Method of enhancing electromagnetic conductivity in a structural joint assembly

Abstract

To provide an economical CFRP fastening system design method for enhancing EME conductivity.SOLUTION: A method of enhancing EME conductivity between a fastener and at least two structural elements secured thereby after assembly of the fastener and the structural elements. One of the structural elements is formed from a carbon fiber reinforced plastic layer. One method includes the steps of a) forming a first hole through a first structural element and a second hole through a second structural element, each of the holes being formed to be aligned with one another, b) melting and applying an electrically conductive gap filler to sidewalls of the holes, c) passing a fastener shank portion through the first and second holes to complete the installation assembly, and d) applying heat to the fastener and gap filler after assembly to remelt and reflow the gap filler. Another method includes applying a conductive coating to the shank portion instead of applying a gap filler to the hole sidewall.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to methods for increasing electromagnetic energy (EME) conductivity in structural joint assemblies, and more particularly to methods for creating fastening systems with enhanced EME conductivity.

[0002] A method for enhancing EME conductivity in a fastening system utilizing metal fasteners inserted into two or more structural elements, at least one of which is made of a composite material such as carbon fiber reinforced plastic ("CFRP"), is disclosed. The fasteners are used to secure the structural elements together in a manner designed to enhance EME conductivity between the fasteners and the carbon fibers in the CFRP. [Background technology]

[0003] Lightweight composite materials such as CFRP are routinely used in major structural components of modern commercial aircraft, offering significant advantages in strength and durability compared to traditional metal alloys.

[0004] Furthermore, composites tend to be lighter than traditional metal alloys, which can result in fuel savings and lower operating costs. In addition to these properties, composites are more resistant to corrosion and fatigue than traditional metal alloys.

[0005] CFRP contains a material matrix with a plastic resin that acts to bond fibrous materials, such as carbon fiber, together. Structural elements formed from such a matrix are manufactured in layers. The layers are secured together with metal fasteners to form a CFRP laminate. The fasteners are inserted into holes punched, reamed, or otherwise formed through the layers.

[0006] Fasteners formed from aluminum alloys containing titanium may be rivets, bolts or pins and often include a mating part such as a nut or collar.

[0007] Metal fasteners are known to be electrically conductive, making electromagnetic energy (EME) management a consideration for aircraft. Because electrical current flows through structural joints in aircraft, structural elements containing fasteners must have adequate current paths, so fasteners must be able to withstand lightning strikes. CFRP materials are known to be more resistant to EME flow than traditional metal alloys because only the carbon fibers within the CFRP matrix are electrically conductive. Furthermore, drilling holes to install fasteners within CFRP materials increases the existing material resistance due to rough surface pits and protrusions on the sidewalls of the holes created by drilling. The pits on the sidewalls can introduce gaps between the holes and the fasteners, creating undesirable discontinuities in the flow of electrical current between the mating surfaces of the metal fasteners and the CFRP material.

[0008] As a result, when a CFRP assembly containing metal fasteners is struck by lightning, poor electrical conductivity between the CFRP material and the associated fasteners can prevent current flow, causing a momentary increase in current density and potentially heat spikes and thermal decomposition in the surrounding CFRP material. This can result in a phenomenon known as hot particle emission (HPE), in which particles can be expelled from the affected structure, including the fasteners. As a result, aircraft structures must be designed to contain and manage lightning strikes, HPE, and its associated effects.

[0009] A common solution has been to actively manage the interference fit to increase the level of contact between the fastener and the carbon fiber, however, such solutions often come at a significant cost. Summary of the Invention [Problem to be solved by the invention]

[0010] Therefore, it is desirable to provide a more economical method for designing CFRP fastening systems to suitably solve the problem of EME conductivity. [Means for solving the problem]

[0011] In one aspect, a method is disclosed for increasing EME conductivity between a fastener and at least two structural elements secured together by the fastener after assembly of the fastener and the structural elements. The fastener includes a shank, and at least one of the structural elements is also formed from carbon fiber reinforced plastic. The method includes the steps of: a) forming a first hole (32) through a first structural element and a second hole (42) through a second structural element, each hole aligned with the other; b) applying a conductive gap filler to a sidewall of each of the holes; c) installing a shank portion of the fastener through the first and second holes to complete the assembly; and d) applying heat to the fastener and the conductive gap filler after assembly to remelt and reflow the conductive gap filler.

