Abstract:
Described are channel joints ( 1 ) for bonding a tube or tubular member ( 30 ) to an end fitting ( 20 ) in double shear. The channel joint may include a receiving channel ( 25 ) in the end fitting ( 20 ) that is complementary in shape to the tube, tubular member, or other hollow member ( 30 ) that is to be fitted and bonded with the end fitting. The use of a channel joint allows for simplified assembly because the receiving channel acts as a reservoir for the bonding agent or adhesive ( 50 ). Upon insertion of the tube, tubular member, or other hollow member into the adhesive-loaded receiving channel, the adhesive will backflow to fill the voids in the joint and expel the excess adhesive. The resulting joint is less likely to have voids, has additional bonding area compared to lap joints, and prevents the adhesive or bonding agent from experiencing tensile loads.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to and claims priority benefits from U.S. Provisional Application Ser. No. 61/983,610 (“the &#39;610 application”), filed on Apr. 24, 2014, entitled “Method for Attaching Carbon Fiber Tubes to Aluminum End Fittings”. The &#39;610 application is hereby incorporated in its entirety by this reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The field of the invention relates to mechanical joints or the like, and more particularly to bonded joints for tubes and end fittings. 
       BACKGROUND 
       [0003]    Structures made from tubes and tubular elements provide high strength to weight ratios. Traditionally, these structures were manufactured from metallic tubes, which can be easily welded together to make trusses or other structural components. For improved performance and higher strength to weight ratios, new materials like composites, carbon fiber, polymers, and other materials, which are not easily welded, are being adapted for use in tubular structures. 
         [0004]    To date, solutions for creating structures from tubular components have relied upon mating of the tubular elements with end fittings. The end fittings are typically designed so that the tubular components may slip over or into the end fitting creating a lap joint. The joint may then be bonded or mechanically fastened. However, both of these approaches lead to significant drawbacks. Lap joints often have poor bonding between the parts and are not ideal for use with adhesives. The sliding action of the tubular component onto or into the end fitting can cause a wiping action that removes the adhesive from the joint or causes air gaps to form, leading to poor bonding between the components. Furthermore, the lap joint is a joint in single shear. When the joint is loaded in tension or compression, the joint experiences offset, opposing forces that create a moment that torques the joint. As the joint bends or twists in response to the torque, a portion of the stress on the joint and adhesive may change from a shear stress to a tensile stress and cause peeling or separation of the adhesive. Adhesives, while very strong in shear, are not as effective at resisting tensile loads, and will often prematurely fail with this type of stress. 
         [0005]    Mechanically fastened joints may alleviate some of the structural deficiencies with bonded lap joints, but present additional challenges of their own. Adding mechanical fasteners to these tubular structures increases manufacturing cost and complexity because additional steps must be taken to drill or otherwise form holes for the fasteners. Certain materials, like carbon fiber, may be difficult to drill or cut without splitting or significantly weakening the material. Fasteners may also cause wear or stress points in the tubes, causing structural failures. Fasteners may also interrupt continuous fibers in certain composites that are critical for achieving their desired strength. Tubes may be designed with integrated fastener holes that do not interrupt fiber continuity, but these tubes are often heavier than their non-fastened counterparts. 
         [0006]    In certain cases, it may be desirable to provide a bonded joint with an end fitting that has a channel configured to accept the tubular members. The channel end fitting creates a double shear joint that maintains stress across the adhesive in shear without any bending forces and has twice the bonding area of a lap joint. The channel joint also facilitates improved bonding and simplified assembly. Adhesives or bonding agents may simply be injected into the channel, and the tubular member inserted. Because the adhesive is confined to a closed space, it will be forced back past the surfaces of the channel and tubular member. The result is a strong, void-free joint that automatically rejects excess adhesive. 
