Abstract:
Adhesion testing systems, methods of fabrication, and methods of testing are disclosed. Test systems include test coupons with non-metallic test adherends. Test coupons are configured to test bonds to the non-metallic test adherends under peeling stress and/or shearing stress. Test methods are simplified and rapid as compared to standard adhesion tests and include methods of accelerated environmental testing. Test methods also are adapted for qualitative and quantitative measurement of bond performance.

Description:
RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application No. 61/818,598, filed May 22, 2013. The complete disclosure of which is incorporated herein by reference for all purposes. 
    
    
     FIELD 
     The present disclosure relates to methods and systems for rapidly testing adhesion. 
     BACKGROUND 
     Joints between components are of great importance in structural design in such industries as aerospace, transportation, and medicine. Mechanically fastened joints leave material discontinuities between components and produce localized, highly stressed areas. Adhesive joints may effectively replace mechanically fastened joints in certain situations. Adhesive joints may form a continuous bond between components, minimizing material discontinuities, and may distribute stress across the bonded joint, minimizing stress concentration. Further, adhesive joints may be tailored to the material properties of the bonded components, e.g., the properties of fiber-reinforced plastics (sometimes referred to as fiber-reinforced polymers or fiber-reinforced composites). 
     However, adhesion and adhesive joints are less well understood than mechanical fastening mechanisms. Adhesive bond quality is dependent on many factors including chemical bonding, mechanical factors (e.g., interlocking parts), material compatibility, surface preparation, and surface chemistry. Moreover, ensuring and verifying a quality adhesive bond are difficult tasks. Microscopic differences in composition and chemical state may be the difference between a strong bond and a weak bond. Non-destructive testing (e.g., x-ray inspection, ultrasonic inspection) generally indicates only gross material discontinuities but typically fails to indicate adhesion parameters such as chemical state and contamination. Hence, careful characterization of adhesive bonding schemes is important to preparing a quality bond. 
     Bond quality may be tested by applying forces to a bonded joint until the joint fails. Such destructive testing is impractical for products in service but is suitable for test samples and test coupons embodying a sample adhesive bonding scheme. Adhesion testing protocols designed primarily for metallic components exist (e.g., ASTM D1781 and ASTM D3165 published by ASTM International), but they require precise set-up, calibration, and measurement, and, in some cases, simply are not suitable for adhesion between non-metallic components. Further, adhesion testing protocols typically quantitate the strain energy release rate of a bond as it fails, requiring careful execution of the protocol and measurement of the results. Hence, there is a need for rapid, simplified adhesion testing protocols suitable for non-metallic components, which include simplified determination of results. 
     SUMMARY 
     The present disclosure includes methods of fabricating layered test coupons configured for peeling testing and/or shearing testing of adhesive bonds to non-metallic adherends. Fabrication methods may include incorporating a plurality of test bonds within a test structure. Fabrication methods may include environmental conditioning of test structures including test bonds prior to assembling the final test coupon. 
     A layered test coupon may be fabricated by adhering a first test adherend with a first test adhesive to a first location on a base support to create a first test bond, adhering a second test adherend with a second test adhesive to a second location, adjacent the first location, on the base support to create a second test bond, bonding the first test adherend to a peeling support, and bonding the second test adherend to the peeling support. 
     A layered test coupon may be fabricated by adhering a rigid test adherend with a test adhesive to a peeling support to create a test bond. A layered test coupon may be fabricated by adhering a test adherend with a test adhesive to a peeling support to create a test bond, and bonding the test adherend to a rigid base support. 
     A layered test coupon may be fabricated by adhering a test adherend with a test adhesive to a first peeling support to create a test bond and to form a test structure, and bonding the test adherend to a second peeling support. A layered test coupon may be fabricated by adhering a test adherend with a test adhesive to a peeling adherend to create a test bond and to form a test structure, bonding the peeling adherend to a first peeling support, and bonding the test adherend to a second peeling support. 
     A layered test coupon may be fabricated by adhering a test adherend with a test adhesive to a shearing adherend to create a test bond and to form a test structure, bonding the shearing adherend to a first shearing support, and bonding the test adherend to a second shearing support. 
     Test coupons may comprise layers in the following sequence: (a) a base support with a first location and a second location, (b) an adhesive layer including a first test adhesive adjacent to the first location and a second test adhesive adjacent to the second location, (c) an adherend layer including a first test adherend and a second test adherend, and (d) a peeling support bonded to the first test adherend and bonded to the second test adherend. Further, the first test adherend is coupled to the first location on the base support with a first test bond including the first test adhesive, and the second test adherend is coupled to the second location on the base support with a second test bond including the second test adhesive. 
     Test coupons may comprise layers in the following sequence: (a) a peeling support, (b) a test adhesive, and (c) a rigid test adherend. Further, the test adherend is coupled to the peeling support with a test bond including the test adhesive. 
     Test coupons may comprise layers in the following sequence: (a) a peeling support, (b) a test adhesive, (c) a test adherend, and (d) a rigid base support. Further, the test adherend is coupled to the peeling support with a test bond including the test adhesive, and the base support is bonded to the test adherend. 
     Test coupons may comprise layers in the following sequence: (a) a test structure and (b) a second peeling support. The test structure includes layers in the following sequence: (i) a first peeling support, (ii) a test adhesive, and (iii) a test adherend. Further, the test adherend is coupled to the first peeling support with a test bond including the test adhesive, and the second peeling support is bonded to the test adherend. 
     Test coupons may comprise layers in the following sequence: (a) a first peeling support, (b) a test structure, and (c) a second peeling support. The test structure includes layers in the following sequence: (i) a peeling adherend, (ii) a test adhesive, and (iii) a test adherend. Further, the test adherend is coupled to the peeling adherend with a test bond including the test adhesive, the first peeling support is bonded to the peeling adherend, and the second peeling support is bonded to the test adherend. 
     Test coupons may comprise layers in the following sequence: (a) a first shearing support, (b) a test structure, and (c) a second shearing support. The test structure includes layers in the following sequence: (i) a shearing adherend, (ii) a test adhesive, and (iii) a test adherend. Further, the test adherend is coupled to the shearing adherend with a test bond including the test adhesive, the first shearing support is bonded to the shearing adherend, and the second shearing support is bonded to the test adherend. 
     The present disclosure includes methods of peel testing and/or shear testing of layered test coupons with adhesive bonds to non-metallic adherends. Testing methods may comprise peeling and/or shearing the layered test coupon, optionally followed by classifying and/or quantifying the resulting failure of the adhesive bonds. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of test systems for rapidly testing adhesion and adhesives. 
         FIG. 2  is an illustrative, non-exclusive example of a peeling configuration. 
         FIG. 3  is an illustrative, non-exclusive example of a drum peeling configuration. 
         FIG. 4  is an illustrative, non-exclusive example of a double cantilever peeling configuration. 
         FIG. 5  is an illustrative, non-exclusive example of a wedge peeling configuration. 
         FIG. 6  is an illustrative, non-exclusive example of a shearing configuration. 
         FIG. 7  is an illustrative, non-exclusive example of a series of test structures in a test coupon. 
         FIG. 8  is another illustrative, non-exclusive example of a series of test structures in a test coupon. 
         FIG. 9  is a flowchart of methods of fabricating test coupons and interrogating bonds. 
         FIG. 10  is a schematic representation of the location of failure zones within illustrative, non-exclusive examples of test structures. 
         FIG. 11  is an image of a test structure after peeling. 
         FIG. 12  is a representation of various failure regions of the test structure shown in  FIG. 11 . 
         FIG. 13  is a schematic representation of test systems for rapid adhesion testing. 
         FIG. 14  is a schematic representation of test systems for backing rapid adhesion testing. 
         FIG. 15  is a schematic representation of test systems for modified double cantilever beam testing. 
         FIG. 16  is a schematic representation of test systems for back-bonded double cantilever beam testing. 
         FIG. 17  is an illustrative, non-exclusive example of a pair of test structures in a test coupon. 
         FIG. 18  is a schematic representation of test systems for modified wide area lap shear testing. 
     
    
    
