Fibrous preform with a thickness variation having yarn crossings

Abstract

The invention relates to a fibrous preform (1) produced by weaving between warp yarns and weft yarns, the preform (1) comprising first and second portions (100, 200) connected by a transition portion (500), the first portion (100) being thicker than the second portion (200) in a thickness direction (DE), each portion (100, 200, 500) comprising, in the thickness direction (DE), a core part (110, 210, 510) provided between two surface parts (121, 122, 221, 222, 521, 522), the core part (110) of the first portion (100) comprising a plurality of first warp yarns (c1) and a plurality of second warp yarns (c2), the preform (1) being characterised in that the first warp yarns (c1) cross the second warp yarns (c2) in the transition portion (500).

Description

Description Title of the invention: FIBROUS BLANK WITH A VARIATION IN THICKNESS HAVING THREAD CROSSINGS Technical Field

[0001] The invention relates to a fiber blank having a sudden variation in thickness, for example a fiber blank intended to form the fiber reinforcement of a turbomachine part, and in particular of a blade with integrated root. Prior art

[0002] In order to obtain lightweight turbomachine parts with excellent thermomechanical properties, composite material parts are produced in a well-known manner, i.e. parts comprising a fiber reinforcement densified by a matrix. The use of composite materials contributes to optimizing the performance of the turbomachine, in particular by reducing the overall mass of the turbomachine, which contributes to a reduction in fuel consumption and therefore to a significant reduction in pollutant emissions.

[0003] Furthermore, ceramic matrix composite materials can withstand temperatures ranging from 600°C to 1400°C. Due to their better resistance to high temperatures, ceramic matrix composite materials require less cooling. Since this cooling traditionally comes from a tap in the compressor, which impacts the efficiency of the turbomachine, composite materials therefore make it possible to further improve engine efficiency and further reduce fuel consumption.

[0004] In particular, it is known to produce the fibrous blank of the part by three-dimensional weaving on a jacquard-type loom, said blank then being shaped to obtain a fibrous preform of the part to be produced, which will be densified by the matrix.

[0005] For the production of parts with sudden or significant variations in thickness, such as a blade with a thick root portion and a thinner aerodynamic profile portion, several methods are known from the prior art.

[0006] A first method consists of using a jacquard-type loom compatible with large thicknesses of roughing and capable of handling a very large number of threads. The large thickness part of the roughing to be produced is thus produced with a very large number of threads, then numerous layer exits are carried out in order to remove a large number of threads from the weaving in the small thickness part of the roughing to be produced. However, this expensive method requires the use of non-standard looms, in particular having a jacquard head and a harness of a much larger size than those conventionally used for these types of pieces. In addition, the large number of threads to be handled and the layer exits to be carried out greatly complicate the weaving and increase the risks of defects in the roughing obtained.

[0007] A second method consists of using thicker weft yarns in the portions of the blank that one wishes to thicken, or even assemblies of yarns, for example in the form of a braid. Such a method is described in particular in documents WO 2021 / 005286 A1 and WO 2010 / 061140 A1. However, the use of such thick fibrous elements causes unwanted local increases in the fiber volume ratio and promotes densification defects in the final part by hindering the infiltration of gas, powder or resin into the blank. The use of this method for producing a blank must therefore be limited so as not to harm the mechanical characteristics of the final densified part.

[0008] Finally, a third method consists of making changes in weaving pattern between the different portions of the fiber blank to produce different thicknesses. Such a method is described in particular in document EP 1 526 285 A1. However, this method does not allow sudden variations in thickness to be made between two portions of the fiber blank without generating an irregular fiber volume ratio and weaving defects in the short transition zone between the two portions of very different thicknesses having distinct weaves.

[0009] Furthermore, in all the methods described above, the curvature that the rigid surface fibers must adopt at the location of a large variation in thickness is too great. Thus, in the final part obtained, the fibers do not adequately fill the areas with a large variation in thickness at the surface of the part, which are then essentially made up of matrix and insufficiently reinforced. Statement of the invention

[0010] The main aim of the present invention is therefore to remedy the aforementioned drawbacks by proposing a method for weaving a fibrous blank exhibiting a sudden and significant variation in thickness.

[0011] To this end, the invention proposes a fiber blank produced in a single piece by three-dimensional weaving comprising a plurality of warp threads extending in a longitudinal direction and a plurality of weft threads extending in a transverse direction, said blank comprising in the longitudinal direction a first and a second portion connected by a transition portion, the first portion being thicker than the second portion in a thickness direction perpendicular to the transverse and longitudinal directions, each portion comprising in the thickness direction a core portion present between two surface portions, the core portion of the first portion comprising a plurality of first warp threads and a plurality of second warp threads, said blank being characterized in that the first warp threads cross the second warp threads in the transition portion.

[0012] Thus, the creation of warp thread crossings at the heart of the fiber blank in the transition portion makes it possible to increase the maximum achievable thickness of the fiber blank without modifying the size or elements of the loom. This technique also makes it possible to increase the maximum achievable thickness of the fiber blank without increasing the number of layers of threads handled during weaving and without carrying out complex weaving operations such as layer exits. The present invention therefore makes it possible to produce a fiber blank having significant thickness variations over a very short distance, while limiting variations in the fiber content.

[0013] Furthermore, by making the crossings of the threads in the transition portion, the expansion inside the transition portion is increased, thus allowing the fibers located on the surface of the transition portion to have the desired trajectory. Therefore, in the final part obtained by densification of the fiber blank, the transition portion of the final part between the thick portion and the thin portion is suitably reinforced by the fibers, including at its surface.

