Patent Publication Number: US-2023158789-A1

Title: Lap shear bonding fixture

Description:
STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT 
     This invention was made with Government support under Contract No.: DE-NA0002839 awarded by the United States Department of Energy/National Nuclear Security Administration. The Government has certain rights in the invention. 
    
    
     FIELD OF THE INVENTION 
     Embodiments of the current invention relate to fixtures for lap shear bonding. 
     DESCRIPTION OF THE RELATED ART 
     Lap shear bonding involves the bonding, or joining, of two objects together in order to test a lap shear strength of an adhesive, epoxy, glue, or the like that creates the bond. Referring to  FIG.  4   , a portion of the testing process is illustrated. Two objects, such as a bottom panel and a top panel, have been bonded together using an adhesive, which has been applied to the surface of one or both panels where the two panels overlap and contact one another through the adhesive. A shear force is applied to the bonded panels. That is, a first force is applied to an edge of the bottom panel, and a second force is applied to an opposing edge of the top panel, wherein the forces are applied in opposing directions. The forces are applied until the bond breaks and the panels separate. The lap shear strength of the bond is determined from the force applied when the bond breaks and an area over which the adhesive was applied. 
     The panels are typically bonded to one another using a fixture, or apparatus, that includes a bottom tool, a top tool, a top shim, and a bottom shim. The shims provide the proper spacing between the bottom tool and the top tool to match the thickness of the two panels. The bottom shim and the bottom panel with adhesive already applied are positioned on the bottom tool. The top shim is positioned on the bottom panel, and the top panel with adhesive already applied is positioned on the bottom shim. The top tool is placed on the top shim and the top panel. Release sheets may also be used to separate the surfaces of the panels from the fixture components. After the top tool is placed, the assembly may be tightened to apply pressure to the bond between the two panels. One problem is that the shims and the panels may need to be carefully positioned to ensure alignment before the top tool is placed. And, since the top tool and the bottom tool are each full length, once the top tool is placed, the bond cannot be seen or accessed. Thus, it is not known whether the panels are properly aligned, whether excess adhesive has squeezed out, or whether there is uniform distribution of the adhesive in all areas of the bond. 
     SUMMARY OF THE INVENTION 
     Embodiments of the current invention address one or more of the above-mentioned problems and provide an advance in the art of lap shear bonding. The current invention provides a fixture and a method that utilize a bottom tool, a top tool, and spacers instead of shims. The spacers attach to the bottom tool along its sides in order to provide the proper spacing between the bottom tool and the top tool. The bottom panel attaches directly to the bottom tool, and the top panel attaches directly to the top tool, eliminating the need for careful positioning of the panels and the shims. In addition, the bottom tool has an opening and the top tool extends about half the length of the bottom tool so that when the top tool and the top panel are placed on the bottom tool and the bottom panel, the bond between the top panel and the bottom panel can be viewed from above and below. Alignment can be checked, excess adhesive can be wiped away, and the distribution of the adhesive in all areas of the bond between the top panel and the bottom panel can be checked. 
     An embodiment of the fixture broadly comprises a bottom tool, a first spacer, a second spacer, and a top tool. The bottom tool has a quadrilateral shape including a planar top surface, a bottom surface, and four side surfaces and is configured to retain the bottom panel on the top surface. The first spacer is attached to the top surface of the bottom tool adjacent to one edge, and the second spacer is attached to the top surface of the bottom tool adjacent to an opposing edge. The top tool has a quadrilateral shape including a top surface, a planar bottom surface, and four side surfaces and is configured to retain the top panel on the bottom surface. The top tool is further configured to attach to the first spacer and the second spacer such that a portion of the top panel contacts a portion of the bottom panel. 
     Another embodiment of the fixture broadly comprises a bottom tool, a first spacer, a second spacer, and a top tool. The bottom tool has a quadrilateral shape including a planar top surface, a bottom surface, and four side surfaces and is configured to retain the bottom panel on the top surface. The first spacer is attached to the top surface of the bottom tool adjacent to one edge, and the second spacer is attached to the top surface of the bottom tool adjacent to an opposing edge. The first spacer and the second spacer each have a thickness equal to the combined thicknesses of the bottom panel and the top panel. The bottom tool is configured to retain the bottom panel on the top surface between the first spacer and the second spacer. The top tool has a quadrilateral shape including a top surface, a planar bottom surface, and four side surfaces and is configured to retain the top panel on the bottom surface. The top tool is further configured to attach to the first spacer and the second spacer such that a portion of the top panel contacts a portion of the bottom panel. 
