Abstract:
A sandwich-structural composite is assembled from a front sheet and a back sheet that sandwich between them first and second open cell core panels that are spliced together along intermeshing edges of the panels with projections from the panels engaging into slots into the panels. There is no adhesive substance employed between the intermeshing edges of the two core panels. The joining and splicing of the intermeshing core panel edges retains the structural and acoustic capability of the composite without the need for adhesives (film, foaming, paste, potting compound, etc.) between the intermeshing edges of the core panels.

Description:
FIELD 
       [0001]    This disclosure pertains to a sandwich-structural composite and its method of construction. The composite is comprised of a front sheet and a back sheet that sandwich between them first and second core panels. 
       BACKGROUND 
       [0002]    Sandwich-structural composites are typically constructed of thin, stiff sheets that are attached to opposite sides of an open cell core panel. A layer of adhesive typically adheres the two sheets to the opposite sides of the core panel. 
         [0003]    The open cell core panels that are used in the assembly of sandwich-structural composites are fabricated in sizes, shapes and types that must be joined end to end or edge to edge when assembling large sandwich-structural composites. The opposing panel edges are typically spliced or seamed together by an adhesive, for example a foaming adhesive that is applied between the opposing edges, fills the open cells along the edges and secures the edges together. This joining, slicing or seaming process employing the structural adhesive injected between the edges of two panels impacts the structural capability, acoustic performance, cost and manufacturability of the sandwich-structural composite. 
         [0004]    In the current method of constructing a sandwich-structural composite the two or more open cell core panels that are being spliced, seamed and/or joined at their opposing edges can move relative to each other during the assembly process to positions away from their desired relative positions for the structural composite. Additionally, the adhesive application between the abutting edges of two adjacent open cell core panels could be lacking in steadiness or regularity along the abutting edges, leaving adhesive voids that compromise the integrity of the joint between the abutting edges. The positioning of the abutting panel edges and the application of the adhesive between the abutting edges requires accurate handling and positioning of the open cell panels and accurate application of the adhesive that increase the time and cost of manufacturing the structural composite. The cost of the adhesive also adds to the overall cost of the sandwich-structural composite. The adhesive applied between the open cell core panel abutting edges could also migrate away from the abutting edges during the curing process of the adhesive, thereby compromising the strength of the adhesive bond. In constructing a sandwich-structural composite having a capacity for acoustic attenuation, the blockage of open cells along the abutting edges of the open cell core panels detracts from the acoustic attenuation capability of the blocked cells. After completion of the sandwich-structural composite it is difficult to inspect the completed composite for defects that may have occurred during the application of the adhesive between the abutting edges of the core panels or defects that occurred during the curing process of the adhesive. 
       SUMMARY 
       [0005]    The sandwich-structural composite and its method of assembly of this disclosure are unique in that the need for an adhesive to join together abutting edges of two or more adjacent open cell core panels in the construction of the composite is eliminated. The lack of adhesive in the sandwich-structural composite provides an acoustically smooth core panel splicing construction and method. The elimination of the adhesive (film, foaming, paste, potting compound, etc.) from the sandwich-structural composite construction removes the primary cause of acoustic performance degradation in composites which is the blockage of the core panel acoustic features (the open cells) by the adhesive. The cost of constructing the sandwich-structural composite is reduced and the efficiency of manufacturability is increased due to the elimination of the adhesive and the time needed to apply the adhesive in the construction of the composite. 
         [0006]    The sandwich-structural composite of the disclosure is basically comprised of a first open cell core panel, a second open cell core panel, a front sheet (planar or non-planar) and a back sheet (planar or non-planar). These basic component parts are constructed of materials typically employed in the constructions of sandwich-structural composites that best suit the sandwich-structural composite for its intended purpose. These materials could include paper or card stock, aluminum, fiberglass or any other types of materials employed in constructing sandwich-structural composites. 
         [0007]    The first open cell core panel is constructed with at least one edge of the panel having at least one projection from the panel and at least one slot into the panel. The projection and the slot have basically the same configurations. This enables the projection of one core panel to extend into the slot of an adjacent core panel. In other embodiments the first open cell core panel could be constructed with an edge having a plurality of projections from the core panel and a plurality of slots into the core panel. 
         [0008]    The second open cell core panel is also constructed with at least one edge of the panel having at least one projection from the panel and at least one slot into the panel. Again, the projection and the slot of the second core panel have basically the same configurations. Also, the projection and the slot of the second core panel have basically the same configurations as the projection and the slot of the first core panel. In other embodiments the second open cell core panel could be constructed with an edge having a plurality of projections from the core panel and a plurality of slots into the core panel. 
