HYBRIDIZATION OF THE FIBERS OF THE FIBER REINFORCEMENT OF A FAN BLADE

Description

FIELD OF THE INVENTION

[0001] The invention relates generally to the field of turbomachines, and more particularly to that of the fan blades of these turbomachines and their manufacturing method.

[0002] The invention applies more particularly to fan blades made of composite material and their interaction with the inlet of the primary vein. TECHNOLOGICAL BACKGROUND

[0003] Turbomachine blades, and particularly fan blades, are subject to significant mechanical and thermal stresses and must meet strict weight and size requirements. It has therefore been proposed to use blades made from a composite material comprising a fiber reinforcement densified by a polymer matrix, which are lighter than metal blades with equivalent propulsive characteristics and which have satisfactory heat resistance.

[0004] During certification and engine life, fan blades are subject to bird and hailstone ingestion. However, depending on the type of object impacting the blade (including its size and mass) and the type of fan (rotation speed and number of blades), the preferred areas for damage initiation and propagation are different. The mechanical behavior of fan blades is therefore optimized during the blade design phase to comply with certification rules.

[0005] Furthermore, current designs tend to reduce the thickness of the composite material structure of the blades in the leading edge, trailing edge or even over the entire structure in order to improve aerodynamic performance. Iso-material and iso-law Document WO 2019 / 097147 describes a blade in accordance with the preamble of claim 1. SUMMARY OF THE INVENTION

[0006] An objective of the invention is therefore to remedy the aforementioned drawbacks, by proposing a fan blade for a turbomachine whose ingestion behavior is improved.

[0007] For this, the invention proposes a fan blade of a turbomachine comprising a structure made of composite material comprising a fibrous reinforcement obtained by three-dimensional weaving of strands and a matrix in which the fibrous reinforcement is embedded, the composite material structure comprising a leading edge and a trailing edge, the fiber reinforcement comprising a first portion forming the leading edge and a second portion forming all or part of the trailing edge, the strands of the fiber reinforcement comprising first strands having a predefined elongation at break.

[0008] Furthermore, the strands of the fibrous reinforcement further comprise second strands having an elongation at break greater than that of the first strands, the first portion comprising all or part of the first strands while the second portion comprises all or part of the second strands.

[0009] Some preferred but non-limiting features of the above-described blade are the following, taken individually or in combination: the first portion is devoid of second strands and the second portion comprises warp strands and weft strands, the warp strands of said second portion being devoid of first strands. the second portion extends from a tip of the blade. the blade further comprises an aerodynamically profiled blade adapted to extend in an air flow, a root configured to be fixed to a disk of the fan and a stilt extending between the root and the blade, and in the blade further comprises an aerodynamically profiled blade adapted to extend in an air flow, a root configured to be fixed to a disk of the fan and a stilt extending between the root and the blade, and in which the second portion forms the trailing edge over all or part of a height of the blade. the second portion extends over at least 35% of a height of the blade, for example between 35% and 100% of the height of the blade. the second portion does not include the foot.the second portion extends over a portion of rope length of between one centimeter and fifteen centimeters. the fiber reinforcement further comprises a third portion extending between the first portion and the second portion, a density of the second strands gradually increasing in the third portion from the first portion towards the second portion. the third portion extends over a distance of between 1 cm and 10 cm. the first and second strands comprise warp strands distributed so as to form warp columns, a percentage, relative to the total number of warp strands in a warp column of the third portion, of second strands introduced between two immediately adjacent warp strand columns being at most equal to 30%, and preferably between 5% and 15%.the blade further has a plurality of warp planes intersecting the warp columns, each warp plane being separated from an immediately adjacent warp plane by a line of weft strands, at most 30% of the warp strands being modified between two immediately adjacent warp planes in the third portion which is intermediate, and preferably between 5% and 15% of the warp strands. the first strands have a Young's modulus greater than the Young's modulus of the second strands. the elongation at break of the second strands is between 1.5 and 3 times the elongation at break of the first strands. the first strands comprise carbon or aramid fibers whose Young's modulus is greater than 250 GPa and the elongation at break is between 1.5% and 2.5%. the elongation at break of the second strands is between 3% and 6%, preferably between 4% and 5%.the second strands comprise glass fibers or basalt fibers. the second strands comprise warp strands. .

