Patent Description:
It is generally known that sound-absorbing panels are used in aviation, particularly arranged on the engine nacelle around the engine to absorb its dispersed sound power. In general, said sound-absorbing panels have a so-called "sandwich" structure, that is, comprising a pair of outer skins interspersed with a central layer called the core. Typically, the core is made with a honeycomb structure, and the skin facing the engine or noise source is provided with a plurality of holes; in this way, the sound wave may enter the interior of the central layer and remain confined in the volumes of the honeycomb structure, i.e., hexagonal cells, also called resonance chambers.

Such a sound-absorbing panel for aircraft use is known, for example, from European patent <CIT> or from European patent <CIT>.

A further example is known from the international patent application <CIT>.

In the prior art mentioned above, the core has a honeycomb structure, i.e., wherein the resonance chambers, or cells, are all the same shape and size, and are, therefore, unable to abate noise over a wide spectrum of frequencies. Indeed, the state of the art of the research focuses exclusively on defining complex core shapes for sound-absorbing panels for multi-frequency noise abatement, typically in the frequency range of <NUM> to <NUM> and even more particularly in the frequency range of <NUM> to <NUM>.

Moreover, in light of the evolution of turbofan engines toward higher and higher dilution ratios, the need arises to abate noise at lower and lower frequencies, and, at the same time, abate noise over an increasingly broad frequency spectrum.

patent documents <CIT> and <CIT> describe several possible geometries for the central layer, i.e., the core, of a sound-absorbing panel, but they do not solve the problem of manufacturing said core.

The method for manufacturing cores for sound-absorbing panels presently starts from expanded cores. For example, <CIT> shows a panel having a central layer or a core with honeycomb with hexagonal cells obtained by means of a conventional bonding method with glue distributed in strips, and mechanical expansion. The European patent <CIT> shows the same configuration, but applied to a component made of a composite material and therefore subjected to co-curing. The European patents <CIT> and <CIT> also show the possibility of improving noise absorption by plasma or ion discharges interacting with acoustic waves within the core cells. The <CIT> also shows that adjacent cells of a honeycomb-shaped core may be connected through apertures that conduct acoustic waves on differentiated paths. Finally, the international patent application <CIT> shows differentiated paths for acoustic waves through microdrillings in the two walls, or skins, that enclose and seal the core.

The manufacturing methods according to the prior art, however, have several disadvantages and many limitations in applicability. Specifically, in a honeycomb-shaped core: the cell sizes are constant, and all cells have the same shape; any partitioning partitions must be inserted cell-by-cell individually and glued there; finally, the core has difficulty adapting to complex geometries, particularly when those geometries have small curvature radii.

The object of the present invention is to overcome the drawbacks of the prior art, and thus to provide a method for manufacturing a sound-absorbing panel core for aeronautical application that does not suffer from the drawbacks described above and that is flexible and cheap.

A further object of the invention is to provide a core for a sound-absorbing panel for aeronautical application that is easy to make, inexpensive, and suitable for absorbing noise on many different frequencies distributed along a broad frequency spectrum.

This and other objects are fully achieved according to the present invention by a method for manufacturing a core for a sound-absorbing panel with a sandwich structure for noise reduction in an aircraft as defined in the attached independent claim <NUM>, as well as by a core for a sound-absorbing panel with sandwich structure for noise reduction in an aircraft as defined in the attached independent claim <NUM>.

Advantageous embodiments of the invention are specified in the dependent claims, the content of which is to be understood as an integral and integrating part of the following description.

In summary, the invention is based on the idea of providing a method for manufacturing a core for a sound-absorbing panel with sandwich structure for noise reduction in an aircraft, the method comprising the steps of:.

Preferably, moreover, step a) of providing the first partitioning elements comprises the sub-step of:.

In general, within the scope of the present description and the attached claims, a material is defined as 'microporous' when it has a plurality of pores or holes having an average diameter between about <NUM> and about <NUM> nanometers. Furthermore, within the scope of the present description and the attached claims, a material is defined as 'microdrilled' when it has a plurality of pores or holes having an average diameter between about <NUM> micrometer and about <NUM> micrometers. Finally, within the scope of this description and the attached claims, a material is defined as "drilled" when it has a plurality of pores or holes having an average diameter greater than about <NUM> micrometers.

Advantageously, according to an embodiment of the method for manufacturing the core according to the invention, step c) follows step d).

Finally, preferably, such a method further comprises the step of:
h) following step d), strengthening the assembly formed by the first partitioning elements and the second partitioning elements by means of immersion in resin, preferably epoxy or phenolic resin, and subsequent curing.

Also forming part of the present invention is a method for manufacturing a sound-absorbing panel with a sandwich structure for noise reduction in an aircraft, comprising the steps of:.

Preferably, this method further comprises the steps of:.

Preferably, this method further comprises the step of:.

