Methods and systems for rapidly testing adhesion

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.

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.

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. 1-18illustrate various embodiments of test systems10, test coupons20, and methods100of fabricating and/or testing test systems10and/or test coupons20. Elements that serve a similar, or at least substantially similar, purpose are labeled with numbers consistent among the figures. Like numbers in each ofFIGS. 1-18, and the corresponding elements, may not be discussed in detail herein with reference to each ofFIGS. 1-18. Similarly, all elements may not be labeled in each ofFIGS. 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 ofFIGS. 1-18may be included in and/or used with any ofFIGS. 1-18without 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 systems10and/or test coupons20in exploded view. In exploded view, the spaces between the elements are for illustration purposes only.

FIG. 1is a schematic representation, in exploded view, of test systems10for testing bond adhesion to test adherends32. The test system10comprises a test coupon20, a layered structure including a series of layers22and one or more test bonds40to be tested. The test coupon20includes one or more test structures30, layered structures that each include at least two layers22: a test adherend32and a test adhesive42. Within the test structure30, and between the test adherend32and the test adhesive42, is a test interface24. The test adhesive42bonds to the test adherend32at the test interface24to form the test bond40. The test coupon20includes a test region26, sometimes referred to as a peel region or a shear region, depending on type of test performed. The test coupon20includes a force application region52where forces50may be applied to the test coupon20. Depending on the type of test being performed, forces50may be referred to as peeling forces or shearing forces. The test region26is the region of the test structure30where the test bond40may be interrogated, for example by applying peeling forces (perpendicular to the layers22) and/or shearing forces (parallel to the layers22).

The test coupon20also includes a layer22adhered to the test adhesive42opposite the test adherend32. The adhered layer22may be a second test adherend32, a structural adherend33(e.g., a peeling adherend34and/or a shearing adherend35), and/or a structural support36(e.g., a base support37, a peeling support38, and/or a shearing support39). When present, a second test adherend32and/or a structural adherend33may be supported by a structural support36bonded to the second test adherend32and/or the structural adherend33. Further, the test structure30may be supported by a structural support36bonded to the test adherend32.

Generally, the test systems10, the test coupons20, and the test structures30are configured to test the quality (e.g., the strength, the durability, and/or the extent) of the test bond40. One method to test the quality of the test bond40is through peel testing, where forces50are applied perpendicular to the layers22to stress the test bond40perpendicular to the layer22of the test adhesive42. Peel testing is designed to ultimately peel apart the test coupon20, generally by fracturing the test bond40along the test interface24, within the test adherend32and/or within the layer22adhered to the test adhesive42. In peel testing, the fracture, or crack, generally propagates perpendicular to the externally applied forces50. Another method to test the quality of the test bond40is through shear testing, where forces50are applied parallel to the layers22to stress the test bond40parallel to the layer22of the test adhesive42. Shear testing is designed to ultimately laterally pull apart the test coupon20, generally by fracturing the test bond40along the test interface24, within the test adherend32and/or within the layer22adhered to the test adhesive42. In shear testing, the fracture, or crack, generally propagates parallel to the externally applied forces50.

Test coupons20include test adherends32that are non-metallic (not essentially composed of metal). Test adherends32may be laminar and/or composite materials and may include polymeric material, plastic, glass, and/or ceramic materials. Though test adherends32are non-metallic, test adherends32may 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 adherend32is a laminar material, the assembled plies of test adherend32may be handled and assembled onto other layers22while the test adherend is uncured, partially cured, and/or fully cured. In the uncured and partially cured states, the test adherend32may be pliable and/or malleable. Upon fully curing, the test adherend32may solidify and become relatively stiff and/or rigid. Some test adherends32may remain and/or become flexible and/or elastic in the fully cured state.

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 coupons20include test adhesives42that are adhesives configured to bond the test adherend32to another layer22. Adhesives may be referred to as binders, glues, cements, and pastes. Prior to bonding, test adhesives42may be in the form of a liquid, a solid, a suspension, an emulsion, and/or a mastic composition. Test adhesives42may 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 adhesives42may be room temperature cured (e.g., pressure sensitive adhesive, contact adhesive, moisture-cured adhesive), and/or heat cured. Test adhesives42may 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 coupons20may include structural adherends33that are non-metallic (e.g., laminar components, composite components, and/or fiber-reinforced plastic components). When present, structural adherends33are adhered to the test adhesive42opposite the test adherend32. When present, structural adherends33form a part of the test structure30. Structural adherends33may have any of the properties disclosed herein with respect to test adherends32. Structural adherends33may be configured similarly or identically to a test adherends32in the same test structure30. For example, a structural adherend33may be selected to cure under the same conditions as a test adherend32in the same test structure30. In certain embodiments, the structural adherend33is substantially the same as the test adherend32. In certain other embodiments, the structural adherend33is configured to adhere more strongly to the test adhesive42than the adhesion of the test adherend32to the test adhesive42. The structural adherend33may be configured to be thin, and may be configured to have substantially the same thickness as the test adherend32.

Where the test system10, the test coupon20, and/or the structural adherend33are configured for peel testing, the structural adherend33may be referred to as a peeling adherend34. The peeling adherend34may be configured to transmit peeling stress to the test bond40and may be configured to avoid shearing while peeling forces are applied. The peeling adherend34may be configured to be flexible, optionally as flexible as the test adherend32.

Where the test system10, the test coupon20, and/or the structural adherend33are configured for shear testing, the structural adherend33may be referred to as a shearing adherend35. The shearing adherend35may be configured to transmit shearing stress to the test bond40and may be configured to avoid peeling while shearing forces are applied.

