Method for manufacturing an intermediate crankcase shell with locally optimized properties

Abstract

A manufacturing process for an intermediate casing shell with locally optimized properties. A manufacturing process for an external intermediate casing shell of a turbofan engine made of composite material comprises: - the production by three-dimensional or multi-layer weaving of a fibrous texture (140) in the form of a strip, - the winding of the fibrous texture (140) in several superimposed layers (141, 142, 143, 144) on a mandrel (200) of profile corresponding to that of the external shell to be manufactured, in order to obtain a fibrous preform of shape corresponding to that of the external shell to be manufactured, - the densification of the fibrous preform by a matrix.During the winding of the fibrous texture (140) onto the mandrel, a textile strip (150) is placed at least between one or more adjacent turns of the fibrous texture, the textile strip (150) having a structure different from a three-dimensional weave and having a width less than the width of the fibrous texture (140) along an axial direction (DA). Figure for the abbreviation: Fig. 2.

Description

Title of the invention: Method for manufacturing an intermediate casing shell with locally optimized properties Technical field

[0001] The present invention relates to the manufacture of an outer shell of an intermediate casing present downstream of a fan casing of a dual-flow turbojet engine. Prior art

[0002] A bypass turbojet engine comprises a fan which is normally located at the front of the turbojet engine. It then delivers an airflow divided into a primary flow and a secondary flow annular around the primary flow. The primary flow is guided towards a compressor, a combustion chamber, a turbine driving the compressor and the fan, and ejected, with the combustion gases, through an exhaust nozzle in order to produce reaction thrust. The secondary flow is straightened downstream of the fan and ejected in substantially the same direction. Thus, the majority of the thrust is due to the secondary flow of fresh air driven by the fan, a lesser part coming from the primary flow with the hot combustion gases. In the following description, the terms "upstream" and "downstream" are defined relative to the normal direction of airflow through the fan, and the terms "inside" and "outside" indicate the region inside and outside the fan casing, respectively. "Bypass ratio" is understood to mean the ratio between the mass flow rates of the secondary and primary streams. Except at very high speeds, particularly supersonic speeds, the propulsive efficiency of a bypass turbojet engine increases with said bypass ratio. Increasing the bypass ratio is therefore an appropriate way to reduce the energy consumption of bypass turbojet engines, and consequently reduce both operating costs and emissions of polluting and greenhouse gases. A high bypass ratio also offers additional advantages, such as lower noise impact. However, to increase the bypass ratio it is normally necessary to also increase the fan diameter. This has several disadvantages, including an increase in the mass and drag of the casing and nacelle surrounding the fan blades.

[0003] Existing turbojets of bypass design generally comprise a fan casing extended downstream by an intermediate casing. The intermediate casing comprises a core or hub supporting the shafts connecting the different rotors, an external shroud called the "intermediate casing shroud" or "ICS", as well as a plurality of radial guide vanes (or connecting arms) between the hub and the outer ferrule.

[0004] Previously made of metallic material, fan casings are now made of composite material, i.e. from a fibrous preform densified by an organic matrix, which makes it possible to produce parts having a lower overall mass than these same parts when they are made of metallic material while having at least equivalent, if not higher, mechanical strength.

[0005] The manufacture of a fan casing made of an organic matrix composite material is described in particular in document US 8,322,971, the fan casing being formed from a fibrous reinforcement obtained by winding a 3D woven fibrous texture densified by an organic matrix.

[0006] It may be envisaged to also manufacture the outer shell of the intermediate casing from composite material in order to further lighten the fan assembly.

[0007] However, in order to ensure a significant weight saving, the intermediate casing shell must be relatively thin. It then has less resistance to perforating or non-perforating impacts. The shell also has a sensitivity to vibration stresses which can be problematic for the dynamic behavior of the intermediate casing.

