Abstract:
Techniques for providing fastener-free primary structural joint for sandwich panels are disclosed. In one embodiment, a technique includes positioning a first panel having a first edge portion proximate a second panel having a second edge portion such that the first and second edge portions cooperatively form an interior recess on an interior side of the first and second panels, applying adhesive to at least one of the recessed interior side of the panel assembly and a plug configured to occupy the interior recess, inserting the plug into the interior recess, the plug including a cap that extends beyond the interior recess and overlaps adjacent portions of the first and second panels, applying adhesive to at least one of a splice and an exterior side opposite from the interior side, and attaching the splice on the exterior side.

Description:
FIELD OF THE INVENTION 
     The present disclosure teaches techniques for joining panels, and more specifically, techniques for providing a fastener-free primary structural joint for sandwich panels. 
     BACKGROUND 
     Construction of aircraft components may present a number of unique challenges that may not be applicable in most other industries. In particular, aircraft components must be assembled in a manner to provide adequate strength while conforming to aviation design requirements. Therefore, joining aircraft panels, such as those on an aircraft fuselage or wings, present particular challenges. 
     Besides conforming to aviation design requirements for aerodynamics and strength, aircraft panel junctions must also remain within material tolerance. Additional factors such as ease of assembly may also be important when selecting a method of joining panels. Although some aspects may be particularly appurtenant for aviation, other industries such as building construction may benefit from improved techniques for assembling panels. 
     SUMMARY 
     Embodiments of techniques for providing fastener-free primary structural joint for sandwich panels are disclosed. In one embodiment, a technique includes positioning a first panel having a first edge portion proximate a second panel having a second edge portion such that the first and second edge portions cooperatively form an interior recess on an interior side of the first and second panels, applying adhesive to at least one of the recessed interior side of the panel assembly and a plug configured to occupy the interior recess, inserting the plug into the interior recess, the plug including a cap that extends beyond the interior recess and overlaps adjacent portions of the first and second panels, applying adhesive to at least one of a splice and an exterior side opposite from the interior side, and attaching the splice on the exterior side. 
     In another embodiment, a method for manufacturing structural joints includes creating a plug from a sandwich material comprising a core between a first skin and a second skin, the first skin having a greater surface areas than the second skin, creating a splice from a skin, and creating a structural joint between a first and second panel, the panels including a recess complementary to the plug for receiving the plug when the panels are joined for assembly, the splice attached to the first and second panels opposite the recess, the plug and splice securely joining the first and second panels. 
     In a further embodiment, a system for providing a structural joint includes a panel assembly including a first panel and a second panel, the panel assembly further including an interior recess formed by adjacent edge portions of the first and second panels, and an exterior side opposite from the interior recess, a plug inserted into the interior recess, the plug including a cap that extends beyond the interior recess and overlaps the first and second panel, and a splice attached to the exterior side. 
     The features, functions, and advantages can be achieved independently in various embodiments of the present inventions or may be combined in yet other embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of techniques in accordance with the present disclosure are described in detail below with reference to the following drawings. 
         FIG. 1  is a cross-sectional view of a fastener-free primary structural joint for sandwich panels in accordance with an embodiment of the invention; 
         FIG. 2  is an exploded view of the fastener-free primary structural joint for sandwich panels illustrated in  FIG. 1 ; 
         FIG. 3  is a flow diagram of a process for assembling a fastener-free primary structural joint for sandwich panels in accordance with yet another embodiment of the invention; 
         FIG. 4  is a plan view of a fastener-free primary contoured structural joint for sandwich panels in accordance with an embodiment of the invention; and 
         FIG. 5  is a side elevational view of an aircraft utilizing fastener-free primary structural joints for sandwich panels in accordance with yet another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Techniques for providing a fastener-free primary structural joint for sandwich panels are described herein. Many specific details of certain embodiments of the invention are set forth in the following description and in  FIGS. 1 through 5  to provide a thorough understanding of such embodiments. One skilled in the art, however, will understand that the present invention may have additional embodiments, or that the present invention may be practiced without several of the details described in the following description. 
       FIG. 1  illustrates a cross-sectional view of a fastener-free primary structural joint  100  for sandwich panels in accordance with an embodiment of the invention. The joint  100  may include a first panel  102  and a second panel  104 . The first panel  102  and the second panel  104  may have a complementary design. For example, the first panel  102  and the second panel  104  may be substantial mirror copies of each other, thus the first panel  102  may have substantially the same contour as the second panel  104 . In alternate embodiments, the panels  102 ,  104  may have different contours. 
