PATENT ABSTRACT
A bonded composite joint may include a base having a foot configured to couple to a member. The base may include a flange extending outward from the foot. The joint further may include a panel having a core positioned between opposing skins, where the skins have inner walls proximate the core and the skins extend outward beyond the core on at least one end of the panel to define a recess between the skins. The recess between the skins may receive the flange. A bonding agent may be used to couple the flange to the inner walls of the panel.

PATENT DESCRIPTION
CROSS REFERENCE TO RELATED PATENT APPLICATION 
       [0001]    This patent application is a divisional application of co-pending, commonly-owned U.S. patent application Ser. No. 11/948,042 entitled “Double Shear Joint for Bonding in Structural Applications”, filed Nov. 30, 2007, which application is hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure teaches methods and apparatus for bonding panels, and more specifically, to methods and apparatus for providing a double shear joint for bonding structural applications. 
       BACKGROUND 
       [0003]    Composite materials, such as graphite-epoxy, are used in the manufacture of aircraft structures because they have high strength-to-weight ratios. Initially, only lightly loaded or non-critical parts were manufactured from composite materials. As the technology has advanced, however, a greater percentage of aircraft parts, including critical structural members, have been manufactured using composite materials. 
         [0004]      FIG. 1  illustrates a prior art joining apparatus  100  for joining a sandwich panel  102  to a structure  104 . The joining apparatus  100  includes a base  106  having a flange  108  projecting outwardly from a foot  110 . The sandwich panel  102  has a maximum thickness  112  and converges to a minimum thickness  114  at a connection portion  116 . The sandwich panel  102  includes a low density core portion  118  situated between skin portions  120 . The core portion  118  includes a wedge portion  122  where the skin portions converge to form the connection portion  116 . The flange  108  and the connection portion  116  are coupled with a fastener  124 . 
         [0005]    As shown in  FIG. 1 , the connection portion  116  is provided for a number of reasons. One reason is to isolate the core portion  118  with the skin portions  120 . As discussed, the core portion  118  is formed from a low density material and therefore is not ideal for receiving the fastener  124 . Another reason is to increase the strength of the sandwich panel  102  at the connection portion  116 . The connection portion  116  includes increased skin thickness as compared to the thickness of the skin portion  120  adjacent to the core portion  118 . 
         [0006]    There are a number of shortcomings to the joining apparatus  100  described above. For example, the wedge portion  122  and corresponding structure (e.g., converging skin portions  120 ) increase part complexity and typically requires a special manufacturing process and specific design requirements for each different application. This makes modifications difficult when design requirements are not satisfied and increases design and manufacturing costs. In addition, manufacturing processes for securing coupling may be reduced or eliminated by improved methods for fastening the sandwich panel  102  and the base  106 . The fastener  124  also adds additional weight to the joining apparatus  100 , which is disadvantageous in aircraft applications or other applications where weight reduction is beneficial. 
       SUMMARY 
       [0007]    Embodiments of methods and apparatus for providing a double shear joint for bonding in structural applications are disclosed. In one embodiment, a bonded composite joint includes a base having a foot configured to couple to a member, the base including a flange extending outward from the foot. The joint further includes a panel having a core configured between opposing skins, the skins having inner walls proximate the core, the skins extending outward beyond the core on at least one end of the panel to define a recess between the skins, the recess configured to receive the flange. A bonding agent is used to couple the flange to the inner walls of the panel. 
         [0008]    In another embodiment, a method for joining a structure to a base includes removing a core portion configured between skins to create a recess on a structure and positioning the recess of the structure proximate the base, the base including a flange projecting away from the base, the flange configured to insert into the recess. A bonding agent may be applied to a gap defined by the volume between the flange and the skins to couple the structure and the base after a curing process. 
         [0009]    In a further embodiment, a joint apparatus includes a composite sandwich panel having skins for each exterior sidewall and a core configured between the skins, the skins extending beyond the core at an end of the sandwich panel to define a recess. A base may have a foot and a flange extending outward from the foot, the flange configured for insertion into the recess, the flange bonded between two skins with a bonding agent. 
