Fibrous preform intended to form a reinforcement of a part made of composite material

Abstract

The invention relates to a fibrous preform (40) formed by a plurality of superposed fibrous layers (20af; 20bf; 20cf; 20df) and comprising a first annular region (42) and a second flange region (43) extending from an axial edge (BA42) of the first region, the preform comprising a first layer A (20af) of unidirectional fibers oriented at an angle (a1) of between -10° and +100 relative to a circumferential direction (DC), which is formed by continuous fibers (24a) on the first region and by discontinuous fibers (25a) distributed in a plurality of rows (R1f... Rnf) on each second region, wherein a circumferential spacing (e1; en) between adjacent discontinuous fibers of the same row increases with increasing distance from the axial edge of the first region.

Description

Description Title of the invention: Fibrous preform intended to form a reinforcement for a part made of composite material Technical Field

[0001] This presentation concerns composite material parts for propulsion systems such as fan housings, air intakes or thrust reversers for aircraft engines, as well as associated manufacturing processes. Previous technique

[0002] Organic matrix composites (OMCs) can withstand temperatures ranging from 100°C to 250°C. These materials replace metallic components in certain parts of turbomachinery. Furthermore, their use helps optimize the performance of turbomachinery and its components, notably by reducing the overall mass of the turbomachine, thereby decreasing fuel consumption, which in turn leads to a reduction in harmful emissions (CO, CO2, NOx, etc.).

[0003] It is known to produce parts from composite materials by draping pre-impregnated fibrous structures onto a surface. For reasons of production cost and repeatability, the draping can be performed automatically, using the automated fiber placement (AFP) technique. An example of a manufacturing process for a composite part using the AFP method is described in US patent 2020 / 001504.

[0004] However, when it is desired to produce parts comprising a body of partial revolution at the end or ends of which flanges extend, with a restricted angle between the body and at least one flange, in particular an acute angle of 90° or less, the head or roller for depositing fibrous structures may not allow access to the bottom of said angle.

[0005] To address this machine access issue, it has been proposed, for example in document WO 2012 / 046020, to drape the part(s) corresponding to the radial part(s) in a corrugated shape and then straighten all the corrugations. The draping is carried out by draping the portion intended to form the flange in line with the draping. The portion intended to form the cylindrical body is then deformed. Next, the portion intended to form the flange is deformed to position it perpendicular to the axis of revolution of the body. During draping, the flange exhibits circumferential undulations of increasing amplitude as one approaches the free end of the portion, resulting in a smooth flange after deformation. However, this method has the disadvantage of requiring complex tooling and necessitates a relatively slow draping process.

[0006] It is desirable to be able to manufacture, in a relatively simple and rapid manner, a part made of composite material in the shape of an annulus comprising one or more flanges by a technique that overcomes the limitations related to the size of the dispensing head. Description of the invention

[0007] The present exposition relates to a fibrous preform intended to form a reinforcement of a composite material part for a propulsion assembly, the preform being formed by several superimposed fibrous layers and comprising a first annular region and at least a second flange region extending from an axial edge of the first region and transverse to the latter, the preform comprising at least a first layer A of unidirectional fibers, oriented at an angle between -10° and +10° with respect to a circumferential direction, which is formed by continuous fibers on the first region and by discontinuous fibers distributed in several rows on each second region, said rows each extending along the circumferential direction and being offset along a radial direction,a circumferential spacing between adjacent discontinuous fibers in the same row increasing with distance from the axial edge of the first region in proportion to the increase in local circumference, and the discontinuous fibers being selectively located on the second region(s).

[0008] The invention implements at least one layer A formed of discontinuous fibers on each second flange region. These fibers are capable of spreading apart when the second region is folded over the corresponding forming element, thus adapting to the local circumference variation along the flange. Forming the flange(s) by folding after winding eliminates the need to directly drape the flange region(s) into shape, thereby overcoming the limitations encountered in the prior art related to the size of the dispensing head. Furthermore, the discontinuous fibers, due to their spreading capacity, allow the use of a forming element. directly to the shape of the flange to be obtained, thus significantly simplifying the method compared to the prior art solution using a corrugated form that is then deformed. The characteristics relating to the manufacture of the preform will be detailed further below.

