Classifications

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  • B32B7/04—Interconnection of layers
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Definitions

• the invention relates, in general, to the technical field of acoustic attenuation structures or panels.
• the invention relates to the manufacture of composite panels comprising a honeycomb-type central honeycomb core sandwiched between two skins, in particular applied to acoustic attenuation structures used to reduce noise produced in restrictive environments, for example in the aeronautical field in aircraft engines as well as in gas turbines or exhausts thereof, or even in the railway field.
• Acoustic attenuation structures are conventionally made up of, on the one hand, an acoustic plate or skin called “resistive” skin permeable to the acoustic waves that it is desired to attenuate and, on the other hand, a plate or full skin called “reflective” skin, between which is placed a core forming a cellular body, for example a honeycomb-type alveolar structure.
• the acoustic skin is generally acoustically porous and perforated with a multitude of orifices allowing fluid communication between the exterior and the interior of the cellular core of the composite structure, to thus form an acoustic attenuation structure.
• acoustic composite panel type is generally acoustically porous and perforated with a multitude of orifices allowing fluid communication between the exterior and the interior of the cellular core of the composite structure, to thus form an acoustic attenuation structure.
• such acoustic attenuation structures form Helmholtz type resonators which make it possible to attenuate acoustic waves in a certain frequency range, each of the cells of the alveolar core open at the level of the perforation associated with the acoustic skin forming a Helmholtz resonator.
• These acoustic attenuation structures generally have a honeycomb-type honeycomb core and acoustic performance obtained are thus limited to the absorption of a relatively narrow range of frequencies depending on the shape and dimensions of each of the cells.
• the composite attenuation structure with a cellular core can be a structure with 1 degree of freedom (SDOF structure, SDOF for “Simple Degree Of Freedom” ), with 2 degrees of freedom (DDOF structure, DDOF for “Double Degree Of Freedom”) or, more generally, with M degrees of freedom (MDOF structure, MDOF for “Multiple Degree Of Freedom”), M being an integer greater than 2.
• SDOF structure SDOF for “Simple Degree Of Freedom”
• DDOF structure DDOF for “Double Degree Of Freedom”
• M degrees of freedom MDOF structure, MDOF for “Multiple Degree Of Freedom”
• the acoustic composite structure When the acoustic composite structure has several degrees of freedom, it comprises several layers of cellular bodies or superimposed cellular cores, two layers of neighboring stacked cellular cores being separated by a septum. It is known that this septum consists of a microporous wall pierced with holes so that, for two given cells of a pair of superimposed cells, each belonging to one and the other two layers of stacked cellular cores distinct and neighboring, said cells of the given pair of cells communicate acoustically with each other. The septum is therefore similar to an intermediate resistive skin.
• Such an acoustic composite structure has a greater total thickness, such a characteristic makes it possible to enlarge the volume of each cavity forming a Helmholtz resonator and to consequently extend the frequency band of the attenuated acoustic waves towards lower frequencies. , for example between 500 and 1000 Hz.
• Drilling the wall constituting the septum is well known and relatively simple to implement for planar acoustic composite structures, forming regular planar acoustic panels. However, such drilling is complex to implement for acoustic composite structures having curved or even complex shapes.
• inserts intended to be housed in each of the cells of the cellular structure to improve the acoustic performance of an acoustic panel.
• truncated cones are connected together by bars at their large bases which must be positioned in notches made at the end of the cells. The truncated cones are designed to each be housed inside an associated cell, each large base being inscribed in a section of the interior space of the associated cell.
• the invention aims to remedy all or part of the drawbacks of the state of the art by proposing in particular a solution making it possible to obtain a simple composite acoustic structure and which constitutes an efficient acoustic insulator.