[0014] In particular, there is at least one plane of the fiber blank perpendicular to the transverse direction in which the first warp threads cross the second warp threads in the transition portion. Preferably, the first warp threads cross the second warp threads in the core portion of the transition portion, in order to preserve the surface layers of the fiber blank and to maintain a satisfactory surface condition.

[0015] According to a particular embodiment of the invention, the core part of the first portion has a weave pattern different from the weave pattern of the core part of the second portion.

[0016] The use of different weave patterns between the two portions further increases the thickness variation in the fiber blank, with the crossovers in the transition portion ensuring a satisfactory transition between the two weave patterns.

[0017] According to another particular embodiment of the invention, the core part of the first portion comprises weft threads having a larger section than the section of the weft threads of the core part of the second portion.

[0018] The use of weft threads having a large cross-section, or more generally of expansion elements having a large cross-section, makes it possible to further increase the variation in thickness in the fiber blank, the crossings in the transition portion ensuring a satisfactory transition between the weft threads of large cross-section and those of smaller cross-section.

[0019] According to another particular embodiment of the invention, the surface parts of the first portion, the transition portion and the second portion have the same weave pattern.

[0020] Thus, the fibrous blank, and by extension the part obtained by densification of the fibrous blank, presents a controlled and constant surface state throughout its length.

[0021] According to another particular embodiment of the invention, the first portion, the transition portion and the second portion comprise the same number of warp threads in each plane of the blank perpendicular to the transverse direction.

[0022] This makes it easier to weave the fiber blank by maintaining a constant number of warp threads, and promotes a relatively variable fiber volume ratio in the fiber blank.

[0023] According to a particular embodiment of the invention, each first warp thread crosses each of the second warp threads in the transition portion in said at least one plane of the fiber blank perpendicular to the transverse direction. Preferably, each first warp thread crosses each of the second warp threads once in the transition portion in said at least one plane of the fiber blank perpendicular to the transverse direction.

[0024] Conversely, each second warp yarn may cross each of the first warp yarns in the transition portion in said at least one plane of the fiber blank perpendicular to the transverse direction. Preferably, each second warp yarn may cross each of the first warp yarns once in the transition portion in said at least one plane of the fiber blank perpendicular to the transverse direction.

[0025] In particular, each first warp thread crosses, preferably only once, each of the second warp threads in the transition portion in all planes of the fiber blank perpendicular to the transverse direction. Conversely, every second warp thread crosses, preferably a single times, each of the first warp threads in the transition portion in all planes of the fiber blank perpendicular to the transverse direction.

[0026] According to a particular embodiment of the invention, each first warp thread crossing a second warp thread in the transition portion crosses in the transition portion all of the second warp threads crossing first warp threads in said at least one plane of the fiber blank perpendicular to the transverse direction. Conversely, each second warp thread crossing a first warp thread in the transition portion may cross in the transition portion all of the first warp threads crossing second warp threads in said at least one plane of the fiber blank perpendicular to the transverse direction. These characteristics may be achieved in all planes of the fiber blank perpendicular to the transverse direction.

[0027] According to another particular embodiment of the invention, the core part of the first portion comprises a first and a second core part along the thickness direction, the first core part comprising the first warp threads and the second core part comprising the second warp threads.

[0028] The first core portion and the second core portion may be distinct, and may be adjacent. Thus, crossing the wires in the transition portion ensures better expansion.

[0029] According to another particular embodiment of the invention, the blank comprises at least one plane perpendicular to the transverse direction in which the transition portion comprises a plurality of successive frame columns T nwith n between 1 and N, the weft column Ti being the weft column adjacent to the first portion of the blank, N corresponding to the number of first warp threads of the first portion crossing second warp threads of the first portion, so that in the weft column T n , first n warp threads of the first portion cross second n warp threads of the first portion.

[0030] The threads are thus crossed regularly, allowing optimal expansion while limiting the variation in the volume rate of fibers.

[0031] The invention also relates to a method of manufacturing a fiber preform for a composite material part, the method comprising the following steps: - the production of a fiber blank according to the invention, - shaping the fiber blank so as to obtain a fiber preform comprising an adjacent sacrificial portion and a useful portion, the sacrificial portion being formed at least by the first portion of the fiber blank and the useful portion being formed by the second portion of the fiber blank and at least part of the transition portion of the fiber blank.

[0032] Furthermore, the invention relates to a method for manufacturing a part made of composite material comprising at least the following steps: - the production of a fiber preform in accordance with the method of manufacturing a fiber preform according to the invention, - the introduction of a composition comprising at least one precursor of a matrix material into the fibrous preform, - the transformation of the composition into a matrix so as to obtain an intermediate part made of composite material comprising a fibrous reinforcement densified by a matrix, the intermediate part comprising a sacrificial portion whose fibrous reinforcement is formed by the sacrificial portion of the fibrous preform, - the removal of the sacrificial portion of the intermediate part to obtain the final part.

[0033] According to a preferred embodiment of the invention, the invention relates to a method for manufacturing a part made of ceramic matrix composite material comprising the following steps: - the production of a fiber preform in accordance with the method of manufacturing a fiber preform according to the invention, - consolidation of the fiber preform by chemical vapor infiltration, - impregnation of the consolidated fiber preform with a suspension comprising ceramic particles, then - the infiltration of liquid silicon into the fiber preform so as to obtain an intermediate part made of ceramic matrix composite material comprising a fiber reinforcement densified by a ceramic matrix, the intermediate part comprising a sacrificial portion whose fiber reinforcement is formed by the sacrificial portion of the fiber preform, - the removal of the sacrificial portion of the intermediate part to obtain the final part.

