Fibrous preform having a localized stiffness increase

Abstract

The present invention relates to a fibrous preform (500) made by three-dimensional weaving of first yarns with second yarns and comprising a first region (502) in which the second yarns have a first titer, a second region (504), offset from the first region, in which at least a portion of the second yarns have a second titer which is lower than the first titer, the preform having a quantity of reinforcing yarns that is maintained between the first region and the second region, and a third region (506) located as an extension of the second region along the second direction, at least a portion of the second yarns having the second titer being taken out between the second region and the third region to impart to the third region an increased volume ratio of first yarns to second yarns.

Description

Description Title of the invention: Fibrous preform having a localized increase in stiffness Technical Field

[0001] This presentation relates to a fibrous preform for a turbomachine component made of composite material, particularly for an aeronautical turbomachine component, as well as an associated turbomachine component. The fibrous preform is notable in that it features a localized area where stiffness is increased. The invention is of particular interest for the production of cold-section components of aeronautical turbomachines, such as fan blades or outlet guide vanes (OGVs), especially for manufacturing a portion of a blade such as an airfoil or platform. However, the invention is not limited to application to a particular component or part of a component. Previous technique

[0002] Organic matrix composite (OMC) materials generally withstand temperatures ranging from 100°C to 250°C. These materials are used to replace metallic parts in certain sections of turbomachinery.

[0003] Furthermore, their use helps to optimize the performance of turbomachinery or turbomachinery equipment, particularly by reducing the overall mass of the turbomachine, thereby reducing fuel consumption which in turn leads to a reduction in harmful emissions (CO, CO2, NO). X ...). We know of EP 1 526 285 which describes a turbomachine blade, in particular a blower blade and its manufacturing process.

[0004] It remains desirable to improve the performance of composite material parts reinforced by a three-dimensional fabric, and in particular to have a localized area where stiffness, especially tensile stiffness, is increased. Description of the invention

[0005] This presentation concerns a fibrous preform intended to form a fibrous reinforcement of a turbomachine part made of composite material or of part of a turbomachine part made of composite material, the preform being produced by three-dimensional weaving of first yarns extending along a first direction with second yarns transverse to the first yarns and extending along a second direction, the preform comprising: - a first region in which the second threads have, at least on a skin area of ​​the preform, a first title, - a second region, offset from the first region along the first direction, in which at least some of the second yarns have, at least in the skin zone, a second yarn count that is lower than the first yarn count and corresponding to a divisor of the first yarn count, the preform having a ratio [sum of the linear masses of the second yarns in the region considered] / [dimension of the region considered measured along the first direction] conserved between the first region and the second region, and - a third region, present at least on the skin area, located in the extension of the second region along the second direction, at least part of the second second threads having come out between the second region and the third region to give the third region a volume ratio of first threads relative to second threads which is greater than that in the first region and that in the second region.

[0006] The volume ratio of first wires relative to second wires in a given region corresponds to the ratio [volume occupied by first wires in the region] / [volume occupied by second wires in the region]. For the sake of brevity, this ratio may be referred to hereafter as the term "F1 / F2 ratio." In the specific case where the first few threads correspond to the warp threads, this ratio is the warp / weft ratio. In one variation, the first few threads can correspond to the weft threads and the second few to the warp threads.

[0007] The invention is based on locally increasing stiffness, particularly tensile stiffness, by locally increasing the F1 / F2 ratio. To achieve this, it is proposed to replace, in a specific area of ​​the preform, second wires of a certain size The "standard" (having the first yarn) is modified by using a greater number of second yarns of a lower yarn count, while ensuring that the quantity of reinforcing yarns is maintained to preserve satisfactory mechanical properties despite this adaptation. The desired increase in the F1 / F2 ratio is achieved by selectively extending some of the second yarns of the lower yarn count locally in the region where stiffness needs to be increased, which corresponds to the third region described above.

[0008] In one embodiment, another part of the second threads of the second region have, at least on the skin area, a third thread count that is less than the second thread count and corresponding to a divisor of the first thread count, and at least part of the second threads of third thread count have exited between the second region and the third region.

[0009] The presence of second third-title threads advantageously allows for further expansion of the possibilities for local increase of the F1 / F2 ratio if this is desired for the application under consideration.

[0010] In one embodiment, at least one additional layer of first wires is added in the third region relative to the first region.

[0011] Such a characteristic contributes advantageously to maintaining the fiber content in the third region if this is desired for the application under consideration.

