Belted mechanical part with no stress-concentration triple point

Abstract

The invention relates to a mechanical part (100) comprising a core (110) that extends lengthwise between a first end (110a) and a second end (110b) in a longitudinal direction (DL) and extends widthwise between two lateral edges (111, 112) in a transverse direction (DT), the core (110) comprising, at least at its first end (110a), a hole (131) intended to have a shaft pass therethrough in order to make a connection to another part, the mechanical part (100) further comprising a belt (120) surrounding the core (100), the belt (120) being formed by a fiber reinforcement densified by a matrix, the fiber reinforcement of the belt (120) being formed by a winding of fibers wound around the core (110), the winding of fibers having a preload exerting a compressive force on the core (110).

Description

Description Title of the invention: Belted mechanical part without triple stress concentration point 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 opening that houses the ring 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. Furthermore, it was observed that these cracks could be exacerbated by residual manufacturing stresses, particularly those occurring during the cooling of the part during its production process.

[0007] To address these cracking issues, it is possible to add material to reinforce the part. However, this would increase the part's weight, which is undesirable.

[0008] 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, without adding mass to the part.

[0009] To this end, the invention proposes a mechanical part comprising a core extending lengthwise between a first end and a second end along a longitudinal direction and extending widthwise between two lateral edges along a transverse direction, the core comprising at least at its first end an orifice intended to be traversed by a shaft to achieve a connection with another part, the mechanical part further comprising a belt surrounding the core, the belt being formed by a fibrous reinforcement densified by a matrix, the fibrous reinforcement of the belt being formed by a winding of fibers wound around the core, the winding of fibers having a prestress exerting a compressive force on the core.

[0010] Thus, the stress concentration point at the interface between the web, the belt, and the opening is eliminated. Since the web is now interposed between the belt and the opening, it is essential to prevent it from experiencing tensile stress. Indeed, the web is optimized to resist compressive forces, not tensile ones. To this end, the belt fibers are wound in such a way as to exert a compressive prestress on the web, thereby preventing the web from experiencing tensile stress. This prestress also improves the quality of the interface between the web and the belt.

[0011] According to a particular embodiment of the invention, the prestress of the fiber winding is between 300 MPa and 1500 MPa, preferably between 600 MPa and 1500 MPa.

[0012] A prestressing pressure between 300 MPa and 1500 MPa, preferably between 600 MPa and 1500 MPa, provides optimal mechanical properties. This represents a compromise between sufficient prestressing to prevent the web from being subjected to tension, but not so high as to subject the web and flange to excessive prestressing.

[0013] According to another particular embodiment of the invention, the core is formed by a fibrous reinforcement made by three-dimensional weaving and densified by a matrix.

[0014] Therefore, the core exhibits excellent mechanical characteristics for a reduced mass.

[0015] According to another particular embodiment of the invention, the core is made in one piece.

[0016] Thus, the transmission of compressive forces is excellent. Furthermore, a multi-piece core would create unwanted stresses at the interface between the different parts, which could generate cracks or even separation of said parts. This problem is avoided by making the core from a single piece.

[0017] According to another particular embodiment of the invention, the distance between the orifice and the edge of the first end is between 2 mm and 20 mm.

[0018] Indeed, the core must surround the opening with sufficient thickness to prevent any risk of breakage, but not so thick as to limit the risk of the core being subjected to tension. Thus, a thickness between 2 mm and 20 mm is optimal to prevent the formation of cracks in the core, or even its rupture.

[0019] According to a particular embodiment of the invention, the lateral edges of the core are curved outwards.

[0020] The winding of the belt fibers around the core is thus greatly facilitated, and the prestress in the winding as well as the force applied by the belt on the core are better controlled.

[0021] According to a particular embodiment of the invention, the belt is directly in contact with the two lateral edges of the core.

[0022] According to a particular embodiment of the invention, the mechanical part further comprises at least one ring disposed in the orifice.

[0023] The invention also relates to a method for manufacturing a mechanical part comprising:

[0024] - the winding of fibres around a core, the core extending lengthwise between a first end and a second end in a longitudinal direction and extending widthwise between two lateral edges in a transverse direction and comprising at least at its first end an orifice intended to be passed through by a shaft to make a connection with another part, the winding being carried out under tension so as to present a prestress exerting a compressive force on the core,

[0025] - the densification of the fiber winding by a matrix in order to obtain a belt made of composite material.

