ACOUSTIC PANEL FOR AN AIRCRAFT TURBOMACHINE HOUSING

Abstract

The invention relates to an acoustic panel (2121-2) for a housing (200) of an aircraft turbomachine (100), comprising a sandwich structure, said structure comprising a cellular material (300) sandwiched between a first layer (302) of composite material on which rests a lower surface of the core, and a second layer (304) of composite material having perforations (PF304) and disposed on an upper face of the cellular material and opposite its lower surface, characterized in that the panel further comprises at least one non-woven strip (400) containing a fibrous and porous network comprising at least some carbon fiber scraps (402) having a length less than or equal to 160 mm, and a binder ensuring the cohesion of the fibers to each other and the stability of the strip, said strip covering at least a portion of the upper skin. Figure for the abstract: Figure 3A

Description

Title of the invention: ACOUSTIC PANEL FOR AN AIRCRAFT TURBOMACHINE HOUSING Technical field of the invention

[0001] The present invention relates to an acoustic panel for a casing of an aircraft turbomachine, a casing comprising this panel, a turbomachine comprising the casing, a panel on a casing, an assembly comprising at least this tooling and a panel, and a method for manufacturing this panel. Technological background

[0002] Generally, a turbomachine 100, in particular an aircraft turbomachine, as illustrated in [Fig.1A], comprises from upstream to downstream (i.e. in the direction of flow of the gas flows F), a blower 110, one or more compressors 102 12, a combustion chamber 104, one or more turbines 106i, 1062 and an ejection nozzle 108 for the combustion gases exiting the turbine(s).

[0003] Figure 1B schematically and partially illustrates a fan 110 of a turbomachine. The fan 110 comprises a blade wheel 112 which is surrounded by a fan housing 200, also called a retention housing because of its function of retaining the blades in the event of their breakage, or in the event of debris entering the fan.

[0004] With reference to [Fig. IC], a fan casing 200, and more generally a casing, typically comprises an annular shell 202, which may be, for example and without limitation, made of metallic material or of composite material made from woven fibers embedded in a polymer resin. Preferably, the annular shell is made of composite material. This annular shell 202 has an axis of revolution A and extends around the turbomachine's fan blades 112. The casing 200 includes an annular mounting flange 204b 2042 at each of the axial ends of the annular shell 202. These flanges 204b 2042 are used to fix the casing 200 to annular walls of a nacelle that surrounds the turbomachine to form an aircraft propulsion assembly.

[0005] The housing 200 can be connected by flanges 204b to 2042 on one side to an air inlet sleeve 4a located upstream of the blower housing 200, and on the other side to an intermediate housing ferrule 4b located downstream of the blower housing 200, as illustrated in [Fig. 1D]. The blower housing 200 also includes upstream acoustic panels 212i and downstream acoustic panels 2122.

[0006] Still with reference to [Fig.1D], an abradable annular cartridge 208 can be positioned on an internal annular surface S202 of the casing 202 of the housing 200, between the upstream acoustic panels 212i and the downstream acoustic panels 2122. This abradable cartridge 208 may include an annular layer 210 of abradable material and an annular panel or support 206 supporting the annular layer 210, the support 206 being attached to the casing 202. This abradable annular layer 210 is designed to wear in a controlled manner during operation. The panel 206 may, for example, be solid or have a honeycomb structure.

[0007] The acoustic panels 212b 2122 contribute to reducing the acoustic emission of the turbomachine.

[0008] The acoustic panels 212b 2122 are generally in the form of a sandwich structure as illustrated in [Fig.1E].

[0009] The sandwich structure comprises a cellular material 300 called "core" comprising acoustic cells C3Oo and, sandwiched between a first layer 302 of composite material called "lower skin" on which rests a lower surface of the core 300 and, a second layer 304 called "upper skin" of composite material comprising perforations PF304 and disposed on an upper face of the cellular material 300 and opposite its lower surface.

[0010] The acoustic panel 212b 2122 comprises three characteristic dimensions: - Ln: thickness of the upper skin; - Wn: diameter of the bores / perforations; and - d or Wc: Size of the acoustic cell

[0011] The dimensions Ln, Wn, d or Wc allow us to define the acoustic performance and more precisely the frequency range that we seek to suppress in order to reduce noise emissions.