[0012] In particular, said additional layer of first yarns can be woven with second yarns taken from the second region.

[0013] This characteristic makes it advantageous to use the second yarns that come out to weave the additional layer(s) of first yarns that have been added.

[0014] In one example embodiment, the skin area has a thickness greater than or equal to 2 mm, for example greater than or equal to 5 mm.

[0015] Such a characteristic contributes advantageously to further enhancing the increase in stiffness achieved.

[0016] In one example of implementation, the textile weave is maintained between the first region, the second region and the third region.

[0017] Such a characteristic contributes advantageously to simplifying the manufacture of the preform and eliminates any risk of altering the mechanical behavior of the part to be obtained due to the adaptation made to modify the F1 / F2 ratio.

[0018] In one example embodiment, the preform includes carbon wires, ceramic wires for example silicon carbide, glass wires, aramid wires, or a mixture of such wires.

[0019] The invention also relates to a turbomachine part made of composite material comprising a preform as described above, and a matrix present in the porosity of the fibrous preform.

[0020] In one example implementation, the matrix is ​​an organic matrix.

[0021] The invention also relates to an aeronautical turbomachine comprising at least one part as described above.

[0022] The aforementioned features and advantages, as well as others, will become apparent upon reading the detailed description that follows, which refers to the attached drawings. Brief description of the drawings

[0023] The attached drawings are schematic and primarily intended to illustrate the principles of the presentation. In these drawings, identical elements (or parts of elements) are identified by the same reference symbols from one figure to another.

[0024] [Fig. 1] Figure 1 represents, schematically and partially, a cross-sectional view of a turbofan engine.

[0025] [Fig. 2] Figure 2 represents, schematically and partially, the formation of a fibrous structure by three-dimensional weaving.

[0026] [Fig. 3] Figure 3 represents, schematically and partially, an example of a fibrous preform according to the invention.

[0027] [Fig. 4] Figure 4 represents a detail of the first region of the preform of Figure 3 in a plane transverse to the second direction.

[0028] [Fig. 5] Figure 5 represents a detail of the second region of the preform of Figure 3 in a plane transverse to the second direction.

[0029] [Fig. 6] Figure 6 represents a detail of the third region of the preform of Figure 3 in a plane transverse to the second direction.

[0030] [Fig. 7] Figure 7 represents a detail of a second region variant in a plane transverse to the second direction.

[0031] [Fig. 8] Figure 8 represents a detail of a third region variant in a plane transverse to the second direction.

[0032] [Fig. 9] Figure 9 represents a detail of another variant of the second region in a plane transverse to the second direction.

[0033] [Fig. 10] Figure 10 represents a detail of another variant of the third region in a plane transverse to the second direction.

[0034] [Fig. 11] Figure 11 represents, schematically and partially, an example of a part according to the invention. Description of the implementation methods

[0035] Figure 1 represents, in cross-section along a vertical plane passing through its main axis A, a turbofan engine 1. It comprises, from upstream to downstream along the airflow circulation, a fan 2, a low-pressure compressor 3, a high-pressure compressor 4, a combustion chamber 5, a high-pressure turbine 6, and a low-pressure turbine 7.

[0036] The blower 2 allows the aspiration of an airflow to which two independent circulations are imposed, to form a primary airflow (hot flow) and a secondary airflow (cold flow).

[0037] The primary stream air can for example be compressed within the low pressure compressor 3 and then the high pressure compressor 4, and then mixed with a fuel and burned within a combustion chamber 5. The gases expelled from the combustion chamber can pass through a high pressure turbine 6 and then a low pressure turbine 7 before undergoing acceleration through a nozzle.

[0038] The secondary flow, on the other hand, bypasses the hot part of the reactor.

[0039] Compressors 3, 4 and turbines 5, 6 comprise several stages of fixed blades (called "stators") and moving blades (called "rotors").

[0040] The moving blades consist of a ring of blades mounted radially on a disc, which drives a rotating shaft under the effect of a passing air or gas flow. Each blade comprises a blade connected to a foot that is fitted into a groove in the disc to hold the blade in place during the operation of the turbomachine.

[0041] Fixed blades, usually positioned between each stage of moving blades, allow the airflow to be straightened before the flow enters the next stage of moving blades.

[0042] In this presentation, the terms "axial", "radial", "internal", "external" and their derivatives are defined with respect to the main axis of the turbomachine. The terms "upstream" and "downstream" are defined with respect to the airflow within the turbomachine.