         [0009]    The back sheet has opposite exterior and interior surfaces. In constructing the sandwich-structural composite the back sheet is laid down on its exterior surface and the first and second open cell core panels are positioned on the back sheet interior surface. A film or layer of adhesive can be applied to the back sheet interior surface prior to positioning the first and second core panels on the interior surface. The adhesive is used to secure the back sheet to the first and second core panels. 
         [0010]    The first and second open cell core panels are positioned side by side on the interior surface of the back sheet with the projection from the first core panel extending into the slot into the second core panel and the projection from the second core panel extending into the slot into the first core panel. The engagement or intermeshing of the projections in the slots couples the first and second open cell core panels together along their intermeshing edges without the use of adhesives between the intermeshing edges of the two core panels. 
         [0011]    The front sheet also has opposite exterior and interior surfaces. In constructing the sandwich-structural composite the front sheet is laid down on the coupled, intermeshing first and second core panels with the front sheet interior surface laying down on the core panels. A layer or film of adhesive can be applied to the front sheet interior surface prior to the interior surface being laid down on the coupled, intermeshing core panels. 
         [0012]    The adhesive applied to the interior surfaces of the back sheet and the front sheet secures the sheets to the opposite sides of the coupled, intermeshing core panels and completes the construction of the sandwich-structural composite. The front and back sheets are of sufficient strength to bridge the composite shear loads across the coupled, intermeshing core panels. The composite is constructed without the use of adhesives between the coupled, intermeshing core panel edges and the acoustic capacity across the composite is maintained. 
         [0013]    The sandwich-structural composite construction uses little or no structural adhesive, either film or foaming. The elimination of the adhesive between the intermeshing edges of the two core panels removes the primary cause of acoustic performance degradation in the sandwich-structural composite construction which is the blockage of the open cells between the intermeshing panels by the adhesive. The cost of the adhesive between the intermeshing panels and the cost of the adhesive application is eliminated, thereby reducing the manufacturing costs of the sandwich-structural composite. The removal of the adhesive from the sandwich-structural composite construction, the core panel to core panel intermeshing and stabilization, and the front and back sheet interlocking of the coupled core panels improves manufacturability and reduces defects and rework to correct defects in the composite. 
         [0014]    The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a representation of an exploded view of the sandwich-structural composite of the disclosure and its method of assembly. 
           [0016]      FIG. 2  is a representation of a plan view of the sandwich-structural composite with a portion of the composite removed. 
           [0017]      FIG. 3  is a representation of a plan view of a further embodiment of the sandwich-structural composite similar to  FIG. 2 . 
           [0018]      FIG. 4  is a representation of a plan view of a further embodiment of the sandwich-structural composite similar to  FIG. 2 . 
           [0019]      FIG. 5  is a representation of a plan view of a further embodiment of the sandwich-structural composite similar to  FIG. 2 . 
           [0020]      FIG. 6  is a flow diagram of the method described herein. 
           [0021]      FIG. 7  is a flow diagram of aircraft production and service methodology. 
           [0022]      FIG. 8  is a block diagram of an aircraft. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIG. 1  is a representation of a first embodiment of the sandwich-structural composite  10  of the disclosure. The composite  10  is basically comprised of a first open cell core panel  12 , a second open cell core panel  14 , a front sheet  16  (planar or non-planar) and a back sheet  18  (planar or non-planar). These basic component parts of the composite are constructed of materials that are typically employed in the constructions of sandwich-structural composites that best suit the composite for its intended purpose. These materials could include paper or card stock, aluminum, fiberglass or other types of materials employed in constructing sandwich-structural composites as well as equivalents of such materials. 
         [0024]    The first open cell core panel  12  has mutually perpendicular length and width dimensions and a thickness. The core panel  12  has numerous open cells  20  passing through the panel thickness. The open cells  20  are represented schematically in  FIG. 1  as having honeycomb configurations, but the cells  20  could have any one of a variety of known cross-section configurations such as rectangular, triangular, or an equivalent thereof. Each of the open cells  20  is surrounded by cell walls  21  that give the open cell its cross-section configuration. Each of the open cells  20  can have a hollow or completely empty interior volume, or could contain a septum material. 
         [0025]    In the embodiment of the first core panel  12  shown in  FIG. 1 , the panel has a substantially straight edge  22  along its length dimension, and parallel and opposite substantially straight edges  24 ,  26  along its width dimension at opposite sides of the panel length. The panel edge  28  that extends along the panel length dimension and is opposite the substantially straight panel edge  22  has a generally sinusoidal configuration. 