[0012] However, current acoustic panels, having a sandwich structure as described above, may have disadvantages including: - a long manufacturing cycle time. For example, and without limitation, a panel intended for the external shell (called fixed internal structure or FIS) of an aircraft nacelle requires at least one curing operation of several hours; - the need to use an adhesive at the lower / outer skin-core interface.

[0013] Furthermore, the type of architecture shown in [Fig.1D] provides acoustic attenuation over a reduced frequency range as illustrated in [Fig.1F] for example.

[0014] The quality factor of the structure is defined by the ratio fres / Af between the resonant frequency fres and the bandwidth Af. The higher this ratio, the more selective the structure. This means that the structure is only effective for a limited number of frequencies.

[0015] Furthermore, the upper skin 304 (also called the septum) which can be formed at starting from a few composite plies or layers can systematically present a "telegraphing" defect or wave effects, characterized by the appearance of undulations and which can be detrimental to the aerodynamic performance of the turbomachine.

[0016] Just like the upper skin 304, the cores can deform when a bend is applied, in particular a bend of the upper skin as mentioned above.

[0017] This deformation DFi, DF2 as illustrated in [Fig. 2A], can also be detrimental to the acoustic performance of the panels. In particular, it can lead to a loss of performance and / or a shift in the frequencies to be inhibited or attenuated.

[0018] In extreme cases, for example for the attenuation of several natural frequencies, a two-degree-of-freedom acoustic structure or 2 DOF acoustics is often implemented.

[0019] Figure [Fig. 2B] illustrates an example of a 2 DOF structure. The structure consists of a superposition of two panels with different cell sizes.

[0020] In [Fig.2B], the first panel comprises the lower and upper skins 302i and 3022 respectively, and the core 300i.

[0021] The second panel comprises the lower and upper skins 3022 and 304 respectively, and the core 3002.

[0022] In this example, the upper skin 3022 of the first panel is also the lower skin of the second panel. The sizes of the C3Oo cells are different and smaller on the second panel. The cores 300i and 3002 can also have their thickness adjusted as needed.

[0023] However, the attenuation of several frequencies requires the superposition of several acoustic cells (for example of the Nida type), which leads to an increase in the thickness of the panel and therefore a larger footprint.

[0024] One solution to reduce the bulk of acoustic panels is to use open or closed cell thermosetting or thermoplastic foam in the sandwich architecture of the panels.

[0025] However, this solution has disadvantages including: a decrease in acoustic (frequency range), mechanical and thermal performance, a high manufacturing cost and a lack of eco-responsibility.

[0026] It is therefore urgent to design panels (or structures enabling the design of panels) from materials with a smaller footprint without reducing acoustic and / or mechanical and / or thermal performance, while respecting environmental and cost constraints.

[0027] The use of composite materials for manufacturing components for the interior fittings of an aircraft cabin is well known. Such a material includes, Generally, these are fibers embedded in a polymer matrix. For example, glass fibers, carbon fibers, etc., are commonly used. Other materials, such as aluminum or plastic, are also known for making such components.

[0028] Carbon fiber consumption has increased significantly over the past ten years. Production has adapted to meet this growing demand.

[0029] Primarily used in composite structures, carbon fibers are widely used in the production of woven composite parts in the aeronautical field. In particular, woven composite turbine blades for turbojet engines.

[0030] During their manufacture, the layers of warp and weft yarns are released as a preform of the composite material part is created, in order to achieve the desired thicknesses. When the preform is released from the loom, a cutting operation is performed. The cut carbon yarns then become waste from the weaving process.

[0031] Thus, carbon fibre scraps, as illustrated in [Fig.2C], represent a potentially significant volume across all production plants.

[0032] In the present application, carbon fibre scraps are defined as carbon fibres which have a length less than or equal to 100mm.

[0033] Carbon fiber scraps retain their mechanical, acoustic, and / or thermal properties intact because they have not been subjected to stress. They can therefore be reused for the manufacture of new parts made of composite materials.

[0034] However, until recently, carbon fiber scraps were practically unused. Indeed, although recycling channels for such carbon fiber scraps have developed, they are saturated with demand, particularly from the automotive industry.

[0035] Carbon fiber scraps are therefore underutilized, and markets for the reuse of such fibers are still underdeveloped. They are mostly pyrolyzed and then ground into powder, which constitutes fillers for primers, paints, or thermoplastic materials.

[0036] Climate change is a major concern for many legislative and regulatory bodies around the world. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states.