[0008] There is therefore a need for a solution for locally optimizing the mechanical properties of an outer shell of an intermediate casing made of composite material comprising a 3D woven fiber reinforcement while minimizing the mass and / or manufacturing cost of the part. Statement of the invention

[0009] To this end, the invention proposes a method for an external shell of an intermediate casing of a dual-flow turbojet, comprising: - the production by three-dimensional weaving between a plurality of warp threads or strands and a plurality of weft threads or strands of a fibrous texture with varying thickness in the form of a strip,

[0010] - winding the fibrous texture over several turns superimposed on a mandrel of profile corresponding to that of the outer shell of the intermediate casing to be manufactured in order to obtain a fiber preform of revolution shape corresponding to that of the outer shell of the intermediate casing to be manufactured and extending in width in an axial direction and in thickness in a radial direction,

[0011] - densification of the fiber preform by a matrix, characterized in that, when winding the fibrous texture onto the mandrel, at least one textile strip is placed at least between one or more adjacent turns of the fibrous texture, on the inner face of the first winding turn of the texture fibrous, or on the external surface of the fibrous texture, each textile strip having a structure different from a three-dimensional weave, each textile strip having a width less than the width of the fibrous texture in the axial direction.

[0012] The method according to the invention makes it possible to locally optimize mechanical properties in the outer shell of the intermediate casing, without significantly increasing the overall mass of the shell by using one or more textile strips added with the 3D woven fiber texture intended to form the fiber reinforcement of the part. The cost and / or manufacturing time of the locally optimized outer shell are also well controlled because the local optimization of the mechanical properties of the shell fits perfectly into the manufacturing process usually used. Indeed, only one or more textile strips are added to the 3D woven fiber texture during the formation of the fiber preform, which results in very few modifications to the usual manufacturing process.

[0013] According to a particular characteristic of the method of the invention, the width of said at least one textile strip in the axial direction is between 2% and 50% of the internal diameter of the fiber preform.

[0014] The method of the invention makes it possible to confer or locally optimize different mechanical properties, in particular depending on the architecture and the nature of the fibers used in the textile strip.

[0015] According to a first aspect of the invention, said at least one textile strip is formed with fibers having an elongation at break greater than or equal to 1.7%.

[0016] According to a second aspect of the invention, said at least one textile strip is made up of one or more unidirectional, two-dimensional layers or plies, of multiaxial sheets or flat braids. Said at least one textile strip may in particular be made up of one or more two-dimensional layers having a satin-type weave.

[0017] According to a third aspect of the invention, the width of said at least one textile strip in the axial direction corresponds to 10% of the width of the fiber preform.

[0018] According to a fourth aspect of the invention, said at least one textile strip is formed with fibers having a Young's modulus of between 350 GPa and 500 GPa. Said at least one textile strip may consist of one or more unidirectional, two-dimensional or multiaxial layers or plies (NCF), the fibers of the textile strip being oriented in one or more directions different from the direction of the warp threads or strands and / or the direction of the weft threads or strands of the fiber texture. The fibers present in said at least one textile strip may in particular be oriented at an angle of ± 45° relative to the direction of the threads or warp and / or weft strands of the fibrous texture. The width of said at least one textile strip in the axial direction may correspond to 15% of the width of the fibrous preform.

[0019] According to another particular characteristic of the method of the invention, during the winding of the fibrous texture onto the mandrel, first and second textile strips are placed at least between one or more adjacent turns of the fibrous texture, on the internal face of the first winding turn of the fibrous texture, or on the external surface of the fibrous texture, the first and second textile strips being offset from each other in the axial direction in the fibrous preform.

[0020] The invention also relates to an intermediate casing shell made of a composite material manufactured in accordance with the method of manufacturing a revolution part made of composite material of the invention.

[0021] The invention further relates to an intermediate casing of a bypass turbojet engine comprising a core, an outer casing shell according to the invention and a plurality of radial guide vanes extending between said hub and said outer casing shell.