     An embodiment of the method broadly comprises attaching a first spacer and a second spacer to opposing edges of a top surface of a bottom tool; attaching the bottom panel to the top surface of the bottom tool in between the first spacer and the second spacer; attaching a top panel to a bottom surface of a top tool; applying an adhesive to either a portion of the bottom panel or a portion of the top panel; placing the top panel and the top tool on the bottom panel and the bottom tool; placing a first alignment pin and a second alignment pin in the top tool, the top panel, the bottom panel, and the bottom tool to align the bottom panel and the top panel; and attaching the top tool to the first spacer and the second spacer. 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Other aspects and advantages of the current invention will be apparent from the following detailed description of the embodiments and the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       Embodiments of the current invention are described in detail below with reference to the attached drawing figures, wherein: 
         FIG.  1    is an upper perspective view of a fixture, constructed in accordance with various embodiments of the current invention, for lap shear bonding a bottom panel to a top panel; 
         FIG.  2    is a lower perspective of the fixture; 
         FIG.  3    is an exploded view of the fixture, illustrating the bottom panel, the top panel, a bottom tool, a top tool, a first spacer, a second spacer, a first alignment pin, a second alignment pin, a plurality of panel fasteners, and a plurality of top tool fasteners; 
         FIG.  4    illustrates a portion of a lap shear bond test of the bottom panel and the top panel; 
         FIG.  5    is an upper perspective view of the bottom tool; 
         FIG.  6    is an upper perspective view of the bottom tool with the first and second spacers attached thereto; 
         FIG.  7    is an upper perspective view of the bottom tool and the first and second spacers with the bottom panel placed on the bottom tool; 
         FIG.  8    is an upper perspective view of the bottom tool and the first and second spacers with the bottom panel attached the bottom tool using panel fasteners and an adhesive applied to a portion of the bottom panel; 
         FIG.  9    is a lower perspective of the top plate; 
         FIG.  10    is a lower perspective of the top plate with the top panel placed thereon; 
         FIG.  11    is a lower perspective of the top plate with the top panel attached thereto using panel fasteners and the adhesive applied to a portion of the top panel; 
         FIG.  12    is an upper perspective view of the top tool and the top panel placed on the bottom panel and the bottom tool; 
         FIG.  13    is an upper perspective view of the top tool and the top panel placed on the bottom panel and the bottom tool with the alignment pins placed through the stack of components; and 
         FIG.  14    is a listing of at least a portion of the steps of a method of lap shear bonding the bottom panel to the top panel. 
     
    
    
     The drawing figures do not limit the current invention to the specific embodiments disclosed and described herein. The drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The following detailed description of the technology references the accompanying drawings that illustrate specific embodiments in which the technology can be practiced. The embodiments are intended to describe aspects of the technology in sufficient detail to enable those skilled in the art to practice the technology. Other embodiments can be utilized and changes can be made without departing from the scope of the current invention. The following detailed description is, therefore, not to be taken in a limiting sense. The scope of the current invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled. 
     Relational and/or directional terms, such as “above”, “below”, “up”, “upper”, “upward”, “down”, “downward”, “lower”, “top”, “bottom”, “outer”, “inner”, etc., along with orientation terms, such as “horizontal” and “vertical”, may be used throughout this description. These terms are used with reference to embodiments of the technology and the positions, directions, and orientations thereof shown in the accompanying figures. Embodiments of the technology may be positioned and oriented in other ways or move in other directions. Therefore, the terms do not limit the scope of the current technology. 