     DESCRIPTION 
     Characterization of adhesive bonds typically is performed with test coupons that include an adhesive bonding scheme, i.e., an adhesive, an adherend(s), and a bond resulting from surface preparations, adhesive cure method, and environmental conditions (e.g., heat, chemical exposure, static loading, and dynamic loading). Test coupons are layered structures that include a test adherend layer, another adherend layer, and a test adhesive layer sandwiched between the two adherend layers. The test adhesive layer is bonded to the test adherend layer to form a test bond. 
     Test coupons typically are tested with a test fixture configured to subject the test bond to forces that may break the test bond apart. The bond is broken by applying forces to relatively thick supports that include, and/or are bonded to, the two adherend layers. The use of thick supports provides the mechanical stability and structure required to apply testing forces. Testing typically includes peel testing and/or shear testing. For example, the test bond may be subject to peeling forces, forces that tend to pull the test bond perpendicular to the test bond layer. A test fixture configured for peel testing, i.e., configured to apply peeling forces, may be referred to as a peeling fixture. As another example, the test bond may be subject to shearing forces, forces that tend to pull the test bond parallel to the test bond layer. A test fixture configured for shear testing, i.e., configured to apply shearing forces, may be referred to as a shearing fixture. 
     Test methods may be qualitative and/or quantitative. Generally, qualitative test methods are rapid, yielding results that correlate with quantitative test methods. For qualitative test methods, the test bond may be characterized by the type of breakage induced by the test fixture. Further, test fixtures may be configured to characterize the type of breakage induced by the test fixture. For quantitative test methods, the test bond may be characterized by the amount of force required to break the bond and/or the amount of bond fracture caused by a given force. Further, test fixtures may be configured to measure the amount of force required to break the bond and/or the amount of bond fracture caused by a given force. 
     Where preparation of test coupons and/or test methods include environmental exposure (e.g., heat, chemical exposure, static loading, and dynamic loading), use of thin adherends may reduce the time of exposure required to achieve a given result (e.g., thermal equilibrium, water saturation), relative to thick adherends. Test coupons that include thin adherends also may include support structures configured for compatibility with conventional testing apparatuses. 
       FIGS. 1-18  illustrate various embodiments of test systems  10 , test coupons  20 , and methods  100  of fabricating and/or testing test systems  10  and/or test coupons  20 . Elements that serve a similar, or at least substantially similar, purpose are labeled with numbers consistent among the figures. Like numbers in each of  FIGS. 1-18 , and the corresponding elements, may not be discussed in detail herein with reference to each of  FIGS. 1-18 . Similarly, all elements may not be labeled in each of  FIGS. 1-18 , but reference numerals associated therewith may be used for consistency. Elements, components, and/or features that are discussed with reference to one or more of  FIGS. 1-18  may be included in and/or used with any of  FIGS. 1-18  without departing from the scope of the present disclosure. In general, elements that are likely to be included are illustrated in solid lines, while elements that may be optional or alternatives are illustrated in dashed lines. However, elements that are shown in solid lines are not necessarily essential, and an element shown in solid lines may be omitted without departing from the scope of the present disclosure. Some figures illustrate test systems  10  and/or test coupons  20  in exploded view. In exploded view, the spaces between the elements are for illustration purposes only. 
       FIG. 1  is a schematic representation, in exploded view, of test systems  10  for testing bond adhesion to test adherends  32 . The test system  10  comprises a test coupon  20 , a layered structure including a series of layers  22  and one or more test bonds  40  to be tested. The test coupon  20  includes one or more test structures  30 , layered structures that each include at least two layers  22 : a test adherend  32  and a test adhesive  42 . Within the test structure  30 , and between the test adherend  32  and the test adhesive  42 , is a test interface  24 . The test adhesive  42  bonds to the test adherend  32  at the test interface  24  to form the test bond  40 . The test coupon  20  includes a test region  26 , sometimes referred to as a peel region or a shear region, depending on type of test performed. The test coupon  20  includes a force application region  52  where forces  50  may be applied to the test coupon  20 . Depending on the type of test being performed, forces  50  may be referred to as peeling forces or shearing forces. The test region  26  is the region of the test structure  30  where the test bond  40  may be interrogated, for example by applying peeling forces (perpendicular to the layers  22 ) and/or shearing forces (parallel to the layers  22 ). 
     The test coupon  20  also includes a layer  22  adhered to the test adhesive  42  opposite the test adherend  32 . The adhered layer  22  may be a second test adherend  32 , a structural adherend  33  (e.g., a peeling adherend  34  and/or a shearing adherend  35 ), and/or a structural support  36  (e.g., a base support  37 , a peeling support  38 , and/or a shearing support  39 ). When present, a second test adherend  32  and/or a structural adherend  33  may be supported by a structural support  36  bonded to the second test adherend  32  and/or the structural adherend  33 . Further, the test structure  30  may be supported by a structural support  36  bonded to the test adherend  32 . 
     Generally, the test systems  10 , the test coupons  20 , and the test structures  30  are configured to test the quality (e.g., the strength, the durability, and/or the extent) of the test bond  40 . One method to test the quality of the test bond  40  is through peel testing, where forces  50  are applied perpendicular to the layers  22  to stress the test bond  40  perpendicular to the layer  22  of the test adhesive  42 . Peel testing is designed to ultimately peel apart the test coupon  20 , generally by fracturing the test bond  40  along the test interface  24 , within the test adherend  32  and/or within the layer  22  adhered to the test adhesive  42 . In peel testing, the fracture, or crack, generally propagates perpendicular to the externally applied forces  50 . Another method to test the quality of the test bond  40  is through shear testing, where forces  50  are applied parallel to the layers  22  to stress the test bond  40  parallel to the layer  22  of the test adhesive  42 . Shear testing is designed to ultimately laterally pull apart the test coupon  20 , generally by fracturing the test bond  40  along the test interface  24 , within the test adherend  32  and/or within the layer  22  adhered to the test adhesive  42 . In shear testing, the fracture, or crack, generally propagates parallel to the externally applied forces  50 . 
     Test coupons  20  include test adherends  32  that are non-metallic (not essentially composed of metal). Test adherends  32  may be laminar and/or composite materials and may include polymeric material, plastic, glass, and/or ceramic materials. Though test adherends  32  are non-metallic, test adherends  32  may include metal as one of several components (e.g., metal fiber in a composite material) and may have metallic properties (e.g., electrically conductive). Composite materials, such as fiber-reinforced and/or mineral-filled plastic materials, include a matrix material (such as a thermoset, thermoplastic, and/or a resin), and may be reinforced with surface and/or embedded fiber and/or particulate. For example, a composite material may include a matrix material reinforced with at least one of glass fiber, carbon fiber, aramid fiber, mica, talc, and glass particulate. Generally, a laminar material, such as a fiber-reinforced plastic, is composed essentially of one or more plies cured together to form a unified structural material. The plies may be assembled (laid-up) into a variety of forms using for example, dry lay-up techniques, wet lay-up techniques, and/or prepreg techniques. Composite materials typically are cured at elevated temperatures, for example, above 100° C., above 150° C., about 120° C., about 180° C., 100° C.-200° C., and/or 150° C.-200° C. 
     When the test adherend  32  is a laminar material, the assembled plies of test adherend  32  may be handled and assembled onto other layers  22  while the test adherend is uncured, partially cured, and/or fully cured. In the uncured and partially cured states, the test adherend  32  may be pliable and/or malleable. Upon fully curing, the test adherend  32  may solidify and become relatively stiff and/or rigid. Some test adherends  32  may remain and/or become flexible and/or elastic in the fully cured state. 
     Test adherends  32  are generally thin layers  22  and, when a laminar material, typically include less than 20 plies, less than 10 plies, less than 8 plies, less than 6 plies, less than 4 plies, about 20 plies, about 10 plies, 8 plies, 6 plies, 4 plies, 3 plies, 2 plies, 1 ply, 1-20 plies, 1-8 plies, and/or 1-4 plies. In certain embodiments, test adherends  32  may be rigid and, when a laminar material, may include greater than 8 plies, greater than 10 plies, greater than 20 plies, 8-20 plies, and/or 8-40 plies. 
     Laminar materials may include a peel ply, e.g., a tightly woven fabric embedded near the surface of the laminar material. The peel ply is typically co-cured onto the laminar material and is configured to tear away from the bulk of the laminar material. Once the peel ply is stripped from the surface of the laminar material, the newly exposed surface is typically slightly rough and chemically active. Peel plies may include fibers such as polyester, nylon, and glass, and may be treated with release agents such as silicone and fluoropolymers. 
     Test coupons  20  include test adhesives  42  that are adhesives configured to bond the test adherend  32  to another layer  22 . Adhesives may be referred to as binders, glues, cements, and pastes. Prior to bonding, test adhesives  42  may be in the form of a liquid, a solid, a suspension, an emulsion, and/or a mastic composition. Test adhesives  42  may be dry adhesives, pressure sensitive adhesives, contact adhesives, hot-melt adhesives, and/or reactive adhesives (e.g., epoxies, urethanes, acrylics, and polyimides), including one-part and multi-part reactive adhesives. Reactive adhesives may require application of an external stimulant such as light (e.g., UV or visible light), heat, and/or moisture. Test adhesives  42  may be room temperature cured (e.g., pressure sensitive adhesive, contact adhesive, moisture-cured adhesive), and/or heat cured. Test adhesives  42  may be cured at an elevated temperature, for example, at a temperature above 20° C., above 70° C., above 100° C., above 150° C., about 20° C., about 70° C., about 120° C., about 180° C., 20° C.-200° C., 20° C.-100° C., 100° C.-200° C., and/or 150° C.-200° C. 
     Test coupons  20  may include structural adherends  33  that are non-metallic (e.g., laminar components, composite components, and/or fiber-reinforced plastic components). When present, structural adherends  33  are adhered to the test adhesive  42  opposite the test adherend  32 . When present, structural adherends  33  form a part of the test structure  30 . Structural adherends  33  may have any of the properties disclosed herein with respect to test adherends  32 . Structural adherends  33  may be configured similarly or identically to a test adherends  32  in the same test structure  30 . For example, a structural adherend  33  may be selected to cure under the same conditions as a test adherend  32  in the same test structure  30 . In certain embodiments, the structural adherend  33  is substantially the same as the test adherend  32 . In certain other embodiments, the structural adherend  33  is configured to adhere more strongly to the test adhesive  42  than the adhesion of the test adherend  32  to the test adhesive  42 . The structural adherend  33  may be configured to be thin, and may be configured to have substantially the same thickness as the test adherend  32 . 
     Where the test system  10 , the test coupon  20 , and/or the structural adherend  33  are configured for peel testing, the structural adherend  33  may be referred to as a peeling adherend  34 . The peeling adherend  34  may be configured to transmit peeling stress to the test bond  40  and may be configured to avoid shearing while peeling forces are applied. The peeling adherend  34  may be configured to be flexible, optionally as flexible as the test adherend  32 . 
     Where the test system  10 , the test coupon  20 , and/or the structural adherend  33  are configured for shear testing, the structural adherend  33  may be referred to as a shearing adherend  35 . The shearing adherend  35  may be configured to transmit shearing stress to the test bond  40  and may be configured to avoid peeling while shearing forces are applied. 
     Test coupons  20  may include structural supports  36 , sometimes referred to as a base support  37 , a peeling support  38 , and/or a shearing support  39  depending on how forces  50  are configured to be applied to the test coupon  20 . Structural supports  36  are generally rigid structures configured to supply mechanical strength to the test coupon  20 . Further, structural supports  36  are configured to bond strongly to at least one layer  22  of the test structure  30 , for example the test adherend  32 , the test adhesive  42 , and the structural adherend  33 . Structural supports  36  may include, and may consist essentially of, at least one of metal, aluminum alloy, and steel. Further, structural supports  36  may include, and may consist essentially of, at least one of polymeric material, plastic, laminar material (e.g., fiber-reinforced plastic), composite material, glass, and ceramic. 
     Where the test system  10  and/or the test coupon  20  are configured for peel testing, a base support  37  may be bonded to the test adherend  32 , test adhesive  42 , and/or the optional peeling adherend  34 . In such case, the base support  37  would form a stable reference from which other layers  22  could be peeled. Where the test system  10  and/or the test coupon  20  are configured for shear testing, a shearing support  39  may be bonded to the test adherend  32 , test adhesive  42 , and/or the optional shearing adherend  35 . In the case of shear testing, a first shearing support  139  (a shearing support  39 ) may be bonded to the shearing adherend  35  and a second shearing support  239  (a shearing support  39 ) may be bonded to the test adherend  32 . 
     Test coupons  20  may include peeling supports  38  that are support structures configured to supply mechanical strength to the test coupon  20  and to transmit peeling stress to the test bond  40  (through the test adherend  32  and/or the peeling adherend  34 ). Peeling supports  38  may be configured to avoid shearing while peeling forces are applied. Further, peeling supports  38  are configured to bond strongly to at least one layer  22  of the test structure  30 , for example the test adherend  32 , the test adhesive  42 , and the peeling adherend  34 . The peeling support  38  may be configured to be relatively flexible, optionally as flexible as the test adherend  32  and/or the peeling adherend  34 . Peeling supports  38  may include, and may consist essentially of, at least one of metal, aluminum alloy, and steel. 
     Where test coupons  20  include an optional structural support  36 , the structural support  36  may be bonded to the test structure  30  (i.e., the test adherend  32  and/or a structural adherend  33 ) with a structural adhesive  46 . Structural adhesives  46  are adhesives configured to strongly bond the structural support  36  to the test structure  30 . Structural adhesives  46  may have any of the properties disclosed herein with respect to test adhesives  42  and adhesives generally. Structural adhesives  46  may be configured similarly or identically to a test adhesive  42  in the same test coupon  20 . For example, a structural adhesive  46  may be selected to cure under the same conditions as a test adhesive  42  in the same test coupon  20 . 
     Additionally or alternatively, the optional structural support  36  may be directly bonded to the test structure  30 , without any structural adhesive  46 . For example, the test adherend  32  and/or a structural adherend  33  may be cured while assembled on a structural support  36 , the curing process forming a bond between the test structure  30  and the structural support  36 . 
     Overall, test coupons  20  generally include layers  22  in the following sequence: (a) an optional structural support  36 , (b) an optional structural adhesive  46 , (c) a test adherend  32  (a first test adherend  132 ), (d) a test adhesive  42 , (e) an optional second test adherend  232  (a test adherend  32 ) and/or an optional structural adherend  33 , (f) an optional structural adhesive  46 , and (g) an optional structural support  36 . As discussed herein, test coupons  20  include at least one test structure  30  which includes a test adherend  32 , a test adhesive  42  and at least one of optional layers (e) and (g). Hence, test coupons  20  include at least one of optional layers (e) and (g). 
     In certain embodiments, test coupons  20  may include a crack starter  60  in the test structure  30 , at the edge of the test interface  24  between the test adherend  32  and the test adhesive  42 . The crack starter  60  is configured to form a weak bond, and/or to interfere with the formation of a strong bond, along a portion of the test interface  24 , typically in the force application region  52 . The crack starter  60  also is configured to form a crack in the test bond  40 , near the test interface  24 , upon application of a force  50  near the crack starter  60 . The crack starter  60  may be a solid, liquid, and/or mastic applied at the edge of the test interface  24 . Illustrative, non-exclusive example materials suitable for a crack starter  60  include FEP (fluorinated ethylene propylene), PTFE (polytetrafluoroethylene), polyimide, mold release agents, and silicone. 
     In certain embodiments, test coupons  20  may include one or more gaps  48  that define a test region  26  (e.g., between the gaps  48 ). The optional gaps  48  are discontinuities crossing certain layers  22  but do not intersect the test adhesive  42 . For example, a gap  48  may intersect the optional structural support  36  and/or the optional peeling support  38 , the optional structural adhesive  46 , and the test adherend  32 , leaving intact the test adhesive  42 , the optional second test adherend  32  and/or the optional structural adherend  33 , the optional structural adhesive  46 , and the optional structural support  36 . When test coupons  20  include gaps  48 , typically two are included. The two gaps are typically spaced apart from one another and situated on opposite sides of the test coupon  20  (opposite sides of the test adhesive  42 ). The layers between the gaps  48  are generally intact. Typically, the gaps  48  define a test region  26  where the optional structural supports  36  on either side of the test adhesive  42  overlap one another. Such an overlap structure may be useful for shear testing (e.g., pulling oppositely situated structural supports  36  in opposite directions may subject the test bond  40  to shear stress). 
     Test systems  10  may include a test fixture  12  configured to apply forces  50  to the test coupon  20  and the test bond  40 . For example, a test fixture  12  may be configured for peel testing, i.e., configured to apply forces  50  perpendicular to the layers  22  to stress the test bond  40  perpendicular to the layer  22  of the test adhesive  42 . As another example, a test fixture  12  may be configured for shear testing, i.e., configured to apply forces  50  parallel to the layers  22  to stress the test bond  40  parallel to the layer  22  of the test adhesive  42 . The test fixture  12  generally is configured to apply forces  50  to the structural supports  36  and/or the peeling supports  38 , as the structural supports  36  and/or the peeling supports  38  generally are configured to accept and transmit forces  50 . Test fixtures  12  may include a motor, an actuator, and/or a simple machine (e.g., a lever, a plane, a wedge  64 , and/or a drum  62 ). 
     Generally, the test fixture  12  is configured to apply forces  50  to the test coupon  20  at one or more force application regions  52  and to maintain the relative position of the test coupon  20  at one or more stationary regions  54 . Generally, the force application regions  52  are located near an end of the test coupon  20 . The test fixture  12  may be coupled to the test coupon  20  at the force application regions  52  with flexible couplings that allow the force  50  to be applied at a substantially constant direction as the test coupon  20  is split apart. The test fixture  12  may be coupled to the test coupon  20  at the stationary regions  54  with rigid couplings that substantially maintain the relative position of the stationary regions  54  as the test coupon  20  is split apart. In certain configurations, the test fixture  12  is not coupled directly to the stationary regions  54 . 
     Test systems  10  and/or test fixtures  12  may be configured to interrogate test bonds  40  within test coupons  20  in at least one of several modes, as illustrated in  FIGS. 2-6 . In peeling mode, as illustrated in  FIGS. 2-5 , the test bond  40  is subject to forces  50 , perpendicular to the test structure  30  layer  22  (including the test adhesive  42  layer  22 ), that tend to peel the test bond  40  apart. In shearing mode, as illustrated in  FIG. 6 , the test bond  40  is subject to forces  50 , parallel to the test adhesive  42  layer  22 , that tend to shear the test bond  40  apart. 
     In  FIG. 2 , a test coupon  20  is subject to peel testing. One side of the test coupon  20  (the backing structure  58 ) is rigidly coupled to a rigid portion of a test fixture  12  (or is rigid enough to serve as a rigid fixture support) while one end (the force application region  52 ) of a peeling structure  56  (the side of the test coupon  20  opposite the backing structure  58 ) is coupled to a peeling mechanism of the test fixture  12 . The backing structure  58  may include and/or be the test adherend  32 , the structural adherend  33 , and/or the base support  37 . The peeling structure  56  may include and/or be the structural adherend  33 , the test adherend  32 , and/or the peeling support  38 . The test fixture  12  is configured to pull the test coupon  20  apart between the backing structure  58  and the peeling structure  56  (generally at the test bond  40 ). The peeling force  50  may be applied at an angle to the layer  22  of the test structure  30 , generally substantially perpendicular to the layer  22  of the test structure  30 , at least not essentially parallel to the layer  22  of the test structure  30  (as parallel forces would result in more shearing than peeling). 
     Generally, the peeling structure  56  must be flexible enough to bend as the test coupon  20  is pulled apart and stiff enough to transmit the peeling force  50  of the test fixture  12  into the test bond  40 . Typically, the peeling structure  56  includes a thin, metal layer  22  (e.g., the peeling support  38 ). The peeling structure  56  may be coupled to the test fixture  12  with fasteners and/or bonds. For example, the force application region  52  of the peeling structure  56  may be clamped to the test fixture  12 . The backing structure  58  may be stiff and rigid enough to withstand the peeling forces  50  without significant flexing. Additionally or alternatively, the backing structure  58  may be coupled to a rigid portion of the test fixture  12  such that the combination of the rigid portion and the backing structure  58  is stiff and rigid enough to resist significant flexing as the peeling forces  50  are applied. The backing structure  58  may be coupled to the test fixture  12  with fasteners and/or bonds. For example, the backing structure  58  may be clamped to the test fixture  12 . 
     In  FIG. 3 , the test fixture  12  illustrated in  FIG. 2  includes a drum  62 . The drum  62  (i.e., a cylindrical structure) is configured to be coupled to the peeling structure  56 . The drum  62  also is configured to roll along the test coupon  20 , pulling the test coupon  20  apart between the backing structure  58  and the peeling structure  56  (generally at the test bond  40 ). The general procedure and apparatus for metal to metal bond testing are described in ASTM D1781 (ASTM International), herein incorporated by reference. Generally, the peeling structure  56  must be flexible enough to conform to the drum  62  as the drum  62  rolls. The peeling structure  56  may be coupled to the drum  62  with fasteners and/or bonds. For example, the force application region  52  of the peeling structure  56  may be clamped to the drum  62 . Incorporating a drum  62  is one way to configure a test fixture  12  to control the peeling angle (the angle between the peeling structure  56  and the backing structure  58 ) as the peeling structure  56  is peeled from the backing structure  58 . Peeling the peeling structure  56  by rolling around a drum  62  may maintain a substantially constant peeling angle. 
     In  FIG. 4 , a test coupon  20  is subject to peel testing in a double beam cantilever configuration. One end (the force application region  52 ) of one side of a test coupon  20  (the first peeling structure  156 , a peeling structure  56 ) is coupled to a pulling mechanism of a test fixture  12  while the same end (the force application region  52 ) of the second peeling structure  256  (a peeling structure  56  that is the side of the test coupon  20  opposite the first peeling structure  156 ) is coupled to a second pulling mechanism of the test fixture  12 . The first peeling structure  156  may include and/or be the test adherend  32  and/or a first peeling support  138 . The second peeling structure  256  may include and/or be the peeling adherend  34  and/or a second peeling support  238 . The test fixture  12  is configured to pull the end of the first peeling structure  156  and the end of the second peeling structure  256  with substantially equal magnitude forces  50  in generally opposite directions, the forces  50  tending to pull the test bond  40  apart perpendicular to the layer  22  of the test structure  30 . The general procedure and apparatus for double cantilever beam peel testing for composite material failure (not bond failure) are described in ASTM D5528 (ASTM International), herein incorporated by reference. Typically, the ends of the peeling structures  56  are coupled to form a link between two cables, or other flexible pulling elements. In that case, as the cable (or other flexible pulling element) is pulled, the test bond  40  is subject to the tension of the cable (or other flexible pulling element). The ends of the peeling structures  56  may be coupled to the pulling mechanisms with fasteners and/or bonds. For example, a hinge coupled to a pulling mechanism may be bonded to the end of one of the peeling structures  56 . As another example, the end of one of the peeling structures  56  may include a hole configured to receive a hook coupled to a pulling mechanism. 