[0022] The invention also relates to a gas turbine aeronautical engine having an intermediate casing according to the invention. Brief description of the drawings

[0023] [Fig-1] [Fig.l] is a schematic longitudinal section of a turbojet engine with double flow equipped with an external intermediate casing shell made of composite material in accordance with one embodiment of the invention,

[0024] [Fig.2] [Fig.2] is a sectional view of the outer shell of the intermediate casing of the turbojet of [Fig.l],

[0025] [Fig.3] [Fig.3] is a schematic perspective view of a loom showing the weaving of a fibrous texture used for the formation of the fibrous reinforcement of the outer shell of the intermediate casing of figures 1 and 2,

[0026] [Fig.4] [Fig.4] is a perspective view showing the shaping of a texture fibrous and two textile strips intended to form the reinforcement of the external shell of the intermediate casing of figures 1 and 2,

[0027] [Fig.5] [Fig.5] is a schematic view showing the simultaneous winding of the fibrous structure and the textile strip of [Fig.4],

[0028] [Fig.6] [Fig.6] is a sectional view showing the profile of the fiber preform obtained after winding the fibrous structure and the textile strip of figures 4 and 5,

[0029] [Fig.7] [Fig.7] is a schematic view showing a tool for densify with a matrix the fibrous preform of [Fig.6]. Description of the embodiments

[0030] The invention applies to an external shell of an intermediate casing present downstream of a fan casing of a dual-flow turbojet engine.

[0031] A bypass turbojet 1, as shown very schematically by [Fig.l] comprises, from upstream to downstream in the direction of the gas flow E, a fan 2 with a rotor 21 of rotating blades 22 surrounded by a fan casing 23, an intermediate casing 30 comprising an internal hub or core 31 adapted to receive a drive shaft of the turbojet, an external shroud 10 of the bypass turbojet intermediate casing and guide vanes 32 (in English "outlet guide vanes" or OGV) downstream of the rotating blades 24, a combustion chamber 3, a high-pressure turbine 4 and a low-pressure turbine 5.

[0032] Apart from straightening the air flow downstream of the rotating blades 22, the guide vanes 32 connect the outer shroud 10 of the intermediate casing of the bypass turbojet engine to the inner hub 31. The guide vanes 32 also connect, via the outer shroud 10, the inner hub 31 to the fan casing 23. The outer ends of the guide vanes 32 are connected to an inner perimeter of the outer shroud 10 of the intermediate casing of the bypass turbojet engine by fastening members 320, for example of the bolt type. A radial flange 11 on an axial face of the shroud 10 is pressed against a corresponding radial flange 231 of the fan casing 23, and connected thereto by bolts 232 passing through the two flanges 231, 11.

[0033] [Fig. 2] shows the profile (in axial section) of the external shell 10 of the intermediate casing 30 which is here made of organic matrix composite material, that is to say from a fiber reinforcement for example of carbon, glass, aramid or ceramic, densified by a polymer matrix, for example epoxide, bismaleimide or polyimide.

[0034] The outer shroud 10 of the intermediate casing of a dual-flow turbojet extends in width in an axial direction DA between its upstream and downstream ends (from left to right in [Fig.2]) which are here provided with external radial flanges 11, 15 to allow its mounting and connection with other elements. The outer shroud 10 extends in length in a circumferential direction Dc.

[0035] The fibrous reinforcement is formed by winding onto a mandrel a fibrous texture produced by three-dimensional weaving, the mandrel having a profile corresponding to that of the casing to be produced. Advantageously, the fibrous reinforcement constitutes a complete tubular fibrous preform of the external shell 10 forming a single piece.

[0036] According to the invention, the outer shell of the intermediate casing of a bypass turbojet engine comprises at least one local reinforcement portion. In the example described here, the outer shell 10 of the intermediate casing of a bypass turbojet engine double flow comprises a first local reinforcement portion 12 and a second local reinforcement portion 13 present between the flanges 11 and 14. However, it does not go beyond the scope of the invention when the outer shell of the intermediate casing comprises only one local reinforcement portion.

