A GUIDE VANE MADE OF COMPOSITE MATERIAL FOR A GAS TURBINE ENGINE, AND IT'S METHOD OF FABRICATION

Abstract

A guide vane for a gas turbine engine, the guide vane including an airfoil made of composite material having fiber reinforcement densified by a matrix, the fiber reinforcement being obtained from pre-impregnated long fibers agglomerated in the form of a mat, the airfoil being provided at least on a leading edge with a reinforcing strip, the reinforcing strip being made from a single strip of unidirectional fabric or of textile, or by stacking a plurality of pre-impregnated plies of unidirectional fabric or of textile made of carbon fibers or of glass fibers, and at least one platform positioned at a radial end of the airfoil, the platform being made of composite material having fiber reinforcement densified by a matrix, the fiber reinforcement being obtained from pre-impregnated long fibers.

Claims

1. A guide vane for a gas turbine engine, the guide vane comprising: an airfoil made of composite material having fiber reinforcement densified by a matrix, the fiber reinforcement being obtained from pre-impregnated long fibers agglomerated in the form of a mat, the airfoil being provided at least on a leading edge with a reinforcing strip, said reinforcing strip being made from a single strip of unidirectional fabric or of textile, or by stacking a plurality of pre-impregnated plies of unidirectional fabric or of textile made of carbon fibers or of glass fibers; and at least one platform positioned at a radial end of the airfoil, the platform being made of composite material having fiber reinforcement densified by a matrix, said fiber reinforcement being obtained from pre-impregnated long fibers.

2. A guide vane according to claim 1, wherein the reinforcing strip is positioned on the leading edge of the airfoil and covers at least part of one of the side faces of the airfoil.

3. A guide vane according to claim 2, wherein the side face of the airfoil that is not covered by the reinforcing strip is covered in part by another strip of unidirectional fabric so as to limit stiffness and shrinkage asymmetries during fabrication of the airfoil.

4. A guide vane according to claim 1, wherein the reinforcing strip is positioned at the leading edge of the airfoil and covers both side faces of the airfoil, at least in part.

5. A guide vane according to claim 1, wherein the reinforcing strip is positioned on the airfoil and on at least one connection fillet between the airfoil and the platform.

6. A guide vane according to claim 1, further including a layer of viscoelastic material that is interposed between the airfoil and the reinforcing strip or that is positioned within the reinforcing strip.

7. A guide vane according to claim 1, wherein the mats constituting the fiber reinforcement of the airfoil and of the platform are made from carbon fiber chips.

8. A turbine engine including at least one guide vane according to claim 1.

9. A method of fabricating a guide vane according to claim 1, the method comprising in succession: positioning the reinforcing strip and the pre-impregnated long fibers that are agglomerated as mats in cavities of compression tooling in order to make fiber reinforcement making up the airfoil and the platform; closing the compression tooling; compressing the mats and the reinforcing strip while regulating the temperature and the closure pressure of the compression tooling in order to transform the composite used; opening the compression tooling; and unmolding the resulting guide vane.

10. A method of fabricating a guide vane according to claim 1, the method comprising in succession: positioning the reinforcing strip and the pre-impregnated long fibers that are agglomerated as mats in cavities of compression tooling in order to make fiber reinforcement constituting the airfoil; closing the compression tooling; compressing the mats and the reinforcing strip while regulating the temperature and the closure pressure of the compression tooling in order to transform the composite used; opening the compression tooling; unmolding the resulting airfoil; and overmolding a previously-prepared platform on the airfoil by a method of injecting resin under pressure.

11. A method of fabricating a guide vane according to claim 1, the method comprising in succession: positioning the reinforcing strip and the pre-impregnated long fibers that are agglomerated as mats in cavities of compression tooling in order to make fiber reinforcement constituting the airfoil; closing the compression tooling; compressing the mats and the reinforcing strip while regulating the temperature and the closure pressure of the compression tooling in order to transform the composite used; opening the compression tooling; unmolding the resulting airfoil; and adhesively bonding a previously-prepared platform on the airfoil.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Other characteristics and advantages of the present invention appear from the following description made with reference to the accompanying drawings, which show embodiments having no limiting character. In the figures:

[0028] FIG. 1 is a perspective view of a guide vane of the invention;

[0029] FIGS. 2A and 2B are views of the FIG. 1 guide vane, respectively in cross-section and in longitudinal section; and

[0030] FIGS. 3 to 6 are cross-section vies of guide vanes in variant embodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0031] The invention applies to making guide vanes for a gas turbine aeroengine, each vane having a leading edge.