A core for a sound-absorbing panel with sandwich structure for noise reduction in an aircraft is also part of the invention, such core comprising:.

Preferably, the plurality of transverse slits is distributed according to an asymmetrical pattern on each first partitioning element, and the plurality of transverse slits is distributed according to the same pattern on each first partitioning element.

Preferably, in the core according to the third aspect of the invention, the first partitioning elements further have a plurality of first openings adapted to connect adjacent cells of said plurality of cells, and/or the second partitioning elements further have a plurality of second openings adapted to connect adjacent cells of said plurality of cells. In said case, preferably, the core further comprises at least one microporous or microdrilled membrane, arranged to at least partially close at least one of said first or second openings.

Preferably, in the core according to the third aspect of the invention, the distance between two successive vertical slits of the plurality of vertical slits of each first partitioning element is not constant.

Preferably, in the core according to the third aspect of the invention, the distance between two successive first partitioning elements of the plurality of first partitioning elements is not constant.

Finally, according to a fourth aspect of the invention, a sound-absorbing panel with a sandwich structure for noise reduction in an aircraft also forms part of the invention, comprising:.

Preferably, in the panel according to the fourth aspect of the invention, the first skin extends over a surface having a single or double curvature.

Further features and advantages of this invention will be clarified by the detailed description that follows, given purely by way of non-limiting example in reference to the appended drawings, wherein:.

As may be seen in <FIG>, a sound-absorbing panel with sandwich structure for noise reduction in an aircraft is generally indicated by the reference number <NUM>. The panel <NUM> essentially comprises a first skin <NUM>, a second skin <NUM>, and a core <NUM> arranged between the first skin <NUM> and the second skin <NUM>.

As shown in <FIG>, the core <NUM> essentially comprises a plurality of first partitioning elements <NUM>, a plurality of second partitioning elements <NUM>, and horizontal partitioning elements <NUM>.

The first partitioning elements <NUM> are sheet-shaped elements, or they have a plate or sheet structure, or they are thin, two-dimensional elements, or they have an overall shape such that the thickness is negligible with respect to the other two dimensions. Preferably, the thickness of the first partitioning elements is between about <NUM> micrometers and about <NUM> micrometers.

The first partitioning elements <NUM> may be provided in a variety of materials, for example, and without limitation, meta-aramid-based materials such as NOMEX®, or aluminum, thermoplastic materials, such as PEEK (polyether-ether-ketone), PEI (polyether-imide), PEKK (polyether-ketone-ketone), PAEK (polyaryletherketone) or PPS (polyphenylene sulfide), or epoxy resin, or composite materials comprising a matrix phase made of thermoplastic materials, such as PEEK (polyether-ether-ketone), PEI (polyether-imide), PEKK (polyether-ketone-ketone), PAEK (polyaryletherketone) or PPS (polyphenylene sulfide), and a fiber reinforcement phase, such as glass fibers or carbon fibers.

In an embodiment, at least a portion of the surface of at least one of said first partitioning elements <NUM> is provided with micropores or microdrillings.

The first partitioning elements <NUM> are arranged spaced from each other. In a preferred embodiment, the first partitioning elements <NUM> are arranged parallel and spaced from each other. In a preferred embodiment, the distance between two successive first partitioning elements <NUM> of the plurality of first partitioning elements <NUM> is not constant. Alternatively, the first partitioning elements <NUM> are arranged parallel and spaced at a constant distance.

Each first partitioning element <NUM> has a first edge 12a, and a second edge 12b, arranged opposite to said first edge 12a.

Each first partitioning element <NUM> further has a plurality of vertical slits <NUM>, which are arranged, and extend, transversely from the first edge 12a of the respective first partitioning element <NUM>. In an embodiment, the vertical slits <NUM> of the first partitioning elements <NUM> are distributed in an asymmetrical pattern on each first partitioning element <NUM>, and this pattern is repeated equally on each first partitioning element <NUM>. In an embodiment, the distance between two successive vertical slits <NUM> of the plurality of vertical slits <NUM> of each first partitioning element <NUM> is not constant. Alternatively, such as in the embodiments shown in <FIG> and <FIG>, this distance is essentially constant. The vertical slits <NUM> of the first partitioning elements <NUM> may also have different lengths from each other. Vertical slits <NUM> are preferably, but not necessarily, arranged orthogonally with respect to the first edge 12a of the respective first partitioning element <NUM>. Alternatively, the vertical slits <NUM> may be arranged transversely, inclined non-orthogonally with respect to said first edge 12a.