[0037] In particular, an ambitious standard applies both to new types of aircraft and to those already in service, requiring the implementation of technological solutions to bring them into compliance with current regulations. Civil aviation has been actively contributing to the fight against climate change for several years now.

[0038] Technological research efforts have already made it possible to significantly improve the environmental performance of aircraft.

[0039] The Applicant takes into consideration the factors impacting all phases of design and development in order to obtain aeronautical components and products that are less energy-intensive, more environmentally friendly and whose integration and use in civil aviation have moderate environmental consequences with a view to improving the energy efficiency of aircraft.

[0040] The research and development work carried out focuses in particular on the weight reduction of the devices, in particular through the materials used and the lighter on-board equipment.

[0041] It was therefore considered possible to valorize carbon fiber scraps in order to establish a new sector. In this regard, research and development efforts led to the development of a semi-finished recycled product based on carbon fiber scraps and a manufacturing process for such a product.

[0042] The product is in the form of a roll of a non-woven strip or layer comprising scraps of carbon fibers and a binder ensuring the cohesion of the fibers between them and the strength of the strip.

[0043] However, to date, very few measures have been taken to exploit such a product, particularly for the manufacture of acoustic panels. The invention therefore aims to provide an acoustic panel for an aircraft casing, obtained by recycling carbon fiber scraps, which overcomes at least some of the aforementioned problems and constraints.

[0044] To this end, the invention is the result of technological research aimed at significantly improving aircraft performance and, in this sense, contributes to reducing the environmental impact of aircraft. Summary of the invention

[0045] An acoustic panel is therefore proposed for a casing of an aircraft turbomachine, comprising a sandwich structure, said structure comprising a cellular material called "core" interposed between a first layer of composite material called "skin" lower on which rests a lower surface of the core and, a second layer called "skin" upper of composite material having perforations and disposed on a higher face of the cellular material and opposite its lower surface, characterized in that the panel further comprises at least one non-woven strip containing a fibrous and porous network which includes at least scraps of carbon fibers having a length less than or equal to 160mm, and a binder ensuring the cohesion of the fibers to each other and the hold of the strip, said strip covering at least a portion of the upper skin.

[0046] The manufacture of the acoustic panel includes at least the arrangement of the non-woven strip, obtained at least from recycled carbon fiber scraps, on the upper skin of the sandwich structure.

[0047] This porous non-woven strip will introduce new modes of vibration and thus broaden the frequency range (or bandwidth) for which the panel is effective.

[0048] Thus, thanks to the porosity of the non-woven strip and its association with the sandwich structure of the acoustic panel, it is possible to increase the range of acoustic frequencies to be attenuated and thus improve or optimize the performance of the acoustic panel.

[0049] The invention also offers cost and weight savings. Indeed, if the consolidation of the non-woven tape is achieved using thermoplastic and / or miscible materials, it is not necessary to use an adhesive at the interface of the tape and the upper skin. This results in cost savings, as the use of adhesive can be eliminated, as well as the manufacturing operations associated with its use (removal of the adhesive film and related secondary operations).

[0050] The invention also allows a reduction in the ecological footprint related to the manufacture of acoustic panels because it uses recycled materials.

[0051] The stacking of these carbon fibers creates a fibrous and porous network, which provides acoustic / sound attenuation as well as improved mechanical performance of the panel and increased damage tolerance, for example by increasing the stiffness of the panel's sandwich structure. The panel according to the invention is therefore self-stiffened.

[0052] Furthermore, the addition of the non-woven strip on the upper skin provides an ad-hoc surface which improves the aerodynamic performance of the turbomachine, the presence of the strip preventing the occurrence of the "telegraphing" phenomenon at the level of the upper skin and / or the core.

[0053] The invention also allows for a complete reduction in the weight of the structure. Indeed, the non-woven strip obtained from carbon fiber scraps performs as well as current state-of-the-art solutions (fiberglass in particular), but with a lower thickness (or density) (no overlapping acoustic panels). Therefore, the structure is less bulky.

[0054] The invention may further include one or more of the following optional features, according to any technically possible combination: - the binder is made of thermoplastic or thermosetting material; - the band also includes thermoplastic fibers; - the non-woven strip is placed on an external surface of the upper skin; - the band also includes projecting portions housed in the per- drillings; - The panel further includes another non-woven strip arranged on an inner face of the upper skin and opposite its outer face, the inner strip being connected to the outer strip via the protruding portions of said outer strip; - the bands arranged respectively on the inner and outer face of the upper skin have identical or different volume / mass fractions of fibers; - the binder is a thermoplastic and for example PE, PP or a PE-PP copolymer;

[0055] The invention also relates to a housing comprising at least one panel as described above.