Test coupons20may include structural supports36, sometimes referred to as a base support37, a peeling support38, and/or a shearing support39depending on how forces50are configured to be applied to the test coupon20. Structural supports36are generally rigid structures configured to supply mechanical strength to the test coupon20. Further, structural supports36are configured to bond strongly to at least one layer22of the test structure30, for example the test adherend32, the test adhesive42, and the structural adherend33. Structural supports36may include, and may consist essentially of, at least one of metal, aluminum alloy, and steel. Further, structural supports36may 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 system10and/or the test coupon20are configured for peel testing, a base support37may be bonded to the test adherend32, test adhesive42, and/or the optional peeling adherend34. In such case, the base support37would form a stable reference from which other layers22could be peeled. Where the test system10and/or the test coupon20are configured for shear testing, a shearing support39may be bonded to the test adherend32, test adhesive42, and/or the optional shearing adherend35. In the case of shear testing, a first shearing support139(a shearing support39) may be bonded to the shearing adherend35and a second shearing support239(a shearing support39) may be bonded to the test adherend32.

Test coupons20may include peeling supports38that are support structures configured to supply mechanical strength to the test coupon20and to transmit peeling stress to the test bond40(through the test adherend32and/or the peeling adherend34). Peeling supports38may be configured to avoid shearing while peeling forces are applied. Further, peeling supports38are configured to bond strongly to at least one layer22of the test structure30, for example the test adherend32, the test adhesive42, and the peeling adherend34. The peeling support38may be configured to be relatively flexible, optionally as flexible as the test adherend32and/or the peeling adherend34. Peeling supports38may include, and may consist essentially of, at least one of metal, aluminum alloy, and steel.

Where test coupons20include an optional structural support36, the structural support36may be bonded to the test structure30(i.e., the test adherend32and/or a structural adherend33) with a structural adhesive46. Structural adhesives46are adhesives configured to strongly bond the structural support36to the test structure30. Structural adhesives46may have any of the properties disclosed herein with respect to test adhesives42and adhesives generally. Structural adhesives46may be configured similarly or identically to a test adhesive42in the same test coupon20. For example, a structural adhesive46may be selected to cure under the same conditions as a test adhesive42in the same test coupon20.

Additionally or alternatively, the optional structural support36may be directly bonded to the test structure30, without any structural adhesive46. For example, the test adherend32and/or a structural adherend33may be cured while assembled on a structural support36, the curing process forming a bond between the test structure30and the structural support36.

Overall, test coupons20generally include layers22in the following sequence: (a) an optional structural support36, (b) an optional structural adhesive46, (c) a test adherend32(a first test adherend132), (d) a test adhesive42, (e) an optional second test adherend232(a test adherend32) and/or an optional structural adherend33, (f) an optional structural adhesive46, and (g) an optional structural support36. As discussed herein, test coupons20include at least one test structure30which includes a test adherend32, a test adhesive42and at least one of optional layers (e) and (g). Hence, test coupons20include at least one of optional layers (e) and (g).

In certain embodiments, test coupons20may include a crack starter60in the test structure30, at the edge of the test interface24between the test adherend32and the test adhesive42. The crack starter60is configured to form a weak bond, and/or to interfere with the formation of a strong bond, along a portion of the test interface24, typically in the force application region52. The crack starter60also is configured to form a crack in the test bond40, near the test interface24, upon application of a force50near the crack starter60. The crack starter60may be a solid, liquid, and/or mastic applied at the edge of the test interface24. Illustrative, non-exclusive example materials suitable for a crack starter60include FEP (fluorinated ethylene propylene), PTFE (polytetrafluoroethylene), polyimide, mold release agents, and silicone.

In certain embodiments, test coupons20may include one or more gaps48that define a test region26(e.g., between the gaps48). The optional gaps48are discontinuities crossing certain layers22but do not intersect the test adhesive42. For example, a gap48may intersect the optional structural support36and/or the optional peeling support38, the optional structural adhesive46, and the test adherend32, leaving intact the test adhesive42, the optional second test adherend32and/or the optional structural adherend33, the optional structural adhesive46, and the optional structural support36. When test coupons20include gaps48, typically two are included. The two gaps are typically spaced apart from one another and situated on opposite sides of the test coupon20(opposite sides of the test adhesive42). The layers between the gaps48are generally intact. Typically, the gaps48define a test region26where the optional structural supports36on either side of the test adhesive42overlap one another. Such an overlap structure may be useful for shear testing (e.g., pulling oppositely situated structural supports36in opposite directions may subject the test bond40to shear stress).

Test systems10may include a test fixture12configured to apply forces50to the test coupon20and the test bond40. For example, a test fixture12may be configured for peel testing, i.e., configured to apply forces50perpendicular to the layers22to stress the test bond40perpendicular to the layer22of the test adhesive42. As another example, a test fixture12may be configured for shear testing, i.e., configured to apply forces50parallel to the layers22to stress the test bond40parallel to the layer22of the test adhesive42. The test fixture12generally is configured to apply forces50to the structural supports36and/or the peeling supports38, as the structural supports36and/or the peeling supports38generally are configured to accept and transmit forces50. Test fixtures12may include a motor, an actuator, and/or a simple machine (e.g., a lever, a plane, a wedge64, and/or a drum62).

Generally, the test fixture12is configured to apply forces50to the test coupon20at one or more force application regions52and to maintain the relative position of the test coupon20at one or more stationary regions54. Generally, the force application regions52are located near an end of the test coupon20. The test fixture12may be coupled to the test coupon20at the force application regions52with flexible couplings that allow the force50to be applied at a substantially constant direction as the test coupon20is split apart. The test fixture12may be coupled to the test coupon20at the stationary regions54with rigid couplings that substantially maintain the relative position of the stationary regions54as the test coupon20is split apart. In certain configurations, the test fixture12is not coupled directly to the stationary regions54.

