BR112020009347B1 - FIBROUS STRUCTURE, PART OF COMPOSITE MATERIAL, AND METHOD OF MANUFACTURING A FIBROUS STRUCTURE - Google Patents

Abstract

The invention relates to a fibrous structure (200) comprising a plurality of weft layers and warp layers connected by multilayer three-dimensional weaving, the fibrous structure (200) having at least first (203) and second (204) portions which are adjacent in the warp direction, the first portion (203) having, in a direction perpendicular to the warp and weft directions, a thickness that is greater than the thickness of the second portion (204), distinguished by the fact that the first portion (203) comprises, in its core (2031), at least one fibrous texture (ML) obtained by three-dimensional weaving of warp yarns and weft yarns in the form of a Mock-Leno weaving grid, said at least one texture ( ML) being present between two covers (2032; 2033) present on the surface of the first portion (203) and being connected to the covers (2032; 2033) by warp threads (C3; C16) belonging to said covers which are locally deflected towards the said texture.

Description

Fundamentals of the invention

[001] The present invention is related to the creation of parts from composite material, and more particularly to the creation of fiber reinforcement structures for such parts by three-dimensional or multilayer weaving.

[002] One field of application of the invention is the creation of parts from structural composite material, that is, parts having a fiber reinforcement structure and densified by a matrix. Composite materials enable parts to be made having an overall weight that is lower than that of the same parts when made from a metallic material.

[003] The invention relates more particularly to parts made from composite material that includes one or more portions of extra local thickness, as applies, for example, to the root of an aircraft blade, which corresponds to a zone having large variation in thickness in the composite material piece. For a part made from a composite material that has varying thickness, the thickness variation is controlled in the fibrous structure that must constitute the reinforcement of the part.

[004] Obtaining blades from composite material for turbine engines has already been proposed. Reference may be made in particular to US patent application 2011/0311368 jointly filed by Snecma and Snecma Propulsion Solide. This application describes the manufacture of a turbine engine blade from a composite material comprising fiber reinforcement densified by a matrix, the outline of the fiber that must constitute the reinforcement is made by multilayer weaving and comprises a first portion of small thickness forming the airfoil preform and a second portion of greater thickness forming a blade root preform. Under such circumstances, the blade root preform is made using an insert so as to form a bulb-shaped region in the portion of the blade corresponding to its root.

[005] However, this technique for forming the blade root makes the industrial manufacture of the blade more complex and increases its manufacturing cost since it leads to large material losses and requires difficult handling, which reduces production speed. Furthermore, the insert, which is also made of composite material, needs to be densified and machined, thus leading to additional costs and possibly parts being rejected.

[006] The preform textile, which is naturally flexible, interacts mechanically with the insert and can lead, in particular, to shear in the textile, turning movements of the insert, loss of interconnection between the insert and the textile, etc.

[007] Furthermore, it appears that the molding and densification of the portion of the preform that is to form the root is difficult, in particular because the tolerances for the bulb-shaped root profile are very small (on the order of a tenth of a millimeter) and because this portion of the blade presents severe requirements in terms of mechanical properties, given that the root of the blade concentrates most of the forces that are applied to the blade.

[008] Another solution, as described in particular in documents US 7,101,154 and US 2011/0311368, consists of increasing the weight (and thus the cross-section) of the yarns in the thickest portions of the fibrous structure in order to reduce the capacity to decrease thickness while the 3D fibrous structure is being formed with compression. However, the use of high weight yarns locally increases the fiber fraction in the preform. If the fiber fraction is too large, the resulting pore network may not be sufficient to enable the matrix components to have good access to the preform core and consequently to obtain a composite material that is uniform and thus presents good mechanical properties. .

[009] It is, therefore, desirable to be able to have 3D or multilayer fibrous structures available including portions of greater thickness, but which do not present the drawbacks mentioned above.

Object and summary of the invention

[0010] To this end, in a first aspect, the invention provides a fibrous structure comprising a plurality of weft layers and warp layers interconnected by three-dimensional multilayer weaving, the fibrous structure having at least first and second portions that are adjacent in the warp direction, the first portion having, in a direction perpendicular to the warp and weft directions, a thickness that is greater than the thickness of the second portion, the structure being distinguished by the fact that the first portion has, at its core , at least one fibrous texture obtained by three-dimensional weaving of warp yarns and weft yarns in the form of a Mock-Leno weaving grid, said at least one texture being present between two coverings present on the surface of the first portion and being attached to the coverings by the warp threads belonging to said coverings which are locally deflected in said texture.

[0011] Using the fibrous texture of Mock-Leno weaving in the core of the fibrous structure makes it possible to obtain a large variation in thickness between the first and second portions while controlling the fiber fraction in the core of the first portion. Furthermore, this Mock-Leno weave texture allows the matrix ingredients to infiltrate the fibrous structure to the core very well because of its aerated structure in the form of a grid, and is compatible with the use of high weight filaments. The fibrous structure of the invention is entirely textile (that is, without any added insert) and the structure's threads are interconnected by weaving in 3D multilayers, thus ensuring that the structure cannot be delaminated.

