Patent ID: 12241184

DETAILED DESCRIPTION OF THE INVENTION

In the embodiments detailed below, the fibrous structure woven from SiC fibres preferably has a target fibre content of between 25 and 50% by volume.

FIG.5is a diagram of a fibrous structure20according to the invention in which a warp direction C and a weft direction T and a direction E are shown, these directions being perpendicular to each other. This fibrous structure20has the same number of warp yarns woven at any level of the fibrous structure along the warp direction C.

The fibrous structure20comprises a first part22, a second part24and a third part26along the warp direction C, best seen in the schematic illustration of the fibrous structure20before shaping. The first22, second24and third26parts each have a thickness e1, e2, e3measured in a direction E perpendicular to the warp and weft directions. In this example, the fibrous structure20comprises a second part24whose thickness e2is lower than the thickness e1, e2of each of the first part22and the third part26.

The first22and third26parts each comprise a first portion16and a second portion18. Once the fibrous structure20has been formed into the shape of Pi as seen inFIG.5, the first portions16of the first22and third26parts are arranged to form a non-zero angle, preferably between 0° and 45°, with the second portions18of the first22and third26parts respectively. Prior to this shaping of the fibrous structure20, i.e. at the end of the three-dimensional weaving, for each of the first22and third26parts, the first portion16is arranged above the second portion18along the E-direction, also called the thickness direction. The first16and second18portions, although woven simultaneously, are structurally independent, i.e. they are not woven to each other, which allows an arrangement of the first16portions at a non-zero angle to the second18portions and the second24part. The first16and second18portions of the first22and third26parts each have a thickness, in the E direction, of ep11, ep12, ep31and ep32respectively, such that ep11+ep12=e1et ep31+ep32=e3.

For the following, it will be assumed that the thicknesses of the first and second portions are identical for the first and third parts, i.e ep11=ep31et ep12=ep32.

Of course, it is possible that the thicknesses e1and e3are different, and also that the thicknesses ep11, ep31, ep12et ep32are different from each other in pairs.

The first portion16and the second portion18of the first part22are woven to the second part24at a transition from the first part22to the second part24. The first portion16and the second portion18of the third part26are woven to the second part24at a transition from the third part26to the second part24. These transitions, indicated by two boxes A and B, correspond to an intertwining of the wires from the first portion16and the second portion18of the first part22, to form the second part24.

The fibrous structure20is characterised by the spacing between two weft planes along the warp direction C being greater in the second part24than in the first part22and the third part26. In addition, the number of weft yarns is lower in the second part24than in the first part22and in the third part26. The number of weft yarns per weft plane of the second part may be less than the number of weft yarns per weft plane of the first part. The number of weft yarns per weft plane of the second part may be less than the number of weft yarns per weft plane of the first part. This allows the warp-weft ratio of the first22and third26parts to be influenced relative to that of the second part24, to limit the thickness of the second part24, without trimming. The second part24of the fibrous structure20thus has a thickness such that e2≤e1et e2≤e3.

Table 1 below illustrates an example of a fibrous structure12according to the prior art, comprising a first part and a second part comprising a first portion16and a second portion18, wherein the second part14has a thickness e2>ep12and in particular wherein e1=e2.

TABLE 11stpart2ndAreas1st portionportion2nd partNumber of layers14721Number of weft planes14721Number of warp planes14721Warp spacing (mm)1.251.251.25Weft spacing (mm)1.251.251.25WWR (warp/weft ratio)50/5050/5050/50Moulding thickness (mm)426

This fibrous structure12made in the previous technique from 21 textile layers by a three-dimensional multi-layer weaving of the fibrous structure12has a warp-weft ratio of 50/50 invariant in the different parts of the fibrous structure12.

In this case, the number of layers, warp and weft planes in the second part14is equal to the sum of the number of layers, warp and weft planes in the first16and second18portions of the second part14(and the third part if applicable), respectively.

The fibrous structure20according to the invention makes it possible to limit the thickness e2of the second part24, intended to form the bathtub, so that its thickness e2is close to the thickness ep12of the second portion18of the first part22(and the third part26if applicable). In other words, e1, e2and e3can thus be different and this without trimming.

Table 2 illustrates a fibrous structure20according to a first embodiment of the invention, comprising a first part22and a second part24comprising a first16and a second18portion:

TABLE 21stpart2ndAreas1st portionportion2nd partNumber of layers14721Number of weft planes1479Number of warp planes14721Warp spacing (mm)1.251.251.25Weft spacing (mm)1.251.251.5WWR (warp/weft ratio)50/5050/5074/26Moulding thickness (mm)424.1

The thickness e2of the second part24of this fibrous structure20, once shaped, is reduced to 4.1 mm, with parameters for the first16and second18portions of the first part22unchanged from table 1 illustrating the prior art. For this purpose, the spacing between two weft planes along the warp direction is increased from 1.25 mm to 1.5 mm so that it is greater than the spacing between two consecutive weft planes in the first part22, in particular in the first16and second18portions of the first part22. Furthermore, the number of weft yarns of the second part24is lower than the sum of the numbers of weft yarns of the first part22, i.e. the sum of the weft yarns of the first16and second18portions of the first part22, by locally disengaging weft yarns at the transition A between the first22and second24parts, in order to achieve a warp-weft ratio close to the 75/25 limit.