In an embodiment, at least one first partitioning element <NUM> has a first opening <NUM>, in the form of a through-hole, for example, with a quadrangular cross section, as shown in <FIG>, or circular cross section, or again in the form of a gap from the first edge 12a or the second edge 12b or of a notch, as shown in the same figure. In said case, it is also possible that the core <NUM> comprises a microporous or microdrilled membrane <NUM> (or a plurality of membranes <NUM>) arranged so as to at least partially close at least one of said first openings <NUM>. Said membrane <NUM> preferably has an acoustic resistance feature designed specifically to maximize sound absorption. The same membrane <NUM> may be assembled on the first partitioning element <NUM>, for example, by a bonding, welding, or heat-welding method.

According to the invention, at least some of the first partitioning elements <NUM> have respective transverse slits <NUM>. The transverse slits extend along a direction transverse to the direction of extension of the vertical slits <NUM> of the respective first partitioning elements <NUM>, e.g., inclined by <NUM>°, <NUM>° or <NUM>° thereto. The transverse slits <NUM> of the first partitioning elements <NUM> are not necessarily all equal to each other, either with respect to their length or with respect to their slope or orientation. According to the invention, the core <NUM> further comprises horizontal partitioning elements <NUM> that are preferably made of flexible material, and which are arranged in such a way as to pass through a pair of transverse slits <NUM> of a respective pair of first successive partitioning elements <NUM>. Preferably, said horizontal partitioning elements <NUM> are likewise arranged in such a manner so as to pass through a plurality of transverse slits <NUM> of a respective plurality of successive first partitioning elements <NUM>, for example, in such a manner so as to pass through all first partitioning elements <NUM> by interlocking in a respective transverse slit <NUM> of each.

As is clear, the horizontal partitioning elements <NUM> must have a shape suitable to be inserted inside said transverse slits <NUM>; preferably, the horizontal partitioning elements <NUM> are also, like the first partitioning elements <NUM>, sheet-shaped elements, or they have a plate or sheet structure, or they are thin, two-dimensional elements, that is, they have a general shape such that the thickness is negligible with respect to the other two dimensions, and even more preferably they have a plank or bar shape. Preferably, the thickness of the first partitioning elements is between about <NUM> micrometers and about <NUM> micrometers.

The horizontal partitioning elements <NUM> may be provided in a variety of materials, for example, and without limitation, meta-aramid-based materials such as NOMEX®, or aluminum, thermoplastic materials, such as PEEK (polyether-ether-ketone), PEI (polyether-imide), PEKK (polyether-ketone-ketone), PAEK (polyaryletherketone) or PPS (polyphenylene sulfide), or epoxy resin, or composite materials comprising a matrix phase made of thermoplastic materials, such as PEEK (polyether-ether-ketone), PEI (polyether-imide), PEKK (polyether-ketone-ketone), PAEK (polyaryletherketone) or PPS (polyphenylene sulfide), and a fiber reinforcement phase, such as glass fibers or carbon fibers.

In an embodiment, the horizontal partitioning elements <NUM> may also have one or more openings of the same type as those previously described relative to the first partitioning elements <NUM>, and made and shaped in a similar manner thereto.

In an embodiment, the horizontal partitioning elements <NUM> may also have at least one portion with a microporous or microdrilled surface.

In an embodiment, as shown in <FIG>, the horizontal partitioning elements <NUM> are not all equal to each other, but rather have different lengths. In this way, it is possible to make core <NUM> configurations in which some horizontal partitioning elements <NUM> are arranged through respective transverse slits <NUM> of two successive first partitioning elements <NUM>, some other horizontal partitioning elements <NUM> are arranged through respective transverse slits <NUM> of three successive first partitioning elements <NUM>, some other horizontal partitioning elements <NUM> are arranged through respective transverse slits <NUM> of four successive first partitioning elements <NUM>, and so on, so as to make cells <NUM> of different shapes.

The second partitioning elements <NUM> are sheet-shaped elements, or they have a plate or sheet structure, or they are thin, two-dimensional elements, or they have a general shape such that the thickness is negligible with respect to the other two dimensions. Preferably, the thickness of the second partitioning elements <NUM> is between about <NUM> micrometers and about <NUM> micrometers.

The second partitioning elements <NUM> may be provided in a variety of materials, for example, and without limitation, meta-aramid-based materials such as NOMEX®, or aluminum, thermoplastic materials, such as PEEK (polyether-ether-ketone), PEI (polyether-imide), PEKK (polyether-ketone-ketone), PAEK (polyaryletherketone) or PPS (polyphenylene sulfide), or epoxy resin, or composite materials comprising a matrix phase in thermoplastic materials, such as PEEK (polyether-ether-ketone), PEI (polyether-imide), PEKK (polyether-ketone-ketone), PAEK (polyaryletherketone) or PPS (polyphenylene sulfide), and a fiber reinforcement phase, such as glass fibers or carbon fibers.

In an embodiment, at least a portion of the surface of at least one of said second partitioning elements <NUM> is provided with micropores or microdrillings.

Each second partitioning element <NUM> has a first edge 14a, and a second edge 14b, arranged opposite to said first edge 14a.