[0012] In another aspect, a method is disclosed for increasing EME conductivity between a fastener and at least two structural elements secured together by the fastener after assembly of the fastener and the structural elements. The fastener includes a shank, and at least one of the structural elements is also formed from carbon fiber reinforced plastic. The method includes: a) forming a first hole through a first structural element and a second hole through a second structural element, each hole aligned with the other and each hole defining a sidewall; b) applying a conductive coating to the shank portion of the fastener to form a coated shank portion; c) installing the coated shank portion of the fastener through the first and second holes to complete the assembly; and d) applying heat to the fastener after assembly sufficient to remelt and reflow the conductive coating.

[0013] In yet another aspect, a method is disclosed for increasing EME conductivity between a fastener and at least two structural elements secured together by the fastener after assembly of the fastener and the structural elements. The fastener includes a shank, and at least one of the structural elements is also formed from carbon fiber reinforced plastic. The fastener also includes a cylindrical sleeve having an inner surface portion frictionally secured to the shank. The method includes: a) forming a first hole through a first structural element and a second hole through a second element, each hole aligned with the other and each hole defining a sidewall; b) applying a conductive coating to the outer surface portion of the sleeve; c) installing the sleeve and shank portions of the fastener through the first and second holes to complete the assembly; and d) applying heat to the fastener after assembly sufficient to remelt and reflow the conductive coating.

[0014] Further aspects and advantages of the methods disclosed herein, which are effective in increasing electrical conductivity by reducing voids in conductive gap fillers and / or coatings applied between fasteners and structural elements after the latter components are assembled together, can be further appreciated through the examples and further examples provided herein and will be better understood with reference to the following description and drawings. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is an elevational view of an exemplary fastener that may be used in accordance with the methods of the present disclosure. [Figure 2] 1 is a cross-sectional view of a pair of layers shown prior to fastening that may be fastened together to form a laminate according to the method of the present disclosure. [Figure 3] 3 is a cross-sectional view of the pair of layers of FIG. 2 shown after being fastened together with the fastener of FIG. 1 having a conductive gap filler material applied in accordance with the method of the present disclosure. [Figure 4]4 is a cross-sectional view of the pair of layers of FIG. 3 shown after being fastened together with the fastener of FIG. 1 having a conductive gap filler material applied thereto in accordance with the method of the present disclosure and a nut or collar applied to the fastener. [Figure 5] 1 is a flowchart illustrating one of the disclosed methods. [Figure 6] 1 is an alternative embodiment of a fastener constructed in accordance with the method of the present disclosure. [Figure 7] 10 is a second flowchart illustrating another disclosed method. [Figure 8] 10A-10C illustrate another alternative embodiment of a fastener constructed in accordance with the method of the present disclosure. [Figure 9] 10 is a third flowchart illustrating yet another method of the disclosure. [Figure 10] 10A-10C illustrate another alternative embodiment of a fastener constructed in accordance with the method of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0016] 1 illustrates an exemplary fastener 10 suitable for use in at least one method of the present disclosure for increasing the EME conductivity of aircraft and / or other structural elements fastened together by the fastener. Fastener 10 has a head 12, a shank portion 14, and a threaded end 16. Head 12 defines a first or top end 18 and a second or bottom end 20.

[0017] Fastener 10 may be constructed of a metallic material such as titanium, stainless steel, aluminum, and combinations or alloys thereof. A nut 60 (FIG. 4) including internal threads (not shown) fits onto threaded end 16 (FIG. 1) and cooperates with head 12 to secure at least one pair of structural elements 30, 40 together, as described below.

[0018] As used herein, the term "fastener" 10 includes, but is not limited to, any type of bolt, pin, rivet, and / or any other suitable device for fastening structural elements together. The term nut 60 includes any internally threaded nut, which may be described as a "mating part" that can engage with fastener 10. While fastener 10 is shown and disclosed in FIG. 1 as a rivet that includes a threaded end for engaging nut 60, the concepts disclosed herein may be applicable in other situations, such as when fastener 10 may comprise a bolt or pin, and the mating part may include a collar, whether crimped or not, that engages with the threaded end 16 of the pin.