Test systems10and/or test fixtures12may be configured to interrogate test bonds40within test coupons20in at least one of several modes, as illustrated inFIGS. 2-6. In peeling mode, as illustrated inFIGS. 2-5, the test bond40is subject to forces50, perpendicular to the test structure30layer22(including the test adhesive42layer22), that tend to peel the test bond40apart. In shearing mode, as illustrated inFIG. 6, the test bond40is subject to forces50, parallel to the test adhesive42layer22, that tend to shear the test bond40apart.

InFIG. 2, a test coupon20is subject to peel testing. One side of the test coupon20(the backing structure58) is rigidly coupled to a rigid portion of a test fixture12(or is rigid enough to serve as a rigid fixture support) while one end (the force application region52) of a peeling structure56(the side of the test coupon20opposite the backing structure58) is coupled to a peeling mechanism of the test fixture12. The backing structure58may include and/or be the test adherend32, the structural adherend33, and/or the base support37. The peeling structure56may include and/or be the structural adherend33, the test adherend32, and/or the peeling support38. The test fixture12is configured to pull the test coupon20apart between the backing structure58and the peeling structure56(generally at the test bond40). The peeling force50may be applied at an angle to the layer22of the test structure30, generally substantially perpendicular to the layer22of the test structure30, at least not essentially parallel to the layer22of the test structure30(as parallel forces would result in more shearing than peeling).

Generally, the peeling structure56must be flexible enough to bend as the test coupon20is pulled apart and stiff enough to transmit the peeling force50of the test fixture12into the test bond40. Typically, the peeling structure56includes a thin, metal layer22(e.g., the peeling support38). The peeling structure56may be coupled to the test fixture12with fasteners and/or bonds. For example, the force application region52of the peeling structure56may be clamped to the test fixture12. The backing structure58may be stiff and rigid enough to withstand the peeling forces50without significant flexing. Additionally or alternatively, the backing structure58may be coupled to a rigid portion of the test fixture12such that the combination of the rigid portion and the backing structure58is stiff and rigid enough to resist significant flexing as the peeling forces50are applied. The backing structure58may be coupled to the test fixture12with fasteners and/or bonds. For example, the backing structure58may be clamped to the test fixture12.

InFIG. 3, the test fixture12illustrated inFIG. 2includes a drum62. The drum62(i.e., a cylindrical structure) is configured to be coupled to the peeling structure56. The drum62also is configured to roll along the test coupon20, pulling the test coupon20apart between the backing structure58and the peeling structure56(generally at the test bond40). 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 structure56must be flexible enough to conform to the drum62as the drum62rolls. The peeling structure56may be coupled to the drum62with fasteners and/or bonds. For example, the force application region52of the peeling structure56may be clamped to the drum62. Incorporating a drum62is one way to configure a test fixture12to control the peeling angle (the angle between the peeling structure56and the backing structure58) as the peeling structure56is peeled from the backing structure58. Peeling the peeling structure56by rolling around a drum62may maintain a substantially constant peeling angle.

InFIG. 4, a test coupon20is subject to peel testing in a double beam cantilever configuration. One end (the force application region52) of one side of a test coupon20(the first peeling structure156, a peeling structure56) is coupled to a pulling mechanism of a test fixture12while the same end (the force application region52) of the second peeling structure256(a peeling structure56that is the side of the test coupon20opposite the first peeling structure156) is coupled to a second pulling mechanism of the test fixture12. The first peeling structure156may include and/or be the test adherend32and/or a first peeling support138. The second peeling structure256may include and/or be the peeling adherend34and/or a second peeling support238. The test fixture12is configured to pull the end of the first peeling structure156and the end of the second peeling structure256with substantially equal magnitude forces50in generally opposite directions, the forces50tending to pull the test bond40apart perpendicular to the layer22of the test structure30. 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 structures56are 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 bond40is subject to the tension of the cable (or other flexible pulling element). The ends of the peeling structures56may 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 structures56. As another example, the end of one of the peeling structures56may include a hole configured to receive a hook coupled to a pulling mechanism.

InFIG. 5, a test coupon20is subject to peel testing in a double beam cantilever configuration using a wedge64(part of the test fixture12). The test fixture12may be configured to drive the wedge64along the test bond40(along the peeling direction70) to separate the test coupon20along the test bond40. In this configuration, the wedge64is placed with its tip at the test structure30. The wedge64may 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 wedge64. The test coupon20may be coupled to the test fixture12at the end opposite the wedge64(at the stationary region54), using fasteners and/or bonds. The end where the wedge will be driven (the force application region52) need not be substantially constrained. The test fixture12may be configured to allow the force application region52to flex enough to accommodate the wedge64as it is driven through the test coupon20.

InFIG. 6, a test coupon20is subject to shear testing. One end of a test coupon20(a first force application region152) is coupled to a pulling mechanism of a test fixture12while the other end of the test coupon20(a second force application region252) is coupled to a second pulling mechanism of the test fixture12. The test fixture12is configured to apply to the test coupon20substantially equal magnitude pulling forces50in opposite directions, substantially parallel to the test adhesive42layer22. The test coupon20includes a test region26where a first shearing structure166(a shearing structure66) overlaps a second shearing structure266(a shearing structure66), however neither shearing structure66is continuous from end to end of the test coupon20. Each shearing structure66may include and/or be a test adherend32, a structural adherend33, and/or a shearing support39. Each shearing structure66includes at least one gap48between the ends of the test coupon20. Hence, when the force50is applied at the force application regions52, to pull the test coupon20in opposite directions, the test adhesive42experiences a shear (a force parallel to the test adhesive42layer22), the test adhesive42being the only continuous layer of the test coupon20between the two ends of the test coupon20. 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 coupon20may be coupled to the test fixture12with fasteners and/or bonds. For example, a force application region52may define an aperture through the test coupon20, which is configured to couple to a cable. As another example, a force application region52may be clamped to a pulling mechanism of the test fixture12.

