Apparatus and Method for an Electrically Conductive Coating Fastening System

Abstract

The present application discloses a conductive coating fastening system. The device includes a fastening system and a structural assembly. The structural assembly includes a first structural element and a second structural element made of conductive fiber-reinforced plastic. The first structural element includes a first hole and the second structural element includes a second hole. Before assembly of the structural assembly, the first hole and the second hole are separately pre-formed. The structural assembly further includes a conductive gap filler applied to the sidewall of the first structural element of the first hole. The fastening system includes a fastener, which includes a head and a shank extending from the head. The shank is configured to be inserted into the first hole and the second hole.

Description

Technical Field

[0001] The present disclosure relates to a conductive coated fastening system for full size determinant assembly (FSDA). Background Art

[0002] Many aircraft structures are constructed of lightweight composite materials, such as carbon fiber reinforced plastics (CFRP), because they are stronger and lighter than conventional metal alloys. The weight savings provided by these lightweight materials reduces fuel consumption and operating costs. Additionally, composite materials are more corrosion resistant and fatigue resistant than conventional metal alloys. CFRP includes a matrix material (usually a resin) and a fiber material (such as carbon fiber). CFRP structural elements can be fastened to other CFRP, metal, or metal alloy structural elements. The structural elements are held together by metal fasteners inserted through holes formed in the structural elements. The fasteners typically include bolts or pins and mating parts such as nuts or collars.

[0003] Conventional assembly and fastening methods are both expensive and time consuming. Specifically, conventional structural assembly processes are time consuming because they require the parts in a component to be stacked and aligned twice - one alignment for drilling the holes, and then again for installing the fasteners. This is because after matching the drilled holes in the aligned stack of parts, the parts must be disassembled so that they can be cleaned and deburred before making the joint seal. The parts are then put back together a second time so that the fasteners can be inserted and secured with washers, nuts, and / or collars. Additionally, these assembly methods may require expensive and time consuming tools and alignment equipment, which increases the time and cost of the production process.

[0004] Accordingly, it may be desirable to utilize a more efficient assembly process, such as full size determinant assembly (FSDA) to reduce production time and expense. In FSDA, the holes in each part are drilled individually before the parts are stacked together. However, it may be difficult to utilize FSDA with composite parts while still providing sufficient electromagnetic effect (EME) protection against lightning strikes. Specifically, during a lightning strike, the fasteners provide a path for the current to flow through the structural joint. Because CFRP is brittle, drilling through CFRP causes the CFRP to locally break at the edges of the holes. These non-uniform hole sidewalls create gaps between some of the carbon fibers in the CFRP and the fasteners, thereby restricting the current path between the CFRP and the fasteners. FSDA may further restrict these current paths because it may cause the holes in the stacked parts to be misaligned. These misaligned holes may further restrict the contact between the CFRP and the fastener shanks.

[0005] Accordingly, there is a desire to provide a fastening system for composite structures that overcomes EME problems and provides installation and production efficiency. Summary of the Invention

[0006] Apparatuses and methods for a conductive coated fastening system are disclosed. For example, an apparatus includes a fastening system and a structural assembly. The structural assembly includes a first structural element and a second structural element made of a conductive fiber reinforced plastic. The conductive fibers in the conductive fiber reinforced plastic include a conductive material such as carbon, metal, or metal alloy. The first structural element includes a first hole and the second structural element includes a second hole. The first hole and the second hole are separately pre-formed and at least a portion of the first hole and the second hole are misaligned prior to assembling the structural assembly. The structural assembly also includes a conductive gap filler applied to a first structural element sidewall of the first hole of the first structural element. The fastening system includes a fastener that includes a head and a shank extending from the head. The shank is configured to be inserted into the first hole and the second hole. In some examples, the fastener includes a conductive coating.

[0007] As another example, a method for assembling and fastening a first structural element and a second structural element including a conductive fiber reinforced plastic includes: using full-size deterministic assembly (FSDA) to assemble the first structural element and the second structural element; and fastening the first structural element and the second structural element by inserting a fastener into overlapping holes of the first structural element and the second structural element, wherein at least one of the overlapping holes is pre-formed and at least one of the overlapping holes is coated with a conductive gap filler prior to assembling the first structural element and the second structural element. In some examples, the assembling further includes pre-forming the overlapping holes and pre-coating a first structural element hole of the overlapping holes of the first structural element. In some examples, the method additionally or alternatively includes coating the fastener with a conductive coating. Brief Description of the Drawings

[0008] Figure 1 is a cross-sectional schematic view of a conductive fastening system according to the present disclosure that fastens a structural assembly including two aircraft components assembled using full-size deterministic assembly (FSDA).

[0009] Figure 2 is of the Figure 1 structural assembly prior to being fastened by the fastening system.

[0010] Figure 3A is of the Figure 1 structural assembly in a first condition.

[0011] Figure 3B is of the Figure 1 structural assembly in a second condition.

[0012] Figure 3C is in the third condition Figure 1 Top schematic view of the overlapping holes of the structural components of

[0013] Figure 4 is Figure 1 Cross-sectional view of a first exemplary fastener of the fastening system of

[0014] Figure 5 is Figure 1 Cross-sectional view of a second exemplary fastener of the fastening system of

[0015] Figure 6 is Figure 1 Cross-sectional view of a third exemplary fastener of the fastening system of

[0016] Figure 7 is a flowchart schematically showing a method for using FSDA to assemble at least two aircraft structural components and fasten the assembled structural components through a fastening system.

[0017] Figure 8 is a flowchart of an aircraft production and service method.

[0018] Figure 9 is a block diagram of an aircraft. Detailed Description

[0019] The present invention discloses devices and methods for a conductive coated fastening system for full-scale deterministic assembly (FSDA). Generally, in the figures, elements that may be included in a given example are shown with solid lines, while elements that are optional for a given example are shown with dashed lines. However, the elements shown with solid lines are not essential for all examples of the present disclosure, and the elements shown with solid lines may be omitted from a particular example without departing from the scope of the present disclosure.

[0020] As Figure 1 schematically shown in, aircraft components (e.g., a first structural element 16 and a second structural element 18) can be assembled into a structural component 12 (e.g., a fuel tank joint, a body side joint, a wing joint, a fuselage joint, a main fitting, etc.) using FSDA, and then fixed to each other using a fastening system 10. As will be discussed in more detail below, FSDA includes: pre-forming (e.g., pre-drilling) holes in different structural elements respectively (e.g., at remote geographical locations, at different times, at different locations within the same geographical area, etc.), and then once the holes are formed, putting the structural elements together and assembling them (e.g., aligning, stacking, and fastening) to form a structural component. Since the holes of at least two structural elements are drilled separately, the holes may not be perfectly aligned when assembling the structural elements, as Figure 2As shown. Additionally, drilling holes in the conductive fiber reinforced plastic structural element will make the edges of the structural element jagged and uneven. Therefore, a conductive gap filler (CGF) 24 is applied to the holes of the conductive fiber reinforced plastic structural element and / or a conductive coating 32 is applied to the fasteners. Coating the fasteners and / or the holes with a conductive layer increases the surface area contact between the fasteners and the side walls of the holes in the structural element, thereby providing a greater current path for charge flow. Additionally, when the structural component is made of conductive fiber reinforced plastic, as described herein, coating the holes with CGF 24 fills the rough surfaces of the holes and electrically connects the exposed ends of the conductive fibers. Dispersing the current in this way minimizes the peak component temperature and thus reduces the likelihood that these components will act as an ignition source. By providing this ignition protection and electromagnetic effect (EME) protection, even temperature-sensitive components such as fuel tank components can use cost-saving FSDA. The FSDA in turn significantly reduces the time and cost of producing / manufacturing these structural assemblies. Therefore, the combination of FSDA and conductive coated holes can reduce production costs and time without sacrificing safety.

[0021] As Figure 1 shown, the apparatus 8 includes a structural assembly 12 and a fastening system 10. The structural assembly 12 includes at least two structural elements (e.g., a first structural element 16 and a second structural element 18), and the at least two structural elements are fastened to each other via the fastening system 10. The structural assembly 12 can be a fitting and / or a joint, such as one or more of the following: a fuel tank joint, a wing joint, a fuselage joint, a body side joint, and a main fitting. In Figure 1 an example, the at least two structural elements include two structural elements, namely a first structural element 16 and a second structural element 18. However, in other examples, the structural assembly 12 includes more than two structural elements, such as three, four, five, six, seven, or eight or more structural components, which are fastened together by the fastening system 10. Thus, in some such examples, FSDA is used to pre-form, stack, and assemble more than two components, and then they are fastened to each other using conductive coated fasteners and / or conductive filled holes.

[0022] The first structural element 16 includes components of an aircraft part (e.g., a fuel tank, a wing, a fuselage, etc.), including one or more of the following: a fuel tank component, a wing component (e.g., a wing spar, an outer wing skin, a wing panel, a front trunnion, a drag strut, an engine support fitting, a rear wing fitting, etc.), and a fuselage component. At least one of the first structural element 16 and the second structural element 18 is made of a conductive fiber-reinforced plastic. In one such example, the first structural element 16 is made of a conductive fiber-reinforced plastic. In another such example, the second structural element 18 is made of a conductive fiber-reinforced plastic. In yet another such example, both the first structural element 16 and the second structural element 18 are made of a conductive fiber-reinforced plastic.

[0023] In some examples, the conductive fiber-reinforced plastic is constructed only of carbon fiber-reinforced plastic (CFRP). In some such examples, the CFRP includes CFRP layers that include a matrix material and a plurality of carbon fibers extending through the matrix material. In further such instances, the matrix material includes one or more thermoplastic resins (such as polypropylene, polyethylene, and nylon) or thermosetting resins (such as epoxy resin). In other examples, the conductive fiber-reinforced plastic includes different types of conductive fibers other than carbon fibers, such as one or more metal fibers. In still other examples, the structural element including the conductive fiber-reinforced plastic is constructed of CFRP and one or more additional metallic materials (including one or more of aluminum and titanium).