[0019] Referring now primarily to FIG. 2 , a completed structural assembly 70 ( FIG. 4 ) begins by stacking two or more structural elements 30 and 40 ( FIG. 2 ) together to create a so-called parallel-ply stack 28. The first structural element 30, typically presenting an outward-facing surface, is disclosed herein as a composite ply. Thus, the composite ply is formed from a carbon fiber reinforced plastic (CFRP) material, a matrix material such as a plastic resin 36, and a plurality of carbon fibers 38 supported by and extending through the matrix material. Other composite materials, such as thermosetting polymer resins, e.g., epoxies, may be used in place of the plastic resin. The carbon fibers 38 of the CFRP can be replaced with other types of electrically conductive materials, as would be understood by one skilled in the art.

[0020] Such structural assemblies 70 (FIG. 4) are often formed from CFRP laminates or CFRP-metal hybrid laminates. The various assemblies 70 have applications in a wide range of industries, including the formation of aircraft structures such as side-fuselage joints, wing structures, and fuselage components, as well as other applications not limited to aircraft structures.

[0021] 2, the second structural element may also be a composite material, such as a CFRP layer 30, but may also be a metallic material layer 40 formed from aluminum, titanium, or an alloy of these metals. In the disclosed example of FIG. 2, the laminate 28 includes only two structural layers 30 and 40. It should be understood that layers 30 and 40 may be supplemented with additional layers of CFRP material and / or metallic material.

[0022] As shown in Figure 2, each layer 30 and 40 has at least one hole formed therein. A first hole 32 is formed through layer 30 and is a composite hole having a tapered portion 32a that receives the tapered head 12 (Figure 1) of fastener 10 and a straight cylindrical portion 32b that houses the shank portion 14 of the fastener. A second hole 42 is cylindrical and is formed through metal layer 40. The hole may be drilled, reamed, or otherwise formed through layers 30, 40 after they are combined to form laminate 28, or may be pre-drilled through the layers prior to combining them.

[0023] First hole 32 and second hole 42 are aligned when layers 30 and 40 are placed together to assemble them. Each of the holes is defined by a roughened sidewall 34 that may be produced by a drilling or reaming process, and although shown roughened in FIG. 2, may optionally be formed as a smooth surface on sidewall 34 of hole 42 in metal layer 40.

[0024] The roughened sidewalls 34 defining the holes 32 in the CFRP layer 30 present an irregular surface including depressions 44 and jagged edges 46 that facilitate the application of a conductive gap filler material between the fastener and the hole, as described below.

[0025] As will be appreciated by those skilled in the art, the actual diameter of each hole 32, 42 will depend on the composition of the conductive gap filler used to form the structural assembly 70 (FIG. 4), as well as the dimensions, including the thickness, of the assembly, and the shape of the fasteners used. Also, while this disclosure refers to only one pair of aligned holes 32, 42, it should be understood that any given structural assembly 70 may include multiple such holes, depending on the size and shape of the particular assembly 70, and may receive the level of fastening desired for any given application.

[0026] Method using conductive gap filler 3 and 4, one method of forming the assembly 70 includes applying a conductive material, referred to herein as a conductive gap filler (CGF) 50. As is apparent from both FIGS. 3 and 4, the CGF 50 is disposed between the fastener 10 and the holes 32, 42 of the laminate 28. Thus, the CGF 50 is applied to the holes prior to insertion of the fastener 10. As will be appreciated by those skilled in the art, the CGF 50 can enhance EME conductivity between the carbon fibers 38 of the CFRP and the fastener 10. In the disclosed method applicable to this embodiment, the CGF 50 is applied to the entire circumferential sidewall 34 of each hole 32, 42. Furthermore, in a structural assembly 70 having only two layers, one formed of CFRP and the other formed of metal, such as the example disclosed herein, the CGF 50 may more optimally be applied only to the roughened sidewalls 34 of the CFRP holes.

