Patent Publication Number: US-11040765-B2

Title: Advanced composite heated floor panel

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of India Provisional Application No. 201841023912 filed Jun. 27, 2018 for “ADVANCED COMPOSITE HEATED FLOOR PANEL” by Aruna Kumar Huluvangala Krishnappa and Guru Prasad Mahapatra. 
     BACKGROUND 
     Heated floor panels are often used in aircraft to mitigate the effects of cold underfloor temperatures and to help maintain a comfortable cabin temperature. The floor panels are typically supported by an aircraft structure arranged, for example, in a grid-like pattern. The floor panels have structural integrity sufficient to support the weight of people and objects resting on the panels. A face sheet typically forms the top surface of the panel to protect the underlying layers (e.g. weight supporting layers and/or a heating layer) from punctures from high heels, chips from dropped objects, scratches from dragged luggage, and/or other floor-traffic related hazards. Such face sheets can be formed from two-dimensional (2D) fabrics extending, for example, in the x and y planes. 
     2D fabrics have poor out-of-plane mechanical properties, and are thus vulnerable to surface cracking and/or delamination upon impact loading. Delamination can occur when bonds between individual layers break down from impact or other forces. Seepage and moisture absorption through surface cracks can lead to degradation of panel material properties and subsequent field failures. Further, some underlying layers may be formed from materials with relatively low thermal conductivity, requiring greater power input to the heating element to maintain panel surface temperature. Thus, the need exists for a panel having improved mechanical and thermal properties. 
     SUMMARY 
     A composite panel suitable for heating an environment includes a face sheet having a 3D woven structure and abutting the environment, and a first core layer positioned on a side of the face sheet opposite the environment. The 3D woven structure includes at least one z-fiber extending in a first direction, the first direction representing a thickness of the face sheet. The woven structure further includes a plurality of weft layers, each having a weft fiber extending in a second direction, and a warp layer disposed between the plurality of weft layers, the warp layer having a warp fiber extending in a third direction. The z-fiber extends along the plurality of weft layers across a full extent of the 3d woven structure in the first direction. 
     A method of forming a composite panel suitable for heating an environment includes positioning a face sheet having a 3D woven structure in communication with the environment, and positioning a first core layer on a side of the face sheet opposite the environment. The 3D woven structure includes at least one z-fiber extending in a first direction, the first direction representing a thickness of the face sheet. The woven structure further includes a plurality of weft layers, each having a weft fiber extending in a second direction, and a warp layer disposed between the plurality of weft layers, the warp layer having a warp fiber extending in a third direction. The z-fiber extends along the plurality of weft layers across a full extent of the 3D woven structure in the first direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified cross-sectional view showing the various layers of a composite panel. 
         FIG. 2  is a simplified cross-sectional view of a 3D woven face sheet belonging to the composite panel. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is directed to a composite panel, and more specifically, to a heated floor panel with a three-dimensional (3D) woven face sheet. The face sheet includes three orthogonal fiber components in multiple layers. Binding “z-fibers” interlock the other layers to prevent delamination. The panel further includes a metallic core layer above the heating element, which, along with the z-fibers, improves thermal conductivity to the panel surface. 
       FIG. 1  is a simplified cross-section of composite panel  10 . Panel  10  includes heating layer  12 , adhesive layers  14  and  16 , honeycomb core layers  18  and  20 , structural layers  22  and  24 , and face sheet  26 . Surface  28  of face sheet  26  represents the upper (external) surface of panel  10 . Panel  10  is positioned over substrate S, and provides heat to environment E, which is located on a side of panel  10  opposite substrate S. 
     Heating layer  12  can include a thermoelectric heating element (not shown). The heating element can be a resistive heating element formed, for example, from a metallic material, Positive Temperature Control (PTC) ceramic, PTC polymer, or carbon allotrope material. The heating element can be arranged as an etched foil, wire, or printed-ink element. Other suitable heating elements are contemplated herein. Heating layer  12  can be used to control the temperature of surface  28  of panel  10 , which can be installed, for example, in an aircraft cabin or cockpit. In certain embodiments, the heating element can extend across the entire area of heating layer  12 . In other embodiments, the heating element can be inset some distance from the edges of heating layer  12  in order to protect the element from fluid spills along or damage at the edges of panel  10 . 