Thus, the combination of increasing the spacing between two consecutive weft planes and not inserting weft yarns locally, so as to reduce the weft planes [, unbalances the warp-weft ratio, in the example shown at 74/26. This allows the thickness e2of the second part24of the fibrous structure20intended to form the bathtub of the ring sector to be reduced by 1.9 mm compared to the prior art fibrous structure12illustrated in table 2.

Thus, in the second part24of the fibrous structure20, the number of weft yarns is lower than the number of warp yarns, respectively9and21. For practical reasons, the imbalance in the warp-weft ratio is achieved by adjusting the spacing between two successive weft planes, not the spacing between two successive warp planes. As a result, the distance between two warp planes is identical between the first part22and the second part24.

In the particular case, not illustrated, of weaving parts at 90° to the orientation presented in this document, it is possible to play with the spacing between two successive warp planes and keep the spacing between two successive weft planes constant.

Although the example illustrated here describes the particular situation with a fibrous structure20having a first22and second24part, the fibrous structure20may comprise a third part26identical to the first part22and woven to the second part24along the warp direction opposite the first part22.

Table 3 illustrates a fibrous structure20according to a first embodiment of the invention, comprising a first part22and a second part24comprising a first16and a second18portion:

TABLE 31stpart2ndAreas1st portionportion2nd partNumber of layers10616Number of weft planes15716Number of warp planes10616Warp spacing (mm)1.251.251.25Weft spacing (mm)111.5WWR (warp/weft ratio)35/6541/5955/45Thickness obtained in4.12.14.2moulding (mm)

In this structure20, the warp-weft ratio is varied in the first16and second18portions of the first part22, in order to reduce the number of textile layers subsequently woven in the second part24.

Thus, in the second portion18of the first part22, the number of weft planes is greater than the number of warp planes. In the first portion16of the first part22, the number of weft planes is 1.5 times the number of warp planes. The spacing between two successive weft planes in the first16and second18portions is reduced to 1 mm.

The modification of these parameters, unbalancing the warp-weft ratio of the first16and second18portions to 41/59 and 35/65 respectively, combined with an increase in the spacing between two successive weft planes, thus makes it possible to obtain, for a thickness of 2.1 mm and 4.1 mm respectively for the first16and second18portions of the shaped fibrous structure20, a thickness e2of the second part24equal to 4.2 mm.

In this example of a fibrous structure20, the number of weft yarns is greater than the number of warp yarns in the first portion16and in the second portion18of the first part22of the fibrous structure20.

The invention also relates to a fibrous structure22, the thickness of which e2of the second part24is lower than the thickness of the first portion22, i.e. the sum of the thicknesses of the first16and second18portions. Table 4 illustrates a third embodiment of the invention:

TABLE 41stpart2ndAreas1st portionportion2nd partNumber of layers10616Number of weft planes1577Number of warp planes10616Warp spacing (mm)1.251.251.25Weft spacing (mm)111.5WWR (warp/weft ratio)35/6541/5973/27Thickness obtained in4.12.13.1moulding (mm)

Keeping the parameters of the first16and second18portion of the first part22of the fibrous structure20of the example in table 3, the thickness of the second part24is further reduced, changing the warp-weft ratio to 73/27 by reducing the number of weft planes of the second part24of the fibrous structure20from 16 to 7.

A thickness of 3.1 mm is then obtained for this second part24compared to 4.2 mm for the structure described with reference to table 3.

Thus, the invention also relates to the method of making the fibrous structures20as described with reference to tables 2 to 4.

The method for manufacturing the weaving of a fibrous structure20according to the invention thus comprises a step consisting of decreasing the spacing between two successive weft planes along the warp direction and decreasing the number of weft yarns during a transition in the warp direction from a first part of the fibrous structure to a second part24of the fibrous structure20having a thickness greater than that of the first part22.

The manufacturing process also includes a step of increasing the number of weft yarns and decreasing the spacing between two successive weft planes along the warp direction, during the transition in the warp direction from the second part24of the fibrous structure20to the first part22of the fibrous structure20.

The resulting fibrous structures20can then be used to manufacture a composite part, for example a stator sector12, as described above.

Thus, the invention also relates to a method for manufacturing a composite material, comprising the following steps:a) Obtaining a fibrous structure20by means of the method as presented above;b) Shaping the fibrous structure20;c) Obtaining a composite material by injecting or densifying a matrix inside the fibrous structure.

Step b) consists in obtaining from the fibrous structure20a fibrous preform intended to form the fibrous reinforcement of the composite part. This fibrous preform has a shape similar to that of the composite part. Thus, in the example of a stator sector12as described above, the woven fibrous structure20is “Pi” shaped, that is, the first portions16of the first22and third26parts of the fibrous structure20, are arranged so as to form an angle with the second portions18of the first22and third26parts and with the second part24(the latter three being substantially aligned). This is done with the help of shaping tools, allowing the preform to be held in a shape close to that of the part to be manufactured.

The composite part is then obtained by densifying the fibrous preform, i.e. by injecting a matrix inside the shaped fibrous structure. The matrix may be a resin or, in the case of a thermostructural composite, a refractory material such as carbon or ceramic.

The matrix injection can be carried out for example by Chemical Vapour Infiltration (CVI), by the process known by the acronym PIP for Polymer Infiltration and Pyrolysis or any other process conventionally known for the design of CMC parts.