         [0010]    The features, functions, and advantages can be achieved independently in various embodiments of the present disclosure or may be combined in yet other embodiments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Embodiments of methods and apparatus in accordance with the present disclosure are described in detail below with reference to the following drawings. 
           [0012]      FIG. 1  illustrates a joining apparatus including a first and a second structure coupled with a fastener in accordance with the prior art. 
           [0013]      FIG. 2  is an exploded isometric view of an illustrative structure and a base in accordance with an embodiment of the disclosure. 
           [0014]      FIG. 3  is an isometric view of an illustrative joint assembly including the structure and the base of  FIG. 2  in accordance with an embodiment of the disclosure. 
           [0015]      FIG. 4  is a side elevation view of the joint assembly of  FIG. 3  in accordance with an embodiment of the disclosure. 
           [0016]      FIG. 5  is a cross-sectional view of the joint assembly of  FIG. 3  including apertures in accordance with another embodiment of the disclosure. 
           [0017]      FIG. 6  is a side elevational view of an illustrative joint assembly including a fastener and reinforcing panels in accordance with another embodiment of the disclosure. 
           [0018]      FIG. 7  is a side elevational view of an illustrative joint assembly including spacing panels in accordance with still another embodiment of the disclosure. 
           [0019]      FIG. 8  is a flow diagram illustrating an example process for assembling a joint assembly in accordance with an embodiment of the disclosure. 
           [0020]      FIG. 9  is a side elevational view of an aircraft having one or more joint assemblies in accordance with another embodiment of the disclosure. 
           [0021]      FIG. 10  is a cut-away isometric view of an aircraft wing structure having a plurality of panels joined by an illustrative joint assembly in accordance with still another embodiment of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Methods and apparatus for providing a double shear joint for bonding in structural applications are described herein. Many specific details of certain embodiments of the disclosure are set forth in the following description and in  FIGS. 2 through 9  to provide a thorough understanding of such embodiments. One skilled in the art, however, will understand that the present disclosure may have additional embodiments, or that the present disclosure may be practiced without several of the details described in the following description. 
         [0023]      FIG. 2  is an exploded isometric view of an illustrative structure  202  and a base  204  in accordance with an embodiment of the disclosure. In an environment  200 , the structure  202  may be a sandwich panel structure including a core portion  206  configured between skin portions  208 . The core portion may be formed from a low density material such as foam, honeycomb, or another low density core material. The skin portions  208  may be formed from a composite material, such as graphite-epoxy or other composite materials. The skin portions  208  may extend beyond the core portion  206  to create a recess  210 . The recess  210  exposes the inner side  212  of the skin portions  208 . In some embodiments, the skin portions  208  include apertures  214 , which will be described in further detail below. 
         [0024]    The base  204  may be situated on a second structural portion  216 . The second structural portion  216  may be substantially similar to the structure  202  and may, in some embodiments, include the core portion  206  and skin portions  208 . Alternately, the second structural portion  216  may be formed from other materials and/or configurations, such as without limitation metal, wood, composites, plastics or other polymer based materials, and the like. 
         [0025]    The structure  202  may be used in any suitable structural application. In particular, the structure  202  may be advantageous in applications where reduced weigh is an important design consideration, such as vehicle manufacture applications. One application may include aircraft assembly, such as using the structure  202  as a skin panel or rib panel in an aircraft wing or fuselage, among a variety of possible applications. 