Each second partitioning element <NUM> further has, similarly to the first partitioning elements <NUM>, a plurality of vertical slits <NUM>, which are arranged and extend transversely from the first edge 14a of the respective second partitioning element <NUM>. In an embodiment, the vertical slits <NUM> of the second partitioning elements <NUM> are distributed in an asymmetrical pattern on each second partitioning element <NUM>, and this pattern is repeated equally on each second partitioning element <NUM>. In an embodiment, the distance between two successive vertical slits <NUM> of the plurality of vertical slits <NUM> of each second partitioning element <NUM> is not constant. Alternatively, such as in the embodiments shown in <FIG> and <FIG>, this distance is essentially constant. The vertical slits <NUM> of the second partitioning elements <NUM> may also have different lengths from each other. The vertical slits <NUM> are preferably, but not necessarily, arranged orthogonally to the first edge 14a of the respective second partitioning element <NUM>. Alternatively, the vertical slits <NUM> may be arranged transversely, inclined non-orthogonally with respect to said first edge 14a.

The second partitioning elements <NUM> are arranged on the first partitioning elements <NUM>, transversely thereto, for example crossing at about <NUM>° or at different angles, such as at about <NUM>° or about <NUM>°. Preferably, the second partitioning elements <NUM> are all arranged parallel to each other, but in an alternative embodiment the mutual inclination between the first partitioning elements <NUM> and the second partitioning elements <NUM> is not necessarily the same for all the first partitioning elements <NUM> and all the second partitioning elements <NUM>. In a preferred embodiment, the distance between two successive second partitioning elements <NUM> of the plurality of second partitioning elements <NUM> is not constant. Alternatively, the second partitioning elements <NUM> are arranged parallel and spaced at a constant distance.

Anyway, the second partitioning elements <NUM> are arranged on the first partitioning elements <NUM> so that each vertical slit <NUM> of the plurality of vertical slits <NUM> of the second partitioning elements <NUM> interlocks, that is, engages, or connects or couples by shape coupling, with a respective vertical slit <NUM> of a respective first partitioning element <NUM>. To facilitate such interlocking or shape coupling, clearly the thickness of the second partitioning elements <NUM> may be approximately equal to, or slightly greater than, that of the vertical slits <NUM> of the first partitioning elements <NUM>, and, similarly, the thickness of the first partitioning elements <NUM> may be approximately equal to, or slightly greater than, that of the vertical slits <NUM> of the second partitioning elements <NUM>. In this way, first partitioning elements <NUM> and second partitioning elements <NUM> fit together and define between them a plurality of cells <NUM>, each of said cells <NUM> being delimited laterally by a pair of opposing first partitioning elements <NUM> and a pair of opposing second partitioning elements <NUM>. The cells <NUM>, therefore, may have basically a prism shape with a quadrangular base, or a shape composed of the sum of prisms with a quadrangular base. Clearly, therefore, the arrangement of the second partitioning elements <NUM> depends on the arrangement of the vertical slits <NUM> on the first partitioning elements <NUM>. The cells <NUM> may, therefore, have different shapes and sizes depending on the relative distance between the pairs of opposing first partitioning elements <NUM> and opposing second partitioning elements <NUM> that delimit them laterally, as well as on the additional optional features that determine their shape.

In an embodiment, at least one second partitioning element <NUM> has a second opening <NUM> in the form of a through hole, for example, with a quadrangular cross section, as shown in <FIG>, or circular cross section, or again in the form of a gap from the first edge 14a or the second edge 14b or of a notch, as shown in the same figure. In such a case, it is also possible for the core <NUM> to comprise a microporous or microdrilled membrane <NUM> (or a plurality of membranes <NUM>) arranged to at least partially close at least one of said second openings <NUM>. Said membrane <NUM> preferably has an acoustic resistance feature designed specifically to maximize sound absorption. Said membrane <NUM> may be assembled on the second partitioning element <NUM>, for example, by a bonding, welding, or heat-welding method. Of course, since the relative arrangement between the first partitioning elements <NUM> and the second partitioning elements <NUM> forms a plurality of cells <NUM>, the first openings <NUM> and/or the second openings <NUM>, when present, connect adjacent cells <NUM> of said plurality of cells <NUM>. The first openings <NUM> and/or the second openings <NUM>, when present, may also serve the function of a drainage hole for any liquids accumulated within the core <NUM>.