     In  FIG. 5 , a test coupon  20  is subject to peel testing in a double beam cantilever configuration using a wedge  64  (part of the test fixture  12 ). The test fixture  12  may be configured to drive the wedge  64  along the test bond  40  (along the peeling direction  70 ) to separate the test coupon  20  along the test bond  40 . In this configuration, the wedge  64  is placed with its tip at the test structure  30 . The wedge  64  may be driven by a mechanical device such as a hydraulic press and/or a threaded mechanism, and may be driven by a series of impacts, e.g., by the operator hitting the wedge  64 . The test coupon  20  may be coupled to the test fixture  12  at the end opposite the wedge  64  (at the stationary region  54 ), using fasteners and/or bonds. The end where the wedge will be driven (the force application region  52 ) need not be substantially constrained. The test fixture  12  may be configured to allow the force application region  52  to flex enough to accommodate the wedge  64  as it is driven through the test coupon  20 . 
     In  FIG. 6 , a test coupon  20  is subject to shear testing. One end of a test coupon  20  (a first force application region  152 ) is coupled to a pulling mechanism of a test fixture  12  while the other end of the test coupon  20  (a second force application region  252 ) is coupled to a second pulling mechanism of the test fixture  12 . The test fixture  12  is configured to apply to the test coupon  20  substantially equal magnitude pulling forces  50  in opposite directions, substantially parallel to the test adhesive  42  layer  22 . The test coupon  20  includes a test region  26  where a first shearing structure  166  (a shearing structure  66 ) overlaps a second shearing structure  266  (a shearing structure  66 ), however neither shearing structure  66  is continuous from end to end of the test coupon  20 . Each shearing structure  66  may include and/or be a test adherend  32 , a structural adherend  33 , and/or a shearing support  39 . Each shearing structure  66  includes at least one gap  48  between the ends of the test coupon  20 . Hence, when the force  50  is applied at the force application regions  52 , to pull the test coupon  20  in opposite directions, the test adhesive  42  experiences a shear (a force parallel to the test adhesive  42  layer  22 ), the test adhesive  42  being the only continuous layer of the test coupon  20  between the two ends of the test coupon  20 . The general procedure and apparatus for bond shear testing are described in ASTM D3165 (ASTM International), herein incorporated by reference. The ends of the test coupon  20  may be coupled to the test fixture  12  with fasteners and/or bonds. For example, a force application region  52  may define an aperture through the test coupon  20 , which is configured to couple to a cable. As another example, a force application region  52  may be clamped to a pulling mechanism of the test fixture  12 . 
     As illustrated in the fragmentary views of  FIGS. 7-8 , test coupons  20  may include a plurality of test bonds  30  resulting from a plurality of adhesive bonding schemes, e.g., different test adherends  32 , different test adhesives  42 , different preparations, and/or different environmental conditions. For example, test coupons  20  may incorporate more than one test structure  30 . Each test structure  30  may be completely independent or some test structures  30  may share common materials (e.g., test adherends  32 , test adhesives  42 , and/or structural adherends  33 ) and/or bond processing conditions (e.g., surface preparations, adhesive cure methods, and environmental conditions). A test coupon  20  may include a first test structure  130  (a test structure  30 ) at a first location (e.g., a first test region  126 ) and a second test structure  230  (a test structure  30 ) at a second location (e.g., a second test region  226 ) spaced apart from the first location. Each test structure  30  includes a test bond  40  (e.g., a first test bond  140  in the first test structure  130  and a second test bond  240  in the second test structure  230 ). Where test adherends  32  differ between test bonds  40 , the difference may be the result of different materials, different surface preparations, and/or exposure to different environmental conditions. Where the test adhesives  42  differ between test bonds  40 , the difference may be the result of different materials, different adhesive cure methods, and/or exposure to different environmental conditions. When plural test structures  30  are present, they are arranged in the same layer  22  of the test coupon  20 . Hence, a test fixture  12  may be configured to sequentially and/or concurrently test the quality of the test bonds  40  within the plural test structures  30 .  FIG. 7  illustrates a series of test structures  30  arranged such that peeling along the peeling direction  70  would sequentially interrogate each test structure  30 .  FIG. 8  illustrates a series of test structures  30  arranged such that peeling along the peeling direction  70  would simultaneously interrogate each test structure  30 . 
       FIG. 9  is a flowchart of methods  100  for fabricating test coupons  20  and/or interrogating test bonds  40 . Methods  100  include adhering  102  layers  22  together to form a test structure  30 . Adhering  102  includes adhering a test adherend  32  with a test adhesive  42  to an opposing adherend (e.g., a structural adherend  33  and/or a structural support  36 ) to create a test bond  40 . Adhering  102  may include applying the test adhesive  42  between the test adherend  32  and the opposing adherend, e.g., by spraying, painting, spreading, placing, and/or contacting. Adhering  102  may include curing the test adhesive  42 . Curing may include heating, cooling, compressing, and/or applying an external stimulant (such as light, e.g., UV or visible light, and/or moisture). Curing may include curing at a temperature above 20° C., above 70° C., above 100° C., above 150° C., about 20° C., about 70° C., about 120° C., about 180° C., 20° C.-200° C., 20° C.-100° C., 100° C.-200° C., and/or 150° C.-200° C. Further, adhering  102  may include preparing the surface of test adherend  32  to be adhered. The prepared surface may become part of the test interface  24 . For example, preparing may include peeling a peel ply, priming, cleaning (e.g., wiping with solvent), contaminating, sanding, and/or grit blasting. Preparing may be selected to affect the test bond  40  and may be one of the variables interrogated with the test structure  30  and/or the test coupon  20 . For example, where the test adherend  32  includes a peel ply, the peel ply may be removed from the surface of the test adherend  32 , exposing a fresh surface for the test interface  24 . 
     Methods  100  may include adhering  102  layers  22  to form a plurality of test structures  30 . Each test structure  30  may be in a different location and spaced apart from other test structures  30 . The test structures  30  may share a common test adherend  32 , a common test adhesive  42 , and/or a common opposing adherend. For example, adhering  102  may include adhering a first test adherend  32  with a first test adhesive  42  to a first location on an opposing adherend to create a first test bond  40 , and include adhering a second test adherend  32  with a second test adhesive  42  to a second location, adjacent the first location, on the opposing adherend to create a second test bond  40 . Adhering  102  may be performed such that one of the plurality of test structures  30  is formed at least partially concurrently and/or at least partially sequentially with another of the plurality of test structures  30 . Where adhering  102  includes curing the test adhesive(s)  42 , curing each test adhesive  42  of the plurality of test structures  30  may be performed under substantially the same conditions (e.g., temperature, time, application method, etc.). 
     Methods  100  may include bonding  104  the test structure  30  to one or more supports (e.g., a structural support  36 ). Bonding  104  may include bonding a first support on one side of the test structure  30  (e.g., bonding a peeling support  38  to a test adherend  32 ) and/or bonding a second support on the opposite side of the test structure  30  (e.g., bonding a base support  37  to a structural adherend  33 ). Bonding  104  may include curing a composite material. Curing a composite material may bond the composite material to other materials in contact. For example, where bonding  104  includes bonding the test adherend  32  (potentially a laminar and/or composite material) to a structural support  36  (potentially a laminar and/or a composite material), bonding  104  may include curing the test adherend  32  and/or the structural support  36  in contact with each other. Bonding  104  may include applying a structural adhesive  46  between the support (e.g., the structural support  36 ) and the test structure  30 , and optionally may include curing the structural adhesive  46  to bond the two components. Bonding  104  may be performed at least partially concurrently and/or at least partially sequentially with adhering  102 . For example, where adhering  102  includes curing the test adhesive  42 , bonding  104  may include curing a composite material at least partially concurrently with the curing of the test adhesive  42 , e.g., the curing of the test adhesive  42  and the curing of the composite material may occur under similar conditions (such as time, temperature, humidity, etc.). Where methods  100  include two or more bonding  104  operations, e.g., bonding a structural support  36  to a structural adherend  33  and bonding a peeling support  38  to the test adherend  32 , one bonding  104  may be performed at least partially concurrently and/or partially sequentially with another bonding  104 . For example, bonding  104  a structural support  36  to a structural adherend  33  and bonding  104  a peeling support  38  to the test adherend  32  may be performed at least partially concurrently, e.g., the two bonding operations may occur under similar conditions (such as time, temperature, humidity, etc.). Where methods  100  include adhering  102  to form a plurality of test structures  30 , bonding  104  may include bonding each test structure  30  to one or more common supports (e.g., a structural support  36  and/or a peeling support  38 ). 
     Methods  100  may include curing  106  composite structures such as the test adherend  32 , the structural adherend  33 , the structural support  36 , and/or the peeling support  38 . Composite structures may be assembled in an uncured or partially cured state (a green state). For example, prepreg composites require a final curing step to harden the matrix and form the final material. Any test adherend  32 , any support adherend  33 , and/or any structural support  36  including composite materials may be assembled in a green state. After assembly of the test structure  30  and/or the test coupon  20 , the green composite material may be cured, typically by heating the whole assembly to the curing temperature of the green composite material. Curing  106  of the green composite material generally results in bonding the green composite material to the adjacent layers  22 . Where the test adhesive  42  and/or the structural adhesive  46  requires curing at an elevated temperature, the green composite material and the adhesive may be cured at the same time by subjecting the assembly to the elevated temperature. Additionally or alternatively, any composite material may be fully cured before assembly into the test structure  30  and/or the test coupon  20 . Curing  106  may include heating the composite structure to a temperature of above 100° C., above 150° C., about 120° C., about 180° C., 100° C.-200° C., and/or 150° C.-200° C. Curing  106  of a composite structure may be before, during, or after adhering  102 . Curing  106  of a composite structure may be before or during bonding  104 . For example, curing  106  the test adherend  32  and curing the test adhesive  42  (as part of adhering  102 ) may be performed at least partially concurrently and/or at least partially sequentially. Where methods  100  include two or curing  106  operations, one curing  106  operation may be performed at least partially concurrently and/or partially sequentially with another curing  106  operation. For example, curing  106  the test adherend  32  and curing  106  a structural adherend  33  may be performed at least partially concurrently, e.g., the two curing operations may occur under similar conditions (such as time, temperature, humidity, etc.). 
     Methods  100  may include fabricating composite structures such as the test adherend  32 , the structural adherend  33 , and/or the structural support  36 . Fabricating may include assembling laminar materials and/or composite materials (e.g., assembling the matrix material and the fiber of a fiber-reinforced plastic). Fabricating may include dry lay-up techniques, wet lay-up techniques, and/or prepreg techniques. Fabricating may include assembling plies of fiber and may include assembling less than 20 plies, less than 10 plies, less than 8 plies, less than 6 plies, less than 4 plies, about 20 plies, about 10 plies, 8 plies, 6 plies, 4 plies, 3 plies, 2 plies, 1 ply, greater than 8 plies, greater than 10 plies, greater than 20 plies, 1-20 plies, 1-8 plies, 1-4 plies, 8-20 plies, and/or 8-40 plies. 
     Methods  100  may include forming a crack initiation site at the test bond  40  in the force application region  52 . For example, forming a crack initiation site may include placing a crack starter  60  between a portion of the test adherend  32  and the test adhesive  42  before adhering  102 . As another example, forming a crack initiation site may include placing a crack starter  60  between a portion of the structural adherend  33  and the test adhesive  42  before adhering  102 . Placing the crack starter may include applying a crack starter  60  to the test adherend  32 . As another example, forming a crack initiation site may include forming a weak bond between a portion of the test adherend  32  and the test adhesive  42 . As another example, forming a crack initiation site may include initiating a crack in the test bond  40  in the force application region  52 , e.g., by driving a wedge into the test bond  40 , applying a wedge between layers  22  of the test structure  30 , and/or by applying a force  50 . Where methods  100  include forming a plurality of test structures  30 , methods  100  may include forming a crack initiation site in each test structure  30 . 
     Methods  100  may include applying  108  test conditions to the test structure  30  prior to bonding  104 . Test structures  30  may be exposed to environmental conditions (e.g., heat, chemical exposure, static loading, and dynamic loading) to investigate the effects of such conditions on the test bond  40 . Exposure may include moisture, liquids, elevated temperatures, depressed temperatures, temperature cycles, corrosives, and ambient conditions for a predetermined amount of time. Applying  108  test conditions may include wetting, aging, and/or heating a test structure  30 . Conditions may be applied for a period of time, for example, less than 100 days, less than 50 days, less than 20 days, less than 15 days, less than 10 days, less than 200 hours, less than 150 hours, less than 100 hours, at least 48 hours, at least 72 hours, at least 100 hours, at least 150 hours, at least 200 hours, at least 10 days, 48 hours-100 days, 48 hours-20 days, and/or 100 hours-20 days. Thinner and/or lower volume test structures  30  generally respond to condition effects quicker than thicker and/or higher volume test structures  30 . Hence, steady state (quasi-equilibrium) effects may be observed sooner in thinner and/or lower volume test structures  30  than in thicker and/or higher volume test structures  30 . For example, water saturation of a test structure  30  including a fiber-reinforced plastic test adherend  32  of 2 plies may occur in less than 20 days, whereas a test structure  30  differing only by including a test adherend of 10 plies may require more than 200 days for saturation. Additionally or alternatively, thinner and/or lower volume test structures  30  may reduce preparation time and materials cost relative to thicker and/or higher volume test structures  30 . 
     Methods  100  may include forming a gap  48  through a shearing structure  66 , and/or through shearing structures  66  on opposite sides of a test coupon  20 , to define a test region  26  where all layers  22  of the test coupon  20  are intact. Forming a gap  48  may include cutting, notching, and/or nicking a shearing structure  66 . Forming a gap  48  may include bonding discontinuous sections of a support structure (e.g., a structural support  36 ) to the test structure  30  and cutting, notching, and/or nicking the test structure  30  in a location corresponding to the discontinuity in the support structure. Forming a gap  48  does not generally include affecting the test adhesive  42 , at least not within the test region  26 . Forming a gap  48  may be performed before, during, or after applying  108  test conditions. 
     Methods  100  may include selecting a test coupon  20  fabricated by adhering  102 , optional bonding  104 , and/or optional curing  106 . Test coupons  20  selected and/or fabricated according to the present disclosure may be tested. For example, the quality (including the strength, the durability, and/or the extent) of test bonds  40  may be tested by applying  110  force and optionally measuring  112  the result. 
     Methods  100  may include applying  110  force to the test coupon  20 , the test structure  30 , and/or the test bond  40  to separate the test coupon  20 , generally along the test bond  40 . Applying  110  force may be used to test the quality of the test bond  40 . Where test coupons  20  include a plurality of test structures  30  and test bonds  40 , applying  110  force may include applying  110  force to each of the plurality of test structures  30  and/or test bonds  40  at least partially concurrently and/or at least partially sequentially. Applying  110  force may include applying a force  50  to a test structure  30  and/or a test bond  40  and applying a different force  50  to a different test structure  30  and/or a different test bond  40 . 
     Applying  110  force may include peeling one side (e.g., the test adherend  32 , the structural support  36 , and/or the peeling support  38 ) of the test coupon  20  from the other side (e.g., the structural adherend  33 , and/or the structural support  36 ), generally by applying forces  50  perpendicular to the layers  22 . Peeling may stress the test bond  40  perpendicular to the layer  22  of the test adhesive  42 . Peeling may fracture the test bond  40  along the test interface  24 , within the test adherend  32  and/or within the layer  22  adhered to the test adhesive  42 . Peeling may include controlling the angle of the peeling support  38  relative to the base support  37  as the peeling support  38  separates from the base support  37 , e.g., by using a drum peel technique. Where test coupons  20  include a plurality of test structures  30  and test bonds  40 , peeling may include partially peeling the peeling support  38  from a structural support  36  to test one test bond  40  and partially peeling the peeling support  38  from the structural support  36  to test a different test bond  40 . 
     Applying  110  force may include shearing one end (e.g., a first force application region  52 ) of the test coupon  20  from another end (e.g., a second force application region  52 ), generally by applying forces  50  parallel to the layers  22 . Shearing may stress the test bond  40  parallel to the layer  22  of the test adhesive  42 . Shearing may fracture the test bond  40  along the test interface  24 , within the test adherend  32  and/or within the layer  22  adhered to the test adhesive  42 . 
     Methods  100  may include measuring  112  the result of applying  110  force. Measuring  112  may include classifying the failure mode of a test bond  40  after the force  50  has broken the test bond  40  (resulting in a split test coupon  20 ). Classifying may include observing the bond residue on the split test coupon  20 , optionally observing by electronic imaging. As illustrated in  FIG. 10 , generally, a test bond  40  may fail at a laminal failure zone  81 , an interfacial failure zone  82 , and/or a cohesion failure zone  83 . Hence, failure modes may be classified as laminal failure, interfacial failure, cohesion failure, and/or some combination of these failure modes. Failure at the interfacial failure zone  82 , the zone at the test interface  24 , between the test adherend  32  and the test adhesive  42 , generally is indicative of a weak bond. Strong bonds generally result in failures at the laminal failure zone  81 , the zone within the (potentially laminar) test adherend  32 , and at the cohesion failure zone  83 , the zone within the test adhesive  42 , the structural adherend  33 , and/or the structural support  36 . In failure at the laminal failure zone  81 , the test bond  40  remains intact yet the test adherend  32  separates within and/or between the adherend plies. In failure at the cohesion failure zone  83 , the test bond  30  also remains intact. Instead, at least one of the test adhesive  42 , the structural adherend  33 , and the structural support  36  separates. 
     Measuring  112  may include quantifying the extent of failure of the test bond  40  after the force  50  has broken the test bond  40  (resulting in a split test coupon  20 ). Quantifying may include observing the bond residue on the split test coupon  20  by electronic imaging. Quantifying may include determining at least one of a fraction of laminal failure, a fraction of interfacial failure, a fraction of cohesion failure, an extent of laminal failure, an extent of interfacial failure, and an extent of cohesion failure. Where a test coupon  20  includes a plurality of test structures  30  and/or test bonds  40 , measuring  112  may include comparing the classification, fraction and/or extent of failure between at least two of the test bonds  40 . 
     The extent (the total area of failure) and the fraction of failure may be quantified by processing images  80  of the split test coupon  20 , as illustrated in  FIG. 11 . Image  80  of  FIG. 11  shows the residue of three failure modes: failure at the laminal failure zone  81 , failure at the interfacial failure zone  82 , and failure at the cohesion failure zone  83 . Each failure zone may leave a distinctive imprint and/or residue on the split test coupon  20 . For example, failure at the laminal failure zone  81  may leave an imprint and/or residue of the plies of the test adherend  32 , generally a broad repeating texture. Failure at the interfacial failure zone  82  may leave an imprint and/or residue of surface contour of the test adherend  32 , e.g., when the test adherend  32  is prepared by peeling a peel ply, the test adherend  32  surface has an imprint of the removed peel ply, a tightly woven texture. Failure at the cohesion failure zone  83  may leave an imprint and/or residue of the test adhesive  42 , generally a low texture region. Image processing may distinguish these failure regions, for example by pattern recognition and/or thresholding the image  80 . For example,  FIG. 12  illustrates a classification image  90  where each pixel of image  80  is classified as part of a laminal failure region  91 , an interfacial failure region  92 , or a cohesion failure region  93 . The extent of failure of a particular type may be quantified by a parameter related to the image area of that failure in a classification image  90 . The fraction of failure of a particular type may be quantified by a parameter related to the fractional image area of that failure in a classification image  90 . Strong bonds may be classified as test bonds  40  where the predominant failure modes are at the laminal failure zone  81  and/or the cohesion failure zone  83 . Additionally or alternatively, strong bonds may be classified as test bonds  40  where the fraction of failure at the interfacial failure zone  82  is less than 20%, less than 10%, less than 5%, less than 2%, and/or less than 1%. Weak bonds may be classified as test bonds  40  where the predominant failure mode is at the interfacial failure zone  82 , optionally when the fraction of failure at the interfacial failure zone  82  is greater than 5%, greater than 10%, greater than 20%, and/or greater than 50%. 
     Further aspects of inventive subject matter are illustrated without limitation in the following illustrative, non-exclusive examples. These examples are included for illustration and are not intended to limit or define the entire scope of the present teachings. 
     Example 1 
     Rapid Adhesion Testing 
       FIG. 13  is a schematic representation, in exploded view, of test systems  10  and test coupons  20  for rapid adhesion testing. Rapid adhesion testing may be useful to simply and quickly interrogate a series of test bonds  40 . The test coupons  20  comprise at least two test structures  30 , namely a first test structure  130  and a second test structure  230 . The first test structure  130  includes a first test adhesive  142  (a test adhesive  42 ), a first test adherend  132  (a test adherend  32 ), a first test interface  124  (a test interface  24  which is the interface between the first test adherend  132  and the first test adhesive  142 ), and a first test bond  140  (a test bond  40 ) to a first location  126  (a test region  26 ) on a base support  37 . The second test structure  230  includes a second test adhesive  242  (a test adhesive  42 ), a second test adherend  232  (a test adherend  32 ), a second test interface  224  (a test interface  24  which is the interface between the second test adherend  232  and the second test adhesive  242 ), and a second test bond  240  (a test bond  40 ) to a second location  226  (a test region  26 ) on the base support  37 . 
     The test coupons  20  comprise layers in the following sequence: (a) the base support  37 , (b) an adhesive layer  22 , including the first test adhesive  142  adjacent to the first location  126  and the second test adhesive  242  adjacent to the second location  226 , (c) an adherend layer  22 , including the first test adherend  132  adjacent to the first test adhesive  142  and the second test adherend  232  adjacent to the second test adhesive  242 , and (d) a peeling support  38  bonded to the first test adherend  132  and bonded to the second test adherend  232 . Further, the first test adherend  132  is coupled to the first location  126  on the base support  37  with the first test bond  140 , including the first test adhesive  142 , and the second test adherend  232  is coupled to the second location  226  on the base support  37  with the second test bond  240  including the second test adhesive  242 . Test coupons  20  comprise a peeling structure  56 , which includes the adherend layer  22  (layer c) and the peeling support  38  (layer d), and a backing structure  58 , which includes the base support  37  (layer a). Peeling structures  56  are relatively thin, with a thickness generally less than 2 mm, less than 1.5 mm, less than 1 mm, less than 0.8 mm, and/or less than 0.5 mm. Backing structures  58  are relatively thick to provide rigidity, with a thickness generally greater than 0.8 mm, greater than 1 mm, greater than 1.5 mm, greater than 2 mm, and/or greater than 2.5 mm. 
     As the first test structure  130  and the second test structure  230  are sandwiched between the base support  37  and the peeling support  38 , generally the thickness of the first test structure  130  and the second test structure  230  are approximately the same. For example, the first test adherend  132  and the second test adherend  232  may be essentially the same thickness, e.g., including the same number of plies. 
     The first test structure  130  and the second test structure  230  may share common components. For example, the first test adherend  132  and the second test adherend  232  may be the same test adherend  32 . As another example, the first test adhesive  142  and the second test adhesive  242  may be the same test adhesive  42 . 
     Test coupons  20  may comprise a crack starter  60  in the first test structure  130 , at the edge of the first test interface  124  between the first test adherend  132  and the first test adhesive  142 . Test coupons  20  may comprise a crack starter  60  in the second test structure  230 , at the edge of the second test interface  224  between the second test adherend  232  and the second test adhesive  242 . Each test structure  30  independently may include a crack starter  60 . Additionally or alternatively, the test coupon  20  may comprise a single crack starter  60 . 
