Patent Description:
During operation of a vehicle, noise can be generated from multiple sources. For example, in an aircraft, noise can be generated from exterior turbulent flow, aircraft engine jet exhaust, and vibrations resulting therefrom. In addition, noise from within the passenger compartment, for example, climate control features, passenger conversation, movement and use of food and drink service items, and water closet activity, among others, can also add to interior sound levels, and possibly to passenger discomfort.

Solid surfaces within the interior of the vehicle can reflect sound waves, which can result in the need for personnel within the vehicle to wear ear protection and communicate via headsets and microphones. For crew and passenger comfort and safety within commercial vehicle, noise-attenuation techniques are typically incorporated to reduce the transfer of sound through the flight deck and passenger compartment. One common technique employs the use of sound absorbing panels attached to vertical surfaces of an interior of the vehicle to reduce reflected sound waves. However, reflection of sound waves can be particularly difficult to mitigate with flat panels where other interior surfaces are contoured, such as, for example, overhead storage bin, fuselage liners, and within galleys of an aircraft.

Some conventional sound absorbing panels (i.e., acoustic structures) include a back skin, an open-cell honeycomb core having a back surface attached to the back skin, an open weave reinforcement attached to a front surface of the honeycomb core, and a rigid perforated face sheet attached to the leno weave reinforcement. Some acoustic structure designs further include a mesh layer positioned between the honeycomb core and the perforated face sheet, where the mesh layer is acoustically transparent. The acoustic structures are attached to interior surfaces of the aircraft flight deck and passenger compartment and provide some level of noise attenuation within the vehicle. The perforated face sheet provides a durable surface that is resistant to damage from physical contact and is generally flame resistant.

<CIT> describes an automobile door panel composite fabric which comprises a knitted fabric layer, a breathable eyelet fabric layer, an activated carbon layer, a hot melt adhesive layer and a suede layer. The knitted fabric layer is attached to the inner side of the vehicle door; the breathable eyelet fabric layer is laid on the knitted fabric layer; the activated carbon layer is laid on the side, back to the knitted fabric layer, of the breathable eyelet fabric layer. The hot melt adhesive layer is laid on one side, back to the breathable eyelet fabric layer, of the activated carbon layer; the suede layer is laid on the side, back on to the activated carbon layer, of the hot melt adhesive layer. The knitted fabric layer is soft in texture; moisture absorption and ventilation, the elasticity and the extensibility are realized; the breathable eyelet fabric layer improves breathability, reduces noise in the automobile, the activated carbon layer is good in breathability, absorbs moisture and peculiar smell and has a good antibacterial effect, the activated carbon layer and the suede layer are bonded through the hot melt adhesive layer, the process is simple, durability is achieved, the suede layer is good in sound insulation performance and rebound resilience, and the attractiveness of the automotive trim is enhanced.

<CIT> describes a sandwich panel made of a composite material with acoustical attenuation for a wall and/or self-supporting covering, more particularly for doubling the bulkheads or cabin walls of aircraft, and including an alveolar structural core especially a honeycomb core, and two skins disposed and rendered integral on both sides of the core, wherein the two skins include holes and wherein the holes of at least one of the two skins are micropores. A method for producing this panel is also disclosed.

<CIT> describes a sandwich element for a sound-absorbing inner cladding of transport means, such as aircraft fuselage cells, comprising a honeycomb-shaped core structure and cover layers applied to both sides of the core structure. At least one cover layer is constructed as permeable to air at least in sections and a covering is disposed at least in sections on at least one cover layer, wherein a sound absorption layer is disposed at least in sections in the area of at least one cover layer. A plurality of passages in the cover layers allow efficient transmission of the sound impinging on the sandwich element from outside as far as the sound absorption layer of the sandwich element.

<CIT> describes a method of repairing an acoustically treated area of a composite honeycomb sandwich structure restores the acoustic performance of the structure. An impaired section of the honeycomb core is removed and replaced with a honeycomb repair plug. Cell walls of the repair plug are bonded to cell walls of the core.

<CIT> describes a repair method includes the steps of: (A) forming a repair cavity by removing a honeycomb core including a damaged portion with a front-side skin; (B) inserting, into the repair cavity, a repair honeycomb core whose end surface <NUM> on a side to which a repair patch is bonded is subjected to flattening treatment; (C) disposing the repair patch on the flattened end surface of the repair honeycomb core via a film-like adhesive; and (D) bonding the repair honeycomb core to an existing portion of the honeycomb sandwich structural body and to the repair patch, and curing the repair patch under a reduced-pressure atmosphere associated with heating.

The present invention provides an acoustic structure as defined in independent claim <NUM>.

Further advantageous aspects of the present invention are defined in the dependent claims.

The following presents a simplified summary in order to provide a basic understanding of some aspects of one or more implementations of the present disclosure. This summary is not an extensive overview, nor is it intended to identify key or critical elements of the present disclosure, nor to delineate the scope of the disclosure. Rather, its primary purpose is merely to present one or more concepts in simplified form as a prelude to the detailed description presented below.

The present inventors have recognized that conventional panels can be expensive to manufacture and are generally limited to panel-like surfaces that are substantially flat, and without complex contours, limiting where such structures can be installed. As used herein, a "complex contour" shall be understood to mean that, when tracing a bounding shape of the acoustic structure, the curvature of the surface of the acoustic structure is multi-directional. For example, a ceiling panel design can exhibit curvature in two orthogonal directions, such as forward and aft, and left to right within the envelope of the pressurized fuselage. In addition, such conventional panels increase weight of the vehicle, thereby increasing energy consumption during travel. While the surface of the acoustic structure can be printed to incorporate a graphic design, it is most common for these structures to feature a simple aesthetic such as a solid color. An acoustic structure design having improved sound attenuation while reducing weight and conforming to desired contours and color within a vehicle are desirable.

