Method for producing an assembly of two co-densified parts made of composite material having an organic matrix

Abstract

The invention relates to a method for producing an assembly, comprising: - forming an assembly (1) comprising two fibrous textures (3; 5) placed one on top of the another, and at least one spacer element (10) present on an interface (7) between the two textures and defining flow channels (12) that bring the two textures into communication; - shaping the assembly by applying a compression pressure (PC); and - co-densifying the textures of the assembly shaped in this way, comprising injecting a resin (20) into a porosity of these textures, the resin flowing into the flow channels of the spacer element in order to connect the textures over the interface, the spacer element being (i) made of polymer material having a glass transition temperature Tg which is greater than a temperature Tr of the resin introduced into the moulding cavity, or (ii) made of metal material.

Description

Description Title of the invention: Method for manufacturing an assembly of two parts made of co-densified organic matrix composite material Technical Field

[0001] The present invention relates to a method for manufacturing an assembly comprising two co-densified organic matrix composite material parts in which the thickness of the interface between the two parts is controlled. Prior art

[0002] It is known to produce assemblies of composite material parts by co-densification during which two textures are positioned one on top of the other in a molding cavity, and a compressive pressure is exerted on the assembly when the mold is closed. A matrix material is then introduced so as to densify the textures and ensure their joining by forming a common matrix. The co-densification technique advantageously makes it possible to avoid the use of a third-party adhesion material to carry out the assembly and thus simplify manufacturing. Nevertheless, there may remain a certain variability in the mechanical strength of the assemblies thus obtained. Statement of the invention

[0003] The present invention relates to a method for manufacturing an assembly comprising two co-densified organic matrix composite material parts, comprising: - the formation of an assembly comprising two superimposed fibrous textures, each corresponding to the fibrous reinforcement of one of the parts to be obtained, and at least one spacing element present on an interface between the two textures and defining flow channels connecting the two textures, said assembly being present in a molding cavity, - shaping said assembly in the molding cavity by applying compression pressure, and - the co-densification of the textures of the assembly thus shaped comprising the injection of a resin into a porosity of these textures, the resin flowing in the flow channels of the spacer element to connect the textures on the interface, said spacer element being (i) made of polymeric material having a transition temperature Tg vitreous greater than a temperature Tr of the resin introduced into the molding cavity, or (ii) made of metallic material.

[0004] The glass transition temperature Tg can be determined by differential scanning calorimetry (DSC). Unless otherwise stated, the temperature Tr of the resin introduced into the molding cavity is taken at the time of introduction of the resin into the molding cavity.

[0005] The inventors found that the techniques of the prior art led to a thickness of the interface between the two parts which was not controlled during the co-densification in the molding cavity. Figure 1 illustrates an interface 16 between two textures 14, 30 obtained in the context of the prior art which has an irregular thickness with in particular interface zones Z1, Z2 having significantly different quantities of material. The invention proposes the use of a spacing element which is stable during the co-densification, that is to say that its dimensions and its shape are not substantially altered, in order to control the thickness of the interface and thus limit the variability of the mechanical strength of the assemblies obtained. To ensure this stability, the spacing element is chosen from a metallic material, or from a polymeric material with a glass transition temperature higher than the temperature of the resin introduced.

[0006] In an exemplary embodiment, the spacer element is made of polymeric material and satisfies the condition Tg > Tr + 10°C.

[0007] Such a feature allows for further improvement in the control of the interface thickness.

[0008] In one exemplary embodiment, the spacer element has a honeycomb structure, for example having a grid shape.

[0009] Such a feature concerns spacer elements of aerated structure which do not penalize the mass of the resulting assembly.

[0010] In an exemplary embodiment, the spacer element comprises a first layer defining first material shortage zones, and a second layer, covered by the latter, defining second material shortage zones in partial overlap with the first material shortage zones and together defining at least a section of the flow channels.

[0011] Such a feature helps to improve the homogeneity of the resin flow and the quality of densification, thus further improving the mechanical properties of the assembly. Partial overlap can also allow the resin flow rate to be adjusted according to the injection requirement.