[0009] In one example of an embodiment, the discontinuous fibers have a median length between 40 mm and 150 mm.

[0010] The use of discontinuous fibers with a median length of at least 40 mm further improves mechanical performance. Limiting this length to 150 mm, on the other hand, facilitates the forming of the flange region(s) by folding them onto a die.

[0011] In particular, discontinuous fibers can have a median length between 40 mm and 80 mm.

[0012] In one embodiment, the fibrous preform further comprises a second layer A of unidirectional fibers, the second layer A being in contact with the first layer A and the discontinuous fibers of the second layer A connecting adjacent discontinuous fibers of the first layer A.

[0013] Such a characteristic further improves mechanical performance by allowing the forces to be transferred between the opposing layers by shearing the matrix connecting these layers, providing continuity of mechanical strength in the circumferential direction.

[0014] In one embodiment, the fibrous preform further comprises one or more additional layers of unidirectional fibers oriented at an angle distinct from the fibers of the first layer A, and of the possible second layer A.

[0015] Such a characteristic allows for fine parameterization of the fibrous orientation of the constituent layers of the preform according to the expected stresses for the intended application in order to optimize the performance of the part.

[0016] In particular, the fibrous preform may comprise at least two additional layers of unidirectional fibers oriented at an angle distinct from the fibers of the first layer A and the possible second layer A, one of these additional layers having unidirectional fibers oriented at an angle between +20° and +90° with respect to the circumferential direction, and another of these additional layers having unidirectional fibers oriented at an angle between -90° and -20° with respect to the circumferential direction.

[0017] More specifically, the preform may include, in addition to the first layer A and the possible second layer A: - a first additional layer of unidirectional fibers oriented at an angle between +20° and +70°, for example between +35° and +55°, relative to the circumferential direction, - a second additional layer of unidirectional fibers oriented at an angle between +80° and +100°, for example between +85° and +95°, with respect to the circumferential direction, and - a third additional layer of unidirectional fibers oriented at an angle between -70° and -20°, for example between -55° and -35°, relative to the circumferential direction.

[0018] In one embodiment, the fibrous preform comprises a single second flange region or several second flange regions, each extending from the same axial edge of the first region.

[0019] Such a feature relates to the case of a so-called "L-shaped" structure to which the invention can be applied. Generally speaking, it should also be noted that a flange region can extend over the entire circumference of the preform or only over an angular sector thereof, depending on the intended application.

[0020] Alternatively, the fibrous preform includes at least one second flange region extending from a first axial edge of the first region, and an additional second flange region extending from a second axial edge of the first region opposite the first axial edge.

[0021] Such a characteristic relates to the case of a so-called "U-shaped" structure to which the invention can also be applied.

[0022] In one example of the implementation, the constituent layers of the preform have a thickness between 0.04 mm and 0.5 mm.

[0023] Such a characteristic contributes advantageously to optimizing the compromise between mechanical performance and draping speed.

[0024] In particular, the constituent layers of the preform can have a thickness of between 0.1 mm and 0.3 mm.

[0025] In one embodiment example, the preform is a preform of an air inlet lip of a turbomachine nacelle, a preform of a turbomachine fan casing or a preform of a thrust reverser.

[0026] The present presentation also relates to a composite material part for a propulsion assembly, comprising a fibrous reinforcement formed by a fibrous preform as described above, and an organic matrix densifying a porosity of the fibrous preform.

[0027] This presentation also concerns a manufacturing process for a fibrous preform as described above, comprising: - the draping of the superimposed fibrous layers constituting the preform onto a support form, - the winding of the superimposed layers thus draped over an inner surface of a mandrel, distinct from the support form, the mandrel having an annular portion opposite the first region and at least one flange intended to form a flange, and - the forming of each second region by folding the superimposed and rolled layers onto the flask transversely to the first region, this folding producing an increase in the circumferential spacing between the adjacent discontinuous fibers of the same row when moving away from the axial edge of the first region in proportion to the increase in local circumference.

