FR3139290A1 - Fabric and resin composite material part - Google Patents

Abstract

This concerns a method of manufacturing a molded part and the part itself, molded in three dimensions, comprising a composite material including a fibrous preform and a resin, the part having a cavity (230') filled with a material honeycomb (50). The cellular material comprises an expanded cellular polymer material. Figure 20

Description

Fabric and resin composite material part

The present invention relates to the field of parts for aircraft, such as in particular blades or propeller blades, which may be present on turboprops or on aeronautical turbomachines, including those with non-ducted propellers. In particular, aeronautical turbomachinery casings are also targeted.

Hereinafter the term “blades” covers both blades as such and aeronautical propeller blades.

Often, such parts for aircraft are made of metallic material. Although they then have good mechanical resistance, they nevertheless pose the problem of a relatively large mass.

In order to obtain lighter parts, it is known to make them in composite material, that is to say as structural parts with fibrous reinforcement and resin matrix.

EP3511240 thus presents a fibrous structure solution for aeronautical blade (or propeller blade) reinforcement made of composite material. This structure is woven in a single piece integrating an aerodynamic profile, a spar portion and a bulged portion. The fibrous structure comprises a debonding zone(s) making it possible to form a housing inside the fibrous structure in which a part of a reinforcing insert is inserted, which here is a spar, part of which therefore extends to inside the aerodynamic profile, at the level of the delinking zone(s), and another part of which opens outside the aerodynamic profile at the level of the foot edge of the profile. The bulged portion extends in the extension of the spar portion outside the aerodynamic profile. The aerodynamic profile comprises, at the level of the unbinding zone(s), skins unbound in relation to each other and enclosing the spar portion. The skins delimit inside the aerodynamic profile respectively two housings present on one side and the other of the spar portion and opening at the level of the foot edge of the aerodynamic profile. The final blade is a part with a cavity into which inserts made of traditional, rigid foam, in solid form, have been introduced.

In the field of aeronautical turbomachines with propellers or ducted blades, numerous turbomachines are also known through which multiple gas flows pass, in particular with primary flow and secondary flow, or double flow.

Technical problem

For several years, at least on dual-flow aeronautical turbomachines, increasing the dilution ratio (ratio between the flow rate of the primary flow and the secondary flow) has been a solution favored by engine manufacturers in order to improve engine performance and to reduce their specific fuel consumption.

This results in an increase in the diameter of the iso-thrust blades of turbomachines, in particular concerning the first blade, that of air inlet into the turbomachine: fan blade - fan in English - or propeller, and its associated rectifier (OGV or Outlet Guide Vane, in English).

This increase is even more significant for non-streamlined architectures.

However, increasing these dimensions has the particular disadvantage of leading to an increase in the mass of the blades and/or casings, which is detrimental to the performance of the turbomachine.

Until now, a solution to limit this mass impact has been to manufacture the blades and/or casings in solid composite materials (3D woven composite material by RTM process for example - Resin Transfer Molding or resin injection molding -, instead of metallic materials (e.g. titanium).

However, taking into account the predictable dimensions of the future blades, such as for example on an unducted architecture of an aeronautical turbomachine of the type ('Open FAN', 'Unducted Single FAN' or 'Propfan') non-ducted fan in French, it seems necessary to be able to increase this reduction in mass.

One of the possible solutions to overcome this problem is to design and/or produce hollow aeronautical parts (called hollowed parts).

But, during the operation of an aeronautical turbomachine and if hollow parts are used, in particular blades, these are subjected to significant pressure from the air flow moved by the turbomachine to ensure thrust. This pressure can deform the part where it is hollowed out, by crushing the cavity of the part and thus, for example on a fan blade, risk significantly reducing its efficiency, due to the deformation of the aerodynamic profiles of the part.

We can use a honeycomb material such as high-density foam to fill the cavity, which helps meet the need to lighten the part and limit or even completely eliminate the crushing of the skins.

However, during the operation of the turbomachine, the parts (in particular the blades) work mechanically, particularly or mainly in bending, under the influence of the air flow. To limit the impact of the force, it is known - as in EP3511240 - to add one or more inserts forming a stiffener. In the case where the stiffener is, or includes, a spar, and the composite part is a blade, the spar can also be used as a fixing point for the blade on the disk of the turbomachine and thus makes it possible to create a link between the aerodynamic skins of the blade, the honeycomb material in the cavity and the rest of the turbomachine.

The production of hollow parts composed of numerous sub-components is also always difficult because their handling before they are consolidated with a resin is delicate. The assembly of the different sub-components must be very precise and repeatable so that the parts are compliant without a high rate of manufacturing scrap.

The supply of a part with a traditional, rigid foam, in solid form and with precise geometric dimensions also represents a significant logistical and financial effort for a filling insert whose mechanical properties are weak, or even negligible regarding the general behavior of the finished piece.

Any stiffeners, which can therefore be spars, are generally designed as separate parts, subject to the same disadvantages as rigid foam (sensitivity to assembly, logistical complexity, etc.).

In view of the prior art, this application proposes both a (molded) composite part and a process for manufacturing a composite part.

More specifically, the present invention relates in particular to a part (which can be in three dimensions) comprising a composite material including a fabric and a resin, the part having a cavity filled with a honeycomb material (also called alveolar) hereinafter, this material cellular comprising a cellular polymer material, which is an expanded foam (from a) polymer.

