Fiber reinforcement for the manufacture of a composite part intended to be articulated with other parts

Abstract

Fiber reinforcement for the manufacture of a composite part intended to be articulated with other parts The present invention relates to a fibrous preform (1) of a part of the core of a fibrous reinforcement for a part made of composite material, the preform having a slender shape along a longitudinal direction (X) and being formed by three-dimensional weaving of first yarns extending along the longitudinal direction with second yarns transverse to the first yarns, the preform comprising two longitudinal ends (3a;3b) intended for articulation with other parts and a median zone (MZ) situated between the longitudinal ends, each longitudinal end having a thickness greater than one thickness of the median zone, the median zone having a first volume ratio of first wires relative to second wires which is greater than one, and each longitudinal end having a second volume ratio of first wires relative to second wires which is less than the first ratio and closer to one than this first ratio. Figure for the abbreviation: Fig. 1.;

Description

Title of the invention: Fibrous reinforcement for the manufacture of a composite part intended to be articulated with other parts. Technical field

[0001] The invention relates to a fibrous preform intended to form part of a fibrous reinforcement of a composite material part, which part is intended to be articulated with other parts at its ends, and an associated manufacturing process. Prior art

[0002] The use of composite materials as a replacement for metallic materials can be proposed with a view to weight reduction, which is a constant concern in the particular case of aircraft parts. In this regard, US patent 7,704,429 proposed the manufacture of landing gear struts from composite material that include regions, called cleats, intended for articulation and load transfer with other parts and formed by a laminated structure with intercalated plies between primary plies extending from the body of the reinforcement. This solution may nevertheless present drawbacks. Indeed, cleats with a laminated configuration may lead to an increase in the size of the load transfer areas compared to metallic parts in order to avoid the risk of delamination.The overall system mass reduction then becomes less advantageous, and the integration of the part becomes more challenging due to its increased size. Another issue is that the proposed manufacturing technique involves significant manual intervention, which can lead to non-conformities and increased costs. Finally, the mechanical performance of the composite material proposed in this document can be improved, particularly in terms of compressive strength in a mid-length area of ​​the part, known as the "current zone." One option to address this is to add material to the current zone, which increases the mass and therefore does not provide a fully satisfactory solution.

[0003] The invention proposes to address all or part of the aforementioned drawbacks. Description of the invention

[0004] The present invention relates to a fibrous preform of a core portion of a fibrous reinforcement for a part made of composite material, the preform having a slender shape along a longitudinal direction and being formed by three-dimensional weaving of first yarns extending along the longitudinal direction with second yarns transverse to the first yarns, the preform comprising two longitudinal ends intended for articulation with other parts and a median zone situated between the longitudinal ends, each longitudinal end having a thickness greater than a thickness of the median zone, the median zone having a first volume ratio of first wires relative to second wires which is greater than one, and each longitudinal end having a second volume ratio of first wires relative to second wires which is less than the first ratio and closer to one than that first ratio.

[0005] The volume ratio of the first yarns relative to the second yarns corresponds to the ratio [volume occupied by the first yarns] / [volume occupied by the second yarns]. For the sake of brevity, this ratio may be referred to hereafter as the "F1 / F2 ratio." In the specific case where the first yarns correspond to the warp yarns, this ratio corresponds to the warp / weft ratio. According to one variant, the first yarns may correspond to the weft yarns and the second yarns to the warp yarns.

[0006] The invention proposes an optimized design for a core preform of a fiber reinforcement of the core-belt assembly type, based on three-dimensional weaving techniques and on joint zones that are thicker than the central, or normal, zone, in order to obtain improved resistance to stress. Furthermore, it is proposed to rebalance the F1 / F2 ratio in these joint zones so as to control the fiber content while allowing a design with a constant or substantially constant number of first yarn layers along the entire length of the preform. The manufacturing process is thus repeatable by minimizing manual steps and allows for the production of a higher-quality reinforcement by avoiding, or significantly limiting, the local addition of first yarns at the ends in excess thickness and their subsequent cutting, which can result in production non-conformities due to slight residual excess lengths.