     The panels  102 ,  104  may be sandwich panels. In some embodiments, the panels  102 ,  104  may include a core  106  situated between an interior skin  108  and an exterior skin  110 . The core  106  may be secured between the skins  108 ,  110  by an adhesive or other bonding agent. The core  106  may be a foam material that includes a relatively low density value therefore having properties of reduced weight, thereby creating efficiencies in aviation applications, while including considerable resistance to compressive forces. In some embodiments, the interior skin  108  and exterior skin  110  may be the same material. For example, the core  106  may be a Nomex-type honeycomb core and the interior skin  108  and the exterior skin  110  may be carbon epoxy face sheets. In other embodiments, the exterior skin  110  may be a different material than the interior skin  108 , such as the exterior skin  110  may include a polished surface material ideal for reducing unintended drag when exposed to outside airflow during a flight of an aircraft while the interior skin  108  may include properties to enhance attachment of other components. 
     The first panel  102  and the second panel  104  may be positioned as a panel assembly  112 . The panel assembly  112  includes the panels  102 ,  104  situated in their design orientation after assembly or joining of the panels has occurred. The panel assembly  112  may define an interior recess  114  and an exterior recess  116 . In some embodiments, the interior recess  114  includes a depth substantially equivalent to the thickness of the core  106 . The interior recess  114  may be formed by machining the panels to remove the core  106  from the panels  102 ,  104 ; by creating panels  102 ,  104  including the interior recess  114  in the form; or by removing the core  106  in other processes such as by utilizing releasing agents. The interior recess  114  may further include an outlet gap  118  between the panels  102 ,  104 . The outlet gap  118  provides an outlet for air, adhesive, or other elements during an assembly process, as described below. 
     The joint  100  may further include a plug  120 . The plug  120  may include a structure substantially similar to the panels  102 ,  104 . For example, the plug  120  may include a plug core  122  secured between a plug interior skin  124  and a plug exterior skin  126 . The plug core  122  may be secured between the plug skins  124 ,  126  by an adhesive or other bonding agent. In some embodiments, the plug  120  may be composed of substantially the same materials as the panels  102 ,  104 . In an exemplary embodiment, the plug core  122  and the plug exterior skin  126  are shaped complementary to the interior recess  114 , such that when the plug core  122  and plug exterior skin  126  are inserted into the interior recess  114 , only a small gap  121  remains around the perimeter of the plug  120 . The small gap  121  surrounding the perimeter of the plug  120  may be designed to accommodate an optimum application of adhesive or bonding material for joining the plug  120  and panel assembly  112 . 
     Preferably, the interior skin  124  extends beyond the interior recess  114  formed by the panel assembly  112 . Therefore, when the plug  120  is inserted into the panel assembly  112 , the plug interior skin  124  completely covers the interior recess  114 , and extends beyond the interior recess  114  to partially overlap the adjacent first and second panels  102 ,  104 . The interior skin  124  may prevent water or other contaminates from entering the interior recess  114  after assembly of the plug  120  and the panel assembly  112 . 
     The plug  120  may be inserted into the interior recess  114  and secured to the panel assembly  112  with an adhesive or bonding agent disposed within the gap  121 , such as Hysol EA-9394 room temperature paste adhesive manufactured by the Dexter Corporation of Windsor Locks, Conn. In some embodiments, the attachment of the plug  120  and the panel assembly  112  may require a curing agent, clamps, or similar apparatus to secure the plug and panel assembly until a secure bond is realized. 
     The joint  100  may further include a splice  128 . The splice  128  may be composed of the same, or substantially the same material as the exterior skin  110 . The splice  128  may be designed in a complementary shape for the exterior recess  116 , therefore creating a smooth and continuous exterior surface when the splice  128  is attached to the panel assembly  112 . For example, the splice  128  may be exposed to airflow external to an aircraft, therefore necessitating a smooth and continuous contour from the first panel  102  to the splice  128  to the second panel  104 , therefore creating minimal drag or airflow disturbance. 
     The splice  128  may be inserted into the exterior recess  116  and secured to the panel assembly  112  with an adhesive or bonding agent. In some embodiments, the joining of the splice  128  and the panel assembly  112  may require a curing agent, clamps, or similar apparatus to securely position the splice and panel assembly in position until a secure bond is realized. 
     In other embodiments, the splice  128  may be attached across a substantially planar surface of the exterior skin  110  of the panel assembly  112 , therefore creating a non-continuous or non-contoured surface. For example, in applications where aerodynamics are not important, such as in building construction applications, a smooth continuous or contoured surface may not be important and may result in additional unnecessary cost or time during assembly or manufacturing of the structural joint  100 . 
       FIG. 2  is an exploded view  200  of the fastener-free primary structural joint  100  for sandwich panels illustrated in  FIG. 1 . As illustrated, the first panel  102  and the second panel  104  are moved along a first direction  202  and a second direction  204  in an assembly process, respectively, to create the panel assembly  112 . Similarly, the plug  120  may be inserted into the panel assembly  112  along an insertion direction  206 , and the splice  128  may be attached to the panel assembly  112  in an attachment direction  208 . 