     Referring to  FIGS.  1 - 3   , a fixture  10  for lap shear bonding, constructed in accordance with various embodiments of the current invention, is shown. The fixture  10  broadly comprises a bottom tool  12 , a top tool  14 , a first spacer  16 , a second spacer  18 , a first alignment pin  20 , a second alignment pin  22 , a plurality of panel fasteners  24 , and a plurality of top tool fasteners  26 . The fixture  10  is utilized to bond a bottom panel  28  to a top panel  30  in order to test the lap shear strength of an adhesive  32  (or epoxy, glue, or the like) used to create the bond. 
     Each panel  28 ,  30 , as shown in  FIGS.  1 - 4 ,  7 ,  8 , and  10 - 13   , is formed from material of relatively high strength so that the bond of the adhesive breaks before the panels  28 ,  30  break or tear. Typically each panel  28 ,  30  is formed from a metal or metal alloy. Each panel  28 ,  30  may be quadrilateral shaped with a thickness that is small compared to its surface area, resulting in each panel  28 ,  30  having a top surface, a bottom surface, and four side edges. Other shapes and relative dimensions of the panels  28 ,  30  are possible. Each panel  28 ,  30  may also include a plurality of slot openings cut into the panel  28 ,  30  from the top surface to the bottom surface. The slot openings are spaced apart from one another and may include a first group positioned adjacent to one side edge and a second group aligned with the first group and extending through an opposing side edge. The second group of slot openings also creates a plurality of spaced apart tabs  34 . The slot openings allow for the bottom and top panels  28 ,  30  to be attached to the fixture  10 , as described in more detail below. In addition, each panel  28 ,  30  includes a plurality of alignment or registration holes which receive the first and second alignment pins  20 ,  22 . 
     The bottom tool  12 , as shown in  FIGS.  1 ,  2 ,  5 - 8 ,  12  and  13   , generally retains the bottom panel  28  during the bonding process. The bottom tool  12  is typically formed from a metal or metal alloy and may be quadrilateral shaped with a planar top surface, a bottom surface, and four side surfaces. The bottom tool  12  includes a quadrilateral shaped opening  36  from the top surface to the bottom surface. The bottom tool  12  also includes a plurality of first fingers  38 , spaced apart from one another and extending into one side of the opening  36 . The bottom tool  12  may also include a plurality of other threaded openings and holes which receive screws and/or bolts. In addition, the bottom tool  12  includes a plurality of alignment or registration holes which receive the first and second alignment pins  20 ,  22 . 
     The top tool  14 , as shown in  FIGS.  1 ,  2 , and  9 - 13   , generally retains the top panel  30  during the bonding process. The top tool  14  is typically formed from a metal or metal alloy and may be quadrilateral shaped with a top surface, a planar bottom surface, and four side surfaces. The top tool  14  includes a plurality of second fingers  40 , spaced apart from one another and positioned along one side of the top tool  14 . The top tool  14  may also include a plurality of other threaded openings and holes which receive screws and/or bolts. The top tool  14  has a width that is the same as a width of the bottom tool  12  and has a length that is roughly half a length of the bottom tool  12 . In addition, the top tool  14  includes a plurality of alignment or registration holes which receive the first and second alignment pins  20 ,  22 . 
     Each spacer  16 ,  18 , as shown in  FIGS.  1 - 3 ,  6 - 8 ,  12 , and  13   , generally provides a spacing between the bottom tool  12  and the top tool  14  during the bonding process. Each spacer  16 ,  18  is quadrilateral shaped and has a top surface, a bottom surface, and four side edges. Each spacer  16 ,  18  has a length that is the same as the length of the bottom tool  12  and has a width roughly equal to a distance from a side surface of the bottom tool  12  to the opening  36  in the bottom tool  12 . Each spacer  16 ,  18  has a thickness that is equal to a total, or combined, thickness of the bottom panel  28  and the top panel  30 . Alternatively, each spacer  16 ,  18  may have a thickness that is equal to one of a plurality of different values, such as 0.5 millimeter (mm), 1 mm, 1.5 mm, and so forth. 
     Each alignment pin  20 ,  22 , as shown in  FIGS.  1 - 3  and  13   , generally provides alignment of the top tool  14  and the top panel  30  with the bottom tool  12  and the bottom panel  28 . Each alignment pin  20 ,  22  includes a rod  42  and a handle  44 . The rod  42  has an elongated cylindrical with a first end and a tapered second end. The handle  44  has a cylindrical shape with a length that is shorter than a length of the rod  42  and a diameter that is larger than a diameter of the rod  42 . A first end of the handle  44  is attached to the first end of the rod  42 . 
