Classifications

• • G—PHYSICS
  • G10—MUSICAL INSTRUMENTS; ACOUSTICS
  • G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
  • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
  • G10K11/162—Selection of materials
  • G10K11/168—Plural layers of different materials, e.g. sandwiches

Definitions

• the present invention relates to acoustic attenuation panels, in particular to panels intended to be mounted in the walls of nacelles of aircraft turbojets, in engine housings, in conduits to be soundproofed and, in general , to panels combining good properties both acoustic and structural strength.
• this type of panel incorporates a honeycomb core, such as a flanked honeycomb structure, on the incident sound wave side, with a layer of acoustic damping and, on the opposite side, a rear reflector.
• a honeycomb core such as a flanked honeycomb structure
• the acoustic damping layer is a porous structure with a dissipative role, that is to say partially transforming the acoustic energy of the sound wave passing through it into heat.
• This porous structure can be, for example, a metallic fabric or a fabric of carbon fibers whose weaving makes it possible to fulfill its dissipative function.
• These acoustic panels in front for example in the case of panels equipping nacelles with turbojets, also have sufficient structural properties to in particular receive and transfer aerodynamic, inertial forces and those related to the maintenance of the nacelle, to the nacelle / structural connections. engine, it is necessary to give the acoustic damping layer structural properties.
• the invention relates more precisely to panels of the latter type, that is to say comprising a resistive layer with a structural component facing the incident sound wave, but also applies to panels whose resistive layer comprises a component structural interposed between the dissipative component and the alveolar structure.
• the structure of the panel according to EP 0 911 803 has the drawback of a resistive layer formed by two superimposed metallic layers, namely a fabric and a sheet.
• the metal used to make the metallic fabric is preferably stainless steel, while the structural layer is aluminum foil.
• the use of two metals of different structure induces corrosion by the appearance of a galvanic couple.
• the density, although low, of the metals used significantly increases the mass of the acoustic panel.
• sandwich type acoustic attenuation panels comprising an acoustically resistive layer formed from a pierced non-metallic sheet used alone or in combination with a porous layer.
• these sheets are generally made of plastics with high temperature resistance or plastics reinforced with fibers, in particular graphite.
• the shape of the orifices, their symmetrical distribution in the structural layers of the above type give them an isotropic mechanical strength which in no way takes account of the distribution of the forces which the acoustic panel must support.
• These forces being greater in the longitudinal direction than in the radial direction, it is therefore necessary to produce a panel having a thickness suitable for the passage of the longitudinal forces but oversized for the passage of the radial forces.
• the subject of the invention is an acoustic attenuation panel comprising a resistive layer with a reinforced structural component, of the type comprising at least one layer of honeycomb structure flanked, on one side, by a resistive layer composed of at least one porous layer and at least one perforated structural layer, and, on the other side, a layer forming a total reflector, characterized in that said structural layer is pierced with non-circular holes each having its largest dimension and its smallest dimension along respectively two perpendicular axes.
• the smallest dimension of the holes is greater than or equal to 0.5 mm and the largest dimension is greater than or equal to 1.5 times the smallest.
• the largest dimension of the holes is parallel to the direction of the main forces to be supported.
• the largest dimension of the holes is parallel to the longitudinal axis of the engine and the holes are distributed in alignments both parallel to said axis of the engine and orthogonal to the latter.
• the perforated structural layer consists of mineral or organic fibers, natural or synthetic, impregnated with a thermosetting or thermoplastic resin, polymerized.
• the fibers can be unidirectional and parallel in particular to said direction of the main forces.
• the fibers may also be in the form of a fabric or a stack of fabrics whose weft or warp threads are parallel to said direction of the main forces.
• the shape of the holes is chosen from the group comprising rectangular, oblong, hexagonal shapes.
• the panels produced in accordance with the invention have the essential advantage that the structural layer thus perforated offers, compared to a perforated structural layer of the prior art and with an equal open surface area, a better distributed material between the holes, c that is to say grouped along one and / or the other of the two privileged axes defined respectively by the largest dimension and the smallest dimension of the holes.