[0028] This presentation also concerns a manufacturing process for a fibrous preform as described above, comprising: - the draping of the superimposed fibrous layers constituting the preform onto an annular outer surface of a mandrel, the first region being opposite this surface, - the positioning of one or more forming elements intended to form the flange(s) on the first region thus wound, and - the forming of the second region(s) by folding the superimposed and rolled layers onto the forming element(s) transverse to the first region, this folding producing an increase in the circumferential spacing between adjacent discontinuous fibers of the same row when moving away from the axial edge of the first region in proportion to the increase in local circumference.

[0029] The aforementioned features and advantages, as well as others, will become apparent upon reading the detailed description that follows, which refers to the attached drawings. Brief description of the drawings

[0030] The attached drawings are schematic and are primarily intended to illustrate the principles of the presentation.

[0031] In these drawings, from one figure to another, identical elements (or parts of elements) are identified by the same reference symbols. [Fig. 1] Figure 1 is a perspective and partial sectional view of an aircraft engine equipped with a fan housing made of composite material according to one embodiment of the invention. [Fig. 2] Figure 2 is a cross-sectional view along plane II-II of the housing of Figure 1. [Fig. 3] Figure 3 represents a succession of steps of an example of a process according to the invention. [Fig. 4] Figure 4 represents, schematically and partially, a strip formed by superimposed layers of unidirectional fibers intended to form an example of a fibrous preform according to the invention after winding. [Fig. 5] Figure 5 shows a detail of the band in Figure 4. [Fig. 6] Figure 6 schematically and partially represents the shaping of the strip on a mold to obtain the example of fibrous preform according to the invention. [Fig. 7] Figure 7 represents, schematically and partially, the example of fibrous preform according to the invention obtained after the shaping illustrated in Figure 6. [Fig. 8] Figure 8 represents, schematically and partially, the placement of a counter-mold on the example of fibrous preform of figure 7 in order to obtain the part in composite material from it. [Fig. 9] Figure 9 represents, schematically and partially, a first step of a variant of a manufacturing process for a fibrous preform according to the invention. [Fig. 10] Figure 10 schematically and partially represents a second step of the variant of the manufacturing process for a fibrous preform according to the invention. [Fig. 11] Figure 11 schematically and partially represents a detail of another example of a fibrous preform according to the invention in cross-section to a second region at a given radial position. [Fig. 12] Figure 12 represents, schematically and partially, another example of a part made of composite material according to the invention. Description of the implementation methods

[0032] To make the explanation more concrete, the following description is provided with reference to the attached drawings. It should be noted that the invention is not limited to these examples.

[0033] The invention applies generally to any composite material component for a propulsion system that extends circumferentially around an axis, forming, for example, a duct. Such components for propulsion systems include, but are not limited to, gas turbine fan housings, nacelle air intakes, and nacelle cowlings found in aircraft engines. The component may be a part of revolution. The component may also have a pseudo-annular shape, that is, an open ring.

[0034] The invention will be described below in the context of its application to a fan housing for an aircraft gas turbine engine, but a person skilled in the art will recognize that the invention can be applied to other types of parts and, in particular, to parts comprising only a single flange.

[0035] Such an engine, as schematically shown in Figure 1, comprises, from upstream to downstream in the direction of airflow, a fan 1 located at the engine inlet, a compressor 2, a combustion chamber 3, a high-pressure turbine 4, and a low-pressure turbine 5. The engine is housed within a casing comprising several parts corresponding to different engine components. Thus, the fan 1 is surrounded by a fan casing 100.

[0036] The blower 1 allows the aspiration of an airflow to which two independent circulations are imposed, to form a primary airflow (hot flow) and a secondary airflow (cold flow).

[0037] The air from the primary stream can, for example, be compressed within the compressor 2 and then mixed with a fuel and burned within the combustion chamber 3. The gases expelled from the combustion chamber can pass through the high-pressure turbine 4 and then the low-pressure turbine 5 before undergoing acceleration through a nozzle.

[0038] The secondary flow, on the other hand, bypasses the hot part of the reactor.

[0039] Compressor 3 and turbines 4, 5 comprise several stages of fixed blades (called "stators") and moving blades (called "rotors").