     The first test adherend  132  and the second test adherend  232  each independently may be directly or indirectly bonded to the peeling support  38  (e.g., by curing the first test adherend  132  and/or the second test adherend  232  to the peeling support  38 , and/or by using one or more structural adhesives  46 ). 
     The test coupon  20  is configured to peel apart along the peeling direction  70 . The test coupon  20  may be configured with test structures  30  spaced along the peeling direction  70 , as illustrated, and/or may be configured with test structures  30  spaced perpendicular to the peeling direction. When the test structures  30  are spaced along the peeling direction  70 , the test coupon is configured to peel the test structures  30  sequentially. 
     Test systems  10  may include a test fixture  12  which may include a drum  62 . The test fixture  12  is configured to pull the test coupon  20  apart between the backing structure  58  and the peeling structure  56  (generally at the first test bond  140  and the second test bond  240 ). The test fixture  12  is configured to apply a peeling force  50  at an angle to the test support  30 , generally substantially perpendicular to the test support  30  layer  22 , at least not essentially parallel to the layers  22  of the test coupon  20 . The force application region  52  of the peeling structure  56  is coupled to the drum  62 . For example, the drum  62  may define a slot configured to accept the force application region  52  of the peeling structure  56 . Additionally or alternatively, the peeling structure  56  may be clamped to drum  62 . The test fixture  12  is configured such that rolling the drum  62  rolls the peeling structure  56  around the drum  62  and peels the test coupon  20  at the test structures  30 . Further, the test fixture  12  is configured to control the peeling angle by maintaining a substantially constant peeling angle. The peeling angle, and the required flexibility of the peeling structure  56 , substantially is determined by the diameter of the drum  62 . The drum  62  may have a diameter of at least 50 mm, at least 100 mm, at least 150 mm, and/or at least 200 mm. 
     Example 2 
     Backing Rapid Adhesion Testing 
       FIG. 14  is a schematic representation, in exploded view, of test systems  10  and test coupons  20  for backing rapid adhesion testing. Backing rapid adhesion testing may be suitable to interrogate a test bond  40  to a test adherend  32  that is rigid, e.g., too rigid to peel with the peeling support  38  in example 1, though test adherends  32  are not required to be rigid. Illustrative, non-exclusive examples of test adherends  32  suitable for backing rapid adhesion testing include frames, stringers, girders, and larger bonded assemblies. The test systems  10  and the test coupons  20  of this example 2 are configured to interrogate the test bond  40  coupled to the backing structure  58  rather than coupled to the peeling structure  56  (as is the case for example 1). 
     The test coupons  20  comprise a test structure  30  which includes a test adhesive  42 , a test adherend  32 , a test interface  24 , and a test bond  40  to a peeling support  38 . The test coupons  20  comprise layers in the following sequence: (a) the peeling support  38 , (b) the test adhesive  42 , (c) the test adherend  32 , and optionally (d) a base support  37  bonded to the test adherend  32 . Further, the test adherend  32  is coupled to the peeling support  38  with the test bond  40 , including the test adhesive  42 . The test adherend  32 , the base support  37 , and/or the combination of the two may be rigid. Test coupons  20  comprise the peeling structure  56 , which includes the peeling support  38  (layer a), and the backing structure  58 , which includes the test adherend  32  (layer c) and the optional base support  37  (layer d). The test adherend  32  may be directly or indirectly bonded to the base support  37  (e.g., by curing the test adherend  32  to the base support  37  and/or by using a structural adhesive  46 ). Relative properties, including thicknesses, of the peeling structures  56  and backing structures  58  are the same as example 1. Test coupons  20  may comprise a crack starter  60  in the test structure  30 , at the edge of the test interface  24 , between the test adherend  32  and the test adhesive  42 . 
     Test systems  10  may include a test fixture  12  which may include a drum  62 . Generally, the test fixtures  12  described with respect to example 1 are suitable for backing rapid adhesion testing as well. 
     Example 3 
     Double Cantilever Beam Testing 
       FIG. 15  is a schematic representation, in exploded view, of test systems  10  and test coupons  20  for double cantilever beam testing of test structures  30  including test adherends  32 . This configuration may be suitable to interrogate a test bond  40  within a test structure  30  that includes a test adherend  32  (that is non-metallic) and a first peeling support  138  (a peeling support  38 ). 
     The test coupons  20  comprise a test structure  30  which includes a test adhesive  42 , the test adherend  32 , a test interface  24 , and the test bond  40  to the first peeling support  138 . The test coupons  20  comprise layers in the following sequence: (a) the first peeling support  138 , (b) the test adhesive  42 , (c) the test adherend  32 , and (d) a second peeling support  238  (a peeling support  38 ) bonded to the test adherend  32 . Further, the test adherend  32  is coupled to the first peeling support  138  with the test bond  40 , including the test adhesive  42 . Test coupons  20  comprise a first peeling structure  156 , which includes the first peeling support  38  (layer a), and a second peeling structure  256 , which includes the test adherend  32  (layer c) and the second peeling support  238  (layer d). The test adherend  32  may be directly or indirectly bonded to the second peeling support  238  (e.g., by curing the test adherend  32  to the second peeling support  238  and/or by using a structural adhesive  46 ). First peeling structure  156  and second peeling structure  256  each independently are relatively thin, with a thickness generally less than 2 mm, less than 1.5 mm, less than 1 mm, less than 0.8 mm, and/or less than 0.5 mm. 
     Test coupons  20  may comprise a peeling adherend  34  between the first peeling support  138  and the test adhesive  42 . The peeling adherend  34  may be directly or indirectly bonded to the first peeling support  138  (e.g., by curing the peeling adherend  34  to the first peeling support  138  and/or by using a structural adhesive  46 ). The peeling adherend  34 , when present, may be substantially the same as the test adherend  32 . Test coupons  20  may comprise a crack starter  60  in the test structure  30 , at the edge of the test interface  24 , between the test adherend  32  and the test adhesive  42 . 
     Example 4 
     Double Cantilever Beam Testing 
       FIG. 16  is a schematic representation, in exploded view, of test systems  10  and test coupons  20  for double cantilever beam testing of thin test structures  30 . This configuration may be suitable to rapidly apply environmental conditions to the test structure  30  before bonding supports required for peel testing. For example, a thin test structure  30  may be wetted, aged, and/or heated faster than a thicker test structure  30 . 
     The test coupons  20  comprise a test structure  30  which includes a test adhesive  42 , a test adherend  32 , a test interface  24 , and a test bond  40  to a peeling adherend  34 . The test coupons  20  comprise layers in the following sequence: (a) a first peeling support  138  (a peeling support  38 ) bonded to the peeling adherend  34 , (b) the peeling adherend  34 , (c) the test adhesive  42 , (d) the test adherend  32 , and (e) a second peeling support  238  (a peeling support  38 ) bonded to the test adherend  32 . Further, the test adherend  32  is coupled to the peeling adherend  34  with the test bond  40 , including the test adhesive  42 . Test coupons  20  comprise a first peeling structure  156 , which includes the first peeling support  138  (layer a) and the peeling adherend  34  (layer b), and a second peeling structure  256 , which includes the test adherend  32  (layer d) and the second peeling support  238  (layer e). The peeling adherend  34  may be directly or indirectly bonded to the first peeling support  138  (e.g., by curing the peeling adherend  34  to the first peeling support  138  and/or by using a structural adhesive  46 ). The test adherend  32  may be directly or indirectly bonded to the second peeling support  238  (e.g., by curing the test adherend  32  to the second peeling support  238  and/or by using a structural adhesive  46 ). The peeling adherend  34  may be substantially the same as the test adherend  32 . Hence, the test structure  30  may be a substantially symmetric structure. 
     The test adherend  32  and the peeling adherend  34  each independently may include one or more plies, for example less than 20 plies, less than 10 plies, less than 8 plies, less than 6 plies, less than 4 plies, about 20 plies, about 10 plies, 8 plies, 6 plies, 4 plies, 3 plies, 2 plies, 1 ply, 1-20 plies, 1-8 plies, and/or 1-4 plies. The first peeling support  138  may be a laminar material and may include more plies than the peeling adherend  34 , for example, 1.5-8 times as many plies as the peeling adherend  34 . The second peeling support  238  may be a laminar material and may include more plies than the test adherend  32 , for example, 1.5-8 times as many plies as the test adherend  32 . The total thickness of the peeling adherend  34  and the first peeling support  138  may be equivalent to at least 6 plies, at least 8 plies, at least 10 plies, and/or about 20 plies. The total thickness of the test adherend  32  and the second peeling support  238  may be equivalent to at least 6 plies, at least 8 plies, at least 10 plies, and/or about 20 plies. 
     The test structure  30  may be subject to environmental conditions before bonding to the first peeling support  138  and the second peeling support  238 . After environmental conditions are applied the first peeling support  138  and the second peeling support  238  may be bonded to the test structure  30  such that the environmental conditioning is not substantially disturbed. For example, where temperature and/or moisture is a part of environmental conditioning, the first peeling support  138  and the second peeling support  238  may be bonded with room temperature cure structural adhesives  46 . 
     Example 5 
     Double Cantilever Beam Testing 
       FIG. 17  is a schematic representation, in exploded view, of test systems  10  and test coupons  20  for double cantilever beam testing of at least two test structures  30  within a test coupon  20 . This configuration may be suitable for rapidly testing a series of test bonds  40  and/or to compare adhesive bonding schemes. Test structures  30 , such as a first test structure  130  and a second test structure  230 , may share components, as discussed with respect to example 1, and/or may be subject to the same environmental conditions. Hence, the first test structure  130  and the second test structure  230  may be analogous structures that essentially differ only in the adhesive bond scheme (if at all). Related samples may be used to reduce the effects of systematic and sample related errors that may be present in testing. For example, effects of batch to batch variation in preparation of test adherends  32  may be greatly reduced by comparing the results of testing a first test structure  130  and a second test structure  230  that share a test adherend  32 . 
     Test coupons  20  comprise at least two test structures  30 , namely a first test structure  130  and a second test structure  230 . The first test structure  130  includes a first test adhesive  142  (a test adhesive  42 ), a first test adherend  132  (a test adherend  32 ), a first test interface  124  (a test interface  42  which is the interface between the first test adherend  132  and the first test adhesive  142 ), and a first test bond  140  (a test bond  40 ) to a first location  126  (a test region  26 ) on a peeling adherend  34 . The second test structure  230  includes a second test adhesive  242  (a test adhesive  42 ), a second test adherend  232  (a test adherend  32 ), a second test interface  224  (a test interface  24  which is the interface between the second test adherend  232  and the second test adhesive  242 ), and a second test bond  240  (a test bond  40 ) to a second location  226  (a test region  26 ) on the peeling adherend  34 . 
     The test coupons  20  comprise layers in the following sequence: (a) a first peeling support  138  (a peeling support  38 ) bonded to the peeling adherend  34 , (b) the peeling adherend  34 , (c) an adhesive layer  22 , including the first test adhesive  142  adjacent to the first location  126  and the second test adhesive  242  adjacent to the second location  226 , (d) an adherend layer  22 , including the first test adherend  132  adjacent to the first test adhesive  142  and the second test adherend  232  adjacent to the second test adhesive  242 , and (e) a second peeling support  238  (a peeling support  38 ) bonded to the first test adherend  132  and bonded to the second test adherend  232 . 
     Further, the first test adherend  132  is coupled to the first location  126  on the peeling adherend  34  with the first test bond  140 , including the first test adhesive  142 , and the second test adherend  232  is coupled to the second location  226  on the peeling adherend  34  with the second test bond  240  including the second test adhesive  242 . Test coupons  20  comprise a first peeling structure  156 , which includes the first peeling support  138  (layer a) and the peeling adherend  34  (layer b), and a second peeling structure  256 , which includes the adherend layer  22  (layer d) and the second peeling support  238  (layer e). The peeling adherend  34  may be directly or indirectly bonded to the first peeling support  138  (e.g., by curing the peeling adherend  34  to the first peeling support  138  and/or by using a structural adhesive  46 ). The first test adherend  132  may be directly or indirectly bonded to the second peeling support  238  (e.g., by curing the first test adherend  132  to the second peeling support  238  and/or by using a structural adhesive  46 ). The second test adherend  232  may be directly or indirectly bonded to the second peeling support  238  (e.g., by curing the second test adherend  232  to the second peeling support  238  and/or by using a structural adhesive  46 ). The peeling adherend  34  may be substantially the same as the first test adherend  132  and/or the second test adherend  232 . Hence, the test structure  30  may be a substantially symmetric structure. 
     Test systems  10  may include a test fixture  12  configured to apply peeling forces  50  at the first force application region  152  of the first peeling structure  156  and at the first force application region  152  of the second peeling structure  256 . The test fixture  12  may be configured to apply peeling forces  50  at the second force application region  252  of the first peeling structure  156  and at the second force application region  252  of the second peeling structure  256 . Additionally or alternatively, the test fixture  12  may be configured to allow the test coupon  20  to be rotated such that the first force application region  152  and the second force application region  252  are swapped with respect to the test fixture  12 . 
     Example 6 
     Wide Area Lap Shear Testing 
       FIG. 18  is a schematic representation of test systems  10  and test coupons  20  for wide area lap shear testing of test structures including test adherends  32 . This configuration may be suitable to interrogate a test bond  40  within a test structure  30  that includes a test adherend  32  (that is non-metallic) and a shearing adherend  35 . Also, this configuration may be suitable to rapidly apply environmental conditions to the test structure  30  before bonding supports required for shear testing. For example, a thin test structure  30  may be wetted, aged, and/or heated faster than a thicker test structure  30 . 
     The test coupons  20  comprise a test structure  30  which includes a test adhesive  42 , a test adherend  32 , a test interface  24 , and a test bond  40  to a shearing adherend  35 . The test coupons  20  comprise layers in the following sequence: (a) a first shearing support  139  (a shearing support  39 ) bonded to the shearing adherend  35 , (b) the shearing adherend  35 , (c) the test adhesive  42 , (d) the test adherend  32 , and (e) a second shearing support  239  (a shearing support  39 ) bonded to the test adherend  32 . Further, the test adherend  32  is coupled to the shearing adherend  35  with the test bond  40 , including the test adhesive  42 . Test coupons  20  comprise a first shearing structure  166  (a shearing structure  66 ), which includes the first shearing support  139  (layer a) and the shearing adherend  35  (layer b), and a second shearing structure  266  (a shearing structure  66 ), which includes the test adherend  32  (layer d) and the second shearing support  239  (layer e). The shearing adherend  35  may be directly or indirectly bonded to the first shearing support  139  (e.g., by curing the shearing adherend  35  to the first shearing support  139  and/or by using a structural adhesive  46 ). The test adherend  32  may be directly or indirectly bonded to the second shearing support  239  (e.g., by curing the test adherend  32  to the second shearing support  239  and/or by using a structural adhesive  46 ). The shearing adherend  35  may be substantially the same as the test adherend  32 . Hence, the test structure  30  may be a substantially symmetric structure. 
     The test adherend  32  and the shearing adherend  35  each independently may include one or more plies, for example less than 20 plies, less than 10 plies, less than 8 plies, less than 6 plies, less than 4 plies, about 20 plies, about 10 plies, 8 plies, 6 plies, 4 plies, 3 plies, 2 plies, 1 ply, 1-20 plies, 1-8 plies, and/or 1-4 plies. The first shearing support  139  may be a laminar material and may include more plies than the shearing adherend  35 , for example, 1.5-8 times as many plies as the shearing adherend  35 . The second shearing support  239  may be a laminar material and may include more plies than the test adherend  32 , for example, 1.5-8 times as many plies as the test adherend  32 . The total thickness of the shearing adherend  35  and the first shearing support  139  may be equivalent to at least 6 plies, at least 8 plies, at least 10 plies, and/or about 20 plies. The total thickness of the test adherend  32  and the second shearing support  239  may be equivalent to at least 6 plies, at least 8 plies, at least 10 plies, and/or about 20 plies. 
     The test structure  30  may be subject to environmental conditions before bonding to the first shearing support  139  and the second shearing support  239 . After environmental conditions are applied the first shearing support  139  and the second shearing support  239  may be bonded to the test structure  30  such that the environmental conditioning is not substantially disturbed. For example, where temperature and/or moisture is a part of environmental conditioning, the first shearing support  139  and the second shearing support  239  may be bonded with room temperature cure structural adhesives  46 . 
     Illustrative, non-exclusive examples of inventive subject matter according to the present disclosure are described in the following enumerated paragraphs: 
     A1. A method of fabricating a layered test coupon, the method comprising: 
     adhering a first test adherend with a first test adhesive to a first location on a base support to create a first test bond, wherein the first test adherend is non-metallic; 
     adhering a second test adherend with a second test adhesive to a second location on the base support to create a second test bond, wherein the second location is adjacent the first location, and wherein the second test adherend is non-metallic; 
     bonding the first test adherend to a peeling support; and 
     bonding the second test adherend to the peeling support. 
     A2. The method of paragraph A1, wherein the adhering the first test adherend includes applying the first test adhesive between the first test adherend and the first location of the base support. 
     A3. The method of any of paragraphs A1-A2, wherein the adhering the second test adherend includes applying the second test adhesive between the second test adherend and the second location of the base support. 
     A4. The method of any of paragraphs A1-A3, wherein the adhering the first test adherend includes curing the first test adhesive, optionally at a temperature above 20° C., above 70° C., above 100° C., above 150° C., about 20° C., about 70° C., about 120° C., about 180° C., 20° C.-200° C., 20° C.-100° C., 100° C.-200° C., and/or 150° C.-200° C. 
     A5. The method of any of paragraphs A1-A4, wherein the adhering the second test adherend includes curing the second test adhesive, optionally at a temperature above 20° C., above 70° C., above 100° C., above 150° C., about 20° C., about 70° C., about 120° C., about 180° C., 20° C.-200° C., 20° C.-100° C., 100° C.-200° C., and/or 150° C.-200° C. 
     A6. The method of any of paragraphs A1-A5, wherein the adhering the first test adherend and the adhering the second test adherend include curing the first test adhesive and curing the second test adhesive under the same conditions. 
     A7. The method of any of paragraphs A1-A6, wherein the adhering the first test adherend and the adhering the second test adherend are performed at least partially concurrently. 
     A8. The method of any of paragraphs A1-A7, wherein the adhering the first test adherend includes curing the first test adherend and the first test adhesive at least partially concurrently. 
     A9. The method of any of paragraphs A1-A8, wherein the adhering the second test adherend includes curing the second test adherend and the second test adhesive at least partially concurrently. 
     A10. The method of any of paragraphs A1-A9, wherein the bonding the first test adherend includes curing the first test adherend onto the peeling support. 
     A11. The method of any of paragraphs A1-A10, wherein the bonding the second test adherend includes curing the second test adherend onto the peeling support. 
     A12. The method of any of paragraphs A1-A11, wherein the bonding the first test adherend and the adhering the first test adherend are performed at least partially concurrently. 
     A13. The method of any of paragraphs A1-A12, wherein the bonding the second test adherend and the adhering the second test adherend are performed at least partially concurrently. 
     A14. The method of any of paragraphs A1-A13, wherein the bonding the first test adherend and the bonding the second test adherend are performed at least partially concurrently. 
     A15. The method of any of paragraphs A1-A14, wherein the bonding the first test adherend includes applying a structural adhesive between the first test adherend and the peeling support, and optionally includes curing the structural adhesive. 
     A16. The method of any of paragraphs A1-A15, wherein the bonding the second test adherend includes applying a structural adhesive between the second test adherend and the peeling support, and optionally includes curing the structural adhesive. 
     A17. The method of any of paragraphs A1-A16, further comprising: 
     placing a first crack starter between the first test adhesive and the first test adherend before the adhering the first test adherend, optionally wherein the first crack starter includes at least one of FEP, PTFE, and silicone. 
     A18. The method of any of paragraphs A1-A17, further comprising: 
     placing a second crack starter between the second test adhesive and the second test adherend before the adhering the second test adherend, optionally wherein the second crack starter includes at least one of FEP, PTFE, and silicone. 
     A19. The method of any of paragraphs A1-A18, wherein the first test adherend includes less than 20 plies, less than 10 plies, less than 8 plies, less than 6 plies, less than 4 plies, about 20 plies, about 10 plies, 8 plies, 6 plies, 4 plies, 3 plies, 2 plies, 1 ply, 1-20 plies, 1-8 plies, and/or 1-4 plies. 
     A20. The method of any of paragraphs A1-A19, wherein the second test adherend includes less than 20 plies, less than 10 plies, less than 8 plies, less than 6 plies, less than 4 plies, about 20 plies, about 10 plies, 8 plies, 6 plies, 4 plies, 3 plies, 2 plies, 1 ply, 1-20 plies, 1-8 plies, and/or 1-4 plies. 
     A21. The method of any of paragraphs A1-A20, wherein the peeling support consists essentially of at least one of metal, aluminum alloy, and steel. 
     A22. The method of any of paragraphs A1-A21, wherein the base support includes at least one of metal, aluminum alloy, steel, polymeric material, plastic, laminar material, composite material, fiber-reinforced plastic, mineral-filled plastic, glass, and ceramic. 
     A23. The method of any of paragraphs A1-A22, further comprising: 
     fabricating the first test adherend. 
     A24. The method of any of paragraphs A1-A23, further comprising: 
     fabricating the second test adherend. 
     A25. The method of any of paragraphs A1-A24, further comprising: 
     curing the first test adherend. 
     A26. The method of any of paragraphs A1-A25, further comprising: 
     curing the second test adherend. 
     A27. The method of any of paragraphs A1-A26, further comprising: 
     preparing a surface of the first test adherend for adhering to the first location on the base support. 
     A27.1. The method of paragraph A27, wherein the preparing includes peeling a peel ply from the first test adherend. 
     A28. The method of any of paragraphs A1-A27.1, further comprising: 
     preparing a surface of the second test adherend for adhering to the second location on the base support. 
     A28.1. The method of paragraph A28, wherein the preparing includes peeling a peel ply from the first test adherend. 
     A29. The method of any of paragraphs A1-A28.1, wherein the first test adherend is laminar and/or composite, and optionally wherein the first test adherend includes at least one of a laminar material, a composite material, a fiber-reinforced plastic, a mineral-filled plastic, a polymeric material, a plastic, a glass, and a ceramic material. 
     A30. The method of any of paragraphs A1-A29, wherein the second test adherend is laminar and/or composite, and optionally wherein the second test adherend includes at least one of a laminar material, a composite material, a fiber-reinforced plastic, a mineral-filled plastic, a polymeric material, a plastic, a glass, and a ceramic material. 
     A31. A layered test coupon fabricated according to any of the methods of paragraphs A1-A30. 
     A32. A layered test coupon comprising layers in the following sequence: 
     a base support with a first location and a second location, 
     an adhesive layer including a first test adhesive adjacent to the first location and a second test adhesive adjacent to the second location, 
     an adherend layer including a first test adherend that is non-metallic and a second test adherend that is non-metallic, and 
     a peeling support bonded to the first test adherend and bonded to the second test adherend; 
     wherein the first test adherend is coupled to the first location on the base support with a first test bond including the first test adhesive, and wherein the second test adherend is coupled to the second location on the base support with a second test bond including the second test adhesive. 
     A32.1. The layered test coupon of paragraph A32, further comprising:
         a first crack starter between the first test adhesive and the first test adherend, optionally wherein the first crack starter includes at least one of FEP, PTFE, and silicone.       