As illustrated in the fragmentary views ofFIGS. 7-8, test coupons20may include a plurality of test bonds30resulting from a plurality of adhesive bonding schemes, e.g., different test adherends32, different test adhesives42, different preparations, and/or different environmental conditions. For example, test coupons20may incorporate more than one test structure30. Each test structure30may be completely independent or some test structures30may share common materials (e.g., test adherends32, test adhesives42, and/or structural adherends33) and/or bond processing conditions (e.g., surface preparations, adhesive cure methods, and environmental conditions). A test coupon20may include a first test structure130(a test structure30) at a first location (e.g., a first test region126) and a second test structure230(a test structure30) at a second location (e.g., a second test region226) spaced apart from the first location. Each test structure30includes a test bond40(e.g., a first test bond140in the first test structure130and a second test bond240in the second test structure230). Where test adherends32differ between test bonds40, the difference may be the result of different materials, different surface preparations, and/or exposure to different environmental conditions. Where the test adhesives42differ between test bonds40, the difference may be the result of different materials, different adhesive cure methods, and/or exposure to different environmental conditions. When plural test structures30are present, they are arranged in the same layer22of the test coupon20. Hence, a test fixture12may be configured to sequentially and/or concurrently test the quality of the test bonds40within the plural test structures30.FIG. 7illustrates a series of test structures30arranged such that peeling along the peeling direction70would sequentially interrogate each test structure30.FIG. 8illustrates a series of test structures30arranged such that peeling along the peeling direction70would simultaneously interrogate each test structure30.

FIG. 9is a flowchart of methods100for fabricating test coupons20and/or interrogating test bonds40. Methods100include adhering102layers22together to form a test structure30. Adhering102includes adhering a test adherend32with a test adhesive42to an opposing adherend (e.g., a structural adherend33and/or a structural support36) to create a test bond40. Adhering102may include applying the test adhesive42between the test adherend32and the opposing adherend, e.g., by spraying, painting, spreading, placing, and/or contacting. Adhering102may include curing the test adhesive42. 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, adhering102may include preparing the surface of test adherend32to be adhered. The prepared surface may become part of the test interface24. 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 bond40and may be one of the variables interrogated with the test structure30and/or the test coupon20. For example, where the test adherend32includes a peel ply, the peel ply may be removed from the surface of the test adherend32, exposing a fresh surface for the test interface24.

Methods100may include adhering102layers22to form a plurality of test structures30. Each test structure30may be in a different location and spaced apart from other test structures30. The test structures30may share a common test adherend32, a common test adhesive42, and/or a common opposing adherend. For example, adhering102may include adhering a first test adherend32with a first test adhesive42to a first location on an opposing adherend to create a first test bond40, and include adhering a second test adherend32with a second test adhesive42to a second location, adjacent the first location, on the opposing adherend to create a second test bond40. Adhering102may be performed such that one of the plurality of test structures30is formed at least partially concurrently and/or at least partially sequentially with another of the plurality of test structures30. Where adhering102includes curing the test adhesive(s)42, curing each test adhesive42of the plurality of test structures30may be performed under substantially the same conditions (e.g., temperature, time, application method, etc.).

Methods100may include bonding104the test structure30to one or more supports (e.g., a structural support36). Bonding104may include bonding a first support on one side of the test structure30(e.g., bonding a peeling support38to a test adherend32) and/or bonding a second support on the opposite side of the test structure30(e.g., bonding a base support37to a structural adherend33). Bonding104may include curing a composite material. Curing a composite material may bond the composite material to other materials in contact. For example, where bonding104includes bonding the test adherend32(potentially a laminar and/or composite material) to a structural support36(potentially a laminar and/or a composite material), bonding104may include curing the test adherend32and/or the structural support36in contact with each other. Bonding104may include applying a structural adhesive46between the support (e.g., the structural support36) and the test structure30, and optionally may include curing the structural adhesive46to bond the two components. Bonding104may be performed at least partially concurrently and/or at least partially sequentially with adhering102. For example, where adhering102includes curing the test adhesive42, bonding104may include curing a composite material at least partially concurrently with the curing of the test adhesive42, e.g., the curing of the test adhesive42and the curing of the composite material may occur under similar conditions (such as time, temperature, humidity, etc.). Where methods100include two or more bonding104operations, e.g., bonding a structural support36to a structural adherend33and bonding a peeling support38to the test adherend32, one bonding104may be performed at least partially concurrently and/or partially sequentially with another bonding104. For example, bonding104a structural support36to a structural adherend33and bonding104a peeling support38to the test adherend32may be performed at least partially concurrently, e.g., the two bonding operations may occur under similar conditions (such as time, temperature, humidity, etc.). Where methods100include adhering102to form a plurality of test structures30, bonding104may include bonding each test structure30to one or more common supports (e.g., a structural support36and/or a peeling support38).

Methods100may include curing106composite structures such as the test adherend32, the structural adherend33, the structural support36, and/or the peeling support38. 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 adherend32, any support adherend33, and/or any structural support36including composite materials may be assembled in a green state. After assembly of the test structure30and/or the test coupon20, the green composite material may be cured, typically by heating the whole assembly to the curing temperature of the green composite material. Curing106of the green composite material generally results in bonding the green composite material to the adjacent layers22. Where the test adhesive42and/or the structural adhesive46requires 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 structure30and/or the test coupon20. Curing106may 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. Curing106of a composite structure may be before, during, or after adhering102. Curing106of a composite structure may be before or during bonding104. For example, curing106the test adherend32and curing the test adhesive42(as part of adhering102) may be performed at least partially concurrently and/or at least partially sequentially. Where methods100include two or curing106operations, one curing106operation may be performed at least partially concurrently and/or partially sequentially with another curing106operation. For example, curing106the test adherend32and curing106a structural adherend33may be performed at least partially concurrently, e.g., the two curing operations may occur under similar conditions (such as time, temperature, humidity, etc.).