At least some of the second partitioning elements <NUM> have respective transverse slits <NUM>. The transverse slits extend along a direction transverse to the direction of extension of the vertical slits <NUM> of the respective second partitioning elements <NUM>, e.g. inclined by <NUM>°, <NUM>° or <NUM>° thereto. The transverse slits <NUM> of the second partitioning elements <NUM> are not necessarily all equal to each other, either with respect to their length or with respect to their inclination or orientation. In such an embodiment, even more preferably, the core <NUM> further comprises, as mentioned, horizontal partitioning elements <NUM>, preferably made of flexible material, and which may also be arranged in such a way as to pass through a pair of transverse slits <NUM> of a respective pair of second successive partitioning elements <NUM>, in addition to, or as an alternative to, the horizontal partitioning elements <NUM> arranged in such a way as to pass through a pair of transverse slits <NUM> of a respective pair of first successive partitioning elements <NUM> already described above. Preferably, said horizontal partitioning elements <NUM> are likewise arranged in such a manner as to pass through a plurality of transverse slits <NUM> of a respective plurality of second successive partitioning elements <NUM>, for example in such a way as to pass through all of the second partitioning elements <NUM> by interlocking in a respective transverse slit <NUM> of each of these, in addition to horizontal partitioning elements <NUM> arranged in such a way as to pass through a plurality of transverse slits <NUM> of a respective plurality of first successive partitioning elements <NUM>, for example, in such a manner as to pass through all first partitioning elements <NUM>, interlocking in a respective transverse slit <NUM> of each of these, as previously described.

Preferably, the first partitioning elements <NUM> are all equal to each other, but it is also possible that some first partitioning elements <NUM> of the plurality of first partitioning elements <NUM> are different from the others, in terms of thickness, size, or otherwise, with regard to the pattern of arrangement of the vertical slits <NUM>, and in particular with regard to the presence of the optional features just described (presence of first openings <NUM>, presence of partitions <NUM>, and so on).

Similarly, preferably, the second partitioning elements <NUM> are all the same as each other, but it is also possible that some of the second partitioning elements <NUM> are different from the others, in terms of thickness, size, or otherwise, with regard to the pattern of arrangement of the vertical slits <NUM>, and in particular with regard to the presence of the optional features just described (presence of second openings <NUM>, presence of membranes <NUM>, and so on).

As mentioned previously, the core <NUM> according to the invention may be used as the central layer of the sound-absorbing panel <NUM>, which also comprises the first skin <NUM> and the second skin <NUM>. In said case, the core <NUM> is arranged between the first skin <NUM> and the second skin <NUM>, so that the second edge 12b of each partitioning element <NUM> is resting on, or in contact with, the first skin <NUM>, and so that the second edge 14b of each second partitioning element <NUM> is in contact with the second skin <NUM>.

The first skin <NUM> has a generally thin, or pellicular, structure, or it has a much smaller thickness than the other two dimensions, and, when the panel <NUM> is mounted in use, it is arranged facing the sound source; in particular, the first skin <NUM> may be facing the engine, in a radially inward direction of the nacelle.

The first skin <NUM> may be made of different materials, such as aluminum or polymeric materials. In an embodiment, the first skin <NUM> is made of epoxy resin. In other purely illustrative and non-limiting embodiments, the first skin <NUM> may be made, for example, of a thermoplastic polymeric material from the list comprising: PEEK (polyether-ether-ketone), PEK (polyether-ketone), PEI (polyether-imide), nylon, PET (polyethylene terephthalate), PAEK (polyaryletherketone), PPS (polyphenylene sulfide), PA (polyamides), PPSU (polyphenylsulfone), PC (polycarbonate) and PP (polypropylene). Alternatively, the first skin <NUM> may be made, for example, of a thermosetting polymeric material from the non-exhaustive list comprising: epoxy resin, bismaleimide resin, cyanate esters and polyimide. In an embodiment, the first skin <NUM> may be made of composite material, such as, for example, a composite material having an epoxy or bismaleimide resin matrix and a carbon fiber reinforcement phase.

The first skin <NUM> may preferably be between about <NUM> and about <NUM> micrometers thick. Even more preferably, the first skin <NUM> is between about <NUM> and about <NUM> micrometers thick.

The first skin <NUM> is made as an acoustically permeable component, for example, it is drilled or microdrilled or microporous, while the second skin <NUM> is made as an acoustically impermeable body. For this purpose, preferably, the first skin <NUM> is provided with a plurality of through holes, micropores, or microholes, which may be made, for example, by a conventional mechanical punching method or by a mechanical drilling or boring method, and distributed, preferably homogeneously, over its entire area. The microholes are adapted to allow sound waves to pass from the outside of the panel <NUM> to its central layer, or to the inner volumes of the cells <NUM> of the core <NUM>.

Preferably, the microholes cover a percentage of the area of the first skin <NUM> between about <NUM>% and about <NUM>%, and more preferably between about <NUM>% and about <NUM>%. In a preferred embodiment, the diameter of the microholes or micropores or holes is between about <NUM> micrometers and about <NUM> micrometers. Even more preferably, the holes are about <NUM> to about <NUM> micrometers in diameter. Nevertheless, both the percentage of area covered by the microholes <NUM> and their diameter may also be smaller or larger than described here purely by way of non-limiting example.