[0056] The invention also relates to a turbomachine comprising at least one casing as mentioned above.

[0057] The invention also relates to a method for manufacturing an acoustic panel as described above, the method comprising at least: a. a step of depositing a non-woven strip onto a portion of the upper skin; b. a compression of the assembly formed by the sandwich structure and the strip non-woven. Brief description of the figures

[0058] The invention will be better understood with the aid of the following description, given solely by way of example and made with reference to the accompanying drawings in which: - [Fig. 1A] is a schematic representation of a simplified view of a turbomachine according to the prior art, - Figure [1B] is a schematic representation of a partial axial cross-sectional view of a fan of an aircraft turbomachine, according to the prior art, - [Fig.lC] is a schematic representation of a perspective view of a blower housing, according to the prior art; - [Fig.1D] is a schematic representation of a partial axial cross-sectional view of a blower housing, according to the prior art; - [Fig.1E] is a schematic representation of a sandwich structure of an acoustic panel, according to the prior art; - [Fig.1F] is a schematic representation of an acoustic gain curve for the sandwich structure of [Fig.1E], according to the prior art; - [Fig.2A] is a schematic perspective view of an open cellular material exhibiting curvature; - Figure [Fig. 2B] is a schematic perspective view of an acoustic panel of type 2 DOF; - [Fig.2C] is a schematic perspective view of carbon fiber scraps; - [Fig.2D] is a schematic perspective view of a non-woven strip of carbon fiber scraps; - [Fig.3A] is a schematic representation of a sandwich structure of an acoustic panel, according to a first variant of the invention; - [Fig.3B] is a schematic representation of the evolution of the microstructure of a nonwoven strip as a function of the density of carbon fiber drops; - [Fig.3C] is a schematic representation of the acoustic gain curve for the sandwich structure of [Fig.3A] as a function of the porosity of the non-woven strip; - [Fig.4A] is a schematic representation of a sandwich structure of an acoustic panel, according to a second variant of the invention; - [Fig.4B] is a schematic representation of a sandwich structure of an acoustic panel, according to a third variant of the invention; - [Fig.4C] is a schematic representation of the acoustic gain curves for the sandwich structure of [Fig.1E] and for the three variants of sandwich structures in figures 3A, 4A and 4B; - [Fig.5] is a schematic representation of the manufacturing process of an acoustic panel, according to the invention; Detailed description of the invention

[0059] Although the following description refers to acoustic panels for a turbomachine casing, those skilled in the art will understand that this is in no way limiting and that the invention can be applied for the production of semi-structural or non-structural parts in the aeronautical field (in particular for interiors, cabin and seat in particular, or for IFS type assemblies, etc.), but also in the broader field of transport (automotive, nautical, rail) in order to obtain an improvement in acoustic performance.

[0060] With reference to Figures 3A, an acoustic panel for a housing of an aircraft turbomachine according to the invention will now be described.

[0061] Structural elements analogous to those of the prior art according to figures 1A-2B bear the same numerical references.

[0062] As illustrated in [Fig. 3A], showing a partial view of a first variant of the acoustic panel, the acoustic panel 212b 2122 comprises a sandwich structure. The sandwich structure includes a cellular material 300 referred to as the "core". comprising acoustic cells C3Oo and, interposed between a first layer 302 of composite material called lower "skin" on which rests a lower surface of the core 300 and, a second layer 304 called upper "skin" of composite material comprising perforations PF304 and disposed on an upper face of the cellular material 300 and opposite its lower surface.

[0063] The upper skin has an inner face Sint opposite the C300 cells of the core and an outer face Sext opposite the inner face Sint.

[0064] The panel 212b 2122 further comprises at least one non-woven strip 400 covering an external face Sext of the upper skin 304 of the panel.

[0065] The nonwoven tape 400 comprises at least one fibrous and porous network which includes at least some scraps of carbon fibers 402 having a length less than or equal to 100 mm. Preferably the carbon fibers have a length between 10 and 25 mm.

[0066] In this first variant, the non-woven strip preferably has a thickness ei between 1mm and 50mm. For example, and without limitation, the thickness ei can be on the order of 10mm.