[0024] At least a portion of the second structural element 18 is positioned adjacent to the first structural element 16 such that at least a portion of the first structural element 16 and the second structural element 18 are in direct physical contact with each other. Due to their proximity, in some examples, the first structural element 16 and the second structural element 18 include components of the same aircraft part (e.g., both structural elements can be components of a fuel tank). However, in other examples, the first structural element 16 and the second structural element 18 include components of different but adjacent aircraft parts (e.g., a wing and a fuel tank, a wing and an engine, a wing and a fuselage, etc.), and in some such examples, the first structural element 16 and the second structural element 18 are fastened to each other to couple the different aircraft parts. The first structural element 16 and the second structural element 18 together form a structural assembly 12.

[0025] In some examples, the second structural element 18 is constructed of the same material as the first structural element 16. As one such example, both the first structural element 16 and the second structural element 18 are constructed of CFRP. In other examples, the second structural element 18 is constructed of a material different from that of the first structural element 16. As one such example, one of the structural elements (the first structural element 16 or the second structural element 18) is constructed of a conductive fiber-reinforced plastic and the other is constructed of a metal alloy. As another example, both structural elements are constructed of conductive fiber-reinforced plastics but include different types of conductive fiber-reinforced plastics. As yet another example, the two structural elements are constructed of the same and / or different conductive fiber-reinforced plastics, but one of the structural elements additionally includes other conductive fibers.

[0026] According to the FSDA, prior to assembling the structural elements into the structural assembly 12, holes are pre-formed (e.g., pre-drilled, pre-molded, pre-reamed, or otherwise pre-formed) in the first structural element 16 and the second structural element 18. Specifically, the first structural element hole 48 is drilled, molded, reamed, or otherwise formed into the first structural element 16, and the second structural element hole 50 is drilled, molded, reamed, or otherwise formed into the second structural element 18, although only one hole of each of the first structural element hole 48 and the second structural element hole 50 is shown in Figure 1-3C , but in other examples, the first structural element 16 and the second structural element 18 include multiple first structural element holes 48 and second structural element holes 50. In some such examples, the number of the first structural element holes 48 and the second structural element holes 50 included in the first structural element 16 and the second structural element 18 depends on the size and shape of the structural assembly 12 and the desired level of fastening for a particular application.

[0027] Drilling and / or forming the first structural element hole 48 and the second structural element hole 50 may make the edges of the structural element in which the holes are located (i.e., the sidewalls of the holes) uneven, undulating, rough, irregular, serrated, etc., especially when the first structural element 16 and the second structural element 18 include conductive fiber-reinforced plastics. In Figure 1-2 's example, the first structural element 16 includes a first structural element sidewall 22 that is irregular and / or not smooth (e.g., serrated, undulating, rough, etc.) and includes a plurality of gaps on its uneven surface. In examples where the second structural element 18 includes conductive fiber-reinforced plastics, the second structural element 18 also includes a similarly irregular and / or not smooth second structural element sidewall 41. However, it should be understood that in other examples, such as in cases where one of the first structural element 16 or the second structural element 18 includes a metal alloy instead of a fiber-reinforced plastic, the sidewalls of the non-plastic structural element are less irregular and are much smoother than Figure 1 depicted.

[0028] To fill the gaps created by these undulating surfaces on the sidewalls of the holes in a structural element comprising a conductive fiber reinforced plastic and to form a smoother surface that is more conductive, CGF 24 is applied to the sidewalls of the structural elements of a first structural element 16 and a second structural element 18 that comprise a conductive fiber reinforced plastic. At least one of the first structural element 16 and the second structural element 18 comprises a conductive fiber reinforced plastic. In some examples, only one of the first structural element 16 or the second structural element 18 comprises a conductive fiber reinforced plastic. In such examples, where one of the first structural element 16 or the second structural element 18 comprises only a metal or a metal alloy, CGF 24 is not applied to the sidewalls of the non-plastic structural element. In such examples, CGF 24 is applied only to the structural element that comprises a conductive fiber reinforced plastic. However, in other examples, both the first structural element 16 and the second structural element 18 comprise a conductive fiber reinforced plastic, and the sidewalls of the holes in the first structural element 16 and the second structural element 18 are both coated with CGF 24. CGF 24 is applied to one or more of the first structural element sidewall 22 and the second structural element sidewall 41 by one or more of grinding, injecting, and spraying.

[0029] In one example, CGF 24 is frictionally or mechanically abraded against one or more of the sidewalls 22 of the first structural element and the sidewalls 41 of the second structural element at room temperature. In one such abrasion method, the abrasion is accomplished using an apparatus that includes: a support structure; a bearing supported by the support structure; a spindle rotatably supported by the bearing; an electric motor mechanically coupled to the spindle for driving rotation of the spindle; a chuck coupled to the spindle; and a hole coating applicator that includes a shaft made of a material that is not a low melting alloy (LMA) and clamped by the chuck, and an LMA pad supported by the shaft and radially movable relative to the shaft. In some such coating apparatuses, the hole coating applicator further includes a flexure element configured to bend relative to the shaft due to flexure of a flexure hinge, and the LMA pad is attached to the flexure element. In other such abrasion apparatuses, the hole coating applicator further includes: a cam surface; a cam block that carries the LMA pad and has an inclined surface that contacts the cam surface; and a spring that applies an axial spring force on the cam block, wherein when the axial spring force is applied on the cam block, the cam surface deflects the cam block to move radially outward. Other methods and apparatuses for abrading CGF 24 onto one or more of the sidewalls 22 of the first structural element and the sidewalls 41 of the second structural element are described in co-owned U.S. Patent Application No. 15 / 923,630, titled "METHOD, APPARATUS AND APPLICATOR FOR APPLYING A COATING ON A SURFACE OF A LAMINATION", the disclosure of which is incorporated herein by reference in its entirety.

[0030] In another example, the CGF 24 is heated to a molten state and the molten CGF 24 is applied to one or more of the sidewalls 22 of the first structural element and the sidewalls 41 of the second structural element, alternatively the CGF 24 is applied to one or more of the sidewalls 22 of the first structural element and the sidewalls 41 of the second structural element. In some such examples, any suitable method known in the art is used to inject the molten CGF 24 into one or more of the sidewalls 22 of the first structural element and the sidewalls 41 of the second structural element. As one such example, the CGF 24 is heated to a temperature corresponding to the lowest melting point of the CGF 24 (i.e., the "eutectic melt temperature") to cause the CGF 24 to be in a molten state. Then a nozzle having an internal channel system is inserted into the hole 48 of the first structural element and / or the hole 50 of the second structural element. A narrow gap separates the sidewalls 22 of the first structural element and the sidewalls 41 of the second structural element from the nozzle. Then the nozzle is withdrawn from the hole 48 of the first structural element and / or the hole 50 of the second structural element. As the nozzle is withdrawn, the molten CGF 24 is forced into and through the internal channel system and out of the circular circumferential orifices of the nozzle, and is injected into the gap separating the nozzle so as to coat the sidewalls 22 of the first structural element and the sidewalls 41 of the second structural element with the molten CGF 24. When the molten CGF 24 solidifies, the resulting CGF-coated hole will have a diameter defined by the outer diameter of the nozzle. However, the thickness of the LMA applied to the sidewalls of the hole will reduce the diameter of the hole, preferably by no more than about 0.0005 inches. Other methods and apparatus for injecting molten LMA into the sidewalls 22 of the first structural element and the sidewalls 41 of the second structural element are described in the co-owned U.S. patent application Ser. No. 15 / 786,665, titled "APPARATUS AND METHODS FOR INJECTING FILLER MATERIAL INTO A HOLE IN A COMPOSITE LAYER", the disclosure of which is incorporated herein by reference in its entirety.

[0031] In yet another example, CGF 24 is applied to one or more of the sidewalls 22 of the first structural element and the sidewalls 41 of the second structural element by spraying the CGF 24 onto one or more of the sidewalls 22 of the first structural element and the sidewalls 41 of the second structural element. In some such examples, the CGF 24 is a pure metal, preferably nickel or zinc. Suitable spraying methods include, but are not limited to, cold spraying (also known as supersonic particle deposition or gas dynamic cold spraying) and thermal spraying (e.g., plasma spraying). In an embodiment using cold spraying, nickel in the form of fine powder is accelerated to a very high speed by a carrier gas and forced through a nozzle onto the sidewalls 22 of the first structural element and the sidewalls 41 of the second structural element. Upon impact, the nickel particles plastically deform and mechanically bond to the sidewalls 22 of the first structural element and the sidewalls 41 of the second structural element to form a coating. The thickness of the CGF 24 depends on various factors, such as the type of metal used and the spraying method. Generally, however, the thickness of the CGF 24 applied to the sidewalls of the hole will reduce the diameter of the hole by no more than about 0.0005 inches.

[0032] To ensure that a sufficient amount of CGF 24 is applied to one or more of the sidewalls 22 of the first structural element and the sidewalls 41 of the second structural element, in some examples, a real-time monitoring system is employed to verify that the contact resistance is within an acceptable range. As one such example, the monitoring system utilizes a capacitive coupling to measure the effective resistance of the CGF 24 and the random parallel resistance of the carbon fibers in the CFRP layers in the structural assembly 12 in series. A feedback loop is used to control the CGF application process and confirm its completion to a satisfactory resistance level based on the response of the monitoring system. By applying CGF 24 in the hole to form a coating while measuring the effective resistance of the carbon fibers and the CGF 24 in series, and then stopping the application of CGF 24 when a specified effective resistance is achieved, in the final structural assembly 12, at least a minimum acceptable conductivity can be achieved at the interface of the holes 48 in the first structural element and the holes 50 in the second structural element with the inserted fasteners. In some such examples, the resistance level of the CGF 24 is within a threshold resistance level that depends on factors such as the thickness of the structural assembly 12 and the size and geometry of the inserted fasteners. Other methods and apparatuses for verifying that the contact resistance is within an acceptable range are described in the above-mentioned co-owned U.S. Patent Application No. 15 / 923,630 and co-owned U.S. Patent Application No. 15 / 923,436 titled "SYSTEMS AND METHODS FOR MEASURING THE ELECTRICAL CONTACT RESISTANCE AT AN INTERFACE", the disclosures of which are incorporated herein by reference in their entirety.