[0032] Non-limiting examples of such guide vanes include in particular outlet guide vanes (OGV), inlet guide vanes (IGV), and variable stator vanes (VSV), etc.

[0033] FIG. 1 is a diagrammatic perspective view showing an example of such a guide vane 2.

[0034] In known manner, the guide vane 2 comprises an airfoil 4 having a pressure side face 4a and a suction side face 4b, an inner platform 6 that is assembled on a radially inner end of the airfoil, and an outer platform 8 that is assembled on the radially outer end of the airfoil.

[0035] In accordance with the invention, the airfoil 4 is made of composite material having fiber reinforcement densified by a matrix, the fiber reinforcement being obtained from pre-impregnated long fibers, e.g. discontinuous fibers that are agglomerated in the form of a mat. The fabrication of such an airfoil is described below.

[0036] In the same manner, the inner and outer platforms 6 and 8 are made out of composite material with fiber reinforcement likewise obtained from pre-impregnated long fibers, e.g. discontinuous fibers that are agglomerated in the form of a mat.

[0037] Furthermore, still in accordance with the invention, and as shown in FIGS. 2A and 2B, the leading edge of the airfoil 4 is formed by a reinforcing strip 10-1 made of unidirectional fabric (UD) or of pre-impregnated textile, this reinforcing strip being positioned on the airfoil at its leading edge and at least on the connection fillets 12 between the airfoil and the inner and outer platforms 6 and 8. The reinforcing strip could optionally not cover the connection fillets.

[0038] In the left-hand portion of FIG. 2B, the reinforcing strip 10-1 extends only over the connection fillets 12 between the airfoil and the inner and outer platforms 6 and 8. Alternatively, and as shown in the right-hand portion of FIG. 2B, the reinforcing strip 10-2 could extend not only over the connection fillets, but also over the platforms 6 and 8.

[0039] Furthermore, in another embodiment that is not shown in the figures, the reinforcing strip may be embedded directly in the thickness of the platforms 6 and 8. This technique serves to avoid any delamination between the reinforcing strip and the mat constituting the platforms during drilling and rolling of the platforms for the purpose of fastening them to a casing.

[0040] Furthermore, and as shown in FIG. 2A, the reinforcing strip 10-1 may present positioning that is said to be “simple”, in which case it is positioned only on the leading edge of the airfoil 4.

[0041] In a variant shown in FIG. 3, the reinforcing strip 10-3 is positioned asymmetrically, covering not only the leading edge of the airfoil, but also a portion of one of the side faces of the airfoil (specifically in this example the pressure side face 4a). This configuration makes it possible to increase the stiffness of the airfoil, thereby improving its ability to withstand stresses and improving its protection against erosion.

[0042] In another variant that is shown in FIG. 4, the reinforcing strip 10-4 is symmetrically positioned, covering not only the leading edge of the airfoil 4, but also portions of both side faces of the airfoil (namely the pressure side face 4a and the suction side face 4b). Compared with the previous variant, this configuration serves to further increase the stiffness of the airfoil and to avoid post-fabrication deformation.

[0043] It should be observed that the greater the coverage of the side faces of the airfoil by the strip, the greater the stiffness imparted to the airfoil.

[0044] It should also be observed that the shape of the reinforcing strip is not necessarily rectangular: for example, it may be of wave shape so as to respond to problems of deformation along the trailing edge at a common frequency.

[0045] In yet another variant that is shown in FIG. 5, the reinforcing strip 10-5 is positioned asymmetrically, covering the leading edge and a portion of the suction side face 4b of the airfoil 4. Furthermore, the side face of the airfoil that is not covered by the reinforcing strip (specifically the pressure side face 4a) is covered in part by another strip 14, likewise made of unidirectional fabric or of pre-impregnated textile.

[0046] The presence of this additional strip 14 serves to limit asymmetries of stiffness and/or of shrinkage/deformation during fabrication of the airfoil. In particular, the width of the strip 14 is a function of the amount of deformation to which the airfoil is subjected during fabrication.