[0026] During winding, the fibers can be wound in contact with both lateral edges of the core. In particular, the fibers can be wound so that they are in contact along the entire length of the lateral edges of the core.

[0027] According to one particular aspect of the invention, the core is made of metal.

[0028] According to another particular aspect of the invention, the core is made of composite material formed by a fibrous reinforcement densified by a matrix.

[0029] According to a particular aspect of the invention, the fibrous reinforcement of the core is made in one piece by three-dimensional weaving.

[0030] According to one particular aspect of the invention, the core matrix has the same composition as the composition of the belt matrix. Brief description of the drawings

[0031] [Fig. 1] Figure 1 is a schematic view of a landing gear.

[0032] [Fig. 2] Figure 2 is a schematic view of a strut of the landing gear of Figure 1.

[0033] [Fig. 3] Figure 3 is a partial schematic view of a connecting rod according to the prior art showing cracks.

[0034] [Fig. 4] Figure 4 is a schematic top view of an example of a mechanical part according to the invention.

[0035] [Fig. 5] Figure 5 is a detailed view of Figure 4. Description of the implementation methods

[0036] Figures 4 and 5 illustrate an example of mechanical part 100 according to the invention.

[0037] Part 100 includes a web 110. The web 110 extends lengthwise along a longitudinal direction DL between a first end 110a and a second end 110b. The web 110 extends along a transverse direction DT between a first lateral edge 111 and a second lateral edge 112. The longitudinal direction DL is preferably perpendicular to the transverse direction DT. The core 110 extends in thickness along a thickness direction DE perpendicular to the longitudinal direction DL and transverse direction DT.

[0038] The web 110 includes an outer edge 110e. The outer edge 110e delimits the web along the longitudinal direction DL and along the transverse direction DT. The outer edge 110e of the web 110 completely surrounds the web 110. The outer edge 110e is formed in part by the first lateral edge 111 and by the second lateral edge 112. Thus, the first lateral edge 111 and the second lateral edge 112 belong to the outer edge 110e of the web 110. The first lateral edge 111 connects the first end 110a of the web 110 to the second end 110b of the web 110. The second lateral edge 112 connects the first end 110a of the web 110 to the second end 110b of the web 110.

[0039] The core 110 can be made of metal, for example steel or titanium. However, to reduce weight, the core 110 is preferably made of a composite material, that is, a material comprising a fibrous reinforcement densified by a matrix. The core 110 can, for example, be made of a ceramic matrix composite (CMC). However, the core 110 is preferably made of an organic matrix composite (CMO). The fibers used for the fibrous reinforcement of the core 110 are preferably carbon.

[0040] To achieve excellent mechanical properties, the web reinforcement 110 preferably has a three-dimensional weave. "Three-dimensional weave" here refers to a weaving method in which at least some of the warp yarns intertwine with weft yarns across multiple weft layers. A reversal of roles between warp and weft is possible.

[0041] The core 110 includes at least one orifice 131, 132 located at one of its ends 110a, 110b. In particular, the core may include a first orifice 131 and a second orifice 132. The first orifice 131 is located at the first end 110a of the core 110. The first orifice 131 extends along a first axis Ai. The second orifice 132 is located at the second end 110b of the core 110. The second orifice 132 extends along a second axis A2. The first axis Ai and the second axis A2 are preferably parallel. The orifice(s) 131, 132 extend around the thickness direction DE. The orifice(s) 131, 132 extend along the thickness direction DE.

[0042] The mechanical part 100 as illustrated has only single clevises. Of course, we do not depart from the scope of the invention if the mechanical part has double clevises, as is for example the case of the parts illustrated in document FR 2 887 601 A1.

[0043] The orifice(s) 131, 132 are formed in the web 110. Thus, the orifice(s) 131, 132 are entirely delimited by the web 110. The internal surface 131b of the orifice(s) 131, 132 belongs entirely to the web 110. The internal surface 131b of the orifice(s) 131, 132 may be cylindrical. The orifice(s) 131, 132 may have a round or oval cross-section. In the example illustrated in Figures 4 and 5, the first orifice 131 and the second orifice 132 have a round cross-section. Thus, the first orifice 131 has a first radius mi. The second orifice 132 has a second radius m2.

[0044] The orifice(s) 131, 132 are intended to be traversed each by an axis to make a connection with another part.