• a structural element for an acoustic composite structure, the structural element comprising at least one cellular core comprising a network of hollow cells delimited by partitions extending between two faces of the cellular core, and at least one resistive skin covering one of the faces of the cellular core, the structural element being remarkable in that it comprises a plurality of attached inserts, each insert having a through tubular body open at its ends and a collar projecting from the associated tubular body, and in that the resistive skin is perforated by each of the inserts positioned opposite all or part of the cells so that, for each insert, the collar is positioned against the resistive skin on a first side, and the tubular body opens onto a second side, opposite the first side.
• the inserts are formed in one piece, the tubular body of each of the inserts extending between a first end presenting the collar and a second end.
• the second end is circumferentially beveled, that is to say that the tubular body has a reduction or narrowing in its external diameter towards, preferably as far as, the second end.
• the end then has a frustoconical outer envelope.
• Such a beveled end makes it easier to perforate the resistive skin.
• the first side of the resistive skin corresponds to the exterior side of the structural element with respect to the resistive skin, opposite the cellular core, the second side of the resistive skin being the side next to the alveolar core.
• the resistive skin is formed of a multilayer composite structure.
• the resistive skin comprises a prepreg fabric, more preferably a layer of fabric interposed between two layers of glue.
• the characteristics of the structural element during its manufacture are also the same once the structural element has been manufactured.
• the autoclave cooking which allows the manufacturing to be finalized does not in fact modify the structure of the structural element nor of the acoustic composite structure in which it is integrated if applicable.
• the tubular body of each of the inserts extends between a first and a second end along an opening axis, the tubular body having, at the first end, the flange extending in plane orthogonal to the opening axis, the tubular body being open axially at its two ends.
• the tubular body of the inserts has a constant section, for example cylindrical.
• the inserts are distinct from each other. In this way the inserts are not secured to each other before the perforation of resistive skin. The rigidity of the structural element obtained is thus minimized.
• the added inserts are formed in one piece, preferably in thermoplastic material(s), more preferably obtained by molding, for example by injection.
• thermoplastic material(s) more preferably obtained by molding, for example by injection.
• Such inserts are simple to manufacture, resistant, and inexpensive.
• the acoustic structure can form a simple acoustic panel, in particular when a reflective skin is added so as to cover the other of the two faces of the cellular core, namely the opposite face of the resistive skin relative to the cellular core.
• a simple acoustic composite structure forming a panel, planar or not, whose cellular core is interposed between the reflective and resistive skins.
• the acoustic composite structure comprises a composite structure with N degrees of freedom comprising a superposition of N layers of cellular cores, N being greater than or equal to 2, the composite structure comprising at least one septum separating two layers of neighboring stacked cellular cores, the resistive layer perforated by the inserts forming the septum or one of the septa of the acoustic composite structure.
• the composite structure forms a DDOF, the resistive layer perforated by the inserts forming the septum of the DDOF.
• An acoustic composite structure is obtained whose exterior resistive skin, that is to say open to the outside, can have an aerodynamic shape and which at the same time responds to the problems of absorption of sounds at low frequencies and at high frequencies. frequencies by a Helmholtz resonator adapted using tubular inserts.
• the invention also relates to a method of manufacturing a structural element for an acoustic composite structure, the structural element comprising at least one cellular core comprising a network of hollow cells delimited by partitions extending between two faces of the cellular core, and at least one resistive skin covering one of the faces of the cellular core, the structural element comprising a plurality of attached inserts, each insert having a through tubular body open at its ends and a collar projecting from the associated tubular body, the resistive skin being perforated by each of the inserts positioned opposite all or part cells so that, for each insert, the collar is positioned against the resistive skin on a first side, and the tubular body emerges from a second side, opposite the first side, the method of manufacturing the structural element being remarkable in that it includes the following stages: manufacturing of the cellular core; positioning of the resistive skin so that it covers one of the faces of the cellular core; positioning of the inserts in the resistive skin opposite all or part of the cells so that, for each
• the method of manufacturing the structural element comprises a step of coating a preparation such as an adhesive, for example based on polymer material(s), so as to coat the first side of the resistive skin perforated by the added inserts and the upper faces of the collars of the inserts, the coating step being preferably followed by a crosslinking step, more preferably by adding heat.