[0037] The fibrous reinforcement of the outer shell 10 consists of a plurality of superimposed layers 141 to 144 of a fibrous texture 140 in the form of a strip having a three-dimensional or multi-layer weave, each layer 141 to 144 corresponding to one turn of winding of the fibrous texture 140 (in [Fig. 2] the layers 141 to 144 are densified by a matrix). In addition, a first textile strip 150 is interposed between two adjacent layers of the fibrous texture at the first local reinforcement portion 12, the textile strip 150 having a width l150 less than the width l140 of the fibrous texture 140 ([Fig. 4]). Likewise, a second textile strip 160 is interposed between two adjacent layers of the fibrous texture at the level of the second local reinforcement portion 13, the textile strip 160 having a width li60 less than the width li40 of the fibrous texture 140 ([Fig.4]).In the example described here, three layers 151 to 153 of first textile strip 150 and three layers 161 to 163 of second textile strip 160 are interposed between the superimposed layers 141 to 144 of the fibrous texture 140, each layer 151 to 153 and each layer 161 to 163 corresponding to one winding turn of the textile strip 150.

[0038] Generally, each textile strip making it possible to form a local reinforcement portion can be interposed between two or more superimposed layers of fibrous texture, each corresponding to a winding turn of said fibrous texture. According to an alternative embodiment, each textile strip making it possible to form a local reinforcement portion can also be present on the internal face of the first winding turn and / or on the external face of the last winding turn of the fibrous texture of the fibrous reinforcement.

[0039] As described in detail below, by adding a textile strip to the fiber reinforcement of the part, it is possible to locally give the part particular mechanical properties.

[0040] A method of manufacturing an external shroud 10 of an intermediate casing of a dual-flow turbojet engine is now described.

[0041] As shown in [Fig. 3], a fibrous texture 140 is produced in a known manner by weaving using a jacquard type loom 60 on which a bundle of warp threads or strands 70 has been arranged in a plurality of layers, the warp threads being linked by weft threads or strands 80. The fibrous texture is produced by three-dimensional weaving.

[0042] By “three-dimensional weaving” or “3D weaving” is meant here a weaving method whereby at least some of the weft threads bind warp threads across several layers of warp threads or vice versa. An example of a three-dimensional weave is the so-called interlock weave. By interlock weave is meant a weave pattern in which each layer of warp threads binds several layers of weft threads, with all the threads in the same warp column having the same movement in the plane of the weave.

[0043] The production of the fibrous texture by 3D weaving makes it possible to obtain a connection between the layers, thus providing good mechanical strength for the fibrous structure and the resulting composite material part, in a single textile operation.

[0044] As illustrated in Figures 3 and 4, the fibrous texture 140 has a strip shape which extends in length in a direction X ([Fig.3]) corresponding to the direction of travel of the warp threads or strands 70 and in width or transversely in a direction Y ([Fig.3]) corresponding to the direction of the weft threads or strands 80. As explained below, the fibrous reinforcement of the outer shell 10 is formed by the fibrous texture 140 which is shaped by winding on itself. Consequently, in the fibrous reinforcement of the outer shell, the warp threads or strands extend in the circumferential direction Dc (Figures 1, 2 and 6) while the weft threads or strands extend in the axial direction DA (Figures 1, 2, 4 and 6).

[0045] The fibrous structure may in particular be woven from carbon, ceramic such as silicon carbide, glass, or aramid fiber threads.

[0046] The first and second textile strips 150, 160 are each produced independently. They each have a different textile structure of a three-dimensional weave. Each textile strip may in particular, but not exclusively, be formed by one or more unidirectional (UD), two-dimensional (2D) layers or plies with fibers oriented at 0790° or +457-45° or by one or more multiaxial sheets (“Non Crimp Fabric” in English or NCF) which is a textile fabric which generally has several layers of non-woven unidirectional fibers oriented in different directions linked by a fine knitting yarn.

[0047] Depending on the mechanical properties that one wishes to confer locally, one chooses a specific textile structure and one or more types of fibers.

[0048] Generally speaking, the width of each textile strip along the axial direction Da is between 2% and 50% of the width of the fiber preform.