     Core layers  18  and  20  provide impact resistance to panel  10 , and carry shear loads to stiffen floor panel  10 . Upper core layer  18  can, in an exemplary embodiment, be a high-density honeycomb core formed from a metallic material, such as aluminum. Lower core layer  20  can be formed from an expanded honeycomb polymer, such as aramids (e.g., Kevlar® or Nomex®), as well as an open-cell or closed-cell polymer foam. Generally speaking, metallic upper core layer  18  has greater thermal conductivity than polymer lower core layer  20 , which improves the heat transfer properties of panel  10  in the direction of surface  28 , where heating is desired. In another embodiment, however, both core layers  18  and  20  can be formed from the same material (e.g., metal or polymer), and such an arrangement will depend on factors such as weight limitations and panel heating/insulation requirements. 
     Adhesive layers  14  and  16  can be located between heating layer  12  and core layers  18  and  20 , respectively, to help secure the core structure about the heating layer. Adhesive layers  14  and  16  can include film adhesives (e.g., epoxy) or a prepreg (composite fibers impregnated with a matrix material) having a high resin content. Additional and/or alternative adhesive layers can be positioned at other locations between or within layers to further solidify panel structure. 
     Structural layers  22  and  24  provide additional reinforcement to panel  10 . Structural layers  22  and  24  can be a reinforced polymer, such as a carbon fiber or fiberglass impregnated with a resin system such as epoxy, polyurethane, phenolic, cyanate ester, bismaleimide, or other appropriate resins. Each of structural layers  22  and  24  can include a single ply, or a plurality of plies, depending on, for example, the material chosen to form the structural layers, or the particular need for reinforcement. Additional and/or alternative structural layers can also be added in other embodiments. 
       FIG. 2  is a simplified cross-sectional view of face sheet  26 , shown for simplicity without the other layers of panel  10 . Face sheet  26  provides structural support, and more specifically, impact strength to panel  10  on the side of panel  10  exposed to environment E, which can be, for example, an aircraft cabin, cockpit, or other compartment. In an exemplary embodiment, face sheet  26  is structured as a 3D woven composite, having fiber components in three, generally orthogonal axes (x, y, z) as labeled in  FIG. 2 . Face sheet  26  includes a plurality of warp layers  30  extending along the x-axis. Each warp layer  30  can be formed from a single warp fiber  32 , or from a number of warp fibers  32  arranged, for example, as a bundle of fibers (e.g., yarn). Weft layers  34  extend along the y-axis in an alternating fashion with warp layers  30 . Weft layers  34  can also be formed from one or more weft fibers  36 . 
     Face sheet  26  further includes at least one z-fiber  38  extending along the z-axis, which, as shown, is the thickness direction of face sheet  26 . In the embodiment shown, one z-fiber  38  extends from an uppermost weft layer  34  (relative to surface  28 ) along the plurality of weft layers  34  and crosses along the neighboring, lowermost weft layer  34 . A second z-fiber  38  traverses the thickness of face sheet in the opposite direction, such that the two z-fibers  38  cross one another between individual weft columns  40  (i.e. “stacks” of individual weft layers  34  in the thickness direction), thus interlocking and securing weft layers  34  through the thickness of face sheet  26 . This particular arrangement of fibers is generally known as orthogonal fiber architecture. In an alternative embodiment, the weft, warp, and z-fiber components can be arranged differently, for example, in a ply-to-ply interlock architecture, or a through-thickness angle interlock architecture, depending on such factors as manufacturing capabilities, fiber materials, or desired in-plane and/or out-of-plane mechanical properties of face sheet  26 . 
     The various fibers of face sheet  26  can be formed from different materials depending on the composite scale of the face sheet. For example, where face sheet  26  is formed as a nanocomposite, warp fibers  32  and weft fibers  36  can be formed from glass, aramid, carbon, or metallic materials, while z-fibers  38  can be formed from steel nanotubes or carbon nanotubes. For larger (e.g., macro) scale composites, warp fibers  32 , weft fibers  36 , and z-fibers  38  can be formed from glass, aramid, or metallic materials. Other suitable high-strength, high-stiffness, and low-density materials are contemplated herein. Face sheet  26  can further be reinforced with polymer matrix  42 , represented in  FIG. 2  as the space between the warp, weft, and z-fibers. Matrix  42  can be formed from a thermoplastic, such as polyether ether ketone (PEEK) or polycarbonate, or a thermoset, such as epoxy or phenolic resin. 
