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
  • G10K11/172—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using resonance effects
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T156/00—Adhesive bonding and miscellaneous chemical manufacture
  • Y10T156/10—Methods of surface bonding and/or assembly therefor
  • Y10T156/1052—Methods of surface bonding and/or assembly therefor with cutting, punching, tearing or severing
  • Y10T156/1056—Perforating lamina

Definitions

• the present invention relates to an acoustic attenuation panel more particularly intended for the at least partial absorption of sound energy from gas flows at high speed.
• the invention will be described in its application to the production of noise attenuation panels generated in particular by aircraft turbine engines, in certain locations of the nacelle, for example at the entrance and at the exit of the fan channel, but it is understood that the invention is capable of applications in any other environment where it is necessary or desirable to use a structure of the panel type combining lightness, high mechanical strength and acoustic properties.
• the panel according to the invention is of the well known type consisting of a sandwich comprising a honeycomb structure of the honeycomb type flanked, aerodynamic vein side, an acoustically resistive layer and, on the opposite side, a rear reflector.
• the honeycomb structure may be simple, that is to say with a single resonator or with a monolayer honeycomb core, or else multiple, that is to say with superimposed resonators or with honeycomb core formed by several superimposed layers separated or not by septa.
• the acoustically resistive layer has a dissipative role. When the sound wave passes through it, viscous effects occur which partially transform acoustic energy into heat. The alveolar structure behind the resistive layer traps this sound wave thanks to the cells which behave like waveguides perpendicular to the surface of said layer, the wave reflecting on the rear reflector of the panel.
• such a panel must, because of its environment, withstand severe conditions of use. In particular, it must not present any risk of delamination of the resistive layer even in the presence of a high vacuum and must be resistant to erosion or abrasion as well as to corrosion, have good electrical conductivity and be able to absorb the energy of a mechanical impact.
• Such a panel must also and of course have sufficient structural properties to in particular receive and transfer the aerodynamic, inertial forces and those related to the maintenance of the nacelle, towards the structural nacelle / engine connections.
• the surface condition of the resistive layer must finally meet the aerodynamic requirements of the environment.
• Such a panel comprises a honeycomb flanked, on one side, by an acoustic resistive layer constituted by a rigid and thin lattice of composite material and, on the other side, by a reflector.
• Such a structure has the advantage of good control of the percentage of open area of the resistive layer because said lattice is formed of orthogonal wicks of fibers, for example carbon, delimiting between them openings the size of which can be adjusted during process of impregnating the fibers with the aid of a thermosetting resin and then hardening of the resin, the fabric being subjected to shaping under pressure and at temperature in order to obtain said rigid and thin lattice.
• the resistive layer thus obtained also has good structural strength and finally has the advantage of being a monolayer component.
• This resistive layer has a high acoustic non-linearity which means that its surface impedance varies significantly with the acoustic level.
• the grazing flow will produce a phenomenon of narrowing of the air passage sections in the holes.
• the acoustic resistance of this layer will also depend on the speed of this grazing flow.
• the resistive layer offers a frequency window of limited efficiency, as well as a low resistance to erosion.
• the resistive layer is formed of two components, namely, a structural layer, on the honeycomb side, and a microporous layer on the surface.
• the structural layer is formed from a fabric of relatively wide mesh carbon fibers defining an opening rate of approximately 30% of the total surface of the layer.
• the surface microporous layer is a fine mesh fabric of mineral or synthetic fibers or a metallic fabric, acting as an acoustic damper.
• such a structure has the major drawback of an additional assembly penalizing in time and cost, due to the two-component nature of the resistive layer. If the increased assembly constraints of this structure are not well controlled, there are risks of acoustic non-uniformity, as well as delamination of the resistive layer.
• the panel comprises a resistive layer on the surface, two superposed honeycombs separated by a resistive layer, called a septum, generally microporous and a reflector.
• an acoustic attenuation panel formed of a sandwich comprising a honeycomb structure flanked, on one side, by a reflector and, on the other side, by a fabric. metal itself covered with a perforated metal sheet.
• the metal sheet is first prepared and then pierced before being put in place and shaped on the assembly, produced in addition, of the honeycomb structure, the reflector and the metallic fabric.
• the shaping of the pre-perforated sheet will cause local deformations of parts of the sheet and therefore holes located in these parts. These deformations are capable of appreciably modifying the area of the holes and therefore the local porosity rate of the perforated sheet, thus causing inhomogeneity of the porosity of the sheet, detrimental to its effectiveness in terms of acoustic attenuation. Furthermore, such shaping is difficult because the sheet is relatively rigid.