Methods100may include forming a crack initiation site at the test bond40in the force application region52. For example, forming a crack initiation site may include placing a crack starter60between a portion of the test adherend32and the test adhesive42before adhering102. As another example, forming a crack initiation site may include placing a crack starter60between a portion of the structural adherend33and the test adhesive42before adhering102. Placing the crack starter may include applying a crack starter60to the test adherend32. As another example, forming a crack initiation site may include forming a weak bond between a portion of the test adherend32and the test adhesive42. As another example, forming a crack initiation site may include initiating a crack in the test bond40in the force application region52, e.g., by driving a wedge into the test bond40, applying a wedge between layers22of the test structure30, and/or by applying a force50. Where methods100include forming a plurality of test structures30, methods100may include forming a crack initiation site in each test structure30.

Methods100may include applying108test conditions to the test structure30prior to bonding104. Test structures30may 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 bond40. Exposure may include moisture, liquids, elevated temperatures, depressed temperatures, temperature cycles, corrosives, and ambient conditions for a predetermined amount of time. Applying108test conditions may include wetting, aging, and/or heating a test structure30. 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 structures30generally respond to condition effects quicker than thicker and/or higher volume test structures30. Hence, steady state (quasi-equilibrium) effects may be observed sooner in thinner and/or lower volume test structures30than in thicker and/or higher volume test structures30. For example, water saturation of a test structure30including a fiber-reinforced plastic test adherend32of 2 plies may occur in less than 20 days, whereas a test structure30differing 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 structures30may reduce preparation time and materials cost relative to thicker and/or higher volume test structures30.

Methods100may include forming a gap48through a shearing structure66, and/or through shearing structures66on opposite sides of a test coupon20, to define a test region26where all layers22of the test coupon20are intact. Forming a gap48may include cutting, notching, and/or nicking a shearing structure66. Forming a gap48may include bonding discontinuous sections of a support structure (e.g., a structural support36) to the test structure30and cutting, notching, and/or nicking the test structure30in a location corresponding to the discontinuity in the support structure. Forming a gap48does not generally include affecting the test adhesive42, at least not within the test region26. Forming a gap48may be performed before, during, or after applying108test conditions.

Methods100may include selecting a test coupon20fabricated by adhering102, optional bonding104, and/or optional curing106. Test coupons20selected 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 bonds40may be tested by applying110force and optionally measuring112the result.

Methods100may include applying110force to the test coupon20, the test structure30, and/or the test bond40to separate the test coupon20, generally along the test bond40. Applying110force may be used to test the quality of the test bond40. Where test coupons20include a plurality of test structures30and test bonds40, applying110force may include applying110force to each of the plurality of test structures30and/or test bonds40at least partially concurrently and/or at least partially sequentially. Applying110force may include applying a force50to a test structure30and/or a test bond40and applying a different force50to a different test structure30and/or a different test bond40.

Applying110force may include peeling one side (e.g., the test adherend32, the structural support36, and/or the peeling support38) of the test coupon20from the other side (e.g., the structural adherend33, and/or the structural support36), generally by applying forces50perpendicular to the layers22. Peeling may stress the test bond40perpendicular to the layer22of the test adhesive42. Peeling may fracture the test bond40along the test interface24, within the test adherend32and/or within the layer22adhered to the test adhesive42. Peeling may include controlling the angle of the peeling support38relative to the base support37as the peeling support38separates from the base support37, e.g., by using a drum peel technique. Where test coupons20include a plurality of test structures30and test bonds40, peeling may include partially peeling the peeling support38from a structural support36to test one test bond40and partially peeling the peeling support38from the structural support36to test a different test bond40.

Applying110force may include shearing one end (e.g., a first force application region52) of the test coupon20from another end (e.g., a second force application region52), generally by applying forces50parallel to the layers22. Shearing may stress the test bond40parallel to the layer22of the test adhesive42. Shearing may fracture the test bond40along the test interface24, within the test adherend32and/or within the layer22adhered to the test adhesive42.

Methods100may include measuring112the result of applying110force. Measuring112may include classifying the failure mode of a test bond40after the force50has broken the test bond40(resulting in a split test coupon20). Classifying may include observing the bond residue on the split test coupon20, optionally observing by electronic imaging. As illustrated inFIG. 10, generally, a test bond40may fail at a laminal failure zone81, an interfacial failure zone82, and/or a cohesion failure zone83. 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 zone82, the zone at the test interface24, between the test adherend32and the test adhesive42, generally is indicative of a weak bond. Strong bonds generally result in failures at the laminal failure zone81, the zone within the (potentially laminar) test adherend32, and at the cohesion failure zone83, the zone within the test adhesive42, the structural adherend33, and/or the structural support36. In failure at the laminal failure zone81, the test bond40remains intact yet the test adherend32separates within and/or between the adherend plies. In failure at the cohesion failure zone83, the test bond30also remains intact. Instead, at least one of the test adhesive42, the structural adherend33, and the structural support36separates.

Measuring112may include quantifying the extent of failure of the test bond40after the force50has broken the test bond40(resulting in a split test coupon20). Quantifying may include observing the bond residue on the split test coupon20by 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 coupon20includes a plurality of test structures30and/or test bonds40, measuring112may include comparing the classification, fraction and/or extent of failure between at least two of the test bonds40.