The term “fabric” means surface obtained by the assembly of threads or fibers which can be arranged in two crossed series. The term therefore includes a fibrous preform or woven preform. It can be any fabric, a woven or non-woven, and therefore a fabric itself.

The “fabric” or fibrous structure, and therefore the part that results from it, can be formed from any type of weaving: two dimensions (2D), three dimensions (3D), in particular.

By "two-dimensional weaving" or "2D weaving", we mean here a classic weaving mode by which each warp thread passes from one side to the other of threads of a single weft layer.

By "three-dimensional weaving" or "3D weaving", we mean here a mode of weaving by which at least some of the warp threads bind weft threads on several weft layers.

The term “room” covers any type of room. This may be an unfinished part, such as a semi-finished part. It can be a preform; the preform of a finished part.

The term "foam", in the expression expansive or expanded foam, has the meaning: Medium resulting from the expansion of an expandable paste capable of expanding to form a foam (solid continuous phase in which is dispersed in the form of cells a gas phase). The emulsion and the creation of the gas phase generating the foam come from the expansion reaction of a paste previously existing in the liquid phase. Thus, unlike a traditional foam supplied in solid form (called solid foam hereinafter) and therefore having its own shape before its use in the production process, the present "foam from an expanded polymer" will be supplied in liquid form (polymer clay) but becomes solid during the expansion reaction and only has its own shape once solidified and expanded in the cavity of the part.

“Solid foam” means: a rigid foam machined directly to the final shape, such as the products used in the State of the Art, the expansive foam used here allowing on the contrary to “make up” for any deviations from the geometric tolerances.

Among the advantages, we can note a simplification of the manufacturing process. Other advantages are noted below.

In the part, the expanded cellular polymer material may in particular be polyurethane. Advantage: widely used material, well controlled, inexpensive, very effective for volume/space filling.

In terms now of a process for manufacturing a part (which can be as above) comprising a weaving, the process of the invention responds at least in part to the problem stated previously and thus presents as steps (which can possibly be interleaved , that is to say carried out at least partially together):
- weaving the part, integrating a cavity,
- placing the part in a first part of an injection mold,
- placing, in the cavity, a soluble core or a removable, demouldable core, or a flexible membrane, the soluble core or the membrane (including its internal space) occupying the volume of said cavity,
- closing the injection mold, via at least a second part of the injection mold,
- an injection of resin into the weaving of the part, in order to form a woven part made of composite material,
- demoulding of the part, out of the injection mold,
- depending on the case, a dissolution of the soluble core or a withdrawal, outside the cavity, of the removable core or of the flexible membrane,
- placing in the cavity an expansive paste suitable for forming a honeycomb material,
- waiting for the dough to react to form (preferably completely) said cellular material, in the cavity,
- elimination of a possible surplus of cellular material having overflowed from the cavity, if necessary.

The wait will be a time (tmin) greater than a second. The wait will depend on the precise reference of the expansive product used, the manufacturer's recommendations, and the production experience allowing adaptation to the geometry and volume to be filled. Generally speaking, the delay varies from a few seconds to less than 5 minutes.

The elimination of a possible surplus of honeycomb material may include or consist of final machining of the part, making it possible to obtain a finished part (in the exact desired shape) or semi-finished (for example, there may remain the setting place of certain reinforcements, or a surface treatment). It may also involve deburring, checks of the conformity of the part (check of the composite material, dimensional checks). The whole thing can thus be defined as a completion of the piece. If a possible surplus is eliminated, the cavity is then already rigid. The foam only needs to fill the cavity. Thus, if excess expanded foam is removed, it will a priori be advantageous to wait for the end of the reaction so as not to have to remove this excess in several steps.

Thus, after waiting for the reaction of the paste to have allowed it to become (preferably completely) said cellular material, we can usefully:
- eliminate the excess expanded material overflowing from the cavity if necessary, and
- check the conformity of the part (check of the composite material, dimensional checks, etc.), then
- lead the completion of the part.

In the above process, the cellular material will usefully comprise, as noted above, an expanded cellular polymer material which may therefore be an expanding or expanded foam.

The use of an expansive polymer material, whose expansion reaction takes place during the densification of the preform woven by the resin can lead to high rates of porosity (gas bubbles in the material due to the gas release produced by the foam expansion reaction) negatively impacting the mechanical properties of the part.

The use of such an expansive material in place of a solid foam with a finished dimension can lead to irregularities in the shape of the internal cavity of the part. Although these shape irregularities are less penalizing than deviations on the external surface (in the aerodynamic flow), they must nevertheless remain under control.

All of this therefore poses problems that this solution seeks to take into account.

The weaving of the part (blank or preform) could be in three dimensions, which will favor obtaining a high-performance industrial part, such as a blade. To ensure industrially as best as possible (if it is retained) the aforementioned function of “flexible membrane”, it is proposed to use:
- an inflatable bladder, which will be inflated in the cavity, or
- a preformed part (reusable or not) in silicone or polyurethane elastomer.

Thus, we will associate the advantage of an adapted deformation of the flexible membrane, necessary for its installation in the cavity, or even for its removal, with that of a mechanical resistance adapted to the injection pressure and to the preservation of the required volume of the cavity.