[0007] In one embodiment, each longitudinal end has a spacing between consecutive columns of second wires that is less than a spacing between consecutive columns of second wires in the median area.

[0008] Such a characteristic constitutes a first lever allowing the F1 / F2 ratio to be modified so as to rebalance it at the longitudinal ends.

[0009] In alternative or combination, each longitudinal end has a second wire title greater than a second wire title in the median zone.

[0010] Such a feature constitutes a second lever allowing the F1 / F2 ratio to be modified so as to rebalance it at the longitudinal ends.

[0011] Of course, the F1 / F2 ratio can be modified by changing both the inter-column spacing and the title of the second threads.

[0012] In one embodiment, the preform defines, on its upper and lower sides, positioning edges having a transverse dimension, measured transversely to the longitudinal direction, that is evolving and passing through a maximum in the middle zone.

[0013] This increased transverse dimension increases the inertia of the part, which is beneficial for resistance to buckling, bending, and certain vibration modes. Furthermore, the strength of the interface increases with the surface area.

[0014] In one embodiment, the preform is made of carbon fibers.

[0015] The invention also relates to a method for manufacturing a fibrous reinforcement for a part made of composite material, comprising: - the positioning of a woven fibrous belt texture on a preform of a core part as described above, the belt texture defining a loop around the preform of the core part so as to define, at the longitudinal ends, free spaces intended for articulation with other parts.

[0016] In one embodiment, the belt texture is made of carbon fibers.

[0017] The invention also relates to a method for manufacturing a composite part intended to be articulated with other parts, comprising: - the formation of a fibrous reinforcement as described above, and - the formation of a matrix in a porosity of the fibrous reinforcement thus obtained.

[0018] In one embodiment, the matrix is ​​an organic matrix.

[0019] In one embodiment, the part is a landing gear strut, part of a landing gear strut or a brake bar. Brief description of the drawings

[0020] [Fig.1] Fig.1 represents an example of a fibrous core preform according to the invention.

[0021] [Fig.2A] The [Fig.2A] represents the cross-section of the preform of the [Fig.1] over a first area of ​​its length.

[0022] [Fig.2B] The [Fig.2B] represents the cross-section of the preform of the [Fig.1] over a second area of ​​its length.

[0023] [Fig.2C] The [Fig.2C] represents the cross-section of the preform of the [Fig.1] over a third zone of its length.

[0024] [Fig.3] The [Fig.3] represents a detail of an example of a longitudinal end of a core preform according to the invention.

[0025] [Fig.4] The [Fig.4] represents a detail of an example of a longitudinal end of a core preform according to the invention.

[0026] [Fig. 5] [Fig. 5] represents a fibrous reinforcement of a part made of composite material obtained after positioning the belt texture on the preform of [Fig. 1]. Description of embodiments