[0027] CGF 50 is ideally formed from a low melting point alloy ("LMA") composed of elements compatible with the desired application, e.g., aircraft components. As used herein, the term LMA is applicable to alloys having a melting temperature greater than about 140°F and less than about 400°F, preferably in the range of about 170°F to about 400°F. LMAs suitable for use with structural assembly 70 include alloys of two or more of the following elements: indium, bismuth, tin, nickel, and zinc (e.g., Indalloy, manufactured by Indium Corporation). A suitable LMA is a ternary alloy of a mixture of bismuth (preferably greater than 50%), indium, and tin. Due to its softness, LMA can function as a solid lubricant, making fastener 10 easier to insert with less insertion force but still with a suitable interference fit, depending on the fastener shank size and hole diameter.

[0028] Alternatively, instead of using an LMA, the CGF 50 may be made of a pure metal, such as 100% pure indium, or the LMA may be made of any conductive alloy material that has EME conductivity equal to or greater than that of the carbon fibers 38 in the CFRP material. The CGF 50 is ideally deposited within the recesses 44 in the sidewalls 34 of the holes 32, 42 to form a smooth, conductive surface. Thus, the thickness of the CGF applied to the sidewalls 34 effectively reduces the physical diameter of the holes 32, 42.

[0029] The CGF 50 may be applied to the sidewalls 34 of the holes 32, 42 as a paste, for example, by grinding, or as a liquid by pouring, and / or by any other method known in the art.

[0030] Referring now specifically to FIG. 4 , a completed structural assembly 70 in which the fastener 10 is fully installed may also include a nut 60 secured to its threaded end 16. Of course, the fastener 10 is installed within the mating hole 32, 42 after the hole has been coated with the CGF 50. According to this particular method, the fastener 10 is inserted into the hole with the shank 14 engaging the CGF at a predetermined clearance, as shown, so that the threaded end 16 extends beyond the bottom end 54 of the second structural element 40. A nut 60 can then be attached to the fastener's threaded end 16. Thus, the layers 30 and 40 are secured together via the head and nut, which hold the shank in tension, the tension being provided by the torque engagement of the nut 60 against the bottom end 54.

[0031] Figure 5 is a flow chart illustrating a method 300 for increasing EME conductivity between a fastener 10 and a pair of structural elements 30 and 40 after assembly of these components, in accordance with the description of Figures 1-4. The fastener includes a shank portion 14 and secures the pair of structural elements together. At least one of the pair of structural elements, e.g., "30," is formed from carbon fiber reinforced plastic. The method 300 includes: a) 310: forming a first hole 32 through a first structural element 30 and a second hole 42 through a second structural element 40, each hole aligned with the other and defining a sidewall 34; b) 320: melting a conductive gap filler 50 and applying the molten conductive gap filler to the sidewall 34 of each of the holes 32, 42 (see FIG. 4 ); c) 330: installing a fastener shank portion 14 through the first and second holes to complete assembly; and d) 340: applying heat to the fastener 70 and the conductive gap filler 50 after assembly to remelt and reflow the conductive gap filler 50. The method 300 reduces and / or minimizes voids and discontinuities in the conductive gap filler, thereby effectively increasing EME conductivity. Heat may be generated and / or applied via any suitable heating source, including, by way of example, induction, such as by use of an induction coil applied directly to the fastener, a heat gun, resistance, etc. As will be appreciated by those skilled in the art, heat may also be applied robotically through the use of an end effector.

[0032] Proof-of-principle example We have begun a process to measure the increase in EME conductivity obtained by remelting and reflowing a conductive gap filler compared to conventional use of the same conductive gap filler (wherein the post-apply remelting and reflow process of the present disclosure was not performed).

[0033] For this purpose, a carbon fiber reinforced plastic (CFRP) composite was formed having dimensions of approximately 6 inches by 6 inches and a thickness of 0.2 inches.

[0034] A 0.252" diameter hole was drilled through the center of the composite. A conductive gap filler was applied to the sidewalls of the hole, and an aircraft fastener having part number B3NR4 with a 0.250" shank diameter was then installed into the hole.

[0035] To obtain conductivity measurements, adhesive conductive foil was attached to the edge of the composite for use as an electrical lead. For measurements, a Fluke Multimeter Model 87V was attached to the foil after the fastener was installed in the hole. The measured resistance was 9.9 ohms.