To promote the reinforcement of the woven composite part, by carrying out this at a favorable moment of the process in terms of ease of implementation, it is also proposed that the process defined here also includes, between the weaving of the part integrating the cavity and the stage where the expanding paste is contained in the cavity:
- the weaving of an insert (which can therefore be in three dimensions), which can be adapted to define a stiffener (also defined as a possible spar below), for the part presenting the cavity,
- the insertion of the woven insert into the cavity of the part.

This solution, however, requires manufacturing of the woven insert independent of that of said part with an integrated cavity.

To avoid this and create an insert in this cavity by a local modification of the weaving weave, it is also proposed that the weaving of the part includes a co-weaving with a woven insert (which can therefore be in three dimensions) that said piece will thus integrate. In other words, the weaving of the part (integrating the cavity) will include a co-weaving with a woven insert (which can therefore be in three dimensions) which said part will then integrate in one piece with it.

In general, and depending on the type of core (soluble or removable) chosen for the formation of the cavity, the geometry of the cavity, and the need for stiffeners or spars, it will be possible to carry out the densification of these at the same time as that of the preform of the part to be produced, instead of producing these sub-components during separate prior injections.

Typically, all woven textiles may include an interweaving of threads divided into two categories: "warp threads", which are threads parallel to the edges of the fabric, and "weft threads" which are threads perpendicular to the warp threads. and interwoven with them, according to a pattern called "weave", the simplest weave consisting of an alternation in which each weft thread passes successively above and below a warp thread, with an offset of one weft to another (so-called “plain weave” solution).

Furthermore, providing that the weaving of the part integrating the cavity includes unbinding will facilitate the formation of the cavity, or housing, inside the fibrous structure intended to form said woven composite part.

For placing the expanding paste in the cavity, two possibilities are available:
- either the introduction of the paste directly into the cavity, in contact with the wall which limits the cavity,
- either the installation of a (other) flexible membrane or hollow flexible bladder in the cavity, the expansive paste being contained (after having been introduced) in this (other) flexible membrane or flexible bladder, said (other) membrane flexible or flexible bladder forming an interface between the composite part and the paste, then the expanded foam, and being permanently held in place in the mold. This could make it easier to handle the expanding paste and limit the risk of leaks.

In addition to simplicity of implementation and possible manufacturing in fairly large series, the advantages of the different aspects of the process which has just been presented are those of the part, itself already presented.

For here also the advantages already mentioned, the following is proposed, as embodiments which can be implemented optionally, independently or in combination, in whole or in part, as the case may be:
- the cavity has a bottom and an opening, and the placement of the expanding paste includes its introduction to the bottom of the cavity so that the expanding paste expands from the bottom towards the opening,
- expanding paste is placed in the cavity, after having selected as expanding paste an expandable polymer whose gas release during a polyaddition reaction will form said cellular material, which will then be dense in the cavity (well-controlled process and reproducible in series),
- polyurethane is selected as the expandable polymer, the release of CO2 during the polyaddition reaction forming said dense honeycomb material (well-controlled process reproducible in series and initial paste without difficulty in supply).

“Dense” means uniformly and completely filling the cavity with a sufficiently high density to guarantee good mechanical performance of the foam in relation to its functions detailed previously. This density nevertheless remains significantly lower than the other materials constituting the blade, and preferably greater than 50 kg/m ^3, or even between 100 kg/m ³ and 300 kg/m ³

As will be understood, the process presented, with all or part of its characteristics, will make it possible to manufacture as a part in particular a blade preform for an aeronautical turbomachine.

Other characteristics, details and advantages of the invention will appear on reading the detailed description below of non-limiting examples of embodiment, and on analysis of the appended drawings, in which:
is a schematic view of a blade in accordance with one embodiment of the invention,
is a cross section of the blade of the according to section plane A of the ;
is a cross section of the blade of the according to section plane B of the ;
is a cross section of the blade of the according to section plane C of the ;
is a longitudinal section of the blade of the according to cutting plane D of the ;
is a longitudinal section of the blade of the according to section plane E of the ;
is a longitudinal section of the blade of the according to the cutting plane F of the ;
is a schematic perspective view of the fibrous structure blank after cutting the external floated wires;
is a schematic perspective view of the fibrous structure blank after cutting the floated wires present on the spar portion of the blank;
is a schematic perspective view of the fibrous structure obtained, as well as its shaping with conforming parts
schematizes a variant of the dawn of the , in a state where the part is still only fibrous, in the preform state;
is a cross section of the blade of the , according to the section plane H;
,
,
,
And
schematize successive stages of manufacturing, in an injection mold, a fibrous hollow part, these stages consisting of a densification which can be that of the preform of the ,
schematizes, according to the same section, the state of the part of the after said densification and addition, into the preserved cavity of said hollow part, of an expansive foam;
schematizes, again in the same section, a preparatory state for the supply of said expansive foam into the cavity, according to a variant, and
schematizes, always using the same cut, the state of the part of the after adding the expanding foam into the bladder placed in the cavity at the stage of .

The drawings and the description below contain elements which may not only serve to better understand the present invention, but also contribute to its definition, where appropriate.