         [0026]      FIG. 3  is an isometric view of an illustrative joint assembly  300  including the structure  202  of  FIG. 2  and the base  204  in accordance with an embodiment of the disclosure. As illustrated, the joint assembly  300  includes the structure  202  having a length e bonded or otherwise coupled to the base  204 . In some embodiments, an adhesive may be applied to a gap  302 . The gap  302  may be defined between a first surface  304 , including the inner side  212  (shown in  FIG. 2 ) of the skin portions  208  and the core  206  portion, and a second surface  306 , including the exterior of the base  204 . In some embodiments, the gap  302  may be at least 0.02 inches wide at all locations within the gap  302  to provide adequate clearance to receive a bonding agent for bonding the joint assembly  300 . The gap may also be as much as 0.120 inches wide to allow for part tolerance buildup on an assembly. An overlap  308  is defined by the overlap of material along the flange of the first continuous surface  304  and the second continuous surface  306 . In some embodiments, the overlap  308  is at least 1.0 inches to enable adequate application of a bonding agent to resist a shear stress when the joint assembly  300  is subjected to a tensile force. 
         [0027]      FIG. 4  is a side elevation view of the joint assembly  300  of  FIG. 3  in accordance with an embodiment of the disclosure. In some embodiments, the skin portions  208  are substantially parallel in the structure  202  and therefore do not converge. As previously described, the skin portions  208  extend beyond the core portion  206  to form the recess  210  shown in  FIG. 2 . In some embodiments, the structure  202  may require a manufacturing operation to create the recess  210 . In one example operation, the recess  210  is formed by machining, boring, milling, or otherwise removing a portion of the core portion  206  to create the recess  210 . Alternatively, the core may be configured with removable sections. For example, a removable core section may be taped to the skin portion  208  and/or the non-removable section of the core portion  206 . Maintaining a removable core section in the structure  202  prior to assembly may be advantageous to protect the skin portions  208  and to enable customized fitting and assembly of the joint assembly  300 , as discussed in further detail below. 
         [0028]    In accordance with some embodiments, the base  204  includes a foot  402  and a flange  404 . As shown in  FIG. 4 , the flange  404  may be configured at an approximately  90  degree angle with respect to the foot  402  to form a T-shape. In other implementations, the flange  404  may be configured at other angles with respect to the foot  402 . The base  204  may be a standardized size and therefore used with many different structures. For example, the width of the flange  404  may be a predetermined width that does not vary based on the width of the structure  202 . A standardized base may reduce part inventories and manufacturing time, and therefore advantageously reduce cost of the joint assembly  300 . The base  204  may be formed from a composite material, such as graphite-epoxy or other composite materials. Alternatively, the base may be formed from metal, plastics or other polymer based materials, or other materials sufficient for meeting design requirements of the joint assembly  300 . 
         [0029]    In further embodiments, the structure  202  and the base  204  may be bonded using a bonding agent  406 . The bonding agent  406  may be any adhesive capable of securely bonding the structure  202  to the base  204 . In some embodiments, the bonding agent  406  is a room temperature cure paste such as EA9394 adhesive. The bonding agent  406  creates a double bonding between the skin portions  208  and the flange  404 , such that the bonding agent secures each of the skin portions  208  to a different face of the flange  404 , thereby creating a double shear strength bonding resistance when the structure  202  and the base  204  are subjected to a tensile force applied substantially parallel to a centerline of the flange  404 . The bonding agent  406  may be applied into the gap  302  (shown in  FIG. 3 ) at inlets  408 . In some embodiments, the bonding agent  406  may be applied to the joint assembly  300  using a pressurized applicator or other device for injecting the bonding agent into the gap  302  at the inlets  408 . 
         [0030]      FIG. 5  is a cross-sectional view of the joint assembly  300  of  FIG. 3  including the apertures  214  in accordance with another embodiment of the disclosure. In some embodiments, the apertures  214  enable an alternative entry point  502  for an application of the bonding agent  406  used to secure the joint assembly  300 . The apertures  214  may be spaced apart along the length e of the structure  202 . In some instances, the location of the apertures  214  may alternate from side to side along each of the skin portions  208  (shown in  FIG. 2 ) while in other instances the apertures may be substantially aligned for each of the skin portions  208 . In some embodiments, the apertures advantageously enable improved access for the application of the bonding agent  406  to a top portion  504  of the gap  302 , thereby creating a stronger bond between the structure  202  and the base  204 . 