[0010] According to a second aspect, the invention also provides a fan for a turbomachine comprising a plurality of blades as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Other characteristics, aims and advantages of the present invention will appear more clearly on reading the detailed description which follows, and with regard to the appended drawings given as non-limiting examples and in which: There figure 1 is a schematic view representing a first example of fiber reinforcement for a fan blade according to an embodiment, on which the introduction of second strands and the exit of first strands in the intermediate portion have been shown diagrammatically as well as three chain planes. figure 2is a schematic view showing a second example of fiber reinforcement for a fan blade. Figures 3a to 3c schematically and partially represent the three chain plans shown on the figure 2 . There figure 4 is a perspective view of an exemplary embodiment of a fan comprising blades according to the invention. DETAILED DESCRIPTION OF AN EMBODIMENT

[0012] In the present application, upstream and downstream are defined relative to the normal flow direction of the gas in the fan 1 through the turbomachine. Furthermore, the axis of revolution of the fan 1 turbomachine is called the X axis of radial symmetry of the fan 1. The axial direction corresponds to the direction of the X axis of the fan 1, and a radial direction is a direction perpendicular to this axis and passing through it. Finally, internal and external will be used, respectively, in reference to a radial direction such that the internal part or face of an element is closer to the X axis than the external part or face of the same element.

[0013] A turbomachine fan 1 comprises a fan 1 disc 2 carrying a plurality of fan 1 blades 3, associated with inter-blade platforms.

[0014] Each blade 3 comprises a structure made of composite material comprising a fibrous reinforcement 4 obtained by three-dimensional weaving and a matrix in which the fibrous reinforcement 4 is embedded.

[0015] This composite material structure comprises a root 5, a stilt 6 and an aerodynamically profiled blade 7. The root 5 is intended to allow the blade to be fixed to the fan disk 2 and extends for this purpose between a bottom of an indentation formed in the disk 2 and the outlet of the bearing surfaces of the indentation. The aerodynamically profiled blade 7 is suitable for being placed in an air flow, when the turbomachine is in operation, in order to generate lift. Finally, the stilt 6 corresponds to the area of the blade 7 which extends between the root 5 and the blade 7, that is to say between the outlet of the bearing surfaces and the inter-blade platforms.

[0016] The blade 3 also comprises, in a manner known per se, a leading edge 8, a trailing edge 9, a pressure side wall and an extrados wall. The leading edge 8 is configured to extend opposite the flow of gases entering the turbomachine. It corresponds to the front part of an aerodynamic profile which faces the air flow and which divides the air flow into a pressure side flow and an extrados flow. The trailing edge 9 corresponds to the rear part of the aerodynamic profile, where the pressure side and extrados flows meet.

[0017] Finally, the structure is formed from a plurality of blade sections 3 stacked from the root 5 along a stacking axis Z extending radially relative to the axis of revolution X of the fan 1.

[0018] In the following, "height" will mean a distance along the stacking axis Z.

[0019] Thus, the blade 7 has a height h corresponding to the distance along the stacking axis Z between its lower limit 10, at the intersection with the stilt 6, and its apex 11. The height h of the blade 7 can for example be measured at the intersection between the trailing edge 9 and the lower limit 10 of the blade 7. The height H of the blade 3 corresponds to the distance along this axis Z between a lower face of the root 5 (configured to come opposite the bottom of the imprint of the fan disk 2) and the apex 11, measured at the intersection between the trailing edge 9 and the lower limit 10 of the blade 7.

[0020] The fiber reinforcement 4 may be formed from a single-piece fiber preform obtained by three-dimensional or multi-layer weaving with varying thickness. It comprises warp and weft strands which may in particular comprise carbon, glass, basalt, and / or aramid fibers. The matrix is typically a polymer matrix, for example epoxy, bismaleimide, or polyimide. The blade 3 is then formed by molding using a vacuum resin injection process of the RTM (Resin Transfer Molding) type, or VARRTM (Vacuum Resin Transfer Molding).

[0021] The strands forming the fiber reinforcement 4 comprise first strands 12 having a predefined elongation at break and second strands 14 having an elongation at break greater than that of the first strands 12. The fiber reinforcement 4 is therefore obtained by hybridization of the strands constituting it in order to make the best use of the mechanical properties of each strand depending on the zones of the blade 3 and the type of stress.

