Acoustic attenuation panel comprising at least one C-shaped reinforcement held by at least one expandable core and method for manufacturing such a panel

Abstract

Acoustic attenuation panel comprising at least one C-shaped reinforcement held by at least one expandable core and method for manufacturing such a panel. The invention relates to an acoustic attenuation panel comprising at least one resistive acoustic layer (42), at least one reflective layer (46), at least one honeycomb structure (44), and at least one C-shaped reinforcement (50) interposed between the acoustically resistive and reflective layers (42, 46), as well as at least one expandable core (52), positioned between the first and second wings of the C-shaped reinforcement (50), which increases in volume during a polymerization cycle. Thanks to this expandable core (52), it is no longer necessary to perform two polymerization cycles, one of which is required to stiffen the C-shaped reinforcement (50). The invention also relates to a method for manufacturing such a panel. Figure 4

Description

Title of the invention: Acoustic attenuation panel comprising at least one C-shaped reinforcement held by at least one expandable core and method for manufacturing such a panel

[0001] The present application relates to an acoustic attenuation panel comprising at least one C-shaped reinforcement held by at least one expandable core and to a method of manufacturing such a panel.

[0002] According to an embodiment visible in [Fig. 1], an aircraft 10 comprises a fuselage 12, wings 14 positioned on either side of the fuselage 12 and several propulsion units 16 positioned under the wings 14 and connected to them by masts 18. Each propulsion unit 16 comprises a motor 20 and a nacelle 22 surrounding the motor 20 and allowing in particular to channel an incoming airflow towards the motor 20.

[0003] The motor 20 has a rotation axis A20. For the remainder of this description, a longitudinal direction is a direction parallel to the rotation axis A20. A longitudinal plane is a plane containing the rotation axis A20. A radial direction is perpendicular to the rotation axis A20.

[0004] Each nacelle 22 includes, at the front, an air inlet 24 having a lip 26, which has a C-shaped cross-section in a longitudinal plane, as well as an internal duct 28 which extends the lip 26 inside the nacelle 22 and channels the incoming airflow towards the motor 20.

[0005] According to one configuration, the inner duct 28 comprises at least one acoustic attenuation panel 30 (illustrated in [Fig.2]) which extends between front and rear edges 30.1, 30.2 and includes, moving away from the axis of the motorization A20, at least one porous acoustically resistive layer 32, at least one honeycomb structure 34 and a reflective layer 36 (non-porous or airtight).

[0006] According to one embodiment, at the front edge 30.1, the honeycomb structure 34 comprises a honeycomb reinforcement 34.1 having a triangular or trapezoidal cross-section. In addition, the reflective layer 36 is pressed against and connected to the acoustically resistive layer 32. At the rear edge 30.2, the acoustic attenuation panel 30 comprises a C-shaped reinforcement 38 having a core 38.1 and two wings 38.2, 38.3 located at the ends of the core 38.1, the first wing 38.2 being pressed against and connected to the acoustically resistive layer 32, and the second wing 38.3 being pressed against and connected to the reflective layer 36.

[0007] According to one configuration, the acoustic attenuation panel is essentially made of composite material. In this case, a method for manufacturing an acoustic attenuation panel includes a first step of laying an acoustically resistive layer 32 on a first mold, a step of winding a wire around the acoustically resistive layer 32 and a step of placing a C-shaped reinforcement.

[0008] Next, the process includes a step of setting up a polymerization tooling as well as a first polymerization cycle of the acoustically resistive layer 32 and the C reinforcement 38.

[0009] The process also includes a step of obtaining a honeycomb structure 34, a step of placing said honeycomb structure 34 on the acoustically resistive layer 32 already at least partially polymerized, a step of draping the reflective layer 36 and then a second polymerization cycle aimed at hardening and connecting the wound acoustically resistive layer 32, the C reinforcement 38, the honeycomb structure 34 and the reflective layer 36.