The invention applies generally to the production of different parts, in particular blades or propeller blades used in aircraft engines. A blade according to the invention may in particular constitute a blade for a ducted moving wheel such as a fan blade or a blade for a non-ducted moving wheel as in so-called “open rotor” aeronautical engines.

There represents a blade 10 intended to be fixed on an aeronautical turbomachine.

Like any aeronautical blade (or propeller blade) concerned here, the blade 10 has a free edge, or end 11d and, opposite, a foot 12 by which the blade is fixed to a rotor disk 101 of the turbomachine.

More precisely, the blade 10 comprises an aerodynamic profile 11 intended to form the aerodynamic part of the blade and a foot 12 formed by a part of greater thickness, for example with a bulb-shaped section. A stilt 13 can be interposed between the foot 12 and the aerodynamic profile 11. The aerodynamic profile structure 11 has in cross section a curved profile of variable thickness between its leading edge 11a and its trailing edge 11b in a direction DT transverse to the longitudinal direction DL, or elongation, of the blade. Along the longitudinal direction DL, the aerodynamic profile 11 extends between a root edge 11c (or edge of attachment to the rotor disc 101) and a free edge (or apex edge) 11d. The foot 12 extends in the transverse direction DT over a length less than the length of the foot edge 11c of the aerodynamic profile 11.

As shown in Figures 1 to 7, the blade 10 comprises a fibrous reinforcement, marked 20 in certain figures and densified by a resin matrix. The fibrous reinforcement 20 comprises in a single piece:
- an aerodynamic profile structure 21 intended to form the aerodynamic profile of the blade 10,
- a spar portion 22 extending inside the aerodynamic profile structure 21,
- a swollen portion 24 forming the blade root 12 extending in the extension of the spar portion 22 outside the aerodynamic profile structure 21.

The spar portion 22 can present, in one piece:
- a part 22a extending inside the aerodynamic profile structure 21, and
- a part 22b located outside the aerodynamic profile structure 21 and forming both the swollen portion 24 and, if it exists, the stilt 13 of the blade 10.

The fibrous reinforcement 20 mainly comprises first and second parts 25 and 26 separated from each other by an intermediate zone 27. The first part 25 delimits a debonding zone(s) Zd inside the aerodynamic profile structure 21 , the delinking zone extending between the intermediate zone 27 and the foot edge 21c of the aerodynamic profile structure 21 corresponding to the foot edge 11c of the aerodynamic profile 11 in the longitudinal direction DL and between the front and rear edges 21a and 21b of the aerodynamic profile structure 21 corresponding respectively to the leading edge 11a and the trailing edge 11b of the aerodynamic profile 11 in the transverse direction DT. The first part 25 comprises first and second skins 28 and 29 untied relative to each other and untied from the spar portion 22, the first and second skins 28 and 29 extending between the front and rear edges 21a and 21b of the aerodynamic profile structure 21 in the transverse direction and between the intermediate zone 27 and the foot edge 21c of the aerodynamic profile structure 21 in the longitudinal direction, the skins 28 and 29 enclosing the spar portion 22. The first and second skins 28 and 29 delimit inside the aerodynamic profile structure 21 the first and second housings 30 and 31 present respectively on one side and the other of the spar portion 22 in the transverse direction, the first and second housings 30 and 31 opening out at the foot edge 21c of the aerodynamic profile structure 21. A first conforming element 40 is present in the first housing 30. Likewise, a second conforming element 41 is present in the second housing 31.

Often, conformational elements, such as 40,41, are referred to in the art as "cores"; see below.

The conformation elements, such as 40,41, or the cores, can typically each be formed from a solid block, typically a rigid foam element produced by molding or by machining in a block of material. Each is soluble in the cavity or removable (removable from the cavity).

As an alternative to the spar portion 22, an insert 300 (which can be defined as a reinforcing insert or stiffener) could extend inside an aerodynamic profile structure where it would then be temporarily surrounded by a conformation element or a membrane under pressure occupying the remaining volume of the cavity 230', around the insert 300, according to an embodiment which would for example conform to the schematic illustrations in Figures 11 to 17.

Part 22a and the swollen portion 24, or part 22b, could appear as such an insert, corresponding to insert 300.

In this solution:
- blade 10 becomes blade or blade 10',
- the fibrous reinforcement 20 in 3D woven material remains; he just changes reference point: 20',
- the spar portion 22 is therefore replaced by at least one insert or stiffener, such as that 300, 3D woven and ultimately made from the same composite material (resin + fibers) as the fibrous structure 200' if it is not not (which is possible) metallic, or even co-woven with it,
- the first and second housings 30, 31 can be maintained or replaced by a single housing defined below by the cavity 230' which extends inside the aerodynamic profile 11'.

Applicable in particular in these two cases and as illustrated in the example of Figures 8 to 10, the method of manufacturing an aeronautical part according to the invention comprises the production of a fibrous structure, not yet impregnated with resin, such as blank of fibrous structure 100 intended to form the fibrous preform of the part to be produced.