[0022] The first strands 12 preferably have a high Young's modulus, for example greater than 250 GPa, and have the function of making it possible to comply with the design criteria of the blade 3, and in particular the frequency status of the blade 3. These first strands 12 are therefore used in the weaving of the fiber reinforcement 4 to form the portion of the reinforcement 4 (or first portion 13) which generally comprises the lower and thick parts of the blade 3, so that the natural frequencies of the blade 3 are high. This thus makes it possible to limit or at least distance the frequency crossovers between the first natural modes of the blade 3, which are energetic, and the engine harmonics. The lower and thick parts here comprise the root 5 of the blade 3, the stilt 6, a lower part of the blade 7 and the leading edge 8. In one embodiment, only the first strands 12 are used as warp and weft strands in the weaving of the first portion 13.

[0023] The second strands 14, for their part, whose breaking strength is greater than that of the first strands 12, have the function of limiting the initiation and propagation of damage to the blade 3 during ingestion of objects, and in particular birds. These second strands 14 are therefore used in the weaving of the fibrous reinforcement 4 to form the portion of the reinforcement 4 (or second portion 15) which comprises all or part of the trailing edge 9, insofar as this zone is highly stressed in the event of ingestion of an object. Preferably, the elongation at break of the second strands 14 is between 1.5 and 3 times the elongation at break of the first strands 12. In one embodiment, only the second strands 14 are used as warp and / or weft strands in the weaving of the second portion 15.

[0024] In order to optimize the resistance of the blade 3 to impacts from objects, the second strands 14 are warp strands of the reinforcement 4 (i.e. strands extending along the stacking axis Z of the blade sections 3). Furthermore, the second portion 15 preferably extends from a lower zone of the blade 3 (which will be detailed later in the description) to the top 11 of the blade 3.

[0025] The reinforcement 4 further comprises an intermediate portion 16 extending between the first portion 13 and the second portion 15 which is formed by both the first strands 12 and the second strands 14. In one embodiment, only the first and second strands 14 are used as warp and weft strands in the weaving of the intermediate portion 16.

[0026] This intermediate portion 16 is configured to serve as an interface between the first portion 13 and the second portion 15 in order to limit the fragilities due to discontinuities in materials. When the fiber reinforcement 4 comprises only first strands 12 in the first portion 13 of the blade 3 and only second strands 14 in the second portion 15 of the blade 3, and the first portion 13 and the second portion 15 are end-to-end in the reinforcement 4, the blade 3 thus obtained effectively makes it possible to avoid damage to the blade 3 in the areas comprising the second strands 14.However, the Applicant realized that in the absence of an intermediate portion 16, that is to say by abruptly introducing second strands 14 and simultaneously removing the first strands 12 at the interface between the first portion 13 and the second portion 15 of the fiber reinforcement 4, the blade 3 obtained risked being seriously damaged at this interface in the event of an impact, because the interface between the two portions 11, 12 of the reinforcement 4 is weakened by the strong discontinuity of the material properties.

[0027] The intermediate portion 16 thus makes it possible to make a transition between the material properties of the first portion 13 and the material properties of the second portion 15. For this, the density of the second strands 14 is progressively increased within the intermediate portion 16 from the first portion 13 to the second portion 15. More precisely, at the interface 14 between the first portion 13 and the intermediate portion 16, the density of the second strands 14 is very low while the density of the first strands 12 is very high. On the other hand, at the interface 15 between the intermediate portion 16 and the second portion 15, the density of the second strands 14 is very high while the density of the first strands 12 is very low.

[0028] The second portion 15 extends over a portion of chord length L between one centimeter and fifteen centimeters at any point on the stacking axis Z of the blade 3. By chord, we will understand here, for a given section of the blade 3 (and therefore for a given point on the stacking axis Z), the straight line segment connecting the leading edge 8 to the trailing edge 9 of the blade 3.

[0029] The height h' of the intermediate portion 16 is determined according to the dimensioning of the blade 3, and therefore the type of fan 1 and more generally of turbomachine in which it is intended to be integrated.

[0030] As indicated previously, the second portion 15 extends to the top 11 of the blade 3. Ideally, in order to optimize the resistance of the blade 3 to bird impacts, the second portion 15 extends substantially over the entire height H of the blade 3, that is to say from the root 5 of the blade 3 or from the stilt 6 (see figure 2) to vertex 11, along trailing edge 9.