[0010] The first polymerization cycle gives the C 38 reinforcement a certain rigidity enabling it to withstand the compressive forces which tend to bring the reflective layer 36 and the acoustically resistive layer 32 closer together during the second polymerization cycle.

[0011] This method for manufacturing an acoustic attenuation panel is not satisfactory because the presence of two polymerization cycles leads to an increase in the time and energy consumption required for manufacturing the panel. Furthermore, the assembly of the first polymerized sub-assembly after the first polymerization cycle, of the honeycomb structure 34 and the reflective layer 36, requires the use of specific composite materials, in particular thermoplastic composite materials, and / or the presence of joining elements interposed between, on the one hand, the acoustically resistive layer 32 and the already polymerized C-reinforcement 38, and on the other hand, the honeycomb structure 34 and the reflective layer 36, in order to obtain a solid bond between these elements during the second polymerization cycle.

[0012] The present invention aims to remedy all or part of the drawbacks of the prior art.

[0013] For this purpose, the invention relates to an acoustic attenuation panel comprising at least one resistive acoustic layer, at least one reflective layer, as well as at least one honeycomb structure and at least one C-shaped reinforcement interposed between the acoustically resistive and reflective layers, said C-shaped reinforcement comprising a core and first and second wings in contact respectively with the acoustically resistive and reflective layers.

[0014] According to the invention, the acoustic attenuation panel comprises at least one expandable core positioned between the first and second wings of the C-shaped reinforcement and configured to occupy a first unexpanded state, at a first temperature, in which the expandable core occupies a first volume and a second expanded state, at a second temperature higher than the first temperature, in which the expandable core occupies a second volume larger than the first volume.

[0015] The expandable core prevents the C-shaped reinforcement from deforming and allows it to withstand the compressive forces that tend to bring the reflective layer and the acoustically resistive layer closer together during the polymerization cycle. Therefore, it is not necessary to perform two polymerization cycles, the first of which is to stiffen the C-shaped reinforcement. Requiring only one polymerization cycle reduces manufacturing time and costs.

[0016] According to another characteristic, the expandable core has, in the first state, shapes conforming to those of the core and the first and second wings of the C-shaped reinforcement.

[0017] According to another feature, the expandable core has, in the first state, a substantially rectangular section which has a length substantially equal to a distance between the first and second wings and a width substantially equal to that of the first and second wings.

[0018] According to another feature, the acoustic attenuation panel comprises several expandable cores placed end to end.

[0019] According to another feature, at least one expandable core is made from a solid material such as an expandable foam.

[0020] According to another feature, at least one expandable core comprises at least one bladder containing an expandable fluid.

[0021] According to another feature, at least one expandable core is permanently positioned in the acoustic attenuation panel.

[0022] According to another feature, the first temperature is equal to an ambient temperature, of the order of 20°C, and the second temperature is equal to a polymerization temperature greater than or equal to 100°C.

[0023] The invention also relates to a method for manufacturing an acoustic attenuation panel according to one of the preceding characteristics.

[0024] This manufacturing process comprises a step of placing at least one acoustically resistive layer, at least one C-reinforcement, at least one honeycomb structure, and at least one reflective layer, each honeycomb structure and each C-reinforcement being intercalated between the acoustically resistive and reflective layers; a step of placing at least one polymerization tool; a polymerization cycle; and a demolding step. According to the invention, the process comprises a step of placing at least one expandable core between the first and second wings of the C reinforcement prior to the polymerization cycle, said expandable core being configured to occupy a first unexpanded state, at a first temperature, in which the expandable core occupies a first volume and a second expanded state, at a second temperature higher than the first temperature, in which the expandable core occupies a second volume larger than the first volume.