According to examples of the present disclosure, an acoustic structure presenting a front surface and a back surface is provided. The acoustic structure includes a support layer comprising the back surface, a honeycomb core comprising a thickness defined between a back and a front, and a plurality of walls that define a plurality of honeycomb cells, wherein the plurality of honeycomb cells extend through the thickness of the honeycomb core opening out toward at least the front, and wherein the back of the honeycomb core is affixed to the support layer, a mesh layer affixed to the front of the honeycomb core, and a knit fabric layer affixed to the mesh layer and conforming to the front surface of the acoustic structure.

By providing an acoustic structure according to the recited structure, a lightweight sound-reducing structure can be obtained, with the structure conforming to any number of desired contours of an application. In addition, based on the use of readily available knitted fabrics as the top layer, restoration of the acoustic structure to a like new or nearly new state can be achieved without removal of the acoustic structure from an installed location.

According to further examples, a noise-reducing system comprising an acoustic structure forming a surface defining at least a portion of a passenger compartment of an aircraft, is provided. The acoustic structure includes a support layer, a honeycomb core comprising a thickness defined between a back and a front, and a plurality of walls that define a plurality of honeycomb cells, wherein the plurality of honeycomb cells extend through the thickness of the honeycomb core opening out toward at least the front, and wherein the back of the honeycomb core is affixed to the support layer, a mesh layer affixed to the front of the honeycomb core, and a knit fabric layer affixed to the mesh layer and conforming to the front surface of the acoustic structure.

By providing an acoustic structure according to the recited structure within an aircraft, fuel savings can be achieved based on reduced weight, while providing a desired level of sound reduction. In addition, because many contoured surfaces exist within an aircraft, the recited structure can be implemented in any number of applications within the aircraft, thereby leading to greater sound reduction, and in turn, greater passenger comfort.

According to still further examples of the disclosure, not forming part of the claimed invention, a method for repairing an acoustic structure installed within an aircraft, is provided. The method includes separating an existing knit fabric layer from a mesh layer of the acoustic structure installed within a passenger cabin of the aircraft, applying an adhesive to at least one of the mesh layer and a replacement knit fabric layer, and adhering the replacement knit fabric layer to the mesh layer via the adhesive.

Implementation of such a method can allow for rapid restoration of a contoured acoustic structure to a like new or nearly new condition, even in an installed location. This leads to cost savings both as a result of implementation of readily available knit fabrics, and because replacement time is greatly reduced.

It is intended that combinations of the above-described elements and those within the specification can be made, except where otherwise contradictory.

It is to be understood that the scope of the present invention is defined by the appended claims.

The accompanying drawings, which are incorporated in, and constitute a part of this specification, illustrate implementations of the present disclosure and, together with the description, serve to explain the principles of the disclosure. In the figures:.

It should be noted that some details of the figures have been simplified and are drawn to facilitate understanding of the present disclosure rather than to maintain strict structural accuracy, detail, and scale.

Reference will now be made in detail to example implementations of the present disclosure, examples of which are illustrated in the accompanying drawings. Generally, and/or where convenient, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

Some conventional acoustic structures include a back skin, an open-cell honeycomb core having a back surface attached to the back skin, a leno weave reinforcement mesh layer, and a rigid perforated face sheet provided by a perforated laminate attached to a front surface of the honeycomb core. While these conventional acoustic structures are effective in reducing reflection of sound waves, they suffer some limitations. For example, the perforations through the face sheet, which allow sound waves to pass through the face sheet and enter the honeycomb core, are difficult and expensive to manufacture. The perforations in the structure must be done precisely to provide an aesthetically pleasing surface, as the face sheet is visible to passengers and crew. Additionally, the acoustic structures are relatively heavy, resulting at least partially from a relatively large mass of the perforated face sheet, which is manufactured from fiber-reinforced plastics and can include an aluminum foil. Still further, these panels are generally limited to flat panel structures due to their construction, and are often limited to use as, for example, bulkheads within an aircraft. Therefore, such panels are also generally not aesthetically useful.

Examples of the present disclosure provide acoustic structures that can be implemented as a noise reducing system, and in some implementations, be lighter in weight, more easily manufactured at a lower cost, have improved sound dampening characteristics over some conventional acoustic structures, and/or can be contoured to perform as various in-cabin structures (e.g., overhead storage bin, galley cabinetry, fuselage lining such as ceilings and walls, closet interior surfaces, etc.). An acoustic structure according to the present disclosure can have a decreased weight compared to conventional acoustic structures, resulting at least partially from use of a knit fabric layer instead of a fiber-reinforced plastic perforated face sheet. The weight of an acoustic structure according to the present disclosure can be reduced by as much as <NUM> kilograms per square meter (kg/m<NUM>) compared to conventional acoustic structure designs. In addition, restoration of acoustic structures of the present disclosure to a like new or nearly new state can be rapidly performed, even while the acoustic structure remains in an installed location.

In-process structures which can be formed during an implementation of the present disclosure not forming part of the claimed invention, are depicted in <FIG> depicts an exploded cross section of a small portion of an acoustic structure <NUM> in accordance with an implementation of the present disclosure, and <FIG> depicts an assembled cross section of the <FIG> implementation. For purposes of simplicity, contours of the acoustic structure are not shown in <FIG>. This implementation includes a support layer <NUM> such as a moisture-resistant backing layer having a back surface <NUM> and a front surface <NUM>, and a honeycomb core <NUM> (e.g., fiberglass, carbon fiber, a poly-paraphenylene terephthalamide fabric such as Kevlar®, a meta-aramid fabric including meta-aramid fibers such as Nomex®, etc.) in a thermoset or thermoplastic matrix (e.g., phenolic, epoxy, polyester, etc.). The honeycomb core <NUM> can include a back surface <NUM> and a front surface <NUM>. This implementation can further include a mesh layer <NUM> as described in more detail below, having a back surface <NUM> and a front surface <NUM>. The mesh layer <NUM> improves structural stiffness and/or strength of the acoustic structure while allowing sound to enter the honeycomb core. Implementations of the present disclosure further include a knit fabric layer <NUM> having a back surface <NUM> and a front surface <NUM>. In this implementation for purposes of description, the "back surface" is the surface of a structure that is closest to an attachment surface to which the acoustic structure <NUM> will be attached, and/or the surface which, in an installed configuration, would not typically be visible to individuals in a personnel space, for example, a passenger compartment or flight deck, within a vehicle (e.g., an aircraft). The "front surface" is the surface of the structure opposite to the back surface, closest to and generally visible from within a personnel space. It will be appreciated that the figures depict generalized illustrative implementations, and an actual acoustic structure in accordance with the present disclosure can include other structures that, for simplicity, are not depicted, while various depicted structures can be removed or modified.