     A32.2. The layered test coupon of any of paragraphs A32-A32.1, further comprising:
         a second crack starter between the second test adhesive and the second test adherend, optionally wherein the second crack starter includes at least one of FEP, PTFE, and silicone.       

     A32.3. The layered test coupon of any of paragraphs A32-A32.2, wherein the first test adherend includes less than 20 plies, less than 10 plies, less than 8 plies, less than 6 plies, less than 4 plies, about 20 plies, about 10 plies, 8 plies, 6 plies, 4 plies, 3 plies, 2 plies, 1 ply, 1-20 plies, 1-8 plies, and/or 1-4 plies. 
     A32.4. The layered test coupon of any of paragraphs A32-A32.3, wherein the second test adherend includes less than 20 plies, less than 10 plies, less than 8 plies, less than 6 plies, less than 4 plies, about 20 plies, about 10 plies, 8 plies, 6 plies, 4 plies, 3 plies, 2 plies, 1 ply, 1-20 plies, 1-8 plies, and/or 1-4 plies. 
     A32.5. The layered test coupon of any of paragraphs A32-A32.4, wherein the peeling support consists essentially of at least one of metal, aluminum alloy, and steel. 
     A32.6. The layered test coupon of any of paragraphs A32-A32.5, wherein the base support includes at least one of metal, aluminum alloy, steel, polymeric material, plastic, laminar material, composite material, fiber-reinforced plastic, glass, and ceramic. 
     A32.7. The layered test coupon of any of paragraphs A32-A32.6, wherein the first test adherend is laminar and/or composite, and optionally wherein the first test adherend includes at least one of a laminar material, a composite material, a fiber-reinforced plastic, a mineral-filled plastic, a polymeric material, a plastic, a glass, and a ceramic material. 
     A32.8. The layered test coupon of any of paragraphs A32-A32.7, wherein the first test adherend is laminar and/or composite, and optionally wherein the first test adherend includes at least one of a laminar material, a composite material, a fiber-reinforced plastic, a mineral-filled plastic, a polymeric material, a plastic, a glass, and a ceramic material. 
     A33. A method of testing a quality of bonds to non-metallic materials, the method comprising: 
     selecting the layered test coupon of any of paragraphs A31-A32.8; and 
     peeling the peeling support from the base support to test a strength of the first test bond and a strength of the second test bond. 
     A34. A method of testing a quality of bonds to non-metallic materials, the method comprising: 
     fabricating a layered test coupon according to the method of any of paragraphs A1-A30; and 
     peeling the peeling support from the base support to test a strength of the first test bond and a strength of the second test bond. 
     A35. The method of any of paragraphs A33-A34, further comprising: 
     initiating a crack in the first test bond by applying a wedge between the peeling support and the base support. 
     A36. The method of any of paragraphs A33-A35, further comprising: 
     initiating a crack in the second test bond by applying a wedge between the peeling support and the base support. 
     A37. The method of any of paragraphs A33-A36, wherein the peeling includes attaching a peeling mechanism to the peeling support and applying a force with the peeling mechanism to peel the peeling support from the base support. 
     A37.1. The method of paragraph A37, wherein the peeling mechanism is a drum, and wherein the peeling includes rolling at least a portion of the peeling support around the drum. 
     A38. The method of any of paragraphs A33-A37.1, wherein the peeling includes controlling the angle of the peeling support relative to the base support as the peeling support separates from the base support. 
     A39. The method of any of paragraphs A33-A38, further comprising: 
     classifying a failure mode of the first test bond, optionally wherein the classifying includes electronic imaging the first test bond after the peeling. 
     A40. The method of any of paragraphs A33-A39, further comprising: 
     classifying a failure mode of the second test bond, optionally wherein the classifying includes electronic imaging the second test bond after the peeling. 
     A41. The method of any of paragraphs A33-A40, further comprising: 
     quantifying an extent of failure of the first test bond. 
     A41.1. The method of paragraph A41, wherein the quantifying includes electronic imaging the first test bond after the peeling. 
     A41.2. The method of any of paragraphs A41-A41.1, wherein the quantifying includes determining at least one of a fraction of laminal failure, a fraction of interfacial failure, a fraction of cohesion failure, an extent of laminal failure, an extent of interfacial failure, and an extent of cohesion failure. 
     A42. The method of any of paragraphs A33-A41.2, further comprising: 
     quantifying an extent of failure of the second test bond. 
     A42.1. The method of paragraph A42, wherein the quantifying includes electronic imaging the second test bond after the peeling. 
     A42.2. The method of any of paragraphs A42-A42.1, wherein the quantifying includes determining at least one of a fraction of laminal failure, a fraction of interfacial failure, a fraction of cohesion failure, an extent of laminal failure, an extent of interfacial failure, and an extent of cohesion failure. 
     B1. A method of fabricating a layered test coupon, the method comprising: 
     adhering a test adherend with a test adhesive to a peeling support to create a test bond, wherein the test adherend is non-metallic, and wherein the test adherend is a base support that is rigid. 
     B2. A method of fabricating a layered test coupon, the method comprising: 
     adhering a test adherend with a test adhesive to a peeling support to create a test bond, wherein the test adherend is non-metallic; and 
     bonding the test adherend to a base support that is rigid. 
     B2.1. The method of paragraph B2, wherein the bonding the test adherend includes curing the test adherend onto the base support. 
     B2.2. The method of any of paragraphs B2-B2.1, wherein the bonding the test adherend and the adhering the test adherend are performed at least partially concurrently. 
     B2.3. The method of any of paragraphs B2-B2.2, wherein the bonding the test adherend includes applying a structural adhesive between the test adherend and the base support, and optionally includes curing the structural adhesive. 
     B2.4. The method of any of paragraphs B2-B2.3, wherein the base support includes at least one of metal, aluminum alloy, steel, polymeric material, plastic, laminar material, composite material, fiber-reinforced plastic, mineral-filled plastic, glass, and ceramic. 
     B2.4.1. The method of paragraph B2.4, wherein the base support is laminar. 
     B2.4.2. The method of any of paragraphs B2.4-B2.4.1, wherein the base support is composite. 
     B2.4.3. The method of any of paragraphs B2.4-B2.4.2, wherein the base support consists essentially of fiber-reinforced plastic. 
     B3. The method of any of paragraphs B1-B2.4.3, wherein the adhering the test adherend includes applying the test adhesive between the test adherend and the peeling support. 
     B4. The method of any of paragraphs B1-B3, wherein the adhering the test adherend includes curing the test adhesive, optionally at a temperature above 20° C., above 70° C., above 100° C., above 150° C., about 20° C., about 70° C., about 120° C., about 180° C., 20° C.-200° C., 20° C.-100° C., 100° C.-200° C., and/or 150° C.-200° C. 
     B5. The method of any of paragraphs B1-B4, wherein the adhering the test adherend includes curing the test adherend and the test adhesive at least partially concurrently. 
     B6. The method of any of paragraphs B1-B5, further comprising: 
     placing a crack starter between the test adhesive and the test adherend before the adhering the test adherend, optionally wherein the crack starter includes at least one of FEP, PTFE, and silicone. 
     B7. The method of any of paragraphs B1-B6, wherein the test adherend includes less than 20 plies, less than 10 plies, less than 8 plies, less than 6 plies, less than 4 plies, about 20 plies, about 10 plies, 8 plies, 6 plies, 4 plies, 3 plies, 2 plies, 1 ply, 1-20 plies, 1-8 plies, 1-4 plies, 8-20 plies, 8-40 plies, greater than 8 plies, greater than 10 plies, and/or greater than 20 plies. 
     B8. The method of any of paragraphs B1-B7, wherein the peeling support consists essentially of at least one of metal, aluminum alloy, and steel. 
     B9. The method of any of paragraphs B1-B8, further comprising: 
     fabricating the test adherend. 
     B10. The method of any of paragraphs B1-B9, further comprising: 
     curing the test adherend. 
     B11. The method of any of paragraphs B1-B10, further comprising: 
     preparing a surface of the test adherend for adhering to the peeling support. 
     B11.1. The method of paragraph B11, wherein the preparing includes peeling a peel ply from the test adherend. 
     B12. The method of any of paragraphs B1-B11.1, wherein the test adherend is laminar and/or composite, and optionally wherein the test adherend includes at least one of a laminar material, a composite material, a fiber-reinforced plastic, a mineral-filled plastic, a polymeric material, a plastic, a glass, and a ceramic material. 
     B13. A layered test coupon fabricated according to any of the methods of paragraphs B1-B12. 
     B14. A layered test coupon comprising layers in the following sequence: 
     a peeling support, 
     a test adhesive, and 
     a test adherend that is non-metallic and that is a base support that is rigid; 
     wherein the test adherend is coupled to the peeling support with a test bond including the test adhesive. 
     B15. A layered test coupon comprising layers in the following sequence: 
     a peeling support, 
     a test adhesive, 
     a test adherend that is non-metallic, and 
     a base support that is rigid; 
     wherein the test adherend is coupled to the peeling support with a test bond including the test adhesive, and wherein the base support is bonded to the test adherend. 
     B15.1. The layered test coupon of paragraph B15, wherein the base support includes at least one of metal, aluminum alloy, steel, polymeric material, plastic, laminar material, composite material, fiber-reinforced plastic, mineral-filled plastic, glass, and ceramic. 
     B15.1.1. The layered test coupon of paragraph B15.1, wherein the base support is laminar. 
     B15.1.2. The layered test coupon of any of paragraphs B15.1-B15.1.1, wherein the base support is composite. 
     B15.1.3. The layered test coupon of any of paragraphs B15.1-B15.1.2, wherein the base support consists essentially of fiber-reinforced plastic. 
     B15.2. The layered test coupon of any of paragraphs B15-B15.1.3, further comprising:
         a structural adhesive between the base support and the test adherend, optionally wherein the structural adhesive is at least one of a room temperature adhesive, a pressure sensitive adhesive, and a contact adhesive.       