[0034] Finally, the invention relates to a use of the method for manufacturing a part made of a composition material according to the invention for the manufacture of a turbomachine blade made of a composite material. Brief description of the drawings

[0035] [Fig. 1] Figure 1 is a schematic perspective view of a fiber blank according to the invention.

[0036] [Fig. 2] Figure 2 is a schematic representation of a weaving plan belonging to the fiber blank according to the invention.

[0037] [Fig. 3] Figure 3 is an exploded perspective schematic view showing a forming tool in accordance with one embodiment of the invention and the placement of the fiber blank of Figures 1 and 2 therein.

[0038] [Fig. 4] Figure 4 is a schematic perspective view of a fiber preform according to the invention obtained by shaping the fiber blank of Figures 1 and 2, and comprising a sacrificial portion.

[0039] [Fig. 5] Figure 5 is a schematic perspective view showing an operation of injecting a liquid matrix precursor composition into the fiber preform of Figure 5.

[0040] [Fig. 6] Figure 6 is a schematic perspective view of a composite material part obtained following the injection operation of Figure 6 with the removal of the sacrificial portion. Description of the embodiments

[0041] Figures 1 to 3 illustrate a fiber blank 1 according to the invention produced by three-dimensional weaving between a plurality of layers of warp threads and a plurality of layers of weft threads. By "three-dimensional weaving" or "3D weaving" is meant here a weaving method by which at least some of the warp threads bind weft threads on several weft layers. A reversal of roles between warp and weft is possible. The fiber blank 1 is preferably produced by means of a jacquard type loom. Such a weaving loom is for example described in document FR 3 047 744 A1.

[0042] As illustrated in Figure 1, the fiber blank 1 extends in the warp direction along a longitudinal direction D L and in the weft direction following a transverse direction DT. The fiber blank 1 extends in thickness following a thickness direction D E perpendicular to the longitudinal directions D L and transverse D T . In Figure 2, a schematic plan of weaving of the fiber blank 1 is shown perpendicular to the transverse direction DT.

[0043] The fiber blank 1 comprises, along the longitudinal direction D: L at least a first portion 100 and a second portion 200, separated by a transition portion 500. The first portion 100 is thicker than the second portion 200, that is to say its dimension along the thickness direction D E is greater than the dimension of the second portion 200 along the thickness direction D E. The first portion 100 and the transition portion 500 are adjacent along the longitudinal direction D. L . The second portion 200 and the transition portion 500 are adjacent along the longitudinal direction D. L . Preferably, the first portion 100 and the second portion 200 extend over the entire thickness of the fiber blank 1 along the thickness direction D. E , and over the entire width of the fibrous blank 1 in the transverse direction D T .

[0044] In the example illustrated in Figures 1 and 2, the fiber blank 1 comprises only the first portion 100, the transition portion 500 and the second portion 200. It is of course not departing from the scope of the invention if the fiber blank comprises additional portions in the longitudinal direction D. L .

[0045] The first portion 100 of the fiber blank 1 comprises a core part 110 and two surface parts 121 and 122. The core part 110 of the first portion 100 of the fiber blank 1 extends along the thickness direction D E between the first surface part 121 of the first portion 100 and the second surface part 122 of the first portion 100. The first surface part 121 and the second surface part 122 of the first portion 100 can join on either side of the core part 110 along the transverse direction D T . In this configuration, the first and second surface portions 121 and 122 form an overall surface portion of the first portion 100 surrounding the core portion 110 of said first portion 100.

[0046] The second portion 200 of the fiber blank 1 comprises a core part 210 and two surface parts 221 and 222. The core part 210 of the second portion 200 of the fiber blank 1 extends along the thickness direction D E between the first surface part 221 of the second portion 200 and the second surface part 222 of the second portion 200. The first surface part 221 and the second surface part 222 of the second portion 200 can join on either side of the core part 210 along the transverse direction D T . In this configuration, the first and second surface portions 221 and 222 form an overall surface portion of the second portion 200 surrounding the core portion 210 of said second portion 200.

[0047] The transition portion 500 of the fiber blank 1 comprises a core portion 510 and two surface portions 521 and 522. The core portion 510 of the transition portion 500 of the fiber blank 1 extends along the thickness direction D Ë between the first surface part 521 of the transition portion 500 and the second surface part 522 of the transition portion 500. The first surface part 521 and the second surface part 522 of the transition portion 500 can join on either side of the core part 510 along the transverse direction D T . In this configuration, the first and second surface portions 521 and 522 form an overall surface portion of the transition portion 500 surrounding the core portion 510 of said transition portion 500.

[0048] Preferably, the first surface portion 521 of the transition portion 500 is located in the extension of the first surface portion 121 of the first portion 100 and in the extension of the first surface portion 221 of the second portion 200. Preferably, the second surface portion 522 of the transition portion 500 is located in the extension of the second surface portion 122 of the first portion 100 and in the extension of the second surface portion 222 of the second portion 200. Therefore, preferably, the core portion 510 of the transition portion 500 is located in the extension of the core portion 110 of the first portion 100 and in the extension of the core portion 210 of the second portion 200.

[0049] The core portion 110 of the first portion 100 comprises a first core portion 111 and a second core portion 112. The first core portion 111 extends along the thickness direction D Ë between the first surface portion 121 and the second core portion 112. The second core portion 112 extends along the thickness direction D Ë between the first core part 111 and the second surface part 122.