The support layer <NUM> can comprise, for example, fiber (e.g., fiberglass, carbon fiber, a poly-paraphenylene terephthalamide fabric such as Kevlar®, a meta-aramid fabric such as Nomex®, etc.) The support layer <NUM> can further be or include a material that is pre-impregnated with an adhesive <NUM>, commonly referred to as a prepreg. The adhesive <NUM> (e.g., thermoset polymer matrix material such as epoxy, or a thermoplastic resin) incorporated into the support layer <NUM> adheres the front surface <NUM> of the support layer <NUM> to the back surface <NUM> of the honeycomb core <NUM> as described below. The support layer <NUM> can thus be or include a thermoset composite or thermoplastic composite (e.g., phenolic, epoxy, polyester, etc.). The support layer <NUM> can also be or include any material such as metal, paper, wood, plastic, etc., that is suitably rigid to allow secure attachment to a structure such as a surface of a transportation vehicle. The support layer <NUM> can have a thickness that is sufficient to provide structural integrity for supporting loads and stresses without damage in the intended application of the acoustic structure <NUM>, for example, from about <NUM> inch to about <NUM> inch (<NUM> to about <NUM>). During use, the acoustic structure <NUM> can be attached to a surface <NUM> (<FIG>) of a transportation vehicle using an adhesive layer <NUM> (e.g., an epoxy), and/or one or more fasteners (not shown), for example, mechanical fasteners such as bolts, screws, hangers, etc..

The support layer <NUM> can present single- or multi-directional contours depending on, for example, an intended installation and/or operation with a vehicle. For example, where the acoustic structure <NUM> is intended to be implemented as an overhead storage bin closure within the passenger cabin of an aircraft, the support layer <NUM> can be contoured according to an intended shape for the overhead storage bin, such that subsequent components of the acoustic structure <NUM>, as described below, can substantially conform to the desired shape. In another example, where the acoustic structure <NUM> is intended to be implemented as a galley cabinet component (e.g., a cabinet door), the support layer <NUM> can be suitably contoured to match the intended shape of such a component.

According to some examples, the contours of the acoustic structure <NUM> can be complex. <FIG> show an illustrative acoustic structure including complex contours over its surface, and are described in greater detail below.

The honeycomb core <NUM> can comprise fiber reinforced composite (e.g., fiberglass, carbon fiber, a poly-paraphenylene terephthalamide fabric such as Kevlar®, a meta-aramid fabric including meta-aramid fiber such as Nomex®, etc.) in, for example, a thermoset or thermoplastic polymer matrix (e.g., phenolic, epoxy, polyester, etc.). The honeycomb core <NUM> can also be or include any sufficiently rigid material such as metal, paper, wood, plastic, etc. for the purpose of providing structural integrity. The honeycomb core <NUM> has a thickness "T<NUM>" that extends from the back surface <NUM> to the front surface <NUM>, wherein the thickness T<NUM> of the honeycomb core <NUM> can be from about <NUM> inches to about <NUM> inches (<NUM> to about <NUM>), although other thinner or thicker dimensions are contemplated depending on the intended use and design of the acoustic structure. The honeycomb core <NUM> includes a plurality of walls <NUM> that define a plurality of honeycomb cells <NUM>, wherein the plurality of honeycomb cells <NUM> extend through the thickness T<NUM> of the honeycomb core <NUM> from the back surface <NUM> to the front surface <NUM>. The honeycomb core <NUM> is further depicted in plan view in <FIG>, where the honeycomb core <NUM> can have a width "W" of from about <NUM> inches to about <NUM> inches (<NUM> to about <NUM>) and a length or height "H" of from about <NUM> inches to about <NUM> inches (<NUM> to about <NUM>), although other widths and/or height dimensions are contemplated depending on the intended use and design of the acoustic structure.

The mesh layer <NUM> can comprise a woven fabric, for example, a fabric with a leno weave, and can be configured to improve structural stiffness and/or strength of the acoustic structure while allowing sound waves to enter the honeycomb core to which the mesh layer <NUM> is affixed.

The mesh layer <NUM> can be fabricated from any suitable material, and can comprise, for example, a fiberglass fabric, carbon fiber fabric and/or a polyester fabric, and can comprise synthetic fibers such as nylon, rayon, acrylic, etc., and natural fibers such as cotton, wool, etc. Suitable mesh layers include Kevlar®, Nomex®, and HexForce™ <NUM> available from Hexcel®.

According to some examples the mesh layer <NUM> can be a prepreg, where the material of the mesh layer <NUM> is pre-impregnated with an adhesive <NUM> (e.g., thermoset polymer matrix material such as epoxy, or a thermoplastic resin). The adhesive <NUM> incorporated into the mesh layer <NUM> can be configured to adhere the back surface <NUM> of the mesh layer <NUM> to the front surface <NUM> of the honeycomb core <NUM> as described below. The mesh layer <NUM> can thus be or include a thermoset composite or thermoplastic composite (e.g., phenolic, epoxy, polyester, etc.).