[0043] The invention applies generally to all fibrous preforms formed by three-dimensional weaving that are suitable for providing fibrous reinforcement for the manufacture of composite material parts for turbomachinery, particularly aeronautical turbomachinery. The parts are obtained by densifying the fibrous preforms with a matrix. The matrix can be a resin, in the case of cold-weather parts used at relatively low temperatures, typically up to 300°C.

[0044] The term "three-dimensional weaving" or "3D weaving" refers to a weaving method in which at least some of the warp yarns interlock with weft yarns across multiple weft layers. It should be noted that a reversal of roles between warp and weft is possible and should be considered as also covered by the claims.

[0045] The creation of the fibrous structure by 3D weaving makes it possible to obtain a bond between the layers, thus having good mechanical strength of the fibrous structure and the part made of composite material obtained, in a single textile operation.

[0046] Figure 2 illustrates a loom 100 equipped with a Jacquard mechanism 101 supported by a superstructure not shown in Figure 2. The loom 100 also includes a harness 110 consisting of a heddle board 111 and control wires or heddles 113, each heddle 113 being connected at one end to a control hook 1010 of the Jacquard mechanism 101 and at the other end to one of the return springs 102 fixed to the frame 103 of the loom 100. Each heddle 113 includes an eyelet 114 through which a warp wire 201 passes. The heddles 113 and their associated eyelet 114 extend into an area in which the heddles 113 and the eyelets 114 are animated by a substantially vertical oscillating motion represented by the double arrow F. The heddles 113 are subjected to tensile forces respectively exerted by the control hooks 1010 and by the return springs 102.The heddles 113 allow certain warp yarns 201 to be lifted according to a defined weaving program. By lifting certain warp yarns 201, the heddles 113 create a swarm that allows the introduction of weft yarns 202 for the 3D weaving of fibrous structures. The warp yarns 201 are arranged in a plurality of warp yarn layers Ci to C. n .

[0047] The warp threads 201 are drawn from bobbins arranged on a creel (not shown in Figure 1) upstream of the Jacquard mechanism 101 of the loom 100. For this purpose, as illustrated in Figure 2, a warp thread drawing system 300 is associated with the loom 100 downstream of it. The frame 120 delimits the exit of the loom 100, that is, the area beyond which the warp threads 201 are no longer woven with the weft threads 202. The warp thread drawing system 300 includes a clamping device 340 designed to hold, by clamping, a set of layers Ci to C n of warp threads downstream of the loom 100.

[0048] During the weaving of a fibrous structure 400, the warp yarns 201 are driven in the feed direction D Aby the clamping device. More specifically, in the example described here, the clamping device 340 is mounted on rails 351 and 352 of a frame 350 of the warp thread taking system 300 so as to allow the clamping device to move. The movement of the clamping device 300 is achieved by a motor, for example a stepper motor (not shown in Figure 2). Each time a column of weft threads 202 is completely woven with the warp thread layers Ci to C n The clamping device 340 is driven in the direction D A over a distance allowing the insertion and weaving in loom 100 of the next weft column.

[0049] In the example described here, the fibrous structure 400 is woven using a 3D interlock weave. An interlock weave is defined here as a weave structure in which each layer of warp yarns interlocks several layers of weft yarns, with all yarns in the same warp column having the same movement within the plane of the weave. A detailed example of producing a fibrous preform for forming the fibrous reinforcement of an aircraft engine blade from a 3D woven fibrous blank is described in detail in US documents 7,101,154, US 7,241,112, and WO 2010 / 061140. The fibrous structure 400 can be shaped to obtain a preform 500 of the desired part in a manner known per se.

[0050] An example of a preform 500 according to the invention is illustrated in Figure 3. The example shown in Figure 3 concerns a preform 500 intended to form the fibrous reinforcement of an aerodynamic profile of a blade, such as a fan blade or a fixed outlet guide blade of a secondary flow straightener in an aircraft turbomachine. As mentioned above, the invention is not limited to application to a particular part but is of interest for any type of turbomachine component for which it is desired to locally increase stiffness.

[0051] The 500 preform was obtained by three-dimensional weaving of first yarns (corresponding here to the warp yarns) extending along a first direction D1, corresponding here to the radial direction or the direction according to the height of the blade to be obtained, with second yarns (corresponding here to the weft yarns) extending along a second direction D2, corresponding here to the axial direction or the direction according to the chord of the blade to be obtained. The 500 preform can be formed in a single piece of three-dimensional fabric.