[0036] To accomplish the remelt and reflow process, a 2500 watt ZVS induction heater coil was applied to the fastener until it reached a temperature of 193°C. After cooling for 30 minutes, the measured resistance was 5.8 ohms, thus representing a decrease of 4.1 ohms.

[0037] Method using conductive coating Another method for obtaining improved EME performance utilizes an alternative fastener embodiment, namely fastener 80 of FIG. 6, to enhance electrical conductivity between the fastener and the carbon fibers 38 within the CFRP layer 30. In this case, instead of a CGF being applied as in the first-described method, a conductive coating 90 is applied to the circumferential head portion 82 and shank portion 84 of the fastener 80, respectively. The conductive coating 90 can be remelted after fastener insertion to provide the same level of enhanced EME conductivity between the fastener and the carbon fibers as achieved using the CGF method.

[0038] Conductive coating 90 can be an LMA having a melting temperature range of 140°F to 400°F. One example of such an LMA is a tin-zinc-bismuth alloy composed of approximately 65% ​​tin, 32-33% zinc, and 2-3% bismuth. A non-LMA example of conductive coating 90 is 100% pure indium, which has a melting temperature of 313°F.

[0039] The conductive coating 90 may be applied to the fastener 80 to obtain a uniform thickness, ideally less than the entire fastener 80, such as only around the circumferential shank 84 and a circumferential portion of the head 82. Application of the coating 90 may be by spraying in liquid form or by otherwise melting and applying by any other means known to those skilled in the art. The thickness of the conductive coating 90 may be determined based on factors such as the applied coating composition and the size and geometry of the structural assembly 70.

[0040] The conductive coating 90 has a melting temperature that is lower than any maximum temperature that the CFRP in the structural assembly 70 is expected to experience during aircraft operation as well as any finish curing processes.

[0041] FIG. 7 is a flowchart illustrating a method 400 for increasing EME conductivity between the coated fastener 80 (FIG. 6) described above, including the shank portion 84, and a pair of structural elements 30, 40 (FIG. 2) after assembly of these components, in accordance with the description of FIG. 6, the method including attaching the fastener to the pair of structural elements, at least one of which is formed from carbon fiber reinforced plastic. The method 400 includes the steps of: a) 410: forming a first hole 32 through a first structural element 30 and a second hole 42 through a second structural element 40, each hole aligned with the other and each hole defining a sidewall 34; b) 420: melting and applying a conductive coating 90 to a shank portion 84 of a fastener to form a coated shank portion 88; c) 430: installing the coated shank portion 88 of the fastener 80 through the first and second holes to complete assembly; and d) 440: applying heat to the fastener 80 after assembly sufficient to remelt and reflow the conductive coating 90. This method is effective in reducing voids and discontinuities in the melted conductive coating 90, thereby increasing EME conductivity.

[0042] How to use sleeved fasteners In the method examples described above, fasteners 10 and 80 were sleeveless fasteners. Other types of fasteners 80 may also be used in the methods of the present disclosure. For example, FIG. 8 shows a sleeved fastener 100, in which a sleeve 110 frictionally engages the shank portion 104 of the fastener. Electrical conductivity between the sleeve and shank portion may be effectively ensured by an interference fit between the inner surface of the sleeve and the outer surface of the shank. However, in this case, the outer surface of the sleeve 110 may be treated with the same conductive coating 90 as described above with reference to fastener 80. Alternatively, a conductive gap filler 50 may be applied to the sidewall of the hole into which the sleeved fastener 100 will be installed, similar to the approach described above with reference to fastener 10. However, in the example of FIG. 8, optimal results would be achieved if both the outer tapered head portion 112 of the sleeve 110 and the outer shank portion 114 of the sleeve 110 were provided with a conductive coating. Alternatively, a conductive gap filler could be used.