[0050] First warp threads Ci bind together the weft threads ti of the first core part 111 of the first portion 100 of the blank 10. Second warp threads C2 bind together the weft threads t2 of the second core part 112. The first and second warp threads Ci and C2 then bind together the weft threads t 5of the core portion 510 of the transition portion 500. Preferably, all the warp threads of the first core portion 111 of the first portion 100 of the blank 10 are first warp threads Ci and all the warp threads of the second core portion 112 of the first portion 100 of the blank 1 are second warp threads C2.

[0051] In the example illustrated in Figure 2, a portion of the first warp threads Ci from the first core part 111 of the first portion 100 crosses a portion of the second warp threads C2 from the second core part 112 of the first portion 100 in the core part 510 of the transition portion 500. It is of course not outside the scope of the invention if all of the first warp threads Ci from the first core part 111 of the first portion 100 crosses all of the second warp threads C2 from the second core part 112 of the first portion 100 in the core part 510 of the transition portion 500.

[0052] The transition portion 500 comprises a plurality of frame columns Ti, T2, ... T 7 adjacent oriented along the thickness direction D E . In particular, the transition portion 500 extends in the longitudinal direction D. L between on the one hand the first column of frame Ti and the last column of frame T 7 . The first weft column Ti of the transition portion 500 is defined as the weft column comprising at least one crossing between a first warp yarn Ci and a second warp yarn C2 closest to the first portion 100 of the fiber blank 1. The last weft column T 7of the transition portion 500 is defined as the weft column comprising at least one crossing between a first warp yarn Ci and a second warp yarn C2 closest to the second portion 200 of the fiber blank 1. Preferably, the first weft column Ti of the transition portion 500 is the weft column of the transition portion 500 adjacent to the first portion 100 of the blank 10. Preferably, the last weft column T 7 of the transition portion 500 is the frame column of the transition portion 500 adjacent to the second portion 200 of the blank 10.

[0053] Preferably, as illustrated in Figure 2, in each plane the blank 1 perpendicular to the transverse direction D T, there are no crossings between the warp threads in the first portion 100, and there are no crossings between the warp threads in the second portion 200. Preferably, there are also no crossings between or with warp threads originating from a surface portion 121, 122, 521, 522, 221, 222 of the first portion 100, the transition portion 500 or the second portion 200 of the fiber blank 1.

[0054] The crossings between warp threads from the first portion 100 of the fiber blank 1 in the transition portion 500 may be present in all the planes of the fiber blank 1 perpendicular to the transverse direction D T , or only in a part of the planes of the fiber blank 1 perpendicular to the transverse direction DT.

[0055] Preferably, as illustrated in Figure 2, each first warp thread Ci crossing a second warp thread C2 crosses each second warp thread C2 only once. Conversely, each second warp thread C2 crossing a first warp thread Ci crosses each first warp thread Ci only once.

[0056] Preferably, as illustrated in FIG. 2, the crossing of the first warp threads Ci from the first core part 111 of the first portion 100 with the second warp threads C2 from the second core part 112 of the first portion 100 is done in a regular manner, by first crossing the first warp threads Ci closest to the second core part 112 and the second warp threads C2 closest to the first core part 111, then by progressively crossing warp threads Ci and C2 that are increasingly distant.Thus, in the first weft column Ti closest to the first portion 100 belonging to the transition portion 500, a single first warp thread Cn from the first core part 111 of the first portion 100 crosses a single second warp thread C21 from the second core part 112 of the first portion 100: the first warp thread Cn closest to the second core part 112 in the first portion 100 crosses the second warp thread C21 closest to the first core part 111 in the first portion 100. In the second weft column T. 2closest to the first portion 100 belonging to the transition portion 500, only two first warp threads C11, C12 coming from the first core part 111 of the first portion 100 cross only two second warp threads C21, C22 coming from the second core part 112 of the first portion 100: the first warp thread Cn crosses the second warp thread C22 and the first warp thread C12 crosses the second warp thread C21.In the third weft column T3 closest to the first portion 100 belonging to the transition portion 500, only three first warp threads C11, C12, C13 from the first core part 111 of the first portion 100 cross only three second warp threads C21, C22, C23 from the second core part 112 of the first portion 100: the first warp thread Cn crosses the second warp thread C23, the first warp thread C12 crosses the second warp thread C22 and the first warp thread C13 crosses the second warp thread C21.

[0057] Generally, we denote by T nthe n-th frame column of the transition portion 500 closest to the first portion 100 for n between 1 and N inclusive, N being the number of first wires Cn, C12, C13, C14 crossing second wires C21, C22, C23, C24 in the transition portion 500 or N being the number of second wires C21, C22, C23, C24 crossing first wires Cn, C12, C13, C14 in the transition portion 500. In the example illustrated in Figure 2, the number N has the value 4. Thus, in each column T n , n first warp threads from the first core part 111 of the first portion 100 cross n second warp threads from the second core part 112 of the first portion 100. In the example illustrated in figure 2, for n = N, we have in the fourth column T 44 first warp threads Cn, C12, C13, C14 from the first core part 111 of the first portion 100 which cross 4 second warp threads C21, C22, C23, C24 from the second core part 112 of the first portion 100.