[0012] In an exemplary embodiment, the spacer element comprises two faces each in contact with a distinct texture, each face having openings having a dimension less than or equal to half the diameter of the skin strands of the texture in contact.

[0013] Such a feature helps avoid any risk of distorting textures at the interface.

[0014] It will be noted that the spacing element may be in a single piece, or alternatively be formed by the union of several spacing units each defining contact zones with the textures. In this case, the positioning of these units may be carried out so as to avoid any risk of deforming the textures at the interface. Generally speaking, the spacing element may define continuous contact zones with the textures (surface contact), or discontinuous with for example a plurality of point contacts.

[0015] In an exemplary embodiment, at least one face of the texture-contacting spacer has a planar surface. Alternatively or in combination, at least one face of the texture-contacting spacer has a curved surface. Alternatively or in combination, at least one face of the texture-contacting spacer has a rough surface. Alternatively or in combination, at least one face of the texture-contacting spacer perfectly conforms to a surface of said texture.

[0016] In an exemplary embodiment, a thickness of the spacer element is greater than or equal to 700 μm, for example greater than or equal to 1 mm, or even greater than or equal to 2 mm.

[0017] Such a characteristic is of particular interest in the case of parts subjected to a high shear rate in order to limit the concentration of stresses.

[0018] In an exemplary embodiment, the method further comprises manufacturing by additive manufacturing of the spacer element, prior to forming said assembly.

[0019] Such a feature advantageously allows access to a wide variety of geometries for the spacer element.

[0020] In one embodiment, the fibrous textures are made of carbon threads.

[0021] In one example, the fibrous textures are obtained by three-dimensional weaving.

[0022] In an exemplary embodiment, a first fibrous texture forms a core having a slender shape and comprising two longitudinal ends, and a second fibrous texture forms a belt defining a loop around the core so as to define, at longitudinal ends, free spaces intended for articulation with other parts, at least one spacer element as described above being positioned adjacent to each of these longitudinal ends.

[0023] The area adjacent to the free spaces is the most mechanically stressed because it is closest to the stress concentrations. The invention is of particular interest in this application in order to optimize the mechanical performance of the part and improve the resistance in this area by controlling the thickness of the interface between the textures. Of course, the invention is not limited to a particular type of assembly as will be apparent from the description provided below. Brief description of the drawings [Fig. 1] Figure 1 represents, schematically and partially, an uncontrolled interface during co-densification carried out with a prior art technique. [Fig. 2] Figure 2 represents, schematically and partially, an example of an assembly usable within the framework of the invention. [Fig. 3] Figure 3 shows, schematically and partially, the whole of Figure 2 shaped by applying compression pressure when closing the mold. [Fig. 4] Figure 4 corresponds to a detail of the spacer element implemented in Figures 2 and 3 in zone A. [Fig. 5] Figure 5 is a photograph of an example of a spacer element usable in the context of the invention. [Fig. 6] Figure 6 represents, schematically and partially, the assembly obtained after co-densification of the assembly illustrated in Figures 2 and 3. [Fig. 7] Figure 7 represents, schematically and partially, an overall variant usable within the framework of the invention. [Fig. 8] Figure 8 shows, schematically and partially, a view of a variant of the spacer element according to a first section plane. [Fig. 9] Figure 9 represents, schematically and partially, a view of the variant of figure 8 according to a second section plane. Description of the embodiments

[0024] The invention is now described by means of figures, present for descriptive purposes to illustrate certain embodiments of the invention and which should not be interpreted as limiting the latter.

[0025] Figure 2 illustrates an example of an assembly 1 positioned on a counter-mold 11. The assembly 1 comprises a first texture 3 which is superimposed on a second texture 5 along an interface 7. The textures 3, 5 are superimposed in a direction D. The textures 3, 5 may be formed from carbon threads. The textures 3, 5 may be obtained from at least one textile operation, for example by three-dimensional weaving, in a manner known per se. The textures 3, 5 are intended to form the fibrous reinforcement of the assembly to be obtained.