[0043] Figure 9 is a flow chart illustrating yet another method 500 for increasing EME conductivity between the above-described sleeved fastener 100 (Figure 8) including sleeve 110 and a pair of structural elements 30, 40 (Figure 2) after assembly of these components, consistent with the description of Figure 8. Method 500 further includes attaching the fastener to the pair of structural elements, at least one of which is formed from carbon fiber reinforced plastic. The method includes the steps of: a) forming 510 a first hole 32 through a first structural element 30 and a second hole 42 through a second structural element 40, each hole aligned with the other and defining a sidewall 34; b) 520 melting and applying a conductive coating 90 to the outer surface portions 112 and 114 of a sleeve 110; c) 530 attaching coated sleeve portions through the first and second holes to complete assembly of all components; and d) 540 applying heat to the fastener 100 after assembly sufficient to remelt and reflow the conductive coating 90. Method 500, like methods 300 and 400 described above, can be effective in reducing voids and discontinuities in the remelted and reflowed conductive coating 90 between the sleeve 110 and the sidewall 34, which can enhance EME conductivity.

[0044] How to Use Blind Fasteners Finally, with reference to FIG. 10, a blind fastener 200, commonly known as a one-sided fastener, is another type of fastener that may be suitable for use in the conductive fastener assembly 70 (FIG. 4). Blind fasteners, as shown, include a head 202 and a shank portion 204 and are most often used in structural elements formed from two thin layers. Thus, such fasteners can be inserted into holes 32, 42 of the structural assembly 70 to engage the assembly from only one side, without needing to access the other side of the assembly, as would be required to secure a nut or collar to the end of a fastener having a threaded end.

[0045] The blind fastener may also be constructed from the types of metallic materials described above, including titanium, stainless steel, aluminum, and alloys thereof. The outer circumferential surface of the tapered head 202 and the shank portion 204 may be treated with a conductive coating, as described above. Alternatively, a conductive gap filler may be applied to the sidewalls of the hole into which the blind fastener will be installed, as also described above.

[0046] While various methods have been disclosed for using conductive gap fillers and / or conductive coatings to enhance the EME properties of fasteners 10, 80, 100, and 200 used to secure multiple layers, at least one of which comprises a CFRP material, modifications of the disclosed methods may occur to those skilled in the art. Accordingly, the present disclosure, including any such modifications, is herein limited only by the appended claims.

[0047] Terms Clause 1. A method of increasing EME conductivity between a fastener and at least two structural elements secured together by the fastener after assembly of the fastener and the structural elements, wherein at least one of the structural elements is formed from carbon fiber reinforced plastic and the fastener includes a shank portion, the method comprising: a) forming a first hole through a first structural element and a second hole through a second structural element, each of the first hole and the second hole defining a sidewall; b) applying a molten conductive gap filler to the sidewalls of each of the holes; c) installing a shank portion of a fastener through the first hole and the second hole to complete the assembly; d) after assembly, applying heat to the fastener and conductive gap filler to remelt and reflow the conductive gap filler; A method comprising:

[0048] Clause 2. The method of clause 1, wherein at least one of the structural elements formed from carbon fiber reinforced plastic is a matrix composed of carbon fiber and plastic resin.

[0049] Clause 3. The method of clause 1 or 2, wherein the conductive gap filler is applied to the sidewall as a heated paste that hardens into a solid mass upon cooling.

[0050] Clause 4. The method of any one of clauses 1 to 3, wherein the conductive gap filler is a conductive metal comprising a combination of indium, tin, and zinc.

[0051] Clause 5. The method of any one of clauses 1 to 4, wherein the fastener includes a shank portion, a head, and a threaded end, the shank portion extending between and integral with the head and the threaded end, and a nut engaging the threaded end, whereby the fastener secures at least two structural elements together with the head and nut holding the shank portion in tension.

[0052] Clause 6. The method of any one of clauses 1 to 5, wherein the first hole and the second hole are pre-formed.

[0053] Clause 7. The method of any one of clauses 1 to 6, wherein the structural element comprises parallel layers.

[0054] Clause 8. The method of any one of clauses 1 to 7, wherein the conductive gap filler is a conductive metal comprising 100% indium.

[0055] Clause 9. A method of increasing EME conductivity between a fastener and at least two structural elements secured together by the fastener after assembly of the fastener and the structural elements, wherein at least one of the structural elements is formed from carbon fiber reinforced plastic and the fastener includes a shank portion, the method comprising: a) forming a first hole through a first structural element and a second hole through a second structural element, each of the first hole and the second hole defining a sidewall; b) melting and applying a conductive coating to the shank portion of the fastener to form a coated shank portion; c) installing the coated shank portion of the fastener through the first hole and the second hole to complete the assembly; d) applying sufficient heat to the fastener after assembly to remelt and reflow the conductive coating; A method comprising:

[0056] Clause 10. The method of clause 9, wherein at least one of the structural elements formed from carbon fiber reinforced plastic is a matrix composed of carbon fiber and plastic resin.