[0012] A Mock-Leno weave texture comprises a plurality of weft layers and is distinguished by the fact that it is formed by weaving a plurality of warp yarns with a plurality of weft yarns and by the fact that it comprises at least : a first group of warp yarns comprising at least one interlayer binding warp yarn that connects the weft yarns of a first texture layer to the weft yarns of a second texture layer that is adjacent to the first layer; and a second group of warp threads, distinct from and adjacent to the first group of warp threads in the weft direction, said second group comprising at least one interlayer binding warp thread connecting the weft threads of the first layer to the weft yarns of the second layer and presenting an interconnection direction with the weft yarns that is inverted in relation to the interconnection direction presented by the interlayer binding warp yarn of the first group with the weft yarns.

[0013] Throughout this text and in all drawings, it is stated and shown, by convention and for reasons of convenience, that it is the warp threads that are deflected from their paths in order to trap the weft threads. However, these roles between warp and weft may be reversed, and such reversal should also be considered to be covered by the claims.

[0014] The fact that the interlayer binding warp threads in each of the first and second groups are interconnected with the weft threads in reversed interconnecting directions makes it possible to prevent these two binding threads from coming into contact. This feature makes it possible to maintain non-zero spacing along the weft direction between the first and second groups of warp threads, thus giving a grid format to the texture presenting channels formed through its thickness, each of these channels being defined in the weft direction. by two adjacent groups of warp threads and in the warp direction by two adjacent groups of weft threads. The presence of these channels makes it possible to give the Mock-Leno texture an aerated structure, thus serving in particular to allow the matrix ingredients to infiltrate well into the core.

[0015] Preferably, each of the first and second groups of warp threads comprises at least two side warp threads located on both sides of the interlayer connecting warp thread, each of these side warp threads interconnecting with the first layer weft threads.

[0016] Also preferably, the side warp threads of the first group have an interconnection direction with the weft threads that is inverted in relation to the interconnection direction presented by the side warp threads of the second group with the weft threads.

[0017] In one embodiment, the fibrous texture of the MockLeno weaving presents, in a direction perpendicular to the warp and weft directions, a thickness that decreases going towards the second portion.

[0018] This feature is advantageous for controlling the shape of the first portion and ensuring the thickness transition with the second portion.

[0019] In one embodiment, the first and second portions have the same number of warp threads woven continuously between said first and second portions, and the first portion includes, in its core, a number of layers of warp thread that is greater than the number of layers of warp yarn present in the core of the second portion.

[0020] By subdividing the layers of warp yarns in the core of the first portion (i.e., by varying their count), it is possible to control the fiber fraction in the core of the first portion while maintaining a satisfactory warp/weft ratio in the covering. over the entire fibrous structure. By way of example, the first portion may include, in its core, a number of layers of warp yarn that is equal to twice the number of layers of warp yarn present in the core of the second portion.

[0021] In one embodiment, the structure comprises carbon wires or ceramic material wires. The ceramic material of the wires may, for example, be an oxide material such as alumina, or a non-oxide material such as silicon carbide.

[0022] The present invention also provides a piece of composite material comprising fiber reinforcement densified by a matrix, said fiber reinforcement being constituted by a fibrous structure as described above.

[0023] In one embodiment, the part corresponds to a turbine blade, the first portion of the fibrous structure constituting the root portion of the fiber reinforcement blade.

[0024] The present invention also provides a method of manufacturing a fibrous structure by three-dimensional multilayer weaving between a plurality of weft yarns and warp yarns, the fibrous structure having at least first and second portions that are adjacent in the warp direction. , the first portion having, in a direction perpendicular to the warp and weft directions, a thickness greater than the thickness of the second portion, the method being distinguished by the fact that the first portion is made by means of a three-dimensional weaving step warp and weft layers in which a fibrous texture is formed in the shape of a Mock-Leno weaving grid in the core of the first portion together with coverings on the surface of the first portion, the weaving of the coverings being locally modified so as to deflect certain threads of warp of said coverings and weave them with the texture of Mock-Leno weaving.

[0025] In an implementation of such a method, the Mock-Leno weaving texture presents, in a direction perpendicular to the warp and weft directions, a thickness that decreases going towards the second portion.

[0026] In an implementation of such a method, the first and second portions have the same number of warp threads woven continuously between the first and second portions, and the first portion comprises, at its core, a number of layers of warp thread which is greater than the number of warp yarn layers present in the core of the second portion.

[0027] In an implementation of such a method, the first portion comprises, in its core, a number of layers of warp yarn equal to twice the number of layers of warp yarn present in the core of the second portion.

[0028] In one implementation of such a method, the fibrous structure comprises carbon strands or strands of ceramic material. The ceramic material of the wires may, for example, be an oxide material, such as alumina, or a non-oxide material, such as silicon carbide.