[0031] In an alternative embodiment, in order to simplify the certification of the root 5 / stilt 6 zone of the blade 3 and for manufacturing constraints, the second portion 15 only extends over a part of the blade 7 (see Figures 1 and 2 ), especially from a peak 11 of dawn.

[0032] In particular, in a first embodiment (see figure 1 ), the interface between the second portion 15 and the intermediate portion 16 may be located at a distance (along the stacking axis Z of the blade 3) from the lower limit 10 of the blade 7 of between 0% (case where the second portion 15 extends over the entire blade 7) and 65% of the height h of the blade 7. The height h of the second portion 15 is therefore between 35% and 100% of the height h of the blade 7.

[0033] This first embodiment in fact makes it possible to improve the behavior of the trailing edge 9 with respect to the ingestion of all types of objects (heavy birds, medium-sized birds and light birds).

[0034] In a second embodiment, the distance between the lower limit 10 of the blade 3 and the interface (along the stacking axis Z of the blade 3) is greater than 65% of the height h of the blade 7. The height h of the second portion 15 is therefore less than 35% of the height h of the blade 7.

[0035] This second embodiment makes it possible to facilitate manufacturing and to limit the additional untwisting induced by the fact that the second strands 14 have a lower Young's modulus than the first strands 12. However, the improvement in the behavior of the trailing edge 9 with respect to the ingestion of objects of the medium-sized bird and light bird type is less in comparison with the first embodiment.

[0036] It follows that the dimensioning of the blade 3 makes it possible to determine the distance from which to introduce second strands 14 into the fiber reinforcement 4, in order to combine the stiffness necessary for the frequency status (first strands 12) and elongation at break (second strands 14) for resistance to ingestion.

[0037] The height h' (dimension along the stacking axis Z) of the intermediate portion 16 is between 5% and 30% of the height h of the blade 3. Thus, the height h' of the intermediate portion 16 can be between one centimeter and ten centimeters.

[0038] THE Figures 1 and 2schematically represent a blade 3 whose fiber reinforcement 4 has been shaped from a three-dimensional woven fiber preform, before resin injection or densification by a matrix and possible machining, in order to obtain a fan blade 3 1 made of composite material in accordance with the invention. By three-dimensional weaving, it will be understood that the warp strands follow sinuous paths in order to link together weft strands belonging to different weft strand layers except for delinks, it being noted that a three-dimensional weave, in particular with interlock weave, can include 2D weaves on the surface. Different three-dimensional weave weaves can be used, such as interlock, multi-satin or multi-veil weaves, for example, as described in particular in document WO 2006 / 136755.

[0039] Three chain plans C1, C2, C3 have been represented on the figure 1. A warp plane C1, C2, C3 is a sectional view of the fiber preform along a plane normal to the stacking axis Z. In the fiber reinforcement 4, each warp plane C1, C2, C3 is separated from the immediately adjacent warp plane by a line of weft strands.

[0040] Furthermore, the Figures 3a to 3b are top views of the chain planes C1, C2, C3 of the figure 1, in which only the warp strands (i.e. the strands of the fiber reinforcement 4 extending in the stacking direction of the sections) have been shown, the weft strands having been omitted in order to simplify the reading of the figure. These figures schematically illustrate an example of hybridization of the strands by insertion of the second strands 14 in the warp direction at the vertical interface 17 (i.e. the interface which is substantially parallel to the trailing edge 9) and the horizontal interface 18 (i.e. the interface which is substantially parallel to the root 5 of the blade and which is located radially inwards relative to the intermediate portion 16) between the first portion 13 and the intermediate portion 16.

[0041] As can be seen on the Figure 3a , the first warp plane C1, which is part of the first portion 13 of the fiber reinforcement 4, only comprises first strands 12.