[0040] The moving blades consist of a ring of blades mounted radially on a disc, which drives a rotating shaft under the effect of a passing air or gas flow. Each blade comprises a blade connected to a foot that is fitted into a groove in the disc to hold the blade in place during the operation of the turbomachine.

[0041] Fixed blades, usually positioned between each stage of moving blades, allow the airflow to be straightened before the flow enters the next stage of moving blades.

[0042] In this exposition, the terms 'axial', 'radial', 'circumferential', and their derivatives are defined with respect to the main axis of the turbomachine, and the terms 'upstream' and 'downstream' are defined with respect to the airflow in the turbomachine.

[0043] Figure 2 shows a profile of a fan casing 100 made of composite material as obtained by a process according to the invention. The internal surface 101 of the casing defines the air inlet duct. It can be provided with a layer of abradable coating 102 along the path of the fan blade tips, one blade 13 being partially shown schematically. The abradable coating is therefore disposed over only a portion of the length (in the axial direction) of the casing. A coating of acoustic treatment (not shown) can also be placed on the internal surface 101 in particular upstream of the abradable coating 102.

[0044] The housing 100 can be fitted with external flanges 104, 105 at its upstream and downstream ends to allow for its mounting and connection with other components. The housing 100 is made of a fiber-reinforced composite material densified by a matrix. The reinforcement is made of fibers, for example, carbon, glass, or aramid, and the matrix is ​​made of a polymer, for example, epoxy, bismaleimide, or polyimide.

[0045] In the example described here, the fibrous reinforcement is formed by winding a fibrous strip onto a mandrel, the mandrel having a profile corresponding to that of the housing to be made.

[0046] The following section describes an example of a manufacturing process for a fibrous preform according to the invention, and an associated part.

[0047] Figure 3 represents a sequence of steps of an example of a process according to the invention.

[0048] In the example considered here, a fibrous strip 20, formed by superimposed layers 20a-20d of unidirectional fibers, is first produced on a support mold, which is generally flat (not shown) (step E10). Flat draping advantageously eliminates the constraints related to the size of the dispensing head. The strip 20 extends along a longitudinal axis X and is laterally delimited by two lateral edges BL20. The layers 20a-20d can be in contact with each other, as illustrated. The invention is not limited to draping on a flat form and the fibrous preform can, according to one variant, be directly draped on an annular form as will be described later in relation to figures 9 and 10. In the illustrated example, the strip 20 comprises four superimposed layers 20a-20d each having a predetermined fibrous orientation which is a function of the desired application for the part in composite material.Of course, a person skilled in the art will recognize that the invention is not limited to the orientation or number of layers illustrated for the strip and that these parameters are adjusted according to the objective sought.

[0049] The strip 20 comprises a first layer 20a of unidirectional fibers 24a, 25a oriented at an angle cii between -10° and +10° with respect to the X-axis. The angle eu can, for example, be between -5° and +5° and is substantially zero (0°) in the illustrated example. The first layer 20a constitutes, in the illustrated example, the outer layer of the strip 20, although the invention is not limited to this configuration.

[0050] The band 20 includes a first region 22 corresponding to a central zone in the direction of the width of the band 20 and, in the illustrated example, two second regions 23 each present on the side of an edge BL20, the first region 22 being located between the second regions 23.

[0051] The first layer 20a is formed by continuous unidirectional fibers 24a in the first region 22 and by discontinuous unidirectional fibers 25a in every other region 23. The discontinuous fibers 25a are arranged in several rows RI ... Rn in every other region 23. The RI ... Rn rows each extend along the X-axis. The RI ... Rn rows may be parallel to each other. Different techniques can be used to form the discontinuous fibers 25a, such as Automated Fiber Placement (AFP) or continuous fiber incision. The strip 20 may be pre-impregnated with a resin, the resin contributing to the cohesion of the layers 20a-20d, or dry. In the latter case, a fugitive binder may be deposited to ensure the cohesion of the strip.In general, the 25a fibers are selectively located on the second regions 23, that is to say, only present on the second regions 23. The 25a fibers are therefore not present over the entire width of the band 20, but only on the second regions 23, and therefore in particular not on the first region 22.