Brief description of the drawings

[0029] Other features and advantages of the invention appear from the following description of particular embodiments of the invention given as non-limiting examples and described with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic view showing the multilayer weaving of a fibrous structure for manufacturing an aeroengine blade in an embodiment of the invention; Figures 2 to 17 are weft sectional views on an enlarged scale showing in part sixteen successive planes of weaving a portion of greater thickness in the fibrous structure of Figure 1; Figure 18 is a diagrammatic perspective view of a blade fiber preform obtained from the fibrous structure of Figure 1; Figure 19 is a diagrammatic perspective view of a composite material preform obtained by densifying the preform of Figure 18 with a die; and Figure 20 is a photograph showing a texture woven with Mock-Leno weaving.

Detailed description of modalities

[0030] The invention generally applies to making fibrous structures suitable for constituting fiber reinforcement or preform for use in the manufacture of a part of composite material, in particular an aeroengine blade, the part being obtained by densification of the fibrous structure with a matrix. For composite materials that are used at relatively low temperatures, normally up to 300°C, the matrix is normally a resin or a refractory material such as carbon or ceramic, for example, silicon carbide, when composites that are thermostructural are obtained.

[0031] The fibrous structure of the invention is obtained by three-dimensional weaving or multilayer weaving.

[0032] The term “three-dimensional weaving” or “3D weaving”, is used here to mean weaving in which at least some of the warp threads interconnect weft threads over a plurality of weft layers.

[0033] The term “multilayer weaving” is used herein to designate 3D weaving with a plurality of weft layers in which the base weaving for each layer is equivalent to a conventional 2D texture weaving, such as a plain type weaving, satin or twill, but with certain weaving points connecting the weft layers together.

[0034] Obtaining the fibrous structure through 3D or multilayer weaving makes it possible to obtain a connection between the layers and thus have good mechanical behavior for the fibrous structure and the resulting piece of composite material, while performing a single textile operation.

[0035] It is important to improve the achievement of a surface state, after densification, that is free from major irregularities, that is, that has a good finishing state in order to avoid or limit machining finishing operations or to avoid formation of resin lumps in resin matrix composites. To this end, for a fibrous structure having an inner portion or core and an outer portion or covering adjacent to the outer surface of the fibrous structure, the covering is preferably made by weaving with a plain, satin or twill type weave in order to limit irregularities. of the surface, with a satin-like weave, also providing a surface appearance that is smooth. The weave in the cover can be varied on the outer surface of the fibrous structure in order to impart particular desired properties, for example, going from a smooth type weave which gives preference to close bonding to a satin type weave which gives preference to a surface state. straight.

[0036] According to the invention, to form a thick portion of the fibrous structure while controlling the fiber fraction in that portion, a Mock-Leno type fibrous texture is used for weaving the core of the fibrous structure. It is also possible to use yarns of different weights between the core and cover and/or between warp and weft in order to obtain a ratio within the desired limits between the volume fraction of the warp fiber and the volume fraction of the weft fiber.

[0037] In order to obtain mechanical properties that are as little non-uniform as possible within the piece of composite material, it is also advantageous to enhance the densification of the reinforcing fibrous structure with a densification gradient that is as small as possible between the core of the composite material. fibrous structure and its covering, in particular when densification is carried out by chemical vapor infiltration (CVI). To this end, to improve access to the preform core, the core is woven with a Mock-Leno weave that establishes easy communication for the matrix ingredients because of its airy grid shape.

[0038] It may be desirable to vary the weight, that is, the cross-section, of the yarns or filaments used to weave the fibrous structure, in particular by using yarns of different weights between the core and cover and/or between warp and weft. Reducing the weight between the core and shell makes it easier to access the core for gas passing through the shell when performing CVI densification. The weights can also be selected to obtain a ratio within the desired limits between the volume fraction of the warp fiber and the volume fraction of the weft fiber.

[0039] In one example, it is possible to use braids to form all or part of the core of the fibrous structure and use yarns of smaller thickness than the braids in the covering of the fibrous structure. Such an example makes it possible to further increase the thickness of the fibrous structure while controlling the average fiber fraction.

[0040] It may also be desirable to use yarns of different chemical natures between the various portions of the fibrous structure, in particular between the core and the covering, in order to impart particular properties to the resulting piece of composite material, in particular in terms of ability to withstand oxidation or wear.

[0041] An embodiment of a fibrous structure according to the invention is described below. In this modality, weaving is carried out on a Jacquard-type loom.

[0042] Figure 1 is a highly diagrammatic view of a fibrous structure 200 that is intended to form the fiber reinforcement of an aeroengine blade.

[0043] The fibrous structure 200 is obtained by three-dimensional weaving (or “3D weaving”), or by multilayer weaving, carried out in a known manner using a Jacquard-type loom having a bundle of warp yarns or filaments 201 in a plurality of layers , the warp threads connecting the weft threads 202 together also arranged in a plurality of layers. A detailed embodiment of a fiber preform which is for forming the fiber reinforcement of a blade for an aeroengine is described in particular in the following documents: US7,101,154; US 7,241,112; and WO 2010/061140.