[0045] The orifice(s) 131, 132 can each accommodate a ring 141, 142. In particular, the first orifice 131 can accommodate a first ring 141. The second orifice 132 can accommodate a second ring 142. The ring 141, 142 comprises an external surface 141a and an internal surface 141b. The external surface 141a of the ring 141, 142 is in contact with the internal surface 131b of the orifice 131, 132. Thus, the external surface 141a of the ring 141, 142 is in contact with the core 110. The core 110 then conforms to the external surface 141a of the ring 141, 142.

[0046] The core 110 includes at least a first end portion extending between the first orifice 131 and the edge of the first end 110a of the core 110. The first end portion may extend along half the perimeter of the first orifice 131. The first end portion may extend along one-third of the perimeter of the first orifice 131.

[0047] The first end portion extends over a determined distance dnoa between the first orifice 131 and the edge of the first end 110a of the core 110. The dnoa distance lies in a plane perpendicular to the thickness direction DE. The dnoa distance can extend radially from the first orifice 131. The dnoa distance is preferably between 2 mm and 20 mm.

[0048] The core 110 includes a second end portion extending between the second orifice 132 and the edge of the second end 110b of the core 110. The second end portion may extend along half the perimeter of the second orifice 132. The second end portion may extend along one-third of the perimeter of the second orifice 132.

[0049] The second end portion extends over a determined distance between the second orifice 132 and the edge of the second end 110b of the core 110. This distance lies in a plane perpendicular to the thickness direction DE. This distance may extend radially with respect to the second orifice 132. This distance is preferably between 2 mm and 20 mm.

[0050] To greatly facilitate the winding of the fibers around the core 110, thereby achieving controlled prestress and stresses around the entire circumference of the belt 120, it is preferable that the lateral edges 111 and 112 be curved outwards from the core 110. Thus, the width along the transverse direction DT of the middle of the mechanical part 100 is greater than the widths along the transverse direction DT of the first and second ends 110a and 110b. The lateral edges 111 and 112 are free of sharp edges. The outer edge 110e of the core 110 is also free of sharp edges.

[0051] The 120 belt surrounds the 110 core. The 120 belt includes an inner edge 120b. The inner edge 120b of the 120 belt is closed. The belt 120 is preferably in contact with the core 110. In particular, the inner edge 120b of the belt 120 is in contact with the core 110. Only the inner edge 120b of the belt 120 can be in contact with the core 110; that is, the other portions of the belt 120 are not in contact with the core 110. Thus, the belt 120 is in contact with the outer edge 110e of the core 110. In particular, the inner edge 120b of the belt 120 is in contact with the outer edge 110e of the core 110. The belt 120 can be in contact with the first end 110a of the core 110 and / or the second end 110b of the core 110. The belt 120 can be in contact with the first lateral edge 111 of core 110 and / or second lateral edge 112 of core 110. Preferably, the belt 120 is in contact with the entire outer edge 110e of core 110. In particular, the inner edge 120b is in contact with the entire outer edge 110e of core 110. Thus, the entire outer edge 110e of core 110 is in contact with the belt 120. The entire outer edge 110e of core 110 may be in contact with the entire inner edge 120b of the belt 120.

[0052] The inner edge 120b of the belt 120 has no sharp edges. The inner edge 120b of the belt 120 consists only of curved surfaces.

[0053] The belt 120 is arranged around the orifice(s) 131, 132. In particular, the belt 120 is maintained at a non-zero distance from the orifice(s). 131, 132. The soul 110 is interposed between the belt 120 and the orifice(s) 131, 132.

[0054] The belt 120 is made of composite material, that is, a material comprising a fibrous reinforcement densified by a matrix. The belt 120 can, for example, be made of ceramic matrix composite (CMC). However, the belt 120 is preferably made of organic matrix composite (CMO). Preferably, in order to improve the mechanical properties of the part 100, the same matrix is ​​used for the web 110 and the belt 120. The matrix used for the web 110 and the matrix used for the belt 120 can be epoxy resins of the same composition, or of different compositions.

[0055] The fiber reinforcement of belt 120 is formed by fibers wound around the core 110. The material used for the fibers of the belt 120 reinforcement can be the same as the material used for the fibers of the core 110 reinforcement. The fibers of the belt 120 reinforcement are preferably carbon fibers. The fibers of the belt 120 reinforcement are preferably category "T" fibers, i.e., fibers with high tensile strength. Thus, category "T" fibers are preferred to category "M" fibers, which have a high tensile modulus. The fibers of the belt 120 reinforcement preferably have a tensile strength greater than 6000 MPa. For example, the fibers used for the belt 120 reinforcement could be category "Tl 100" fibers.