[0052] In the illustrated example, the 25a fibers have the same length I (measured along the X-axis), but this does not, of course, depart from the scope of the invention if they exhibit a variation in length. The discontinuous fibers may have a median length greater than or equal to 40 mm, for example, between 40 mm and 150 mm or even between 40 mm and 80 mm.

[0053] Band 20 here includes additional layers 20b-20d of unidirectional fibers oriented at an angle distinct from the fibers 24a, 25a of the first layer 20a. More specifically, in the illustrated example, band 20 includes an additional layer 20b of unidirectional fibers 24b oriented at an angle 02 between +20° and +70°, for example between +35° and +55°, with respect to the X-axis. Angle 02 can, for example, be between +40° and +50° and is here approximately equal to +45° in the illustrated example. The band 20 further comprises another additional layer 20c of unidirectional fibers 24c which are oriented at an angle 03 between +80° and +100° with respect to the X axis. The angle 03 can for example be between +85° and +95° and is here approximately equal to +90° in the illustrated example.The band 20 further comprises another additional layer 20d of unidirectional 24d fibers which are oriented at an angle 04 between -70° and -20°, par. For example, the angle between -55° and -35°. The angle eu can, for instance, be between -50° and -40° and is approximately -45° in the illustrated example. Along the thickness of strip 20, the illustrated example shows, in this order, the first layer 20a, the additional layer 20b, the additional layer 20c, and the additional layer 20d. The fibers 24b-24d of the additional layers 20a-20d can be continuous fibers. The fibers 24b-24d can extend across the entire width of the strip 20. The fibers 24b-24d can be uniformly distributed across the width and length of the strip 20. Generally, the layers 20a-20d constituting the strip 20 can have a thickness eo greater than or equal to 0.04 mm, for example, between 0.04 mm and 0.5 mm or even between 0.04 mm and 0.3 mm. The thickness eo can be greater than or equal to 0.1 mm, for example, between 0.1 mm and 0.5 mm or even between 0.1 mm and 0.3 mm.

[0054] The strip 20 is then shaped to obtain the fibrous preform of the part to be produced (step E20). This shaping is illustrated in Figures 6 and 7, where the strip 20 is draped over an internal surface Si of a mandrel 30 whose profile corresponds to an external surface of the housing to be produced. For the sake of simplicity, Figures 6 and 7 only show half of an angular segment of the mandrel 30, it being understood that a similar shaping process is carried out on the unshown areas of the mandrel 30. The strip 20 is wound around the mandrel 30 to form one or more turns. By winding it around the mandrel 30, the strip 20 conforms to its profile. The mandrel 30 includes an annular portion 32 and two flanges 34, located on either side, to form the flanges 104 and 105 of the housing 100.The shaping process involves positioning the first region 22 on the portion 32 (arrow Fl) and folding the second regions 23 onto the flanges 34 (arrow F2). This results in the fibrous preform 40 of the housing to be obtained, as illustrated in Figure 7, which comprises a fibrous stack formed by the turn(s) of the strip 20. The preform 40 here comprises a first annular region 42 and two second flange regions 43. Generally, the first region 42 can have a cylindrical or frustoconical shape, allowing, in particular, a variation in its cross-section in an axial direction DA, as can be the case in a blower housing. Thus, the generatrix of the first region 42 can form a non-zero angle of less than or equal to 20%, for example, 15%, with the direction DA. In a particular case, the first region 42 can have a cylindrical shape.Each second region 43 extends from a respective axial edge BA42 of the first region 42. Each second region 43 is transverse to the first region 42. The first region 42 is located between the second regions 43. Each second region 43 can form, with the. first region 42, an angle P less than or equal to 120°, for example less than or equal to 100°, for example between 80° and 100°, for example approximately 90° as illustrated.

[0055] The preform 40 here comprises four superimposed layers 20af, 20bf, 20cf and 20df, each having a predetermined fibrous orientation, which correspond to the layers 20a-20d previously described, once shaped by folding over the flanges 34.