[0033] InFigure 1 In the example, both the first structural element 16 and the second structural element 18 include a conductive fiber-reinforced plastic and are thus coated with CGF 24. However, as described above, in other examples, only one of the first structural element 16 or the second structural element 18 includes a conductive fiber-reinforced plastic and is coated with CGF 24. The CGF 24 substantially fills the gaps formed by the serrated edges of one or more of the first structural element sidewalls 22 and the second structural element sidewalls 41 (thereby covering the first structural element sidewalls 22 and the second structural element sidewalls 41), forms a first structural element hole sidewall 35 on the first structural element hole 48 of the first structural element 16, and forms a second structural element hole sidewall 37 on the second structural element hole 50 of the second structural element 18, thereby providing a smoother, flatter, and more conductive surface on the first structural element sidewalls 22 and the second structural element sidewalls 41 of the first structural element hole 48 and the second structural element hole 50 of the first structural element 16 and the second structural element 18, respectively. Thus, for the CGF 24, the first structural element hole 48 and the second structural element hole 50 are defined by the CGF 24 that forms a substantially flat and smooth surface. Therefore, after being coated with CGF 24, the first structural element 16 includes a first structural element hole sidewall 35 (which covers the first structural element sidewall 22 and defines the first structural element hole 48), and the second structural element 18 includes a second structural element hole sidewall 37 (which covers the second structural element sidewall 41 and defines the second structural hole 50). In this way, the CGF 24 forms the first structural element hole sidewall 35 and the second structural element hole sidewall 37, and the first structural element hole sidewall 35 and the second structural element hole sidewall 37 in turn define the first structural element hole 48 and the second structural element hole 50 of the first structural element 16 and the second structural element 18, respectively. That is, within the first structural element hole 48 and the second structural element hole 50, the first structural element hole sidewall 35 and the second structural element hole sidewall 37 are the outer surfaces of the first structural element 16 and the second structural element 18 coated with CGF, respectively. For the CGF 24, the first structural element hole sidewall 35 and the second structural element hole sidewall 37 are flat and smooth.

[0034] CGF 24 is constructed from an LMA and consists of components that are compatible with all cross-functional requirements of the desired application, such as an aircraft fuel tank environment. As used herein, the term "LMA" is defined as an alloy having a melting temperature in the range of greater than about 140 degrees Fahrenheit (°F) (60 degrees Celsius (°C)) and less than about 400 °F (204 °C). In some such examples, the melting temperature of the LMA is in the range between about 140 °F (60 °C) and about 400 °F (204 °C). When the carbon fiber is the conductive fiber of the corresponding first structural element 16 or second structural element 18, the LMA is constructed from a conductive material having an electrical conductivity equal to or greater than that of the carbon fiber. In one such example, the LMA is constructed from two or more of the following elements: bismuth, indium, tin, nickel, and zinc (e.g., ). In another such example, the LMA is a ternary alloy consisting of a mixture of bismuth (preferably greater than 50%), indium, and tin. Due to its softness, the properties of the LMA act like a solid lubricant, which makes the insertion of the fastener 30 easier while requiring less insertion force. In other examples, instead of the LMA, the CGF 24 alternatively includes a pure metal, such as tin.

[0035] After the first structural element hole 48 and the second structural element hole 50 have been formed (e.g., drilled), and the first structural element sidewall 22 and the second structural element sidewall 41 have been coated with CGF 24, the first structural element 16 and the second structural element 18 are aligned and assembled according to the FSDA procedure (described in more detail below with reference to Figure 7 ). Figure 2 A schematic view of the first structural element hole 48 and the second structural element hole 50 is shown after the first structural element 16 and the second structural element 18 have been aligned and assembled, but before they have been fastened by the fastening system 10. As discussed above, and as shown in the examples of Figure 1 and Figure 2 , because the first structural element hole 48 and the second structural element hole 50 are drilled separately, in the FSDA, when the first structural element 16 and the second structural element 18 are assembled to form the structural assembly 12, they are not always aligned with each other. Therefore, as shown in the exemplary misalignment conditions of Figure 1 and Figure 2 , the first structural element hole 48 and the second structural element hole 50 are not aligned. Specifically, the first structural element hole sidewall 35 of the first structural element hole 48 and the second structural element hole sidewall 37 of the second structural element hole 50 are not aligned with each other. Instead, the first structural element hole sidewall 35 and the second structural element hole sidewall 37 are not aligned, and thus, as shown in the cross-sectional views of Figure 1 and Figure 2 , the first structural element hole sidewall 35 and the second structural element hole sidewall 37 are offset from each other. Figure 3A-3CAn additional condition is shown where at least a portion of the first structural element hole sidewall 35 and the second structural element hole sidewall 37 are misaligned. However, in other examples, the holes do align. For example, when the first structural element 16 and the second structural element 18 include multiple holes, some of the holes align and others do not.

[0036] In some examples, such as Figure 1 and Figure 2 the example shown, the first structural element hole 48 and the second structural element hole 50 are circular or substantially circular and include substantially the same dimensions (i.e., the same diameter and depth). However, in other examples, the first structural element hole 48 and the second structural element hole 50 include different sizes and / or dimensions. As one such example, the first structural element hole 48 and the second structural element hole 50 include different diameters. As another such example, the first structural element hole 48 and the second structural element hole 50 include different depths. As yet another such example, the first structural element hole 48 and the second structural element hole 50 include different diameters and different depths. In additional examples, the first structural element hole 48 and the second structural element hole 50 additionally or alternatively include different shapes (e.g., oval versus circular, rectangular versus circular, triangular, circular, etc.), profiles (e.g., tapered versus straight), cross-sections, etc.

[0037] As Figure 1 and Figure 2 the example shows, the first structural element hole sidewall 35 and the second structural element hole sidewall 37 are substantially straight and have no taper. However, in other examples, the first structural element hole sidewall 35 and the second structural element hole sidewall 37 include different shapes, such as being tapered. In one such example, the first structural element hole sidewall 35 of the first structural element hole 48 (specifically, the top of the first structural element hole 48) tapers in an outward direction to allow the fastener 30 to sink into the top of the first structural element 16.

[0038] Return Figure 1 , which shows a schematic representation of the fastening system 10 and how it fastens the structural assembly 12 to secure the first structural element 16 and the second structural element 18 together once the first structural element 16 and the second structural element 18 have been assembled together in accordance with the FSDA. The fastening system 10 includes a fastener 30, which in some examples includes a conductive coating 32, and the fastener 30 includes a fastener head 38 and a shank 40.

[0039] The fastener 30 is constructed of a metallic material including, but not limited to, one or more of combinations of titanium, stainless steel, aluminum, and their alloys. The size of the fastener 30 depends on the number of structural elements stacked in the structural assembly 12, the thickness of the structural elements, the type of fastener, and the diameters of the first structural element hole 48 and the second structural element hole 50 of the structural elements. In some examples (e.g., Figure 4 the example shown), the fastener includes a non-sleeved fastener (i.e., a solid shank fastener). In other examples (e.g., Figure 5 and Figure 6 the examples shown), the fastener 30 includes a sleeved fastener that includes a solid shank and a sleeve.

[0040] In some examples, a conductive coating 32 is applied to the outer surface 33 of the fastener 30 and includes a conductive material. Specifically, when the fastener 30 includes a non-sleeved (i.e., solid shank) fastener, the conductive coating 32 is applied to the fastener. In such examples, when the fastener 30 is in a clearance fit with one or more of the first structural element hole 48 and the second structural element hole 50, the conductive coating 32 is applied to ensure sufficient current flow between the fastener 30 and the first structural element 16 and the second structural element 18. In some examples, the conductive coating 32 is also applied when the fastener is a single-sided fastener. However, in other examples, such as when the fastener is a sleeved fastener, the conductive coating 32 is not applied to the fastener 30.

[0041] A method and apparatus for coating the fastener 30 with a conductive coating are described in co-owned U.S. Patent Application No. 16 / 693,613, titled "METHOD FOR PLATING AMETALLIC MATERIAL ONTO A TITANIUM SUBSTRATE," and U.S. Patent Application No. 16 / 242,115, titled "CONDUCTIVE FASTENING SYSTEMAND METHOD FOR IMPROVED EME PERFORMANCE," the disclosures of which are incorporated herein by reference in their entirety.

[0042] In some examples, the conductive coating 32 is applied to the entire outer surface 33 of the fastener 30 such that the entire fastener 30 is covered in the conductive coating 32 (i.e., the fastener 30 is encapsulated by the conductive coating 32). However, in other examples, the conductive coating 32 is applied only to a portion of the outer surface 33. As one such example, as Figure 1As shown, the conductive coating 32 is applied only to the shank 40. In further such examples, the conductive coating 32 is applied only to a portion of the shank 40.

[0043] In some examples, the conductive coating 32 is applied with a uniform thickness. The thickness of the conductive coating 32 ranges from 0.0001 inches (0.003 mm) to 0.0006 inches (0.02 mm) and is determined based on a number of factors such as coating composition, the size and geometry of the structural component 12, and the desired application of the structural component 12. By providing a sacrificial layer in a manner similar to cadmium plating, the conductive coating 32 enhances conductivity, provides lubricity, and helps mitigate corrosion.