[0027] Figure 1 shows a fibrous preform 1 of a core of a fibrous reinforcement for a part made of composite material. The preform 1 has a slender shape extending the along a longitudinal direction X. It can be obtained by three-dimensional weaving in a single piece using, for example, an interlock weave. Three-dimensional weaving, or 3D weaving, refers to a weaving method in which at least some of the first yarns oriented along the X direction interlock second yarns transverse to the first yarns over several layers of second yarns. Such a weave can be produced on a Jacquard loom in a manner known per se. The preform 1 comprises, successively along the X direction, a first longitudinal end 3a, a mid-zone ZM, and a second longitudinal end 3b. Each of the first end 3a, the mid-zone ZM, and the second end 3b can be obtained by three-dimensional weaving and be located in the textile extension of one another. The mid-zone ZM can be designed to withstand tensile and compressive forces.The longitudinal ends 3a, 3b have a curved shape, for example, approximately circular, and are intended to define free spaces in the final part for articulation with other parts. As an example, the mid-zone ZM can have a length L1 between 50% and 98% of the length LO of the preform 1, and each end 3a, 3b can have a length L2, L3 between 1% and 25% of the length LO. The lengths are measured along the X direction. The mid-zone ZM can be centered with respect to a plane P50 located at mid-length of the preform 1 and perpendicular to the X direction. The longitudinal ends 3a, 3b have different dimensions, specifically different widths LA2, LA3, which are measured along the width direction L.The preform 1 defines positioning edges 12 on its upper and lower sides, extending along the longitudinal direction X and defining a positioning surface 30 for the belt texture. The transverse dimension DT of the positioning edges 12 in the mid-zone ZM is greater than that at the ends 3a and 3b. This dimension DT can, as illustrated, increase in the mid-zone ZM when moving from the first end 3a, be at its maximum near the mid-length plane P50 of the preform 1, for example, at least on the section between planes P40 and P60 located at 40% and 60% of the length LO and perpendicular to the X direction, and then decrease in the mid-zone ZM towards the second end 3b. In cross-section, the preform 1 includes a central portion 10 which has the two positioning edges 12 on its upper and lower sides.In the illustrated example, the edges 12 and the central portion 10 are offset along the width (direction L). The preform 1 can be obtained by three-dimensional weaving of a single-piece fibrous strip, creating unbonds so as to form, after folding, the unbonded portions 16a, 16b the positioning edges 12. An intercalated portion 18, allowing for a generally flat positioning surface 30, can be present between the portions 16a, . 16b and can be obtained by cutting an interlayer texture separated from portions 16a and 16b. In the illustrated example and as shown in Figures 2A to 2C, the thickness e2 of the first end 3a is greater than the thickness el of the mid-zone ZM. The thickness e3 of the second end 3b is less than the thickness e2 but greater than the thickness el. The thicknesses are measured along the thickness direction (direction E) and correspond to the smallest dimension. As an example, the ratio e2 / el can be greater than 1 and less than or equal to 4, for example, between 1.5 and 2.5, and the ratio e3 / el can be greater than 1 and less than or equal to 4, for example, between 1.5 and 2.5. The preform 1 can, as illustrated, have an I-shaped form (called double angle shape) in cross-section with respect to the longitudinal direction X. In the illustrated example, the positioning edges 12 each form an angle approximately equal to 90° with the direction L.The positioning edges 12 form lateral fins for positioning the belt texture. The preform 1 defines, at the positioning edges 12, the positioning surface 30 on which the belt texture is intended to be deposited.

[0028] As indicated above, the F1 / F2 ratio in ends 3a and 3b is lower than the F1 / F2 ratio in the middle zone ZM and closer to unity. Thus, the absolute value of the difference [(second volume ratio of first wires relative to second wires) - 1] is less than the difference [(first volume ratio of first wires relative to second wires) - 1]. By way of example, the F1 / F2 ratio in the middle zone ZM can be between 1.2 and 9, and the F1 / F2 ratio in ends 3a and 3b can be between 0.6 and 4. Note that ends 3a and 3b can have the same or different F1 / F2 ratios. Figures 3 and 4 show different ways of varying the F1 / F2 ratio. In the example of [Fig.[3] The ESN spacing between consecutive columns CLN and CLN+1 of second sons 22 is modified so as to decrease to a value ES2 in an end zone 3a, 3b lower than an ESI value in the middle zone ZM. As illustrated, this evolution can be gradual, passing through one or more intermediate values ​​ES3 lower than ESI but greater than ES2. In one example, the ES1 / ES2 ratio can be between 1 and 5. [Fig. 4] represents the case where the title of the second sons is increased in the end zone 3a, 3b relative to the middle zone ZM between a first title t1 and a second title t2 (son 221 with title t1 and son 222 with title t2). This evolution can be gradual, passing through second sons 223 having one or more intermediate titles t3 greater than t1 but less than t2.