[0056] Thus, the preform 40 comprises, in particular, the first layer 20af of unidirectional fibers 24a, 25a oriented at an angle cii between -10° and +10° with respect to the circumferential direction DC. The angle eu can, for example, be between -5° and +5° and is approximately zero (0°) in the illustrated example. The fibers 24a, 25a of the first layer 20af (and of any additional layers 20bf-20df) are, for example, made of carbon, glass, or aramid, or a mixture of such fibers. The layer 20a comprises the rows Rlf ... Rnf of discontinuous fibers 25a, which correspond to the rows RI ... Rn described previously, once formed by folding onto the flanges. The rows Rlf ... Rnf which each extend along the DC direction, these rows being offset from each other along a radial DR direction.

[0057] As mentioned above for band 20, the first layer 20af is formed by the continuous unidirectional fibers 24a in the first region 42 and by the discontinuous unidirectional fibers 25a in each second region 43. Generally, the fibers 25a are selectively located in the second regions 43, i.e., they are present only in the second regions 43. Therefore, the fibers 25a are not present across the entire width of the preform 40, measured along the axial direction DA, but only in the second regions 43, and thus specifically not in the first region 42. The second regions 43 are non-cylindrical and extend along the direction DR.

[0058] Following the folding onto the flanges 34, the fibers 25a move apart from each other according to the increase in perimeter corresponding to the increase in local radius along the radial surface of the corresponding flange 34. Each second region 43 thus exhibits a circumferential spacing between adjacent discontinuous fibers 25a of the same row Rlf ... Rnf that increases with distance from the axial edge BA42 of the first region 42 in proportion to the increase in local circumference. Thus, the spacing el between adjacent discontinuous fibers 25a of the first row Rlf, closest to the axial edge BA42, is less than the spacing en between adjacent discontinuous fibers 25a of the last row Rnf, which is furthest from the axial edge BA42. More precisely, the ratio en / el corresponds approximately to the ratio of local circumference. between the areas covered by the Rnf and Rlf rows. Thus, due to the folding onto the flanges 34, the spacing between the fibers 25a is modified relative to the spacing in the strip insofar as the circumference increases the closer one moves towards a free end 43e of the second regions 43. Thus, the spacing of the fibers 25a increases the closer one approaches the end 43e. The fibers 25a can be substantially parallel to each other, and to the fibers 24a.

[0059] The characteristics described above for the length I of the discontinuous fibers in the strip remain applicable to the discontinuous fibers after shaping.

[0060] The fiber orientations described above for layers 20b-20d remain largely applicable to the 20bf-20df layers obtained after forming, with the orientations in layers 20bf-20df being measured relative to the DC direction. The fibers in layers 20b-20d move only slightly apart when folded onto the flanges.

[0061] Thus, in the illustrated example, the preform 40 comprises an additional layer 20bf of unidirectional fibers 24b oriented at an angle 02 between +35° and +55° to the DC direction. Angle 02 can, for example, be between +40° and +50° and is approximately +45° in the illustrated example. The preform 40 also comprises another additional layer 20cf of unidirectional fibers 24c oriented at an angle 03 between +80° and +100° to the DC direction. Angle 03 can, for example, be between +85° and +95° and is approximately +90° in the illustrated example. The preform 40 further comprises another additional layer 20df of unidirectional fibers 24d oriented at an angle 04 between -55° and -35°. Angle 04 can, for example, be between -50° and -40° and is here approximately equal to -45° in the illustrated example.In the direction of the thickness of the preform 40, the illustrated example shows, in succession in this order, the first layer 20af, the additional layer 20bf, the additional layer 20cf, and the additional layer 20df. The fibers 24b-24d of the additional layers 20bf-20df can be continuous fibers. The fibers 24b-24d can extend across the entire width of the preform 40. The fibers 24b-24d can be uniformly distributed across the width and circumference of the preform 40. The details relating to the thickness ep of the layers 20a-20d described above remain applicable to the layers 20af-20df.

[0062] The preform 40 is then densified by an organic matrix.

[0063] The matrix can be obtained using a method known per se via a liquid process, for example by resin transfer molding (RTM) or by infusion. The liquid process consists of impregnating the preform with a composition liquid containing an organic precursor of the matrix material. The organic precursor is usually in the form of a polymer, such as a resin, possibly diluted in a solvent.