[0044] The melting temperature of the conductive coating 32 is greater than the highest temperature expected to be experienced by the CFRP in the structural component 12 during use (e.g., operation of an aircraft) and during the final curing process. Thus, the conductive coating 32 will not melt or soften during use or during the final curing process of the CFRP. The conductive coating 32 is made of one or more of tin, zinc, indium, bismuth, or combinations and alloys thereof. One example is that the conductive coating 32 consists of 100% indium or consists essentially of indium. Another example is a tin - zinc - bismuth alloy consisting of approximately 65% tin and approximately 32 - 33% zinc (the remainder including bismuth). Bismuth does not react with either titanium or CFRP, which helps extend the service life of the fastener 30. Additionally, the melting temperature of bismuth is greater than 180°F, and during use (e.g., operation of an aircraft), or during the final curing process of the CFRP, bismuth will not melt or soften during typical use of the structural component 12. In tin - based coatings, bismuth also helps prevent or retard tin pest, i.e., the low - temperature transformation of tin to a brittle phase. In some examples, solid additives (such as PTFE or boron nitride) that aid in lubrication in the structural component 12 containing CFRP are added to the conductive coating 32. The tin - zinc - bismuth alloy is soft, thus providing a low shear strength to facilitate insertion of the shank 40 of the fastener 30 into the first structural element hole 48 and the second structural element hole 50. The tin - zinc - bismuth alloy also has high conductivity and provides a tight electrical contact between the fastener 30 and the first structural element hole sidewall 35 and the second structural element hole sidewall 37 of the first structural element hole 48 and the second structural element hole 50, respectively. In other examples, the conductive coating 32 is alternatively made of a tin - bismuth alloy (without any zinc) or an indium - based alloy (such as tin - indium or zinc - indium), which are soft and electrically compatible with aluminum.

[0045] Apply a conductive coating 32 to the fastener 30 using one or more of vacuum deposition, electroplating, and thermal spraying. In one embodiment, the conductive coating 32 is sprayed onto the fastener 30 as a liquid. In another example, the conductive coating 32 is applied by immersing the fastener 30 in a volume of the liquid conductive coating 32. In some such examples, multiple applications of the conductive coating 32 are applied to the fastener 30 to achieve a desired thickness of the conductive coating 32. For example, the fastener 30 is repeatedly immersed in the volume of the liquid conductive coating 32 to form a coating having a desired thickness that is substantially uniform along the length of the shank 40. Although alternative methods for applying the conductive coating 32 are described herein as being applied to a single fastener 30, in other examples, the conductive coating 32 is applied to dozens or hundreds of fasteners 30.

[0046] In some examples, the conductive coating 32 also receives a conversion treatment (e.g., phosphate conversion or chromate conversion) on all or only a portion of the fastener 30 (e.g., only applied to the fastener head 38 of the fastener 30) to promote paint adhesion. Alternatively, instead of the conversion treatment, a sol treatment is performed on all or only a portion of the fastener 30 prior to painting. The term "sol" (an abbreviation for solution-gelation) refers to a series of reactions in which a soluble metal substance (usually a metal alkoxide or metal salt) hydrolyzes to form a metal hydroxide. Additionally, a lubricating coating consisting of a lubricant (such as cetyl alcohol) may also be applied over the conductive coating to a thickness of less than about 0.0002 inches and preferably less than about 0.0001 inches.

[0047] In examples where the fastener 30 includes a single-sided fastener, in some examples, the conductive coating 32 is applied to the core bolt, the sleeve, or both in the same manner as described above with respect to the non-sleeved fastener. In some such examples, the conductive coating 32 is applied to the inner surface and / or outer surface of the sleeve and covers the entire sleeve or only a portion of the sleeve.

[0048] In some examples, an adhesion layer (not shown) is deposited on the fastener 30 prior to applying the conductive coating 32 to increase the adhesion of the conductive coating 32 to the fastener 30. As one such example, a nickel strike is employed as the adhesion layer. In other such examples, a copper or iron strike is used. The adhesion layer is applied by one or more of a vacuum deposition process, electroplating, or by any other process known in the art suitable for applying an adhesion layer.

[0049] Because the conductive coating 32 is applied on the outer surface 33 of the fastener 30, it covers the portion of the fastener 30 on which the conductive coating is applied.

[0050] The fastener 30 is inserted into the first structural element hole 48 and the second structural element hole 50 to fix the first structural element 16 and the second structural element 18. Specifically, the shank 40 extends into the first structural element hole 48 and the second structural element hole 50, and in some examples, extends all the way through them. As Figure 1 shown, the shank 40 is first inserted through the first structural element hole 48 of the first structural element 16 such that the fastener head 38 of the fastener 30 protrudes from the first structural element 16. Specifically, in Figure 1 the example, the shank 40 includes a straight cylindrical shape, and the fastener head 38 includes a cylindrical shape with a diameter larger than that of the shank 40 and the first structural element hole 48, such that the fastener head 38 remains outside the first structural element hole 48 and the second structural element hole 50 on the outer surface of the first structural element 16. However, in other examples, the shank 40 and / or the fastener head 38 include other shapes and / or dimensions.

[0051] As just one alternative example, the portion of the shank 40 adjacent to the mating portion 42 forms a tapered introduction section that tapers linearly towards the mating portion 42 with a taper angle equal to or less than 20 degrees. In another example, the fastener head 38 of the fastener 30 is tapered and also extends into the first structural element hole 48 (i.e., the fastener head 38 sinks into the first structural element 16). In some such examples where the fastener head 38 sinks, the fastener head 38 extends all the way into the first structural element hole 48 so that it does not protrude from the surface of the first structural element 16. The sunk head can be used for aircraft skins so that the fasteners do not protrude from the outer surface of the aircraft.

[0052] As another example, the shank 40 is not straight, but is one or more of curved, angled, bent, helical, etc.

[0053] In some examples, when the first structural element hole sidewall 35 of the first structural element hole 48 and the second structural element hole sidewall 37 of the second structural element hole 50 are not aligned, the fastener 30 forms a clearance fit with one or more of the first structural element hole 48 and the second structural element hole 50. That is, although the fastener 30 does physically contact at least a portion of the first structural element 16 and the second structural element 18, in some examples, the fastener 30 does not contact all surfaces of the first structural element hole sidewall 35 and the second structural element hole sidewall 37, and thus one or more voids or clearances are formed between the fastener 30 and the first structural element hole sidewall 35 and the second structural element hole sidewall 37 of the first structural element hole 48 and the second structural element hole 50. In some such examples, such as in Figure 1In the example shown, a first gap 62 is formed between the outer surface 33 of the fastener and the first structural element hole sidewall 35 of the first structural element hole 48. Additionally or alternatively, a second gap 64 is formed between the outer surface 33 of the fastener and the second structural element hole sidewall 37 of the second structural element hole 50. It should be understood that, for illustrative purposes, the first gap 62 and the second gap 64 are exaggerated in Figure 1 such that they can be seen more easily. However, in other examples, the first gap 62 and the second gap 64 can be significantly smaller.

[0054] In the first gap 62 and the second gap 64, the fastener 30 (and in particular the outer surface 33 of the fastener 30) does not directly contact or physically contact the first structural element hole sidewall 35 of the first structural element hole 48 and the second structural element hole sidewall 37 of the second structural element hole 50 of the first and second structural elements 16 and 18, respectively. Thus, in some such examples, only air is present in the first gap 62 and the second gap 64. Figure 3A-3C Other exemplary clearance fit conditions are shown.

[0055] However, in Figure 1 example, a portion of the fastener 30 does directly physically contact the first structural element hole sidewall 35 and the second structural element hole sidewall 37. Specifically, in Figure 1 as shown in Figure 1 the left side of the fastener 30 directly physically contacts the first structural element hole sidewall 35, and the right side of the fastener 30 directly contacts the second structural element hole sidewall. Thus, this physical contact between the fastener 30 and the structural elements (the first structural element 16 and the second structural element 18) creates a current path for current between them. An exemplary current path 70 is shown in Figure 1 to show how current flows between the fastener 30 and two exemplary structural elements (the first structural element 16 and the second structural element 18). Specifically, current can flow between the conductive fibers in the structural elements (the first structural element 16 and the second structural element 18) and the fastener 30 via the CGF 24 in the region where the CGF 24 physically contacts the handle 40.

[0056] In some examples, the fastener 30 is sized to be smaller than the first structural element hole 48 and the second structural element hole 50. However, in other examples, the fastener 30 is sized to be equal to or larger than the size of one of the first structural element hole 48 and the second structural element hole 50. In such examples, there is only one of the first gap 62 or the second gap 64. In still other examples, the shank 40 is sized to be as large (having the same diameter) as the first structural element hole 48 and the second structural element hole 50, or larger than both of them (having a larger diameter), but is still at least partially fitted into the two holes because the conductive coating 32 on the fastener and / or the CGF 24 of the first structural element sidewall 22 and the second structural element sidewall 41 are soft enough to deform and allow the over-sized shank 40 to enter.

[0057] However, even in such examples where there are gaps 62 and / or 64 respectively between the fastener 30 and the first structural element hole sidewall 35 and the second structural element hole sidewall 37, the conductive coating 32 and the CGF 24 act together to provide a more continuous electrical connection between the fastener 30 and the first structural element 16 and the second structural element 18 in the regions where the fastener 30 does contact the first structural element hole sidewall 35 and the second structural element hole sidewall 37 of the first structural element 16 and the second structural element 18. Specifically, due to their high electrical conductivity and because they provide a smoother and flatter surface that increases the surface area contact between the fastener 30 and the first structural element hole sidewall 35 and the second structural element hole sidewall 37 of the first structural element 16 and the second structural element 18, the conductive coating 32 and the CGF 24 increase the electrical conductivity between the fastener 30 and the first structural element 16 and the second structural element 18.

