Lightning protection assembly, lightning protection system, and method of using the same

Abstract

To provide assemblies, systems, and methods of lightning strike protection for aircraft composite structures.SOLUTION: The lightning strike protection material assembly 10 includes a lightning strike expanded metal foil layer 16 having a lightning strike expanded metal foil 18 and a resin-infused scrim layer having a non-metallic scrim infused with an infusion resin 45 having a tailored viscosity and a tailored cure profile. The lightning strike protection assembly 10 is configured to be laid up on and co-cured with an uncured composite laminate assembly having a plurality of structural ply layers pre-impregnated with a structural resin. The structural resin has a structural resin viscosity and a structural resin cure profile that are different from the tailored viscosity and the tailored cure profile, thereby preventing intermixing of the structural resin and the infusion resin during co-curing and allowing the infusion resin to effectively encapsulate the lightning strike expanded metal foil 18 and form a cured lightning strike protected composite structure 80 capable of achieving a defined resin boundary.SELECTED DRAWING: Figure 2D

Description

[Technical Field]

[0001] The present disclosure relates generally to lightning protection assemblies, systems, and methods, and more particularly to lightning protection assemblies, systems, and methods for composite structures, such as aircraft composite structures. [Background technology]

[0002] Lightning protection systems and methods have been developed to provide lightning protection to composite structures, such as aircraft composite structures, rotorcraft composite structures, spacecraft composite structures, and other aerospace vehicle composite structures. Some known lightning protection systems and methods incorporate various configurations of metal foil systems on the composite outer aerosurfaces of aircraft (e.g., wings, horizontal stabilizers, and fuselage skin panels) to improve electrical conductivity and to dissipate and divert electrical current away from flight-critical areas and underlying aircraft components, thereby minimizing physical damage from a lightning strike event.

[0003] Known lightning protection systems and methods may include a lightning protection material comprised of an expanded metal foil with a resin that has a similar cure profile and viscosity to the structural resin in a composite structure underlying the lightning protection. Due to the similar cure profile and viscosity, the resin in the lightning protection mixes with the structural resin upon curing, creating areas where the two dissimilar materials are in close proximity, leaving less resin available to seal and protect the expanded metal foil. Thus, in an operational environment, when the composite structure, along with the lightning protection, is repeatedly exposed to heat and humidity, the lightning protection may expand faster than the underlying composite structure due to differences in the coefficients of thermal expansion (CTE) and hygroscopic expansion (CME) between the lightning protection and the underlying composite structure, and because the lightning protection typically has a higher CTE than the underlying composite structure. This exposure to heat and humidity can create stresses and strains, ultimately resulting in microcracks in the dissimilar lightning protection and the underlying composite structure due to the large difference in CTE. These microcracks can form in the expanded metal foil area and propagate through the intermixed resin area into the underlying composite structure, potentially increasing repair and rework costs and compromising the lightning strike protection system.

[0004] Therefore, there is a need in the art for improved lightning protection assemblies, systems, and methods that prevent intermixing of the lightning protection resin with the underlying composite structure structural resin during curing or co-curing, avoiding areas where the two dissimilar materials are in close proximity to one another, provide sufficient lightning protection resin during curing or co-curing to effectively encapsulate the lightning protection expanded metal foil, minimize or prevent microcracking to improve microcracking resistance, prevent damage to the underlying composite structure to avoid repair or rework, and provide advantages over known lightning protection assemblies, systems, and methods. Summary of the Invention

[0005] Exemplary embodiments of the present disclosure provide improved lightning protection assemblies, systems, and methods. As described in the detailed description below, aspects of the improved lightning protection assemblies, systems, and methods can provide significant advantages over known assemblies, systems, and methods.

[0006] In one aspect of the present disclosure, a lightning strike protection assembly is provided. The lightning strike protection assembly includes a lightning strike expanded metal foil layer including a lightning strike expanded metal foil. The lightning strike protection assembly further includes a resin-infused scrim layer laminated to the lightning strike expanded metal foil layer. The resin-infused scrim layer includes a non-metallic scrim infused with an infusion resin. The infusion resin has a tailored viscosity and a tailored cure profile.

[0007] The lightning strike protection assembly is configured to be laid up on and co-cured with an uncured composite layup assembly comprised of multiple structural ply layers pre-impregnated with a structural resin. The structural resin has a structural resin viscosity and a structural resin cure profile that are different from the tailored viscosity and tailored cure profile of the infusion resin, thereby preventing intermixing of the structural resin and the infusion resin during co-curing, allowing the infusion resin to effectively encapsulate the lightning strike expanded metal foil and achieving a defined resin boundary. Co-curing of the lightning strike protection assembly and the uncured composite layup assembly forms a cured lightning strike protection composite structure. The cured lightning strike protection composite structure provides lightning strike protection as well as improved micro-cracking resistance and degradation resistance.

[0008] In another aspect of the present disclosure, a lightning strike protection system is provided. The lightning strike protection system includes a lightning strike protection assembly. The lightning strike protection assembly includes a lightning strike expanded metal foil layer including a lightning strike expanded metal foil.

[0009] The lightning strike protection assembly further includes a resin-infused scrim layer laminated to the lightning strike expanded metal foil layer, the resin-infused scrim layer including a non-metallic scrim infused with an infusion resin, the infusion resin having a controlled viscosity and a controlled cure profile.