[0067] The non-woven tape 400 may also include a binder or a binding material to ensure the cohesion of the fibers between them and the strength of the tape.

[0068] The binder can be a thermoplastic or a thermosetting.

[0069] The binder may be in the form of particles and / or fibers, for example, of a thermoplastic resin-based type, such as polyethylene (PE), polypropylene (PP), or a PE-PP copolymer. The binder may also be a sizing or coating with thermoplastic resins.

[0070] As for the thermosetting binder, it can be, for example, and without limitation, polybismaleimides (BMI) or epoxy resin.

[0071] The 400 band may further comprise thermoplastic fibers, by poly(phenylene sulfide) (PPS), polyetherimides (PEI), polyetheretherketone (PEEK), polycarbonate (PC), polyethersulfone (PESU) and / or polyphenylsulfone (PPSU).

[0072] These thermoplastic fibers preferably have a glass transition temperature higher than that of the material intended to form the binder.

[0073] The nonwoven tape can be in different states depending on the parts or the final application. Indeed, an interior aeronautical part (for example a cabin / seat) will not have the same acoustic requirements and associated thermomechanical constraints as an IFS nacelle.

[0074] Thus, one can distinguish between unconsolidated, partially consolidated and fully consolidated strips.

[0075] An unconsolidated strip is characterized by the absence (or very few) elements cohesive or binding agents between the fibers. The strip then appears as an entanglement of fibers.

[0076] To obtain a partially consolidated nonwoven tape, the carbon fibers (or the binder, for example a resin) are heated sufficiently to melt and bond to the other impregnated fibers. The fibers then appear as stacked layers with very little contact at the interfaces between adjacent layers. A low but sufficient compression is then applied to this stack of fiber layers to ensure bonding between the fiber layers. The resulting tape is weakly compacted, has low density, and high porosity for a given frequency range.

[0077] The fully consolidated nonwoven tape is obtained using the same principle as a partially consolidated nonwoven tape, but with more intense processing conditions (higher time, pressure, and temperature). As a result, the density is increased and the porosity is lower than that of a partially consolidated tape. The resin's crystallinity is higher, which can lead to a higher Young's modulus or stiffness and improved finishing properties.

[0078] Figure 3B illustrates examples of unconsolidated strips. Strip 400a has a lower porosity (or a higher density) than strip 400b (lower density).

[0079] Fig. 3C illustrates an example of curves showing the acoustic gain obtained with the panel of Fig. 3A as a function of the density or porosity of the non-woven strip 400.

[0080] Curve G1 corresponds to the gain of an unconsolidated nonwoven tape (therefore with very high porosity) and curve G2 to that of a partially consolidated tape (therefore with relatively low porosity). A better gain is thus observed for a partially consolidated tape.

[0081] Thus, depending on the density (or porosity) of the bandwidth used, the gain can be improved for specific optimization. The bandwidth density allows the frequency and amplitude of a signal to be modified.

[0082] Preferably, the non-woven strip used in the 212x2 acoustic panel is partially consolidated, i.e. that the strip has low porosity.

[0083] The acoustic optimization of the panels can also depend on the mass ratio or the porosity of the core 300. It is therefore possible to significantly improve the acoustic gain of the panels by adjusting the porosity of the nonwoven strip and that of the core.

[0084] Advantageously, those skilled in the art will understand that positioning a fibrous and porous non-woven strip 400 on the upper skin 304 of the panel structure 212x2 improves the acoustic performance of the panel acoustic 212i_2.

[0085] For a strip having, in particular, areas with different porosities or densities, local acoustic attenuation and / or adjustment can be achieved, adapted to the porosity or density of each area. Thus, by controlling the homogeneity of the porosity or density of the strip, it is also possible to broaden the frequency absorption spectrum and therefore significantly improve the acoustic gain of the panels.

[0086] In another variant of the invention illustrated in [Fig.4A], the non-woven band further comprises protruding portions housed in the perforations PF304 of the upper skin 304.

[0087] In this configuration, the nonwoven strip has an effective thickness e2 which is considered to be equal to the sum of the thickness ei of the nonwoven strip of the variant of the panel shown in [Fig.3A] and the thickness of one of the protruding portions housed in the perforations.

[0088] The effective thickness e2 in this second variant of the acoustic panel is on the order of ten millimeters, for example, and not limited to, 12mm.