Anyway, the first skin <NUM> of the panel <NUM> allows a sound wave to pass through the first skin <NUM> and up to the inner volume of the plurality of cells <NUM> of the core <NUM>, but the second skin <NUM> does not allow said sound wave to escape from the second skin <NUM>.

The second skin <NUM> has a generally thin, or pellicular, structure, or it has a much smaller thickness than the other two dimensions, and, when the panel <NUM> is mounted in use, it faces the side opposite the sound source; in particular, the second skin <NUM> may face the side opposite the motor, or in a direction radially outward from the nacelle. The second skin <NUM> may be equal or equivalent to the first skin <NUM> in terms of thickness, area, and shape, but has no microholes.

The second skin <NUM> may be made of different materials, such as aluminum or polymeric materials. In an embodiment, the second skin <NUM> is made of epoxy resin. In other purely illustrative and non-limiting embodiments, the second skin <NUM> may be made, for example, of a thermoplastic polymeric material from the list comprising: PEEK (polyether-ether-ketone), PEK (polyether-ketone), PEI (polyether-imide), nylon, PET (polyethylene terephthalate), PAEK (polyaryletherketone), PPS (polyphenylene sulfide), PA (polyamides), PPSU (polyphenylsulfone), PC (polycarbonate) and PP (polypropylene). Alternatively, the second skin <NUM> may be made, for example, of a thermosetting polymeric material from the non-exhaustive list including: epoxy resin, bismaleimide resin, cyanate esters, and polyimide. In an embodiment, the second skin <NUM> may be made of a composite material, such as, for example, a composite material having an epoxy or bismaleimide resin matrix and a carbon fiber reinforcement phase.

The second skin <NUM> may preferably be between about <NUM> and about <NUM> micrometers thick. Even more preferably, the second skin <NUM> is between about <NUM> and about <NUM> micrometers thick.

Advantageously, the second skin <NUM>, the core <NUM> and the first skin <NUM> may be made from the same material.

As is visible in <FIG>, the panel <NUM> may also be formed with a single curvature, or in the shape of the side surface portion of a cylinder with a circular or ellipsoidal base, or with a double curvature, or in the shape of the surface portion of a sphere or ellipsoid. In said case, at least the first skin <NUM> extends over a surface having single or double curvature. Preferably, the first edge 12a of the first partitioning elements <NUM> also follows said curvature. Even more preferably, the panel <NUM> is suitable to be used to make up an insulating skin having as a whole a substantially cylindrical shape, or a shape suitable to at least partially surround an aircraft engine nacelle. For example, in an embodiment, the aircraft engine sound insulation is achieved by joining a plurality of sound-absorbing panels <NUM> having the shape of portions of cylindrical surfaces. In further embodiments, the panel <NUM> may have a substantially flat shape, or one with limited curvature, as for example shown in <FIG>.

As mentioned previously, the above-described core <NUM> may be obtained by the method for manufacturing the core <NUM> for a sound-absorbing panel <NUM> with sandwich structure for noise reduction in an aircraft according to an aspect of the invention.

The method for manufacturing the core <NUM> essentially comprises the steps of:.

Once the second partitioning elements <NUM> have been arranged on the first partitioning elements <NUM>, the connection between them may be strengthened through a dedicated method that may also be selected by taking into consideration the material of which the first partitioning elements <NUM> and the second partitioning elements <NUM>, and therefore the core <NUM>, are made. For example, for this purpose, the method may additionally comprise the step of:
h) following step d), strengthening the assembly formed by the first partitioning elements <NUM> and the second partitioning elements <NUM>, or the core <NUM>, by resin immersion and subsequent curing.

Preferably, in said case, the resin used is an epoxy resin or a phenolic resin.

Alternatively, the assembly formed by the first partitioning elements <NUM> and the second partitioning elements <NUM>, or the core <NUM>, may be strengthened by bonding, such as by glue spraying.

Alternatively, the assembly formed by the first partitioning elements <NUM> and the second partitioning elements <NUM>, or the core <NUM>, may be strengthened by welding/soldering, or by heat welding.

As mentioned previously, preferably, step e) is carried out in such a way as to arrange respective horizontal partitioning elements <NUM> through a plurality of transverse slits <NUM> of a respective plurality of successive first partitioning elements <NUM>, even more preferably in such a way as to arrange respective horizontal partitioning elements <NUM> through a plurality of transverse slits <NUM> of all the successive first partitioning elements <NUM>.

Moreover, when the second partitioning elements <NUM> are also provided in an embodiment having a plurality of transverse slits <NUM>, as mentioned above in relation to the first aspect of the invention, the method may preferably comprise the step of:
e2) arranging respective horizontal partitioning elements <NUM> through a pair of transverse slits <NUM> of a respective pair of second successive partitioning elements <NUM>.

