Patent ID: 12227885

DESCRIPTION OF THE EMBODIMENTS

FIG.1shows an exemplary composite material part comprising a fibrous reinforcement densified by a matrix, the fibrous reinforcement of which can be obtained from a fibrous preform according to the invention. The part1comprises a first wall2, a second wall3and a stiffening element4extending between the first wall2and the second wall3. The stiffening element4takes the shape of a beam that extends in this case in a first direction or longitudinal direction L of the part1between the walls2and3. Each wall2,3extends in the longitudinal direction L and in a second direction or transverse direction T perpendicular to the longitudinal direction L.

Such a part1may form, for example, by adjusting its shape, a turbomachine blade or a landing gear reinforcement bar.

In the example described here, the part1is divided in the longitudinal direction and has an intermediate portion5which extends between two end portions6. The weaves of the intermediate portion5and of the end portions6are different and will be described below. In another embodiment of the invention, the intermediate portion can be defined in the transverse direction.

FIG.2shows a cross-sectional view of a fibrous preform100according to an embodiment of the invention used for forming the fibrous reinforcement of the part of theFIG.1.

The preform100is made as a single piece and obtained by three-dimensional weaving. In three-dimensional weaving, the weft threads connect together warp threads belonging to different layers of warp threads, with the exception of the weft threads which may be present at the surface in order to produce a two-dimensional weaving and the possible presence of local separations between adjacent layers of warp threads. Various 3D or multilayer weaves can be used, such as interlock, multiple satin or multiple plain weaves for example, as described in document WO 2006/136755.

The preform100comprises a first skin110intended here to form the first wall2of the part1, and a second skin120intended to form the second wall3of the part1. The first skin110and the second skin120are connected by a stiffening portion130intended to form the stiffening element4of the part1. In the example described here, the stiffening portion extends in the longitudinal direction. In another embodiment of the invention, the stiffening portion can extend in the transverse direction.

FIG.2shows layers c1-c16of warp (longitudinal) threads or strands and the paths of weft (transverse) threads or strands t1-t8. For the purposes of simplification, the terms warp thread and weft thread are used in the rest of the description. Thus,FIG.2shows a weft plane of the fibrous preform100.

More precisely,FIG.2shows a weave example in a transverse plane II ofFIG.1located in the intermediate portion5of the part1.

Here, the first skin110comprises four layers of warp threads c1-c4, which are connected by weft threads t1-t4. Similarly, the second skin120comprises four layers of warp threads c13-c16, which are connected by weft threads t5-t8. The longitudinal stiffening portion130comprises eight layers of warp threads c5-c12. The weft threads t1to t8can be unitary or be in the form of pairs of the threads.

The first skin110can be divided into three portions110a,110band110cin the transverse direction T. The first portion110aand the third portion110cconstitute free portions of the first skin110which are located on either side of the central portion130. Similarly, the second skin120can be divided into three portions120a,120band120cin the transverse direction T. The first portion120aand the third portion120cconstitute free portions of the second skin120which are located on either side of the central portion130.

The weft thread t1is woven at the surface of the first skin110with a two-dimensional weaving. The weft threads t2and t3are woven in the first skin110with a three-dimensional weaving. The weft thread to is woven at the surface of the first skin110(an internal surface) in the portions110aand110c.

Symmetrically, the weft thread t8is woven at the surface of the second skin120with a two-dimensional weaving. The weft threads t6and t7are woven in the second skin120with a three-dimensional weaving. The weft thread to is woven at the surface of the second skin120(an internal surface) in the portions120aand120c.

In the intermediate portion5of the part, the longitudinal stiffening portion130is formed by a plurality of layers of non-woven warp threads c5to c12which are held together by the weft threads t4and t5coming, respectively, from the first skin110and the second skin120. The weft threads t4and t5cross twice on either side of the longitudinal stiffening portion130so as to enclose the non-woven warp threads c5to c12.

In the longitudinal stiffening portion130in the intermediate portion5of the part, the weft threads t4and t5of all the weft layers together form a sort of tube in which the warp threads c5to c12are held straight, giving the longitudinal stiffening portion130its stiffness.

An alternative embodiment of the weave ofFIG.2is shown with fibrous preform100′ inFIG.3. In this alternative, the weft threads t4and t5cross only once, close to the centre of the longitudinal stiffening portion130, and enclose the warp threads c5to c12in two groups. In this case, the weft thread to encloses the warp threads of layers c5to c8, whereas the weft thread t5encloses the warp threads c9to c12. As before, the warp threads c5to c12are held straight by the weft threads in order to give the longitudinal stiffening portion130its stiffness.

In accordance with the invention, the warp threads c5to c12which are not woven in the intermediate portion5are then woven in the end portions6in order to keep them straight and taut. They can be woven in the end portions6in conventional manner with the weft threads, for example with an interlock weave, or having a particular weave such as that ofFIG.3.

FIG.3shows a particular weave example in the end portions of the preform100, in the transverse planes IV ofFIG.1.