[0056] The fibers of the belt 120 are wound around the outer edge 110e of the core 110. At least a portion of the fibers of the belt 120 may be wound directly in contact with the outer edge 110e of the core 110. The fibers may be wound in contact with both lateral edges 111, 112 of the core 110. In particular, the fibers may be wound so as to be in contact along the entire length of the lateral edges 111, 112 of the core 110 in the longitudinal direction DL.

[0057] The wound fibers exhibit a prestress exerting a compressive force on the core 110; that is, they exhibit a stress exerting a compressive force when the mechanical part 100 is at rest. The mechanical part 100 is said to be at rest when it is not subjected to any mechanical stress. Thus, when the mechanical part 100 is at rest, it is not subjected to either tension or compression. The fiber winding can have a prestress ranging from 300 MPa to 1500 MPa, preferably between 600 MPa and 1500 MPa.

[0058] The fiber winding also exerts a compressive stress on the core 110 to prevent it from being subjected to tensile stress. Thus, the core 110 is prestressed in compression by the fiber winding of the belt 120. The tension in the fiber winding also compresses the interface between the core 110 and the belt 120, thereby improving the mechanical properties of this interface.

[0059] We will now describe an example of a manufacturing process for a mechanical part as described previously.

[0060] The manufacturing process includes the supply of the core 110. If the core 110 is made of metal, for example steel or titanium, it is obtained by appropriate processes which are well known.

[0061] If the core 110 is made of composite material, it can be produced by forming a fibrous reinforcement and densifying said fibrous reinforcement with a matrix. The fibrous reinforcement of the core 110 can be obtained by weaving. In particular, the fibrous reinforcement of the core 110 can be obtained in a single piece by three-dimensional weaving, as described previously. The fibers used for the fibrous reinforcement of the core 110 are preferably carbon fibers.

[0062] The fiber reinforcement of the core 110 is then densified by a matrix. Indeed, the core 110 must be consolidated and densified prior to winding to allow for said winding and to obtain the desired prestress within the winding. For example, the consolidation or densification of the core 110 can be carried out using a resin transfer molding technique (RTM), which is a well-established technique.

[0063] The orifice(s) 131, 132 of the core 110 may be present in the fiber reinforcement before densification by the matrix. One or more inserts may then be placed in the orifice(s) during the densification of the fiber reinforcement of the core 110, in order to prevent matrix material or matrix precursor material from entering the orifice(s). Such inserts may then be removed after densification so as to obtain the orifice(s) 131, 132 of the core 110.

[0064] The orifice(s) 131, 132 of the core 110 can also be formed by machining after densification by the die. In particular, the orifice(s) 131, 132 of the core 110 can be formed by machining before the fibers are wound around the core 110.

[0065] The outer edge 110e of the core 110 can also be produced by machining after densification, and before winding the fibers around the core 110.

[0066] The ring(s) 141, 142 can be arranged in the orifice(s) 131, 132 before the fibers are wound around the core 110. The ring(s) 141, 142 can be arranged in the orifice(s) 131, 132 after the fibers are wound around the core 110.

[0067] The manufacturing process then includes winding fibers around the core 110. The fiber winding is carried out under tension, in order to obtain the desired prestress.

[0068] Winding can be carried out using a winding machine. The winding machine includes at least one fixed frame. The winding machine also includes a system for distributing the fibers to be wound. The fiber distribution system is configured to ensure constant tension on the fibers to be wound at the output of said distribution system. In particular, the The fiber distribution system may include one or more pulleys. Preferably, the exit point of the fiber distribution system is fixed relative to the frame.

[0069] The winding machine also includes two movable jaws that rotate relative to the frame. The jaws are configured to retain the core 110. When the core 110 is mounted on the winding machine, the jaws are positioned on either side of the core 110 in a retention direction. This retention direction corresponds to the thickness direction ΔE of the core 110. The jaws allow the core 110 to be rotated. This enables the fibers delivered by the fiber distribution system to be wound around the core 110 with the appropriate tension.