     The plug  120  may include contoured plug edges  210  on the plug interior skin  124 . In some embodiments, the exposed surface of the plug interior skin  124  may include a gradual slope forming the contoured plug edges  210  near the outer edges of the plug interior skin  124  to create a relatively smooth junction with the interior skin  108  of the panels  102 ,  104 . One should appreciate that the actual thickness of the interior skin  108  and the exterior skin  110  may be significantly less than the thickness of the core  106 . The contoured plug edges  210  may protect the plug interior skin  124  from damage and further prevent contaminants from penetrating between the plug interior surface  124  and the interior skin  108  of the panels  102 ,  104 . 
     The panels  102 ,  104  may include a ramped surface  212  with a ramped angle  214 . The ramped surface  212  may create the exterior recess  116  to accommodate the attachment of the splice  128 . The splice  128  may include an angled splice edge  216  complementary to the ramped angle  214  of the ramped surface  212 . For example, the splice  128  may be attached into the exterior recess  116  formed by the ramp surface  212  while maintaining a smooth continuous and contoured surface for minimal aerodynamic drag or airflow disturbance across the exterior skin  110  of the first panel  102 , the splice  128 , and the exterior skin  110  of the second panel  104 . In an exemplary embodiment, the angled splice edge splice  216  may be substantially parallel with the ramping angle  214  while the ramped surface  212  may be substantially parallel to surface of the splice  128  when the splice is attached to the panel assembly  112 . In other embodiments, additional complementary contours may be included on the panels  102 ,  104 , particularly in the ramped surface  212 , to properly align the splice  128  during an assembly process. For example, the splice  128  may include one or more grooves  252  (shown in dotted lines) near the angled splice edge  216  that may mate with a complementary feature (or projection, protuberance, etc.)  254  on the panels  102 ,  104  when the splice is properly aligned on the panel assembly  112  during assembly of the structural joint  100 . Alternately, an alignment member  256  may project outwardly from the slice  128  and may engage a corresponding alignment recess  258  disposed within one or more of the panels. In further embodiments, any suitable arrangements of alignment members may be employed. 
       FIG. 3  is a flow diagram of a process  300  for assembling a fastener-free primary structural joint for sandwich panels in accordance with yet another embodiment of the invention. The process  300  begins at a block  302 . At a block  304 , the panels to be assembled are selected, such as panels  102 ,  104 . In some embodiments, the panels may be designed for assembly with a unique complementary panel, such as in aviation assembly where each panel may include a distinct contour. 
     At an optional block  306 , the panels may be trimmed or otherwise prepared before they are joined in an assembly. For example, the panels  102 ,  104  may include a removable core portion in the interior recess  114 , such that the removable core portion is removed at the optional block  306 . In other embodiments, the panels  102 ,  104  may be created or manufactured with the core  106  and skins  108 ,  110  ready for assembly without removing or trimming the panels  102 ,  104 . At a block  308 , the panels are placed into an adjacent position for assembly, such as the intended assembled panel position. 
     At a block  310 , a plug is selected for insertion into the recess formed by the interior side of the panels. In some embodiments, the plug may be designed for a particular joint assembly. The plug may also require removal of a portion of the plug core  122  or trimming of the plug interior surface  124  before insertion of the plug into the recess  116  formed by the panel assembly  112 . At a block  312 , adhesive may be applied to the adjacent surfaces of the plug and panel assembly. For example, the underside of the plug interior surface  124 , the plug exterior skin  126 , and any surfaces exposed on the panel assembly  112  in the interior recess  114  may have adhesive applied to them at the block  312 . At a block  314 , the plug is inserted into the recess formed by the interior side of the panels. After the plug is inserted at the block  314 , some adhesive may necessitate removal. For example, some adhesive may be forced through the outlet gap  118  and/or out gaps near the contoured plug edges  210  and need to be removed. 
     At a block  316 , a splice is selected for attachment to the exterior side of the panels. In some embodiments, the splice may be selected for insertion into the exterior recess  116  of the panel assembly  112  at the block  316 . At a block  318 , adhesive is applied to the adjacent surfaces of the splice and panel assembly. For example, adhesive may be applied to the surfaces of the panel assembly  112  exposed by the exterior recess  116  and the underside of the splice  128  adjacent to the exterior recess  116 . At a block  320 , the splice is attached to the exterior side of the panel assembly  112 . For example, the splice  128  may be inserted into the exterior recess  116 . If the splice  128  is configured with an alignment mechanism (e.g. a groove, protuberance, etc.) then at block  320 , the alignment mechanism may be aligned with its counterpart mechanism on the adjacent panel of the panel assembly  112 . If excess adhesive is present, it may necessitate removal from the splice  128  or panel assembly  112 . 