       SUMMARY 
       [0007]    The terms “invention,” “the invention,” “this invention” and “the present invention” used in this patent are intended to refer broadly to all of the subject matter of this patent and the patent claims below. Statements containing these terms should be understood not to limit the subject matter described herein or to limit the meaning or scope of the patent claims below. Embodiments of the invention covered by this patent are defined by the claims below, not this summary. This summary is a high-level overview of various aspects of the invention and introduces some of the concepts that are further described in the Detailed Description section below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to appropriate portions of the entire specification of this patent, any or all drawings and each claim. 
         [0008]    According to certain embodiments of the present invention, a bonded joint may comprise a hollow member that may comprise a wall having a wall thickness, a receiving member that may comprise a receiving channel of complementary shape to the hollow member and having a channel width. The channel width may be greater than the wall thickness, and the hollow member may be disposed at least partially within the receiving channel and secured within the receiving channel by a bonding agent. 
         [0009]    In come embodiments, the hollow member may comprise carbon fiber. 
         [0010]    In certain embodiments, the receiving member may comprise aluminum. 
         [0011]    In some embodiments, the hollow member may comprise a tube. 
         [0012]    In certain embodiments, the tube may comprise a shape selected from the group consisting of circular, square, oval, and rectangular. 
         [0013]    In some embodiments, the bonded joint may further comprise an alignment key. 
         [0014]    In certain embodiments, the channel width of the receiving channel may be constant. 
         [0015]    In some embodiments, the receiving channel may be tapered. 
         [0016]    In some embodiments, the receiving member may be hollow. 
         [0017]    According to certain embodiments of the present invention, a method of manufacturing a bonded joint may comprise providing a hollow member, providing a receiving member, forming a receiving channel in the receiving member that may be complementary in shape to the hollow member, injecting a bonding agent into the receiving channel, and inserting the hollow member at least partially into the receiving channel. 
         [0018]    In some embodiments, the hollow member may comprise carbon fiber. 
         [0019]    In certain embodiments, the receiving member may comprise aluminum. 
         [0020]    In certain embodiments, the hollow member may comprise a tube. 
         [0021]    In some embodiments, the tube may comprise a shape selected from the group consisting of circular, square, oval, and rectangular. 
         [0022]    In some embodiments, the method may further comprise aligning the hollow member and the receiving channel with an alignment key. 
         [0023]    In certain embodiments, the receiving channel may have a constant channel width. 
         [0024]    In some embodiments, the receiving channel may be tapered. 
         [0025]    In certain embodiments, the receiving member may be hollow. 
         [0026]    In certain embodiments, the method may further comprise wiping excess bonding agent from the bonded joint. 
         [0027]    According to certain embodiments of the present invention, a receiving member may comprise a receiving channel of complementary shape to a hollow member and the receiving channel may be configured to receive a bonding agent and bond to the hollow member in double shear. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  is a sectional view of a bonded joint with a tapered receiving channel, according to certain embodiments of the present invention. 
           [0029]      FIG. 2A  is a sectional view of the tapered receiving channel of  FIG. 1  with adhesive. 
           [0030]      FIG. 2B  is a sectional view of the bonded joint of  FIG. 1  during assembly. 
           [0031]      FIG. 2C  is a sectional view of the bonded joint of  FIG. 1  after assembly. 
           [0032]      FIG. 3  is a sectional view of a bonded joint with a straight receiving channel, according to certain embodiments of the present invention. 
           [0033]      FIG. 4A  is a sectional view of the straight receiving channel of  FIG. 3  with adhesive. 
           [0034]      FIG. 4B  is a sectional view of the bonded joint of  FIG. 3  during assembly. 
           [0035]      FIG. 4C  is a sectional view of the straight receiving channel of  FIG. 3  after assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    The subject matter of embodiments of the present invention is described here with specificity to meet statutory requirements, but this description is not necessarily intended to limit the scope of the claims. The claimed subject matter may be embodied in other ways, may include different elements or steps, and may be used in conjunction with other existing or future technologies. This description should not be interpreted as implying any particular order or arrangement among or between various steps or elements except when the order of individual steps or arrangement of elements is explicitly described. 