     The panel fasteners  24  include a first group that is used to attach the bottom panel  28  to the bottom tool  12  and a second group that is used to attach the top panel  30  to the top tool  14 . Each panel fastener  24  is typically a threaded screw or bolt that includes an enlarged head, such as a thumb screw, or other feature that allows the panel fastener  24  to be handled and tightened easily. 
     The top tool fasteners  26  generally attach the top tool  14  to the bottom tool  12 . Each top tool fastener  26  is typically a threaded screw or bolt that includes a head with screwdriver or hex key features or an enlarged head, such as a thumb screw. 
     The bonding process using the fixture  10  may be implemented as follows. Starting with the bottom tool  12 , as shown in  FIG.  5   , the first and second spacers  16 ,  18  are attached thereto. The first spacer  16  may be attached to a left side of the bottom tool  12 , and the second spacer  18  may be attached to a right side of the bottom tool  12 , as shown in  FIG.  6   . The spacers  16 ,  18  are attached using threaded fasteners such as screws or bolts. The thickness of each spacer  16 ,  18  is generally equal to the total, or combined, thickness of the bottom panel  28  and the top panel  30 . In other embodiments, each of the first spacer  16  and the second spacer  18  may include a plurality of spacers that are stacked one on top of another and have a total, or combined, thickness generally equal to the total, or combined, thickness of the bottom panel  28  and the top panel  30 . For example, if the total thickness of the bottom panel  28  and the top panel  30  is 1 mm, then the first spacer  16  and the second spacer  18  may each include a single spacer having a thickness of 1 mm or may each include two spacers (with one stacked on top of the other) that have a total thickness of 1 mm. 
     The bottom panel  28  is placed on the top surface of the bottom tool  12  between the first spacer  16  and the second spacer  18  such that the first group of slot openings and the second group of slot openings are aligned with screw or bolt openings on the top surface of the bottom tool  12 , as shown in  FIG.  7   . In addition, the tabs  34  of the bottom panel  28  align with the first fingers  38 , and the second group of slot openings align with the spaces between the first fingers  38 . Furthermore, the alignment holes of the bottom panel  28  should align with the alignment holes of the bottom tool  12 . The first group of panel fasteners  24  is used to attach the bottom panel  28  to the bottom tool  12 . The panel fasteners  24  may be staggered so that some of the panel fasteners  24  are inserted through the first group of slot openings and the rest of the panel fasteners  24  are inserted through the second group of slot openings, as shown in  FIG.  8   . The adhesive  32  is applied to the top surface of the tabs  34  on the bottom panel  28 . In some embodiments, the adhesive  32  may be applied to only one of either the bottom panel  28  or the top panel  30 . 
     With the bottom surface of the top tool  14  exposed, as shown in  FIG.  9   , the top panel  30  is placed thereon. The first group of slot openings and the second group of slot openings are aligned with screw or bolt openings on the bottom surface of the top tool  14 , as shown in  FIG.  10   . In addition, the tabs  34  of the top panel  30  align with the second fingers  40 , and the second group of slot openings align with the spaces between the second fingers  40 . Furthermore, the alignment holes of the top panel  30  should align with the alignment holes of the top tool  14 . The second group of panel fasteners  24  is used to attach the top panel  30  to the top tool  14 . The panel fasteners  24  may be staggered so that some of the panel fasteners  24  are inserted through the first group of slot openings and the rest of the panel fasteners  24  are inserted through the second group of slot openings, as shown in  FIG.  11   . The adhesive  32  is applied to the bottom surface of the tabs  34  on the top panel  30 . In some embodiments, the adhesive  32  may be applied to only one of either the bottom panel  28  or the top panel  30 . 