         [0026]    The sinusoidal edge  28  is formed by a plurality of alternating wave projections  30  from the first core panel  12  and a plurality of trough slots  32  into the first core panel  12 . As represented in  FIG. 1 , each of the projections  30  from the first core panel  12  is dimensioned where numerous open cells  20  of the first core panel  12  are in each of the projections  30 . In variant embodiments of the first core panel  12  the sinusoidal panel edge  28  could be dimensioned so that fewer of the panel open cells  20  are positioned in each projection  30 , or more of the panel open cells  20  are positioned in each projection  30 . 
         [0027]    The second open cell core panel  14  is constructed as substantially a mirror image of the first open cell core panel  12 . The second core panel  14  is also comprised of numerous open cells  34  passing through the panel. The open cells  34  are represented in  FIG. 1  as having honeycomb configurations, but the cells  34  could have any known configuration or an equivalent thereof. Furthermore, the second core panel open cells  34  need not have the same configurations as the open cells  20  of the first core panel  12 . As with the open cells of the first core panel  12 , the cross-section configurations of the open cells  34  of the second core panel are defined by the cell walls  36  that surround the cells. The second core panel cells  34  could have hollow or completely empty interior volumes, or could contain a septum material. 
         [0028]    In the embodiment of the composite  10  represented in  FIG. 1 , the second core panel  14  has mutually perpendicular length and width dimensions that are substantially the same as those of the first core panel  12 , and a thickness dimension that is substantially the same as that of the first core panel  12 . In other embodiments of the composite these dimensions could vary. 
         [0029]    The second core panel  14  has a substantially straight edge  38  along its length dimension, and parallel and opposite substantially straight edges  40 ,  42  along its width dimension at opposite sides of the panel length. In the same manner as the first core panel  12 , the second core panel  14  has a generally sinusoidal shaped edge  44  opposite its length dimension edge  38 . 
         [0030]    The second panel sinusoidal edge  44  is also formed with a plurality of alternating wave projections  48  from the second core panel  14  and a plurality of trough slots  50  into the second core panel. As represented in  FIG. 1 , each of the projections  48  from the second core panel  14  is dimensioned where numerous open cells  34  of the second core panel  14  are in each of the projections  48 . In variant embodiments of the second core panel  14  the sinusoidal panel edge  44  could be dimensioned so that fewer of the panel open cells  34  are positioned in each projection  48 , or more of the panel open cells  34  are positioned in each projection. 
         [0031]    The first core panel projections  30  are configured to engaged into the second core panel slots  50  and the second core panel projections  48  are configured to engage into the first core panel slots  32 . This engagement of the projections into the slots of the first  12  and second  14  core panels intermeshes the projections and slots of the panels and couples the panels together along the abutting edges without the use of adhesives. The lack of the adhesive provides an acoustically smooth splice between the two core panels  12 ,  14 . The intermeshing of the projections and slots of the two panels bridges sheer loads between the two core panels across the intermeshing joint which enables the removal of adhesive between the joint. The intermeshing of the two panels projections and slots also stabilizes the panels relative to each other during the assembly of the back sheet  18  and front sheet  16  to the composite. 
         [0032]    The back sheet  18  is a thin, stiff sheet having opposite interior  52  and exterior  54  surfaces. The back sheet  18  has a peripheral edge  56  having a configuration that is substantially the same as that of the combined first core panel  12  and second core panel  14 . In securing the back sheet  18  to the intermeshing first  12  and second  14  core panels, the back sheet is laid on its exterior surface  54  on any support surface, exposing the back sheet interior surface  52 . This is represented in  FIG. 6 . A thin layer of adhesive material can then be applied to the back sheet interior surface  52 . 
         [0033]    The intermeshing first  12  and second  14  core panels are then positioned on the back sheet interior surface  52  as represented in  FIG. 2 . The edges of the cell walls of the first  12  and second  14  core panels contact the adhesive on the back sheet interior surface  52  and the first  12  and second  14  core panels are thereby adhered to the back sheet interior surface without the need for adhesive (film, foaming, paste, potting compound, etc.) adhering together the two core panels  12 ,  14  along their intermeshing sinusoidal edges  28 ,  44 . 