[0058] Additionally, in each column T n , the first warp thread Ci n -i crosses the second warp thread C2 i+i for i between 0 and n-1 inclusive. Thus, in the example illustrated in Figure 2, in column T2, i.e. n = 2, the increment i = 0 indicates that the first warp thread Ci 2-0, i.e. C12, crosses the second warp thread C20+1, i.e. C21, and the increment i = 1 indicates that the first warp thread Ci 2-1, i.e. Cn, crosses the second warp thread C21+1, i.e. 022-

[0059] The fiber blank 1 according to the invention may further comprise expansion elements in the core part 110 of the first portion 100 of the blank 1. These expansion elements are preferably weft threads with a high count, i.e. having a high thickness and section. Thus, a portion of the weft threads of the core portion 110 of the first portion 100 have a larger cross-sectional size than the weft threads of the surface portions 121 and 122 of the first portion 100 and have a larger cross-sectional size than the weft threads of the core portion 210 of the second portion 200. Thus, the weft threads located in the surface portions 121 and 122 of the first portion 100 may thus have a first cross-sectional size, i.e. a first thickness, and the weft threads located in the center of the core portion 110 of the first portion 100 may have a second cross-sectional size, i.e. a second thickness. section, i.e. a second thickness. In the example illustrated in FIG. 2, the weft threads of the core portion 110 furthest from the center of said core portion 110 also have the first section size, i.e. the first thickness.

[0060] The weft threads may have different section sizes, for example so as to obtain progressive weft thread section sizes in the thickness of the first portion 100. Intermediate weft threads may be present between the weft threads having the first section size, i.e. the first thickness, and the weft threads having the second section size, i.e. the second thickness, said intermediate weft threads having an intermediate section size between the first and second sections, i.e. an intermediate thickness between the first and second sections. For example, the second section size is two to ten times greater than the first section size.

[0061] The swelling elements, or the weft threads corresponding to the swelling elements, can be in the form of an assembly of filaments or in the form of a braid.

[0062] The presence of such expansion elements in the first portion 100 may make it possible to increase the thickness of the transition portion 500. Expansion elements may also be present in the transition portion 500, in the part of the transition portion 500 directly adjacent to the first portion 100. Preferably, the expansion elements of the first portion 100 and of the transition portion 500 are not intended to be part of the final composite material part, but are only means of increasing the thickness and expansion of the fiber blank.

[0063] As illustrated in Figure 2, the core portion 110 of the first portion 100 has a first weave pattern and the core portion 210 of the second portion 200 has a second weave pattern, the second weave pattern preferably being different from the first weave pattern. In order to increase the expansion, and therefore the thickness, of the first portion 100 compared to the second portion 200, a first weave is chosen allowing a greater expansion than the second weave. Preferably, the first weave and the second weave are chosen so as to allow a similar fiber volume ratio in the first and second portions 100 and 200.

[0064] In order to further increase the abundance of the core part 110 of the first portion 100, it is possible to produce weft doublings, as illustrated in FIG. 2. By weft doubling, it is meant that, in a plane of the fiber blank 1 perpendicular to the transverse direction DT, the warp threads Ci and C2 of the core part 110 of the first portion 100 bind the weft threads in pairs, that is to say that the pairs of weft threads are not separated by a warp thread in said plane perpendicular to the transverse direction D T .

[0065] Preferably, the core portion 110 of the first portion 100 or the core portion 210 of the second portion 200 is made by interlock weaving, in order to obtain mechanical properties as homogeneous as possible within said core portion 110 or 210 and to promote homogeneous densification by the matrix. By "interlock weaving" is meant here a three-dimensional weaving weave in which each warp layer links several weft layers with all the threads of the same warp column having the same movement in the plane of the weave.

[0066] If, in a plane of the fiber blank 1 perpendicular to the transverse direction D T, warp threads from the core part 110 of the first portion 100 do not cross other warp threads in the transition portion 500, these may have a weave pattern in the transition portion 500 identical to the weave pattern of the core part 110 of the first portion 100.

[0067] As illustrated in Figure 2, the surface portions 121 and 122 of the first portion 100, the surface portions 521 and 522 of the transition portion and / or the surface portions 221 and 222 of the second portion 200 are preferably made by weaving with a plain, satin or twill weave in order to limit surface irregularities, a satin weave also providing a smooth surface appearance. Thus, after densification of the fiber blank 1, the use of these types of weave promotes obtaining a surface condition free from significant irregularities, i.e. a good finishing condition to avoid or limit finishing operations by machining or to avoid the formation of resin clumps. in the case of resin matrix composites. Preferably and as illustrated in FIG. 2, the first surface part 121 of the first portion 100, the first surface part 521 of the transition portion 500 and the first surface part 221 of the second portion 200 have an identical and continuous weave pattern along the longitudinal direction DL, in order to ensure a controlled surface condition over the entire length of the final densified part obtained from the blank 1.

[0068] Therefore, it is possible according to the invention to combine the methods of the prior art, which relate to the addition of weft yarns of high thickness and the use of different weaving weaves, with the method of the invention which describes the crossing of warp yarns within the transition portion. Tests have been carried out to study the combination of the methods described previously with the new method proposed in the present invention, with the aim of obtaining high thickness portions in a fiber blank by means of a standard weaving loom.