[0025] Other features and advantages will become apparent from the following description of the invention, given by way of example only, with reference to the accompanying drawings, among which:

[0026] [Fig-1] is a perspective view of an aircraft and propulsion assembly illustrating one embodiment,

[0027] [Fig.2] is a longitudinal section of an acoustic attenuation panel illustrating an embodiment of the prior art,

[0028] [Fig.3] is a longitudinal section of a rear portion of the acoustic attenuation panel visible in [Fig.2],

[0029] [Fig.4] is a longitudinal section of an acoustic attenuation panel illustrating one embodiment of the invention,

[0030] [Fig.5] is a longitudinal section of a rear portion of the acoustic attenuation panel visible in [Fig.4],

[0031] [Fig.6] is a longitudinal section of an acoustically resistive layer, a back reinforcement and an expandable core illustrating one embodiment of the invention.

[0032] According to an embodiment shown in Figures 4 and 5, a sound-attenuating panel 40 extends between first and second faces F40, F40' offset along a first direction and front and rear edges 40.1, 40.2 offset along a second direction. During operation, the first face F40 is in contact with an environment containing sound waves.

[0033] According to one application, an aircraft includes at least one acoustic attenuation panel 40, in particular at an air intake of a nacelle of a propulsion unit. In this case, the first and second directions correspond respectively to the radial and longitudinal directions of the propulsion unit.

[0034] Of course, the invention is not limited to this application for the acoustic attenuation panel 40.

[0035] The acoustic attenuation panel 40 comprises, moving away from the first face F40, at least one porous acoustically resistive layer 42, at least one honeycomb structure 44 and at least one reflective layer 46.

[0036] The acoustically resistive layer 42 has a first face 42.1 forming the first face F40 of the acoustic attenuation panel 40 and a second face 42.2 opposite to the first face 42.1 and oriented towards the alveolar structure 44.

[0037] In one arrangement, the acoustically resistive layer 42 is tubular and shaped like an internal duct of an air inlet. Alternatively, the acoustically resistive layer 42 is substantially flat or corresponds to a portion of a cylinder. Of course, the invention is not limited to these arrangements.

[0038] According to one configuration, the acoustically resistive layer 42 comprises at least one wire 48 (visible in [Fig.6]) in contact with the second face 42.2 of the acoustically resistive layer 42. For the present application, wire means a single wire or several stranded wires, for example.

[0039] According to one method, the wire 48 is wound around the second face 42.2 of the acoustically resistive layer 42 when the latter is tubular. This wire 48 may be self-adhesive to reinforce the bond between the acoustically resistive layer 42 and the honeycomb structure 44. Alternatively, the wire 48 could be replaced by at least one gripping fold and / or at least one self-adhesive strip or any other element promoting the bond between the acoustically resistive layer 42 and the honeycomb structure 44.

[0040] According to one embodiment, the acoustically resistive layer 42 is a perforated plate made of thermoplastic material. Of course, the invention is not limited to this embodiment. Thus, the acoustically resistive layer 42 may be metallic, made of composite material, or be composed of a mixture of elements made of composite material, metallic material, solid material, or woven material. By way of example, the acoustically resistive layer 42 has a thickness of approximately 0.3 mm, to within a few millimeters.

[0041] The reflective layer 46 has a first face 46.1 forming the second face F40' of the acoustic attenuation panel 40 and a second face 46.2 opposite to the first face and oriented towards the honeycomb structure 44.

[0042] According to one embodiment, the reflective layer 36 may be metallic, made of a composite material, or composed of a mixture of composite and metallic elements. By way of example, the reflective layer 36 has a thickness on the order of a few tenths of a millimeter to a few millimeters.

[0043] According to embodiments, the acoustic attenuation panel 40 can comprise a single honeycomb structure 44 or several superimposed honeycomb structures 44 separated by porous layers.

[0044] According to one configuration, the honeycomb structure 44 comprises at least one honeycomb reinforcement 44.1, which has a triangular or trapezoidal cross-section, positioned at a first edge among the front and rear edges 40.1, 40.2. At this first edge, the reflective layer 46 is pressed against the acoustically resistive layer 42 and connected to the latter.