[0026] The assembly 1 further comprises a spacer element 10 which is present on the interface 7. The element 10 is interposed between the textures 3, 5 and makes it possible to maintain them at a controlled distance in the assembly. The element 10 has two opposite faces 10a and 10b which are each in contact with a respective texture 3, 5. The element 10 defines flow channels 12 which extend between the faces 10a and 10b so as to put the textures 3, 5 in communication and allow the resin to flow from one texture to another. Figures 2 and 3 are not to scale, in particular with regard to the dimensions of the element 10 and the size of the channels 12 for reasons of readability. The faces 10a, 10b extend transversely, for example perpendicularly, to the direction D. The channels 12 extend transversely, for example perpendicularly to the faces 10a, 10b.

[0027] The element 10 implemented in the example considered has a grid shape of the type illustrated in figure 5. The element 10 thus has areas of lack of material, here forming cells, which define the channels 12. Generally, the element 10 can have a cell structure with a volume rate of areas of lack of material greater than or equal to 70%, for example greater than or equal to 80%.

[0028] According to a preferred embodiment, the element 10 is formed by additive manufacturing so as to be able to access a wide range of geometries. As illustrated in Figure 4 which represents an enlargement of the zone A, the element 10 is formed by a superposition of several layers 103, 104 and 105 each having a grid shape. The faces 10a, 10b have openings 113, 115 which here have a dimension DI 13, DI 15 less than or equal to half the diameter of the skin strands of the texture 3, 5 in contact. In the example considered, the areas of lack of material of each of the layers 103-105 overlap exactly but it is not outside the scope of the invention when this is not the case, as will be illustrated in connection with Figures 8 and 9. By way of example, the element 10 can be produced by filament fusion or stereolithography.It will be advantageous to use a thermoplastic polymer in order to produce an element 10 in polymeric material by additive manufacturing, but a metallic element 10 can also be formed by this. technique. In this respect, additive manufacturing can be of particular interest for giving the channels 12 a complex shape, or for locally varying the thickness of the element 10 by varying the number of constituent layers. According to a variant, the element 10 is not formed by additive manufacturing but by molding.

[0029] As illustrated in Figure 2, a mold 13 is positioned on the counter-mold 11 so as to define a molding cavity CM in which the assembly 1 is present. The mold 11 comprises one or more ports 15 through which a resin is intended to be injected into the cavity CM. Alternatively or in combination, one or more ports could be provided in the counter-mold 11. The sealing of the cavity CM can be ensured by a sealing gasket 17 present between the mold 13 and the counter-mold 11.

[0030] The positioning of the mold 13 makes it possible to close the cavity CM and to apply a compression pressure PC to the assembly 1. In this way, the assembly 1 can be shaped into the assembly to be obtained by adjusting in particular the thicknesses e3 and e5 of the textures 3, 5. The thicknesses e3 and e5 are reduced during shaping as illustrated in FIG. 3, for example by at least 20%. On the other hand, the thickness e7 of the interface 7 (which also corresponds to the thickness of the element 10) does not vary significantly during shaping. It will be advantageous to choose a material for the element 10 having a stiffness greater than that of the textures along the direction of application of the compression pressure PC, so as to avoid any risk of the element 10 being damaged when the mold is closed.

[0031] Generally, the element 10 may be formed from a polymeric material, for example thermoplastic, or metallic. In the case of a metallic element 10, the materials are chosen to avoid galvanic coupling with the fibers of the textures, or by providing an insulating coating on the fibers, for example glass, to avoid this phenomenon.