According to some examples, the adhesive <NUM> can be configured so as to avoid interfering with passage of sound waves from the exterior of the acoustic structure <NUM> into the honeycomb core <NUM>. For example, the adhesive <NUM> can be a high viscosity adhesive (e.g., having a viscosity greater than <NUM> centiPoise (<NUM> pascal-second)) to prevent bleeding and/or other transmission of the adhesive into orifices formed in the mesh and/or the honeycomb core <NUM>.

The knit fabric layer <NUM> can comprise a flexible flame-resistant material that is durable and resists damage from physical contact with other structures that the knit fabric layer <NUM> is likely to come into contact with. Additionally, the knit fabric layer <NUM> should be manufactured from a material that is washable or cleanable so that the knit fabric layer <NUM>, which is visually exposed during use, remains visually attractive.

The material of the knit fabric layer <NUM> can further be printable such that a desired design (e.g., a graphic), for example, an airline logo, can be applied (e.g., via inkjet printing, silk screening, dye sublimation, etc.) and retained on or within the knit fabric layer <NUM>. An illustrative graphic design <NUM> imprinted on an acoustic structure according to examples of the present disclosure is highlighted at <FIG>.

The knit fabric layer <NUM> can comprise, for example, a cotton, a wool, a polyester, an aramid polymer, an aromatic polyamide, meta-aramid fibers, a modacrylic fabric, and/or para-aramid fibers. Other suitable flame retardant knitted fabrics are available from Trevira®, Tisca®, Neotex®, Lantal®, and/or Replin.

The knit fabric layer <NUM> can have a thickness "T<NUM>" of from about <NUM> inch to about <NUM> inch (<NUM> to about <NUM>), and a basis weight of about <NUM> grams per square meter (g/m<NUM>) to about <NUM>/m<NUM>, for example <NUM>/m<NUM>, although larger and smaller thicknesses and basis weights are contemplated depending on the intended use and design. By implementing fabrics according to these specifications, desirable sound attenuation can be achieved without introducing undesired weight. Further, the width and length or height of the knit fabric layer <NUM> can approximate the width W and length or height H of the honeycomb core <NUM>.

Pore density of material comprised by the knit fabric layer <NUM> can vary according to, for example, a knitting technique (e.g., weft-knit, weft-knit, etc.), a yarn density, tension used during the knitting operation, a thickness of the knitted fabric, etc. For example, an illustrative weft-knit fabric can be prepared using a single jersey-style knitting operation using a yarn of a desired density and at a desired carriage tension, resulting in a particular pore density. Another illustrative warp-knit fabric can be prepared using a tricot-style knitting operation and a yarn of a desired density at a desired carriage tension, resulting in a pore density different from that of the jersey-style knit fabric. One of skill will understand upon review of the present disclosure that different desirable pore densities can be obtained using various knitting techniques and yarn density.

For example, a pore density of the knit fabric layer can be configured such that pores of the knit fabric layer align substantially with the honeycomb cell openings. Such a configuration can allow sound waves to be initially dissipated by the fabric. Further, openings in the mesh layer can enable fluid communication between pores of the knit fabric layer and the openings of the honeycomb cells thereby causing remaining sound to directed to within the honeycomb cells for additional attenuation.

A knit fabric for a particular acoustic structure can be selected based on, for example, contours of the acoustic structure, intended placement of the acoustic structure, desired sound attenuation (e.g., based on intensity and/or frequency), etc. For example, a knit fabric having a first thickness, knitting technique, and a first pore density can be selected for use on an acoustic structure acting as an overhead storage bin in an aircraft, and a second knit fabric having a second thickness, knitting technique, and pore density can be selected for use as galley cabinetry in the aircraft. By varying the fabric according to location, different attenuation characteristics can be achieved leading to great sound reduction and improved passenger comfort.

During manufacture of the acoustic structure <NUM>, the support layer <NUM>, the honeycomb core <NUM>, and the mesh layer <NUM> can be stacked as depicted in the upper portion of <FIG> to form a panel subassembly <NUM>, which is then processed to cure the panel subassembly <NUM>. The processing can include, for example, an application of pressure to the panel subassembly <NUM> within a vacuum bag <NUM>. Air <NUM> from within the vacuum bag <NUM> and around the panel subassembly <NUM> can be evacuated from the vacuum bag <NUM> through a vacuum bag exhaust port <NUM> using conventional processing techniques. Optionally, heat can be applied to the panel subassembly <NUM> within the vacuum bag <NUM> for a suitable duration of time, or the panel subassembly <NUM> can be cured at ambient (e.g., room) temperature. The application of pressure and (optional) heat cures the panel subassembly <NUM>, for example, by curing the adhesive <NUM> that impregnates the support layer <NUM>, thereby bonding the front surface <NUM> of the support layer <NUM> to the back surface <NUM> of the honeycomb core <NUM> using the adhesive <NUM> within the support layer <NUM>. Further, the application of pressure and (optional) heat cures the panel subassembly <NUM>, for example, by curing the adhesive <NUM> that impregnates the mesh layer <NUM>, thereby bonding the back surface <NUM> of the mesh layer <NUM> to the front surface <NUM> of the honeycomb core <NUM>.