[0047] In yet another variant shown in FIG. 6, the guide vane 2 also has a layer of viscoelastic material 16 that is interposed between the airfoil 4 and the reinforcing strip 10-6. This layer (or patch) 16 in the example shown in FIG. 6 is positioned over the pressure side face 4a of the airfoil and is covered by the reinforcing strip 10-6, which reinforcing strip may be positioned symmetrically so that it covers portions both of the pressure side and of the suction side of the airfoil.

[0048] The presence of this layer of viscoelastic material 16 thus serves to respond to vibratory, acoustic, or damping problems that are encountered by the guide vane. Specifically, this layer serves to absorb energy, and frequencies, and to attenuate vibratory modes, thereby limiting the vibration and deformation to which the guide vane is subjected in operation.

[0049] The layer of viscoelastic material 16 may be interposed between the airfoil and the reinforcing strip. Alternatively, it may be positioned within the reinforcing strip, i.e. it may be added between two successive plies making up the reinforcing strip.

[0050] By way of example, the viscoelastic material used may be of the elastomer, rubber, etc. . . . type.

[0051] There follows a description of various methods of fabricating the guide vane in accordance with the invention.

[0052] A first fabrication method is said to be a “thermo-compression” method. It enables a guide vane of the invention to be made as a single piece.

[0053] This thermo-compression fabrication method requires compression tooling made up of a shell having indentations (or cavities) formed therein for the guide vane that is to be fabricated, and possibly provided with an ejector system for extracting the fabricated part. These indentations are temperature regulated so as to bring the injected resin up to its melting temperature and thus “transform” the mat.

[0054] A first step of the method consists in making the fiber reinforcement that is to constitute the airfoil and the platforms of the guide vane. For this purpose, pre-impregnated “chips” are cut out from a strip of unidirectional or textile fabric, typically made of carbon fibers, with the dimensions (length and width) and the type of carbon used for the chips being a function of the level of stiffness desired for the guide vane. For example, the chips may present a width lying in the range 4 millimeters (mm) to 15 mm, and a width lying in the range 4 mm to 150 mm, or indeed 2 mm of width and/or of length.

[0055] The long fibers may be continuous or discontinuous prior to transformation as a function of the selected injection method. Discontinuous fibers present a length lying substantially in the range 2 mm to 100 mm, as a function of the size of the granules making up the resin.

[0056] The fibers are often discontinuous or they may be continuous as a function of the topology of the part, of the fiber volume content present in the resin, of the method used, of parameters of the transformation process, of rheological phenomena, and/or of interaction phenomena between fibers. The fibers conserve their initial length or else they are broken during the dynamic stage corresponding to filling so as to present a final fiber length distribution lying substantially in the range 0.1 mm to 100 mm.

[0057] These carbon fiber chips are then agglomerated so as to form a mat. This solution enables the chips to be manipulated easily prior to being positioned in the compression tooling. It is also possible merely to create a mass of chips (which are then positioned, “injected”, and inserted into the compression tooling).

[0058] The superposing and positioning of chips within the mat is random, but where possible with a pattern that can be repeated for reproducibility of the guide vanes. Preferably, the mat presents a structure that is isotropic in order to obtain mechanical properties that are uniform in a plane. The shape of the mat depends on the complexity of the guide vane that is to be fabricated (size, thickness, variation in shape, etc.).

[0059] It should be observed that the fiber reinforcement for making the platforms of the guide vane may be made using the same mat as is used for making the airfoil. Alternatively, the platforms may be made from a mat in which the aspect ratio (length/width of the carbon fiber chips) is smaller than for the airfoil. Indeed, the platforms are less stressed than the airfoil.

[0060] It should also be observed that the mat may be pre-polymerized, typically up to 20%-50% prior to being positioned in the cavities of the compression tooling, with such pre-polymerization thus making it possible to conserve resin for providing cohesion between the chips and the reinforcing strip. This leads to a so-called “washout” effect corresponding to resin migrating around the reinforcement. By way of example, for a resin of the epoxy family, the mat may be pre-polymerized to 30%.

[0061] Parallel to the step of creating such mats, the thermo-compression fabrication method consists in creating the reinforcing strip. This is made by a single strip of UD fabric or textile, typically made of carbon fibers, that is cut out, e.g. into the form of a rectangle. Alternatively, the reinforcing strip may be made by stacking a plurality of pre-impregnated plies of UD fabric or of textile, likewise made of carbon fibers.