[0052] The preform 500 includes a first region 502, here located on the foot side of the blade to be obtained, in which the second yarns 202 have, at least in a skin area P of the preform 500, a first count (see Figure 4). The second yarns 202 are bonded by several layers C1-C5 of first yarns. The first region 502 can extend from an end 501, for example from a longitudinal end, of the preform 500. The first region 502 has a dimension Hl, corresponding here to its height, measured along the first direction Dl. The weave structure considered here is a "Interlock" but other weaves can, of course, be used. The skin zone P corresponds to an area defining a surface S, for example an external surface S, of the preform 500. The skin zone P can have a thickness e p greater than or equal to 2 mm, for example greater than or equal to 5 mm.

[0053] The preform 500 further includes a second region 504, distinct from the first region 502 and offset from it along the first direction D1. The second region 504 does not overlap with the first region 502 (it is located on a band of distinct height in the illustrated example). The first region 502 can, as illustrated, extend between the end 501 and the second region 504.

[0054] Figure 5 illustrates the adaptation of the second yarn count in the second region 504, at least in the skin zone P. A first group of second yarns, corresponding to the yarns designated 202a, has a second count that is lower than the first count and corresponds to a divisor of the first count. In other words, this means that, if we denote the first count as ti and the second count as t2, the following relationship holds: ti = ni*t2, where ni is an integer greater than or equal to 2. Thus, and by way of example, the second yarns 202 can correspond to yarns made of 48k filaments, and the second yarns 202a can correspond to yarns made of the same material but with only 24k filaments, that is, with a linear density divided by 2 (m=2 in this example).

[0055] In the example considered here, a second part of the second yarns, corresponding to the yarns designated 202b, has a third yarn count that is lower than the second yarn count and is a divisor of the first yarn count. In other words, this means that, if we denote the first yarn count as ti, the second yarn count as t2, and the third yarn count as t3, the following relationships hold: ti = n2*t3, where n2 is an integer greater than or equal to 3 and t3 < t2. Still within the context of the example mentioned above, the second yarns 202b could correspond to yarns made of the same material but with only 12k filaments, that is, with a linear density divided by 4 compared to the 202 yarns (n2=4 in this example).

[0056] The second region 504 has a dimension H2, corresponding here to its height, measured along the first direction Dl. The dimension H2 can be different from the dimension H1 or equal to the latter.

[0057] The ratio [sum of linear masses of the second wires in the region considered] / [dimension of the region considered measured along the first direction] is conserved between the first region 502 and the second region 504, thus allowing the quantity of reinforcing wires to be conserved between these regions 502, 504. In other words, this means that the following relationship is verified: [sum of linear masses of the second wires 202a, 202b in the second region 504] / [dimension H2 of the second region 504] = [sum of linear masses of the second wires 202 in the first region 502] / [dimension H1 of the first region 502]. To maintain this ratio, the width between consecutive columns of second sons can be adjusted to have a lower LCT2 width between consecutive columns of second sons in the second 504 region than the LCT1 width between consecutive columns of second sons in the first 502 region.In the numerical example given above, we can take an LCT2 width equal to half the LCT1 width in order to distribute more second 202a, 202b threads across a spacing between consecutive columns corresponding to the "standard" LCT1 value. Alternatively, or in combination, second threads from the second 504 region can be present in the same position; this is the case, in particular, for the 202b second threads of the third heading in the example discussed here.

[0058] The preform 500 further includes a third region 506, distinct from the first 502 and second 504 regions. The third region 506 is offset from the first region 502 along the first direction DI and from the second region 504 along the second direction D2. The third region 506 does not overlap with the first region 502 (it lies on a separate height band in the illustrated example), nor does it overlap with the second region 504 (it lies on a separate chord band in the illustrated example). As illustrated, the third region 506 can lie on the same height band (the band bounded along the first direction D1) as the second region 504. The dimension H3 of the third region 506, measured along the first direction D1, can be substantially equal to the dimension H2 of the second region 504.The third region 506 is located in the textile extension of the second region 504 along the second direction D2; that is, some of the second yarns extending into the second region 504 also extend into the third region 506. As mentioned above, the F1 / F2 ratio is increased in the third region 506 by extending some of the second yarns between the second region 504 and the third region 506. Thus, the F1 / F2 ratio in the third region 506 is greater than the F1 / F2 ratio in the second region 504 and the F1 / F2 ratio in the first region 502. The F1 / F2 ratio in the second region 504, on the other hand, can be equal to the F1 / F2 ratio in the first region 502.The exit of the second sons is materialized in Figure 6 where we see that, in the example considered here, the second sons 202a of second title are no longer present in the third region 506 and only half of the second sons 202b of third title are still present in the third region 506. The width between consecutive columns of second sons can, again, be adjusted in the third region 506 to take a greater value than in the second region 504, and for example to return to the LCT1 value corresponding to that of the first region, as illustrated.