     B16. The layered test coupon of any of paragraphs B14-B15.2, further comprising: 
     a crack starter between the test adhesive and the test adherend, optionally wherein the crack starter includes at least one of FEP, PTFE, and silicone. 
     B17. The layered test coupon of any of paragraphs B14-B16, wherein the test adherend includes less than 20 plies, less than 10 plies, less than 8 plies, less than 6 plies, less than 4 plies, about 20 plies, about 10 plies, 8 plies, 6 plies, 4 plies, 3 plies, 2 plies, 1 ply, 1-20 plies, 1-8 plies, 1-4 plies, 8-20 plies, 8-40 plies, greater than 8 plies, greater than 10 plies, and/or greater than 20 plies. 
     B18. The layered test coupon of any of paragraphs B14-B17, wherein the peeling support consists essentially of at least one of metal, aluminum alloy, and steel. 
     B19. The layered test coupon of any of paragraphs B14-B18, wherein the test adherend is laminar and/or composite, and optionally wherein the test adherend includes at least one of a laminar material, a composite material, a fiber-reinforced plastic, a mineral-filled plastic, a polymeric material, a plastic, a glass, and a ceramic material. 
     B20. A method of testing a quality of a bond to non-metallic materials, the method comprising: 
     selecting the layered test coupon of any of paragraphs B13-B19; and 
     peeling the peeling support from the base support to test a strength of the test bond. 
     B21. A method of testing a quality of a bond to non-metallic materials, the method comprising: 
     fabricating a layered test coupon according to the method of any of paragraphs B1-B12; and 
     peeling the peeling support from the base support to test a strength of the test bond. 
     B22. The method of any of paragraphs B20-B21, further comprising: 
     initiating a crack in the test bond by applying a wedge between the peeling support and the base support. 
     B23. The method of any of paragraphs B20-B22, wherein the peeling includes attaching a peeling mechanism to the peeling support and applying a force with the peeling mechanism to peel the peeling support from the base support. 
     B23.1. The method of paragraph B23, wherein the peeling mechanism is a drum, and wherein the peeling includes rolling at least a portion of the peeling support around the drum. 
     B24. The method of any of paragraphs B20-B23.1, wherein the peeling includes controlling the angle of the peeling support relative to the base support as the peeling support separates from the base support. 
     B25. The method of any of paragraphs B20-B24, further comprising: 
     classifying a failure mode of the test bond, optionally wherein the classifying includes electronic imaging the test bond after the peeling. 
     B26. The method of any of paragraphs B20-B25, further comprising: 
     quantifying an extent of failure of the test bond. 
     B26.1. The method of paragraph B26, wherein the quantifying includes electronic imaging the test bond after the peeling. 
     B26.2. The method of any of paragraphs B26-B26.1, wherein the quantifying includes determining at least one of a fraction of laminal failure, a fraction of interfacial failure, a fraction of cohesion failure, an extent of laminal failure, an extent of interfacial failure, and an extent of cohesion failure. 
     C1. A method of fabricating a layered test coupon, the method comprising: 
     adhering a test adherend with a test adhesive to a first peeling support to create a test bond and to form a test structure, wherein the test adherend is non-metallic; and 
     bonding the test adherend to a second peeling support. 
     C2. The method of paragraph C1, wherein the adhering the test adherend includes applying the test adhesive between the test adherend and the first peeling support. 
     C3. The method of any of paragraphs C1-C1.1, further comprising:
         preparing a surface of the test adherend for adhering to the first peeling support.       