[0032] Once the mold 13 is closed, a resin 20 is injected into the cavity CM through the port 15 and fills the porosity of the textures 3, 5 by flowing in particular through the channels 12 to pass from one texture 3 to the other 5. Thus, the resin 20, once solidified to form the organic matrix, makes it possible to bind the textures 3, 5 together to produce the assembly. Care will of course be taken to choose the element 10 so that it is chemically compatible with the resin 20 used, and in particular not reactive or not altered in contact with the latter. The material of the element 10 is chosen so as to be thermally compatible with the method used. Thus, in the case where a polymeric material is used, the latter has a glass transition temperature Tg higher than the temperature Tr of the resin 20 introduced into the cavity CM, verifying advantageously the condition Tg > Tr + 10°C. In the case where a thermosetting resin is used and this is crosslinked, after injection, by curing at a temperature Te higher than Tr, the temperature Tg can also be higher than the temperature Te. Alternatively, the element 10 is made of a metallic material which gives it sufficient thermal stability compared to the temperatures typically used to introduce the resin and possibly crosslink it. In this way, the thickness of the interface 7 is guaranteed during the manufacture of the assembly. For example, the resin 20 can be the epoxy resin marketed under the reference CYCOM® PR 520N RTM by the company Solvay, and the element 10 can be made of polyethyleneimine (PEI). Alternatively, polyetherketoneketone (PEKK) could be used for the element 10.

[0033] Figure 6 illustrates the assembly 50 obtained by co-densification after injection of the resin 20, and possible crosslinking, so as to form an organic matrix 40 which densifies the textures 3, 5 and mechanically connects them through the interface 7. The matrix 40 is in particular present through the channels 12 of the element 10 so as to ensure this mechanical connection. The element 10 is an integral part of the assembly 50 obtained. The element 10 is embedded in the matrix 40. The matrix 40 densifies the majority (more than 50%), for example at least 80%, or even substantially all, of the volume of the porosity of the textures 3, 5 and the channels 12. The dimension, in particular the thickness, and the shape of the spacing element are not altered so as to guarantee an interface 7 of regular thickness between the two parts unlike the techniques of the prior art.The assembly 50 is removed from the cavity CM after formation of the die 40, for storage or assembly to other elements. The assembly 50 may form an aircraft part, such as a part of an aircraft landing gear, but it will be recognized that other applications are possible.

[0034] By way of example, Figure 7 represents a variant of assembly 100 which is intended to form an assembly intended to be articulated to other parts at its ends. The assembly considered here is intended to be an integral part of an aircraft landing gear; it may be a connecting rod, a landing gear strut or a constituent element thereof, or even a brake bar.

[0035] The assembly 100 here comprises a first fibrous texture 300 which forms a core having a slender shape and comprising two longitudinal ends 301, 302, and a second fibrous texture 500 which forms a belt defining a loop around the core so as to define, at the longitudinal ends, free spaces 401, 402 intended for articulation with other parts, at least one spacing element 10 as described above being positioned adjacent to the free spaces 401, 402.

[0036] We have just described the case of a multi-layer spacer element 10 in which the lack of material of the layers overlap exactly to provide the flow channels 12 for the resin 20. The example which will be described below, in connection with figures 8 and 9, concerns another type of spacer element 101 in which the material of the superimposed layers is arranged in a staggered pattern.

[0037] Thus, the spacer element 101 has a multi-layer structure, each of the layers 131-135 having a grid shape, but with an offset between different superimposed layers so that the resin 20 can flow along the direction D but also in the deposition plane P of the element 101, as illustrated in FIG. 9.

[0038] The element 101 here comprises five layers 131, 132, 133, 134 and 135 which each define a grid offset from the adjacent layer(s). The section plane of Figure 8 contains filaments of the layers 132 and 134 which each define one side of the honeycomb patterns of the respective grids. The section plane of Figure 9 is intermediate between two opposite sides of the honeycomb patterns. The element 101 comprises a first layer 131 defining first areas 141 of lack of material, and a second layer 133, covered by the latter, defining second areas 143 of lack of material in partial overlap with the first areas 141 of lack of material and together defining at least a section of the resin flow channels 12. The surface overlap between the areas of lack of material 141 and 143 may be between 20% and 80%.The illustrated example comprises a third layer 135 defining third areas 145 of lack of material, covered by the first 131 and second 133 layers, in partial overlap with the second areas 143 of lack of material, also making it possible to define a section of the channels 12. The surface overlap between the areas of lack of material 143 and 145 can be between 20% and 80%.