[0059] In general, all or part of the second sons 202a of second title came out between the second region 504 and the third region 506. We can thus come out, between the second 504 and the third 506 regions, at least 10% of the second sons 202a of second title, for example at least 25% of these second sons 202a, for example at least 50% of these second sons 202a, for example at least 75% of these second sons 202a, for example substantially all of these second sons 202a. In the case where second sons 202b of third title are present, we can extract all or part of these second sons 202b between the second region 504 and the third region 506, for example at least 10% of the second sons 202b of third title, for example at least 25% of these second sons 202b, for example at least 50% of these second sons 202b.

[0060] After the third region 506 along the second direction D2, a weave corresponding to that of the second region 504 can be returned to a fourth region 508. In this case, the second yarns present in the second region 504 are found in the fourth region 508. The third region 506 is intercalated between the second region 504 and the fourth region 508. The fourth region 508 is in the textile extension of the second 504 and third 506 regions. Similarly, along the first direction D1, a weave corresponding to that of the first region 502 can be returned to a fifth region 510. The third region 506 is intercalated between the first region 502 and the fifth region 510. The fifth region 510 can extend to an end 511 of the preform opposite end 501.

[0061] We have just described a first example of adjusting the second yarn count using two types of yarns, 202a and 202b, with different counts. The example illustrated in Figures 7 and 8 concerns a variant in which only the second yarns, 202a, with the second count, are used instead of the second yarns, 202. Figure 7 shows the corresponding textile architecture in the second region, and Figure 8 shows the corresponding textile architecture in the third region. In the example considered here, half of the 202a second yarns have been removed to form the third region.

[0062] Other variations are, of course, possible such as replacing four times as many 202a second wires with one 202 second wire, for example four 12k grade second wires with one 48k grade.

[0063] We can favor one or another adjustment of the second yarn counts depending on the need for local increase in stiffness and the time available to carry out the weaving, insofar as increasing the number of yarns increases the duration of the textile operation.

[0064] The examples just described have shown that the textile weave is preserved between the first, second, and third regions, or more generally across the entire preform, which is advantageous in order to guarantee no modification of the mechanical behavior of the resulting part. However, this does not depart from the scope of the invention if the weave pattern were adjusted locally in an application where the local increase in stiffness would allow for a slight degradation of other mechanical properties. Furthermore, the proposed solution makes it possible to use the same constituent material of the yarns in the first, second, and third regions. The yarn material (and the matrix material to be obtained) depends on the intended application. For example, the preform may include carbon yarns, ceramic yarns (e.g., silicon carbide), glass yarns, aramid yarns, or a mixture of such yarns.

[0065] The examples just described show the adaptation of the titles and the presence of the second threads in the skin zone P and in the core zone which is located deeper in the thickness of the preform 500 so as to increase the F1 / F2 ratio in skin P and in the core zone.

[0066] As an example, the F1 / F2 ratio can be selectively increased in the skin zone P (only in the skin zone P and not in the core zone C). This is illustrated in Figures 9 and 10, which use the same reference symbols for the second wires 202a and 202b. Depending on the requirement, it may be desirable to also include the core zone C in increasing stiffness, in which case second wires of a suitable grade can also be used in the core zone C. The skin zone P makes the greatest contribution to increasing stiffness; therefore, the grade adjustment is minimally performed in this zone. It should be noted that the invention remains within the scope of the invention if the grade of the second wires is not adjusted in the core zone C, as this adjustment is only made in the skin zone P to achieve the desired increase in stiffness.