[0069] With the standard loom used in these tests, without resorting to the two methods of the prior art and the crossing method of the invention, it is possible to produce fiber blanks having a maximum thickness of 7 mm. According to the tests carried out, using a change of weave alone, it is only possible to produce fiber blanks having a thickness of 13 mm. By combining the change of weave and the crossing method of the invention, it is possible to increase the thickness obtained to 14 mm, while maintaining a satisfactory fiber volume ratio. Furthermore, by combining the change of weave with weft yarns of significant thickness, it is only possible to produce fiber blanks having a thickness of 20 mm.By combining the change of weave, the thick weft yarns and the crossing method of the invention, it is possible to exceed 20 mm of thickness of the blank, while maintaining a satisfactory fiber volume rate. The combination of the three methods provided by the invention can therefore make it possible to locally triple the thickness of the fiber blank.

[0070] Preferably, the fiber blank 1 according to the invention does not comprise a layer outlet, which means that the number of layers of warp threads is identical in the first portion 100, in the transition portion 500 and in the second portion 200. In particular, the number of layers of warp threads is preferably identical in the core portion 110 of the first portion 100, in the core portion 510 of the transition portion 500 and in the core portion 210 of the second portion 200 of the fiber blank 1.

[0071] Preferably, the fibrous blank 1 corresponds to a fibrous texture "dry", that is to say not impregnated with a resin or the like. The fibrous blank 100 may comprise a plurality of threads or filaments of various types, in particular ceramic or carbon threads or a mixture of such threads. Preferably, the fibrous blank 100 may be made from silicon carbide fibers. Generally, the fibrous blank 100 may also be made from fibers made of the following materials: alumina, mullite, silica, an aluminosilicate, a borosilicate, carbon, or a mixture of several of these materials.

[0072] Preferably, the fiber blank 1 is shaped by compaction to form a fiber preform ready to be densified. For this purpose, the fiber blank 1 is placed in a forming tool 30 which, as illustrated in FIG. 3, comprises a first shell 31 comprising in its center a first imprint 31a corresponding in part to the shape and dimensions of the part to be produced, the imprint 31a being surrounded by a first contact plane 31b.

[0073] The tool 30 also comprises a second shell 32 comprising in its center a second imprint 32a corresponding in part to the shape and dimensions of the part to be produced, the second imprint 32a being surrounded by a second contact plane 32b intended to cooperate with the first contact plane 31a of the first shell 31.

[0074] The fiber blank 1 is first positioned in the imprint 31a of the first shell 31, the second shell 32 then being placed on the first shell 31 in order to close the forming tool 30. Once the tool 30 is closed, the first and second shells are in a position called “position assembly”, that is to say a position in which the first and second impressions 31a, 32a are placed opposite each other while the first and second contact planes 31b and 32b are also opposite each other. In this configuration, the first and second impressions 31a, 32a together define an internal volume having the shape of the part to be produced and in which the fiber blank 1 is placed.

[0075] In the case of the manufacture of a turbomachine blade, the imprint 31a is intended to form the intrados side of the fiber blade preform while the imprint 32a is intended to form the extrados side of the blade preform. Thanks to the presence of the first portion 100 of the fiber blank 10 and the crossings of wires described previously, the transition portion has a sufficient thickness to fill the enlarged part of the internal volume of the tool 30 intended to shape the blade root.

[0076] Then, the forming tool 30 with the fiber blank 1 inside it is placed in a compacting press. The press comprises a lower part on which the first shell 31 of the forming tool 30 rests and an upper part placed on the second shell 32 of the forming tool 30.

[0077] The forming tool 30 is then subjected to the application of a compacting pressure applied by the press. The application of the pressure causes the first and second shells 31 and 32 to come together until the first and second contact planes 31b and 32b meet, which makes it possible both to compact the fiber blank 1 according to a determined compaction rate in order to obtain a fiber rate that is also determined and to shape the fiber blank according to the profile of the blade to be manufactured. A fiber preform 10 is then obtained having the shape of the part to be produced and comprising a sacrificial portion 12 corresponding at least to the first portion 100 of the fiber blank 1 and an adjacent useful portion 11 corresponding to the second portion 200 of the fiber blank 1 and to at least a part of the transition portion 500 of the fiber blank 1.The transition portion 500 of the blank 1 can be entirely included in the useful portion 11 of the preform 10. A part of the. transition portion 500 of the blank 1 may be included in the sacrificial portion 12 of the preform 10. Preferably, the useful portion 11 does not comprise weft threads having a large cross-section, i.e. having a large thickness. In particular, preferably, the useful portion 11 does not comprise weft threads having a cross-section of size more than twice the maximum cross-section size of the weft threads of the second portion 200 of the fiber blank 1.

[0078] In the case of the manufacture of a turbomachine blade, the useful portion 11 of the fiber preform 10 comprises an aerodynamic profile part 11a intended to form the fiber reinforcement of the aerodynamic profile of the blade, and comprises a root part 11b intended to form the fiber reinforcement of the root of the blade.

[0079] The fibrous preform 10 is then densified. The densification of the fibrous preform 10 intended to form the fibrous reinforcement of the part to be manufactured consists of filling the porosity of the preform, in all or part of its volume, with the material constituting the matrix.

[0080] According to a first embodiment of the invention, the fiber preform 10 is preferably densified by a ceramic matrix, in order to obtain a part made of ceramic matrix composite material, called “CMC”. Indeed, ceramic matrix composite materials have interesting mechanical properties at high temperature, which is particularly useful for the manufacture of turbomachine blades.