     In some embodiments, an adhesive or bonding agent may require curing time. Therefore, a curing process is performed at block  322 . In some embodiments, the curing process includes the application of heat and pressure to the panel assembly according to a carefully controlled curing process. Clamps or other securing mechanisms may be used to maintain the assembly of the structural joint  100  during the curing process at the optional block  322 . Alternatively, adhesives with relatively quick bonding times may not require the use of securing mechanisms. At a block  324 , the process  300  ends. 
     Although the process  300  illustrates attachment of the plug  120  and the splice  128  to the panel assembly  112  using an adhesive or bonding agent, other means of attachment may be utilized while remaining within the spirit and scope of the present disclosure. For example, a plurality of snaps or locking features may be included on the mating surfaces of the plug  120 , the splice  128 , and the panel assembly  112  to facilitate assembly of the structural joint  100 . 
       FIG. 4  is a plan view of fastener-free primary contoured structural joint  400  for sandwich panels in accordance with an embodiment of the invention. In this embodiment, the contoured joint  400  includes first and second panels  402 ,  404 , a contoured plug  420 , and a contoured splice  428 . Except for being contoured, many of the aspects of these components are substantially similar to the non-contoured embodiments described above with respect to  FIGS. 1-3 , and for the sake of brevity, only significant differences will be described below. 
     The contoured structural joint  400  may include a number of radii that define a contour across the panels after assembly. For example, the first panel  402  may have a first radius  452  while the second panel  404  may have a second radius  454 . The contoured plug  420  and the contoured splice  428  may include contours that create an approximately continuous contour between the panels  402 ,  404 . For example, when a structural joint is created on the fuselage of an aircraft, the contoured structural joint  400  may be necessary to maintain the proper design requirements of the aircraft. Further, for more complex geometries, such as those included on aircraft wings, the contoured structural joint  400  may include corresponding complex contours across the contoured panels  402 ,  404 , the contoured plug  420 , and the contoured splice  428 . It should also be appreciated that the thickness of a panel core  406 , plug core  422 , and skins  408 ,  410  may vary based on the application of the contoured structural joint  400 , such as they may vary across any distance within the contoured structural joint. 
       FIG. 5  is a side elevational view of an aircraft  500  utilizing fastener-free primary structural joints  550  for sandwich panels in accordance with yet another embodiment of the invention. One may appreciate that embodiments of structural joint may be employed in a wide variety of locations, including the fuselage, body, walls, and other exterior locations on movable platforms such as motor vehicles, aircraft, maritime vessels, or spacecraft, or other suitable applications including applications of building or product construction where panels are joined to create a structural joint. For example, an aircraft  500  may have one or more fastener-free primary structural joints  550  for sandwich panels in accordance with an embodiment of the invention. 
     In this embodiment, the aircraft  500  includes a fuselage  502  including wing assemblies  504 , a tail assembly  506 , and a landing assembly  508 . The aircraft  500  further includes one or more propulsion units  510 , a control system  512  (not visible), and a host of other systems and subsystems that enable proper operation of the aircraft  500 . One should appreciate that embodiments of the fastener-free primary structural joints for sandwich panels may be employed in any suitable portion of the aircraft  500 , such as in a fuselage  502  ( 550   a ), wing assemblies  504  ( 550   b ), tail assembly  506  ( 550   c ), and any other suitable areas of the aircraft  500 . In general, except for the fastener-free primary structural joints for sandwich panel in accordance with embodiments of the invention, the various components and subsystems of the aircraft  500  may be of known construction and, for the sake of brevity, will not be described in detail herein. 
     Although the aircraft  500  shown in  FIG. 5  is generally representative of a commercial passenger aircraft, including, for example, the 737, 747, 757, 767, 777, and 787 models commercially available from The Boeing Company of Chicago, Ill., the inventive apparatus and methods disclosed herein may also be employed in the assembly of virtually any other types of aircraft. More specifically, the teachings of the present disclosure may be applied to the manufacture and assembly of other passenger aircraft, fighter aircraft, cargo aircraft, rotary aircraft, and any other types of manned or unmanned aircraft, including those described, for example, in The Illustrated Encyclopedia of Military Aircraft by Enzo Angelucci, published by Book Sales Publishers, September 2001, and in Jane&#39;s All the World&#39;s Aircraft published by Jane&#39;s Information Group of Coulsdon, Surrey, United Kingdom, which texts are incorporated herein by reference. 
     While preferred and alternate embodiments of the invention have been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of these preferred and alternate embodiments. Instead, the invention should be determined entirely by reference to the claims that follow.