[0064] The fibrous preform is placed in a mold that can be sealed tightly with a cavity having the shape of the final molded part. As illustrated in Figure 8, the preform 40 is placed here between a plurality of sectors 50 forming a counter-mold and the mandrel 30 forming a support, these elements having respectively the external and internal shape of the housing to be produced (step E30).

[0065] If the preform 40 is not pre-impregnated with the matrix material, the liquid matrix precursor, for example a resin, is then injected throughout the cavity to impregnate the preform 40 (step E40). The transformation of the precursor into an organic matrix, namely its polymerization, is carried out by heat treatment, generally by heating the mold, after removing any solvent. The preform remains in the mold, which has a shape corresponding to that of the part to be produced. The organic matrix can be obtained, in particular, from an epoxy, bismaleimide, or polyimide resin. Alternatively, a thermoplastic polymer can be injected, and the part can then be obtained by simple cooling (without crosslinking).

[0066] According to another variant, the preform 40 is already pre-impregnated with the matrix material and the organic matrix can then be obtained following heat treatment to crosslink the resin impregnating the fibers.

[0067] After injection and polymerization, the part is demolded. Finally, the part is trimmed to remove excess resin and the chamfers are machined to obtain the housing 100 illustrated in figures 1 and 2.

[0068] We have just described an example of a manufacturing process for a fibrous preform according to the invention, in which the strip is first draped flat to overcome the limitations related to the size of the dispensing head, then wound inside an annular mandrel where it is shaped with discontinuous fibers separated in the second flange regions. However, the invention is not limited to this embodiment, as will be detailed below with reference to Figures 9 and 10.

[0069] Figures 9 and 10 illustrate another manufacturing example where the strip 20 is directly draped over an annular outer surface Se of a mandrel 320, and where, after draping, one or more forming elements 340 are then brought in to form the second flange regions by folding them over (arrows F12). The process then continues in a similar manner to that described above to obtain the part. The characteristics described above for the constituent layers 20a-20f of the preform remain applicable to this embodiment.

[0070] Figure 11 illustrates a variant where the second region of the preform comprises two superimposed layers A 201af, 202af in contact with each other. The discontinuous fibers 251a of layer 201af connect adjacent discontinuous fibers 252a of layer 202af. Layers 201af and 202af each have the fibrous orientation characteristics described above for layer 20af, that is, they are each formed by unidirectional fibers oriented at an angle between -10° and +10° with respect to the DC direction.They are each formed by continuous fibers on the first region and by discontinuous fibers 251a, 252a distributed in several rows on each second region, said rows each extending along the circumferential direction and being offset from each other along a radial direction, a circumferential spacing between adjacent discontinuous fibers of the same row increasing as one moves away from the axial edge of the first region in proportion to the increase in local circumference, and the discontinuous fibers being selectively localized on the second region(s).

[0071] Figure 12 illustrates a variant of part 110 according to the invention which includes an annular region 111 and a single flange 114 on an axial edge of the region 111.

[0072] Although the present invention has been described with reference to specific embodiments, it is evident that modifications and changes can be made to these examples without departing from the general scope of the invention as defined by the claims. In particular, individual features of the various embodiments illustrated / mentioned can be combined in additional embodiments. Therefore, the description and drawings should be considered in an illustrative rather than restrictive sense.

[0073] It is also evident that all the characteristics described with reference to a process are transposable, alone or in combination, to a device, and conversely, all the characteristics described with reference to a device are transposable, alone or in combination, to a process.

[0074] The expression "between ... and ..." should be understood as including the boundaries.

Claims

Demands

1. A fibrous preform (40) intended to form a reinforcement for a composite part (100) of a propulsion assembly, the preform being formed by several superimposed fibrous layers (20af; 20bf; 20cf; 20df; 201af; 202af) and comprising a first annular region (42) and at least a second flange region (43) extending from an axial edge (BA42) of the first region and transverse to it, the preform comprising at least a first layer A (20af; 201af; 202af) of unidirectional fibers, oriented at an angle (ai) between -10° and +10° with respect to a circumferential direction (DC), which is formed by continuous fibers (24a) on the first region and by discontinuous fibers (25a; 251a; 252a) distributed in several rows (Rlf ...Rnf) on each second region, said rows each extending along the circumferential direction and being offset along a radial direction (DR), a circumferential spacing (el; en) between adjacent discontinuous fibers of the same row increasing with distance from the axial edge of the first region in proportion to the increase in local circumference, and the discontinuous fibers being selectively localized on the second region(s).