     C4. The method of paragraph C1.2, wherein the preparing includes peeling a peel ply from the test adherend. 
     C5. The method of any of paragraphs C1-C1.2.1, further comprising:
         applying test conditions to the test structure prior to the bonding the test adherend, optionally wherein the applying includes at least one of wetting, aging, and heating.       

     C6. The method of paragraph C1.3, wherein the applying is performed for less than 100 days, less than 50 days, less than 20 days, less than 15 days, less than 10 days, less than 200 hours, less than 150 hours, less than 100 hours, at least 48 hours, at least 72 hours, at least 100 hours, at least 150 hours, at least 200 hours, at least 10 days, 48 hours—100 days, 48 hours—20 days, and/or 100 hours—20 days. 
     C7. The method of any of paragraphs C1-C1.3.1, wherein the test adhesive is a first test adhesive, wherein the test bond is a first test bond, wherein the adhering includes adhering the test adherend with the first test adhesive to a first location on the first peeling support to create the first test bond and includes adhering the test adherend with a second test adhesive to a second location on the first peeling support to create a second test bond. 
     C8. The method of any of paragraphs C1-C1.4, wherein the test adherend is a first test adherend, wherein the test bond is a first test bond, wherein the adhering includes adhering the first test adherend with the test adhesive to a first location on the first peeling support to create the first test bond and includes adhering a second test adherend with the test adhesive to a second location on the first peeling support to create a second test bond. 
     C9. A method of fabricating a layered test coupon, the method comprising: 
     adhering a test adherend with a test adhesive to a peeling adherend to create a test bond and to form a test structure, wherein the test adherend is non-metallic, and wherein the peeling adherend is non-metallic; 
     bonding the peeling adherend to a first peeling support; and 
     bonding the test adherend to a second peeling support. 
     C10. The method of paragraph C2, wherein the bonding the peeling adherend includes curing the peeling adherend onto the first peeling support. 
     C11. The method of any of paragraphs C2-C2.1, wherein the bonding the peeling adherend and the adhering the test adherend are performed at least partially concurrently. 
     C12. The method of any of paragraphs C2-C2.2, wherein the bonding the peeling adherend and the bonding the test adherend are performed at least partially concurrently. 
     C13. The method of any of paragraphs C2-C2.3, wherein the bonding the peeling adherend includes applying a structural adhesive between the peeling adherend and the first peeling support, and optionally includes curing the structural adhesive. 
     C14. The method of paragraph C2.4, wherein the structural adhesive is at least one of a room temperature adhesive, a pressure sensitive adhesive, and a contact adhesive. 
     C15. The method of any of paragraphs C2-C2.4.1, wherein the adhering the test adherend includes applying the test adhesive between the test adherend and the peeling adherend. 
     C16. The method of any of paragraphs C2-C2.5, wherein the adhering the test adherend includes curing the peeling adherend and the test adhesive at least partially concurrently. 
     C17. The method of any of paragraphs C2-C2.6, wherein the peeling adherend includes less than 20 plies, less than 10 plies, less than 8 plies, less than 6 plies, less than 4 plies, about 20 plies, about 10 plies, 8 plies, 6 plies, 4 plies, 3 plies, 2 plies, 1 ply, 1-20 plies, 1-8 plies, and/or 1-4 plies. 
     C18. The method of any of paragraphs C2-C2.7, further comprising:
         fabricating the peeling adherend.       

     C19. The method of any of paragraphs C2-C2.8, further comprising:
         curing the peeling adherend.       

     C20. The method of any of paragraphs C2-C2.9, further comprising:
         preparing a surface of the test adherend for adhering to the peeling adherend.       

     C21. The method of paragraph C2.10, wherein the preparing includes peeling a peel ply from the test adherend. 
     C22. The method of any of paragraphs C2-C2.10.1, further comprising:
         applying test conditions to the test structure prior to the bonding the peeling adherend and the bonding the test adherend, optionally wherein the applying includes at least one of wetting, aging, and heating.       

     C23. The method of paragraph C2.11, wherein the applying is performed for less than 100 days, less than 50 days, less than 20 days, less than 15 days, less than 10 days, less than 200 hours, less than 150 hours, less than 100 hours, at least 48 hours, at least 72 hours, at least 100 hours, at least 150 hours, at least 200 hours, at least 10 days, 48 hours—100 days, 48 hours—20 days, and/or 100 hours—20 days. 
     C24. The method of any of paragraphs C2-C2.11.1, wherein the test adhesive is a first test adhesive, wherein the test bond is a first test bond, wherein the adhering includes adhering the test adherend with the first test adhesive to a first location on the peeling adherend to create the first test bond and includes adhering the test adherend with a second test adhesive to a second location on the peeling adherend to create a second test bond. 
     C25. The method of any of paragraphs C2-C2.12, wherein the test adherend is a first test adherend, wherein the test bond is a first test bond, wherein the adhering includes adhering the first test adherend with the test adhesive to a first location on the peeling adherend to create the first test bond and includes adhering a second test adherend with the test adhesive to a second location on the peeling adherend to create a second test bond. 
     C26. The method of any of paragraphs C2-C2.13, wherein the peeling adherend is substantially the same as the test adherend. 
     C27. The method of any of paragraphs C2-C2.14, wherein the peeling adherend is laminar and/or composite, and optionally wherein the peeling adherend includes at least one of a laminar material, a composite material, a fiber-reinforced plastic, a mineral-filled plastic, a polymeric material, a plastic, a glass, and a ceramic material. 
     C28. The method of any of paragraphs C1-C2.15, wherein the bonding the test adherend includes curing the test adherend onto the second peeling support. 
     C29. The method of any of paragraphs C1-C3, wherein the bonding the test adherend and the adhering the test adherend are performed at least partially concurrently. 
     C30. The method of any of paragraphs C1-C4, wherein the bonding the test adherend includes applying a structural adhesive between the test adherend and the second peeling support, and optionally includes curing the structural adhesive. 
     C31. The method of paragraph C5, wherein the structural adhesive is at least one of a room temperature adhesive, a pressure sensitive adhesive, and a contact adhesive. 
     C32. The method of any of paragraphs C1-05.1, wherein the adhering the test adherend includes curing the test adhesive, optionally at a temperature above 20° C., above 70° C., above 100° C., above 150° C., about 20° C., about 70° C., about 120° C., about 180° C., 20° C.-200° C., 20° C.-100° C., 100° C.-200° C., and/or 150° C.-200° C. 
     C33. The method of any of paragraphs C1-C6, wherein the adhering the test adherend includes curing the test adherend and the test adhesive at least partially concurrently. 
     C34. The method of any of paragraphs C1-C7, further comprising: 
     placing a crack starter between the test adhesive and the test adherend before the adhering the test adherend, optionally wherein the crack starter includes at least one of FEP, PTFE, and silicone. 
     C35. The method of paragraph C8, when depending from paragraph C1.4, wherein the crack starter is a first crack starter, wherein the placing a crack starter includes placing the first crack starter between the first test adhesive and the test adherend and includes placing a second crack starter between the second test adhesive and the test adherend, optionally wherein the second crack starter includes at least one of FEP, PTFE, and silicone. 
     C36. The method of any of paragraphs C8-C8.1, when depending from paragraph C1.5, wherein the crack starter is a first crack starter, wherein the placing a crack starter includes placing the first crack starter between the test adhesive and the first test adherend and includes placing a second crack starter between the test adhesive and the second test adherend, optionally wherein the second crack starter includes at least one of FEP, PTFE, and silicone. 
     C37. The method of any of paragraphs C8-C8.2, when depending from paragraph C2.12, wherein the crack starter is a first crack starter, wherein the placing a crack starter includes placing the first crack starter between the first test adhesive and the test adherend and includes placing a second crack starter between the second test adhesive and the test adherend, optionally wherein the second crack starter includes at least one of FEP, PTFE, and silicone. 
     C38. The method of any of paragraphs C8-C8.3, when depending from paragraph C2.13, wherein the crack starter is a first crack starter, wherein the placing a crack starter includes placing the first crack starter between the test adhesive and the first test adherend and includes placing a second crack starter between the test adhesive and the second test adherend, optionally wherein the second crack starter includes at least one of FEP, PTFE, and silicone. 
     C39. The method of any of paragraphs C8-C8.4, when depending from paragraph C2.14, wherein the crack starter is a first crack starter, wherein the placing a crack starter includes placing a second crack starter between the test adhesive and the peeling adherend, optionally wherein the second crack starter includes at least one of FEP, PTFE, and silicone. 
     C40. The method of any of paragraphs C1-C8.5, wherein the test adherend includes less than 20 plies, less than 10 plies, less than 8 plies, less than 6 plies, less than 4 plies, about 20 plies, about 10 plies, 8 plies, 6 plies, 4 plies, 3 plies, 2 plies, 1 ply, 1-20 plies, 1-8 plies, and/or 1-4 plies. 
     C41. The method of any of paragraphs C1-C9, wherein the first peeling support consists essentially of at least one of metal, aluminum alloy, and steel. 
     C42. The method of any of paragraphs C1-C10, wherein the second peeling support consists essentially of at least one of metal, aluminum alloy, and steel. 
     C43. The method of any of paragraphs C1-C11, further comprising: 
     fabricating the test adherend. 
     C44. The method of any of paragraphs C1-C12, further comprising: 
     curing the test adherend. 
     C45. The method of any of paragraphs C1-C13, wherein the test adherend is laminar and/or composite, and optionally wherein the test adherend includes at least one of a laminar material, a composite material, a fiber-reinforced plastic, a mineral-filled plastic, a polymeric material, a plastic, a glass, and a ceramic material. 
     C46. A layered test coupon fabricated according to any of the methods of paragraphs C1-C14. 
     C47. A layered test coupon comprising layers in the following sequence: 
     a test structure including layers in the following sequence:
         a first peeling support,   a test adhesive, and   a test adherend that is non-metallic; and       

     a second peeling support; 
     wherein the test adherend is coupled to the first peeling support with a test bond including the test adhesive, and wherein the second peeling support is bonded to the test adherend. 
     C47.1. The layered test coupon of paragraph C16, wherein the test adhesive is a first test adhesive, wherein the test bond is a first test bond, wherein the test structure includes the first test adhesive at a first location between the first peeling support and the test adherend, and includes a second test adhesive at a second location between the first peeling support and the test adherend, wherein the test adherend is coupled to the first peeling support with a second test bond including the second test adhesive. 
     C47.2. The layered test coupon of any of paragraphs C16-C16.1, wherein the test adherend is a first test adherend, wherein the test bond is a first test bond, wherein the test structure includes the first test adherend at a first location between the test adhesive and the second peeling support, and includes a second test adherend at a second location between the test adhesive and the second peeling support, wherein the second test adherend is coupled to the first peeling support with a second test bond including the test adhesive. 
     C48. A layered test coupon comprising layers in the following sequence: 
     a first peeling support; 
     a test structure including layers in the following sequence:
         a peeling adherend that is non-metallic,   a test adhesive, and   a test adherend that is non-metallic; and       

     a second peeling support; 
     wherein the test adherend is coupled to the peeling adherend with a test bond including the test adhesive, wherein the first peeling support is bonded to the peeling adherend, and wherein the second peeling support is bonded to the test adherend. 
     C49. The layered test coupon of paragraph C17, further comprising:
         a structural adhesive between the peeling adherend and the first peeling support, optionally wherein the structural adhesive is at least one of a room temperature adhesive, a pressure sensitive adhesive, and a contact adhesive.       

     C50. The layered test coupon of any of paragraphs C17-C17.1, wherein the peeling adherend includes less than 20 plies, less than 10 plies, less than 8 plies, less than 6 plies, less than 4 plies, about 20 plies, about 10 plies, 8 plies, 6 plies, 4 plies, 3 plies, 2 plies, 1 ply, 1-20 plies, 1-8 plies, and/or 1-4 plies. 
     C50.1. The layered test coupon of any of paragraphs C17-C17.2, wherein the test adhesive is a first test adhesive, wherein the test bond is a first test bond, wherein the test structure includes the first test adhesive at a first location between the peeling adherend and the test adherend, and includes a second test adhesive at a second location between the peeling adherend and the test adherend, wherein the test adherend is coupled to the peeling adherend with a second test bond including the second test adhesive. 
     C50.2. The layered test coupon of any of paragraphs C17-C17.3, wherein the test adherend is a first test adherend, wherein the test bond is a first test bond, wherein the test structure includes the first test adherend at a first location between the test adhesive and the second peeling support, and includes a second test adherend at a second location between the test adhesive and the second peeling support, wherein the second test adherend is coupled to the peeling adherend with a second test bond including the test adhesive. 
     C50.3. The layered test coupon of any of paragraphs C17-C17.4, wherein the peeling adherend is substantially the same as the test adherend. 
     C50.4. The layered test coupon of any of paragraphs C17-C17.5, wherein the peeling adherend is laminar and/or composite, and optionally wherein the peeling adherend includes at least one of a laminar material, a composite material, a fiber-reinforced plastic, a mineral-filled plastic, a polymeric material, a plastic, a glass, and a ceramic material. 
     C51. The layered test coupon of any of paragraphs C16-C17.6, wherein the test structure has been subject to test conditions, wherein the test conditions include at least one of wetting, aging, and heating. 
     C52. The layered test coupon of any of paragraphs C16-C18, further comprising: 
     a crack starter between the test adhesive and the test adherend, optionally wherein the crack starter includes at least one of FEP, PTFE, and silicone. 
     C53. The layered test coupon of paragraph C19, when depending from paragraph C15.1, wherein the crack starter is a first crack starter, further comprising:
         a second crack starter between the second test adhesive and the test adherend, optionally wherein the second crack starter includes at least one of FEP, PTFE, and silicone.       

     C54. The layered test coupon of any of paragraphs C19-C19.1, when depending from paragraph C15.2, wherein the crack starter is a first crack starter, further comprising:
         a second crack starter between the test adhesive and the second test adherend, optionally wherein the second crack starter includes at least one of FEP, PTFE, and silicone.       

     C55. The layered test coupon of any of paragraphs C19-C19.2, when depending from paragraph C16.3, wherein the crack starter is a first crack starter, further comprising:
         a second crack starter between the second test adhesive and the test adherend, optionally wherein the second crack starter includes at least one of FEP, PTFE, and silicone.       

     C56. The layered test coupon of any of paragraphs C19-C19.3, when depending from paragraph C16.4, wherein the crack starter is a first crack starter, further comprising:
         a second crack starter between the test adhesive and the second test adherend, optionally wherein the second crack starter includes at least one of FEP, PTFE, and silicone.       

     C57. The layered test coupon of any of paragraphs C19-C19.4, when depending from paragraph C16.5, wherein the crack starter is a first crack starter, further comprising:
         a second crack starter between the test adhesive and the peeling adherend, optionally wherein the second crack starter includes at least one of FEP, PTFE, and silicone.       