• a preparation such as an adhesive, for example based on polymer material(s)
• the resistive skin with the inserted inserts is thus covered with a film of a predetermined preparation such as a film of glue, for example an epoxy glue which will be crosslinked with the addition of heat, in particular around the orifices delimited by the tubular body of the inserts in order to free the orifices from the glue.
• a film of glue for example an epoxy glue which will be crosslinked with the addition of heat, in particular around the orifices delimited by the tubular body of the inserts in order to free the orifices from the glue.
• the glue also has the advantage of ensuring a dual function, on the one hand to ensure the maintenance of the inserts against the associated skin, and on the other hand, to ensure bonding of the two layers of cellular cores of the DDOF structure when the skin perforated by the inserts constitutes the septum which separates them.
• the step of positioning the inserts in the resistive skin comprises at least: a first positioning step in which a tool carries at least one punch and comes opposite a cell, the punch having a head configured to come into contact against the collar of the associated insert, and a rod, the rod passing axially through the tubular body of the associated insert along its opening axis; a second positioning step, subsequent to the first positioning step, in which the punch is moved by an axial translation along the opening axis so as to perforate the resistive skin, the head of the punch pushing the insert up to that its collar comes into contact directly against the resistive skin; and a third positioning step in which the punch withdraws leaving the insert in the resistive skin.
• the method of manufacturing the acoustic composite structure being characterized in that it comprises the following steps: manufacturing a structural element according to the method described above; assembly of the structural element with at least one skin, preferably a resistive or reflective skin, covering the other of the two faces of the cellular core.
• This distinct skin to which the structural element is assembled is in particular a reflective skin, for example in the case of an SDOF structure or can for example be another reflective skin, for example if the reflective skin of the structural element is intended to form the septum of a DDOS structure.
• the method of manufacturing the acoustic composite structure comprises a step of superimposing at least one layer of cellular core with the acoustic composite structure
• the reflective skin is draped in the form of a prepreg, an autoclave cooking step preferably also being implemented after assembly.
• Figure 1 a schematic sectional view of a part of an acoustic composite structure of complex shape according to a first embodiment
• Figure 2 a schematic sectional view of a part of an acoustic composite structure of planar shape according to another embodiment, shown without the resistive and reflective skins on the end faces
• Figure 3 an isometric perspective view, from below, of the acoustic composite structure of Figure 2
• Figure 4 a top view of the acoustic composite structure of Figure 2
• Figure 5A a view of a first step of positioning an insert in the resistive skin of a method of manufacturing a structural element according to one embodiment
• Figure 5B a view of a second step of positioning the insert in the resistive skin of the method of manufacturing a structural element, this second step being subsequent to the first step of Figure 5A
• Figure 5C a view of a third step of positioning the insert in the resist
• Figure 1 illustrates a schematic sectional view of a part of an acoustic composite structure 100 according to one embodiment of the invention.
• the acoustic attenuation structure 100 here comprises a structure with two degrees of freedom, commonly called “DDOF”.
• the acoustic attenuation structure 100 comprises a superposition of two cellular cores 20, 20', a lower cellular core 20 and an upper cellular core 20', each comprising a network of hollow cells 21, 21' delimited by partitions 22, 22'.
• the two cellular cores 20, 20' are separated from each other by a septum 30'.
• Each of these cellular cores 20, 20' are here made up of a honeycomb type structure, for example of the NIDA® type.
• each of the cellular cores 20, 20' is preferably made of at least one metallic material(s), more preferably of metallic material(s) capable of to withstand high temperatures depending on the desired uses. In the field of aeronautics for example, one can choose one or more metallic material(s) capable of resisting hot ejection temperatures.
• the materials used to constitute the network of cells 21, 21' can of course be different, for example in thermoplastic material(s) or in synthetic material(s), for example in aramid. It will also be noted that other shapes of cells 21, 21' can be used, and not only in hexagonal shapes in the case of honeycombs.