     The top tool  14  and the top panel  30  are placed on the bottom tool  12  and the bottom panel  28 , as shown in  FIG.  12   . The top tool  14 , the top panel  30 , the bottom panel  28 , and the bottom tool  12  may form a stack. The left and right sides of the bottom surface of the top tool  14  contact at least a portion of the upper surfaces of the first spacer  16  and the second spacer  18 . The panel fasteners  24  that attach the top panel  30  to the top tool  14  extend through the opening  36  in the bottom tool  12 , as best seen in  FIG.  2   . The opening  36  also allows for viewing of the contact between the bottom panel  28  and the top panel  30 . In addition, the adhesive  32  applied to the top panel  30  contacts the adhesive  32  applied to the bottom panel  28 . Or, in some embodiments, the adhesive  32  applied to just the bottom panel  28  or the top panel  30  contacts the tabs  34  of the other panel  28 ,  30 . Furthermore, the top tool  14  and the top panel  30  are placed on the bottom tool  12  and the bottom panel  28  so that the alignment holes of the top tool  14  and the top panel  30  align with the alignment holes of the bottom tool  12  and the bottom panel  28 . 
     Referring to  FIG.  13   , the first alignment pin  20  is placed in the alignment holes on the left side of the stack of the top tool  14 , the top panel  30 , the bottom panel  28 , and the bottom tool  12 , and the second alignment pin  22  is placed in the alignment holes on the right side of the stack. The placement of the alignment pins  20 ,  22  in the alignment holes ensures that the bottom panel  28  and the top panel  30  are aligned laterally to provide maximum contact of the adhesive  32  with the bottom panel  28  and the top panel  30 . 
     Referring to  FIGS.  1  and  2   , the top tool fasteners  26  are used to firmly attach the top tool  14  to the first spacer  16  and the second spacer  18 . The tightening of the top tool fasteners  26  also applies a force to press the top panel  30  onto the bottom panel  28 . Specifically, the second fingers  40  apply a surface normal force to press the tabs  34  of the top panel  30  onto the tabs  34  of the bottom panel  28 , which are supported by the first fingers  38 . Some of the adhesive  32  may be pressed out during tightening of the top tool fasteners  26 . The excess may be wiped away. Afterward, the fixture  10  and the panels  28 ,  30  are left alone to allow the adhesive  32  to cure. When the adhesive  32  has cured, the panels  28 ,  30  are removed from the fixture  10 , and a shear test is applied, as shown in  FIG.  4   . The panels  28 ,  30  are pulled in opposing directions. The lap shear strength is determined from the force at which the panels  28 ,  30  separate and the area over which the adhesive  32  covers. 
       FIG.  14    depicts a listing of at least a portion of the steps of an exemplary method  100  for lap shear bonding of a bottom panel  28  and a top panel  30  using an adhesive  32 . The steps may be performed in the order shown in  FIG.  14   , or they may be performed in a different order. Furthermore, some steps may be performed concurrently as opposed to sequentially. In addition, some steps may be optional or may not be performed. 
     Referring to step  101  and  FIGS.  5  and  6   , a first spacer  16  and a second spacer  18  are attached to opposing edges of a top surface of a bottom tool  12 . The bottom tool  12  is typically formed from a metal or metal alloy and may be quadrilateral shaped with a planar top surface, a bottom surface, and four side surfaces. The bottom tool  12  includes a quadrilateral shaped opening  36  from the top surface to the bottom surface, which allows for access to the top tool  14  and the top panel  30 . The bottom tool  12  also includes a plurality of first fingers  38 , spaced apart from one another and extending into one side of the opening  36 . The bottom tool  12  may also include a plurality of other threaded openings and holes which receive screws and/or bolts. In addition, the bottom tool  12  includes a plurality of alignment or registration holes which receive the first and second alignment pins  20 ,  22 . 
     Each spacer  16 ,  18  is quadrilateral shaped and has a top surface, a bottom surface, and four side edges. Each spacer  16 ,  18  has a length that is the same as the length of the bottom tool  12  and has a width roughly equal to a distance from a side surface of the bottom tool  12  to the opening  36  in the bottom tool  12 . Each spacer  16 ,  18  has a thickness that is equal to a total, or combined, thickness of the bottom panel  28  and the top panel  30 . Alternatively, each spacer  16 ,  18  may have a thickness that is equal to one of a plurality of different values, such as 0.5 millimeter (mm), 1 mm, 1.5 mm, and so forth. The first spacer  16  may be attached to a left side of the bottom tool  12 , and the second spacer  18  may be attached to a right side of the bottom tool  12 . The spacers  16 ,  18  are attached using threaded fasteners such as screws or bolts. 