The fibrous structure blank 100 is obtained by three-dimensional (3D) weaving carried out in a known manner using a loom which can be of the jacquard type on which a bundle of warp threads or strands has been arranged in a plurality of layers of several hundred threads each, the warp threads being linked by weft threads. The fibrous structure blank 100 is woven in a single piece. The blank comprises, in example, an aerodynamic profile blank 111, a spar portion blank 122 and a bulged portion blank 112, the spar portion blank 122 extending inside the blank of fibrous structure 100 set back from the front and rear edges 100a and 100b in the transverse direction DT and, in the longitudinal direction DL, between an intermediate zone 103 located between the respectively foot and free (or vertex) parts, 100c and 100d of the fibrous structure blank, the swollen portion blank 112 extending in the extension of the spar portion blank 122.

In the example illustrated, the 3D weave is an “interlock” weave weave. By "interlock" weaving, we mean here a weaving weave in which each layer of weft threads links several layers of warp threads with all the threads of the same weft column having the same movement in the plane of the weave .

Other known types of weaving, in particular three-dimensional, may be used, such as those described in document WO 2006/136755. This document describes in particular the production by weaving in a single piece of fibrous reinforcing structures for parts such as blades having a first type of core armor and a second type of skin armor which makes it possible to confer both the mechanical and aerodynamic properties expected for this type of part.

The fibrous blank according to the invention can be woven in particular from carbon or ceramic fiber threads such as silicon carbide.

As the fibrous blank is weaved, the thickness and width of which can vary, as in the example, a certain number of warp threads can therefore not be woven, which makes it possible to define the contour and the desired thickness, continuously variable, of the blank 100.

Furthermore, during weaving of the fibrous blank, an unbinding 110 can be produced inside the fibrous blank between successive layers of warp threads and on an unbinding zone(s) Zd.

In the direction DL, a connection zone Zl in the fibrous blank extends the debonding zone(s) Zd, so that, if H11 is the length of the aerodynamic profile 11, H11 = Zl + Zd.

More precisely, in the example (see ), the separation 110 extends between an intermediate zone 103 and the foot edge 100c of the fibrous structure blank 100 in the longitudinal direction DL and between the front and rear edges 100a and 100b of the fibrous structure blank 100 following the transverse direction DT. The unbinding 110 separates first and second portions present on either side of the spar portion blank 122 so as to form first and second skin blanks 104 and 105 unbound relative to each other. The first and second skin blanks 104 and 105 extend between the front and rear edges 100a and 100b of the fibrous structure blank 100 in the transverse direction DT and between the intermediate zone 103 and the root edge 100c of the blank of fibrous structure in the longitudinal direction. The skin blanks 104 and 105 enclose the spar portion blank 122 and the swollen portion blank 112. The first and second skin blanks delimit, inside the fibrous structure blank 100, the first and second housings 130 and 131 present respectively on one side and the other of the spar portion blank 122 in the transverse direction DT.

Once the fibrous structure blank 100 is woven, the floated threads present outside the woven mass are cut, for example by water jet, so as to define the exterior contour of a fibrous structure as illustrated on the , for exemple. We also cut the floated threads present on the skin blanks 104 and 105 at the level of the lower part of the fibrous structure blank so as to release the bulged portion blank 112 as well as part of the portion blank of spar 122 intended to subsequently form a blade stilt. We also proceed to cut the floated wires present around the spar portion blank 122 and the swollen portion blank 112 by lifting the skin blanks 104 and 105 as shown in the figure. , for exemple. For this purpose, first and second slots 107 and 108 are formed between the skin blanks 104 and 105.

We then obtain, as illustrated in the by way of example, a fibrous structure 200 woven in a single piece and having, in example, an aerodynamic profile 211, a spar portion 222 and a bulged portion 212, the aerodynamic profile 211 extending in the longitudinal direction DL between a lower end 211c and an upper end 211d and in the transverse direction DT between a leading edge 211a and a trailing edge 211b. The fibrous structure 200 comprises a zone of debonding(s) Zd extending between the leading and trailing edges 211a and 211b of the aerodynamic profile 211 in the transverse direction DT and between an intermediate part 203 and the root edge 211c of the aerodynamic profile 211 following the longitudinal direction DL. The spar portion 222 extends inside the aerodynamic profile 211 at the level of the unlinking zone(s) Zd set back from the leading and trailing edges 211a and 211b in the transverse direction DT and, in the direction longitudinal DL, between an intermediate part 203 located between the lower and upper edges 211c and 211d of the aerodynamic profile 211 and the root edge 211c of said aerodynamic profile at which the spar portion 222 opens. The bulged portion 212 extends in the extension of the spar portion 222 outside the aerodynamic profile 211, the bulged portion 212 extending in the transverse direction DT over a length L212 less than the length L211 of the foot edge 211c of the aerodynamic profile. The swollen portion 212 is intended to subsequently form the blade root 12. The aerodynamic profile 211 comprises, at the level of the unbinding zone(s) Zd, first and second skins 228 and 229 unbound relative to each other. , the first and second skins extending between the leading and trailing edges 211a and 211b of the aerodynamic profile in the transverse direction DT and between the intermediate part 203 and the root edge 211c of the aerodynamic profile in the longitudinal direction DL, the skins 228 and 229 enclosing the spar portion 222.

The first and second skins 228 and 229 delimit, inside the aerodynamic profile, at least one cavity 230 which, in the example, is defined by first and second housings 231a and 231b present respectively on one side and the the other of the spar portion 222 in the transverse direction. The cavity 230, and therefore the first and second housings 231a and 231b in the example, open(s) to the outside. The outlet is, in the example, located at the lower end of the aerodynamic profile 211.