• the cellular structure formed by the superposition of the two cellular cores 20, 20' is covered: on one of its two faces, with a resistive skin 31, also called acoustic skin, permeable to the acoustic waves that we wish to attenuate. and covered, and on another of its two faces, opposite the face covered by the resistive skin 31, with a reflective skin 32, also called solid skin, which is generally oriented opposite a noise source, either at the rear in relation to the acoustic composite structure.
• a resistive skin 31 also called acoustic skin
• a reflective skin 32 also called solid skin
• the septum 30' forms an intermediate resistive skin separating the two cellular cores 20, 20'.
• each of the alveoli of this central cellular structure namely each of the alveoli of the two alveolar cores 20, 20', forms a Helmholtz resonator.
• the resonator is thus constituted by a bottle, formed by a cell of the nest of bees and a collar formed by piercing the resistive skin.
• the septum 30' is itself also pierced and the entire thickness of the DDOF structure is thus used to attenuate the acoustic waves, the cells of the two cellular cores 20, 20' being superimposed , a given pair of superimposed cells 21, 21' communicating with each other via an orifice 55 of the septum 30'. In this way, the septum 30' forms an intermediate resistive skin, between the two cellular cores 20, 20'.
• Each insert 50 has a through tubular body 51 open at its ends 53, 54 and a collar 52 projecting from the associated tubular body 51.
• the tubular body 51 being through, it allows the communication of acoustic waves through it between two cells 21, 21' of a given pair of superimposed cells of the cell cores 20, 20'.
• the intermediate resistive skin 30 formed here by the septum 30' is perforated by each of the attached inserts 50, which are positioned opposite all or part of the cells 21 of the lower cellular core 20.
• the lower cellular core 20 and the septum 30' together form a structural element 10.
• a structural element 10 comprising the septum 30' forming a resistive skin and the upper cellular core 20' is also possible but more complex to be manufactured because this implies that for each positioned insert, the collar is positioned against the resistive skin on a first side, and the tubular body opens out on a second side, opposite the first side, the first side of the resistive skin corresponding to the interior side, facing the cellular core, the second side of the resistive skin being the exterior side of the structural element relative to the resistive skin, opposite the cellular core.
• the structural element 10 can be integrated into a structure other than a DDOF.
• the acoustic composite structure could be a simple composite panel formed from the cellular core 20 sandwiched between the reflective 31 and resistive skins 30, 32.
• the acoustic composite structure could comprise more than 2 degrees of freedom, for example 3.
• the resistive skin pierced by the inserted inserts 50 can be one of the intermediate skins forming the septum, or even the exterior resistive skin.
• the resistive skin pierced by the inserts 50 forms a septum separating two of the layers of cellular cores, for example to guarantee the flatness of the exterior resistive layer in order to guarantee optimal aerodynamic performance.
• the structural element 10 thus formed is configured so that, for each insert 50: the flange 52 of said inserts 50 is positioned against the associated resistive skin 30, here the septum 30', d a first side here exterior of the structural element 10 relative to the associated resistive skin 30, namely here on the side opposite the lower cellular core 20, and the tubular body 51 opens onto a second side, opposite the first side, in particular in one of the associated cells 21 of the lower cellular core 20.
• the added inserts 50 are independent of each other, that is to say they are not linked together, other than of course by the septum 30' once positioned on them. In other words, they are not linked by dedicated fixing means, unlike the prior art.
• the tubular body 51 of the inserts 50 is cylindrical and open axially at its two ends 53, 54. This allows the communication of acoustic waves through the hollow space open in a traversing manner of the tubular body 51 delimiting the associated orifice 55.
• the tubular body 51 of each of the inserts 50 extends between its two ends, namely a first and a second end 53, 54 along an opening axis A.
• the opening axis A is such that it is oriented at least locally perpendicular to the face of the cellular core 20 covered by the septum 30'.