• said material between holes is grouped into strips or wider corridors between the alignments of holes, thus allowing a more efficient transfer of forces, via said strips, towards the structures surrounding the panels.
• Such an improvement in the transfer of forces can be obtained by retaining an open surface area rate of the structural layer adapted to the desired acoustic attenuation conditions, while minimizing the thickness of said structural layer.
• FIG. 1 is a partial perspective view of an acoustic attenuation panel according to the invention.
• FIG. 2 illustrates a first embodiment of a structural panel layer according to the invention
• FIG. 3 shows a conventional structural layer with circular perforations;
• FIG. 4 illustrates a second embodiment;
• FIG. 5 illustrates a third embodiment of a structural layer of panel according to the invention.
• FIG. 1 a sandwich structure of the acoustic attenuation panel according to the invention is shown diagrammatically, comprising a central honeycomb structure 1 flanked, on one side, by an acoustically resistive layer 2 called the front, formed of two components , and on the other side, a layer 3, called rear, forming a total reflector.
• a sandwich structure of the acoustic attenuation panel according to the invention is shown diagrammatically, comprising a central honeycomb structure 1 flanked, on one side, by an acoustically resistive layer 2 called the front, formed of two components , and on the other side, a layer 3, called rear, forming a total reflector.
• the central honeycomb structure 1 is formed, in the embodiment shown, of a single layer of honeycomb type. Of course, several layers of honeycomb separated by septa can be provided, in the known manner, to constitute several superimposed resonators.
• the resistive layer 2 is said to be front in that it is in contact with the aerodynamic flow or the gaseous medium in which the sound waves to be damped move.
• the layer 2 comprises a so-called structural component 2a, responsible for transferring the mechanical, aerodynamic and inertial forces towards the crankcase, in the case of the use of such a panel for covering, for example, the external wall delimiting the fan channel d 'a turbojet engine.
• This structural layer 2a directly in contact with said aerodynamic flow also has an acoustic role because it must allow sound waves to pass towards the resonator or resonators and, for this purpose, is pierced with openings or holes 4, of shape and distributions particular according to the invention.
• the second component 2b of the resistive layer is interposed between the structural layer 2a and the cellular layer 1 and consists, in the known manner, of a layer of breathable material, for example a fabric or a superposition of metallic fabrics formed of stainless steel wire, or one or more carbon fiber fabrics.
• the rear layer 3 is for example and also in the known manner, a non-perforated aluminum metal sheet.
• the structural layer 2a is formed from a rigid or semi-rigid sheet material, which can be a metal, such as aluminum or stainless steel, a composite material, such as a plastic material with high temperature resistance. or a plastic reinforced with fibers, in particular graphite, or a composite material consisting of mineral or organic fibers, natural or synthetic, impregnated with a thermosetting or thermoplastic resin, polymerized.
• the layer 2a is single or else formed by the superposition of several layers of strips such as those shown in FIG. 1.
• the layer 2a is identically pierced with identical holes, rectangular and aligned both in the lengthwise direction and in the widthwise direction.
• Figure 2 there is shown schematically in top view the two superimposed components 2a, 2b.
• the holes 4 have a length to width ratio of 2 and their longitudinal axis is parallel to the direction 5 of passage of the main forces to be supported by the panel.
• This direction 5 corresponds, for a turbojet engine for example, to the axis of the engine, which exerts its thrust, as well as during the reverse thrust, along its axis.
• FIG 3 there is shown in comparison a conventional resistive layer with two components 2'a, 2'b corresponding to the components 2a, 2b of the invention.
• Component 2'a is made of the same material as component 2a, has the same surface as the latter and the same total open surface, the openings being formed by a regular distribution of circular holes 4 'equidistant from each other and aligned at both following direction 5 ' homologous to direction 5 in FIG. 2 and in a direction 6 ′ perpendicular to direction 5 ′ and homologous to direction 6 in FIG. 2.
• the interval 7 between two alignments of holes 4 is greater than the interval 7 'between two homologous alignments of holes 4 'and, in component 2a, the sum of the intervals 7 (including the external intervals) is greater than the sum of the intervals 7' of the component 2'a.