[0089] In a third variant illustrated in [Fig.4B], the acoustic panel 212b 2122 further comprises another nonwoven strip 4002 (or inner strip) disposed on the inner face Sint of the upper skin 304. The inner strip 4002 is connected to the nonwoven strip 400i disposed on the outer face of the skin (or outer strip) via the protruding portions of said outer strip 400i.

[0090] In this configuration, the non-woven strips 4002, 400i arranged respectively on the inner face Sint and the outer face Sext of the upper skin can have identical or different volume / mass fractions of carbon fibers.

[0091] The effective thickness e3 of the band in this configuration is the sum of the thickness e2 of the nonwoven band illustrated in [Fig. 4A] and the thickness of the band located on the inner face Sint of the upper skin 304. Preferably, the thickness of the band located on the inner face is identical to that of the band located on the outer face, i.e., equal to eb

[0092] In some embodiments, the thickness of the strip located on the inner face is different from that of the strip located on the outer face.

[0093] The architectures described above have a structure approaching that of a 2DOF type architecture as illustrated in [Fig.2B] but, with a reduced footprint.

[0094] Fig. 3B illustrates an example of the acoustic gain curve obtained as a function of the variants of the acoustic panel in Figures 3A, 4A and 4B.

[0095] The acoustic gain of the panel in [Fig. 3A] is represented by curve (a) and ca- characterized by the Afa bandwidth.

[0096] Similarly, the acoustic gains of the panels in [Fig.4A] and 4C are represented respectively by curves (b) and (c) and characterized by the bandwidths Afb and Afc.

[0097] It is observed that adding the 400 non-woven strip increases the bandwidth Af or the frequency absorption spectrum and therefore provides a significant acoustic gain. Thus, the quality factor obtained with the acoustic panel according to the invention decreases partially as a function of the addition of the non-woven strip.

[0098] Compared to a prior art acoustic panel, as illustrated in [Fig. 1D], and whose gain curve is shown in [Fig. 1E], the acoustic panel 212i, 2122 of [Fig. 3A] (first variant) provides better gain for high frequencies. However, for low frequencies, the performance is quite similar.

[0099] Thus, depending on the architecture chosen, the acoustic gain can be significantly improved with an increase in the frequency range towards high frequencies or an increase in the frequency range towards low and high frequencies.

[0100] The invention makes it possible to achieve a very wide attenuation of the acoustic frequency range (greater than 82%) unlike acoustic panels having a sandwich structure similar to that illustrated in [Fig.1E] (the performance of the two technologies is combined).

[0101] Furthermore, with the acoustic panel architecture shown in [Fig. 4B], two bands with carbon fiber densities of 304 can be used in the upper skin to improve the acoustic performance of the panel 212b 2122 and / or to target multiple frequencies. This architecture also increases the mechanical / vibrational performance of the panel structure, particularly due to increased stiffness resulting from the presence of the inner and outer bands.

[0102] The invention also relates to a casing 200 comprising an acoustic panel 212i_2 as described above.

[0103] The invention also relates to a turbomachine 100 comprising a casing according to the invention.

[0104] The invention also relates to a method of manufacturing an acoustic panel 212i, 2122 for a casing (200) of an aircraft turbomachine as described above.

[0105] The manufacturing process comprises at least: a. a step of depositing a non-woven strip 400 onto a portion of the upper skin 304; b. a compression of the assembly formed by the sandwich structure and the strip 400 non-woven fabric.

[0106] This manufacturing process can be applied to the acoustic panels described in Figures 3A and 4A.

[0107] In the case of the variant described in [Fig.4B], the manufacturing process further includes a preliminary step of pre-consolidation and / or consolidation of the upper skin 304 and the non-woven strip 400 to form a first block, the strip being arranged on the inner and outer faces and in the perforations PF304 of the inner skin.

[0108] The block formed by the upper skin 304 and the non-woven strip 400 is then assembled with the core 300 and the lower skin 302 by gluing to form the sandwich structure which will subsequently be compressed.

[0109] In the case where a thermosetting binder is used to make the nonwoven strip, the manufacturing process may further include a step of baking the whole.

[0110] Advantageously, those skilled in the art will understand that the use of non-woven tape obtained from recycled materials such as carbon fiber scraps makes it possible to improve or optimize the performance of acoustic panels by increasing (or widening) the range of acoustic frequencies to be attenuated.