[0045] The acoustic attenuation panel 40 comprises at least one C-shaped reinforcement 50, interposed between the acoustically resistive and reflective layers 42, 46, which has a core 50.1 and first and second wings 50.2, 50.3 located at the ends of the core 50.1, the first wing 50.2 being pressed against and connected to the acoustically resistive layer 42, and the second wing 50.3 being pressed against and connected to the reflective layer 46. In one arrangement, the C-shaped reinforcement 50 is positioned at the rear edge 40.2. Of course, the invention is not limited to this arrangement.

[0046] The core 50.1, the first and second wings 50.2, 50.3 of the reinforcement in C 50 form a single piece.

[0047] According to one embodiment, the C 50 reinforcement is a preform of pre-impregnated or non-pre-impregnated fibers.

[0048] The acoustically resistive layer(s) 42, the honeycomb structure(s) 44, the reflective layer 46, and the C-shaped reinforcement(s) are not further described as they may be identical to those of the prior art. Their manufacturing processes are also not described as they may be identical to those of the prior art.

[0049] According to one configuration, when the acoustic attenuation panel 40 is finished, the first and second wings 50.2, 50.3 of the C-brace 50 are substantially parallel and spaced at a given distance. The first and second wings 50.2, 50.3 have (between their free ends and the web 50.1) substantially identical widths.

[0050] According to the invention, the acoustic attenuation panel 40 comprises at least one expandable core 52 positioned between the first and second wings 50.2, 50.3 of a C-shaped reinforcement 50 and configured to occupy a first unexpanded state, at a first temperature, in which the expandable core 52 occupies a first volume, and a second expanded state, at a second temperature higher than the first temperature, in which the expandable core 52 occupies a second volume larger than the first volume. In one configuration, the first temperature is equal to an ambient temperature, on the order of 20°C, and the second temperature is equal to a polymerization temperature greater than or equal to 100°C.

[0051] According to a first embodiment, at least one expandable core 52 is made from a solid material such as an expandable foam.

[0052] According to a second embodiment, at least one expandable core 52 comprises at least one bladder containing an expandable fluid.

[0053] According to one arrangement, the expandable core 52 has in the first state shapes conforming to the shapes of the core 50.1 as well as those of the first and second wings 50.2, 50.3 of the reinforcement in C 50.

[0054] According to one embodiment, the expandable core 52 comprises, in the first state, a substantially rectangular section which has a length substantially equal to the given spacing between the first and second wings 50.2, 50.3 and a width substantially equal to that of the first and second wings 50.2, 50.3.

[0055] The acoustic attenuation panel 40 may comprise a single expandable core 52 or several expandable cores placed end to end. Thus, in the case of a tubular acoustic attenuation panel 40, the latter may comprise a single expandable core extending over the entire circumference of the tubular shape or several expandable cores 52, placed end to end, extending over the entire circumference of the tubular shape.

[0056] Depending on the case, at least one expandable core 52 is removed from the acoustic attenuation panel 40 after a polymerization step. Alternatively, at least one expandable core 52 is permanently positioned in the acoustic attenuation panel 40.

[0057] According to one method, a process for manufacturing an acoustic attenuation panel includes a first step of placing an acoustically resistive layer 42 on a first mold, a step of placing at least one C reinforcement 50, a step of winding a wire 48 around the acoustically resistive layer 42, a step of placing at least one expandable core 52 between the first and second wings 50.2, 50.3 of the C reinforcement 50, a step of placing said honeycomb structure 44 on the acoustically resistive layer 42 already positioned, a step of placing the reflective layer 46, a step of placing at least one polymerization tool, a polymerization cycle and then a demolding step.

[0058] Regardless of the operating method, a process for manufacturing an acoustic attenuation panel 40 includes a step of placing at least one acoustically resistive layer 42, at least one C-reinforcement 50 having a core 50.1 and first and second wings 50.2, 50.3, at least one expandable core 52 between the first and second wings 50.2, 50.3 of the C-reinforcement, at least one honeycomb structure 44 and at least one reflective layer 46; the honeycomb structure 44 and the C-reinforcement 50 being located between the acoustically resistive layer 42 and the reflective layer 46. After placing these elements, the process includes a step of setting up at least one polymerization tool, a polymerization cycle and a demolding step. In all cases, each expandable core 52 is put in place before the polymerization cycle, in particular before the step of setting up the alveolar structure 44.