         [0031]    In alternative embodiments, the bonding agent  406  may be applied to the structure  202  and/or the base  204  prior to assembly of the respective parts. For example, when using slow curing bonding agents, the bonding agent  406  may be applied in advance of an assembly. However, when quick drying adhesives are used to bond the structure  202  to the base  204  to form the joint assembly  300 , the inlets  408  (shown in  FIG. 4 ) or the entry point  502  through the apertures  214  may be advantageous, particularly when complicated structures are jointed to a respective base when securing fixtures for a curing process may require time consuming steps and may not be completed prior to an onset of the bond. 
         [0032]      FIG. 6  is a side elevational view of an illustrative joint assembly  600  including a fastener  602 , a reinforcing structure  604 , and mating structure  606  in accordance with another embodiment of the disclosure. Although fasteners typically add increased weight to the joint assembly  600 , they may be advantageous in some applications such as when the reinforcing structure  604  or the mating structure  606  needs to be fastened to the panel. As shown, the joint assembly  600  includes a bonding agent  608  in the gap  302  (shown in  FIG. 3 ). The bonding agent  608  may act to reinforce the area near the fastener  602  and therefore enable use of the fastener  602  without compromising the strength of the joint assembly  600  such as by creating stress points near the fastener. The fastener  602  may include a threaded bolt and nut fastener, a bolt and secure pin, a U-shaped clip, or any other type of fastener used to connect an adjacent structure. 
         [0033]    In additional embodiments, the joint assembly  600 , or any other joint assembly with or without the fastener  602 , may include one or both of the reinforcing panel  604  or the mating structure  606 . The reinforcing structure  604  may be used to add additional strength skin portions  208 . In other embodiments, the skin portions  208  may vary in thickness along the skin portion to provide increased strength in advantageous locations, such as proximate the recess  210 . The mating structure  606  may be used to enable coupling of an additional structure. In contrast to the prior art joining apparatus  100 , the disclosed joint assembly  600  includes substantially straight skin portions  208  that are bonded around the base  202 , which enable easy application of additional layers of reinforcing materials, such as skin sections or other reinforcing or mating structures and/or materials. 
         [0034]      FIG. 7  is a side elevational view of an illustrative joint assembly  700  including spacing panels  702  in accordance with still another embodiment of the disclosure. As alluded to above, the base  204  may have standardized measurements in some instances while a width w of a structure  704  may vary, therefore creating a variance in a gap spacing  706 . In an instance where an excessively large gap is present, the spacing panels  702  may be coupled to the inside face of the skin portions  208  to reduce the gap spacing  706 . For example, a slight misalignment of the structure and base may cause a non-conforming gap. The gap spacing  706  may be determined by design requirements specific to the bonding agent  406  used to secure the joint assembly  700 . In some embodiments, the gap spacing  706  is greater than 0.02 inches. 
         [0035]      FIG. 8  is a flow diagram illustrating an example process  800  for assembling a joint assembly in accordance with an embodiment of the disclosure. The process  800  is presented in an organization of blocks (operations), however, the order of the operations are not intended as a limitation. Embodiments may include alternative arrangements of the operations, conducted in series and/or in parallel, without departing from the scope of the process  800 . 
         [0036]    The process  800  includes assembling the joint assembly, such as joint assembly  300  including the structure  202  and the base  204 . At  802 , the core of the structure  202  is removed to create the recess  210 . The core may be removed by a machining process such as by drilling, boring, or milling the core portion  206  from the structure  202 . Alternatively, the core portion  206  may be removable without machining, such as an instance where the core portion is secured in the structure with tape or another semi-permanent adhesive. The surfaces forming the recess  210  and portions of the base  204  may be prepared for bonding at  804 . For example, the surfaces may be grit-blasted or chemically treated to prepare the surface for the application of the bonding agent  406 . 