[0111] The stacking of these carbon fibers creates a fibrous and porous network, which provides acoustic / sound attenuation as well as improved mechanical performance of the panel and increased damage tolerance, for example by increasing the stiffness of the panel's sandwich structure. The panel according to the invention is therefore self-stiffened.

[0112] Furthermore, the addition of the non-woven strip on the upper skin provides an ad-hoc surface which improves the aerodynamic performance of the turbomachine, the presence of the strip preventing the occurrence of the "telegraphing" phenomenon at the level of the upper skin and / or the core.

[0113] The invention also allows for acoustic optimization beyond simply adjusting the cell size. Indeed, the fibrous network of the nonwoven fabric creates intrinsic porosity. This porosity is directly related to the local fiber volume / mass fraction, which influences the density and therefore the local porosity, and consequently, the associated level of sound / acoustic attenuation. Therefore, it is possible to optimize or achieve different acoustic performance levels depending on the area of ​​the room by varying this local porosity / density.

[0114] The invention further enables a total weight reduction of the structure while maintaining mechanical performance equivalent (particularly in bending) to that of prior art panels, for example, and without limitation, a self-stiffened panel with an aluminum honeycomb structure. Indeed, the non-woven strip obtained from carbon fiber scraps performs as well as the solutions current state-of-the-art (glass fibers in particular), for a lower thickness (or density) (no overlapping of acoustic panels).

[0115] The invention also allows for a shorter manufacturing time compared to standard solutions using Nida-type sandwich acoustic structures. This reduction in manufacturing time is achieved through the use of thermoplastic materials in the composition of the non-woven tape, which are perfectly compatible with the implementation of rapid compression / stamping / thermoforming processes.

[0116] The invention can also lead to cost and weight savings. Indeed, if the consolidation of the non-woven tape is achieved using thermoplastic and / or miscible materials, it is not necessary to use an adhesive at the interface of the tape and the upper skin. This results in cost savings. The use of adhesive can be eliminated, as well as the manufacturing operations associated with its use (removal of the adhesive film and related secondary operations).

[0117] Finally, the invention allows a reduction in the ecological footprint related to the manufacture of acoustic panels because it uses recycled materials.

Claims

Demands

1. Acoustic panel (212i.2) for a housing (200) of an aircraft turbomachine (100), comprising a sandwich structure, said structure comprising a cellular material (300) referred to as the "core" sandwiched between a first layer (302) of composite material referred to as the "lower skin" on which rests a lower surface of the core, and a second layer (304) referred to as the "upper skin" of composite material having perforations (PF304) and disposed on an upper face of the cellular material (300) and opposite its lower surface, characterized in that the panel (212i_2) further comprises at least one non-woven strip (400) containing a fibrous and porous network comprising at least carbon fiber scraps (402) having a length less than or equal to 160 mm, and a binder ensuring the cohesion of the fibers to each other and the stability of the strip (400), said strip (400) covering at least a portion of the upper skin (304).

2. Panel according to claim 1, wherein the binder is thermoplastic or thermosetting.

3. Acoustic panel according to claim 1 or 2, wherein the strip (400) further comprises thermoplastic fibers.

4. Acoustic panel according to any one of claims 1 to 3, wherein the non-woven strip (400) is disposed on an external face (Sext) of the upper skin (304).

5. Acoustic panel according to the preceding claim, wherein the strip (400i) further comprises protruding portions (404) housed in the perforations (PF304).

6. Acoustic panel according to the preceding claim, wherein it further comprises another non-woven strip (4002) disposed on an inner face (Sint) of the upper skin (304) and opposite its outer face (S ext), the inner strip (4002) being connected to the outer strip (400i) via the protruding portions (404) of said outer strip (400i).

7. Acoustic panel according to the preceding claim, wherein the strips arranged respectively on the inner face (4002) and the outer face (4000) of the upper skin (304) have identical or different fiber volume / mass fractions.

8. Acoustic panel according to any one of the preceding claims, wherein the binder is a thermoplastic and for example PE, PP or a PE-PP copolymer.

9. Carter (200) comprising at least one panel (212i.2) according to any one of claims 1 to 8.

10. Turbomachine (100) comprising at least one casing (200) according to the preceding claim.

11. A method for manufacturing (500) an acoustic panel (212i.2) according to any one of claims 1 to 8, the method (500) comprising at least: a. a step of depositing a nonwoven strip (400) onto a portion of the upper skin (304); b. a compression of the assembly formed by the sandwich structure and the nonwoven strip (400).

Images