[0059] During the polymerization cycle, the expandable core 52 expands and increases in volume. The expansion of the expandable core 52 during the polymerization cycle gives it allows to compensate the phenomena of bulking and to exert a compressive force on the core 50.1 as well as on the first and second wings 50.2, 50.3 against respectively the acoustically resistive layer 42 and the reflective layer 46. In addition, the expandable core 52 prevents the C reinforcement 50 from deforming and allows it to take up the compressive forces tending to bring the reflective layer 46 and the acoustically resistive layer 42 closer together during the polymerization cycle.

[0060] Unlike the prior art, the manufacturing process includes only one polymerization cycle, which reduces manufacturing time and costs.

Claims

Demands

1. Acoustic attenuation panel (40) comprising at least one acoustic resistive layer (42), at least one reflective layer (46) as well as at least one honeycomb structure (44) and at least one C-reinforcement (50) interposed between the acoustically resistive and reflective layers (42, 46), said C-reinforcement (50) comprising a core (50.1) as well as first and second wings (50.2, 50.3) in contact respectively with the acoustically resistive and reflective layers (42, 46); characterized in that the acoustic attenuation panel (40) comprises at least one expandable core (52) positioned between the first and second wings (50.2, 50.3).3) of the reinforcement in C (50) and configured to occupy a first non-expanded state, at a first temperature, in which the expandable core (52) occupies a first volume and a second expanded state, at a second temperature higher than the first temperature, in which the expandable core (52) occupies a second volume larger than the first volume.

2. Acoustic attenuation panel (40) according to the preceding claim, characterized in that the expandable core (52) has, in the first state, shapes conforming to those of the core (50.1) as well as those of the first and second wings (50.2, 50.3) of the C-reinforcement (50).

3. Acoustic attenuation panel (40) according to the preceding claim, characterized in that the expandable core (52) comprises, in the first state, a substantially rectangular section which has a length substantially equal to a spacing between the first and second wings (50.2, 50.3) and a width substantially equal to that of the first and second wings (50.2, 50.3).

4. Acoustic attenuation panel (40) according to any one of the preceding claims, characterized in that the acoustic attenuation panel (40) comprises several expandable cores placed end to end.

5. Acoustic attenuation panel (40) according to any one of the preceding claims, characterized in that at least one expandable core (52) is made from a solid material such as an expandable foam.

6. Acoustic attenuation panel (40) according to any one of the preceding claims, characterized in that at least one expandable core (52) comprises at least one bladder containing an expandable fluid.

7. Acoustic attenuation panel (40) according to any one of the preceding claims, characterized in that at least one expandable core (52) is permanently positioned in the acoustic attenuation panel (40).

8. Acoustic attenuation panel (40) according to any one of the preceding claims, characterized in that the first temperature is equal to an ambient temperature, of the order of 20°C, and the second temperature is equal to a polymerization temperature greater than or equal to 100°C.

9. A method for manufacturing an acoustic attenuation panel (40) according to any one of the preceding claims, the manufacturing method comprising a step of placing at least one acoustically resistive layer (42), at least one C-reinforcement (50), at least one honeycomb structure (44) and at least one reflective layer (46), each honeycomb structure (44) and each C-reinforcement (50) being intercalated between the acoustically resistive and reflective layers (42, 46), a step of placing at least one polymerization tool, a polymerization cycle and a demolding step; characterized in that the method comprises a step of placing at least one expandable core (52) between the first and second wings (50.2, 50.3) of the C reinforcement (50) prior to the polymerization cycle, said expandable core (52) being configured to occupy a first unexpanded state, at a first temperature, in which the expandable core (52) occupies a first volume and a second expanded state, at a second temperature higher than the first temperature, in which the expandable core (52) occupies a second volume larger than the first volume.

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