[0058] In this way, the conductive coating 32 and the CGF 24 provide sufficient EME protection to enable the use of a cheaper and more time-saving FSDA without sacrificing safety. Additionally, the conductive coating 32 prevents wear during the insertion of the fastener 30. The conductive coating 32 also aids in lubrication by providing a smooth surface to reduce the force required to insert the fastener 30 into the first structural element hole 48 and the second structural element hole 50, thereby providing manufacturing efficiency and reducing the likelihood of damaging the structural assembly 12 during the insertion of the fastener 30, while not hindering or degrading the EME performance.

[0059] In some examples, the end of the shank 40 that defines the first end 52 of the fastener 30 extends all the way through the first structural element hole 48 and the second structural element hole 50 and protrudes beyond the second structural element 18 on the other side of the structural assembly 12 (as Figure 1As shown). In some such examples, the fastening system 10 includes a fastener mating element 46 on a side of the structural component 12 opposite the fastener head 38 of the fastener 30. The fastener mating element 46 mates with a portion of the shank 40 that projects from the second structural element 18 and secures (i.e., compresses) the first structural element 16 and the second structural element 18.

[0060] The fastener 30 includes one or more of a bolt, a pin, and a rivet. Correspondingly, the fastener mating element 46 includes one or more of an internally threaded nut or collar and a swaged collar that mates with the particular type of fastener 30 being used. As an example, such as Figure 1 shown, the fastener 30 includes a bolt, wherein at least a portion of the shank 40 includes a threaded mating portion 42 that extends from the first end 52 toward the fastener head 38 of the fastener 30. In some such examples, the fastener mating element 46 includes a nut having an internal thread (not shown), wherein the internal thread of the nut mates with the thread 44 of the threaded mating portion 42 of the shank 40. Thus, the nut is screwed onto the end of the shank 40. In some such examples, a washer 47 is also included between the fastener mating element 46 and the second structural element 18 to distribute the compressive force applied by the fastener mating element 46. However, in other examples, the fastener mating element 46 includes a non-threaded collar that is swaged onto the mating portion 42 of the fastener 30.

[0061] In other examples, the fastener 30 includes a single-sided fastener or a one-sided fastener that does not require a fastener mating element 46. As the name implies, a one-sided fastener is installed and secured from only one side of the structural component 12 and does not require any operation on the other side of the structural component 12. Thus, in examples where the fastener 30 includes a one-sided fastener, the fastening system 10 does not include a fastener mating element 46. One-sided fasteners are particularly suitable for applications where it is difficult or impossible to access one side of the structural component 12.

[0062] During installation, in some examples, the fastener 30 is hammered into the first structural element hole 48 and the second structural element hole 50 using a manual rivet gun or an automated system. In other examples, a robotic system is used to install the fastener 30 by inserting and hammering the fastener 30 into the first structural element hole 48 and the second structural element hole 50, and another robot or person attaches the fastener mating element 46 to the mating portion 42 from the other side of the structural component 12. When using a single-sided fastener, the single-sided fastener is installed into the first structural element hole 48 and the second structural element hole 50 in the structural component 12 using methods known in the art.

[0063] Now turning to Figure 3A-6 illustrates illustrative non-exclusive examples of the fastener 30 and the structural component 12. Where appropriate, Figure 1-2The reference numerals in the schematic diagrams are used to denote Figure 3A-6 the corresponding parts of the examples of Figure 3A-6 However, the examples of Figure 3A-6 are non-exclusive and do not limit the fastener 30 or the structural component 12 to Figure 3A-6 the illustrated embodiments. That is, the fastener 30 and the structural component 12 are not limited to Figure 1-2 the specific embodiments, and the fastener 30 and the structural component 12 can incorporate any number of various aspects, configurations, features, characteristics, etc. of the fastener 30 and the structural component 12, which are shown in Figure 3A-6 the schematic diagrams and / or Figure 3A-6 the embodiments and their variants, and are discussed with reference to these schematic diagrams and embodiments without including all such aspects, configurations, features, properties, etc. For the sake of brevity, with respect to Figure 1-2 the examples, each previously discussed component, part, portion, aspect, region, etc. or its variant may no longer be discussed, shown, and / or labeled; however, within the scope of the present disclosure, the previously discussed features, variants, etc. can be used in conjunction with

[0064] Focusing on Figure 3A-3C which show schematic top views of various examples of the situation where, when the first structural element 16 and the second structural element 18 are assembled into the structural component 12, at least a portion of the first structural element hole sidewall 35 and the second structural element hole sidewall 37 of the first structural element hole 48 and the second structural element hole 50 may be misaligned. Figure 3A and Figure 3B show misaligned conditions where the exemplary holes of the first structural element hole 48 and the second structural element hole 50 are misaligned. In Figure 3A the examples, which respectively reflect Figure 1 and Figure 2 the schematic examples shown, the first exemplary first structural element hole 320 and the first exemplary second structural element hole 310 of the first structural element hole 48 and the second structural element hole 50 are respectively the same size but misaligned. In Figure 3B the example, the second exemplary first structural element hole 340 and the second exemplary second structural element hole 330 of the first structural element hole 48 and the second structural element hole 50 respectively have different sizes and are misaligned. In Figure 3C the example, the third exemplary first structural element hole 360 and the third exemplary second structural element hole 350 of the first structural element hole 48 and the second structural element hole 50 are respectively aligned but have different sizes.

[0065] The greater the misalignment of the holes (the greater the offset between the holes), the smaller the overlapping area between the holes. In some examples, the size of the shank 40 of the fastener 30 is set based on this overlapping amount. Specifically, in such examples, the size of the shank 40 of the fastener 30 is set to be equal to or slightly larger than the minimum diameter of the overlapping area between the holes.

[0066] As shown in Figure 1 and Figure 2 which Figure 3A shows exemplary holes that have the same diameter but are misaligned. Specifically, the first exemplary first structural element hole 320 of the first structural element hole 48 is misaligned with the first exemplary second structural element hole 310 of the second structural element hole 50. That is, the central axis 322 of the first exemplary first structural element hole 320 is offset from the central axis 312 of the first exemplary second structural element hole 310 such that the perimeters of the first exemplary second structural element hole 310 and the first exemplary first structural element hole 320 are not aligned with each other. Accordingly, at least a portion of the sidewall 35 of the first structural element hole and the sidewall 37 of the second structural element hole are not aligned. In one example, the size of the shank 40 of the fastener 30 is set such that its diameter is equal to or slightly larger than the minimum diameter of the overlapping area between the holes as shown in Figure 3A . In another example, the size of the shank 40 of the fastener 30 is set such that its diameter is equal to or slightly larger than the diameters of the first exemplary second structural element hole 310 and the first exemplary first structural element hole 320. The shank 40 can still fit within the overlapping area that is too small because the conductive coating 32 on the fastener and / or the CGF 24 on the sidewall 35 of the first structural element hole and the sidewall 37 of the second structural element hole are soft enough to deform and allow the shank 40 to enter the smaller overlapping area.

[0067] Figure 3B shows exemplary holes that are misaligned and of different sizes. Specifically, the second exemplary first structural element hole 340 of the first structural element hole 48 is misaligned with the second exemplary second structural element hole 330 of the second structural element hole 50. That is, the central axis 342 of the second exemplary first structural element hole 340 is offset from the central axis 332 of the second exemplary second structural element hole 330 such that the perimeters of the second exemplary second structural element hole 330 and the second exemplary first structural element hole 340 are not aligned with each other. However, different from the example of Figure 3A , in Figure 3BIn the example, the entire second exemplary first structural element hole 340 overlaps with the second exemplary second structural element hole 330 because the diameter of the second exemplary first structural element hole 340 is smaller than the diameter of the second exemplary second structural element hole 330. Thus, although a portion of the second structural element hole sidewall 37 and the first structural element hole sidewall 35 are misaligned, at least a portion of the second structural element hole sidewall 37 and the first structural element hole sidewall 35 do align. In one example, the shank 40 of the fastener 30 is sized such that its diameter is equal to or slightly larger than the diameter of the smaller of the two holes. In Figure 3B the example, the smaller hole is the second exemplary first structural element hole 340. However, in another example, the shank 40 of the fastener 30 is sized such that its diameter is approximately equal to or slightly larger than the diameter of the larger of the two holes. In Figure 3B the example, the larger hole is the second exemplary second structural element hole 330. The shank 40 can still fit into the smaller hole ( Figure 3B the second exemplary first structural element hole 340 in the example) because the conductive coating 32 on the fastener and / or the CGF 24 on the first structural element hole sidewall 35 and the second structural element hole sidewall 37 is soft enough to deform and allow the shank 40 to enter the smaller of the two holes.

[0068] Figure 3C Exemplary holes of different sizes but in alignment are shown. Specifically, the third exemplary first structural element hole 360 of the first structural element hole 48 and the third exemplary second structural element hole 350 of the second structural element hole 50 are aligned with each other along a common central axis 355. However, in Figure 3C the example, the diameter of the third exemplary first structural element hole 360 is larger than the diameter of the third exemplary second structural element hole 350 such that the perimeters of the third exemplary second structural element hole 350 and the third exemplary first structural element hole 360 are misaligned with each other. Thus, at least a portion of the first structural element hole sidewall 35 and the second structural element hole sidewall 37 are misaligned. In such examples, the shank 40 of the fastener 30 is sized such that its diameter is equal to or slightly larger than the diameter of the smaller of the two holes. In Figure 3C the example, the smaller hole is the second exemplary first structural element hole 340. In one example, the shank 40 of the fastener 30 is sized such that its diameter is equal to or slightly larger than the diameter of the smaller of the two holes. In Figure 3C the example, the smaller hole is the third exemplary second structural element hole 350. In such examples, the fastener 30 can bring the first structural element 16 into contact with the fastener head 38. However, in another example, the shank 40 of the fastener 30 is sized such that its diameter is approximately equal to or slightly larger than the diameter of the larger of the two holes. In Figure 3CIn the example, the larger hole is the third exemplary first structural element hole 360. The shank 40 can still fit into the smaller hole ( Figure 3C the third exemplary second structural element hole 350 in the example), because the conductive coating 32 on the fastener and / or the CGF 24 on the sidewalls 35 of the first structural element hole and 37 of the second structural element hole are soft enough to deform and allow the shank 40 to enter the smaller of the two holes.