After curing the panel subassembly (e.g., the adhesives <NUM>, <NUM>) the cured panel subassembly <NUM> is removed from the vacuum bag <NUM> as depicted in the lower portion of <FIG>. Subsequently, the back surface <NUM> of the knit fabric layer <NUM> is attached to the front surface <NUM> of the mesh layer <NUM> using an adhesive layer <NUM> that is or can include one or more of a thermoplastic, a thermoset, an acrylic, a polyamide, a polyester, a urethane, and/or a rubberized adhesive, combinations of two or more of these, or another suitable adhesive. There are different methods of application of the adhesive layer <NUM>, for example, by spray, hot melt, or roll coating. As depicted, the adhesive layer <NUM> that attaches the knit fabric layer <NUM> to the mesh layer <NUM> is applied as a non-continuous, patterned layer intended to overlie (as in contact) only the plurality of walls <NUM> of the honeycomb core <NUM>, and not to overlie (as in enter) the plurality of honeycomb cells <NUM>. Adhesive inside the honeycomb cells <NUM> results in undesirable scenarios such as the addition of weight to the structure, and the potential for manufacturing quality challenges due to the presence of improperly located, unusable adhesive. Forming the adhesive layer <NUM> as a blanket layer would result in reflection of sound waves from the adhesive layer <NUM> before the sound waves enter the honeycomb cells <NUM>, thereby decreasing sound wave absorption by the acoustic structure <NUM>. Forming the adhesive layer <NUM> as a patterned layer ensures that the sound waves pass through the cross-sectional openings or voids within the adhesive layer <NUM> and enter the honeycomb cells <NUM> so that reflection of the sound waves from the acoustic structure <NUM> is attenuated.

<FIG> is a graph <NUM> that plots acoustic absorption coefficients for a plurality of different acoustic structures over a range of frequencies, where the frequencies range from about <NUM> hertz (Hz) to about <NUM>. The results were measured using a Brüel & Kjær® brand portable impedance meter, type <NUM>. Reference number <NUM> plots the acoustic absorption coefficients results for a conventional acoustic structure using a perforated rigid face sheet as is known in the art. Reference number <NUM> plots result points for acoustic structures having a knit fabric top layer, according to examples of the present disclosure. Reference numbers <NUM>-<NUM> plot points for acoustic structures having various fabric face sheets overlying a honeycomb core. Reference numbers <NUM> and <NUM> plot the results for two plain weave nylon fabric samples, where the two fabric samples vary with respect to areal weights. Reference numbers <NUM>, <NUM>, and <NUM> plot the results for the acoustic structure surfaced with a Silencio® <NUM>, Silencio® <NUM>, and Silencio® <NUM> materials respectively (commercially available from Pongs® Textil GmbH). Silencio® fabrics are polyester fiber acoustic textiles, where the polyester fibers have a particular chemical structure, and The reference numbers "<NUM>," "<NUM>," and "<NUM>" refer to a dimension of decorative diamonds, in millimeters, that are formed as three-dimensional features of each particular fabric. Each of the samples shown included a honeycomb core having a thickness of <NUM> inch (<NUM>).

As shown in <FIG>, the acoustic structures formed in accordance with the present disclosure include a knit fabric top layer, and have better sound absorbing properties over a wider range of frequencies than the conventional acoustic structure including the perforated rigid face sheet (identified by reference number <NUM>). Particularly at frequencies in the range of about <NUM> to <NUM>, the knit fabric acoustic structure performed better at absorbing and/or attenuating reflected sound waves than the conventional acoustic structure <NUM> using the perforated face sheet. Indeed, in this frequency range, the acoustic structures of the present disclosure outperformed all of the other tested structures for sound attenuation.

Further, it was found that an acoustic structure with knit fabric layer and a honeycomb core having a thickness of approximately <NUM> inch (<NUM>) was better at attenuating reflected sound than a similar acoustic structure with a honeycomb core having a thickness of <NUM> inch (<NUM>). In general, an acoustic structure in accordance with the present disclosure can have a honeycomb core with a thickness of from about <NUM> inch to about <NUM> inches (<NUM> to about <NUM>), or from about <NUM> inch to <NUM> inches (<NUM> to <NUM>), for example about <NUM> inch (<NUM>), or another suitable thickness depending on the use and design. An acoustic structure having a honeycomb core that is excessively thin will not provide suitable sound wave reflection attenuation, while an acoustic structure having a honeycomb core that is too thick will require excessive space within vehicle compartments (e.g., passenger compartment of an aircraft).

In some implementations, the acoustic structure will have an absorption coefficient ranging from about <NUM> to about <NUM> (e.g., from <NUM> to <NUM>) as measured by ASTM E1050-<NUM>, over a broad frequency range from <NUM> to <NUM>,<NUM>. This is compared to the acoustic fabric tested alone which, depending on its air permeability and other factors, will have an absorption coefficient of between <NUM> and <NUM>. A solid-faced honeycomb core panel will have an absorption coefficient near zero, corresponding to <NUM>% of sound waves being reflected.

Methods for forming an acoustic structure and/or for using an acoustic structure in accordance with the present disclosure will now be described. Formation of an acoustic structure depicted in <FIG> and <FIG>, is described herein, but this is not limited to any particular structure or use unless expressly stated herein. The method can be performed before, during, or after other processes, for example, as an assembly sub-process. It will be appreciated that while the process is described as a series of acts or events, the present disclosure are not limited by the ordering of such acts or events. Some acts can occur in different orders and/or concurrently with other acts or events apart from those described herein. Further, a method in accordance with the present disclosure can include other acts or events that have not been depicted for simplicity, while one or more depicted acts or events can be removed or modified as sub-processes of the method.

A panel subassembly <NUM>, not forming part of the claimed invention, <NUM>. can be formed including a support layer <NUM>, a honeycomb core <NUM>, and a mesh layer <NUM>. In this implementation, the support layer <NUM> is pre-impregnated with a first adhesive <NUM> and the mesh layer <NUM> is pre-impregnated with a second adhesive <NUM>, which can be the same or different than the first adhesive <NUM>. (As used herein, unless otherwise specified, the terms "first," "second," and "third," with respect to adhesives impregnated within another structure and/or adhesive layers that mechanically attach two structures together are used merely to uniquely identify distinct adhesive layers or adhesives and do not imply assembly order with respect to any manufacturing process. ) With the honeycomb core <NUM> in physical contact with the support layer <NUM> and the mesh layer <NUM>, heat and/or pressure are applied to the panel subassembly <NUM>, for example within a fixture <NUM> such as a vacuum bag <NUM>, to cure the first adhesive <NUM> and the second adhesive <NUM>, thereby attaching the front surface <NUM> of the support layer <NUM> to the back surface <NUM> of the honeycomb core <NUM>, and the front surface <NUM> of the honeycomb core <NUM> to the back surface <NUM> of the mesh layer <NUM>. The panel subassembly <NUM> can be removed from the fixture <NUM> subsequent to curing the adhesives <NUM>, <NUM>.