In the alternative combining an insert 300 which can therefore be metallic, as in the example of part in Figures 11, 12, it is therefore the insert 300 which replaces the bulging portion 212 and the part 222.

Thus, in each situation of weaving of a part produced, at the end of the manufacturing process, in composite material (resin + fibers), as in particular in the blank of woven fibrous structure 100 and in the woven fibrous structure 200, we will have, in end of the process, integrated in a single piece a cavity 230 or 230' into the woven structure.

Furthermore, with these examples of a possible integrated spar extended by a foot 12, or of a possible reinforcing insert 300 forming a possible stiffener or spar, we were able to:
- reinforce the woven part, at the location of its cavity 230 or 230',
- add or integrate a blade root 12, if necessary,
- and this with an insert 300 which could be in one piece with the woven fibrous structure, or attached to its cavity, such as 230' in the example.

In other words, the insert 300:
- either will have been manufactured separately (in a suitable material, such as metal, or woven, and in two or three dimensions) so as to define a stiffener, with or without foot 12, for the part presenting the cavity, such as 230' in the example, then inserted into this cavity, after having woven the desired preform, 200' in the example,
- either will have been integrated in a single piece with said preform, the weaving of the part (200' in the example) integrating the cavity therefore comprising a co-weaving of such a stiffener; the insert marked 300' simulates and schematizes this hypothesis of a dry woven preform allowing the formation of a stiffener after injection of the resin into the mold (see below).

In the second case, the co-weaving of the reinforcing insert, such as 300', with the woven fibrous structure can be carried out like that of the fibrous structure blank 100, likewise in the second case for the weaving independent of the reinforcing insert 300, but without the cavity.

The conformation of the fibrous structure 200 (making it possible to obtain the aforementioned blade preform, in the example) will then continue:
- by the introduction of at least one conformation element into the or each aforementioned cavity,
- and by placing the part, namely the woven fibrous structure 200 or 200' in the example, in a first part 301 of an injection mold 310 of the part concerned (see Figures 13, 14 according to an example).

The hollow impression part of the part concerned in the first part 301 of the injection mold 310 is marked 330 .

By way of example, Figures 13 to 17 aim to help understand the part of the process relating to the molding of the part by injection of the resin 60 into the heart of the fibers of the fibrous structure, such as that 200' in the 'example.

Thus, it is first in the impression part 330 that the fibrous structure is placed, such as 200' in the example; see example .

It is then possible to insert into the cavity, such as that 230' in the example, the core(s) and/or flexible membrane and/or insert(s) and/or stiffener(s) and/or spar ( s) possible 300 which are suitable.

On the , we have shown the presence of a composite or metallic stiffener 300 manufactured previously, or, alternatively, of a dry woven preform allowing the formation of a stiffener after injection of the resin 60, this dry woven preform may therefore have been co-woven with the rest of the woven fibrous structure (marker 300').

Added to this is the insertion into the or each aforementioned cavity, such as 230' in the example, of at least one soluble core or removable core (see references 40,41 ) or a flexible membrane 430' put under pressure, in the cavity, via a pressurized gas inlet 432, as is the case in the example of the .

In the example of the , we even included:
- at the bottom of the figure, the case where the cavity 230' contains an inflatable removable membrane 430' and,
- at the top, an alternative in which, in the cavity 230', we would insert (arrow 434), around an insert or stiffener 300 or 300', a solid core 430'', of the same nature as the conformation elements 40 .41.

The core 430'' integrates a central volume 436 in the shape of (the part of) the insert or the stiffener 300 or 300' located in the cavity 230' which can thus be engaged therein.

Thus, in one way or another, the volume of the or each aforementioned cavity, such as 230' in the example, will then be occupied by a core or equivalent and will resist the injection pressure of the resin 60 which will now be able to take place:
- within the fibers of the fibrous structure, such as 200' in the example, including the insert or the stiffener if it is a woven part, such as the dry woven preform 300'),
- but not in said cavity.

For this, another part 303 of the mold 310, with a suitable footprint, will close the mold, as shown schematically. , and resin 60 will be injected under pressure (this can be at room temperature) into the two impression parts; arrow 438, within the preform in order to densify it and form the composite material.

When we reopen the mold (as in the example of the ), the resin 60 has infiltrated into the two cavity parts of the mold, but not into the cavity, such as that 230' in the example, thus densifying the fibrous structure and forming the aforementioned composite material.

We can then unmold the blank of the part obtained and deburr it.

If the cavity 230, 230' contains at least one core 430'', it is then dissolved if it is soluble, or removed if it is a removable core or a removable membrane 430'.

The cavity 230, 230' becoming accessible, it is now that we will be able to add a quantity of expanding paste 50 adapted to occupy the entire available volume.

We then wait for the paste 50 to react to form a foam, the expanded paste being adapted to fill the cavity and to ensure that the final part obtained is maintained in shape, in operation.

We can then eliminate any excess foam overflowing from the cavity, if necessary, then carry out conformity checks on the part (check of the composite material, dimensional checks) and complete the composite part obtained.