     Referring to step  102  and  FIGS.  7  and  8   , a bottom panel  28  is attached to the top surface of the bottom tool  12  in between the first spacer  16  and the second spacer  18 . The bottom panel  28  is typically formed from a metal or metal alloy and may be quadrilateral shaped with a thickness that is small compared to its surface area, resulting in each panel  28 ,  30  having a top surface, a bottom surface, and four side edges. The bottom panel  28  may also include a plurality of slot openings cut into the panel from the top surface to the bottom surface. The slot openings are spaced apart from one another and may include a first group positioned adjacent to one side edge and a second group aligned with the first group and extending through an opposing side edge. The second group of slot openings also creates a plurality of spaced apart tabs  34 . In addition, the bottom panel  28  includes a plurality of alignment or registration holes. 
     The bottom panel  28  is placed on the top surface of the bottom tool  12  between the first spacer  16  and the second spacer  18  such that the first group of slot openings and the second group of slot openings are aligned with screw or bolt openings on the top surface of the bottom tool  12 , as shown in  FIG.  7   . In addition, the tabs  34  of the bottom panel  28  align with the first fingers  38 , and the second group of slot openings align with the spaces between the first fingers  38 . Furthermore, the alignment holes of the bottom panel  28  should align with the alignment holes of the bottom tool  12 . The first group of panel fasteners  24  is used to attach the bottom panel  28  to the bottom tool  12 . The panel fasteners  24  may be staggered so that some of the panel fasteners  24  are inserted through the first group of slot openings and the rest of the panel fasteners  24  are inserted through the second group of slot openings, as shown in  FIG.  8   . 
     Referring to step  103  and  FIGS.  9  and  10   , a top panel  30  is attached to a bottom surface of a top tool  14 . The top panel  30  is the same as, or substantially similar to, the bottom panel  28 . The top tool  14  is typically formed from a metal or metal alloy and may be quadrilateral shaped with a planar top surface, a bottom surface, and four side surfaces. The top tool  14  includes a plurality of second fingers  40 , spaced apart from one another and positioned along one side of the top tool  14 . The top tool  14  may also include a plurality of other threaded openings and holes which receive screws and/or bolts. The top tool  14  has a width that is the same as a width of the bottom tool  12  and has a length that is roughly half a length of the bottom tool  12 . In addition, the top tool  14  includes a plurality of alignment or registration holes. 
     The top panel  30  is placed is the top tool  14  so that the first group of slot openings and the second group of slot openings are aligned with screw or bolt openings on the bottom surface of the top tool  14 , as shown in  FIG.  10   . In addition, the tabs  34  of the top panel  30  align with the second fingers  40 , and the second group of slot openings align with the spaces between the second fingers  40 . Furthermore, the alignment holes of the top panel  30  should align with the alignment holes of the top tool  14 . The second group of panel fasteners  24  is used to attach the top panel  30  to the top tool  14 . The panel fasteners  24  may be staggered so that some of the panel fasteners  24  are inserted through the first group of slot openings and the rest of the panel fasteners  24  are inserted through the second group of slot openings, as shown in  FIG.  11   . 
     Referring to step  104  and  FIGS.  8  and  11   , the adhesive  32  is applied to one of either the tabs  34  of the bottom panel  28  or the tabs  34  of the top panel  30 . In some embodiments, the adhesive  32  may be applied to only one of either the bottom panel  28  or the top panel  30 . In other embodiments, the adhesive  32  may be applied to both the bottom panel  28  and the top panel  30 . When the adhesive  32  is applied to the bottom panel  28 , it is applied to the top surface of the tabs  34  adjacent the edge thereof. When the adhesive  32  is applied to the top panel  30 , it is applied to the bottom surface of the tabs  34  adjacent the edge thereof. 