         [0037]    The described embodiments of the invention provide a bonded joint for tubular structures. While the joints are discussed for use with tubular structures, they are by no means so limited. Rather, embodiments of the bonded joints may be used in any structure using hollow or tube-like elements that require connection of tubes. 
         [0038]    In some embodiments of the present invention, as shown in  FIGS. 1-4C , a channel joint  1  comprises a receiving member  20  with a receiving channel  25  and a hollow member  30 .  FIG. 1  illustrates the channel joint  1  as a section. As depicted, the channel joint features a circular section hollow member  30  and complementary receiving channel  25 . However, the hollow member  30  and/or corresponding receiving member  25  may take on any cross-sectional shape including, but not limited to, circular, square, oval, elliptical, rectangular, lobed, triangular, or any other regular or irregular shape as desired or required by a particular application. A central y-axis passes vertically through the channel joint  1  and acts as a point of reference for measurements of the hollow member  30  and receiving channel  25 . 
         [0039]    Still referring to  FIG. 1 , the hollow member  30  has an outer surface  31  and an inner surface  32  of the wall of the hollow member  30 . The outer surface  31  and inner surface  32  may be defined by their distance from the central y-axis by their outer center distance  41  and inner center distance  42 , respectively. Similarly, the receiving channel  25  has an outer channel surface  23  and an inner channel surface  24 . The outer channel surface  23  and inner channel surface  24  may be defined by channel outer center distance  43  and a channel inner center distance  44 , respectively. These center distances,  41 ,  42 ,  43 ,  44  are equivalent to radii for circular section hollow members  30  and receiving channels  25 . In other embodiments, the center distances  41 ,  42 ,  43 ,  44  may represent a maximum, minimum, and/or average center distance at any point around a perimeter of the members  20 ,  30  and/or receiving channel  25 . 
         [0040]    In order for the receiving channel  25  to accept the hollow member  30 , at any point along the perimeter of the hollow member  30 , the inner channel surface  24  must have a channel inner center distance  44  that is less than the inner surface  32  inner center distance  42 . Similarly, at any point along the perimeter of the hollow member  30 , the outer channel surface  23  must have an channel outer center distance  43  that is larger than the outer surface  31  outer center distance  41 . Said differently and by way of example, at any point along the perimeter of the hollow member  30 , outer and inner surfaces  31 ,  32  of the hollow member  30  must fall between the outer and inner channel surfaces  23 ,  24  for the hollow member  30  to properly mate with the receiving channel  25 . In certain embodiments, the thickness of the hollow member  30  wall defined by the difference in the outer center distance  41  and the inner center distance  42  must be less than the channel width of the receiving channel  25  defined by the difference in the channel outer center distance  43  and the channel inner center distance  44 . 
         [0041]    In certain embodiments, the receiving channel  25  may have an outer taper  45  and an inner taper  46 , or both. The outer and inner tapers  45 ,  46 , which in some embodiments may be approximately one degree, may serve any number of functions in the channel joint  1 . For example, the outer and inner tapers  45 ,  46  may facilitate manufacturing. If the receiving member  20  is machined from stock material, the outer taper  45  or inner taper  46  may provide clearance for the machine tools that form the receiving channel  25 . The outer and inner tapers  45 ,  46  may also provide an alignment function during assembly. The hollow member  30  may ride along the outer taper  45  or inner taper  46  and center itself in the receiving channel  25 . Depending upon the clearance between the hollow member  30  and the receiving channel  25  and the degree of slope to the outer taper  45  or inner taper  46 , the outer channel surface  23  or inner channel surface  24  may interfere with the hollow member  30  and limit the depth of insertion of the hollow member  30  into the receiving channel  25 . Alternatively, other alignment or depth control measures may be compatible with the channel joint  1 . For example, in certain embodiments, the hollow member  30 , receiving channel  25 , and/or receiving member  20  may include alignment keys, channels, protrusions, or detents. Also, in some embodiments, an assembly rig may be used to ensure proper alignment and depth of penetration of the hollow member  30  into the receiving channel  25 . 