[0049] As illustrated in [Fig. 4], a fiber preform is formed by winding the fiber texture 140 produced by three-dimensional weaving onto a mandrel 200, the mandrel having a profile corresponding to that of the intermediate casing shell of a dual-flow turbojet engine to be produced. According to the invention, the first and second textile strips 150, 160 are wound simultaneously with the fiber texture 140 at positions offset along the axial direction DA, the strips 150 and 160 being positioned above the first layer 141 of the texture 140 wound on the mandrel 200 so as to interpose a layer of textile strip 150 and a layer of textile strip 160 of smaller width between two adjacent layers of fibrous texture of larger width corresponding to two turns of winding of the fibrous texture 140. The strips 150 and 160 are positioned respectively at locations on the fibrous texture 140 corresponding to the axial zones of the first and second local reinforcement portions 12, 13 to be formed in the outer shell of the intermediate casing.

[0050] Advantageously, the fiber preform constitutes a complete tubular fiber reinforcement of the outer shell of the intermediate casing forming a single piece with at least one portion in which a textile strip is added in order to form a local reinforcement portion (in the example described here two textile strips each forming two local reinforcement portions).

[0051] For this purpose, the mandrel 200 has an external surface 201 whose profile corresponds to the internal surface of the external shell to be produced. By being wound on the mandrel 200, the fibrous texture 140 matches the profile thereof. The mandrel 200 also comprises two flanges 220 and 230 to form parts of fibrous preform corresponding to the flanges 11 and 14 of the external shell 10.

[0052] When forming the fiber preform by winding, the fiber texture 140 and the textile strips 150 and 160 are drawn from drums 60 and 70 respectively on which they are stored as illustrated in [Fig.5].

[0053] [Fig. 6] shows a sectional view of the fiber preform 300 obtained after winding the fiber texture 140 and the textile strips 150 and 160 in several layers on the mandrel 200. The number of layers or turns depends on the desired thickness and the thickness of the fiber texture. It is preferably at least equal to two. In the example described here, the preform 300 comprises four layers 141 to 144 of fiber texture 140, three layers 151 to 153 of textile strip 150 and three layers 161 to 163 of textile strip 160 interposed respectively between the adjacent layers 141 and 142, 142 and 143, and 143 and 144.

[0054] A fiber preform 300 is obtained with a first reinforcing preform part 31 formed by the interposition of the layers 151 to 153 of the textile strip 150 between the superimposed layers 141 to 144 of the fiber texture 140 and a second reinforcing preform part 32 formed by the interposition of the layers 161 to 163 of the textile strip 160 between the superimposed layers 141 to 144 of the fiber texture 140. The fiber preform 300 also comprises flange preform parts 31 and 32 corresponding to the flanges 11 and 14 of the outer shell 10 of the intermediate casing of the bypass turbojet engine.

[0055] As indicated above, the axial zones or extents on which it is desired conferring particular mechanical properties is determined by the width l150 of the textile strip 150 and by the width l160 of the textile strip 160 (figures 4 and 6).

[0056] When it is desired to form a local reinforcement portion having improved non-perforating impact resistance, a textile strip is preferably used comprising fibers having a high strain at break, i.e., fibers having an elongation at break greater than or equal to 1.7%, such as, for example, carbon fibers having an elongation at break greater than 2% or glass fibers having an elongation at break greater than 5%. The textile strip may consist of one or more unidirectional (UD), two-dimensional (2D), multiaxial plies (NCF) or flat braid layers or plies. Structures that are easily deformable, i.e., that do not exhibit sagging, such as UD layers or multiaxial plies, are preferably used for the textile strip. In the case of 2D layers, weave weaves having low sagging, such as satin weaves, will be used.The fibers may be oriented in the same direction as the warp and / or weft yarns of the fiber texture 140 or in a different direction.

[0057] The width of the textile strip has a width preferably corresponding to substantially 10% of the width of the preform in the axial direction DA.