[0081] Thus, the fiber preform can be consolidated or densified in a well-known manner by gaseous means by chemical vapor infiltration of the matrix, called "CVI". The fiber preform corresponding to the fiber reinforcement of the blade to be produced is placed in a furnace into which a reaction gas phase is admitted. The pressure and temperature prevailing in the furnace and the composition of the gas phase are chosen so as to allow the diffusion of the gas phase within the porosity of the preform to form at least part of the matrix by deposition, at the heart of the material in contact with the fibers, of a solid material resulting from a decomposition of a constituent of the gas phase or from a reaction between several constituents, contrary to the pressure and temperature conditions temperatures specific to CVD ("Chemical Vapor Deposition") processes which lead exclusively to a deposition on the surface of the material. The formation of a SiC matrix can be obtained with methyltrichlorosilane (MTS) giving SiC by decomposition of the MTS.

[0082] A densification combining gas and liquid routes can be used in a well-known manner to facilitate implementation and limit costs and manufacturing cycles while obtaining satisfactory characteristics for the intended use. In this configuration, consolidation of the fiber preform is carried out by gas as described previously, then impregnation of the fiber preform is carried out with a slip ("slurry cast") containing for example SiC particles and organic binders, followed by infiltration with liquid silicon ("melt infiltration").

[0083] The consolidation of the fibrous preform can be carried out in a manner known per se using the liquid process (LC). The liquid process consists of impregnating the preform with a liquid composition containing a precursor of the ceramic matrix material. The preform is placed in a mold that can be sealed with a housing having the shape of the final molded blade. Then, the mold is closed and the liquid ceramic matrix precursor is injected into the entire housing to impregnate the entire fibrous part of the preform.

[0084] The transformation of the precursor into a matrix, namely its polymerization, is carried out by heat treatment, generally by heating the mold, after elimination of any solvent and crosslinking of the polymer, the preform always being maintained in the mold having a shape corresponding to that of the part to be produced.

[0085] In the case of the formation of a carbon or ceramic matrix, the heat treatment consists of pyrolyzing the precursor to transform the matrix into a carbon or ceramic matrix depending on the precursor used and the pyrolysis conditions. For example, liquid ceramic precursors, in particular SiC, can be resins of the polycarbosilane (PCS) or polytitanocarbosilane (PTCS) or polysilazane (PSZ) type, while liquid carbon precursors can be resins with a relatively high coke content, such as phenolic resins. Several consecutive cycles, from impregnation to heat treatment, can be carried out to achieve the desired degree of densification.

[0086] According to a second embodiment of the invention, the fiber preform 10 can be densified by an organic matrix, in order to obtain a part made of organic matrix composite material, called “CMO”.

[0087] The densification of the fiber preform can then be carried out by the well-known transfer molding process called RTM ("Resin Transfer Molding"). According to the RTM process, the fiber preform is placed in a mold having the external shape of the part to be produced. A resin is injected into the internal space of the mold which contains the fiber preform. A pressure gradient is generally established in this internal space between the place where the resin is injected and the resin discharge orifices in order to control and optimize the impregnation of the preform by the resin.

[0088] The injection of a liquid matrix precursor composition into the fiber blank and its transformation into a matrix are carried out in an injection tool 70 shown in FIG. 5. As for the forming tool 30, the injection tool 70 comprises a first shell 71 comprising in its center a first impression corresponding in part to the shape and dimensions of the part to be produced and a second shell 72 comprising in its center a second impression corresponding in part to the shape and dimensions of the part to be produced. Once the tool 70 is closed, the first and second impressions respectively of the first and second shells 71 and 72 together define an internal volume 700 having the shape of the part to be produced and in which the fiber preform 10 is placed.

[0089] The tool 70 further comprises means for carrying out the injection of a liquid matrix precursor and the transformation of this precursor into a matrix. More specifically, in the example described here, the first shell 71 of the tool 70 comprises an injection port 71a intended to allow the injection of a liquid matrix precursor composition 7 into the fiber preform while the second shell comprises an evacuation port 72a intended to cooperate with a pumping system for vacuuming the tool and drawing air during injection. The injection tool 70 also comprises a lower part 74 and an upper part 75 between which the first and second shells 71 and 72 are placed, the lower part 74 and the upper part 75 being equipped with heating means (not shown in FIG. 5).

[0090] Once the tool 70 is closed, the blade is molded by impregnating the preform 10 with, for example, a thermosetting resin that is polymerized by heat treatment. For this purpose, the well-known injection or transfer molding process known as RTM ("Resin Transfer Molding") is used. In accordance with the RTM process, a resin 7, for example a thermosetting resin, is injected via the injection port 71a of the first shell 71 into the internal volume 700 occupied by the preform 10. The port 723 of the second shell 720 is connected to a discharge conduit maintained under pressure (not shown in FIG. 5). This configuration allows the establishment of a pressure gradient between the lower part of the preform 10 where the resin is injected and the upper part of the preform located near the port 72a.In this way, the resin 7 injected substantially at the level of the lower part of the preform will gradually impregnate the entire preform by circulating in it up to the evacuation port 72a through which the surplus is evacuated. Of course, the first and second shells 71 and 72 of the tool 70 may respectively comprise several injection ports and several evacuation ports.

[0091] The resin used can be, for example, an epoxy resin with a temperature class of 180 °C (maximum temperature supported without loss of characteristics). Resins suitable for RTM processes are well known. They preferably have a low viscosity to facilitate their injection into the fibers. The choice of temperature class and / or the chemical nature of the resin is determined according to the thermomechanical stresses to which the part must be subjected. Once the resin has been injected throughout the reinforcement, it is polymerized by heat treatment in accordance with the RTM process. After injection and polymerization, the part is demolded.