[0069] Now turning to Figure 4-6 , they show various embodiments of the fastener 30. Figure 4 An example of a sleeve-less fastener is shown, Figure 5 an example of a single-sided fastener is shown, and Figure 6 an example of a sleeve fastener is shown. In Figure 4 the example, the sleeve-less solid shank fastener can form a clearance fit with one or more of the first structural element holes 48 and the second structural element holes 50 of the first structural element 16 and the second structural element 18 respectively, as in Figure 1 the example. However, in Figure 5 and Figure 6 the example, the fastener includes a sleeve that can expand within the first structural element hole 48 and the second structural element hole 50, thereby forming an interference fit with the first structural element hole 48 and the second structural element hole 50 of the first structural element 16 and the second structural element 18 respectively. Thus, the sleeve fastener may not require the conductive coating 32 to meet the EME requirements, and thus in some examples, the sleeve fastener does not include the conductive coating 32. However, Figure 4 the sleeve-less fastener shown includes the conductive coating 32.

[0070] It is important to note that although the first gap 62 and the second gap 64 are not shown in Figure 4-6 , the first gap 62 and the second gap 64 may still exist; they may be too small to be clearly visible. Thus, even if the first structural element hole 48 and the second structural element hole 50 appear to be aligned in Figure 4-6 , they may still not be aligned.

[0071] As Figure 4 shown, the fastener 430 is an example of the fastener 30, which is a sleeve-less solid shank fastener. Thus, as Figure 4 shown, the fastener 30 does not include a sleeve (such as the exemplary fastener shown in Figure 6 ). The fastener 30 includes a conductive coating 32 that is in direct physical contact with the CGF 24 coating the sidewalls of at least one of the first structural element 16 and the second structural element 18. In Figure 4In the example, both the first structural element 16 and the second structural element 18 include a conductive fiber-reinforced plastic, and thus the CGF 24 is respectively coated on the first structural element sidewall 22 and the second structural element sidewall 41 of both the first structural element 16 and the second structural element 18. However, in other examples, one of the first structural element 16 or the second structural element 18 includes a metal or a metal alloy and does not include the CGF 24.

[0072] In Figure 4 the example, the fastener 430 is not a one-sided fastener. Thus, the fastener 430 fixes and compresses the first structural element 16 and the second structural element 18 via the fastener mating element 46. In Figure 4 the example, the fastener mating element 46 is a nut that is screwed or swaged onto the mating portion 42 of the fastener 430. Further, in Figure 4 the example, the fastening system 10 further includes a countersunk washer 402 between the fastener head 38 of the fastener 30 and the first structural element 16, and a pair of leveling washers 404 and 406 between the washer 47 and the second structural element 18. The pair of leveling washers 404 and 406 includes a concave leveling washer 404 and a convex leveling washer 406. In Figure 4 the example, the second structural element 18 is angled and includes the leveling washers 404 and 406 to square the assembly 12.

[0073] As Figure 5 shown, the fastener 530 is an example of the fastener 30 that includes a one-sided fastener. The one-sided fastener 530 further includes a sleeve 534 and a frangible drive element 532 in addition to the shank 40 and the fastener head 38. An example of the one-sided fastener 530 is described in U.S. Patent No. 10,294,976 titled "METHOD OF INSTALLING A STRUCTURAL BLIND FASTENER", the entire content of which is hereby incorporated by reference. As described in the '976 patent, the frangible drive element 532 drives the shank 40 into the sleeve 534 and into the first structural element 16 and the second structural element 18. When the shank 40 is further driven into the sleeve 534, the self-locking mechanism 536 of the sleeve 534 bends backward against the second structural element 18 and compresses the first structural element 16 and the second structural element 18 together. In some examples, the self-locking mechanism 536 includes a softened portion of the sleeve 534 that is softened by heat treatment. In other examples, the self-locking mechanism 536 includes a spring-actuated mechanism that radially expands outward once it clears the second structural element 18.

[0074] In Figure 5In the example, the first structural element 16 forms part of the aircraft skin, and thus the fastener head 38 includes a countersunk fastener head that extends into the first structural element 16 and does not protrude from the surface of the first structural element 16 when fully installed. Figure 5 Illustrated is a fastener 530 that is only partially installed (midway through the installation process). When fully installed (e.g., when the shank 40 and the fastener head 38 are fully inserted into the sleeve 534), the fastener head 38 does not protrude from the first structural element 16, and the frangible drive element 532 breaks off from the fastener head 38.

[0075] In some examples, the sleeve 534 and the shank 40 include a conductive coating 32. However, in other examples, only the shank 40 includes the conductive coating 32. In additional examples, only the sleeve 534 includes the conductive coating 32. In other examples, neither the sleeve 534 nor the shank 40 includes the conductive coating 32.

[0076] As Figure 6 shown, the fastener 630 is an example of the fastener 30 that includes a sleeve fastener and includes a sleeve 632. As the shank 40 is further driven into the sleeve 632 and into the first structural element 16 and the second structural element 18, the sleeve 632 expands to form an interference fit with the first structural element hole 48 and the second structural element hole 50 of the first structural element 16 and the second structural element 18, respectively. Because the sleeve 632 forms an interference fit with the first structural element 16 and the second structural element 18, the fastener 30 may not require the conductive coating 32 to meet the EME requirements. Thus, in Figure 6 the example, the fastener 630 does not include the conductive coating 32. However, in other examples, the fastener 630 does include the conductive coating 32. Specifically, in such examples, the sleeve 632 and / or the shank 40 may include the conductive coating 32.

[0077] In Figure 6 the example, the fastener 630 is not a one-sided fastener. Thus, the fastener 630 secures and compresses the first structural element 16 and the second structural element 18 via the fastener mating element 46. In Figure 4 the example, the fastener mating element 46 is a nut and / or a collar that is screwed or swaged onto the mating portion 42 of the fastener 630.

[0078] Figure 7 Schematically provided is a flowchart representing a schematic, non-exclusive example of a method according to the present disclosure. In Figure 7In some cases, some steps are shown in dashed boxes, thereby indicating that these steps may be optional or may correspond to optional versions of the methods according to the present disclosure. That is, it is not required that all methods according to the present disclosure include the steps shown in the solid boxes. As can be understood from the discussion herein, Figure 7 the methods and steps shown are not restrictive, and other methods and steps are within the scope of the present disclosure, including methods having a greater or lesser number of steps than those shown.

[0079] As Figure 7 shown, a method 700 for assembling and fastening aircraft structural elements using FSDA and conductive coated fasteners and / or holes is shown. According to the FSDA procedure, method 700 at least includes the following steps: at 702, the parts are pre-formed before assembly, and then at 710, the parts are assembled and fastened. Specifically, at 702, according to the FSDA procedure, the parts are pre-formed separately (e.g., at different times and / or different locations). Then at 710, the parts are brought together and fastened using a fastening system (e.g., fastening system 10). The parts include structural elements (e.g., a first structural element 16 and a second structural element 18).

[0080] Pre-forming the parts at 702 includes: pre-forming a hole (e.g., a first structural element hole 48) in a first structural element (e.g., the first structural element 16) at 704, and separately pre-forming a hole (e.g., a second structural element hole 50) in a second structural element (e.g., the second structural element 18) at 706. As described above, the holes are pre-formed separately. Specifically, the holes can be pre-formed at different times and / or different locations. Thus, when the holes are formed, the structural elements are not stacked or otherwise assembled together. In other words, when the structural elements are stacked on top of each other, the holes are not formed.

[0081] These holes are formed by one or more of drilling, reaming, or molding. In some examples, pre-forming the holes at 704 and 706 also includes coating the holes with a conductive coating. Specifically, if the structural element includes a conductive fiber reinforced plastic (e.g., CFRP), the holes of the structural element are covered with a conductive coating. If the structural element includes a metal or metal alloy instead of a conductive fiber reinforced plastic, method 700 does not include coating the structural element with a conductive coating.

[0082] Thus, in an example where the first structural element comprises a conductive fiber reinforced plastic (e.g., CFRP), pre-forming a hole in the first structural element at 704 further comprises coating the hole with a conductive coating (e.g., CGF 24) at 705. Similarly, in an example where the second structural element comprises a conductive fiber reinforced plastic, pre-forming a hole in the second structural element at 706 further comprises coating the hole with a conductive coating at 707. As described above, at least one of the two structural elements comprises a conductive fiber reinforced plastic. Thus, the hole of at least one of the structural elements is coated with a conductive coating at 702. In an example where both structural elements comprise a conductive fiber reinforced plastic, the holes of both structural elements are coated with a conductive coating. Specifically, the coating is applied to the side walls (e.g., the first structural element side wall 22 and the second structural element side wall 41) of the holes (e.g., the first structural element hole 48 and the second structural element hole 50) of the structural elements by conductive coating.

[0083] Coating techniques have been described above, but may include using a split mandrel tool cast with a low melting alloy (LMA), as described in the co-owned U.S. Patent Application No. 15 / 923,630 titled "METHOD, APPARATUS AND APPLICATOR FOR APPLYING A COATING ON A SURFACE OF A LAMINATION", the disclosure of which is incorporated herein by reference in its entirety.