[0058] When it is desired to form a local reinforcement portion having improved stiffness, a textile strip is preferably used comprising fibers having a Young's modulus of between 350 GPa and 500 GPa, such as, for example, Torayca® carbon fibers type M40 or M46J marketed by the company Toray or Tenax™ carbon fibers type UMS40 or UMS45 marketed by the company Teijin. The textile strip may consist of one or more unidirectional (UD), two-dimensional (2D) or multiaxial (NCF) layers or plies.The fibers of the textile strip may be oriented according to the direction(s) in which it is desired to improve or increase the stiffness, in particular in directions different from the direction of the warp threads or strands in the fiber reinforcement of the outer shell of the intermediate casing, i.e. in a direction different from the circumferential direction Dc and / or the direction of the weft threads or strands in the fiber reinforcement of the outer shell of the intermediate casing, i.e. in a direction different from the axial direction DA. The fibers of the textile strip may in particular be oriented at an angle of 30°, 45° or 60° relative to the direction of the warp and / or weft threads or strands of the fiber reinforcement of the outer shell corresponding to the fiber preform.In the case where it is desired to orient the fibers of the fibrous strip in a single direction different from that of the warp and / or weft threads or strands of the fiber reinforcement of the external shell, it is possible to use UD layers oriented according to the chosen angle. In the case where one . wishes to orient the fibers of the fibrous web in several directions different from that of the warp and / or weft yarns or strands, it is possible to use 2D layers or a multiaxial web (NFC) (2 superimposed UD layers) to form a textile web having two different fiber directions relative to the direction of the warp and / or weft yarns or strands of the fiber reinforcement of the outer shell, for example following an orientation ±45°. To form a textile web having more than two different fiber directions relative to the direction of the warp and / or weft yarns or strands of the fiber reinforcement of the outer shell, it is possible to use a multiaxial web (n superimposed UD layers), each UD layer of the web being oriented in a determined direction or angle.An orientation of the fibres of the textile strip at ± 45° relative to the direction of the warp and / or weft threads or strands of the fibre reinforcement of the external shell makes it possible to reinforce the shear / torsion resistance of the external shell.

[0059] The width of the textile strip has a width preferably corresponding to substantially 15% of the width of the preform in the axial direction DA.

[0060] The fiber preform 300 is then densified using a matrix.

[0061] The densification of the fiber preform consists of filling the porosity of the preform, in all or part of its volume, by the material constituting the matrix.

[0062] The matrix can be obtained in a manner known per se using the liquid method.

[0063] The liquid method 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 a resin, optionally diluted in a solvent. The fibrous preform is placed in a mold that can be closed in a sealed manner with a housing having the shape of the final molded part. As illustrated in [Fig. 7], the fibrous preform 300 is here placed between a plurality of sectors 240 forming a counter-mold and the mandrel 200 forming a support, these elements having respectively the external shape and the internal shape of the intermediate casing shell of a bypass turbojet to be produced. Then, the liquid matrix precursor, for example a resin, is injected into the entire housing to impregnate the entire fibrous part of the preform.

[0064] The transformation of the precursor into an organic matrix, namely its polymerization, is carried out by heat treatment, generally by heating the mold, after removal of any solvent and crosslinking of the polymer, the preform still being maintained in the mold having a shape corresponding to that of the part to be produced. The organic matrix can be obtained in particular from epoxy resins, such as, for example, a high-performance epoxy resin present in the trade, or liquid precursors of carbon or ceramic matrices.

[0065] 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. For example, liquid carbon precursors may be resins with a relatively high coke content, such as phenolic resins, while liquid ceramic precursors, in particular SiC, may be resins of the polycarbosilane (PCS) or polytitanocarbosilane (PTCS) or poly-silazane (PSZ) type. Several consecutive cycles, from impregnation to heat treatment, may be carried out to achieve the desired degree of densification.

[0066] According to one aspect of the invention, the densification of the fiber preform can be carried out by the well-known transfer molding process known as RTM ("Resin Transfer Molding"). According to the RTM process, the fiber preform is placed in a mold having the shape of the intermediate casing shell of a bypass turbojet to be produced. A thermosetting resin is injected into the internal space delimited between the mandrel 200 and the counter-molds 240 and which comprises the fiber preform. A pressure gradient is generally established in this internal space between the place where the resin is injected and the orifices for discharging the latter in order to control and optimize the impregnation of the preform by the resin.

[0067] The resin used may be, for example, an epoxy resin. Resins suitable for RTM processes are well known. They preferably have a low viscosity to facilitate their injection into the fibers. The choice of temperature class and / or the chemical nature of the resin is determined according to the thermomechanical stresses to which the part must be subjected. Once the resin has been injected throughout the reinforcement, it is polymerized by heat treatment in accordance with the RTM process.