[0029] We have just described an example of a preform 1 according to the invention. This preform 1 is intended to form only a part of the fibrous reinforcement 50 of the composite part to be obtained. The following section describes the continuation of the manufacturing process of the The component comprises the positioning of a woven belt texture 40 around the preform 1, as illustrated in [Fig. 5]. The texture 40 may be in the form of a strip that is wrapped around the preform 1. During positioning, the texture 40 rests on the positioning surface 30. The texture 40 may be in the form of a single strip of fabric, but it is not outside the scope of the invention if it is in the form of several strips placed end to end or side by side. The texture 40 may also be obtained by three-dimensional weaving, for example, with an interlock weave. The texture 40 defines a closed loop around the preform 1 and defines free spaces 42 for articulation with the other components. The texture 40 may follow the shape of the positioning edges 12 so as to cover them completely.Inserts (not shown) can be temporarily used at the longitudinal ends 3, and the second texture 40 can be wrapped around them to ensure the desired shape for the end regions. The entire preform 1 and texture 40 are then densified, for example, by introducing a resin, such as an epoxy resin, followed by cross-linking if it is a thermosetting resin, or cooling if it is a thermoplastic resin. The matrix can be formed using resin transfer molding, a well-established technique. This produces a composite part designed to be articulated with other parts at its longitudinal ends. The fibrous reinforcement 50 of the part can be made of carbon fibers, and the part can have an organic matrix as described above.The part may or may not be intended for an aeronautical application. For example, it could be a connecting rod, a landing gear strut or component thereof, or a brake rod. The resulting part can be mounted to other parts by positioning a pivot pin through the free spaces 42 for connection to other parts, along with a contact insert for this pin.

Claims

Claims

1. A fiber preform (1) of a core portion of a fiber reinforcement (50) for a composite material part, the preform having a slender shape along a longitudinal direction (X) and being formed by three-dimensional weaving of first yarns extending along the longitudinal direction with second yarns transverse to the first yarns, the preform comprising two longitudinal ends (3a; 3b) intended for articulation with other parts and a middle zone (ZM) located between the longitudinal ends, each longitudinal end having a thickness (e2; e3) greater than a thickness (el) of the middle zone, the middle zone having a first volume ratio of first yarns relative to the second yarns which is greater than unity, and each longitudinal end having a second volume ratio of first yarns relative to the second yarns which is less than the first ratio and closer to unity than this first ratio.

2. A fiber preform (1) according to claim 1, wherein each longitudinal end (3a; 3b) has a spacing (ES2) between consecutive columns of second yarns which is less than a spacing (ESI) between consecutive columns of second yarns in the middle zone (ZM).

3. Fibrous preform (1) according to claim 1 or 2, wherein each longitudinal end (3a; 3b) has a count (t2; t3) of the second yarns greater than a count (tl) of the second yarns in the middle zone (ZM).

4. Fibrous preform (1) according to any one of claims 1 to 3, in which the preform defines, on upper and lower sides, positioning edges (12) having a transverse dimension (DT), measured transversely to the longitudinal direction (X), which evolves and passes through a maximum in the median zone (ZM).

5. A fibrous preform (1) according to any one of claims 1 to 4, wherein the preform is made of carbon yarns.

6. A method of manufacturing a fibrous reinforcement (50) of a composite material part, comprising: - positioning a woven belt fibrous texture (40) on a preform (1) of a core part according to any one of claims 1 to 5, the belt texture defining a loop around the preform of the core part so as to define, at the longitudinal ends (3a; 3b), free spaces (42) intended for articulation with other parts.

7. The method of claim 6, wherein the belt texture (40) is carbon yarn.

8. Method for manufacturing a composite part intended to be articulated with other parts, comprising: - the formation of a fibrous reinforcement (50) according to claim 6 or 7, and - the formation of a matrix in a porosity of the fibrous reinforcement thus obtained.

9. The method of claim 8, wherein the matrix is ​​an organic matrix.

10. A method according to claim 8 or 9 wherein the part is a landing gear strut, a portion of a landing gear strut or a brake bar.

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