Next, a knit fabric layer <NUM> is attached as a face sheet to the panel subassembly <NUM> and, more specifically, the back surface <NUM> of the knit fabric layer <NUM> is attached to the front surface <NUM> of the mesh layer <NUM> subsequent to the curing Of the first adhesive <NUM> and the second adhesive <NUM>, where the first adhesive <NUM> can be the same composition or a different composition than the second adhesive <NUM>. The attachment can include the use of an adhesive layer <NUM> between the mesh layer <NUM> and the knit fabric layer <NUM>. The adhesive layer <NUM> can be applied to either the front surface <NUM> of the mesh layer <NUM>, the back surface <NUM> of the knit fabric layer <NUM>, or both, then the knit fabric layer <NUM> is physically contacted with the mesh layer <NUM> and the adhesive layer <NUM> is cured using any suitable technique. While the adhesive layer <NUM> is being cured, a compressive pressure can be applied to the knit fabric layer <NUM> to maintain alignment with the honeycomb core <NUM>, and to maintain physical contact of the adhesive layer <NUM> with the honeycomb core <NUM> and the knit fabric layer <NUM>.

The adhesive layer <NUM> is applied in a pattern (e.g., a non-continuous pattern) such that, after attaching the knit fabric layer <NUM> to the mesh layer <NUM>, the adhesive layer <NUM> overlies the plurality of walls <NUM> of the honeycomb core <NUM>, and does not overlie the plurality of honeycomb cells <NUM>, for the reasons discussed above.

Compressive pressure applied to the knit fabric layer <NUM> during manufacture of the acoustic structure <NUM> can be low to avoid crushing the knit fabric layer <NUM>, but sufficient to allow for desirable adhesion. In an implementation, a compressive pressure of from about <NUM> pound per square inch (psi) to about <NUM> psi (<NUM> kPa to about <NUM> kPa) can be applied to the knit fabric layer <NUM>, for example, using a suitable fixture <NUM>, although other compressive pressures are contemplated as long as the acoustic properties of the knit fabric layer <NUM> are not negatively affected, compromised, or degraded. Compressive pressures below <NUM> psi (<NUM> kPa) can result in insufficient bonding of the knit fabric layer <NUM> to the underlying structure, while compressive pressures greater than <NUM> psi (<NUM> kPa) can result in damage or deformation of the knit fabric layer <NUM>. As elevated temperatures and atmospheric pressures also tend to damage the knit fabric layer <NUM> during the application of a compressive force, the application of the adhesive layer <NUM> to the knit fabric layer <NUM> is best performed at or near room temperature (e.g., from <NUM>°F to <NUM>°F (<NUM> Kelvin (K) to <NUM>)) and at or near standard atmospheric pressure.

<FIG> is an illustrative acoustic structure exhibiting complex contours over its surface, while <FIG> is an exploded view of a segment of a complex contour shown on the acoustic structure of <FIG>, not forming part of the claimed invention. Additionally, <FIG> shows the acoustic structure of <FIG> with a graphic design <NUM> applied to the knit fabric layer <NUM>. According to some examples, the acoustic structure <NUM> can form the surface <NUM> of a structural component of a transportation vehicle <NUM> (<FIG>). Alternatively, or in addition, the acoustic structure can be attached to a surface <NUM>, such as for example, to a surface of a structural component of a transportation vehicle <NUM> (<FIG>) to form a composite structure <NUM>. Taking an example of an overhead storage bin of an aircraft that is to be provided with sound attenuation capabilities, an acoustic structure <NUM> as described herein can form or be affixed to a surface <NUM> of the overhead storage bin before or after installation within the aircraft to form the composite structure <NUM>.

According to further examples, for example, where load bearing is not under consideration, acoustic structures of the present disclosure can be implemented without attachment to additional surfaces such as composite structure <NUM>.

<FIG> depicts a vehicle <NUM> into which one or more acoustic structures <NUM> in accordance with the present disclosure are installed. While <FIG> depicts an vehicle <NUM> (e.g., an aircraft), it will be appreciated that the one or more acoustic structures <NUM> can be installed in other transportation vehicles such as other types of aerospace vehicles, watercraft, a railway vehicle or other overland vehicles, etc., or applied to other non-vehicle uses where mitigation of reflected sound, such as ambient noise, is desired. In this implementation, the acoustic structures <NUM> are configured as composite structures <NUM> forming overhead storage bins, hung from an upper portion of the fuselage of the aircraft. According to some examples, acoustic structures <NUM> of the present disclosure can be affixed to, for example, vertical sides of a bulkhead that divides areas within a passenger compartment <NUM> of the vehicle <NUM>, galley cabinetry, etc..

An acoustic structure <NUM> in accordance with the present disclosure can have a decreased reflection of sound waves compared to conventional acoustic structures, for example, as demonstrated by the graph <NUM> of <FIG>. Further, the acoustic structures of the present disclosure can be lighter in weight and can be more easily restored to a like new or nearly new condition. In addition, such structures can be provided with a desired graphic design, which can be easily changed at a later time.