[0042] The second chain plan C2 ( Figure 3b ) is part of the intermediate portion 16 of the fiber reinforcement 5, between the horizontal interface 18 and the first portion 13. This second warp plane C2 shows the progressive increase in the density of second strands 14 in the intermediate portion 16, both between the vertical interface 17 and the trailing edge 9 and between the horizontal interface 16 and the lower limit of the second portion 15 (along the stacking direction Z). The increase in the density of second strands 14 from the horizontal interface can be achieved by successively removing the first strands 12 from the weaving of the preform, at the different warp planes constituting the intermediate portion 16, and by cutting them at the surface of the preform before injection, and by simultaneously introducing the second strands 14 between these warp planes (see figure 1). In this way, the first portion 13, the second portion 15 and the intermediate portion 16 are formed from a single piece during weaving.

[0043] The third warp plane C3 intersects the intermediate portion 16 and the second portion 15. This plane C3 therefore extends beyond the part of the intermediate portion 16 which is radially inward relative to the second portion 15. At this warp plane, C3, the first two columns of warp strands, which are part of the first portion 13 of the fiber reinforcement 4, comprise only first strands 12. These first two columns of warp strands are located near the vertical interface 17. The third and fourth columns of warp strands are part of the intermediate portion 16 of the fiber reinforcement 4, near its vertical interface 17. These columns of warp strands comprise two second strands 14 (which represents 88% first strands 12 and 12% second strands 14).The following columns of warp strands each comprise a greater percentage of second strands 14 compared to the percentage of first strands 12, up to the fourteenth column of warp strands and the following ones which comprise only second strands 14 and therefore form part of the second portion 15 of the reinforcement 4.

[0044] Generally, in order to ensure the transition of the mechanical properties between the first portion 13 and the second portion 15 of the reinforcement 4 at the level of the vertical interface 17, the percentage (relative to the total number of warp strands of the column) of second strands 14 introduced between two columns of immediately adjacent warp strands of the intermediate portion 16 is at most equal to 30%. Preferably, this percentage is between 5% and 15%.

[0045] In the part of the intermediate portion which extends from the horizontal interface 18, at most 30% of the warp strands are modified between two immediately adjacent warp planes (i.e. separated by only one line of weft strands). Thus, between two successive warp planes (and immediately adjacent in the fiber reinforcement 4), at most 30% of the first strands 12 are removed from the fiber preform forming the fiber reinforcement 4 and cut at the surface, and as many second strands 14 are introduced into the fiber preform from the surface in order to replace the first strands 12 removed. Preferably, in this part of the intermediate portion 16, between 5% and 15% of the warp strands are modified between two immediately adjacent planes.

[0046] In one embodiment, the first strands 12 have a high Young's modulus E, i.e. greater than 250 GPa, preferably greater than 270 GPa. Their elongation at break A is also between 1.5% and 2.5%.

[0047] For example, the first strands 12 may comprise carbon fibers, typically HS* T300 carbon fibers (E = 284 GPa, A = 1.5%), HS TR30S (E = 356 GPa, A = 1.9%) or HS T700 (E = 395 GPa, A = 2.1%) or high modulus aramid fibers of the Dupont Kevlar 49 type (E = 302 GPa, A = 2.4%).

[0048] The second strands 14 may then have an elongation at break of between 3% and 6%, preferably between 4% and 5%. For example, the second strands 14 may comprise glass fibers, typically glass fibers of the E-GLASS type (E = 165 GPa, A = 4.4%) or glass fibers of the S-2 GLASS type (E = 267 GPa, A = 5.2%), or basalt fibers (E = 227 GPa, A = 3%) or polyester fibers (E = 268 GPa, A = 3.5%).

[0049] Generally speaking, the configurations described are valid for engines whose fan can have an external diameter of the order of 1.8 meters to 3 meters. The number of fan blades can be equal to 16 or 18. Whatever the fan diameter, the number of fan blades will be reduced as much as possible. Among various criteria, a choice of parameters (in particular the distance h1) will depend more particularly on the behavior of the fan blade and the "frequency / sizing in ingestion" combination. Indeed, for the same engine target, it is possible to choose different frequency behavior strategies or frequency responses in different ingestion cases, for example to push back the blade and vane responses while avoiding vibrational crossovers with energetic harmonics of the engine.For example, it is possible to make choices to position these crossovers at transient engine speeds.

[0050] The hybridization of the strands of the fiber reinforcement 4 also makes it possible to open up the design field thanks to the additional contribution in mechanical strength. For example, it becomes possible to refine the profile of the blade 3 at the leading edge of the preform 4 or the trailing edge of the preform 4 or over its entire height h in comparison with a blade 3 comprising only first strands 12 (with high Young's modulus), which makes it possible to optimize the mass of the blade 3 and the aerodynamic performance of the fan 1 (by obtaining finer profiles or by reducing the hub ratio, which is linked to the reduction in the centrifugal force induced by the mass of the blade 3).