[0039] The examples which have just been described correspond to sets comprising exactly two superimposed fibrous textures but the person skilled in the art will recognize that it is not outside the scope of the invention if more than two superimposed textures are co-densified by implementing the principle of the invention with the presence of one or more spacing elements on an interface between each pair of adjacent textures.

[0040] The expression "between ... and ..." must be understood as including the limits.

Claims

Claims

1. Method for manufacturing an assembly (50) comprising two co-densified organic matrix composite material parts, comprising: - the formation of an assembly (1; 100) comprising two superimposed fibrous textures (3; 5; 300; 500), each corresponding to the fibrous reinforcement of one of the parts to be obtained, and at least one spacing element (10; 101) present on an interface (7) between the two textures and defining flow channels (12) connecting the two textures, said assembly being present in a molding cavity (CM), - shaping said assembly in the molding cavity by applying a compression pressure (PC), and - the co-densification of the textures of the assembly thus shaped comprising the injection of a resin (20) into a porosity of these textures, the resin flowing in the flow channels of the spacer element to connect the textures on the interface, said spacer element being (i) made of polymeric material having a glass transition temperature Tg higher than a temperature Tr of the resin introduced into the molding cavity, or (ii) made of metallic material.

2. Method according to claim 1, in which the spacer element (10; 101) is made of polymeric material and satisfies the condition Tg > Tr + 10°C.

3. A method according to any one of claims 1 and 2, wherein the spacer element (10; 101) has a honeycomb structure.

4. A method according to any one of claims 1 to 3, wherein the spacer element (101) comprises a first layer (131) defining first areas (141) of lack of material, and a second layer (133), covered by the latter, defining second areas (143) of lack of material in partial overlap with the first areas of lack of material and together defining at least a section of the flow channels (12).

5. Method according to any one of claims 1 to 4, in which the spacer element (10; 101) comprises two faces (10a; 10b) each in contact with a distinct texture (3; 5; 300; 500), each face having openings (113; 115) having a dimension (DI 13; DI 15) less than or equal to half the diameter of the skin strands of the texture in contact.

6. A method according to any one of claims 1 to 5, wherein a thickness (e7) of the spacer element (10; 101) is greater than or equal to 700 pm.

7. A method according to any one of claims 1 to 6, wherein the method further comprises manufacturing by additive manufacturing the spacer element (10; 101), prior to forming said assembly (1; 100).

8. Method according to any one of claims 1 to 7, in which the fibrous textures (3; 5; 300; 500) are made of carbon yarns.

9. Method according to any one of claims 1 to 8, in which the fibrous textures (3; 5; 300; 500) are obtained by three-dimensional weaving.

10. A method according to any one of claims 1 to 9, comprising: - forming an assembly (100) comprising a first and a second superimposed fibrous textures (300; 500), each corresponding to the fibrous reinforcement of one of the parts to be obtained, the first fibrous texture forming a core having a slender shape and comprising two longitudinal ends, and the second fibrous texture forming a belt defining a loop around the core so as to define, at the longitudinal ends, free spaces (401; 402) intended for articulation with other parts, and at least one spacing element (10; 101) present on an interface (7) between the first and the second textures and defining flow channels (12) putting the first and the second textures in communication, said at least one spacing element being positioned adjacent to each of these longitudinal ends, said assembly being present in a molding cavity (CM), - shaping said assembly in the molding cavity by applying a compression pressure (PC), and - co-densifying the first and second textures of the assembly thus shaped comprising injecting a resin (20) into a porosity of these textures, the resin flowing in the flow channels of the spacer element to connect the textures on the interface, said spacer element being (i) made of polymeric material having a glass transition temperature Tg higher than a temperature Tr of the resin introduced into the molding cavity, or (ii) in metallic material. I

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