• the invention aims to overcome the various drawbacks of these known techniques by proposing a method of manufacturing an acoustic attenuation panel of the type with a honeycomb structure flanked, on the one hand, by a reflector and, on the other hand, by an acoustically resistive layer with two components respectively with acoustic property and with structural property, making it possible to obtain panels with complex shape in particular with evolving curvatures which can be significant and in particular monoblock panels of generally annular shape with or without splint, such as those intended at the entrances and nacelle fan channel outlet, having both very good mechanical properties and optimal acoustic properties.
• the subject of the invention is a method of manufacturing an acoustic attenuation panel comprising a honeycomb structure flanked, on the one hand, by a reflector and, on the other hand, by an acoustically resistive layer with two components respectively with acoustic property and with structural property, characterized in that it consists: in placing on a mold of a shape suitable for the panel to obtain a layer with structural property consisting of wires pre-impregnated with a thermoplastic resin or thermosetting, by draping, coiling or wrapping, so that said layer has an open surface rate of the order of 30% of the total surface of the exposed surface, to be placed over the layer with structural property a layer with an acoustic property made up of a microporous fabric and with a thickness of the order of a tenth of that of the layer with a structural property, then putting in place lveolar and the reflector with optionally the addition of an adhesive between components, - at least one autoclave cooking step being
• the method of the invention makes it possible to obtain an acoustically resistive layer with remarkable acoustic and structural properties, in particular the efficiency of the acoustic attenuation due to the very good homogeneity of the porosity rate of said acoustically resistive layer, which can be defined precisely.
• said layer with structural property is given the porosity required by the choice of the spacing of the threads for weaving, in the case of a fabric, the flexibility of the latter allowing it to match the shapes. of the mold without substantial deformation of the mesh of the fabric.
• said layer with structural property is given the porosity required by piercing said layer after baking in an autoclave.
• the drilling is carried out to precise diameters and in a shaped and rigid part, the control of the porosity is perfectly ensured.
• the layer with structural property consists of several layers of crossed wires, the layers being on either side of the layer with acoustic property.
• the invention also relates to the panels obtained in accordance with the above process.
• FIG. 1 is a schematic sectional and exploded view of a panel structure obtained according to the method of the invention
• - Figure 2 is a similar sectional view illustrating another embodiment of the method of the invention
• FIG. 3 is a partial top view of the structural property layer of the panel of Figure 2;
• FIGS. 4a to 4e illustrate different stages in the production of a panel of the type of FIG. 1,
• FIG. 5 is a partial sectional view illustrating a method of bonding the two-component acoustic layer to the cellular structure
• FIG. 6 is a partial section view illustrating a variant of the method illustrated in FIG. 2.
• the panel is in one piece, annular without a splice or with a single splice and is produced using a mold symbolized in M in FIG. 1, of shapes and dimensions appropriate to those of the panel to be obtained. and on which the successive layers of the panel will be draped, wound or wrapped.
• the first of these layers is a layer with a structural property 1 a, on which a layer with acoustic property 1 b will then be put in place, the assembly 1 a-1 b forming the two components of a layer 1 known as acoustically resistive, on which will be placed a honeycomb structure 2, simple as illustrated or multiple as mentioned above.
• the layer with structural property 1a is formed from wires pre-impregnated with an appropriate thermoplastic or thermosetting resin.
• yarn is meant yarn, fiber, wicks in the form of a ribbon of square or rectangular section, of carbon, glass, "Kevlar”, or other mineral or organic, natural or synthetic fibers.
• the acoustic property layer 1b is formed from a very fine fabric of carbon fibers, glass, “Kevlar” or other mineral or organic, natural or synthetic fibers, dry or prepreg.
• the honeycomb structure 2 is for example a paper of aramid fibers such as that commercially called "NOMEX".
• the layer with structural property consisting of a fabric draped over the mold M, or by threads deposited by winding or wrapping, is produced, then polymerized by autoclave cooking.
• This open surface rate is advantageously of the order of 30% of the exposed surface of the layer 1a.
• the perforations 4 produced for this purpose in the layer 1 a preferably have a ratio of the diameter to the thickness of the layer 1 a greater than 1 to reduce the harmful effects of the acoustic non-linearity.
• the perforations 4 are produced by various mechanical means, by laser or by electroerosion.
• the layer 1 a After perforation of the holes 4, the layer 1 a still being in place on the mold M, the layer having an acoustic property 1 b is put in place, with the possible interposition of an adhesive layer 5, then the honeycomb structure 2 is put in place with possible interposition of a second adhesive layer 6 and finally the reflector 3.
• a second polymerization by autoclave cooking can be carried out after the layers 1b and 5 have been put in place, then a third polymerization by autoclave cooking is carried out after the layers 2 and 3 have been put in place, a crosslinking adhesive being advantageously interposed between the layers 2 and 3. Finally, the mold M is removed to release the finished panel.
• FIG. 2 is similar to that of FIG. 1, except that the layer with a structural property Ta of the two-component acoustically resistive layer 1 ′ is formed from strands of fibers deposited in a fabric weft, namely warp wicks 7 and weft wicks 8, the mesh thus produced defining passage openings 9 (FIG. 3) rectangular or square, constituting approximately 30% of the surface of the layer a.