The advantage of only adding the expanding paste 50 after molding, and therefore after densification of the (each) woven part, is precise control of the geometry of the cavity, in addition to control of the exterior geometry of the part .

As already mentioned, we limit the risks in this way:
- a high rate of porosity (gas bubbles in the material due to the gas release produced by the foam expansion reaction) negatively impacting the mechanical properties of the part, and
- irregularities in the shape of the internal cavity of the part.

Furthermore, such a cavity solution filled with expanded foam has the advantage of reducing the cost of the part compared to a solid foam, because the soluble or removable core has a generally low cost per part.

Another advantage can be the guarantee that the gas release producing the expansion of the foam 50 will not pollute the densification resin 60 of the composite, which could have been the case with a chronology as follows: supply of expanding paste 50 - waiting - closure of the mold - densification by injection of resin 60, said pollution being able to result in porosity (gas bubbles) in the matrix of the composite material, with the consequence of a reduction in the mechanical properties of the material.

The use of an expanding paste 50 instead of a solid foam, if (one) said cavity of the part must contain an insert 300, also makes it easier to exempt oneself from an invitation typically made - see above - to weave the aforementioned first and second 3D woven preforms separately, so as not to create constraints during assembly.

By removing this constraint, we will then be able to more easily consider the aforementioned possibility of co-weaving:
- the (each) second preform (and therefore any stiffener(s) and/or spar(s),
- with the first preform, such as the fibrous structure 100,
- this always before molding in the mold 310 then placing the expanding/foaming paste 50.

The 3D weaving of the first preform, as well as the unbindings (above-mentioned Zd zone) and a local adaptation of the weaving weave will then make it possible to form said cavity, such as 230 or 230'. It will thus be possible to create one(s) spar(s) or stiffener(s) in this cavity by a local modification of the weaving weave.

The expansive nature of the cellular material 50 will make it possible to naturally adapt to all the geometries of the cavity in the densified part, by matching the shapes at the ends of the cavity such as around the stiffener(s) and/or spar(s), if they exist.

Concerning the installation of the expanding paste 50, we can in particular provide:
- that the(each) cavity, such as 230 or 230', has a bottom 49 and an opening 51, and
- that this installation includes the introduction of the expanding paste at the bottom 49 of the cavity, so that the expanding paste 50 expands from the bottom 49 towards the opening 51, thus limiting the risks of excessive overflowing out of the cavity .

If the expanding paste 50 can be used directly in contact with the fiber + resin composite, the use of a flexible membrane, such as a flexible (hollow) bladder, such as 431 in the example of Figures 19,20, filled with the expanding paste 50 could be considered, optionally.

Such a flexible membrane, hereinafter called "flexible bladder" so as not to confuse it with the possible membrane 430', will a priori be thinner than the membrane 430', since the injection of the resin 60 has already taken place and that therefore the integrity of the cavity is already assured.

If it exists, the flexible bladder, such as 431, is therefore intended to contain the expanding paste 50 then the expanded cellular polymer which results from it, thus facilitating implementation. But not using a bladder would have the advantage of more direct contact between the cellular material, the fibers and the resin of the composite material, if they are compatible. If these are only slightly compatible, it will be preferable to isolate the different components and therefore maintain the use of a flexible bladder.

The choice between these two options may also be dictated by the mechanical strength of the interface created between the expanded cellular material 50 and said fiber/resin composite. We may wish to ensure that the interface is indeed resistant in terms of effort and lifespan. A solution without a flexible bladder seems more favorable for this aspect, because it allows direct physicochemical contact between the expanded cellular material 50 and the resin of the composite material.

With a flexible bladder, the opening 51 must allow:
- inserting the flexible bladder 431 into said cavity;
- then adding the expanding paste 50 to the bottom 49 of this cavity, in the bladder, so that the expanding paste 50 progresses by expanding from the bottom of the cavity towards its opening 51, without creating a vacuum pocket, during its evolution into foam, by pressing the bladder against the wall 237 of the cavity (see , for example).

As an alternative to a flexible bladder 431 open on the side of the opening 51, as in the example of the , a closed bladder, provided only with an inlet 433 could be provided, the inlet 433 being adapted to the supply of the expanding paste 50 into the bladder (see , for example).

In any case, once in place in the cavity, the flexible bladder will remain there permanently.

As an expansive material, the well-known expandable polymer polyurethane can be used, the release of CO2 of which during the polyaddition reaction forms a cellular material, such as a dense foam, commonly used in industry. .

In the case of the present invention, the parameters to be considered when selecting material 50, expansive polymer, will be favorably:
- the mechanical properties of the material 50 after expansion (density, compressive strength, etc.), in order to guarantee the functionality of the invention;
- the implementation parameters (expansion time, expansion temperature) so as not to complicate the assembly;
- the specific characteristics of the polymer: compatibility with the materials of the bladder if necessary and the disc if it is a blade, etc.

Concerning the injection of resin 60 into the closed mold 310, and therefore the densification of the fibrous preform considered, if slots 107 and 108 are present on the leading and trailing edges 211a and 211b, they will preferably be closed by seam before densification, such densification consisting of filling the porosity of the preform, in all or part of the volume thereof, with the material constituting the matrix.