[0044] The fibrous structure 200 is woven in the form of a strip extending generally in an X direction corresponding to the longitudinal direction of the blade that is to be made. The fibrous structure has a thickness that varies, and this is determined depending on the longitudinal thickness and the aerodynamic profile of the blade that must be made. In its portion that must form a preform of the root, the fibrous structure 200 has a portion 203 of greater thickness that is determined depending on the thickness of the root of the blade that must be made. The fibrous structure 200 extends over a portion 204 of decreasing thickness which is to form the blade tang, followed by a portion 205 which is to form the blade airfoil. In a direction perpendicular to the

[0045] The fibrous structure 200 is woven as a single piece and, after cutting out the non-woven threads, it needs to present almost the final shape and dimensions of the blade (i.e., its “resultant” shape). To this end, in portions where the thickness of the fibrous structure varies, such as portion 204 of decreasing thickness, the reduction in the thickness of the preform is achieved by progressively removing the weft layers while weaving.

[0046] In this example, the same number of warp threads is used in the portion 203 of greater thickness than in the portion 204 of decreasing thickness. To this end, the layers of warp threads present in the core of the portion 203 of greater thickness are separated so as to obtain a greater number of layers of warp thread in the portion 203 of greater thickness than in the portion 204 of decreasing thickness. The layers of warp threads present in the core of the portion 203 of greater thickness then have a lower count than the layers of warp threads present in the portion 204 of decreasing thickness. The term “count” is used here to designate the number of threads per unit length in the warp direction and the weft direction.

[0047] Figures 2 to 17 show a portion of sixteen successive planes of a weaving in the portion 203 of greater thickness in the fibrous structure 200 obtained by 3D weaving, the weft threads being visible in section.

[0048] In its largest thick portion 203, the fibrous structure 200 comprises 22 layers of weft, specifically 44 half layers of weft t1 to t44. The first cover 2032 has weft half layers t1 to t10, the second cover 2033 has weft half layers t35 to t44, and the core has weft half layers t11 to t34. In core 2031 located between the opposing covers 2032 and 2033, the 3D weaving is of the Mock-Leno type (ML fabric). In covers 2032 and 2033, the weaving is three-dimensional. In cover 2032, the weft half layers t1 and t2 are connected together by an irregular satin type weave. Similarly, in cover 2033, the weft half layers t43 and t44 are connected together by an irregular satin type weave. A plurality of warp yarns C1, C2, C3, C16, C17, and C18 connect together weft yarns 20 in the covers 2032 and 2033. The ML Mock-Leno texture of the core 2031 is connected with the covers 2032 and 2033 by deflection of the warp threads of the coverings in this ML texture (see for example threads C3 and C16 in Figure 3). The deflection deviation of these warp threads forms PL connection points connecting the ML Mock-Leno texture to the 2032 and 2033 covers.

[0049] In its portion 204 of decreasing thickness, weft threads are progressively removed in order to reach a number of weft threads that is compatible with the portion 205 that should form the blade airfoil.

[0050] The ML Mock-Leno texture present in the core 2031 of the first portion 203 comprises a plurality of weft yarn layers CT1-CT12 (see Figure 2 in particular). In the embodiment shown, the Mock-Leno texture has twelve layers of weft yarns, but it would not go beyond the scope of the invention if it were to have any other number of layers of weft yarns. Warp threads, such as C51, C71, C91, C111, C131, and C151 which are visible in Figure 2, are interconnected with weft threads 21 and 30 in this ML texture.

[0051] The ML Mock-Leno texture also presents, in a direction perpendicular to the warp and weft directions, a thickness that decreases going towards the second portion 204. By progressively decreasing the thickness of this ML texture, it is possible to control the fraction of fiber in a zone 203a corresponding to the transition between the end of the portion 203 of greater thickness and the beginning of the portion 204 of decreasing thickness, that is, the zone in which the thickness of the fibrous structure begins to decrease. In the presently described embodiment, the weft threads of the ML Mock-Leno texture are replaced progressively in the warp direction by weft threads 24 having the same weight as the weft threads 20 present in the portion 204 of decreasing thickness and in the covers 2032 and 2033 of the fibrous structure.

[0052] In the ML Mock-Leno texture, each weft yarn layer CT1-CT12 also has a plurality of weft yarn groups that are referenced in Figure 2 as GT1 for the weft yarn groups of the first CT1 layer of the texture ML, and GT4 for the weft thread groups of the fourth layer of the ML texture, for example.

[0053] Adjacent columns of weft yarns in the ML MockLeno texture are spaced at a non-zero spacing eT along the warp direction. In particular, adjacent groups of weft yarns in a single layer CTi, where i ranges from 1 to 12 in the example shown, are spaced by spacing eT. The spacing eT may be substantially constant along the warp direction, as shown, or in a variant it may vary along this direction.

[0054] The ML Mock-Leno texture is in the form of a grid having channels running through its thickness. As described in greater detail below, the presence of each of these through channels is the result of the non-zero spacing that exists firstly between adjacent groups of weft threads and secondly between adjacent groups of warp threads.