It will be appreciated that various other acoustic structure implementations and methods of formation are contemplated. <FIG> depicts an acoustic structure <NUM> according to the claimed invention including a backing layer <NUM>, a honeycomb core <NUM>, a mesh layer <NUM> and a knit fabric layer <NUM>. In this implementation, the acoustic structure <NUM> is not formed using prepreg structures, but instead includes a plurality of discrete adhesive layers. The backing layer <NUM> and the mesh layer <NUM> can be analogous to the support layer <NUM> and the mesh layer <NUM> respectively of the <FIG> implementation. However, in contrast to support layer <NUM>, backing layer <NUM> is not impregnated with adhesive <NUM>. Further, in contrast to mesh layer <NUM>, mesh layer <NUM> is not impregnated with adhesive <NUM>. The adhesive layer <NUM> depicted in FIG. <NUM> can be a material as described above with reference to <FIG>, and is thus numbered the same.

In this implementation, the backing layer <NUM> is physically attached to the honeycomb core <NUM> with a first adhesive layer <NUM> and the honeycomb core <NUM> is physically attached to the mesh layer <NUM> with a second adhesive layer <NUM>. The mesh layer <NUM> is physically attached to the knit fabric layer <NUM> as described above with reference to <FIG> using the adhesive layer <NUM> which, in this implementation, thus provides a third adhesive layer <NUM>. Each of the adhesive layers <NUM>, <NUM>, <NUM> can comprise one or more of a thermoplastic, a thermoset, an acrylic, a polyamide, a polyester, a urethane, and/or a rubberized adhesive, combinations of two or more of these, or another suitable adhesive, where each of the adhesive layers <NUM>, <NUM>, <NUM> can be the same or different, each from each other.

As depicted in <FIG>, the first adhesive layer <NUM> can be formed as a blanket layer, while the second adhesive layer <NUM> and the third adhesive layer <NUM> are formed as non-continuous patterned layers, such that they overlie only the plurality of walls <NUM> of the honeycomb core <NUM>, and do not overlie the plurality of honeycomb cells <NUM>, for the reasons discussed above. Forming the second adhesive layer <NUM> and the third adhesive layer <NUM> as a blanket layer would result in reflection of sound waves from these adhesives before the sound waves enter the honeycomb cells <NUM>, thereby decreasing sound wave absorption by the acoustic structure <NUM>. Forming these layers as patterned layers ensures that the sound waves pass through the cross-sectional openings or voids within the adhesive layers and enter the honeycomb cells <NUM> so that reflection of the sound waves from the acoustic structure <NUM> is attenuated.

It will be appreciated that in some methods of formation of the acoustic structure <NUM>, each of the layers are assembled as a single structure as depicted in <FIG>, then all of the adhesive layers <NUM>, <NUM>, <NUM> can be simultaneously cured. In other implementations, formation of the acoustic structure <NUM> can be performed by forming two or more subassemblies, which are then assembled to form the completed acoustic structure <NUM>. For example, in one implementation, the honeycomb core <NUM> can be attached to the backing layer <NUM> using the first adhesive layer <NUM>, which is cured using a suitable curing process. Next, the mesh layer <NUM> can be attached to the honeycomb core <NUM> using the second adhesive <NUM>, which is cured using a suitable curing process. Subsequently, the knit fabric layer <NUM> can be attached to the mesh layer <NUM> using the third adhesive layer <NUM>, which is then cured using a suitable curing process. Other implementations for assembling the acoustic structure <NUM> are contemplated.

<FIG> is a flowchart illustrating a method for repairing an acoustic structure installed in a vehicle, according to examples of the present disclosure not forming part of the claimed invention. Once an acoustic structure <NUM> has been installed in a vehicle, surfaces of the acoustic structure <NUM> can become dirty and/or damaged due to use or misuse, and it can be desirable to repair the acoustic structure to restore the appearance of the installed acoustic structure <NUM> to new or like new. Alternatively, or in addition, it can be desirable to change an existing knit fabric layer <NUM> having a first graphic design with a replacement knit fabric layer <NUM> having a second graphic design, for example, where a vehicle is sold to a new owner.

According to examples of the present disclosure, the knit fabric layer <NUM> can be separated from the mesh layer of an acoustic structure <NUM> even when the acoustic structure is installed in a vehicle (step <NUM>). For example, adhesive holding knit fabric layer <NUM> can be warmed to soften the adhesive and allow for easier separation of the knit fabric layer from the adhesive. The knit fabric layer <NUM> can then be pulled and/or scraped away from the surface of the mesh layer <NUM>, to remove the existing knit fabric layer <NUM>.

Once the existing knit fabric layer <NUM> has been removed, a new adhesive layer can be provided to the surface of the mesh layer <NUM> and/or a replacement knit fabric layer (step <NUM>). For example, the knit fabric layer <NUM> can include an adhesive layer ready for installation on mesh layer <NUM>. Alternatively, or in addition, an adhesive can, for example, be present on mesh layer <NUM> (e.g., a pre-preg mesh layer <NUM>), sprayed or otherwise applied onto mesh layer <NUM> in preparation for installation of the replacement knit fabric layer <NUM>.

According to some examples, new adhesive cannot be applied, and step <NUM> can be considered optional.

The replacement knit fabric layer <NUM> can then be applied to the mesh layer <NUM> for final installation (step <NUM>). For example, a replacement knit fabric layer <NUM> can be stretched to fit the contoured surfaces of the acoustic structure <NUM>, and pressure applied to adhere the replacement knit fabric layer <NUM> to the mesh layer <NUM>.

Thus, an acoustic structure in accordance with the present disclosure can be lighter in weight than conventional acoustic structures, thereby reducing operating costs of transportation vehicles. Additionally, in contrast to conventional acoustic structures that use a rigid perforated face sheet that is difficult to manufacture, an acoustic structure in accordance with the present disclosure uses a flexible knit fabric layer <NUM> as a face sheet that provides a visually appealing surface, accepts graphic designs (e.g., via printing), and offers easier repair and replacement without additional processing. An acoustic structure according to the present disclosure can provide superior sound attenuation and greater flexibility in placement, based on the ability to contour the acoustic structure, as compared to a conventional, flat-panel acoustic structure.