The extent (the total area of failure) and the fraction of failure may be quantified by processing images80of the split test coupon20, as illustrated inFIG. 11. Image80ofFIG. 11shows the residue of three failure modes: failure at the laminal failure zone81, failure at the interfacial failure zone82, and failure at the cohesion failure zone83. Each failure zone may leave a distinctive imprint and/or residue on the split test coupon20. For example, failure at the laminal failure zone81may leave an imprint and/or residue of the plies of the test adherend32, generally a broad repeating texture. Failure at the interfacial failure zone82may leave an imprint and/or residue of surface contour of the test adherend32, e.g., when the test adherend32is prepared by peeling a peel ply, the test adherend32surface has an imprint of the removed peel ply, a tightly woven texture. Failure at the cohesion failure zone83may leave an imprint and/or residue of the test adhesive42, generally a low texture region. Image processing may distinguish these failure regions, for example by pattern recognition and/or thresholding the image80. For example,FIG. 12illustrates a classification image90where each pixel of image80is classified as part of a laminal failure region91, an interfacial failure region92, or a cohesion failure region93. 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 image90. 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 image90. Strong bonds may be classified as test bonds40where the predominant failure modes are at the laminal failure zone81and/or the cohesion failure zone83. Additionally or alternatively, strong bonds may be classified as test bonds40where the fraction of failure at the interfacial failure zone82is less than 20%, less than 10%, less than 5%, less than 2%, and/or less than 1%. Weak bonds may be classified as test bonds40where the predominant failure mode is at the interfacial failure zone82, optionally when the fraction of failure at the interfacial failure zone82is 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.

Rapid Adhesion Testing

FIG. 13is a schematic representation, in exploded view, of test systems10and test coupons20for rapid adhesion testing. Rapid adhesion testing may be useful to simply and quickly interrogate a series of test bonds40. The test coupons20comprise at least two test structures30, namely a first test structure130and a second test structure230. The first test structure130includes a first test adhesive142(a test adhesive42), a first test adherend132(a test adherend32), a first test interface124(a test interface24which is the interface between the first test adherend132and the first test adhesive142), and a first test bond140(a test bond40) to a first location126(a test region26) on a base support37. The second test structure230includes a second test adhesive242(a test adhesive42), a second test adherend232(a test adherend32), a second test interface224(a test interface24which is the interface between the second test adherend232and the second test adhesive242), and a second test bond240(a test bond40) to a second location226(a test region26) on the base support37.

The test coupons20comprise layers in the following sequence: (a) the base support37, (b) an adhesive layer22, including the first test adhesive142adjacent to the first location126and the second test adhesive242adjacent to the second location226, (c) an adherend layer22, including the first test adherend132adjacent to the first test adhesive142and the second test adherend232adjacent to the second test adhesive242, and (d) a peeling support38bonded to the first test adherend132and bonded to the second test adherend232. Further, the first test adherend132is coupled to the first location126on the base support37with the first test bond140, including the first test adhesive142, and the second test adherend232is coupled to the second location226on the base support37with the second test bond240including the second test adhesive242. Test coupons20comprise a peeling structure56, which includes the adherend layer22(layer c) and the peeling support38(layer d), and a backing structure58, which includes the base support37(layer a). Peeling structures56are 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 structures58are 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 structure130and the second test structure230are sandwiched between the base support37and the peeling support38, generally the thickness of the first test structure130and the second test structure230are approximately the same. For example, the first test adherend132and the second test adherend232may be essentially the same thickness, e.g., including the same number of plies.

The first test structure130and the second test structure230may share common components. For example, the first test adherend132and the second test adherend232may be the same test adherend32. As another example, the first test adhesive142and the second test adhesive242may be the same test adhesive42.

Test coupons20may comprise a crack starter60in the first test structure130, at the edge of the first test interface124between the first test adherend132and the first test adhesive142. Test coupons20may comprise a crack starter60in the second test structure230, at the edge of the second test interface224between the second test adherend232and the second test adhesive242. Each test structure30independently may include a crack starter60. Additionally or alternatively, the test coupon20may comprise a single crack starter60.

The first test adherend132and the second test adherend232each independently may be directly or indirectly bonded to the peeling support38(e.g., by curing the first test adherend132and/or the second test adherend232to the peeling support38, and/or by using one or more structural adhesives46).

The test coupon20is configured to peel apart along the peeling direction70. The test coupon20may be configured with test structures30spaced along the peeling direction70, as illustrated, and/or may be configured with test structures30spaced perpendicular to the peeling direction. When the test structures30are spaced along the peeling direction70, the test coupon is configured to peel the test structures30sequentially.

Test systems10may include a test fixture12which may include a drum62. The test fixture12is configured to pull the test coupon20apart between the backing structure58and the peeling structure56(generally at the first test bond140and the second test bond240). The test fixture12is configured to apply a peeling force50at an angle to the test support30, generally substantially perpendicular to the test support30layer22, at least not essentially parallel to the layers22of the test coupon20. The force application region52of the peeling structure56is coupled to the drum62. For example, the drum62may define a slot configured to accept the force application region52of the peeling structure56. Additionally or alternatively, the peeling structure56may be clamped to drum62. The test fixture12is configured such that rolling the drum62rolls the peeling structure56around the drum62and peels the test coupon20at the test structures30. Further, the test fixture12is configured to control the peeling angle by maintaining a substantially constant peeling angle. The peeling angle, and the required flexibility of the peeling structure56, substantially is determined by the diameter of the drum62. The drum62may have a diameter of at least 50 mm, at least 100 mm, at least 150 mm, and/or at least 200 mm.