[0055] In the example shown in Figures 2 to 17, each of the groups of weft threads comprises at least two side threads 21 together with at least one central thread 30 present between them. Each of the groups of weft yarns thus comprises at least three yarns. In the example shown, the central thread 30 is a filament of greater diameter than the diameter of two side threads 21. The example shown relates to groups of weft threads, each of which comprises three weft threads. However, it would not go beyond the scope of the invention for each of the groups of weft threads to comprise more than three weft threads. In one variant, the filament 30 could be replaced by a braid or even by a plurality of central strands arranged side by side and with a diameter equal to or different from the diameter of the lateral strands 21. Furthermore, and as described in detail below, the ML texture in the example shown has a plurality of groups of warp threads, each comprising eight warp threads. It would not be beyond the scope of the invention for the Mock-Leno texture to have groups of warp threads, each having some number of warp threads other than eight. Thus, more generally, each of the groups of warp threads may have at least three warp threads. Furthermore, in the example shown, the number of warp threads in each of the warp thread groups is different from the number of weft threads in each of the weft thread groups, but it would not go beyond the scope of the invention that these two wire numbers are the same.

[0056] The interconnection of the warp threads with the weft threads is described below in greater detail with reference to the several different weft sections shown in Figures 2 to 17. In a given weft section, the warp threads of the weaving texture Mock-Leno all have the same direction of interconnection with the weft threads. Consequently, and for the sake of brevity, the interconnection of a single warp thread with the weft threads is described below for each of the weaving planes shown in Figures 2 to 17.

[0057] It can be seen in Figure 4 that the interlayer binding warp thread C83 of the first group of warp threads connects the weft threads of layer CT4 of the Mock-Leno texture together with the weft threads of layer CT5 of this texture. More precisely, the warp thread C83 passes alternately over each of the threads of a group of weft threads GT4 of a first layer CT4 and under each of the threads of a group of weft threads GT5 of a second layer CT5. Specifically, yarn C83 passes over each of the yarns of a first GT4 group of weft yarns of the first CT4 layer, and then under each of the yarns of a second GT5 group of weft yarns of the second CT5 layer, and then once more about each of the threads of a third GT4 group of weft threads of the first CT4 layer, and so on.

[0058] The above description for the interlayer binding warp yarn C83 of the first group is applicable to the interlayer warp yarn C85 of the first group (see Figure 6).

[0059] Similar observations also apply to the binding warp threads C74 and C76 of the first group of warp threads, each of which binds together the weft threads of layer CT3 of the Mock-Leno texture together with the weft threads of the CT4 layer of this texture (see Figures 5 and 7).

[0060] With respect to the second group of warp threads, and with reference to Figure 12, it can be seen that each interlayer binding warp thread C811 of the second group of warp threads connects the weft threads of layer CT4 of the Mock-Leno texture together with the weft threads of the CT5 layer of the same texture. More precisely, the warp thread C811 passes alternately over each of the threads of a group GT4 of weft threads of the first layer CT4 and under each of the threads of a group GT5 of weft threads of the second layer CT5. Specifically, yarn C811 passes over each of the yarns of a first GT4 group of weft yarns of the first CT4 layer and then under each of the yarns of a second GT5 group of weft yarns of the second CT5 layer and then once more over each of the yarns of a third GT4 group of weft yarns of the first CT4 layer, and so on.

[0061] The above description for the interlayer binding warp yarn C811 of the second group is applicable to the interlayer binding warp yarn C813 of the second group (see Figure 14).

[0062] Similar observations also apply to the binding warp threads C712 and C714 of the second group of warp threads that connect each of the weft threads of layer CT3 of the Mock-Leno texture with the weft threads of layer CT4 of this texture (see Figures 13 and 15).

[0063] It should be noted, however, that the C811 warp thread presents an interconnection direction with the weft threads that is inverted in relation to the interconnection direction presented by the C85 warp thread with the weft thread. In other words, for a given weft column, when warp thread C811 passes over each of the threads of a group of weft threads of the first layer CT4, warp thread C85 passes under each of the threads of a group of weft yarns of the second layer CT5. Similarly, for a given column, when the warp thread C811 passes under each of the threads of a group of weft threads of the second layer CT5, the warp thread C85 passes over each of the threads of a group of threads of weave of the first layer CT4. Binding yarn C83 of the first group also has an interconnection direction with the weft yarns that is reversed in relation to the interconnection direction shown by binding yarn C813 with weft yarns.

[0064] As mentioned above, this reversed interconnection direction between the interlayer binding threads of the first and second group of warp threads participates in obtaining non-zero spacing between the first and second group of warp threads, and thus to form a fibrous texture that is in the form of a grid with pore channels featuring improved accessibility. It should also be noted that the fact that the binding threads in a given group of warp threads have the same direction of interconnection with the weft threads makes it possible to allow the binding threads of a given group of warp threads to come closer together and thus also participate in the formation of pore channels (compact grouping of strands in a given group).

[0065] It should also be noted that, when going in the weft direction, the ML Mock-Leno texture presents an alternation between first groups of warp threads and second groups of warp threads with reversed interconnection directions. In other words, when moving in the weft direction, the ML Mock-Leno texture presents in succession a first group of warp threads and then a second group of warp threads followed once again by a first group of warp threads and then once more for a second group of warp threads, and so on. Each of the first groups of warp threads is adjacent to a second group of warp threads.