[0067] The dimensions of the third region 506 depend on the application. Generally, the area occupied by the third region 506 can be between 5% and 25% of the total area of ​​the preform 500. The dimension H3 of the third region 506 measured along the first direction DI can correspond to at most 50% of the dimension H of the preform 500 measured along the first direction D1; for example, dimension H3 can be between 10% and 50% of dimension H. The dimension L3 of the third region 506 measured along the second direction D2 can correspond to at most 50%, for example, at most 30%, of the dimension L of the preform 500 measured along the second direction D2; for example, dimension L3 can be between 10% and 50% of dimension L, for example, between 10% and 30% of dimension L.The composite part is obtained from the preform by densification with a matrix using well-known techniques. In the case of forming an organic matrix, in particular, the densification of the fibrous preform can be achieved by the well-known resin transfer molding (RTM) process. According to the RTM process, the fibrous preform is placed in a mold with the external shape of the part to be produced. A thermoplastic or thermosetting resin is injected into the internal space of the mold containing the fibrous preform. A pressure gradient is generally established in this internal space between the point where the resin is injected and the resin outlets in order to control and optimize the impregnation of the preform by the resin.

[0068] Figure 11 shows an example of a component according to the invention forming a fixed, guide vane 600 for the outlet of an aircraft turbomachine. The vane 600 comprises a blade 602, inner platform 604 and outer platform 606, and inner mounting lugs 605 and outer mounting lugs 607.

[0069] The outer face 604b of the platform 604 and the inner face 606a of the platform 606 are intended to define the airflow channel after the blade 600 is mounted. The inner mounting bracket 605 is intended to allow the blade 600 to be attached to an inner shell of the turbomachine via mounting holes 650, while the outer mounting bracket 607 is intended to allow the blade 600 to be attached to an outer shell of the turbomachine via mounting holes 670. The blade 602 extends between the platforms 604 and 606 and the mounting brackets 605 and 607, to which it is integral.

[0070] The invention can be applied to other types of parts such as blower blades or blade platforms, as mentioned above.

[0071] Although the present invention has been described with reference to specific embodiments, it is evident that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various embodiments illustrated / mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

[0072] All the characteristics described with reference to a process are transferable, alone or in combination, to a product, and conversely, all the characteristics described with reference to a product are transferable, alone or in combination, to a process.

[0073] The expression "between ... and ..." should be understood as including the boundaries.

Claims

Demands

1. A fibrous preform (500) intended to form a fibrous reinforcement of a part (600) of a turbomachine made of composite material or of a portion of a part of a turbomachine made of composite material, the preform being made by three-dimensional weaving of first yarns (Ci-Cn) extending along a first direction (D1) with second yarns transverse to the first yarns and extending along a second direction (D2), the preform comprising: - a first region (502) in which the second threads (202) have, at least on a skin area (P) of the preform, a first title, - a second region (504), offset from the first region along the first direction, in which at least part of the second yarns (202a) have, at least in the skin zone, a second yarn count that is lower than the first yarn count and corresponding to a divisor of the first yarn count, the preform having a ratio [sum of the linear masses of the second yarns in the region considered] / [dimension of the region considered measured along the first direction] conserved between the first region and the second region, and - a third region (506), present at least on the skin area, located in the extension of the second region along the second direction, at least part of the second second threads having come out between the second region and the third region to give the third region a volume ratio of first threads relative to second threads which is greater than that in the first region and that in the second region.

2. Fibrous preform (500) according to claim 1, wherein another part of the second yarns (202b) of the second region (504) have, at least on the skin area (P), a third count which is lower than the second count and corresponding to a divisor of the first count, and wherein at least a part of the third count second yarns are out between the second region and the third region (506).

3. Fibrous preform (500) according to claim 1 or 2, wherein at least one additional layer of first yarns is added in the third region relative to the first region.

4. A fibrous preform (500) according to claim 3, wherein said additional layer of first yarns is woven with second yarns from the second region.

5. A fibrous preform (500) according to any one of claims 1 to 4, wherein the skin zone (P) has a thickness (e p ) greater than or equal to 2 mm.

6. Fibrous preform (500) according to any one of claims 1 to 5, wherein the textile weave is preserved between the first region (502), the second region (504) and the third region (506).

7. Fibrous preform (500) according to any one of claims 1 to 6, wherein the preform comprises carbon wires, ceramic wires e.g. silicon carbide, glass wires, aramid wires, or a mixture of such wires.

8. Turbomachine part (600) made of composite material comprising a preform (500) according to any one of claims 1 to 7, and a matrix present in the porosity of the fibrous preform.

9. Part (600) according to claim 8, wherein the matrix is ​​an organic matrix.

10. Aeronautical turbomachine comprising at least one part (600) according to claim 8 or 9.

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