[0062] In the following step of the method, the reinforcing strip and the mat for making fiber reinforcement constituting the airfoil and the platforms as prepared in this way are positioned in the cavities of the compression tooling.

[0063] If two types of mat are used, the mat for making the fiber reinforcement of the airfoil is positioned initially in a cavity of the compression tooling together with the reinforcing strip, and then the mat for making the platforms is positioned subsequently. Alternatively, they may be positioned at the same time in the same compression tooling. Also alternatively, they may be positioned at the same time in the same compression tooling in order to be subjected to pre-consolidation prior to being positioned in final compression tooling.

[0064] The compression tooling is then closed. The resin used for the pre-impregnated chips may be a thermosetting resin belonging to the family of epoxies, bismaleimides, polyimides, polyesters, vinylesters, cyanate esters, phenolic resins, etc. Alternatively, the resin may be a thermosetting resin of one of the following types: polyphenylene sulfide (PPS), polysulfone (PS), polyethersulfone (PES), polyamide-imide (PAI), polyetherimide (PEI), or indeed the family of polyaryletherketones (PAEK): PEK, PEKK, PEEK, PEKKEK, etc.

[0065] Closing the compression tooling leads to the mats and the reinforcing strip that have been placed inside the tooling being compressed, thereby enabling the mats to take on the shape of the cavities in the compression tooling. This compression step may be performed either by closing the compression tooling, or by moving movable cores present inside the compression tooling.

[0066] Together with the compression step, provision is made to regulate the temperature of the compression tooling so as to transform and polymerize the resin (i.e. curing a thermosetting resin or cooling a thermoplastic resin).

[0067] More precisely, with a thermosetting resin, it is advantageous to have recourse to a specific first heating cycle that is close to the melting temperature of the resin with controlled temperature-rise ramps for shaping the mats, followed by a second heating cycle that is likewise controlled for the purpose of consolidating/cross-linking/polymerizing the resin. This makes it possible for the mats add the reinforcing strip to be put into shape and to determine their cohesive/adhesive aspects.

[0068] With a thermoplastic resin, this second cycle is constituted by a cooling cycle so s to reach the ejection temperature of the part and thus ensure that the semicrystalline or amorphous polymers are properly crystallized/polymerized in order to obtain good mechanical properties and limit residual stresses and post-injection deformation.

[0069] The temperature of the compression tooling may be regulated by any known regulation means, e.g. by using heating cartridges, by regulation using water or oil, by an induction heating system, etc.

[0070] At the end of this step, the compression tooling is opened and the guide vane as obtained in this way is extracted (by using an ejector system or manually or automatically by means of a gripper).

[0071] A second method of fabricating the guide vane makes use of the above-described thermo-compression method for obtaining the airfoil of the guide vane (without platforms), followed by a step of overmolding previously prepared platforms on the airfoil by a method of injecting resin under pressure.

[0072] The method of fabricating the airfoil by thermo-compression is thus entirely identical to that described above.

[0073] The airfoil of composite material as made in this way is then placed in an injection mold in order to perform overmolding on the airfoil so as to make the platforms by using a thermoplastic or thermosetting resin (which may optionally be filled).

[0074] Reference may be made to French patent application No. 1357485 filed on Jul. 29, 2013 by Safran, which describes a method of assembling a metal leading edge by overmolding onto a composite material vane. In principle, that method can be applied to making platforms out of composite material on the airfoil made of composite material of the guide vane of the invention, likewise by overmolding.

[0075] Briefly, the overmolding method makes provision for a dynamic stage of filling the cavity of the injection mold by injecting resin under pressure, followed by a switching stage, and then a static compacting/holding stage and a stage of solidifying or cross-linking/curing the injected resin. After the resin has solidified, the injection mold is opened and the part (airfoil with its overmolded platforms) is ejected.

[0076] A third method of fabricating the guide vane applies the above-described thermo-compression method to obtain the airfoil of the guide vane possibly together with the platforms, a known injection method for fabricating the platforms (where necessary), and then a step of bonding the platforms on the airfoil by adhesive. This adhesive bonding step may be performed by known methods such as ultrasound bonding, depositing adhesive, etc.