[0066] With reference to Figures 2 and 8, it can be seen that the first group of warp yarns also comprises at least one first side warp yarn C71 situated on a first side of the interlayer binding yarn C83 together with at least a second side warp thread C77 situated on a second side of the binding thread C83, the second side being opposite the first side in the weft direction. In other words, the interply bonding thread C83 is present between the side warp threads C71 and C77. More precisely, in the example shown, the interlayer connecting threads C83 and C85 of the first group of warp threads are both present between the side threads C71 and C77 of the first group of warp threads. Each of the side warp yarns C71 and C77 is interconnected with a plurality of GT4 groups of weft yarns of the first layer CT4.

[0067] The warp thread C71 passes under a first side thread 21 of a first group of GT4 weft threads, and then over the central thread 30 of this first group, and then under a second side thread 21 of this first group. The warp thread C71 then passes over a first side thread 21 of a second group of weft threads GT4 adjacent to the first group in the warp direction, and then under the central thread 30 of this second group, and then over a second side thread 21 of this second group, and so on. The warp thread C71 passes alternately under the side thread 21 of a GT4 group of weft threads and over the side threads 21 of the GT4 group of weft threads which is adjacent in the warp direction. The warp thread C71 passes alternately over a center thread 30 of a GT4 group of weft threads and under the center thread 30 of the adjacent GT4 group of weft threads in the warp direction.

[0068] Similar observations apply to the second side warp thread C77 which has the same direction of interconnection with the weft threads as the first warp thread C71 (see Figure 8).

[0069] Similar observations also apply to the side warp yarns C62 and C68 of the first group of warp yarns, each of which is interconnected with a plurality of GT3 groups of weft yarns in the third weft layer CT3 (see Figures 3 and 9).

[0070] In a variant that is not shown and in which the groups of weft threads have two side weft threads between which at least two central weft threads are present, it is possible to have a warp thread that passes under a first side thread of a first group of weft threads, and then over each of the central threads of the first group, and then under a second side thread of this first group. This warp thread may then pass over a first side thread of a second group of weft threads adjacent to the first group in the warp direction, and then under each of the center threads of this second group, and then over a second side thread of this second group. group, and so on. This is valid for the first and second groups of warp threads present in the Mock-Leno texture in such a variant.

[0071] With respect to the second group of warp threads, it can be seen with reference to Figures 10 and 16 that the second group of warp threads also has at least one first side warp thread C79 situated on a first side of the threads interlayer binding yarn C811 together with at least one second side warp yarn C715 situated on a second side of the binding yarn C811, the second side being opposite the first side in the weft direction. In other words, interply bonding yarn C811 is present between side warp yarns C79 and C715. More precisely, in the example shown, the interlayer binding yarns C811 and C813 of the second group of warp yarns are both present between the side yarns C79 and C715 of the second group of warp yarns. Each of the side warp yarns C79 and C715 is interconnected with a plurality of groups of weft yarns of the first layer CT4.

[0072] The warp thread C79 passes over a first side thread 21 of a first group of GT4 weft threads, and then under the central thread 30 of this first group, and then over a second side thread 21 of this first group. Thereafter, the warp thread C79 passes under a first side thread 21 of a second group of weft threads GT4 adjacent to the first group in the warp direction, then over the central thread 30 of this second group, and then under the second side thread 21 of this second group, and so on. The warp thread C79 passes alternately over the side threads 21 of a GT4 group of weft threads and under the side threads 21 of the GT4 group of weft threads which is adjacent in the warp direction. The weft thread C79 passes alternately under the center thread 30 of a GT4 group of weft threads and over the center thread 30 of the GT4 group of weft threads which is adjacent in the warp direction.

[0073] The same observations apply to the second side warp thread C715, which has the same direction of interconnection with the weft threads as the first warp thread C79 (see Figure 16).

11 and 17).

[0075] It should be noted, however, that the C79 warp thread presents an interconnection direction with the weft threads that is inverted in relation to the interconnection direction presented by the C77 warp thread with the weft threads. In other words, under each circumstance, when the warp thread C79 passes over each of the side threads 21 of a given group of weft threads, the warp thread C77 passes under each of the side threads 21 of that group. Similarly, under such circumstances, when the warp thread C79 passes under the central thread 30 of a given group of weft threads, the warp thread C77 passes over the central thread 30 of that group. The C71 warp thread also has an interconnection direction with the weft threads that is inverted in relation to the interconnection direction presented by the C715 warp thread with the weft threads.

[0076] As mentioned above, this inverted interconnection direction between the side threads of the first and second groups of warp threads contributes to obtaining non-zero spacing between the first and second groups of warp threads and thus to form a texture fibrous in the form of a grid in which the pore channels are particularly accessible. It should also be noted that the fact that the side threads of a given group of warp threads have the same direction of interconnection with the weft threads makes it possible to bring the side threads of a given group of warp threads closer together and thus also contributes to forming pore channels (compact grouping of strands in a given group).