[0084] In some examples, pre-forming the respective parts at 702 further comprises coating a fastener (e.g., fastener 30) with a conductive coating (e.g., conductive coating 32) at 708. Specifically, the conductive coating is applied in an example where the fastener comprises a sleeve-less and / or single-sided fastener. As described above, the method for coating a fastener with a conductive coating is described in the co-owned U.S. Patent Application No. 16 / 693,613 titled "METHOD FOR PLATING A METALLIC MATERIAL ONTO A TITANIUM SUBSTRATE" and U.S. Patent Application No. 16 / 242,115 titled "CONDUCTIVE FASTENING SYSTEM AND METHOD FOR IMPROVED EME PERFORMANCE", the disclosures of which are incorporated herein by reference in their entireties.

[0085] The assembly and fastening at 710 includes assembling a first structural element and a second structural element having pre-formed holes, and fastening the assembly by a fastening system (e.g., fastening system 10) including one or more fasteners (e.g., fastener 30). In some examples, method 700 further includes applying a joint seal to the parts (structural elements) at 720.

[0086] Specifically, the assembly includes putting together all the specific parts (e.g., the first structural element 16 and the second structural element 18), stacking the parts, and aligning the parts to form a structural assembly (e.g., structural assembly 12). Specifically, the assembly may include loading the first structural element and the second structural element into a fixture at 712, and aligning the first structural element and the second structural element through a first set of holes at 714. As indicated at 715, the alignment may include inserting a set of temporary fasteners (e.g., tack fasteners) into the first set of holes. In some examples, the first set of holes includes only a subset of the holes formed at 702. Thus, in some examples, the alignment at 714 includes inserting temporary fasteners into only some of the holes formed at 702 to align the first structural element and the second structural element.

[0087] The fastening includes inserting a fastener (e.g., fastener 30) into the holes (e.g., the first structural element hole 48 and the second structural element hole 50) at 716. In some examples, in the case where temporary fasteners (tack fasteners) are initially inserted to align the structural elements, at 716 method 700 includes: inserting a first set of fasteners into the open holes in which there are no temporary fasteners, removing the temporary fasteners after inserting the first set of fasteners, and then inserting a second set of fasteners into the remaining holes that previously held the temporary fasteners.

[0088] The fastening further includes tightening the fastener at 718 to fix the first structural element and the second structural element. When the fastener includes a one-sided fastener, the tightening may include rotating the fastener beyond the point where its self-locking mechanism engages with the structural assembly. When the fastener does not include a one-sided fastener with a fastener head 38a, the tightening at 718 may include threading a threaded nut onto a mating portion (e.g., mating portion 42) of the fastener that protrudes from an end of the structural assembly opposite the head of the fastener, and twisting the nut at 721. In other examples where the fastener does not include a one-sided fastener, the tightening at 718 may include sliding a collar onto the mating portion of the fastener, and swaging the collar at 719.

[0089] In some examples, method 700 further includes applying a cover seal to the components at 722. However, in other examples, method 700 does not include applying a cover seal to the parts at 722.

[0090] By coating the first structural element sidewall 22 of the first structural element hole 48 and the second structural element sidewall 41 of the second structural element hole 50 with the CGF 24, and / or by coating the fastener 30 with the conductive coating 32, a greater current path (i.e., a larger cross-sectional area) for current from a lightning strike to flow through the fastener 30 to the surrounding first structural element 16 and second structural element 18 is provided. Specifically, the CGF 24 and the conductive coating 32 provide a greater surface area contact between the fastener 30 and the first structural element 16 and the second structural element 18, thereby increasing the number of conductive fibers in contact with the fastener 30, and thus increasing the current path between the fastener 30 and the first structural element 16 and the second structural element 18, and reducing the current density. The CGF 24 and the conductive coating 32 reduce the current density to such an extent that a cheaper and more time-saving FSDA can be used with a cheaper socketless bolt without sacrificing safety. Specifically, the CGF 24 and the conductive coating 32 provide sufficient surface area contact between the socketless fastener and the first structural element 16 and the second structural element 18, thereby ensuring lightning protection even when the first structural element hole 48 and the second structural element hole 50 are misaligned (which may be the case when using FSDA). The FSDA allows for a lower cost and more time-efficient assembly, production, and manufacturing of aircraft components. Additionally, the above features can eliminate the need for capping and / or joint sealing, thereby further reducing production costs.

[0091] Reference Figure 8 and Figure 9 , a maintenance method 800 is shown in Figure 8 , and an aircraft 902 is shown in Figure 9 . During pre-production, the exemplary method 800 may include the specification and design 804 of the aircraft 902 and the material procurement 806, which may include the procurement of the first structural element 16 and the second structural element 18. During production, the component and sub-assembly manufacturing 808 of the aircraft 902 and the system integration 810 are carried out. Production may include the assembly and fastening of the first structural element 16 and the second structural element 18 via the fastening system 10 to form the structural assembly 12. Thereafter, the aircraft 902 may undergo certification and delivery 812 for placement in service 814. When used by a customer, the aircraft 902 is scheduled for routine maintenance and servicing 816 (which may also include modifications, reconfigurations, refurbishments, etc.).

[0092] Each process of the method 800 may be performed or carried out by a system integrator, a third party, and / or an operator (e.g., a customer). For the purposes of this specification, a system integrator may include, but is not limited to, any number of aircraft manufacturers and prime system subcontractors; a third party may include, but is not limited to, any number of suppliers, subcontractors, and vendors; an operator may be an airline, a leasing company, a military entity, a service organization, etc.

[0093] As Figure 9 shown, an aircraft 902 produced by an exemplary method 800 may include a fuselage 918 and an interior 922 having a plurality of systems 920. As described above, the structural components 12 (including the first structural element 16 and the second structural element 18) and the fastening system 10 may include a portion of the fuselage 918. Examples of the advanced systems 920 include one or more of a propulsion system 924, an electrical system 926, a hydraulic system 928, and an environmental system 930. Any number of other systems may be included. Although an aviation example is shown, the principles of the present invention may be applied to other industries, such as the automotive industry.

[0094] The apparatus and methods embodied herein may be employed during any one or more stages of production and servicing methods 800. For example, components or sub-assemblies corresponding to production process 808 may be produced or manufactured in a manner similar to that of components or sub-assemblies produced during servicing of the aircraft 902. Also, for example, by substantially accelerating the assembly of the aircraft 902 or reducing its cost, one or more apparatus embodiments, method embodiments, or combinations thereof may be utilized during production stages 808 and 810. Similarly, during servicing of the aircraft 902, such as, but not limited to, maintenance and repair 816, one or more of apparatus embodiments, method embodiments, or combinations thereof may be utilized.

[0095] Schematic, non-exclusive examples of the inventive subject matter in accordance with the present disclosure are described in the paragraphs listed below:

[0096] A. An apparatus, the apparatus including a fastening system and a structural component, wherein: the structural component includes: a first structural element made of a conductive fiber-reinforced plastic, the first structural element including a first hole having a first structural element sidewall; a second structural element, the second structural element including a second hole having a second structural element sidewall; and a conductive gap filler, the conductive gap filler being applied to the first structural element sidewall of the first hole of the first structural element, wherein the conductive gap filler defines a first hole sidewall of the first hole; wherein at least a portion of the first structural element sidewall and the second structural element sidewall are misaligned; and wherein the fastening system includes: a fastener, the fastener including a head and a shank extending from the head into the first hole and the second hole.

[0097] A1. The apparatus according to paragraph A, wherein the first structural element is made of carbon fiber-reinforced plastic (CFRP).

[0098] A2. The apparatus according to any one of paragraphs A and A1, wherein the fastening system further includes a conductive coating formed on the shank of the fastener.

[0099] A3. The device according to any one of paragraphs A - A2, wherein the first hole comprises a pre - formed hole formed before the assembly of the first structural element and the second structural element.

[0100] A4. The device according to paragraph A3, wherein the conductive gap filler is ground onto the sidewall of the first hole before the assembly of the first structural element and the second structural element.

[0101] A5. The device according to any one of paragraphs A - A4, wherein the sidewall of the first structural element comprises an irregular surface, and wherein the sidewall of the first hole defined by the conductive gap filler comprises a flat surface.

[0102] A6. The device according to any one of paragraphs A - A5, wherein the second hole comprises a pre - formed hole formed before the assembly of the first structural element and the second structural element.

[0103] A7. The device according to any one of paragraphs A - A6, wherein the structural assembly is assembled using full - scale deterministic assembly (FSDA).

[0104] A8. The device according to any one of paragraphs A - A7, wherein the conductive gap filler is applied to the sidewall of the second structural element of the second hole and defines the second sidewall of the second hole, and wherein the fastener physically contacts at least a portion of the sidewall of the first hole and at least a portion of the sidewall of the second hole, but wherein the fastener is in a clearance fit with at least one of the first hole and the second hole.

[0105] A9. The device according to paragraph A8, further comprising a first gap between the fastener and the sidewall of the first hole of the first hole.

[0106] A10. The device according to paragraph A9, further comprising a second gap between the fastener and the sidewall of the second hole of the second hole.

[0107] A11. The device according to any one of paragraphs A - A10, wherein the fastener comprises a sleeve - less fastener.

[0108] A12. The device according to any one of paragraphs A - A11, wherein the fastener comprises a one - sided fastener.

[0109] A13. The device according to any one of paragraphs A - A12, wherein the fastener comprises a sleeve - type fastener.

[0110] B. A method for assembling and fastening a first structural element and a second structural element comprising conductive fiber - reinforced plastics, the method comprising:

[0111] Use full - scale deterministic assembly (FSDA) to assemble the first structural element and the second structural element; and

[0112] Fasten the first structural element and the second structural element by inserting a fastener into overlapping holes of the first structural element and the second structural element, wherein at least one of the overlapping holes is pre - formed before assembling the first structural element and the second structural element and at least one of the overlapping holes is coated with a conductive gap filler.

[0113] B1. The method according to paragraph B, wherein the overlapping holes are misaligned.

