 are attached to the fibrous assembly 200 before densification by the matrix. At least one ring 141, 142 can be positioned in each orifice 131, 132. The external surface of the ring 141, 142 can correspond to the internal surface of the orifice 131, 132. The core 110 can conform to the shape of the ring(s) 141, 142. The band 120 can conform to the shape of the ring(s) 141, 142. The ring(s) 141, 142 can be made of metal. The ring(s) 141, 142 can also be made of composite material.

[0091] The part according to the invention may or may not be intended for an aeronautical application. The part may, for example, be a connecting rod, a landing gear strut or a component thereof, or a brake rod. The part may comprise one or more single clevises. The part may comprise one or more double clevises.

[0092] The component according to the invention thus exhibits better mechanical properties than similar components of the prior art. During tensile loading of a component according to the prior art, the end of the belt surrounding the opening is initially loaded, then the stresses are transferred to the rest of the belt and the web. This transfer of stresses occurs progressively via the interface between the web and the belt, with a stress peak, until the load is homogeneous. A similar phenomenon occurs during compressive loading. The component according to the invention allows for better absorption and reduction of this stress peak thanks to the presence of flexible sections.

[0093] The expression "between ... and ..." should be understood as including the boundaries.

Claims

Demands

1. A fibrous assembly (200) intended to form the fibrous reinforcement of a mechanical part (100) made of composite material, the fibrous assembly (200) comprising a fibrous core preform (210) having a three-dimensional weave extending along a longitudinal direction (D L ) and at least one orifice (231, 232) extending along a thickness direction (D E ) perpendicular to the longitudinal direction (D L ), said at least one orifice (231, 232) being adjacent to the fibrous core preform (210) along the longitudinal direction (D L) and intended to be traversed by an axis to establish a connection with another part, the fibrous assembly (200) further comprising a fibrous belt preform (220) surrounding the fibrous core preform (210) and said at least one orifice (231, 232), the fibrous assembly (200) being characterized in that the fibrous core preform (210) comprises a central portion (211) in which the warp yarns (211c), or respectively the weft yarns, have a first splay and at least one flexible portion (212, 213, 214, 215) present between the fibrous belt preform (220) and the central portion (211) and extending from the orifice (231, 232) in the longitudinal direction (D L ) over a determined distance, the warp yarns (212c), or respectively the weft yarns, of said at least a flexible portion (212, 213, 214, 215) exhibiting a second weaving greater than the first weaving.

2. Fibrous assembly (200) according to claim 1, wherein the central portion (211) and said at least one flexible portion (212, 213, 214, 215) are linked together by a common weave in the fibrous core preform (210).

3. Fibrous assembly (200) according to claim 1, wherein the central portion and said at least one flexible portion each comprise an independent woven fibrous structure in the core fibrous preform.

4. A fibrous assembly (200) according to any one of claims 1 to 3, wherein the flexible portion (212, 213, 214, 215) extends along the longitudinal direction (D L ) from the orifice (231, 232) over a distance between 80% and 220% of a reference distance (d R i, d R2 extending between the axis of the orifice and the point on the external surface (220b) of the belt preform (220) closest to said axis.

5. A fibrous assembly according to any one of claims 1 to 4, wherein the flexible portion (212, 213, 214, 215) extends along a transverse direction (D T ) perpendicular to the thickness direction (D E ) and to the longitudinal direction (D L ) between the belt preform (220) and the central portion (211) of the core preform (210) over a distance between 4% and 40% of a reference distance (d R i, d R2 ) extending between the axis of the orifice and the point on the external surface (220b) of the belt preform (220) closest to said axis.

6. Fiber assembly (200) according to any one of claims 1 to 5, wherein the weave structure of the fiber reinforcement of the core fiber preform (210) is an interlock type weave.

7. A fibrous assembly (200) according to any one of claims 1 to 6, wherein the flexible portion is a first flexible portion (212, 214), the core preform (210) further comprising a second flexible portion (213, 215) present between the fibrous belt preform (220) and the central portion (211) and extending from the orifice (231, 232) in the longitudinal direction (D L ) over a determined distance, the first flexible portion (212, 214) and the second flexible portion (213, 215) being located on either side of the central portion (211), the warp threads of said second flexible portion having a third embuvage greater than the first embuvage.

8. Fibrous assembly (200) according to any one of claims 1 to 7, wherein the central portion (211) of the core preform (210) opens onto the orifice (231, 232).

9. Mechanical part (100) made of composite material having the fibrous reinforcement formed by the fibrous assembly (200) according to any one of claims 1 to 8 densified by a matrix, the core preform (210) densified by the matrix forming a core (110) and the belt preform (220) densified by the matrix forming a belt (120) surrounding the core (110) and at least one orifice (131, 132).

10. Part (100) according to claim 9, the part (100) further comprising at least one ring (141, 142) disposed in the orifice (131, 132) and adjacent to the core (110).

11. A method for manufacturing a fibrous assembly (200) intended to form the fibrous reinforcement of a mechanical part (100) made of composite material, comprising: - the production by three-dimensional weaving of a fibrous core preform (210) extending along a longitudinal direction (D L) comprising a central portion (211) in which the warp threads (211c) have a first embuvage and comprising at least one flexible portion (212, 213, 214, 215) present at the edge of the fibrous core preform (210) in which the warp threads (212c) have a second embuvage greater than the first embuvage, - the production of a fibrous preform belt (220), - the arrangement of the fibrous belt preform (220) around the fibrous core preform (210) such that the fibrous belt preform (220) delimits at least one cylindrical orifice (231, 232) extending along a thickness direction (D E ) perpendicular to the longitudinal direction (D L ), said at least one cylindrical orifice (231, 232) being adjacent to the fibrous core preform (210) along the longitudinal direction (D L), and such that said at least one flexible portion (212, 213, 214, 215) of the core fibrous preform (210) is between the belt fibrous preform (220) and the central portion (211) of the core fibrous preform (210), and that said at least one flexible portion (212, 213, 214, 215) extends from the cylindrical orifice (231, 232) in the longitudinal direction (D L ) over a determined distance.

12. A method for manufacturing a mechanical part (100) comprising: - the manufacture of a fibrous assembly (200) according to claim 11, - the densification of the fibrous assembly (200) by a matrix while retaining the cylindrical orifice (231, 232) without a matrix, so as to obtain a mechanical part (100) made of composite material comprising a core (110), a cylindrical orifice (131, 132) adjacent to the core (110), and a belt (120) surrounding the core (110) and the cylindrical orifice (131, 132).

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