[0057] Clause 11. The method of clause 9 or 10, wherein heat is applied by induction applied directly to the fastener.

[0058] Clause 12. The method of any one of clauses 9 to 11, wherein the conductive coating is formed from a conductive metal comprising a combination of indium, tin, and zinc.

[0059] Clause 13. The method of any one of clauses 9 to 12, wherein the fastener includes a shank portion, a head, and a threaded end, the shank portion extending between and integral with the head and the threaded end, and a nut engaging the threaded end, whereby the fastener secures at least two structural elements together with the head and nut holding the shank portion in tension.

[0060] Clause 14. The method of any one of clauses 9 to 13, wherein the structural element comprises parallel layers.

[0061] Clause 15. The method of any one of clauses 9 to 14, wherein the first hole and the second hole are pre-formed.

[0062] Clause 16. A method of increasing EME conductivity between a fastener and at least two structural elements secured together by the fastener after assembly of the fastener and the structural elements, wherein at least one of the structural elements is formed from carbon fiber reinforced plastic, the fastener has a shank portion, and the fastener also includes a cylindrical sleeve having an inner surface portion frictionally secured to the shank, the method comprising: a) forming a first hole through a first structural element and a second hole through a second structural element, each of the first hole and the second hole defining a sidewall; b) melting and applying a conductive coating to an exterior surface portion of the sleeve; c) installing a sleeve and shank portion of the fastener through the first and second holes to complete the assembly; d) applying sufficient heat to the fastener (10) after assembly to remelt and reflow the conductive coating; A method comprising:

[0063] Clause 17. The method of clause 16, wherein the coating is applied to the sleeve as a liquid that hardens into a solid mass upon cooling.

[0064] Clause 18. The method according to clause 16 or 17, wherein the structural element comprises parallel layers.

[0065] Clause 19. The method of any one of clauses 16 to 18, wherein heat is applied by induction applied directly to the fastener.

[0066] Clause 20. The method of any one of clauses 16 to 19, wherein the conductive coating is a metal containing 100% indium. [Explanation of symbols]

[0067] 10 Fasteners 12 heads 14 Shank part, shank 16 Threaded Ends 18 First or Apical End 20 Second or bottom edge 28 Laminate 30 (first) structural element, CFRP layer, structural layer 32 (first) hole 32a Tapered section 32b Cylindrical part 34 Side wall 36 Plastic Resin 38 Carbon Fiber 40 (Second) structural element, metal material layer, structural layer 42 (Second) hole 44 depression 46 Jagged Edge 50 Conductive Gap Filler 54 Bottom end 60 nuts 70 Structural assemblies, fastening assemblies 80 Fasteners 82 Head part, head 84 Shank part, shank 88 Coated shank 90 Conductive Coating 100 Sleeved Fasteners 104 Shank part 110 Sleeve 112 External tapered head portion, outer surface portion 114 outer shank part, outer surface part 200 Blind Fasteners 202 head 204 Shank part 300 ways 400 ways 500 ways

Claims

1. 1. A method for increasing EME conductivity between a fastener (10) and at least two structural elements (30, 40) secured together by the fastener (10) after assembly of the fastener and the structural elements (70), wherein at least one of the structural elements is formed from carbon fiber reinforced plastic (38), the fastener (10) includes a shank portion (14), the method comprising: a) forming a first hole (32) through a first structural element and a second hole (42) through a second structural element, each of said first hole (32) and said second hole (42) defining a sidewall (34); b) applying a molten conductive gap filler (50) to the sidewalls (34) of each of the holes (32, 42); c) installing the shank portion (14) of the fastener (10) through the first hole (32) and the second hole (42) to complete the assembly; d) applying heat to the fastener (10) and the conductive gap filler (50) after assembly to remelt and reflow the conductive gap filler (50); A method comprising:

2. 10. The method of claim 1, wherein said at least one of said at least two structural elements formed from carbon fiber reinforced plastic (30) is a matrix comprised of carbon fiber (38) and plastic resin.