[0114] B2. The method according to paragraph B, further comprising pre - forming a first - structural - element hole of the overlapping hole in the first structural element and a second - structural - element hole of the overlapping hole in the second structural element separately before assembling the first structural element and the second structural element.

[0115] B2.1. The method according to paragraph B2, wherein pre - forming the first - structural - element hole and the second - structural - element hole comprises drilling the holes.

[0116] B2.2. The method according to any one of paragraphs B2 - B2.1, wherein pre - forming the first - structural - element hole and the second - structural - element hole separately comprises pre - forming the first - structural - element hole in the first structural element at a different time and / or a different position from the second - structural - element hole in the second structural element.

[0117] B3. The method according to any one of paragraphs B2 - B2.2, further comprising coating the first - structural - element hole with the conductive gap filler.

[0118] B4. The method according to any one of paragraphs B - B3, further comprising coating the fastener with the conductive coating.

[0119] B4.1. The method according to paragraph B4, wherein the conductive coating comprises indium and wherein the fastener comprises titanium.

[0120] B4.2. The method according to paragraph B4.1, wherein coating the fastener with the conductive coating comprises activating the fastener and electroplating the fastener with the conductive coating.

[0121] B5. The method according to any one of paragraphs B - B4.2, wherein fastening comprises forming a clearance fit with the at least two structural elements by physically contacting only a part of one or more sidewalls of the misaligned holes.

[0122] B6. A method according to any one of paragraphs B - B4.2, wherein fastening comprises forming an interference fit through at least one of the structural elements.

[0123] B7. A method according to any one of paragraphs B - B6, wherein fastening comprises inserting a plurality of fasteners into a plurality of holes in the first structural element and the second structural element, and wherein assembling comprises inserting a set of temporary fasteners into a first subset of the plurality of holes, and wherein fastening further comprises inserting a first subset of the plurality of fasteners into a second subset of the plurality of holes that does not contain the temporary fasteners, then removing the temporary fasteners and inserting a second subset of the plurality of fasteners into the first subset of the plurality of holes.

[0124] C. A method for assembling and fastening at least two structural elements, the method comprising: using full - scale deterministic assembly (FSDA) to assemble the at least two structural elements; and fastening the at least two structural elements by inserting electrically conductive coated fasteners into misaligned holes in the at least two structural elements.

[0125] C1. A method according to paragraph C, wherein assembling further comprises pre - forming the misaligned holes and pre - coating the misaligned holes with an electrically conductive gap filler before bringing the at least two structural elements together.

[0126] C1.1 A method according to paragraph C1, wherein pre - forming comprises pre - drilling the misaligned holes.

[0127] C2. A method according to any one of paragraphs C1 - C1.1, further comprising coating the electrically conductive coated fasteners with an electrically conductive coating comprising indium, wherein coating comprises activating the fasteners and electroplating the fasteners with the electrically conductive coating, and wherein the electrically conductive coated fasteners comprise titanium.

[0128] C3. A method according to any one of paragraphs C1 - C2, wherein fastening comprises forming a clearance fit with the at least two structural elements by physically contacting only a portion of one or more sidewalls of the misaligned holes.

[0129] As used herein, the terms "adapted" and "configured" mean that an element, component, or other subject is designed and / or intended to perform a given function. Thus, the use of the terms "adapted" and "configured" should not be construed to mean that a given element, component, or other subject is merely "able to" perform the given function, but rather that the element, component, and / or other subject is specifically selected, created, implemented, utilized, programmed, and / or designed for the purpose of performing the function. Within the scope of the present disclosure, an element, component, and / or other recited subject described as being adapted to perform a particular function may additionally or alternatively be described as being configured to perform that function, and vice versa. Similarly, a subject recited as being configured to perform a particular function may additionally or alternatively be described as being operable to perform that function.

[0130] As used herein, the term "and / or" placed between a first entity and a second entity means (1) the first entity, (2) the second entity, and (3) either of the first entity and the second entity. Multiple items listed with "and / or" shall be construed in the same manner, i.e., "one or more" of the entities so connected. There may optionally be other entities in addition to those entities specifically identified by the "and / or" clause, whether related or unrelated to those specifically identified entities. Thus, as a non-limiting example, when used in conjunction with open-ended language such as "comprising," a reference to "A and / or B" may, in one example, refer only to A (optionally including other entities in addition to B); in another example, only to B (optionally including other entities in addition to A); and in yet another example, to both A and B (optionally including other entities). These entities may refer to elements, actions, structures, steps, operations, values, etc.

[0131] The various disclosed elements of the devices and steps of the methods herein are not necessary for all of the devices and methods of the present disclosure, and the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various elements and steps disclosed herein. Moreover, one or more of the various elements and steps disclosed herein may define an independent inventive subject matter that is independent of and distinct from the overall disclosed device or method. Thus, such inventive subject matter need not be associated with the specific devices and methods explicitly disclosed herein, and such inventive subject matter may find utility in devices and / or methods not explicitly disclosed herein.

Claims

1. An apparatus (8) for an electrically conductive coated fastening system, comprising a fastening system (10) and a structural assembly (12), wherein: The structural assembly (12) comprises: a first structural element (16) made of a conductive fiber-reinforced plastic, the first structural element (16) comprising a first hole having a first structural element sidewall (22); a second structural element (18), the second structural element (18) comprising a second hole having a second structural element sidewall (41); and a conductive gap filler (24) applied to the first structural element sidewall (22) of the first hole of the first structural element (16), wherein the conductive gap filler (24) defines a first hole sidewall (35) of the first hole; wherein at least a portion of the first structural element sidewall (22) and the second structural element sidewall (41) are misaligned; and wherein The fastening system (10) comprises a fastener (30), the fastener comprising a head (38) and a shank (40) extending from the head (38) into the first hole and the second hole, wherein the fastener (30) comprises one of a non-sleeved fastener and a sleeved fastener.

2. An apparatus (8) for an electrically conductive coated fastening system, comprising a fastening system (10) and a structural assembly (12), wherein: The structural assembly (12) comprises: a first structural element (16) made of a conductive fiber-reinforced plastic, the first structural element (16) comprising a first hole having a first structural element sidewall (22); a second structural element (18), the second structural element (18) comprising a second hole having a second structural element sidewall (41); and a conductive gap filler (24) applied to the first structural element sidewall (22) of the first hole of the first structural element (16), wherein the conductive gap filler (24) defines a first hole sidewall (35) of the first hole; wherein at least a portion of the first structural element sidewall (22) and the second structural element sidewall (41) are misaligned; and wherein The fastening system (10) comprises a fastener (30), the fastener comprising a head (38) and a shank (40) extending from the head (38) into the first hole and the second hole, wherein the fastener (30) comprises a single-sided fastener.

3. The apparatus (8) for an electrically conductive coated fastening system according to claim 1 or 2, wherein the first structural element (16) is made of carbon fiber-reinforced plastic.

4. The apparatus (8) for an electrically conductive coated fastening system according to claim 1 or 2, wherein the fastening system (10) further comprises an electrically conductive coating (32) formed on the shank (40) of the fastener (30).

5. The device (8) for a conductive coating fastening system according to claim 1 or 2, wherein the first hole comprises a pre-formed hole formed before assembling the first structural element (16) and the second structural element (18), and wherein the conductive gap filler (24) is ground onto the sidewall (35) of the first hole before assembling the first structural element (16) and the second structural element (18).

6. The device (8) for a conductive coating fastening system according to claim 1 or 2, wherein the sidewall (22) of the first structural element comprises an irregular surface, and wherein the sidewall (35) of the first hole defined by the conductive gap filler (24) comprises a flat surface.

7. The device (8) for a conductive coating fastening system according to claim 1 or 2, wherein the second hole comprises a pre-formed hole formed before assembling the first structural element (16) and the second structural element (18).

8. The device (8) for a conductive coating fastening system according to claim 1 or 2, wherein the conductive gap filler (24) is applied to the sidewall (41) of the second structural element of the second hole and defines the second hole sidewall (37) of the second hole, and wherein the fastener (30) physically contacts at least a part of the sidewall (35) of the first hole and at least a part of the sidewall (37) of the second hole, and wherein the fastener (30) is in a clearance fit with at least one of the first hole and the second hole.

9. The device (8) for a conductive coating fastening system according to claim 8, further comprising: a first gap (62) between the fastener (30) and the sidewall (35) of the first hole of the first hole; and a second gap (64) between the fastener (30) and the sidewall (37) of the second hole of the second hole.

10. A method (700) for a conductive coating fastening system for assembling and fastening (710) a first structural element (16) and a second structural element (18), the first structural element (16) being made of a conductive fiber-reinforced plastic, the method (700) comprising: assembling the first structural element (16) and the second structural element (18) using full-size deterministic assembly, the first structural element (16) having a pre-formed first structural element hole (48), and the second structural element (18) having a second structural element hole (50); fastening the first structural element (16) and the second structural element (18) by inserting a fastener (30) into the overlapping holes of the first structural element (16) and the second structural element (18), wherein at least one of the overlapping holes is pre-formed and at least one of the overlapping holes is pre-coated with a conductive gap filler (24) before assembling the first structural element (16) and the second structural element (18); and coating (705) the first structural element hole (48) with the conductive gap filler (24).

11. The method (700) for a conductive coating fastening system according to claim 10, further comprising pre-forming (702) a first structural element hole (48) of the overlapping hole in the first structural element (16) and a second structural element hole (50) of the overlapping hole in the second structural element (18) separately before assembling the first structural element (16) and the second structural element (18).

12. The method (700) for a conductive coating fastening system according to claim 11, wherein pre-forming (702) the first structural element hole (48) and the second structural element hole (50) separately comprises pre-forming the first structural element hole (48) in the first structural element (16) at a different time and / or at a different position from the second structural element hole (50) in the second structural element (18).

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