• the tubular body 51 carries at the first end 53 the flange 52 which extends in a plane P orthogonal to the opening axis A.
• the flange 52 has the shape of a disc crown coaxially surrounding the tubular portion of the first end 53 of the tubular body 51.
• the inserts 50 are each formed in one piece, preferably in thermoplastic materials, more preferably obtained by molding, for example by injection.
• thermoplastic materials that can be used, we can cite for example polyetheretherketone (PEEK), polyetherimide (PEI), polyphenylene sulfide (PPS), or even polycarbonate (PC).
• PEEK polyetheretherketone
• PEI polyetherimide
• PPS polyphenylene sulfide
• PC polycarbonate
• other materials alone or in combination can be used.
• other manufacturing processes can be used such as extrusion or additive manufacturing.
• Each insert 50 may have a second end 54 beveled circumferentially in the direction of a narrowing in diameter of the tubular body towards the second end 54.
• This bevel may make it easier to position the associated insert 50 during perforation. of the skin, this even if the second end 54 is not intended to itself ensure the perforation of said skin, for example when using a punch 60 (see Figures 5A, 5B and 5C described below).
• This bevel can also be obtained to facilitate the manufacture of the insert 50 by forming an undercut.
• the internal diameter of the tubular body 51 is predetermined and calibrated according to the use for which the acoustic composite structure 100 is intended, its dimensions and the frequency ranges of acoustic waves to be attenuated.
• the collar 52 and the tubular body 51 are connected by a fillet oriented towards the second end 54.
• the fillet offers the advantage of allowing a cooling rate more homogeneous, if the insert 50 is made of metallic material(s) in particular, or to ensure good flow in the mold and therefore good filling, if the insert 50 is made of material(s) thermoplastic(s) in particular, or more simply to guarantee good demoulding of the part.
• Figures 2, 3 and 4 illustrate schematic views of a part of an acoustic composite structure 100 shown without the resistive 32 and reflective 31 skins on the end faces, in respectively sectional views, in isometric perspective from below and above.
• This second embodiment illustrated in these Figures 2, 3 and 4 differs from the first embodiment of Figure 1 essentially in that it is planar, that is to say that it does not present a complex curved shape.
• a first step of the manufacturing process consists of manufacturing the structural element 10. Firstly, the cellular core 20 is manufactured, intended to form the lower cellular core 20 of the final DDOS, the cellular core 20here presenting the shape of a honeycomb structure.
• the cellular core 20 can then be formed at this stage of the process.
• the resistive skin 30 of the structural element 10 is positioned so as to cover one of the faces 23, 24 of the cellular core 20.
• the resistive skin is formed of a multilayer composite structure. It is draped on the associated face of the cellular core 20 in the form of a prepreg film composed of several layers.
• This multilayer prepreg skin notably comprises at least one structural ply, for example a fabric formed of glass fibers pre-impregnated with epoxy resin.
• This structural addition is also interposed between two films of epoxy glue, one of the layers of glue of which will be in contact with one end of the partitions 22 of the network of cells 21 of the lower cellular core 20, on the side of the face covered by the skin.
• each layer constituting the resistive skin 30 of the structural element 10 may be different.
• the layers may be woven or non-woven. Several structural folds can be superimposed, which is particularly advantageous in terms of resistance. Strength is further increased when the fibers in the different woven plies have different orientations. The orientation of the fibers is configured to ensure the best resistance depending on the desired end use.
• the layers of glue(s) can also vary and be screened or not.
• the fabric of the woven ply(s) may also be in a material other than glass, for example carbon fibers.
• One of the layers can also be a thermoplastic film or fabric.
• a multi-layer skin comprising an air-impermeable barrier, at least one of the layers being impermeable to air and having a resistance to air flow equal to or greater than approximately 50 rayls MKS, or 50 kg s -1 ⁇ m " 2 in fundamental units SL
• FIG. 5A, 5B and 5C This method of positioning the inserts 50 is illustrated in detail in Figures 5A, 5B and 5C.