Backing Rapid Adhesion Testing

FIG. 14is a schematic representation, in exploded view, of test systems10and test coupons20for backing rapid adhesion testing. Backing rapid adhesion testing may be suitable to interrogate a test bond40to a test adherend32that is rigid, e.g., too rigid to peel with the peeling support38in example 1, though test adherends32are not required to be rigid. Illustrative, non-exclusive examples of test adherends32suitable for backing rapid adhesion testing include frames, stringers, girders, and larger bonded assemblies. The test systems10and the test coupons20of this example 2 are configured to interrogate the test bond40coupled to the backing structure58rather than coupled to the peeling structure56(as is the case for example 1).

The test coupons20comprise a test structure30which includes a test adhesive42, a test adherend32, a test interface24, and a test bond40to a peeling support38. The test coupons20comprise layers in the following sequence: (a) the peeling support38, (b) the test adhesive42, (c) the test adherend32, and optionally (d) a base support37bonded to the test adherend32. Further, the test adherend32is coupled to the peeling support38with the test bond40, including the test adhesive42. The test adherend32, the base support37, and/or the combination of the two may be rigid. Test coupons20comprise the peeling structure56, which includes the peeling support38(layer a), and the backing structure58, which includes the test adherend32(layer c) and the optional base support37(layer d). The test adherend32may be directly or indirectly bonded to the base support37(e.g., by curing the test adherend32to the base support37and/or by using a structural adhesive46). Relative properties, including thicknesses, of the peeling structures56and backing structures58are the same as example 1. Test coupons20may comprise a crack starter60in the test structure30, at the edge of the test interface24, between the test adherend32and the test adhesive42.

Test systems10may include a test fixture12which may include a drum62. Generally, the test fixtures12described with respect to example 1 are suitable for backing rapid adhesion testing as well.

Double Cantilever Beam Testing

FIG. 15is a schematic representation, in exploded view, of test systems10and test coupons20for double cantilever beam testing of test structures30including test adherends32. This configuration may be suitable to interrogate a test bond40within a test structure30that includes a test adherend32(that is non-metallic) and a first peeling support138(a peeling support38).

The test coupons20comprise a test structure30which includes a test adhesive42, the test adherend32, a test interface24, and the test bond40to the first peeling support138. The test coupons20comprise layers in the following sequence: (a) the first peeling support138, (b) the test adhesive42, (c) the test adherend32, and (d) a second peeling support238(a peeling support38) bonded to the test adherend32. Further, the test adherend32is coupled to the first peeling support138with the test bond40, including the test adhesive42. Test coupons20comprise a first peeling structure156, which includes the first peeling support38(layer a), and a second peeling structure256, which includes the test adherend32(layer c) and the second peeling support238(layer d). The test adherend32may be directly or indirectly bonded to the second peeling support238(e.g., by curing the test adherend32to the second peeling support238and/or by using a structural adhesive46). First peeling structure156and second peeling structure256each 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 coupons20may comprise a peeling adherend34between the first peeling support138and the test adhesive42. The peeling adherend34may be directly or indirectly bonded to the first peeling support138(e.g., by curing the peeling adherend34to the first peeling support138and/or by using a structural adhesive46). The peeling adherend34, when present, may be substantially the same as the test adherend32. Test coupons20may comprise a crack starter60in the test structure30, at the edge of the test interface24, between the test adherend32and the test adhesive42.

Double Cantilever Beam Testing

FIG. 16is a schematic representation, in exploded view, of test systems10and test coupons20for double cantilever beam testing of thin test structures30. This configuration may be suitable to rapidly apply environmental conditions to the test structure30before bonding supports required for peel testing. For example, a thin test structure30may be wetted, aged, and/or heated faster than a thicker test structure30.

The test coupons20comprise a test structure30which includes a test adhesive42, a test adherend32, a test interface24, and a test bond40to a peeling adherend34. The test coupons20comprise layers in the following sequence: (a) a first peeling support138(a peeling support38) bonded to the peeling adherend34, (b) the peeling adherend34, (c) the test adhesive42, (d) the test adherend32, and (e) a second peeling support238(a peeling support38) bonded to the test adherend32. Further, the test adherend32is coupled to the peeling adherend34with the test bond40, including the test adhesive42. Test coupons20comprise a first peeling structure156, which includes the first peeling support138(layer a) and the peeling adherend34(layer b), and a second peeling structure256, which includes the test adherend32(layer d) and the second peeling support238(layer e). The peeling adherend34may be directly or indirectly bonded to the first peeling support138(e.g., by curing the peeling adherend34to the first peeling support138and/or by using a structural adhesive46). The test adherend32may be directly or indirectly bonded to the second peeling support238(e.g., by curing the test adherend32to the second peeling support238and/or by using a structural adhesive46). The peeling adherend34may be substantially the same as the test adherend32. Hence, the test structure30may be a substantially symmetric structure.

The test adherend32and the peeling adherend34each 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 support138may be a laminar material and may include more plies than the peeling adherend34, for example, 1.5-8 times as many plies as the peeling adherend34. The second peeling support238may be a laminar material and may include more plies than the test adherend32, for example, 1.5-8 times as many plies as the test adherend32. The total thickness of the peeling adherend34and the first peeling support138may 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 adherend32and the second peeling support238may be equivalent to at least 6 plies, at least 8 plies, at least 10 plies, and/or about 20 plies.

The test structure30may be subject to environmental conditions before bonding to the first peeling support138and the second peeling support238. After environmental conditions are applied the first peeling support138and the second peeling support238may be bonded to the test structure30such that the environmental conditioning is not substantially disturbed. For example, where temperature and/or moisture is a part of environmental conditioning, the first peeling support138and the second peeling support238may be bonded with room temperature cure structural adhesives46.