[0070] The jaws can also be translationally movable relative to the frame. In this case, the jaws are translationally movable along the retention direction. The jaws can thus move in translation along the retention direction during fiber winding. This makes it possible to obtain a controlled winding thickness across the entire width of the outer edge 110e of the core 110.

[0071] The wound fibers may be in the form of single fibers, optionally coated with an interphase. Preferably, the wound fibers may be in the form of a strand pre-impregnated with a matrix precursor, for example, pre-impregnated with resin. The wound fibers may also be in the form of a unidirectional (UD) fabric comprising a plurality of fibers extending in the same direction, the UD fabric being pre-impregnated with a matrix precursor.

[0072] Fiber winding can be performed in a single operation. Alternatively, fiber winding can be performed in several operations. Each fiber winding operation can then be followed by a consolidation or densification operation of the wound fibers. Thus, a consolidation or densification operation is performed between each fiber winding operation. Performing the winding in several operations allows for better control of the desired prestress value in the winding.

[0073] If the wound fibers are pre-impregnated with a matrix precursor, consolidation or densification of the wound fibers can be achieved by curing them to form the matrix from the matrix precursor. If the wound fibers do not have a matrix precursor, consolidation or densification involves adding the matrix material. For example, consolidation or densification can be achieved using a resin transfer molding (RTM) technique, which is a well-established technique.

[0074] The fiber winding is densified by a matrix to obtain the 120 belt.

[0075] 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 even a brake rod.

[0076] The part according to the invention thus exhibits better mechanical properties than similar parts of the prior art.

[0077] The expression "between ... and ..." should be understood as including the boundaries.

Claims

Demands [Claim 1] A mechanical part (100) comprising a core (110) extending lengthwise between a first end (110a) and a second end (110b) along a longitudinal direction (DL) and extending widthwise between two lateral edges (111, 112) along a transverse direction (DT), the core (110) comprising at least at its first end (110a) an opening (131) for a shaft to be passed through to connect with another part, the core (110) being made in one piece, the mechanical part (100) further comprising a belt (120) surrounding the core (100), the lateral edges (111, 112) of the core (110) being in contact with the belt (120), the belt (120) being formed by a fibrous reinforcement densified by a matrix, the reinforcement fibrous belt (120) being formed by a winding of fibers wound around the core (110),the fiber winding exhibiting a prestress exerting a compressive force on the core (110). [Claim 2] Mechanical part (100) according to claim 1, wherein the prestress of the fiber winding is between 300 MPa and 1500 MPa. [Claim 3] Mechanical part (100) according to claim 1 or 2, wherein the prestress of the fiber winding is between 600 MPa and 1500 MPa. [Claim 4] Mechanical part (100) according to any one of claims 1 to 3, wherein the core (110) is formed by a fibrous reinforcement made by three-dimensional weaving and densified by a matrix. [Claim 5] Mechanical part (100) according to any one of claims 1 to 4, wherein the fibers of the fibrous reinforcement of the belt (120) are carbon fibers having a tensile strength greater than 6000 MPa. [Claim 6] Mechanical part (100) according to any one of claims 1 to 5, wherein the distance (dnoa) between the orifice (131) and the edge of the first end (110a) is between 2 mm and 20 mm. [Claim 7] Mechanical part (100) according to any one of claims 1 to 6, wherein the lateral edges (111, 112) of the core (110) are curved outwards. [Claim 8] Mechanical part (100) according to any one of claims 1 to 7, wherein the belt (120) is directly in contact with the two lateral edges (111, 112) of the core (110). [Claim 9] Mechanical part (100) according to any one of claims 1 to 8, the mechanical part (100) further comprising at least one ring (141, 142) disposed in the orifice (131, 132). [Claim 10] A method for manufacturing a mechanical part (100) comprising: - the winding of fibers around a core (110), the core (110) extending lengthwise between a first end and a second end along a longitudinal direction (DL) and extending widthwise between two lateral edges along a transverse direction (DT) and comprising at least at its first end an orifice intended to be traversed by a shaft to make a connection with another part, the core (110) being made in one piece, the winding being carried out under tension so as to present a prestress exerting a compressive force on the core, - the densification of the fiber winding by a matrix so as to obtain a belt (120) of composite material, the lateral edges (111, 112) of the core (110) being in contact with the belt (120). [Claim 11] A manufacturing method according to claim 10, wherein the core (110) is made of composite material formed by a fibrous reinforcement densified by a matrix.

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