     C58. The layered test coupon of any of paragraphs C16-C19.5, wherein the test adherend includes less than 20 plies, less than 10 plies, less than 8 plies, less than 6 plies, less than 4 plies, about 20 plies, about 10 plies, 8 plies, 6 plies, 4 plies, 3 plies, 2 plies, 1 ply, 1-20 plies, 1-8 plies, and/or 1-4 plies. 
     C59. The layered test coupon of any of paragraphs C16-C20, wherein the first peeling support consists essentially of at least one of metal, aluminum alloy, and steel. 
     C60. The layered test coupon of any of paragraphs C16-C21, wherein the second peeling support consists essentially of at least one of metal, aluminum alloy, and steel. 
     C61. The layered test coupon of any of paragraphs C16-C22, further comprising: 
     a structural adhesive between the test adherend and the second peeling support, optionally wherein the structural adhesive is at least one of a room temperature adhesive, a pressure sensitive adhesive, and a contact adhesive. 
     C62. The layered test coupon of any of paragraphs C16-C23, wherein the test adherend is laminar and/or composite, and optionally wherein the test adherend includes at least one of a laminar material, a composite material, a fiber-reinforced plastic, a mineral-filled plastic, a polymeric material, a plastic, a glass, and a ceramic material. 
     C63. A method of testing a quality of a bond to non-metallic materials, the method comprising: 
     selecting the layered test coupon of any of paragraphs C15-C24; and 
     peeling the first peeling support from the second peeling support to test a strength of the test bond. 
     C64. A method of testing a quality of a bond to non-metallic materials, the method comprising: 
     fabricating a layered test coupon according to the method of any of paragraphs C1-C14; and 
     peeling the first peeling support from the second peeling support to test a strength of the test bond. 
     C65. The method of any of paragraphs C25-C26, when depending from C1.4, C1.5, C2.12, or C2.13, wherein the peeling includes partially peeling the first peeling support from the second peeling support to test a strength of the first test bond and includes partially peeling the first peeling support from the second peeling support to test a strength of the second test bond. 
     C66. The method of any of paragraphs C25-C27, further comprising: 
     initiating a crack in the test bond by applying a wedge between the first peeling support and the second peeling support. 
     C67. The method of any of paragraphs C25-C28, wherein the peeling includes attaching a peeling mechanism to the first peeling support and the second peeling support, and further includes applying a force with the peeling mechanism to peel the first peeling support from the second peeling support. 
     C68. The method of any of paragraphs C25-C29, wherein the peeling includes inserting a wedge between the first peeling support and the second peeling support, and further includes applying a force with the wedge to peel the first peeling support from the second peeling support. 
     C69. The method of any of paragraphs C25-C30, further comprising: 
     classifying a failure mode of the test bond, optionally wherein the classifying includes electronic imaging the test bond after the peeling. 
     C70. The method of any of paragraphs C25-C31, when depending from C1.4, C1.5, C2.12, or C2.13, further comprising: 
     classifying a failure mode of the second test bond, optionally wherein the classifying includes electronic imaging the second test bond after the peeling. 
     C71. The method of any of paragraphs C25-C32, further comprising: 
     quantifying an extent of failure of the test bond. 
     C71.1. The method of paragraph C33, wherein the quantifying includes electronic imaging the test bond after the peeling. 
     C71.2. The method of any of paragraphs C33-C33.1, wherein the quantifying includes determining at least one of a fraction of laminal failure, a fraction of interfacial failure, a fraction of cohesion failure, an extent of laminal failure, an extent of interfacial failure, and an extent of cohesion failure. 
     C72. The method of any of paragraphs C25-C33.2, when depending from C1.4, C1.5, C2.12, or C2.13, further comprising: 
     quantifying an extent of failure of the second test bond. 
     C72.1. The method of paragraph C34, wherein the quantifying includes electronic imaging the second test bond after the peeling. 
     C72.2. The method of any of paragraphs C34-C34.1, wherein the quantifying includes determining at least one of a fraction of laminal failure, a fraction of interfacial failure, a fraction of cohesion failure, an extent of laminal failure, an extent of interfacial failure, and an extent of cohesion failure. 
     C73. The method of any of paragraphs C25-C34.2, when depending from C1.4, C1.5, C2.12, or C2.13, further comprising: 
     comparing a failure mode of the first test bond and a failure mode of the second test bond. 
     C74. The method of any of paragraphs C25-C35, when depending from C1.4, C1.5, C2.12, or C2.13, further comprising: 
     comparing an extent of failure of the first test bond and an extent of failure of the second test bond. 
     D1. A method of fabricating a layered test coupon, the method comprising: 
     adhering a test adherend with a test adhesive to a shearing adherend to create a test bond and to form a test structure, wherein the test adherend is non-metallic, and wherein the shearing adherend is non-metallic; 
     bonding the shearing adherend to a first shearing support; and 
     bonding the test adherend to a second shearing support. 
     D2. The method of paragraph D1, further comprising: 
     forming a first gap through the first shearing support and the shearing adherend; 
     forming a second gap, spaced apart from the first gap, through the second shearing support and the test adherend; 
     wherein the first gap and the second gap define a shearing test region where the first shearing support, the shearing adherend, the test adhesive, the test adherend, and the second shearing support are intact. 
     D3. The method of any of paragraphs D1-D2, further comprising: 
     applying test conditions to the test structure prior to the bonding the shearing adherend and the bonding the test adherend, optionally wherein the applying includes at least one of wetting, aging, and heating. 
     D3.1. The method of paragraph D3, wherein the applying is performed for less than 100 days, less than 50 days, less than 20 days, less than 15 days, less than 10 days, less than 200 hours, less than 150 hours, less than 100 hours, at least 48 hours, at least 72 hours, at least 100 hours, at least 150 hours, at least 200 hours, at least 10 days, 48 hours—100 days, 48 hours—20 days, and/or 100 hours—20 days. 
     D4. The method of any of paragraphs D1-D3, wherein the bonding the shearing adherend includes curing the shearing adherend onto the first shearing support. 
     D5. The method of any of paragraphs D1-D4, wherein the bonding the test adherend includes curing the test adherend onto the second shearing support. 
     D6. The method of any of paragraphs D1-D5, wherein the bonding the shearing adherend and the adhering the test adherend are performed at least partially concurrently. 
     D7. The method of any of paragraphs D1-D6, wherein the bonding the test adherend and the adhering the test adherend are performed at least partially concurrently. 
     D8. The method of any of paragraphs D1-D7, wherein the bonding the shearing adherend and the bonding the test adherend are performed at least partially concurrently. 
     D9. The method of any of paragraphs D1-D8, wherein the bonding the shearing adherend includes applying a structural adhesive between the shearing adherend and the first shearing support, and optionally includes curing the structural adhesive. 
     D9.1. The method of paragraph D9, wherein the structural adhesive is at least one of a room temperature adhesive, a pressure sensitive adhesive, and a contact adhesive. 
     D10. The method of any of paragraphs D1-D9.1, wherein the bonding the test adherend includes applying a structural adhesive between the test adherend and the second shearing support, and optionally includes curing the structural adhesive. 
     D10.1. The method of paragraph D10, wherein the structural adhesive is at least one of a room temperature adhesive, a pressure sensitive adhesive, and a contact adhesive. 
     D11. The method of any of paragraphs D1-D10.1, wherein the adhering the test adherend includes applying the test adhesive between the test adherend and the shearing adherend. 
     D12. The method of any of paragraphs D1-D11, wherein the shearing adherend includes less than 20 plies, less than 10 plies, less than 8 plies, less than 6 plies, less than 4 plies, about 20 plies, about 10 plies, 8 plies, 6 plies, 4 plies, 3 plies, 2 plies, 1 ply, 1-20 plies, 1-8 plies, and/or 1-4 plies. 
     D13. The method of any of paragraphs D1-D12, wherein the test adherend includes less than 20 plies, less than 10 plies, less than 8 plies, less than 6 plies, less than 4 plies, about 20 plies, about 10 plies, 8 plies, 6 plies, 4 plies, 3 plies, 2 plies, 1 ply, 1-20 plies, 1-8 plies, and/or 1-4 plies. 
     D14. The method of any of paragraphs D1-D13, wherein the adhering the test adherend includes curing the test adhesive, optionally at a temperature above 20° C., above 70° C., above 100° C., above 150° C., about 20° C., about 70° C., about 120° C., about 180° C., 20° C.-200° C., 20° C.-100° C., 100° C.-200° C., and/or 150° C.-200° C. 
     D15. The method of any of paragraphs D1-D14, wherein the adhering the test adherend includes curing the shearing adherend and the test adhesive at least partially concurrently. 
     D16. The method of any of paragraphs D1-D15, wherein the adhering the test adherend includes curing the test adherend and the test adhesive at least partially concurrently. 
     D17. The method of any of paragraphs D1-D16, wherein the shearing adherend is substantially the same as the test adherend. 
     D18. The method of any of paragraphs D1-D17, wherein the first shearing support consists essentially of at least one of metal, aluminum alloy, and steel. 
     D19. The method of any of paragraphs D1-D18, wherein the second shearing support consists essentially of at least one of metal, aluminum alloy, and steel. 
     D20. The method of any of paragraphs D1-D19, further comprising: 
     fabricating the shearing adherend. 
     D21. The method of any of paragraphs D1-D20, further comprising: 
     fabricating the test adherend. 
     D22. The method of any of paragraphs D1-D21, further comprising: 
     curing the shearing adherend. 
     D23. The method of any of paragraphs D1-D22, further comprising: 
     curing the test adherend. 
     D24. The method of any of paragraphs D1-D23, further comprising: 
     preparing a surface of the test adherend for adhering to the shearing adherend. 
     D24.1. The method of paragraph D24, wherein the preparing includes peeling a peel ply from the test adherend. 
     D25. The method of any of paragraphs D1-D24.1, wherein the test adherend is laminar and/or composite, and optionally wherein the test adherend includes at least one of a laminar material, a composite material, a fiber-reinforced plastic, a mineral-filled plastic, a polymeric material, a plastic, a glass, and a ceramic material. 
     D26. The method of any of paragraphs D1-D25, wherein the shearing adherend is laminar and/or composite, and optionally wherein the shearing adherend includes at least one of a laminar material, a composite material, a fiber-reinforced plastic, a mineral-filled plastic, a polymeric material, a plastic, a glass, and a ceramic material. 
     D27. A layered test coupon fabricated according to any of the methods of paragraphs D1-D26. 
     D28. A layered test coupon comprising layers in the following sequence: 
     a first shearing support; 
     a test structure including layers in the following sequence:
         a shearing adherend that is non-metallic,   a test adhesive, and   a test adherend that is non-metallic; and       

     a second shearing support; 
     wherein the test adherend is coupled to the shearing adherend with a test bond including the test adhesive, wherein the first shearing support is bonded to the shearing adherend, and wherein the second shearing support is bonded to the test adherend. 
     D28.1. The layered test coupon of paragraph D28, wherein the layered test coupon defines a shearing test region between a first gap traversing the first shearing support and the shearing adherend, and a second gap, spaced apart from the first gap, traversing the test adherend and the second shearing support. 
     D28.2. The layered test coupon of any of paragraphs D28-D28.1, wherein the test structure has been subject to test conditions, wherein the test conditions include at least one of wetting, aging, and heating. 
     D28.3. The layered test coupon of any of paragraphs D28-D28.2, further comprising:
         a first structural adhesive between the shearing adherend and the first shearing support, optionally wherein the first structural adhesive is at least one of a room temperature adhesive, a pressure sensitive adhesive, and a contact adhesive.       

     D28.4. The layered test coupon of any of paragraphs D28-D28.3, further comprising:
         a second structural adhesive between the test adherend and the second shearing support, optionally wherein the second structural adhesive is at least one of a room temperature adhesive, a pressure sensitive adhesive, and a contact adhesive.       

     D28.5. The layered test coupon of any of paragraphs D28-D28.4, wherein the shearing adherend includes less than 20 plies, less than 10 plies, less than 8 plies, less than 6 plies, less than 4 plies, about 20 plies, about 10 plies, 8 plies, 6 plies, 4 plies, 3 plies, 2 plies, 1 ply, 1-20 plies, 1-8 plies, and/or 1-4 plies. 
     D28.6. The layered test coupon of any of paragraphs D28-D28.5, wherein the test adherend includes less than 20 plies, less than 10 plies, less than 8 plies, less than 6 plies, less than 4 plies, about 20 plies, about 10 plies, 8 plies, 6 plies, 4 plies, 3 plies, 2 plies, 1 ply, 1-20 plies, 1-8 plies, and/or 1-4 plies. 
     D28.7. The layered test coupon of any of paragraphs D28-D28.6, wherein the shearing adherend is substantially the same as the test adherend. 
     D28.8. The layered test coupon of any of paragraphs D28-D28.7, wherein the first shearing support consists essentially of at least one of metal, aluminum alloy, and steel. 
     D28.9. The layered test coupon of any of paragraphs D28-D28.8, wherein the second shearing support consists essentially of at least one of metal, aluminum alloy, and steel. 
     D28.10. The layered test coupon of any of paragraphs D28-D28.9, wherein the test adherend is laminar and/or composite, and optionally wherein the test adherend includes at least one of a laminar material, a composite material, a fiber-reinforced plastic, a mineral-filled plastic, a polymeric material, a plastic, a glass, and a ceramic material. 
     D28.11. The layered test coupon of any of paragraphs D28-D28.10, wherein the shearing adherend is laminar and/or composite, and optionally wherein the shearing adherend includes at least one of a laminar material, a composite material, a fiber-reinforced plastic, a mineral-filled plastic, a polymeric material, a plastic, a glass, and a ceramic material. 
     D29. A method of testing a quality of a bond to non-metallic materials, the method comprising: 
     selecting the layered test coupon of any of paragraphs D27-D28.11; and 
     shearing the test bond to test a strength of the test bond. 
     D30. A method of testing a quality of a bond to non-metallic materials, the method comprising: 
     fabricating a layered test coupon according to the method of any of paragraphs D1-D26; and 
     shearing the test bond to test a strength of the test bond. 
     D31. The method of any of paragraphs D29-D30, wherein the shearing includes attaching a shearing mechanism to the first shearing support and the second shearing support, and further includes applying a force with the shearing mechanism to shear the test bond. 
     D32. The method of any of paragraphs D29-D31, further comprising: 
     classifying a failure mode of the test bond, optionally wherein the classifying includes electronic imaging the test bond after the shearing. 
     D33. The method of any of paragraphs D29-D32, further comprising: 
     quantifying an extent of failure of the test bond. 
     D33.1. The method of paragraph D33, wherein the quantifying includes electronic imaging the test bond after the shearing. 
     D33.2. The method of any of paragraphs D33-D33.1, wherein the quantifying includes determining at least one of a fraction of laminal failure, a fraction of interfacial failure, a fraction of cohesion failure, an extent of laminal failure, an extent of interfacial failure, and an extent of cohesion failure. 
     As used herein, the terms “adapted” and “configured” mean that the element, component, or other subject matter is designed and/or intended to perform a given function. Thus, the use of the terms “adapted” and “configured” should not be construed to mean that a given element, component, or other subject matter is simply “capable of” performing a given function but that the element, component, and/or other subject matter is specifically selected, created, implemented, utilized, programmed, and/or designed for the purpose of performing the function. It is also within the scope of the present disclosure that elements, components, and/or other recited subject matter that is recited as being adapted to perform a particular function may additionally or alternatively be described as being configured to perform that function, and vice versa. Similarly, subject matter that is recited as being configured to perform a particular function may additionally or alternatively be described as being operative to perform that function. 
     The various disclosed elements of apparatuses and steps of methods disclosed herein are not required to all apparatuses and methods according to the present disclosure, and the present disclosure includes all novel and non-obvious combinations and subcombinations of the various elements and steps disclosed herein. Moreover, one or more of the various elements and steps disclosed herein may define independent inventive subject matter that is separate and apart from the whole of a disclosed apparatus or method. Accordingly, such inventive subject matter is not required to be associated with the specific apparatuses and methods that are expressly disclosed herein, and such inventive subject matter may find utility in apparatuses and/or methods that are not expressly disclosed herein.