[0092] The densification processes described above make it possible to produce, from the fiber blank of the invention, mainly parts made of organic matrix composite (OMC), carbon matrix (C / C) and ceramic matrix (CMC) material. The composite material parts obtained by the preceding densification processes can optionally undergo a post-curing cycle to improve their thermomechanical characteristics. Finally, the part can be trimmed to remove any excess resin and chamfers can be machined.

[0093] As illustrated in Figure 6, a part 1000 is obtained, here a turbomachine blade, formed from a fibrous reinforcement densified by a matrix which comprises in its lower part a root 1100b formed by the root part 11b of the fibrous preform 10 which is extended by a blade or an aerodynamic profile 1100a formed by the aerodynamic profile part 11a of the fibrous preform 10.

[0094] The part 1000 is preferably obtained by removing the sacrificial portion 1200 formed by the densified fibrous reinforcement from the sacrificial portion 12 of the fibrous preform 10.

[0095] The fiber blank according to the present invention can in particular be used to produce a turbomachine blade having a more complex geometry than the blade shown in Figure 6, such as blades comprising, in addition to that of Figure 6, one or more platforms making it possible to perform functions such as those of vein sealing, anti-tilting, etc.

Claims

Claims

1. Fibrous blank (1) produced in a single piece by three-dimensional weaving comprising a plurality of warp threads extending in a longitudinal direction (D L ) and a plurality of weft threads extending in a transverse direction (D T ), said blank (1) comprising in the longitudinal direction (D L ) a first and a second portion (100, 200) connected by a transition portion (500), the first portion (100) being thicker than the second portion (200) along a thickness direction (D E ) perpendicular to the transverse directions (D T ) and longitudinal (D L ), each portion (100, 200, 500) comprising, along the thickness direction (D E) a core portion (110, 210, 510) present between two surface portions (121, 122, 221, 222, 521, 522), the core portion (110) of the first portion (100) comprising a plurality of first warp threads (ci) and a plurality of second warp threads (C2), said blank (1) being characterized in that there is at least one plane of the fibrous blank (1) perpendicular to the transverse direction (D T ) in which the first warp threads (ci) cross the second warp threads (C2) in the transition portion (500).

2. A fiber blank (1) according to claim 1, wherein the core portion (110) of the first portion (100) has a weave pattern different from the weave pattern of the core portion (210) of the second portion (200).

3. Fibrous blank (1) according to claim 1 or 2, wherein the core part (110) of the first portion (100) comprises weft threads having a larger cross-section than the cross-section of the weft threads of the core part (210) of the second portion (200).

4. A fibrous blank (1) according to any one of claims 1 to 3, wherein the surface portions (121, 122, 221, 222, 521, 522) of the first portion (100), the transition portion (500) and the second portion (200) have the same weave pattern.

5. A fibrous blank (1) according to any one of claims 1 to 4, wherein the first portion (100), the transition portion (500) and the second portion (200) comprise the same number of warp threads in each plane of the blank (1) perpendicular to the transverse direction (D T )

6. A fibrous blank (1) according to any one of claims 1 to 5, each first warp yarn crosses each of the second warp yarns in the transition portion (500) in said at least one plane of the fibrous blank (1) perpendicular to the transverse direction (D T ).

7. Fibrous blank (1) according to any one of claims 1 to 6, wherein each first warp thread crossing a second warp thread in the transition portion (500) crosses in the transition portion (500) all of the second warp threads crossing first warp threads in said at least one plane of the fibrous blank (1) perpendicular to the transverse direction (D T ).

8. A fibrous blank (1) according to any one of claims 1 to 7, wherein the core portion (110) of the first portion (100) comprises first and second core portions (111, 112) along the thickness direction (D E ), the first core part (111) comprising the first warp threads (ci) and the second core part (112) comprising the second warp threads (C2).

9. Fibrous blank (1) according to any one of claims 1 to 8, comprising at least one plane perpendicular to the transverse direction (DT) in which the transition portion (500) comprises a plurality of successive weft columns T n (Ti, T2, ... T 7) with n between 1 and N, the weft column Ti being the weft column adjacent to the first portion (100) of the blank (1), N corresponding to the number of first warp threads (ci) of the first portion (100) crossing second warp threads (C2) of the first portion (100), so that in the weft column T n , n first warp threads (ci) of the first portion (100) cross n second warp threads (C2) of the first portion (100).

10. A method of manufacturing a fiber preform (10) for a composite material part, the method comprising the following steps: - the production of a fibrous blank (1) according to any one of claims 1 to 9, - shaping the fibrous blank (1) so as to obtain a fibrous preform (10) comprising an adjacent sacrificial portion (12) and a useful portion (11), the sacrificial portion (12) being formed at least by the first portion (100) of the fibrous blank (1) and the useful portion (11) being formed by the second portion (200) of the fibrous blank (1) and at least part of the transition portion (500) of the fibrous blank (1).

11. Method for manufacturing a part (1000) made of composite material comprising at least the following steps: - the production of a fibrous preform (10) in accordance with the method of manufacturing a fibrous preform according to claim 10, - the introduction of a composition (7) comprising at least one precursor of a matrix material into the fibrous preform (10), - the transformation of the composition (7) into a matrix so as to obtain an intermediate part made of composite material comprising a fibrous reinforcement densified by a matrix, the intermediate part comprising a sacrificial portion (1200) whose fibrous reinforcement is formed by the sacrificial portion (12) of the fibrous preform (10), - the removal of the sacrificial portion (1200) from the intermediate part to obtain the final part (1000).

12. Use of the method according to claim 11, for the manufacture of a turbomachine blade (1000) made of composite material.

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