As mentioned previously, preferably, step e2) is carried out in such a way as to arrange respective horizontal partitioning elements <NUM> through a plurality of transverse slits <NUM> of a respective plurality of second successive partitioning elements <NUM>, even more preferably in such a way as to arrange respective horizontal partitioning elements <NUM> through a plurality of transverse slits <NUM> of all the second successive partitioning elements <NUM>.

Of course, the method according to the invention may comprise only step e), or even both step e) and step e2) in a manner known per se to the person skilled in the art.

Preferably, in the method according to the invention, step a) of providing the first partitioning elements <NUM> comprises the sub-step of:
f1) carrying out a micro drilling method on at least a portion of surface of at least one of the first partitioning elements <NUM> so as to make said at least a portion of surface microporous.

Preferably, in the method according to the invention, step b) of providing the second partitioning elements <NUM> comprises the sub-step of:
f2) carrying out a micro drilling method on at least a portion of surface of at least one of the second partitioning elements <NUM> so as to make said at least a portion of surface microporous.

In both step f1) and in step f2), the micro drilling method may preferably be carried out by means of a laser, but it may also be carried out by other known perforation methods, depending on the material in which the first partitioning elements <NUM> and the second partitioning elements <NUM> are provided, respectively.

Of course, the method according to the invention may comprise only step f1), only step f2), or even both step f1) and step f2) in a manner known per se to the person skilled in the art.

Preferably, in the method according to the invention, step a) of providing the first partitioning elements <NUM> may additionally comprise the sub-step of:
g1) manufacturing the first partitioning elements <NUM> from sheets having a thickness between about <NUM> and about <NUM> micrometers by means of a punching or die-cutting method.

Through the punching or die-cutting method of the sub-step g1), the first edge 12a and the second edge 12b may be obtained, and also the vertical slits <NUM>, and/or the transverse slits <NUM> (when present), and/or the first openings <NUM> (when present).

Preferably, in the method according to the invention, step b) of providing the second partitioning elements <NUM> may additionally comprise the sub-step of:
g2) manufacturing the second partitioning elements <NUM> from sheets having a thickness between about <NUM> and about <NUM> micrometers by means of a punching or die-cutting method.

Through the punching or die-cutting method of sub-step g2) the first edge 14a and the second edge 14b may be obtained, and also the vertical slits <NUM>, and/or the transverse slits <NUM> (when present), and/or the first openings <NUM> (when present).

Alternatively, in sub-steps g1) and/or g2), instead of the punching or die-cutting method, a conventional cutting method may be carried out on the aforesaid sheets, preferably a laser cutting method.

The sheets used in sub-step g1) and/or in sub-step g2) may be provided made of different materials, for example, and without limitation, meta-aramid-based materials such as NOMEX®, or aluminum, thermoplastic materials, such as PEEK (polyether-ether-ketone), PEI (polyether-imide), PEKK (polyether-ketone-ketone), PAEK (polyaryletherketone) or PPS (polyphenylene sulfide), or epoxy resin, or in composite materials comprising a matrix phase in thermoplastic materials, such as PEEK (polyether-ether-ketone), PEI (polyether imide), PEKK (polyether-ketone-ketone), PAEK (polyaryletherketone) or PPS (polyphenylene sulfide), and a fiber reinforcement phase, such as glass fibers or carbon fibers.

Of course, the method according to the invention may comprise only the sub-step g1), only the sub-step g2), or even both the sub-step g1) and the sub-step g2) in a manner known per se to the person skilled in the art.

Alternatively, at least some of the first partitioning elements <NUM>, and/or the second partitioning elements <NUM>, and/or the horizontal partitioning elements <NUM> are manufactured using an additive manufacturing method from a filament using an FFF (i.e., Fused Filament Fabrication) technique or from powders using a laser sintering technique.

As mentioned previously, the core <NUM> may be mounted between the first skin <NUM> and the second skin <NUM> to form the sound-absorbing panel <NUM>.

The method for manufacturing the panel <NUM> essentially comprises the steps of:.

Specifically, the manufacturing method may comprise the steps of:.

Step x2) is carried out so that the second edge 12b of each first partitioning element <NUM> is placed on the first skin <NUM> and remains in contact therewith. Similarly, step x3) is carried out so that the second edge 14b of each second partitioning element <NUM> comes in contact with the second skin <NUM>.

The first skin <NUM> may be provided for use in step x2) already at least partially acoustically permeable, e.g., already equipped with a plurality of through micropores or microholes, or it may be provided initially acoustically impermeable, and then made acoustically permeable following step x2) or following step x3). In fact, it is possible to make the micropores or microholes through the first skin <NUM> also following steps x2) and x3), when the first skin <NUM> is already joined to the core <NUM>, for example, by a conventional mechanical punching method.