The matrix of the composite material can be obtained in a manner known per se following the liquid process. The liquid process consists of impregnating the preform with a liquid composition containing an organic precursor of the matrix material. The organic precursor is usually in the form of a polymer, such as resin, as mentioned above (which the expression “organic precursor” can replace) optionally diluted in a solvent. The mold 310 in which the preform will be placed can be closed in a watertight manner and therefore internally with a housing having the shape of the desired final molded part.

Mold 310 closed, the liquid matrix precursor (for example a resin) can be injected throughout the housing to impregnate the entire fibrous part of the preform.

The transformation of the precursor into an organic matrix, namely its polymerization, is, as known, carried out (by heat treatment or not) after elimination of any solvent and crosslinking of the polymer, the preform still being maintained in the mold. The organic matrix can in particular be obtained from epoxy resins, such as the high-performance epoxy resin sold under the reference PR 520 by the company CYTEC or “2896” resin from the company 3M, or from liquid precursors of carbon or ceramic matrices. .

In the case of the formation of a carbon or ceramic matrix, the heat treatment consists of pyrolyzing the organic precursor to transform the organic matrix into a carbon or ceramic matrix depending on the precursor used and the pyrolysis conditions. Several consecutive cycles, from impregnation to heat treatment, can be carried out to achieve the desired degree of densification.

If instead of a three-dimensional part, we wish to obtain a two-dimensional (2D) part, this will be possible in particular if we drape the 2D fabric over each of the parts of the mold or if, for a blade, we drape the extrados surface of the blade over the expansive paste 50, and then close the mold. Thus, if 2D weaving is planned, it is proposed to weave the extrados part separately from the intrados part and produce them either by co-firing (with a resin interface between the two parts) or by sewing before shaping.

Furthermore, the densification of the fibrous preform can be carried out by the well-known transfer molding process called RTM in which a thermosetting resin is injected into the available internal space of the mold. A pressure gradient is generally established in this internal space between the place where the resin is injected and the evacuation orifices of the latter in order to control and optimize the impregnation of the preform by the resin.

In relation to the placement of any insert, such as 300, in the cavity which receives it, any holding means necessary for suitable positioning of the insert in the cavity (centering arm, etc.) will be used if necessary. .

Claims (13)

Three-dimensional part comprising a composite material including a fabric and a resin, the part having a cavity (230,230') filled with a cellular material (50), characterized in that the cellular material comprises an expanded cellular polymer material. Part according to claim 1, in which the expanded cellular polymer material (50) is polyurethane. Process for manufacturing a composite part, the process having steps of:
- weaving of the part, integrating a cavity (230,230'),
- placing the part in a first part (301) of an injection mold (310),
- installation, in the cavity (230,230'), and which occupies its volume, of a soluble or removable, demouldable core (40,41,430''), or of a flexible membrane (430'),
- closing the injection mold, via at least a second part (303) of the injection mold,
- injection of resin (60) into the weaving, in order to form a woven piece of composite material,
- demoulding of the part, out of the injection mold,
- depending on the case, dissolution of the soluble core or removal, from the cavity, of the removable core or the flexible membrane,
- placement in the cavity of an expansive paste (50) adapted to form a honeycomb material,
- waiting for the dough to react to form said cellular material, in the cavity,
- elimination of excess honeycomb material that has overflowed from the cavity, if necessary. A method according to claim 3, wherein the weaving comprises weaving the part in three dimensions. Method according to claim 3 or 4, in which an inflatable bladder is used as the flexible membrane, which is inflated in the cavity, or a preformed part of silicone or polyurethane elastomer. Method according to claim 3, 4 or 5 further comprising, between the weaving of the part integrating the cavity (230,230') and the step where the expansive paste is contained in the cavity:
- weaving an insert (300') for the part presenting the cavity,
- inserting the woven insert into the cavity (230,230') of the part. Method according to claim 3, 4 or 5, in which the weaving of the part integrating the cavity comprises a co-weaving with a woven insert (22) which said part then integrates, in one piece with it. Method according to one of claims 3 to 7, in which weaving of the part integrating the cavity comprises an unbinding (110) made inside the part. Method according to one of claims 3 to 8 in which, the cavity having a bottom (49) and an opening (51), the placement of the expansive paste (50) comprises its introduction to the bottom of the cavity (230,230' ) so that the expansive paste expands from the bottom towards the opening. Method according to one of claims 3 to 9, in which the placement of the expansive paste (50) in the cavity (230,230') comprises the prior selection of an expandable polymer which releases gas during a reaction of polyaddition forms said cellular material, which is dense in the cavity. Method according to claim 10, wherein the selection of the expandable polymer comprises the choice of polyurethane, the release of CO2 of which during the polyaddition reaction forms said dense cellular material (50). Method according to one of claims 3 to 9, in which the cellular material comprises an expanded cellular polymer material. Method according to one of claims 3 to 12, in which, for placing the expansive paste in the cavity:
- either dough (50) is introduced directly into the cavity, in contact with the wall (237) which limits the cavity,
- either another flexible membrane or flexible bladder (431) is placed in the cavity, the expansive paste being introduced into this other flexible membrane or flexible bladder, said flexible membrane or flexible bladder (431) thus forming an interface between the part composite and the paste (50), then the expanded foam, and being held in place in the cavity (230,230'), permanently.