[0077] The use of a Mock-Leno texture in the core of the first portion of the fibrous structure makes it possible to considerably increase the thickness of the fibrous structure while controlling the average fiber fraction in the core, which is not true when using only yarns having greater weight in the nucleus. Specifically, when using yarns having a high weight in the core of the structure, it is indeed possible to locally increase the thickness of the structure, but this leads to an increase in the average fiber fraction in the core which is not compatible with the required mechanical properties. When the average fiber fraction in the core is too large, it is not possible to have a pore network that is sufficient to allow the matrix ingredients good access to the core of the fibrous structure. The amount of matrix present in the core is then insufficient, which means that it is not possible to obtain a piece of composite material that presents the required mechanical properties in a uniform manner. This problem is solved by using the Mock-Leno texture which, because of the through channels formed in its thickness, makes it possible to locally increase the thickness of the structure while limiting the increase in the average fiber fraction. A fibrous structure is thus obtained which, while being densified, offers very good access to the matrix ingredients to the core of the structure in its thicker portions.

[0078] By way of illustration, Figure 20 shows an example of an ML Mock-Leno texture suitable for use in the core of the first portion of the fibrous structure. It can be seen that CA traversing channels are present extending through the thickness of the texture and giving it an aerated structure that is easily infiltrated by the matrix.

[0079] Particularly, but not exclusively, the fibrous structure of the invention can be woven from yarns made from carbon fibers, from ceramic fibers such as silicon carbide fibers, or from oxide fibers such as alumina fibers.

[0080] Once the fibrous structure 200 has been woven, the non-woven yarns are cut away. This produces the fiber preform 100 shown in Figure 18, which is woven as a single piece.

[0081] Subsequently, the fiber preform 100 is densified in order to form a blade 10 of composite material as shown in Figure 19. The fiber preform that is to form the fiber reinforcement of the part for manufacturing is densified by the material that constitutes the matrix is made to fill the pores of the preform, for all or part of its volume. This densification can be carried out in a known manner using the liquid consolidation method or the chemical vapor infiltration (CVI) method, or even chaining both methods together.

[0082] The liquid consolidation method consists of impregnating the preform with a liquid composition containing a precursor for the matrix material. The precursor is usually in the form of a polymer, such as a high-performance epoxy resin, possibly diluted in a solvent. The preform is placed in a suitable mold to be closed in a sealed manner and having a cavity in the shape of the final molded blade. Subsequently, the mold is closed and the liquid matrix precursor (for example, a resin) is injected throughout the cavity in order to impregnate the entire fiber portion of the preform.

[0083] The precursor is transformed into the matrix, that is, it is polymerized, carrying out heat treatment, generally heating the mold, after eliminating any solvent and after curing the polymer, the preform being maintained throughout the mold having a similar shape. which coincides with the shape of the part that must be made.

[0084] When forming a carbon or ceramic matrix, heat treatment consists of pyrolysis of the precursor in order to transform the matrix into a carbon or ceramic matrix, depending on the precursor used and the pyrolysis conditions. By way of example, liquid precursors for ceramics, in particular SiC, may be resins of the type polycarbosilane (PCS) or polytitanecarbosilane (PTCS) or polysilazane (PSZ), while liquid carbon precursors may be resins having a relatively high coke content. , such as phenolic resins. A plurality of consecutive cycles from impregnation to heat treatment can be carried out in order to achieve a desired degree of densification.

[0085] In one aspect of the invention, in particular when forming an organic matrix, the fiber preform can be densified by the well-known resin transfer molding (RTM) method. According to the RTM method, the fiber preform is placed in a mold having the external shape of the part that is to be made. A thermosetting resin is injected into the interior space of the mold containing the fiber preform. A pressure gradient is generally established in this interior space between the place where the resin is injected and holes for resin evacuation in order to control and optimize the impregnation of the preform by the resin.

[0086] The fiber preform can also be well densified, in a known manner, by the chemical vapor infiltration (CVI) method. The fiber preform corresponding to the fiber reinforcement of the blade that is to be made is placed in a furnace in which a gas phase of the reaction is admitted. The pressure and temperature in the furnace and the composition of the gas phase are selected to allow the gas phase to diffuse into the pores of the preform to form its matrix by depositing a solid material in contact with the preform. preform core fibers, of which the solid material is the result of the decomposition of a gas phase ingredient or a reaction between a plurality of ingredients, as contrasted with pressure and temperature conditions that are specific to deposition methods (CVD) which consist only of the deposit of material on the surface of a substrate.

[0087] A SiC matrix can be formed using methyltrichlorosilane (MTS), giving SiC by decomposition of the MTS, while a carbon matrix can be obtained with hydrocarbon gases such as methane and/or propane that give carbon by cracking.

[0088] Densification combining a liquid technique and a gaseous technique can also be used to facilitate work, to limit costs and to limit manufacturing cycles, while obtaining characteristics that are satisfactory for the intended use.

[0089] It is also possible to use a melt infiltration method to form the matrix in the pores of the fiber preform. In this type of method, the matrix is formed by infiltrating with silicon or a silicon alloy in the molten state. Before infiltration, it is possible to introduce ceramic or carbon particles into the pores of the fiber preform. The ceramic particles may, for example, be silicon carbide particles. When carbon particles are introduced, they react with the molten silicon that is introduced in order to form silicon carbide. Ceramic or carbon particles can be introduced using a paste.