Double Cantilever Beam Testing

FIG. 17is a schematic representation, in exploded view, of test systems10and test coupons20for double cantilever beam testing of at least two test structures30within a test coupon20. This configuration may be suitable for rapidly testing a series of test bonds40and/or to compare adhesive bonding schemes. Test structures30, such as a first test structure130and a second test structure230, may share components, as discussed with respect to example 1, and/or may be subject to the same environmental conditions. Hence, the first test structure130and the second test structure230may 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 adherends32may be greatly reduced by comparing the results of testing a first test structure130and a second test structure230that share a test adherend32.

Test coupons20comprise at least two test structures30, namely a first test structure130and a second test structure230. The first test structure130includes a first test adhesive142(a test adhesive42), a first test adherend132(a test adherend32), a first test interface124(a test interface42which is the interface between the first test adherend132and the first test adhesive142), and a first test bond140(a test bond40) to a first location126(a test region26) on a peeling adherend34. The second test structure230includes a second test adhesive242(a test adhesive42), a second test adherend232(a test adherend32), a second test interface224(a test interface24which is the interface between the second test adherend232and the second test adhesive242), and a second test bond240(a test bond40) to a second location226(a test region26) on the peeling adherend34.

The test coupons20comprise layers in the following sequence: (a) a first peeling support138(a peeling support38) bonded to the peeling adherend34, (b) the peeling adherend34, (c) an adhesive layer22, including the first test adhesive142adjacent to the first location126and the second test adhesive242adjacent to the second location226, (d) an adherend layer22, including the first test adherend132adjacent to the first test adhesive142and the second test adherend232adjacent to the second test adhesive242, and (e) a second peeling support238(a peeling support38) bonded to the first test adherend132and bonded to the second test adherend232.

Further, the first test adherend132is coupled to the first location126on the peeling adherend34with the first test bond140, including the first test adhesive142, and the second test adherend232is coupled to the second location226on the peeling adherend34with the second test bond240including the second test adhesive242. Test coupons20comprise a first peeling structure156, which includes the first peeling support138(layer a) and the peeling adherend34(layer b), and a second peeling structure256, which includes the adherend layer22(layer d) and the second peeling support238(layer e). The peeling adherend34may be directly or indirectly bonded to the first peeling support138(e.g., by curing the peeling adherend34to the first peeling support138and/or by using a structural adhesive46). The first test adherend132may be directly or indirectly bonded to the second peeling support238(e.g., by curing the first test adherend132to the second peeling support238and/or by using a structural adhesive46). The second test adherend232may be directly or indirectly bonded to the second peeling support238(e.g., by curing the second test adherend232to the second peeling support238and/or by using a structural adhesive46). The peeling adherend34may be substantially the same as the first test adherend132and/or the second test adherend232. Hence, the test structure30may be a substantially symmetric structure.

Test systems10may include a test fixture12configured to apply peeling forces50at the first force application region152of the first peeling structure156and at the first force application region152of the second peeling structure256. The test fixture12may be configured to apply peeling forces50at the second force application region252of the first peeling structure156and at the second force application region252of the second peeling structure256. Additionally or alternatively, the test fixture12may be configured to allow the test coupon20to be rotated such that the first force application region152and the second force application region252are swapped with respect to the test fixture12.

Wide Area Lap Shear Testing

FIG. 18is a schematic representation of test systems10and test coupons20for wide area lap shear testing of test structures including test adherends32. This configuration may be suitable to interrogate a test bond40within a test structure30that includes a test adherend32(that is non-metallic) and a shearing adherend35. Also, this configuration may be suitable to rapidly apply environmental conditions to the test structure30before bonding supports required for shear testing. For example, a thin test structure30may be wetted, aged, and/or heated faster than a thicker test structure30.

The test coupons20comprise a test structure30which includes a test adhesive42, a test adherend32, a test interface24, and a test bond40to a shearing adherend35. The test coupons20comprise layers in the following sequence: (a) a first shearing support139(a shearing support39) bonded to the shearing adherend35, (b) the shearing adherend35, (c) the test adhesive42, (d) the test adherend32, and (e) a second shearing support239(a shearing support39) bonded to the test adherend32. Further, the test adherend32is coupled to the shearing adherend35with the test bond40, including the test adhesive42. Test coupons20comprise a first shearing structure166(a shearing structure66), which includes the first shearing support139(layer a) and the shearing adherend35(layer b), and a second shearing structure266(a shearing structure66), which includes the test adherend32(layer d) and the second shearing support239(layer e). The shearing adherend35may be directly or indirectly bonded to the first shearing support139(e.g., by curing the shearing adherend35to the first shearing support139and/or by using a structural adhesive46). The test adherend32may be directly or indirectly bonded to the second shearing support239(e.g., by curing the test adherend32to the second shearing support239and/or by using a structural adhesive46). The shearing adherend35may be substantially the same as the test adherend32. Hence, the test structure30may be a substantially symmetric structure.

The test adherend32and the shearing adherend35each 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 support139may be a laminar material and may include more plies than the shearing adherend35, for example, 1.5-8 times as many plies as the shearing adherend35. The second shearing support239may be a laminar material and may include more plies than the test adherend32, for example, 1.5-8 times as many plies as the test adherend32. The total thickness of the shearing adherend35and the first shearing support139may 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 adherend32and the second shearing support239may be equivalent to at least 6 plies, at least 8 plies, at least 10 plies, and/or about 20 plies.

The test structure30may be subject to environmental conditions before bonding to the first shearing support139and the second shearing support239. After environmental conditions are applied the first shearing support139and the second shearing support239may be bonded to the test structure30such that the environmental conditioning is not substantially disturbed. For example, where temperature and/or moisture is a part of environmental conditioning, the first shearing support139and the second shearing support239may be bonded with room temperature cure structural adhesives46.

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.

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.

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.

A32.5. 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.

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.

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.

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.

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.

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.

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.

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.

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, anda 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, anda 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.

C50.1. 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.

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.

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.

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, anda 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.

D28.7. 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.