         [0037]    The assembly of the structure  202  and the base  204  may include movement or other positioning of the structure  202  and/or the base  204  relative to one another at  806 . In some instances, at  808 , the structure  202  and/or the base  204  may be securely positioned with fixtures to position the assembly. In addition, tape may be applied to cover a portion of the inlets  408  to prevent the bonding agent  406  from exiting the gap  302  before the bonding agent has fully cured. For example, tape or another barrier may be placed over the inlets  408  and then slots may be cut into the tape that enable access to the gap when the bonding agent  406  is applied to the joint assembly. The tape may prevent run off of the bonding agent after an application or it may otherwise constrain the bonding agent in the gap  302 . The bonding agent is applied at  808  to secure the joint assembly. After the application of the bonding agent, the joint assembly typically needs to cure for a number of hours or days before the resulting cured bond is sufficient to secure the joint assembly. 
         [0038]    In some applications, an additional sealant may be applied to one or both sides of the joint assembly along the seam line defined by the exposed bonding agent  406  between the structure  202  and the base  204 . In an implementation when the joint assembly is a sidewall of a fluid container, the additional sealant may be applied to the joint assembly at  814 . For example, the structure  202  may be a sidewall of a fuel tank and the additional sealant may be a fuel sealant which protects the bonding agent  406  from adverse affects from exposure to the fluid (e.g., aircraft fuel). The additional sealant may also delay environmental degradation of the joint assembly. 
         [0039]    An advantage of the disclosed joint assembly is the ability to modify a structure to fit a particular application. For example, a stock (uniform sized) structure may be cut to shape and assembled to the base  204  using the process  800 , thereby reducing cost for design and fabrication. In addition, more than one side of the structure may be assembled to a base, such as the base  204 . For example, an airtight container may be formed by attaching structures with the joint assembly disclosed herein. The joint assembly disclosed herein, therefore, may be used in a variety of applications with a minimal part count. 
         [0040]      FIG. 9  is a side elevational view of an aircraft having one or more joint assemblies in accordance with another embodiment of the disclosure. One may appreciate that joint assemblies may be employed in a wide variety of locations, including the fuselage, wings, empennage, body, and walls of the aircraft  900 . In alternate embodiments, joint assemblies may be used on other types of structures, vehicles, and platforms, such as motor vehicles, aircraft, maritime vessels, or spacecraft, or other suitable applications. For example, the aircraft  900  may include many joint assemblies as disclosed herein throughout the skin of the aircraft in accordance with an embodiment of the disclosure. 
         [0041]    In this embodiment, the aircraft  900  includes a fuselage  902  including wing assemblies  904 , a tail assembly  906 , and a landing assembly  908 . The aircraft  900  further includes one or more propulsion units  910 , a control system  912  (not visible), and a host of other systems and subsystems that enable proper operation of the aircraft  900 . One should appreciate that joint assemblies may be employed in any suitable portion of the aircraft  900 , such as in a fuselage  902  with a fuselage joint assembly  914 , the wing assemblies  904  with a wing assembly joint assembly  916 , the tail assembly  906  with a tail assembly joint assembly  918 , and any other suitable areas of the aircraft  900 . In general, the various components and subsystems of the aircraft  900  may be of known construction and, for the sake of brevity, will not be described in detail herein. 
         [0042]    Although the aircraft  900  shown in  FIG. 9  is generally representative of a commercial passenger aircraft, the apparatus and methods disclosed herein may also be employed in the assembly of virtually any other types of aircraft or vehicles. 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. 
         [0043]      FIG. 10  is a cut-away isometric view of an aircraft wing structure  1000  having a plurality of panels joined by an illustrative joint assembly in accordance with still another embodiment of the disclosure. As illustrated, a structure  1002  may be securely assembled in the aircraft wing structure  1000  with a double sheer joint  1004 , as disclosed herein. 
         [0044]    While preferred and alternate embodiments of the disclosure have been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the disclosure. Accordingly, the scope of the disclosure is not limited by the disclosure of these preferred and alternate embodiments. Instead, the disclosure should be determined entirely by reference to the claims that follow.