[0090] Starting with the fibrous structure of the invention, the densification method described above makes it possible to obtain mainly parts made of organic matrix composite material (OMC), carbon matrix material (C/C), and ceramic matrix composite material ( CMC).

[0091] When making a piece of oxide/oxide composite material, the fibrous structure can be impregnated with a semi-fluid paste carrying refractory oxide particles. After eliminating the liquid phase of the paste, the resulting preform is subjected to heat treatment in order to sinter the particles and obtain a refractory oxide matrix. The structure can be impregnated by methods using a pressure gradient, as in RTM-type injection molding methods, or by suction into a submicrometer powder.

[0092] After densification, a composite material blade 10 is obtained which, as shown in Figure 19, has a root 103 in its lower portion formed by the thicker portion 203 of the fibrous structure 200, which is extended by a spike 104 formed by the portion 204 of decreasing thickness in the structure 200, and an airfoil 105 formed by the portion 205 of the fibrous structure 200.

[0093] The fibrous structure and its manufacturing method, according to the present invention, can be used in particular to make turbine engine blades that have a shape that is more complex than the shape of the blades shown in Figure 19, such as blades that include, in addition to what is shown in Figure 19, one or more platforms serving to perform functions such as sealing the gas flow passage, preventing tilting, etc.

Claims (12)

1. Fibrous structure (200) comprising a plurality of weft layers and warp layers interconnected by multilayer three-dimensional weaving, the fibrous structure (200) having at least first and second portions (203, 204) that are adjacent in the direction of warp, the first portion (203) having, in a direction perpendicular to the warp and weft directions, a thickness that is greater than the thickness of the second portion (204), the first portion (203) has, at its core (2031 ), at least one fibrous texture (ML) obtained by three-dimensional weaving of warp yarns and weft yarns, characterized in that said at least one fibrous texture (ML) is in the form of a Mock-Leno weaving grid, said at least one texture (ML) being present between two covers (2032; 2033) present on the surface of the first portion (203) and being connected to the covers (2032; 2033) by warp threads (C3; C16) belonging to said covers which are locally deflected in said texture. 2. Fibrous structure (200) according to claim 1, characterized by the fact that the Mock-Leno (ML) weaving fibrous texture presents, in a direction perpendicular to the warp and weft directions, a thickness that decreases going towards to the second portion (204). 3. Fibrous structure (200) according to claim 1 or 2, characterized by the fact that the first and second portions (203, 204) have the same number of warp threads woven continuously between said first and second portions, and wherein the first portion (203) includes, in its core, a number of layers of warp yarn that is greater than the number of layers of warp yarn present in the core of the second portion (204). 4. Fibrous structure (200) according to claim 3, characterized in that the first portion (203) includes, in its core, a number of layers of warp yarn that is equal to twice the number of layers of warp thread present in the core of the second portion (204). 5. Fibrous structure (200) according to any one of claims 1 to 4, characterized in that said structure (200) comprises carbon threads or ceramic material threads. 6. Piece of composite material (10), characterized by the fact that it comprises a fiber reinforcement densified by a matrix, said fiber reinforcement being constituted by a fibrous structure (200) as defined in any one of claims 1 to 5. 7. Part (10) according to claim 6, characterized by the fact that said part (10) corresponds to a turbine blade, the first portion (203) of the fibrous structure constituting the blade root portion (103) of the fiber reinforcement. 8. Method of manufacturing a fibrous structure (200) by three-dimensional multilayer weaving between a plurality of weft yarns and warp yarns, the fibrous structure (200) having at least first and second portions (203, 204) that are adjacent in the warp direction, the first portion (203) having, in a direction perpendicular to the warp and weft directions, a thickness greater than the thickness of the second portion (204), the first portion (203) is made by means of a step of three-dimensionally weaving warp and weft layers, characterized by the fact that a fibrous texture (ML) is formed in the form of a Mock-Leno weaving grid in the core (2031) of the first portion (203) together with coverings (2032; 2033) on the surface of the first portion during the three-dimensional weaving step, the weaving of the covers (2032; 2033) being locally modified so as to deflect certain warp threads (C3; C16) from said covers (2032; 2033) and weave them with Mock-Leno (ML) weaving texture. 9. Method according to claim 8, characterized by the fact that the Mock-Leno (ML) weaving texture presents, in a direction perpendicular to the warp and weft directions, a thickness that decreases going towards the second portion (204 ). 10. Method according to claim 8 or 9, characterized in that the first and second portions (203, 204) have the same number of warp threads woven continuously between the first and second portions (203, 204) , and wherein the first portion (203) comprises, in its core, a number of layers of warp yarn that is greater than the number of layers of warp yarn present in the core of the second portion (204). 11. Method according to claim 10, characterized by the fact that the first portion (203) comprises, in its core, a number of layers of warp yarn equal to twice the number of layers of warp yarn present in the core of the second portion (204). 12. Method according to any one of claims 8 to 11, characterized in that the fibrous structure (200) comprises carbon threads or threads of ceramic material.