[0068] After injection and polymerization, the outer shell is demolded. Finally, the outer shell is trimmed to remove excess resin and the chamfers are machined to obtain the outer shell 10 of the intermediate casing of a bypass turbojet engine illustrated in Figures 1 and 2.

[0069] In addition to conferring or improving the mechanical properties of the outer shroud 10 of the intermediate casing of a dual-flow turbojet, the local reinforcement portions 12 and 33 can be used for fixing the outer ends of the fan guide blades, for example by means of the bolt-type assembly members 320 ([Fig. 1]).

Claims

Claims

1. Method for manufacturing an outer shell of an intermediate casing of a turbojet engine, comprising: - producing by three-dimensional weaving between a plurality of warp threads or strands and a plurality of weft threads or strands a fibrous texture (140) of varying thickness in the form of a strip, - winding the fibrous texture (140) over several superimposed turns (141, 142, 143, 144) on a mandrel (200) of profile corresponding to that of the outer shell of the intermediate casing to be manufactured in order to obtain a fibrous preform (300) of revolution shape corresponding to that of the outer shell of the intermediate casing to be manufactured and extending in width in an axial direction (DA) and in thickness in a radial direction (DR), - densifying the fibrous preform (300) by a matrix, characterized in that, during the winding of the fibrous texture (140) on the mandrel (200),at least one textile strip (150) is placed at least between one or more adjacent turns of the fibrous texture, on the inner face of the first winding turn of the fibrous texture, or on the outer surface of the fibrous texture, each textile strip (150) having a structure different from a three-dimensional weave, each textile strip having a width less than the width of the fibrous texture (140) in the axial direction.,

2. Method according to claim 1, wherein the width (1150) of said at least one textile strip (150) in the axial direction is between 2% and 50% of the width of the fibrous preform (300).

3. The method of claim 2, wherein said at least one textile strip is formed with fibers having an elongation at break greater than or equal to 1.7%.

4. A method according to claim 2 or 3, wherein said at least one textile strip is made up of one or more unidirectional, two-dimensional layers or plies of multiaxial webs or flat braids.

5. The method of claim 4, wherein said at least one textile strip is made of one or more two-dimensional layers having a satin-type weave.

6. Method according to any one of claims 2 to 5, wherein the width (1150) of said at least one textile strip (150) in the axial direction corresponds to 10% of the width of the fibrous preform (300).

7. The method of claim 2, wherein said at least one textile strip is formed with fibers having a Young's modulus of between 350 GPa and 500 GPa.

8. Method according to claim 7, wherein said at least one textile strip consists of one or more unidirectional, two-dimensional or multiaxial layers or plies (NCF), the fibers of said at least one textile strip being oriented in one or more directions different from the direction of the warp threads or strands and / or the direction of the weft threads or strands of the fiber texture.

9. Method according to claim 7, in which the fibers present in said at least one textile strip are oriented at an angle of ± 45° relative to the direction of the warp and / or weft threads or strands of the fibrous texture.

10. Method according to any one of claims 7 to 9, wherein the width (li50) of said at least one textile strip (150) in the axial direction corresponds to 15% of the width of the fibrous preform (300).

11. A method according to any one of claims 1 to 10, wherein, when winding the fibrous texture (140) onto the mandrel (200), first and second textile strips (150, 160) are placed at least between one or more adjacent turns of the fibrous texture, on the inner face of the first winding turn of the fibrous texture, or on the outer surface of the fibrous texture, the first and second textile strips being offset from each other in the axial direction (Da) in the fibrous preform.

12. Outer shell (10) of an intermediate casing (30) of a dual-flow turbojet engine made of composite material manufactured in accordance with the method according to any one of claims 1 to 11.

13. Intermediate casing (30) of a bypass turbojet engine (1) comprising a core (31), an outer casing shroud (10) according to claim 12 and a plurality of radial guide vanes (32) extending between said hub and said outer casing shroud.

14. A gas turbine aero engine having an intermediate casing according to claim 13.

Images