     Referring to step  105  and  FIG.  12   , the top panel  30  and the top tool  14  are placed on the bottom panel  28  and the bottom tool  12 . The top tool  14 , the top panel  30 , the bottom panel  28 , and the bottom tool  12  may form a stack. The left and right sides of the bottom surface of the top tool  14  contact at least a portion of the upper surfaces of the first spacer  16  and the second spacer  18 . The panel fasteners  24  that attach the top panel  30  to the top tool  14  extend through the opening  36  in the bottom tool  12 , as best seen in  FIG.  2   . In addition, the adhesive  32  applied to the top panel  30  contacts the adhesive  32  applied to the bottom panel  28 . Or, in some embodiments, the adhesive  32  applied to just the bottom panel  28  or the top panel  30  contacts the tabs  34  of the other panel  28 ,  30 . Furthermore, the top tool  14  and the top panel  30  are placed on the bottom tool  12  and the bottom panel  28  so that the alignment holes of the top tool  14  and the top panel  30  align with the alignment holes of the bottom tool  12  and the bottom panel  28 . 
     Referring to step  106  and  FIG.  13   , a first alignment pin  20  and a second alignment pin  22  are placed in the top tool  14 , the top panel  30 , the bottom panel  28 , and the bottom tool  12  to align the bottom panel  28  and the top panel  30 . The placement of the alignment pins  20 ,  22  in the alignment holes ensures that the bottom panel  28  and the top panel  30  are aligned laterally to provide maximum contact of the adhesive  32  with the bottom panel  28  and the top panel  30 . 
     Referring to step  107  and  FIGS.  1  and  2   , the top tool  14  is attached to the first spacer  16  and the second spacer  18 . Attachment is implement using the top tool fasteners  26 . The tightening of the top tool fasteners  26  also applies a force to press the top panel  30  onto the bottom panel  28 . Specifically, the second fingers  40  apply a surface normal force to press the tabs  34  of the top panel  30  onto the tabs  34  of the bottom panel  28 , which are supported by the first fingers  38 . Some of the adhesive  32  may be pressed out during tightening of the top tool fasteners  26 . The excess may be wiped away. Afterward, the fixture  10  and the panels  28 ,  30  are left alone to allow the adhesive  32  to cure. When the adhesive  32  has cured, the panels  28 ,  30  are removed from the fixture  10 , and a shear test is applied, as shown in  FIG.  4   . The panels  28 ,  30  are pulled in opposing directions. The lap shear strength is determined from the force at which the panels  28 ,  30  separate and the area over which the adhesive  32  covers. 
     Additional Considerations 
     Throughout this specification, references to “one embodiment”, “an embodiment”, or “embodiments” mean that the feature or features being referred to are included in at least one embodiment of the technology. Separate references to “one embodiment”, “an embodiment”, or “embodiments” in this description do not necessarily refer to the same embodiment and are also not mutually exclusive unless so stated and/or except as will be readily apparent to those skilled in the art from the description. For example, a feature, structure, act, etc. described in one embodiment may also be included in other embodiments, but is not necessarily included. Thus, the current invention can include a variety of combinations and/or integrations of the embodiments described herein. 
     Although the present application sets forth a detailed description of numerous different embodiments, it should be understood that the legal scope of the description is defined by the words of the claims set forth at the end of this patent and equivalents. The detailed description is to be construed as exemplary only and does not describe every possible embodiment since describing every possible embodiment would be impractical. Numerous alternative embodiments may be implemented, using either current technology or technology developed after the filing date of this patent, which would still fall within the scope of the claims. 
     Throughout this specification, plural instances may implement components, operations, or structures described as a single instance. Although individual operations of one or more methods are illustrated and described as separate operations, one or more of the individual operations may be performed concurrently, and nothing requires that the operations be performed in the order illustrated. Structures and functionality presented as separate components in example configurations may be implemented as a combined structure or component. Similarly, structures and functionality presented as a single component may be implemented as separate components. These and other variations, modifications, additions, and improvements fall within the scope of the subject matter herein. 
     Certain embodiments are described herein as including logic or a number of routines, subroutines, applications, or instructions. These may constitute either software (e.g., code embodied on a machine-readable medium or in a transmission signal) or hardware. In hardware, the routines, etc., are tangible units capable of performing certain operations and may be configured or arranged in a certain manner. In example embodiments, one or more computer systems (e.g., a standalone, client or server computer system) or one or more hardware modules of a computer system (e.g., a processor or a group of processors) may be configured by software (e.g., an application or application portion) as computer hardware that operates to perform certain operations as described herein. 