Here, the first skin110comprises four layers of warp threads c1-c4, which are connected by weft threads t1-t8. Similarly, the second skin120comprises four layers of warp threads c13-c16, which are connected by weft threads t9-t16. The stiffening portion130comprises eight layers of warp threads c5-c12which correspond to the non-woven warp threads of the intermediate portion5. It should be noted that in the first skin110and in the second skin120there are twice as many weft threads as layers of warp threads because the weft threads are woven in pairs in certain parts of the skins110and120.

In the first110aand in the third portion110c, the weft threads are woven in pairs. Thus, for example, the weft threads t1and t2are woven together in the portion110aand in the portion110c, in other words they follow the same path. In particular, in the portions110aand110c, the weaving can be interlock weaving. It should be noted that on the surface of the first skin110opposite the stiffening portion130, and in portions110aand110c, the weaving of the weft threads t1and t2is two-dimensional so as to give the composite material part a smooth surface.

In the first portion120aand in the third portion120c, the weft threads are woven in pairs. Thus, for example, the weft threads t15and t16are woven together in the portion120aand in the portion120c, in other words they follow the same path. In particular, in the portions120aand120c, the weaving can be interlock weaving. It should be noted that on the surface of the second skin120opposite the stiffening portion130, and in portions120aand120c, the weaving of the weft threads t15and t16is two-dimensional so as to give the composite material part a smooth surface.

In the illustrated example, the weft threads of each pair of weft threads t1-t2, t3-t4, t5-t6and t7-t8are separated into two unitary threads at the stiffening portion130, and in general on either side thereof. Once separated, the unitary threads are woven separately with the warp threads in the portion110band in the stiffening portion130. The term “separately woven” shall mean that the threads no longer follow the same path. The separation of the pairs (or splitting of the pairs) thus makes it possible to double the number of weft threads available at the stiffening portion in order to weave the latter with additional warp thread layers. Hence, the weft threads t1to t8are woven with warp thread layers c1to c4in the portion110bof the first skin110, whereas the weft threads t5to t8are woven respectively with the warp threads layers c5, c6, c8and c9in the stiffening portion130. Some of the unitary weft threads of the first skin110are woven with the warp thread layers of the first skin110, and others of the unitary weft threads of the first skin110are woven with the warp thread layers of the stiffening portion130.

In the illustrated example, the weft threads of each pair of weft threads t9-t10, t11-t12, t13-t14and t15-t16are separated into two unitary threads at the stiffening portion130, and in general on either side thereof. Once separated, the unitary threads are woven separately with the warp threads in the portion120band in the stiffening portion130. Hence, the weft threads t13to t16are woven with warp thread layers c13to c16in the portion120bof the second skin120, whereas the weft threads t9to t12are woven respectively with the warp threads layers c7, c10to c12in the stiffening portion130. Some of the unitary weft threads of the second skin120are woven with the warp thread layers of the second skin120, and others of the unitary weft threads of the second skin120are woven with the warp thread layers of the stiffening portion130.

In the illustrated example, the unitary weft threads obtained by splitting pairs of weft threads are each woven with a different single warp thread layer in the portions110band120band in the stiffening portion130.

In the illustrated example, the unitary weft threads t7and t8coming from the first portion110cross the weft thread t9coming from the second portion120in the stiffening portion130. Here, this crossing enables the warp thread layers c7, c8and c9to be connected to the first skin110by the weft threads t7and t8, and to the second skin120by the weft thread t9. Of course, other weaves can be envisaged keeping the crossing, at least twice, of weft threads coming from the first110and from the second120skin in the stiffening portion130in order to ensure the cohesion of the preform100. Hence, in this example, only some of the unitary weft threads coming from the first skin110cross only some of the unitary weft threads coming from the second skin120; the other unitary weft threads being woven with different warp thread layers without crossing one another.

In the illustrated example, there are four warp threads per column in the first skin110and in the second skin120, i.e. eight threads per column at the free portions110a,120a,110c,120cof the skins. The number of warp threads of a given warp column is progressively increased here in order to attain sixteen warp threads per column in the preform at the stiffening portion130. In this example, the weft threads of the pairs of weft threads are separated at different warp columns, in other words at different locations in the transverse direction T, this enables a gradual introduction of the new warp threads and easier weaving.

It can be advantageous that the titre (i.e. the average number of filaments constituting the threads) of the warp threads of the layers c5to c12in the stiffening portion130is greater than the titre of the warp threads of the layers c1to c4and c13to c16in the skin110and120, in order to increase the stiffening function of the stiffening portion130in a composite material part.

According to an alternative embodiment of the invention, the intermediate portion of the part can extend in the transverse direction. In this case, the longitudinal stiffening portion is formed by a plurality of layers of non-woven weft threads which are held together by the warp threads coming, respectively, from the first skin and the second skin. The warp threads can cross twice on either side of the stiffening portion so as to enclose the non-woven weft threads or only cross once close to the centre of the stiffening portion and enclose the weft threads in two groups.