• the total width of material that is to say said sum of the intervals 7, available for transferring the forces in direction 5, is very substantially greater than the total width of corresponding material in the component 2'a.
• Component 2a according to the invention therefore has better mechanical strength in direction 5.
• the direction 5 is also that of the aerodynamic flow in an engine, the holes 4 are also aligned in the direction of this flow in the air inlet duct, which minimizes the aerodynamic drag.
• the perforation of the layer 2a in accordance with the invention gives the acoustic attenuation panels equipping the air inlets of turbojets a better passage of the main forces, mechanical, aerodynamic and inertial, while retaining a surface rate open adapted to said panels, while minimizing the thickness of said structural layer 2a.
• the perforation according to the invention of the structural layer 2a is particularly advantageous in the case where said layer 2a is formed from fibers, for example carbon, glass or "Kevlar", pre-impregnated with '' a suitable resin.
• the component 2a is formed from a sheet of unidirectional fibers parallel to the direction 5 of the main forces, the fibers located in the corridors between the alignments in the direction 5 of the holes 4 will not be cut during the perforations and thus ensure a transfer of efforts to the maximum of their capacity.
• the weft and warp threads of the fabric (s) are advantageously arranged parallel to directions 5 and 6 so as to have the least number of fibers cut during the perforation of the holes 4, both parallel to the direction 5 and parallel to the direction 6.
• the perforation of the holes 4 is carried out by any appropriate means, for example by punching , all the holes 4 of a strip being perforated in a single pass using a multiple punch press.
• the perforations are produced, for example, on rectangular strips of dimensions appropriate to those of the panel to be produced, flat, whatever the nature of the constituent material. The strips will then be put in place according to the type of panel to be produced.
• the composite material In the case of fibers pre-impregnated with resin, the composite material will be consolidated by polymerization of the resin, before being perforated.
• the direction of the main forces (5) naturally depends on the type of panel to be produced and its destination. Those skilled in the art will in each case be able to determine this direction and adapt the alignment of the holes 4.
• the various constituent layers (1, 2 and 3) of the panel are assembled using conventional techniques.
• the ratio between length and width of the holes 4 is obviously variable. Preferably, it will be greater than or equal to 2.
• the alignment of the holes 4 may be only in one direction, the direction 5 for example as illustrated by FIG. 4 in which the distribution of said holes 4 in the component 2 "a is substantially staggered.
• the shape of the holes perforated in the structural layer according to the invention can vary insofar as this shape lends itself to the production of a passage opening having two main perpendicular axes, one of which is substantially more along the other so as to allow the structural layer a better passage of the forces along one or the other of the two abovementioned axes.
• the component 2 "'a has holes 4" distributed like the rectangular holes 4 in FIG. 2 and of oblong shape, in particular rectangular with rounded ends.
• the component 2 lv a has holes 4 '"distributed like those of FIG. 5 and also of oblong shape, namely rectangular with pointed ends, or hexagonal.
• the elongated shape of the holes combined with an alignment of all the holes in the direction of their elongation allows, with respect to circular holes and with the same opening rate, to obtain a structural layer ensuring better transfer of forces in the direction of the greatest length of the elongated holes, and this, whatever the desired opening rate.

Landscapes

• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Multimedia (AREA)
• Laminated Bodies (AREA)
• Soundproofing, Sound Blocking, And Sound Damping (AREA)
• Vehicle Interior And Exterior Ornaments, Soundproofing, And Insulation (AREA)
• Building Environments (AREA)

Applications Claiming Priority (3)

Publications (2)

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• 2001
  • 2001-04-17 FR FR0105209A patent/FR2823590B1/fr not_active Expired - Fee Related
• 2002
  • 2002-04-17 CA CA2441477A patent/CA2441477C/fr not_active Expired - Lifetime
  • 2002-04-17 DE DE60224924T patent/DE60224924T2/de not_active Expired - Lifetime
  • 2002-04-17 EP EP02738201A patent/EP1380027B1/de not_active Expired - Lifetime
  • 2002-04-17 US US10/473,031 patent/US7484592B2/en not_active Expired - Fee Related
  • 2002-04-17 AT AT02738201T patent/ATE385602T1/de not_active IP Right Cessation
  • 2002-04-17 WO PCT/FR2002/001322 patent/WO2002084642A1/fr active IP Right Grant

Non-Patent Citations (1)

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