     In various embodiments, computer hardware, such as a processing element, may be implemented as special purpose or as general purpose. For example, the processing element may comprise dedicated circuitry or logic that is permanently configured, such as an application-specific integrated circuit (ASIC), or indefinitely configured, such as an FPGA, to perform certain operations. The processing element may also comprise programmable logic or circuitry (e.g., as encompassed within a general-purpose processor or other programmable processor) that is temporarily configured by software to perform certain operations. It will be appreciated that the decision to implement the processing element as special purpose, in dedicated and permanently configured circuitry, or as general purpose (e.g., configured by software) may be driven by cost and time considerations. 
     Accordingly, the term “processing element” or equivalents should be understood to encompass a tangible entity, be that an entity that is physically constructed, permanently configured (e.g., hardwired), or temporarily configured (e.g., programmed) to operate in a certain manner or to perform certain operations described herein. Considering embodiments in which the processing element is temporarily configured (e.g., programmed), each of the processing elements need not be configured or instantiated at any one instance in time. For example, where the processing element comprises a general-purpose processor configured using software, the general-purpose processor may be configured as respective different processing elements at different times. Software may accordingly configure the processing element to constitute a particular hardware configuration at one instance of time and to constitute a different hardware configuration at a different instance of time. 
     Computer hardware components, such as communication elements, memory elements, processing elements, and the like, may provide information to, and receive information from, other computer hardware components. Accordingly, the described computer hardware components may be regarded as being communicatively coupled. Where multiple of such computer hardware components exist contemporaneously, communications may be achieved through signal transmission (e.g., over appropriate circuits and buses) that connect the computer hardware components. In embodiments in which multiple computer hardware components are configured or instantiated at different times, communications between such computer hardware components may be achieved, for example, through the storage and retrieval of information in memory structures to which the multiple computer hardware components have access. For example, one computer hardware component may perform an operation and store the output of that operation in a memory device to which it is communicatively coupled. A further computer hardware component may then, at a later time, access the memory device to retrieve and process the stored output. Computer hardware components may also initiate communications with input or output devices, and may operate on a resource (e.g., a collection of information). 
     The various operations of example methods described herein may be performed, at least partially, by one or more processing elements that are temporarily configured (e.g., by software) or permanently configured to perform the relevant operations. Whether temporarily or permanently configured, such processing elements may constitute processing element-implemented modules that operate to perform one or more operations or functions. The modules referred to herein may, in some example embodiments, comprise processing element-implemented modules. 
     Similarly, the methods or routines described herein may be at least partially processing element-implemented. For example, at least some of the operations of a method may be performed by one or more processing elements or processing element-implemented hardware modules. The performance of certain of the operations may be distributed among the one or more processing elements, not only residing within a single machine, but deployed across a number of machines. In some example embodiments, the processing elements may be located in a single location (e.g., within a home environment, an office environment or as a server farm), while in other embodiments the processing elements may be distributed across a number of locations. 
     Unless specifically stated otherwise, discussions herein using words such as “processing,” “computing,” “calculating,” “determining,” “presenting,” “displaying,” or the like may refer to actions or processes of a machine (e.g., a computer with a processing element and other computer hardware components) that manipulates or transforms data represented as physical (e.g., electronic, magnetic, or optical) quantities within one or more memories (e.g., volatile memory, non-volatile memory, or a combination thereof), registers, or other machine components that receive, store, transmit, or display information. 
     As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. 
     The patent claims at the end of this patent application are not intended to be construed under 35 U.S.C. § 112(f) unless traditional means-plus-function language is expressly recited, such as “means for” or “step for” language being explicitly recited in the claim(s). 
     Although the technology has been described with reference to the embodiments illustrated in the attached drawing figures, it is noted that equivalents may be employed and substitutions made herein without departing from the scope of the technology as recited in the claims. 
     Having thus described various embodiments of the technology, what is claimed as new and desired to be protected by Letters Patent includes the following: