Fiber assembly with improved weave for belted mechanical part

Abstract

Fiber assembly with improved weave for reinforced mechanical part. The invention relates to a fiber assembly (200) intended to form the reinforcement of a part (100) made of composite material, the fiber assembly (200) comprising a core fiber preform (210) produced by three-dimensional weaving, at least one orifice (231) adjacent to the core fiber preform (210) intended to be traversed by a shaft to create a bond, and a belt fiber preform (220) surrounding the core fiber preform (210) and said at least one orifice (231), the core fiber preform (210) comprising a central portion (211) in which the warp (211c) or weft yarns have a first swaging and at least one flexible portion (212) present between the belt fiber preform (220) and the central portion (211) and extending from the orifice (231) in which the warp (212c) or weft yarns exhibit a second over-burdening greater than the first over-burdening.Figure for the abridged version: Fig. 4.

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] Fig. 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 Fig. 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 parts of the landing gear at their ends, by means of pivot pins. Such connecting rods are subjected in operation to significant mechanical stresses, mainly in compression and tension, oriented along the longitudinal axis of the part.

[0003] These connecting rods were usually made of steel, aluminum, or titanium alloys. To reduce their weight, they can now be made of composite material. Indeed, manufacturing connecting rods from composite material allows for lighter rods than those made of metal while maintaining good mechanical properties. Composite connecting rods are thus easier to operate during landing gear operation and reduce the aircraft's mass, thereby 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 web surrounded by a belt, the fibrous reinforcements of the web 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 has been 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 [Fig. 3]. Description of the invention

[0006] It has been observed that these cracks can be caused by a high concentration of stresses at the interface between the web, the belt, and the opening housing the ring under significant loads. Indeed, it has been observed that the fibrous reinforcements of the web and the belt do 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 has been observed that these cracks can 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 core fiber 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 at least one orifice being adjacent to the core fiber preform along the longitudinal direction and intended to be traversed by a shaft to create a connection with another part, the fibrous assembly further comprising a belt fiber preform surrounding the core fiber preform and said at least one orifice, the fibrous assembly being characterized in that the core fiber preform comprises a central portion in which the warp yarns, or respectively the weft yarns,exhibit a first layer of warp and weft, and at least one flexible portion present between the fibrous preform of the belt and the central portion, extending from the opening in the longitudinal direction over a determined distance, the warp yarns, or respectively the weft yarns, of said warp and weft, at least one flexible portion exhibiting a second layer of warp greater than the first layer of warp.

[0009] Thus, a greater degree of flexing in the flexible portion than in 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, which allows the core fiber preform to withstand compressive forces satisfactorily. The flexible portion makes it possible to soften the area of ​​the core fiber preform most at risk of cracking, and thus improve the distribution of the compressive and tensile load at the interface between the fiber preform The core and the fibrous belt preform are designed to work together. In operation, the core and belt preforms each have their own mechanical function and are subjected to different mechanical stresses to ensure the proper functioning of the part. This solution improves the transmission of forces between the core and belt preforms and significantly limits stress concentrations at the interface between them. The crack resistance of the final part, whose fibrous reinforcement is formed by the entire fiber structure, is thus greatly improved without reducing the overall mechanical properties of the 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] Such a solution does not require the addition of any extra material or separate fiber portion. This solution thus limits costs 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, with 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 arranged 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 orifice. Therefore, it is not necessary to unnecessarily extend the flexible portion, at the risk of reducing 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 the part is subjected to compressive loading. The overall stiffness of the part is also reduced. Such a range of values ​​for the width of the flexible portion thus ensures very satisfactory protection against cracking at the interface between the web 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 makes it possible, in particular, to facilitate the transition between the central portion and the flexible portion(s) of the fibrous core preform. The interlock reinforcement can also allow for desired localized plastic deformation near the orifice, and where applicable, 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 embuvage greater than the first embuvage.

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

[0024] The second and third molding processes can be identical. This simplifies the fabrication of the fiber assembly. The second and third molding processes can be different to better adapt to the geometry of the part and the specific mechanical constraints of 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 recovery of compressive forces is easier, without increasing the risk of cracks at the level of 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 preform of core extending along a longitudinal direction comprising a central portion in which the warp threads exhibit a first embuvage and comprising at least one flexible portion present at the edge of the fibrous core preform in which the warp threads exhibit a second embuvage greater than the first embuvage,

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

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

[0033] The fibrous belt preform 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 mass by a matrix while preserving the orifice cylindrical without a die, 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] The [Fig.1] is a schematic view of a landing gear.

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

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

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

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

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

[0045] [Fig.7] The [Fig.7] is a schematic cross-sectional view of a mechanical part obtained by densification of the fibrous assembly of the [Fig.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 may be intended to form the fiber reinforcement of a connecting rod or a lever. The fiber assembly according to the invention may be intended to form the fiber reinforcement of a mechanical part for aeronautical equipment intended for flight. For example, the fiber assembly according to the invention may be intended to form the fiber reinforcement of a connecting rod or a landing gear lever. The fiber assembly according to the invention may be intended to form the fiber reinforcement of a part comprising only single clevises, as in the example illustrated in [Fig. 4]. It is, of course, not beyond the scope of the invention if the fiber assembly is intended 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 [Fig. 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 may comprise two core fiber preforms and one or two belt fiber preforms.

[0049] The fiber assembly 200 comprises at least one orifice 231 delimited by the core fiber preform 210 and the belt fiber preform 220. In the example illustrated in [Fig. 4], the fiber assembly 200 further comprises a second orifice 231 delimited by the core fiber preform 210 and the belt fiber preform 220. The belt fiber preform 220 surrounds the core fiber preform 210 and the orifice(s) 231 and 232. It is, of course, within the scope of the invention whether the fiber assembly 200 comprises a single orifice or more than two orifices. For example, for the manufacture of a connecting rod with double yokes, the fiber 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. Orifices 231 and 232 are through-holes. The axis of orifice 231 extends along a first direction DE, referred to as the thickness direction. All the orifices of the fibrous assembly can extend along the same direction. Orifices 231 and 232 preferably have a cylindrical shape, for example, a cylindrical shape of revolution.

[0051] The core fiber preform 210 extends along a second direction DT, referred to as transverse, between a first longitudinal edge 210a and a second longitudinal edge 210b opposite the first longitudinal edge 210a. The second direction DT is perpendicular to the first direction DE. The 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 opening 231. Thus, a portion of the internal surface of the first opening 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 DL, referred to as longitudinal, from the first curved edge 210c. The third direction DL is perpendicular to the first direction DE and to the second direction DT. In the example illustrated in [Fig.[4], the fibrous core 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 orifice 232. Thus, a portion of the internal surface of the second orifice 232 is defined by the second curved edge 210d of the fibrous core preform 210. The fibrous core preform 210 thus extends along the third direction DL between the first curved edge 210c and the second curved edge 210d.

[0052] The fibrous belt preform 220 comprises a closed internal surface 220a. The belt 220 comprises a closed external surface 220b opposite the closed internal surface 220a. The closed internal surface 220a of the fibrous belt preform 220 is positioned in contact with the longitudinal edges 210a and 210b of the core fiber preform 210. The closed internal surface 220a of the belt fiber preform 220 partially delimits the first orifice 231. Thus, a portion of the internal surface of the first orifice 231 is defined by the closed internal surface 220a of the belt fiber preform 220. Consequently, the internal surface of the first orifice 231 is formed on the one hand by the closed internal surface 220a of the belt fiber preform 220 and on the other hand by the first curved edge 210c of the core fiber preform 210. The closed internal surface 220a of the belt fiber preform 220 partially delimits the second orifice 232. Thus, a portion of the internal surface of the second orifice 232 is defined by the closed internal surface 220a of the 220 belt fibrous preform.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 dRb dR2. The reference distance dRb dR2 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 fibrous belt preform 220 can be produced by weaving. In particular, the fibrous belt preform 220 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 bind weft yarns over several weft layers. A reversal of the roles between warp and weft is possible. The fibrous belt preform 220 can be produced in a well-known manner using a Jacquard-type loom. Preferably, the fibrous belt preform 220 is formed from carbon fibers.

[0055] The core fiber preform 210 is produced by three-dimensional weaving. The core fiber preform 210 can be produced in a well-known manner using a Jacquard-type loom. Preferably, the core fiber preform 210 is formed from carbon fibers. The same type of fibers and fibers of the same material can be used for both the core fiber preform 210 and the 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 a separate fibrous structure created by three-dimensional weaving, the fibrous structure of the central portion is 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). Consequently, the central portion and the flexible portion(s) are not woven together.

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

[0058] The central portion may have a first type of weave structure, and the flexible portion(s) may have a second type of weave structure different from the first type of weave structure. For example, the weave types may be: interlock, 3D multilayer, 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 [Fig.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 core fiber 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 DL from one of the curved edges of the core fiber preform and along the transverse direction DT from one of the longitudinal edges of the core fiber preform. The central portion of the core fiber preform extends along the longitudinal direction DL along the entire length of the core fiber preform.

[0061] In the example illustrated in [Fig. 4], the first flexible portion 212 extends along the longitudinal direction DL from the first curved edge 210c of the core fiber preform 210 and along the transverse direction DT from the first longitudinal edge 210a of the core fiber preform 210. The second flexible portion 213 extends along the longitudinal direction DL from the first curved edge 210c of the core fiber preform 210 and along the transverse direction DT from the second longitudinal edge 210b of the core fiber preform 210. The 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 direction Dt. In the example illustrated in [Fig. 4], the third flexible portion 214 extends along the longitudinal direction DL from the second curved edge 210d of the core fiber preform 210 and along the transverse direction DT from the first longitudinal edge 210a of the core fiber preform 210. The fourth flexible portion 215 extends along the longitudinal direction DL from the second curved edge 210d of the core fiber preform 210 and along the transverse direction DT from the second longitudinal edge 210b of the core fiber preform 210. The third flexible portion 214 and the fourth portion The flexible 215s 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 DT. The central portion 211 extends along the longitudinal direction DL from the first curved edge 210c to the second curved edge 210d. The central portion 211 can extend along the transverse direction DT 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 DL over a distance between 80% and 220% of the reference distance dRb dR2 associated with said orifice, as defined previously. Thus, the flexible portion(s) do not necessarily extend over the entire length of the fiber core preform 210. However, the flexible portion(s) may extend over the entire length of the fiber core preform 210 along the longitudinal direction Dl. The width of the flexible portion(s) along the transverse direction DT may 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 DT may be between 4% and 40% of the reference distance dRb dR2. The flexible portion(s) can extend over the entire thickness of the fibrous core preform 210 along the thickness direction DE.The width of the flexible portion(s) along the transverse direction DT can be constant. The width of the flexible portion(s) along the transverse direction DT can also be variable. In particular, the width of the flexible portion(s) along the transverse direction DT can gradually decrease from the opening along the longitudinal direction DL. If the flexible portion(s) extend along the entire length of the 210 core fiber preform, the width of the flexible portion(s) along the transverse direction DT can gradually decrease from the openings to a narrow central portion.

[0063] The warp yarns of the central portion have a higher initial weave thickness than the warp yarns of the flexible portions. According to one embodiment, the weft yarns of the central portion have a higher initial weave thickness 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 structure. The flexible portions may all have the same weave thickness, or may have different weaves.

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

[0065] [Math.l] embuvage length of the woven thread over a distance d di stan«? d

[0066] The greater the swaging, the more flexible the woven portion will be. The less swaging, the stiffer the woven portion will be.

[0067] Fig. 5 illustrates an example of a weaving plan for the central portion 211 and Fig. 6 illustrates an example of a weaving plan for one of the flexible portions 212. In this example, the weaves are of the interlock type.

[0068] The weaving plan of the central portion 211 shown in [Fig. 5] illustrates warp yarns 21le and weft yarns 211t. Over a distance d, the warp yarns 21le travel a length L2nc. The warp yarns 21le of the central portion 211 thus exhibit a first settling E2nc which is calculated as follows:

[0069] [Math.2] i IC __ j $21 the “d*

[0070] The warp yarns 21 of the central portion 211 plunge into the weft yarn layers 211 at a first mean angle of indentation a2n as illustrated in [Fig. 6]. The mean angle of indentation is defined with respect to the plane of the weft yarn layers 211t.

[0071] The weaving plan of the flexible portion 212 shown in [Fig. 6] illustrates warp yarns 212c and weft yarns 212t. Over a distance d, the warp yarns 212c travel a length L2i2c. The warp yarns 212c of the central portion 212 thus exhibit a second weft E2i2c which is calculated as follows:

[0072] [Math.3]

[0073] In the flexible portion 212, the warp threads 212c travel a greater length L2i2c than the length L2nc traveled by the warp threads 21 le of the central portion 211 over the same distance d. Thus, the second embuvage E2i2c is greater than the first embuvage E2nc.

[0074] The warp yarns 212c of the central portion 212 plunge into the weft yarn layers 212t at a second mean angle of penetration a2i2 as illustrated in [Fig. 7]. The mean angle of penetration is defined with respect to the plane of the weft yarn layers 212t. The second mean angle of penetration a2i2 in the flexible portion 212 is greater than the first mean angle of penetration in the central portion 211.

[0075] The warp wires 21 le, 212c of the fibrous core preform 210 can extend globally along the longitudinal direction DL.

[0076] To create the fibrous 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 belt fiber preform 220 surrounds the core fiber preform 210 and defines the opening(s) 231 and 232. The belt fiber preform 220 is positioned in contact with the flexible portions 212, 213, 214, and 215 of the core fiber preform 210. The central portion 211 of the core preform 210 opens onto the opening(s) 231, 232.

[0077] To facilitate the positioning of the fibrous belt preform 220 around the fibrous 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 fibrous core preform 210. The positioning element(s) define the cylindrical opening(s) 231, 232 intended to form the opening(s) 131, 132.