         [0042]      FIGS. 2A-2C  are sectional views of the channel joint  1  of  FIG. 1  during assembly.  FIG. 2A and 2B  show the receiving member  20  with receiving channel  25  defined by outer channel surface  23  and inner channel surface  24 . As in  FIG. 1 , the receiving channel  25  is tapered. The receiving channel  25  has been filled with a bonding agent or adhesive  50 . The receiving channel  25  acts as a reservoir for the bonding agent or adhesive  50  to hold it and prevent spillage or loss of bonding agent or adhesive  50  during the assembly process. The bonding agent or adhesive  50  may be a glue, epoxy, resin, or any other type of bonding agent or adhesive chosen for the particular strength, ease of use, compatibility with channel joint  1  materials, and application requirements. The bonding agent or adhesive  50  may be injected, sprayed, poured, or otherwise deposited into the receiving channel  25 . The amount of bonding agent or adhesive  50  deposited into the receiving channel  25  depends upon the particular clearance between the receiving channel  25  and hollow member  30 , and the characteristics of the bonding agent or adhesive  50 . However, to simplify manufacturing, a slight excess of bonding agent or adhesive  50  may be desirable so that the channel joint  1  will have a complete bond. The hollow member  30 , with its outer surface  31  and inner surface  32 , is shown in  FIG. 2B  just prior to insertion into the receiving member  20 . The hollow member  30  will follow the insertion motion  47  to mate with the receiving channel  25  of the receiving member  20 . 
         [0043]    In  FIG. 2C , the hollow member  30  has been inserted into the receiving channel  25  of the receiving member  20  to form the channel joint  1 . The outer surface  31  of the hollow member  30  is adjacent to the outer channel surface  23  of the receiving channel  25 . Similarly, the inner surface  32  of the hollow member  30  is adjacent to the inner channel surface  24  of the receiving channel  25 . The bonding agent or adhesive  50  has been displaced in the receiving channel  25  and filled the voids between the hollow member  30  and receiving channel  25 . Any excess bonding agent or adhesive  50  will be expelled at the top end of the receiving channel  25  as shown. Because the bonding agent or adhesive  50  is deposited in the closed space of the receiving channel  25 , the seal effected between the receiving member  20  and hollow member  30  is much less likely to contain voids and other imperfections that would impact bond strength. As the hollow member  30  is inserted into the receiving channel  25 , there is no wiping action of the hollow member  30  displacing the bonding agent or adhesive  50  in the direction of insertion motion  47 . Rather, the bonding agent or adhesive  50  will be forced in a direction opposite to that of the insertion motion  47 , backfilling the voids between the hollow member  30  and the receiving channel  25 . By using a slight excess of bonding agent or adhesive  50 , the excess will be expelled out the top of the receiving channel  25  where it may be easily cleaned, leaving the channel joint  1  with the ideal amount of adhesive for a strong bond. 
         [0044]      FIG. 3  is a sectional view of a channel joint  1  comprising a receiving member  20  and a hollow member  30 . The receiving member  20  comprises a receiving channel  25  defined by outer channel surface  23  and inner channel surface  24 . The hollow member  30  comprises an outer surface  31  and an inner surface  32 . As in  FIG. 1 , a central y-axis passes vertically through the channel joint  1  and serves as a point of reference for the outer center distance  41  of the outer surface  31 , the inner center distance  42  of the inner surface  32 , the channel outer center distance  43  of the outer channel surface  23 , and the channel inner center distance  44  of the inner channel surface  24 . 
         [0045]    The embodiment of  FIG. 3  is similar to the embodiment of  FIG. 1  with the exception of the receiving channel  25  being straight and without outer taper  45  and inner taper  46  noted above. The straight receiving channel  25  lacks the self-aligning features of the tapered receiving channel  25  of  FIG. 1 . However, the straight receiving channel  25  of  FIG. 3  may offer a more consistent bond between the receiving member  20  and the hollow member  30  because the gap between the receiving member  20  and hollow member  30  is substantially constant throughout the bond. All of the other features discussed in reference to  FIG. 1  above, including variations to shape and other alignment and insertion depth control features, may be similarly applicable to the embodiment of  FIG. 3 . 