It is contemplated that acoustic structures according to the present teaching can be installed into a vehicle <NUM> (<FIG>) during an initial manufacture of such vehicles. Furthermore, vehicles manufactured with conventional acoustic structures can be retrofitted with acoustic structures according to the present disclosure, for example, if such retrofitting is cost effective (e.g., results in reduced fuel costs due to decreased weight) or otherwise desirable (e.g., crew and/or passenger fatigue over a period of time is decreased due to reduced noise within the vehicle). Retrofitting can include, for example, removing conventional acoustic structures (e.g., acoustic structures having a perforated metal face sheet) and replacing them with acoustic structures according to the present disclosure (e.g., acoustic structures having a knitted fabric layer).

By installing an acoustic structure that includes a knit fabric layer <NUM> in accordance with the present disclosure into a transportation vehicle, either during an initial manufacturing process or a retrofitting process, noise within the transportation vehicle can be reduced, i.e. the sound can be attenuated. The installation process can include manufacturing an acoustic structure in accordance with the present disclosure or procuring a pre-manufactured acoustic structure in accordance with the present disclosure from a supplier. The acoustic structure can be attached to a surface of the transportation vehicle. In another implementation, an in-process or fully completed transportation vehicle including one or more acoustic structures in accordance with the present teaching can be purchased from a supplier. In any of the foregoing scenarios, during use of the transportation vehicle, noise is reduced or attenuated during use of the transportation vehicle, where the noise reduction or attenuation results, at least in part, from the acoustic structure that includes the knit fabric layer <NUM>.

The numerical ranges and parameters setting forth the broad scope of the present disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein are to be understood to encompass any and all sub-ranges subsumed therein. For example, a range of "less than <NUM>" can include any and all sub-ranges between (and including) the minimum value of zero and the maximum value of <NUM>, that is, any and all sub-ranges having a minimum value of equal to or greater than zero and a maximum value of equal to or less than <NUM>, e.g., <NUM> to <NUM>. In certain cases, the numerical values as stated for the parameter can take on negative values. In this case, the example value of range stated as "less than <NUM>" can assume negative values, e.g. - <NUM>, -<NUM>, -<NUM>, -<NUM>, -<NUM>, -<NUM>, etc..

Specific values for described elements should be understood to be within accepted manufacturing or industry tolerances known to one of skill in the art, and any use of the terms "substantially" and/or "approximately" and/or "generally" should be understood to mean falling within such accepted tolerances.

While examples of the present disclosure have been illustrated with respect to one or more implementations, alterations and/or modifications can be made to the illustrated examples without departing from the scope of the appended claims. For example, it will be appreciated that while the process is described as a series of acts or events, the present disclosure is not limited by the ordering of such acts or events. Some acts can occur in different orders and/or concurrently with other acts or events apart from those described herein. Also, not all process stages can be required to implement a methodology in accordance with one or more aspects or implementations of the present disclosure. It will be appreciated that structural components and/or processing stages can be added or existing structural components and/or processing stages can be removed or modified. Further, one or more of the acts depicted herein can be carried out in one or more separate acts and/or phases. Furthermore, to the extent that the terms "including," "includes," "having," "has," "with," or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term "comprising. " The term "at least one of" is used to mean one or more of the listed items can be selected. As used herein, the term "one or more of" with respect to a listing of items such as, for example, A and B, means A alone, B alone, or A and B. Further, in the discussion and claims herein, the term "on" used with respect to two materials, one "on" the other, means at least some contact between the materials, while "over" means the materials are in proximity, but possibly with one or more additional intervening materials such that contact is possible but not required. Neither "on" nor "over" implies any directionality as used herein. The term "conformal" describes a coating material in which angles of the underlying material are preserved by the conformal material. The term "about" indicates that the value listed can be somewhat altered, as long as the alteration does not result in nonconformance of the process or structure to the illustrated implementation. Other implementations of the present disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure herein. It is intended that the specification and examples be considered as illustrative only, with a true scope of the present disclosure being indicated by the following claims.

Terms of relative position as used in this application are defined based on a plane parallel to the conventional plane or working surface of a workpiece, regardless of the orientation of the workpiece. The term "horizontal" or "lateral" as used in this application is defined as a plane parallel to the conventional plane or working surface of a workpiece, regardless of the orientation of the workpiece. The term "vertical" refers to a direction perpendicular to the horizontal. Terms such as "on," "side" (as in "sidewall"), "higher," "lower," "over," "top," and "under" are defined with respect to the conventional plane or working surface being on the top surface of the workpiece, regardless of the orientation of the workpiece.

Claim 1:
An acoustic structure (<NUM>) presenting a front surface and a back surface, the acoustic structure (<NUM>) comprising:
a backing layer (<NUM>) comprising the back surface;
a honeycomb core (<NUM>) comprising a thickness defined between a back and a front, and a plurality of walls (<NUM>) that define a plurality of honeycomb cells (<NUM>), wherein the plurality of honeycomb cells (<NUM>) extend through the thickness of the honeycomb core (<NUM>) opening out toward at least the front, and wherein the back of the honeycomb core (<NUM>) is affixed to the backing layer (<NUM>) with a first adhesive layer (<NUM>);
a mesh layer (<NUM>) affixed to the front of the honeycomb core (<NUM>) with a second adhesive layer (<NUM>); and
a knit fabric layer (<NUM>) affixed to the mesh layer (<NUM>) with a third adhesive layer (<NUM>) and conforming to the front surface of the acoustic structure (<NUM>),
wherein the second adhesive layer (<NUM>) and the third adhesive layer (<NUM>) are formed as non-continuous patterned layers, such that they overlie only the plurality of walls (<NUM>), and do not overlie the plurality of honeycomb cells (<NUM>).