Claims

1. A blade (3) of a fan (1) of a gas turbine engine comprising a composite material structure comprising a fibrous reinforcement (4) obtained by three-dimensional weaving of strands and a matrix in which the fibrous reinforcement (4) is embedded, - the composite material structure comprising a leading edge (8) and a trailing edge (9), - the fibrous reinforcement (4) comprising a first portion (13) forming the leading edge (8) and a second portion (15) forming all or part of the trailing edge (9), - the strands of the fibrous reinforcement (4) comprising first strands (12) having a predefined elongation at break, the blade (3) being characterized in that the strands of the fibrous reinforcement (4) further comprise second strands (14) having a higher elongation at break than that of the first strands (12), in that the first portion (13) comprises all or part of the first strands (12) while the second portion (15) comprises all or part of the second strands (14), and in that the first portion (13) is devoid of second strands (14).

2. The blade (3) as claimed in claim 1, wherein the second portion (15) comprises warp strands and weft strands, the warp strands of said second portion (15) being devoid of first strands (12).

3. The blade as claimed in one of claims 1 or 2, wherein the second portion (15) extends from a tip (11) of the blade.

4. The blade (3) as claimed in one of claims 1 to 3, wherein the blade further comprises an airfoil (7) having an aerodynamic profile suitable for extending into an air stream, a root (5) configured to be fixed to a disk (2) of the fan and a shank (6) extending between the root (5) and the airfoil (7), and wherein the second portion (15) forms the trailing edge (9) over all or part of a height (h) of the airfoil (7), wherein the second portion (15) may extend over at least 35% of a height (h) of the airfoil (7), for example between 35% and 100% of the height (h) of the airfoil (7).

5. The blade as claimed in 4, wherein the second portion (15) may not comprise the root (5).

6. The blade as claimed in one of claims 1 to 5, wherein the second portion (15) extends over a portion of chord length (L) comprised between one centimeter and fifteen centimeters.

7. The blade (3) as claimed in one of claims 1 to 6, wherein the fibrous reinforcement (4) further comprises a third portion (16) extending between the first portion (13) and the second portion (15), a density of the second strands (14) progressively increasing in the third portion (16) from the first portion (13) toward the second portion (15), wherein the third portion (16) may extend over a distance comprised between 1 cm and 10 cm.

8. The blade (3) as claimed in claim 7, wherein the first and second strands (12, 14) comprise warp strands distributed so as to form warp columns, a percentage, based on the total number of warp strands in a warp column of the third portion (16), of second strands (14) inserted between two immediately adjacent columns of warp strands being at most equal to 30%, and preferably comprised between 5% and 15%.

9. The blade as claimed in claim 8, further comprising a plurality of warp planes (C1, C2, C3) intersecting the warp columns, each warp plane being separated from an immediately adjacent warp plane by a line of weft strands, with no more than 30% of the warp strands being modified between two immediately adjacent warp planes in the third portion that is intermediate (16), and preferably comprised between 5% and 15% of the warp strands.

10. The blade (3) as claimed in one of claims 1 to 9, wherein the first strands (12) have a higher Young modulus than the Young modulus of the second strands (14).

11. The blade (3) as claimed in one of claims 1 to 10, wherein the elongation at break of the second strands (14) is comprised between 1.5 and 3 times the elongation at break of the first strands (12).

12. The blade (3) as claimed in one of claims 1 to 11, wherein: - the first strands (12) comprise carbon or aramid fibers whose Young modulus is greater than 250 GPa and whose elongation at break is comprised between 1.5% and 2.5%, and / or - the elongation at break of the second strands (14) is comprised between 3% and 6%, preferably between 4% and 5%.

13. The blade (3) as claimed in claim 12, wherein the second strands (14) comprise glass fibers or basalt fibers.

14. The blade (3) as claimed in one of claims 1 to 13, wherein the second strands (14) comprise warp strands.

15. A fan (1) for a gas turbine engine comprising a plurality of blades (3) as claimed in one of claims 1 to 14.