[0078] The resulting fiber assembly 200 is then densified by a matrix. The core fiber preform 210 and the belt fiber 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 fiber assembly 200 can be placed in a mold. Densification by the matrix can be achieved by introducing a resin into the fiber assembly 200, such as an epoxy resin. The resin introduction is followed by crosslinking 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 known per se. The positioning elements described above can be retained during densification, in order to prevent the matrix material from filling the orifice(s) 231, 232.

[0079] This gives us a mechanical part 100 made of composite material, as illustrated in [Fig.7], whose fibrous reinforcement is formed by the fibrous assembly 200.

[0080] 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 orifice 131 adjacent to the core 110. In the example illustrated in [Fig. 7], the mechanical part 100 comprises a first orifice 131 and a second orifice 132 adjacent to the core 110. The orifice(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 orifice(s) 131, 132.

[0081] As previously stated, the mechanical part may comprise one or more webs and / or one or more belts. For example, if a connecting rod with a double yoke is to be made, the part may comprise two webs, one or two belts, and two or four ports.

[0082] 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 fibrous core preform 210. The flexible portion(s) 112, 113, 114, 115 of the core 110 are located 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 at belt contact 120.

[0083] 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 numerous mechanical advantages for the part 100.

[0084] The stiffness of the flexible portion(s) can be between 70% and 85% of the stiffness of the central portion by increasing the foaming. In particular, the stiffness of the flexible portion(s) can be between 75% and 85% of the stiffness of the central portion to maintain optimal stiffness. The stiffness can be evaluated in gigapascals (GPa) by conventional means.

[0085] 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.

[0086] The axis of the orifice 131 of the mechanical part 100 extends along the thickness direction DE. The web 110 of the mechanical part 100 extends from the orifice 131 along the longitudinal direction DL. In the illustrated example, the web 110 extends lengthwise along the longitudinal direction DL between the first orifice 131 and the second orifice 132. The web 110 extends widthwise along the transverse direction Dt. Thus, the flexible portions 112, 113, 114, 115 of the web 110 extend from the orifices 131, 132 along the longitudinal direction DL. The flexible portions 112, 113, 114, 115 of the core 110 extend along the transverse direction DT between the central portion 111 of the core 110 and the belt 120.

[0087] The mechanical part 100 can include one or more rings 141, 142. The ring(s) 141, 142 can be added in the orifice(s) 131, 132. We do not, of course, 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 outer surface of the ring 141, 142 can correspond to the inner 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.

[0088] 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.

[0089] The part according to the invention thus exhibits better mechanical properties than similar parts of the prior art. During tensile loading of a part according to the prior art, the end of the belt surrounding the opening is loaded first, then the stresses are transferred to the rest of the belt and to the web. This transfer of stresses occurs progressively via the interface between the web and the belt with a stress peak, until the loading is homogeneous. A similar phenomenon occurs during compressive loading. The part according to the invention makes it possible to better absorb and reduce this stress peak thanks to the presence of flexible portions.

[0090] The expression "between ... and ..." should be understood as including the boundaries.

Claims

Demands

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

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 (DL) from the orifice (231, 232) over a distance between 80% and 220% of a reference distance (dRb dR2) extending between the axis of the orifice and the point on the surface external (220b) of the belt preform (220) closest to said QVO

5. dAC. Fibrous assembly according to any one of claims 1 to 4, wherein the flexible portion (212, 213, 214, 215) extends along a transverse direction (DT) perpendicular to the thickness direction (De) and the longitudinal direction (DL) 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 (dRb dR2) 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 weave.

7. 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) along the longitudinal direction (DL) over a determined distance, the first flexible portion (212, 214) and the second flexible portion (213, 215) being situated on either side of the central portion (211), the warp yarns of said second flexible portion having a third overhang greater than the first overhang.

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 three-dimensional weaving of a core fiber preform (210) extending along a longitudinal direction (DL) comprising a central portion (211) in which the warp yarns (211c) have a first splay and comprising at least one flexible portion (212, 213, 214, 215) located at the edge of the core fiber preform (210) in which the warp yarns (212c) have a second splay greater than the first splay, - the creation of a belt fiber preform (220), - the arrangement of the belt fiber preform (220) around the core fiber preform (210) such that the belt fiber preform (220) delimits at least one cylindrical orifice (231, 232) extending along a thickness direction (DE) perpendicular to the longitudinal direction (DL),said at least one cylindrical orifice (231, 232) being adjacent to the core fiber preform (210) along the longitudinal direction (DL), and such that said at least one flexible portion (212, 213, 214, 215) of the core fiber preform (210) is between the belt fiber preform (220) and the central portion (211) of the core fiber preform (210), and that the at least one flexible portion (212, 213, 214, 215) extends from the cylindrical orifice (231, 232) along the longitudinal direction (DL) over a determined distance.

12. A method for manufacturing a mechanical part (100) comprising: - manufacturing a fibrous assembly (200) according to claim H, - densifying 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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