         [0034]    The front sheet  16  is also a thin, stiff sheet with opposite interior  62  and exterior  64  surfaces. The front sheet  16  also has a peripheral edge  66  that is substantially the same in configuration as the peripheral edge  56  of the back sheet  18 . In securing the front sheet  16  to the intermeshing first  12  and second  14  core panels, a thin layer of adhesive is applied to the front sheet interior surface  62 . The front sheet interior surface  62  is then positioned on the intermeshing first  12  and second  14  core panels with the peripheral edge  66  of the front sheet substantially coinciding with the peripheral edge  56  of the back sheet  18 . The layer of adhesive applied to the front sheet interior surface  62  contacts the edges of the cell walls of the first  12  and second  14  core panels and thereby adheres the front sheet  16  to the intermeshing core panels  12 ,  14 . This completes the construction of the sandwich-structural composite of the disclosure. 
         [0035]    The sandwich-structural composite construction uses little or no structural adhesive, either film, foaming, paste, potting compound, etc. The elimination of the adhesive between the intermeshing edges of the two core panels removes the primary cause of acoustic performance degradation in the sandwich-structural composite construction which is the blockage of the open cells between the intermeshing panels by the adhesive. The cost of the adhesive between the intermeshing panels and the cost of the adhesive application is eliminated, thereby reducing the manufacturing costs of the sandwich-structural composite. The removal of the adhesive from the sandwich-structural composite construction, the core panel to core panel intermeshing and stabilization, and the front and back sheet interlocking of the coupled core panels improves manufacturability and reduces defects and rework to correct defects in the composite. 
         [0036]    The above-described embodiment of the sandwich-structural composite employed intermeshing core panel edges  28 ,  44  having a sinusoidal configuration. This is only one example of the configuration of the core panel intermeshing edges that could be employed in the sandwich-structural composite. 
         [0037]      FIG. 3  is a representation of a first open cell core panel  72  and a second open cell core panel  74  having respective intermeshing edges  76 ,  78  that are formed with pluralities of alternating projections having rectangular configurations and slots having rectangular configurations. The intermeshing edges  76 ,  78  of the first core panel  72  and second core panel  74  form a finger joint configuration  80 . 
         [0038]      FIG. 4  is a representation of a first open cell core panel  82  and a second open cell core panel  84  having respective intermeshing edges  86 ,  88  that are formed with pluralities of alternating projections having dovetail configurations and slots have dovetail configurations. The intermeshing edges  86 ,  88  of the respective first  82  and second  84  core panels form a dovetail joint configuration  90  between the two core panels. The dovetail joint configuration  90  not only couples the two core panels  82 ,  84  together against shear forces, but also couples the two panels  82 ,  84  together against tension. 
         [0039]      FIG. 5  is a representation of a first open cell core panel  92  and a second open cell core panel  94  having respective intermeshing edges  96 ,  98  that are formed with pluralities of alternating projections and slots having rounded dovetail configurations. The intermeshing edges  96 ,  98  produce a rounded dovetail joint configuration  100 . As with the joint configuration of  FIG. 4 , the rounded dovetail configuration  100  of the  FIG. 5  embodiment not only secures the two core panels  92 ,  94  together against shear forces, but also secures the core panels together against tensile forces. 
         [0040]    Embodiments of the disclosure may be described in the context of an aircraft manufacturing and service method  100  as shown in  FIG. 7  and an aircraft  102  as shown in  FIG. 8 . During pre-production, exemplary method  100  may include specification and design  104  of the aircraft  102  and material procurement  106 . During production, component and subassembly manufacturing  108  and system integration  110  of the aircraft  102  takes place. Thereafter, the aircraft  102  may go through certification and delivery  112  in order to be placed in service  114 . While in service by a customer, the aircraft  102  is scheduled for routine maintenance and service  116  (which may also include modification, reconfiguration, refurbishment, and so on). 
         [0041]    Each of the processes of method  100  may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of venders, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on. 
         [0042]    As shown in  FIG. 8 , the aircraft  102  produced by exemplary method  100  may include an airframe  118  with a plurality of systems  120  and an interior  122 . Examples of high-level systems  120  include one or more of a propulsion system  124 , an electrical system  126 , a hydraulic system  126 , and an environmental system  130 . Any number of other systems may be included. Although an aerospace example is shown, the principles of the invention may be applied to other industries, such as the automotive industry. 
         [0043]    Apparatus and methods embodied herein may be employed during any one or more of the stages of the production and service method  100 . For example, components or subassemblies corresponding to production process  108  may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft  102  is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages  108  and  110 , for example, by substantially expediting assembly of or reducing the cost of an aircraft  102 . Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft  102  is in service, for example and without limitation, to maintenance and service  116 . 
         [0044]    As various modifications could be made in the construction of the apparatus and its method of construction herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present disclosure should not be limited by any of the above described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.