Of course, the order of execution of step x3) and step x2) may also be reversed with respect to that which has just been described by carrying out the method in an equivalent manner.

Preferably, the manufacturing method of the panel <NUM> also comprises the step of:
y1) arranging a layer of structural adhesive between the second edge 12b of each first partitioning element <NUM> and the first skin <NUM>, so as to strengthen the connection between the core <NUM> and the first skin <NUM>, and ultimately to strengthen the panel <NUM>.

Preferably, the manufacturing method of the panel <NUM> also comprises the step of:
y2) arranging a layer of structural adhesive between the second edge 14b of each second partitioning element <NUM> and the second skin <NUM>, so as to strengthen the connection between the core <NUM> and the second skin <NUM>, and ultimately to strengthen the panel <NUM>.

Of course, the method for manufacturing the panel <NUM> according to the invention may comprise only step y1), only step y2), or even both step y1) and step y2) in a manner known per se which is evident to the person skilled in the art.

Also, the connection of horizontal partitioning elements <NUM> to the first partitioning elements <NUM> and/or the second partitioning elements <NUM> may also be strengthened through the use of respective layers of structural adhesive.

In addition to, or as an alternative to, using a structural adhesive to strengthen the connection between the first skin <NUM> and the core and/or between the second skin <NUM> and the core, the method for manufacturing the panel <NUM> according to the invention may additionally include a heat welding step. Specifically, the method may comprise at least one of the following steps:.

Also, the connection of the horizontal partitioning elements <NUM> to the first partitioning elements <NUM> and/or to the second partitioning elements <NUM> may be strengthened by using a heat welding method.

As is evident from the description provided above, by virtue of the method for manufacturing the core, it is possible to obtain a core having a plurality of cells of different shapes and/or sizes for a sound-absorbing panel in a manner that is much quicker and cheaper with respect to the prior art.

Moreover, it is possible to obtain a sound-absorbing panel core that has cells, or resonance chambers, of varying shapes and sizes. This is made possible by the relative arrangement of the first partitioning elements and second partitioning elements, as well as by the presence of transverse slits and horizontal partitioning elements threaded in said transverse slits, as well as by the combination of several optional parameters, such as: the not necessarily constant distance between two successive first partitioning elements; the not necessarily constant distance between two successive vertical slits of the first partitioning elements and thus between two second partitioning elements interlocked in said two successive vertical slits; the presence of first and/or second openings, or notches or gaps, in the, respectively, first and/or second partitioning elements, and/or any partitions that at least partially cover at least one of said first and/or second openings; the fact that not all horizontal partitioning elements are necessarily of the same length; the fact that transverse slits may be made at different inclinations to each other and to the vertical slits; and so on.

In this way, the core obtained forms a plurality of cells of different shapes and sizes, and variously connected or separated, so as to make the core according to the invention capable of absorbing noise on many different frequencies, even over a very wide frequency spectrum.

Claim 1:
A manufacturing method for manufacturing a core (<NUM>) for a sound-absorbing panel (<NUM>) with sandwich structure for noise reduction in an aircraft, the method comprising the steps of:
a) providing a plurality of first sheet-shaped partitioning elements (<NUM>), each first partitioning element (<NUM>) having a plurality of vertical slits (<NUM>), which extend transversely from a respective first edge (12a) of each first partitioning element (<NUM>), the first partitioning elements (<NUM>) further having a plurality of transverse slits (<NUM>) extending along a direction transverse to the plurality of vertical slits (<NUM>) of the first partitioning elements (<NUM>);
b) providing a plurality of second sheet-shaped partitioning elements (<NUM>), each second partitioning element (<NUM>) having a plurality of vertical slits (<NUM>), which extend transversely from a respective first edge (14a) of each second partitioning element (<NUM>);
c) arranging the first partitioning elements (<NUM>) on a work surface, spaced from each other, so that a second edge (12b) of each first partitioning element (<NUM>), opposite to said first edge (12a) of each first partitioning element (<NUM>), rests on said work surface;
d) arranging the second partitioning elements (<NUM>) on the first partitioning elements (<NUM>), transversely thereto, so that each vertical slit (<NUM>) of the plurality of vertical slits (<NUM>) of the second partitioning elements (<NUM>) interlocks with a respective vertical slit (<NUM>) of the plurality of vertical slits (<NUM>) of a respective first partitioning element (<NUM>), so that the first partitioning elements (<NUM>) and the second partitioning elements (<NUM>) define between them a plurality of cells (<NUM>), each cell (<NUM>) being delimited laterally by a pair of opposing first partitioning elements (<NUM>) and a pair of opposing second partitioning elements (<NUM>); and
e) arranging respective horizontal partitioning elements (<NUM>), preferably made of flexible material, through a pair of transverse slits (<NUM>) of a respective pair of successive first partitioning elements (<NUM>).