2. Preform (40) according to claim 1, wherein the discontinuous fibers (25a; 251a; 252a) have a median length (I) between 40 mm and 150 mm.

3. Preform (40) according to claim 1 or 2, wherein the fibrous preform further comprises a second layer A (202af) of unidirectional fibers, the second layer A being in contact with the first layer A (201af) and the discontinuous fibers (252a) of the second layer A connecting adjacent discontinuous fibers (251a) of the first layer A.

4. Preform (40) according to any one of claims 1 to 3, wherein the fibrous preform further comprises one or more additional layers (20bf; 20cf; 20df) of unidirectional fibers oriented at an angle (a?; 03; 04) distinct from the fibers (24a; 25a; 251a; 252a) of the first layer A (20af; 201af), and of the possible second layer A (202af).

5. Preform (40) according to claim 4, wherein the fibrous preform comprises at least two additional layers (20bf; 20cf; 20df) of fibers unidirectional oriented with an angle (a? ; 03 ; 04) distinct from the fibers (24a ; 25a ; 251a ; 252a) of the first layer A (20af ; 201af) and of the possible second layer A (202af), one of these additional layers having unidirectional fibers oriented with an angle between +20° and +90° with respect to the circumferential direction (DC), and another of these additional layers having unidirectional fibers oriented with an angle between -90° and -20° with respect to the circumferential direction.

6. Preform (40) according to any one of claims 1 to 5, wherein the fibrous preform comprises a single second flange region or several second flange regions each extending from the same axial edge of the first region.

7. Preform (40) according to any one of claims 1 to 5, wherein the fibrous preform comprises at least a second flange region extending from a first axial edge of the first region, and a second additional flange region extending from a second axial edge of the first region opposite the first axial edge.

8. Preform (40) according to any one of claims 1 to 7, wherein the layers (20af; 20bf; 20cf; 20df; 201af; 202af) constituting the preform have a thickness (ep) between 0.04 mm and 0.5 mm.

9. Preform (40) according to any one of claims 1 to 8, wherein the preform is a preform of an air inlet lip of a turbomachine nacelle, a preform of a turbomachine blower casing (100) or a preform of a thrust reverser.

10. Part (100) of composite material for a propulsion assembly, comprising a fibrous reinforcement formed by a fibrous preform (40) according to any one of claims 1 to 9, and an organic matrix densifying a porosity of the fibrous preform.

11. A method for manufacturing a fibrous preform (40) according to any one of claims 1 to 9, comprising: - draping the superimposed fibrous layers (20a - 20d) constituting the preform onto a support form, - the rolling of the superimposed layers thus draped over an interior surface (Si) of a mandrel (30), distinct from the support form, the mandrel having an annular portion (32) opposite the first region (42) and at least one flange (34) intended to form a flange, and - the forming of each second region (43) by folding the superimposed and rolled layers onto the flask transversely to the first region, this folding producing an increase in the circumferential spacing (el ; en) between the adjacent discontinuous fibers (25a) of the same row (Rlf - Rnf) when moving away from the axial edge (BA42) of the first region in proportion to the increase in local circumference.

12. A method for manufacturing a fibrous preform (40) according to any one of claims 1 to 9, comprising: - the draping of the superimposed fibrous layers (20a - 20d) constituting the preform onto an annular external surface (Se) of a mandrel (320), the first region (42) being opposite this surface, - the positioning of one or more forming elements (340) intended to form the flange(s) on the first region thus wound, and - the forming of the second region(s) by folding the superimposed and rolled layers onto the forming element(s) transverse to the first region, this folding producing an increase in the circumferential spacing (el ; en) between the adjacent discontinuous fibers (25a) of the same row (Rlf - Rnf) when moving away from the axial edge (BA42) of the first region in proportion to the increase in local circumference on the forming element considered.

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