• the layer with a structural property Ta of the two-component acoustically resistive layer 1 ′ is formed from strands of fibers deposited in a fabric weft, namely warp wicks 7 and weft wicks 8, the mesh thus produced defining passage openings 9 (FIG. 3) rectangular or square, constituting approximately 30% of the surface of the layer a.
• the fibers of the locks 7, 8 can be of the type indicated above, dry or prepreg.
• the wicks 7, 8 are deposited individually by winding, wrapping or manual deposit or not on a mold (not shown) similar to the mold M of Figure 1. A polymerization is then carried out.
• the spacing between wicks 7, 8 and the polymerization conditions are defined so as to give the layer 1a the required non-linearity factor.
• the thickness of the layer with structural property 1a, l ' is of the order of 10 times the thickness of the layer with acoustic property 1b, Tb.
• the layer with a structural property 1 a may consist of several plies of fabrics of prepreg yarns or of several layers of superimposed coiled prepreg yarns or streamers.
• the acoustically resistive layers (1, 1 ') of the panels according to the invention although made up of two components, nevertheless have excellent mechanical qualities.
• the materials of the two components, structural and acoustic are identical and compatible and lend themselves to good bonding and, after polymerization, form a single composite sheet with almost zero risk of delamination, very resistant to erosion and abrasion. , shock and moreover easy to repair.
• the resistive layers have, due to the precise control of their porosity rate during manufacture, a very good acoustic performance in particular in terms of non-linearity, their impedance not depending on the Mach number of the grazing flow. .
• the panels according to the invention are also simple and easy to produce.
• Figures 4a to 4d illustrate an embodiment of a panel of the type of Figure 1, on a mold (not shown) similar to the mold M.
• the layer of crosslinking adhesive 5 is applied (FIG. 4a), then the acoustic layer is placed
• the adhesive 6 diffuses well in the porous mass of the layer 1b and the junction between the end edge of the walls of the cells of the honeycomb 2 and the opposite face of the layer 1b is established by constituting good bridging connections at the level of the honeycomb cell bases defining cross-sectional links which increase as one approaches the face of said layer 1b.
• the invention makes it possible to give the acoustic component (layer 1 b) a very fine thickness, much less than that of the structural layer 1 a.
• the layer 1 a could have a thickness of one millimeter, while the thickness of the layer 1 b could be reduced to 0.1 millimeters without degrading its acoustic properties.
• FIG. 4e illustrates an alternative embodiment of the assembly of layers 1 a, 1 b and 2, in which the crosslinking adhesive 5 between the layers
• the assembly 1 a, 1 b, 2 is thus securely fixed.
• the only adhesive used (6) is deposited only at the level of the feet of the cells of the honeycomb 2, which limits the obstruction of the passage openings 4 through the structural layer 1a to the only zones facing said cell feet.
• FIGS. 4a to 4e can be used with the various variants of panel structure described above. This technique makes it possible to easily design and produce acoustic attenuation panels with efficient and homogeneous mechanical characteristics, adapted to various environments, in particular those mentioned above such as the nacelles of turbo-engines.
• FIG. 5 an alternative embodiment of the holes 4 of the structural layer 1 a has also been illustrated during their perforation, according to which the external outlet of said holes 4 is advantageously flared, by any appropriate means, as shown in 1 1, so as to improve the acoustic linearity.
• FIG. 6 illustrates another alternative embodiment of the method of the invention according to which the layer with structural property is reinforced.
• the layer with structural property consists of several layers of crossed prepreg son placed on either side of the layer with acoustic property 1 "b.
• FIG. 6 On the left-hand side of FIG. 6, there is shown a first distribution of two plies of crossed threads, respectively a ply 13 of warp threads, deposited first on a mold (not shown) similar to the mold M of FIG. 1 and a ply 1 4 of weft threads deposited over the layer 1 "b, that is to say after the latter has been removed.
• FIG. 6 On the right-hand side of FIG. 6, a second distribution of three plies is shown, namely two plies crossed in a weaving weft 1 5, deposited first on the mold and a third ply 1 6 of threads parallel to the threads of the 'one of the layers of the weft 1 5, deposited over the layer with acoustic property 1 "b.
• All of the components 1 3, 1 4, 1 5, 1 6, 1 "b thus form an acoustically resistive layer 1" with properties that are both structural and acoustic.
• This assembly is polymerized under pressure before installation of the other components 2, 3.
• the spacing of the son of the plies 13, 14, 15, 16 deposited by winding or wrapping determines the rate of porosity of the layer 1 ".

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Multimedia (AREA)
• Soundproofing, Sound Blocking, And Sound Damping (AREA)
• Laminated Bodies (AREA)

Applications Claiming Priority (3)

Publications (2)

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Family Applications (1)

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• 1999
  • 1999-12-24 FR FR9916447A patent/FR2803078B1/fr not_active Expired - Lifetime
• 2000
  • 2000-12-21 WO PCT/FR2000/003648 patent/WO2001048734A1/fr active IP Right Grant
  • 2000-12-21 ES ES00993660T patent/ES2217038T3/es not_active Expired - Lifetime
  • 2000-12-21 US US09/914,181 patent/US20020157764A1/en not_active Abandoned
  • 2000-12-21 DE DE60008861T patent/DE60008861T2/de not_active Expired - Lifetime
  • 2000-12-21 CA CA2365100A patent/CA2365100C/fr not_active Expired - Lifetime
  • 2000-12-21 EP EP00993660A patent/EP1157372B1/de not_active Expired - Lifetime

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