• a first step of positioning an insert 50 in the resistive skin 30 of the structural element 10 in which a tool (not illustrated) carries a punch 60 and comes opposite a cell 21, the punch 60 having a head 62 configured to come into contact against the collar 52 of the insert 50, and a rod 61, the rod 61 passing axially through the body 51 tubular of the insert 50 along its opening axis A.
• the rod 61 extends axially under the head 62 and has a length greater than that of the insert 50 which guarantees the fact that the rod 61 passes through on either side the tubular body 51 of the insert 50.
• the external diameter of the rod 61 is chosen so as to be substantially equal to the internal diameter of the tubular body 51 so that the friction generated between the punch 60 and the insert 50 are sufficient to keep the insert 50 fitted on the punch during this first step, without however constraining it too much so that it remains possible to remove the insert 50; a second step of positioning the insert 50 in the resistive skin 30 of the method of manufacturing the structural element 10, this second step being subsequent to the first step.
• the punch 60 is moved along the opening axis A so as to perforate the skin 30, the head 62 of the punch pushing the insert 50 until its collar 52 comes into contact directly against the prepreg 30. During this step, the collar 52 sticks against the first layer of the prepreg reflective skin.
• the tool can be for example a robotic arm provided at its end with punch 60.
• the robotic arm can be configured to place an insert 50 each time, and include a single punch 60, or well carry several punches 60 and be thus configured to position several inserts 50 in a synchronized manner.
• the advantage of a positioning tool carried by a robotic arm is to facilitate the installation of the inserts 50 along a complex surface.
• the robotic arm is for example a 6-axis robotic arm.
• a step of coating a preparation 40 is implemented.
• the preparation may for example be a glue, for example based on polymer materials.
• This step consists in particular of coating at least on the one hand the exterior side of the resistive skin 30 perforated by the inserts 50, side against which the lower faces of the flanges 52 of the inserts 50 are in contact, and on the other hand the upper faces flanges 52 of inserts 50.
• the coating step is followed by a crosslinking step, for example by adding heat.
• the multilayer resistive skin 30 provided with inserts 50 then inserted through said skin is thus covered with a film of epoxy glue which is then crosslinked with the addition of heat around the orifices 55 of the inserts 50 in order to to release them from the glue (see Figures 6A and 6 B).
• the crosslinking of the glue hardens the glue, and the glue possibly placed in the orifices 55 of the tubular bodies 51 is withdrawn locally leaving these orifices 55 free.
• This additional layer 40 allows the embedding of the flanges 52 of the inserts 50 between the additional layer of preparation on the one hand, and the resistive skin 30 on the other hand, this to guarantee the maintenance of the inserts 50 during the operating life of the acoustic composite structure 100.
• the structural element 10 is assembled with at least one skin, such as a resistive skin 32 (see for example Figure 1) so that it covers the other of the two faces of the cellular core 20.
• a resistive skin 32 see for example Figure 1
• another cellular core 20' and its reflective skin 31 are also assembled by being glued.
• the assembly is placed in an autoclave to undergo a cooking step.
• the different septa 30' which separate the different layers of cellular cores 20, 20', the different layers of cellular cores 20, 20', the rear reflective skin 32 and the front exterior resistive skin 31 are assembled under the shape of a single piece before being introduced into the autoclave.
• the structural element alone can be cooked in an autoclave and then the structural element can be integrated into an acoustic composite structure by means of another process, for example by brazing.

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• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Soundproofing, Sound Blocking, And Sound Damping (AREA)
• Transducers For Ultrasonic Waves (AREA)

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• 2022
  • 2022-04-11 FR FR2203325A patent/FR3134340B1/fr active Active
• 2023
  • 2023-04-11 US US18/855,818 patent/US20250319685A1/en active Pending
  • 2023-04-11 WO PCT/EP2023/059447 patent/WO2023198715A1/fr not_active Ceased
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