     The 3D woven structure and matrix  42  give face sheet  26  improved damage tolerance over 2D structures. Z-fibers  38 , for example, secure weft layers  34  along the thickness direction to help prevent separation of individual warp and weft layers. Further, z-fibers  38  can absorb energy in the thickness direction and facilitate impact force dissipation. Matrix  42  helps bind the fiber components and maintain the shape of face sheet  26 . Matrix  42  also helps transfer loads to the fiber components. Face sheet  26  also has improved thermal conductivity due to the presence of z-fibers  38 , which can be formed from relatively thermally conductive materials (e.g. carbon, metals, etc.) when compared to matrix  42 , and help transfer heat radiating upward (along the z-axis) from heating layer  12  to surface  28  and environment E. The thickness of face sheet  26  can be varied to further optimize its thermal and mechanical properties. 
     The disclosed panel is highly impact resistant due to the 3D woven structure of face sheet  10 . The combination of face sheet  26  and metallic upper core layer  18  also offer improved thermal conductivity, which lead to reduced power requirements for the heating element(s) within heating layer  12 . The high strength to weight ratio of panel  10  makes it ideal for aerospace applications, but it can also be used in maritime, railroad, and automotive applications, as well as the construction industry. 
     Discussion of Possible Embodiments 
     The following are non-exclusive descriptions of possible embodiments of the present invention. 
     A composite panel suitable for heating an environment includes a face sheet having a 3D woven structure and abutting the environment, and a first core layer positioned on a side of the face sheet opposite the environment. The 3D woven structure includes at least one z-fiber extending in a first direction, the first direction representing a thickness of the face sheet. The woven structure further includes a plurality of weft layers, each having a weft fiber extending in a second direction, and a warp layer disposed between the plurality of weft layers, the warp layer having a warp fiber extending in a third direction. The z-fiber extends along the plurality of weft layers across a full extent of the 3d woven structure in the first direction. 
     The panel of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     In the above panel, the first core layer can include a high-density honeycomb core formed from aluminum. 
     Any of the above panels can further include a second core layer disposed on a side of the first core layer opposite the face sheet. 
     In any of the above panels, the second core layer can include a polymer foam or a polymer honeycomb. 
     In any of the above panels, the at least one z-fiber can be formed from a glass, aramid, or metallic material. 
     In any of the above panels, the at least one z-fiber can include a nanostructure formed from steel nanotubes or carbon nanotubes. 
     In any of the above panels, the at least one z-fiber can include a plurality of z-fibers. 
     In any of the above panels, the weft fiber can be formed from a glass, aramid, or metallic material. 
     In any of the above panels, the warp fiber can be formed from a glass, aramid, or metallic material. 
     In any of the above panels, the face sheet can further include a matrix formed from a thermoset or thermoplastic material. 
     In any of the above panels, the z-fiber can have a higher thermal conductivity than the matrix. 
     In any of the above panels, the first, second, and third directions are orthogonal to one another. 
     Any of the above panels can further include a first reinforcing layer abutting the first core layer, and a second reinforcing layer abutting the second core layer. 
     In any of the above panels, the environment can be an aircraft compartment. 
     A method of forming a composite panel suitable for heating an environment includes positioning a face sheet having a 3D woven structure in communication with the environment, and positioning a first core layer on a side of the face sheet opposite the environment. The 3D woven structure includes at least one z-fiber extending in a first direction, the first direction representing a thickness of the face sheet. The woven structure further includes a plurality of weft layers, each having a weft fiber extending in a second direction, and a warp layer disposed between the plurality of weft layers, the warp layer having a warp fiber extending in a third direction. The z-fiber extends along the plurality of weft layers across a full extent of the 3D woven structure in the first direction. 
     The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components: 
     In the above method, the first core layer can include a high-density honeycomb core formed from aluminum. 
     In any of the above methods, the at least one z-fiber can be formed from a glass, aramid, or metallic material. 
     In any of the above methods, the at least one z-fiber can include a nanostructure formed from steel nanotubes or carbon nanotubes. 
     In any of the above methods, the weft fiber and the warp fiber can be formed from a glass, aramid, or metallic material. 
     In any of the above methods, the face sheet further can include a matrix formed from a thermoset or thermoplastic material. 
     While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.