3. The method of claim 1, wherein the conductive gap filler (50) is applied to the sidewall (34) as a heated paste that hardens into a solid mass upon cooling.

4. The method of claim 1, wherein the conductive gap filler (50) is a conductive metal comprising a combination of indium, tin, and zinc.

5. 2. The method of claim 1, wherein the fastener (10) includes a shank portion (14), a head (12), and a threaded end (16), the shank portion (14) extending between and integral with the head (12) and the threaded end (16), and a nut (60) engaging the threaded end (16), whereby the fastener (10) secures the at least two structural elements (30, 40) together with the head (12) and the nut (60) holding the shank portion (14) in tension.

6. The method of claim 1, wherein the first hole (32) and the second hole (42) are pre-formed.

7. The method of claim 1 , wherein the structural elements (30, 40) comprise parallel layers (28).

8. The method of claim 1, wherein the conductive gap filler (50) is a conductive metal containing 100% indium.

9. 1. A method for increasing EME conductivity between a fastener (10) and at least two structural elements (30, 40) secured together by the fastener (10) after assembly of the fastener (10) and the structural elements (30, 40), wherein at least one of the structural elements is formed from carbon fiber reinforced plastic (30), the fastener (10) includes a shank portion (14), the method comprising: a) forming a first hole (32) through a first structural element and a second hole (42) through a second structural element, each of said first hole (32) and said second hole (42) defining a sidewall (34); b) melting and applying a conductive coating (90) to the shank portion (14) of the fastener (10) to form a coated shank portion (88); c) installing the coated shank portion (88) of the fastener (10) through the first hole (32) and the second hole (42) to complete the assembly; d) applying sufficient heat to the fastener after assembly to remelt and reflow the conductive coating (90); A method comprising:

10. 10. The method of claim 9, wherein said at least one of said at least two structural elements formed from carbon fiber reinforced plastic (30) is a matrix composed of carbon fiber (38) and plastic resin.

11. 10. The method of claim 9, wherein heat is applied by induction applied directly to the fastener (10).

12. The method of claim 9, wherein the conductive coating (90) is formed from a conductive metal comprising a combination of indium, tin, and zinc.

13. 10. The method of claim 9, wherein the fastener (10) includes a shank portion (14), a head (12), and a threaded end (16), the shank portion (14) extending between and integral with the head (12) and the threaded end (16), and a nut (60) engaging the threaded end (16), whereby the fastener (10) secures the at least two structural elements (30, 40) together with the head (12) and the nut (60) holding the shank portion (14) in tension.

14. The method of claim 9, wherein the structural elements (30, 40) comprise parallel layers (28).

15. 10. The method of claim 9, wherein the first hole (32) and the second hole (42) are pre-formed.

16. 1. A method for increasing EME conductivity between a fastener (10) and at least two structural elements (30, 40) secured together by the fastener (10) after assembly of the fastener and the structural elements (70), wherein at least one of the structural elements is formed from carbon fiber reinforced plastic (30), the fastener (10) has a shank portion (14), and the fastener (10) also includes a cylindrical sleeve (110) having an inner surface portion frictionally secured to the shank portion (14), the method comprising: a) forming a first hole (32) through a first structural element (30) and a second hole (42) through a second structural element (40), each of said first hole (32) and said second hole (42) defining a sidewall (34); b) melting and applying a conductive coating (90) to the outer surface portion of the sleeve (110); c) installing the sleeve (110) and the shank portion (114) of the fastener (10) through the first hole (32) and the second hole (42) to complete the assembly; d) applying sufficient heat to the fastener (10) after assembly to remelt and reflow the conductive coating (90); A method comprising:

17. The method of claim 16, wherein the coating (90) is applied to the sleeve (110) as a liquid that hardens into a solid mass upon cooling.

18. The method of claim 16, wherein the structural elements (30, 40) comprise parallel layers (28).

19. 17. The method of claim 16, wherein heat is applied by induction applied directly to the fastener (10).

20. The method of claim 16, wherein the conductive coating (90) is a metal containing 100% indium.

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