FIG.5shows a schematic view in the longitudinal cross-section of a turbofan engine10centred on the axis X. It includes, from upstream to downstream: a fan11, a low-pressure compressor12, a high-pressure compressor13, a combustion chamber14, a high pressure turbine15and a low pressure turbine16. At the inlet to the turbofan engine10, the air stream entering the fan11is divided into a primary stream or hot stream, and a secondary stream or cold stream. The flow channel of the secondary stream conventionally comprises a flow straightener provided with outlet guide blades200(or OGV for Outlet Guide Vanes) arranged downstream of the fan11, which have, in particular, the function of straightening the cold stream at the outlet of the fan11in order to derive the maximum thrust from it. The blades200also have a structural function and must, in particular, be capable of supporting forces exerted by the engine in operation or an impact due to the intake of an object by the fan11, or even the detachment of a blade of the fan11. Hence, these blades200must both have satisfactory mechanical properties while being sufficiently light to improve the propulsive efficiency of the engine.

An example of use of a preform100according to an embodiment of the invention for manufacturing an aeronautical turbomachine blade made of composite material, in particular an outlet guide blade200, will now be described with reference toFIGS.6to8.

FIG.6shows, in a highly schematic manner, an outlet guide blade200of an aeronautical turbomachine. The blade200extends in the longitudinal direction L, and in the transverse direction T between a leading edge201and a trailing edge202. In addition, it has a pressure face210and a suction face220. At each of its longitudinal ends, the blade200has a pair of central flanges230and two pairs of lateral flanges240which enable its fastening in the engine by means of fastening holes231,241. The blade200is hollow and comprises two longitudinal cavities203opening at each longitudinal end of the blade200. The longitudinal cavities are separated by a stiffening element204which extends between the pressure210and suction220faces in the longitudinal direction L.

The blade200is made of composite material with fibrous reinforcement densified by a matrix. The fibrous reinforcement of the blade200(visible by transparency in the blade200ofFIG.4) is obtained in this case from a fibrous preform100such as that illustrated inFIGS.2to4. In particular, the first110and second120skins of the fibrous preform100form the pressure210and suction220faces of the blade200, and the longitudinal stiffening portion130of the preform100forms the stiffening element204. The skins110and120of the fibrous preform100are joined at their free ends in order to form the edges201and202of the blade200.

The fibrous reinforcement of the blade200is, as for the preform100, longitudinally divided between an intermediate portion205in which the warp threads of the stiffening element204are not woven, and two end portions206in which the warp threads of the stiffening element204are woven with the weft threads. The weave in a transverse plane of the intermediate portion205can be like that ofFIG.2or3. The weave in a transverse plane of an end portion206in the body of the blade can be like that of theFIG.4.

The intermediate portion205extends over only a portion of the height of the body of the blade200, and the end portions206extend from the intermediate portion205and extend beyond the body of the blade200in order to form pairs of flanges230and240.

FIG.7shows a longitudinal sectional view of the fibrous reinforcement of the blade200at a pair of lateral flanges240. It can be seen that the fibrous reinforcement is continuous between the pressure and suction faces, and the ends of the flanges of the pair of flanges240. The pair of lateral flanges240is more specifically obtained by extending the first110and second120skins of the fibrous preform100and unfolding these beyond the end of the body of the blade200.

FIG.8shows a longitudinal sectional view of the fibrous reinforcement of the blade200at the pair of central flanges230. It can be seen that the fibrous reinforcement is continuous between the stiffening element204and the ends of the flanges of the central pair of flanges230. The pair of central flanges230is more specifically obtained from a separation232provided in the fibrous preform100during its weaving. In order to obtain such a separation, the weaving together of layers of longitudinal threads by transverse threads has been intentionally omitted, so that the preform can be unfolded. In order to fill the space created by the unfolding of the separated portions of the fibrous preform, an insert233can be placed in the separation232.

FIGS.9to11show an alternative blade300. The reference signs corresponding to blade200and blade300designate identical features (200becomes 300).

In this alternative, the fibrous reinforcement of blade300is different from the preceding one in that the intermediate portion305extends over the entire height of the body of the blade300, and in that the end portions306only form the flanges330and340. In particular, the warp threads of the longitudinal stiffening element204are again woven with the weft threads only at the central flange330by separating into two (FIG.11).

In general, the fibres of the fibrous preform100are made of a material chosen according to the envisaged application, for example made of glass, carbon or ceramic.

The densification of the fibrous preform by a matrix in order to obtain a composite material part is carried out by holding the preform in a shaping tool at least until the preform is rigid (or strengthened). In particular, inflatable bladders can be used in order to form the hollow portions203or303of the blade200or300.

The nature of the matrix is chosen according to the envisaged application, for example an organic matrix obtained, in particular, from a polymer matrix precursor resin such as an epoxy, bismaleimide or polyimide resin, or a carbon matrix or ceramic matrix.

In the case of an organic matrix, the fibrous preform is impregnated by a composition containing the matrix precursor resin, before shaping in a tool, or after shaping, the impregnation in the latter case being carried out, for example, by infusion or a resin transfer moulding (RTM) method, in a suitable mould. In the case of a carbon or ceramic matrix, the densification can be carried out through chemical vapour infiltration (CVI) or through impregnation by a liquid composition containing a carbon or ceramic precursor resin and heat treatment for pyrolysis or ceramisation of the precursor, these methods being known per se.