         [0046]      FIGS. 4A-4C  are sectional views of the channel joint  1  of  FIG. 3  during assembly. Receiving channel  25  of receiving member  20 , defined by outer channel surface  23  and inner channel surface  24 , has bonding agent or adhesive  50  deposited or injected within it. The hollow member  30  with outer surface  31  and inner surface  32  moves along the path of insertion motion  47  to engage the receiving channel  25  of the receiving member  20 . During insertion of the hollow member  30  into the receiving channel  25 , bonding agent or adhesive  50  is displaced in a direction substantially opposite from the insertion motion  47  to backfill the voids between the outer surface  31  and the outer channel surface  23 , as well as the voids between the inner surface  32  and the inner channel surface  24 . Excess bonding agent or adhesive  50  will be expelled from the upper portion of the receiving channel  25 . In certain embodiments, the excess bonding agent or adhesive  50  may be wiped clean in such a way as to form a radius  51  in the bonding agent or adhesive  50 . The radius  51  provides a smooth, clean finish to the channel joint  1  and helps alleviate stress concentrations that might occur from a sharp or irregular bonding agent or adhesive  50  surface. 
         [0047]    Referring to  FIGS. 1-4 , in certain embodiments, the channel joint  1  provides a joint in double shear that maintains the bonding agent or adhesive  50  in shear stress, even when varying forces are applied to the channel joint  1 . Furthermore, the channel joint  1  provides bonding between both the outer surface  31  and inner surface  32  of the hollow member  30  and the receiving channel  25 , giving approximately double the bond area of a lap joint. 
         [0048]    Still referring to  FIGS. 1-4 , in some embodiments, the bond between the hollow member  30  and the receiving member  20  is faster and easier to produce, while still providing enhanced joint quality. The reverse-flow action of the bonding agent or adhesive  50  compared to the insertion motion  47  of the hollow member  30  helps ensure that the bonding agent or adhesive  50  provides a complete seal with no air gaps or breaks to the bond line. In certain embodiments, particularly in channel joints  1  with dissimilar or incompatible materials, the bonding agent or adhesive  50  provides a barrier between the dissimilar materials to prevent or slow galvanic corrosion that would otherwise weaken the channel joint  1  and cause premature failures. In certain embodiments, the channel joint  1  may include fasteners, collars, or other features that improve joint strength. Also, while the receiving member  20  is shown as a hollow component, primarily for lightness, the receiving member may also be solid to provide extra strength, reduce the number of manufacturing steps, provide a seal to the structure to prevent moisture or debris from entering, or to prevent fluid flows from escaping. Similarly, the hollow member  30  may not be hollow along its entire length. While the hollow member  30  may require a hollow or flanged end to mate with the receiving channel  25  of the receiving member  20 , portions of the hollow member  30  may be solid for added strength, prevention of ingress or egress of material or fluid flows, or simplified manufacturing. 
         [0049]    Any of the above described components, parts, or embodiments may take on a range of shapes, sizes, or materials as necessary for a particular application of the described invention. The components, parts, or mechanisms of the described invention may be made of any materials selected for the suitability in use, cost, or ease of manufacturing. Materials including, but not limited to aluminum, stainless steel, fiber reinforced plastics, carbon fiber, composites, polycarbonate, polypropylene, other metallic materials, or other polymers may be used to form any of the above described components. 
         [0050]    Different arrangements of the components depicted in the drawings or described above, as well as components and steps not shown or described are possible. Similarly, some features and sub-combinations are useful and may be employed without reference to other features and sub-combinations. Embodiments of the invention have been described for illustrative and not restrictive purposes, and alternative embodiments will become apparent to readers of this patent. Accordingly, the present invention is not limited to the embodiments described above or depicted in the drawings, and various embodiments and modifications may be made without departing from the scope of the claims below.