[0010] The lightning strike protection system further includes an uncured composite layup assembly comprised of a plurality of structural ply layers pre-impregnated with a structural resin having a structural resin viscosity and a structural resin cure profile that differs from the tailored viscosity and the tailored cure profile of the infusion resin.

[0011] The lightning protection assembly is laid up on and co-cured with the uncured composite layup assembly, and during co-curing, the structural resin and the infusion resin do not intermix to provide a defined resin boundary, and the infusion resin effectively encapsulates the lightning expanded metal foil. The co-curing of the lightning protection assembly and the uncured composite layup assembly forms a cured lightning protection composite structure. The cured lightning protection composite structure provides lightning protection as well as improved micro-cracking resistance and degradation resistance.

[0012] In another aspect of the present disclosure, there is provided a method of using a lightning protection material system to impart improved microcracking resistance and degradation resistance to a cured lightning protection composite structure, the method comprising providing the lightning protection material system.

[0013] The lightning strike protection system includes a lightning strike protection assembly including a lightning strike expanded metal foil layer including a lightning strike expanded metal foil, and a resin-infused scrim layer laminated to the lightning strike expanded metal foil layer, the resin-infused scrim layer including a non-metallic scrim infused with an infusion resin, the infusion resin having a tailored viscosity and a tailored cure profile.

[0014] The lightning strike protection system further includes an uncured composite layup assembly including a plurality of structural ply layers pre-impregnated with a structural resin having a structural resin viscosity and a structural resin cure profile that differs from the tailored viscosity and the tailored cure profile of the infusion resin.

[0015] The method further includes laying up the lightning strike protection assembly to the uncured composite layup assembly.

[0016] The method further includes co-curing the uncured composite laminate assembly and the lightning strike protection assembly thereon using heat in an autoclave, during which the structural resin and the infusion resin do not intermix to provide a defined resin boundary, and the infusion resin effectively encapsulates the lightning strike expanded metal foil.

[0017] The method further includes obtaining the cured lightning protection composite structure formed by co-curing the lightning protection material assembly and the uncured composite layup assembly, and using the lightning protection material system to impart the improved micro-cracking resistance, the degradation prevention capabilities, and the lightning protection capabilities to the cured lightning protection composite structure.

[0018] The above-described features, functions, and advantages can be achieved individually in various aspects of the present disclosure or may be combined in yet other aspects, further details of which will become apparent by reference to the following description and drawings. [Brief explanation of the drawings]

[0019] The present disclosure can be better understood by reference to the following detailed description in conjunction with the accompanying drawings illustrating preferred and exemplary embodiments, which are not necessarily to scale, and which are illustrative only and are not intended to limit the scope of the specification or claims.

[0020] [Figure 1A]FIG. 1 is a block diagram of an exemplary lightning protection assembly of the present disclosure. [Figure 1B] FIG. 1 is a block diagram of an exemplary lightning strike protection system of the present disclosure. [Figure 2A] FIG. 1 is a cross-sectional front view of an exemplary lightning strike protection assembly of the present disclosure. [Figure 2B] FIG. 2B is a cross-sectional front view of an exemplary lightning protection system of the present disclosure, showing the lightning protection assembly of FIG. 2A positioned in an uncured composite layup assembly. [Figure 2C] FIG. 2C is a cross-sectional front view of the lightning protection system of FIG. 2B in an autoclave. [Figure 2D] 1 is a cross-sectional front view of an exemplary hardened lightning strike protection composite structure of the present disclosure; FIG. [Figure 2E] FIG. 2E is a cross-sectional front view of the hardened lightning strike protection composite structure of FIG. 2D, illustrating microcracks. [Figure 3A] 1 is a graph illustrating viscosity versus temperature during curing of an exemplary lightning strike protection system of the present disclosure. [Figure 3B] 1 is a graph showing viscosity versus temperature during curing of a conventional known resin system for lightning strike protection. [Figure 4] 1 is a flowchart of an exemplary embodiment of a method of the present disclosure. [Figure 5] 1 is a perspective view of an aircraft incorporating an exemplary hardened lightning strike protective composite structure of the present disclosure; FIG. [Figure 6] 1 is a flowchart of an exemplary aircraft production and service method. [Figure 7] FIG. 1 is an exemplary block diagram of an aircraft. DETAILED DESCRIPTION OF THE INVENTION

[0021] Aspects of the disclosure will now be described in more detail with reference to the accompanying drawings, in which some, but not all, aspects of the disclosure are shown. Indeed, several different aspects may be presented, and should not be construed as being limited to the aspects set forth herein. Rather, these aspects are presented so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0022] This specification includes the phrase "one embodiment" or "embodiment." The phrases "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. Particular features, structures, or characteristics may be combined in any suitable manner consistent with this disclosure. All features disclosed in this specification, including the claims, abstract, and drawings, and all steps in the disclosed methods or processes, may be combined in any combination, except combinations in which at least some of such features and / or steps are mutually exclusive. Each feature disclosed in this specification, including the claims, abstract, and drawings, may be replaced with an alternative feature serving the same, equivalent, or similar purpose, unless expressly stated otherwise.

[0023] As used herein, "comprising" is an open-ended term, and in the claims, the term does not exclude additional structures or steps.

[0024] As used herein, "configured" means that various parts or components may be described or claimed as being "configured" to perform one or more tasks. In this context, "configured" is used to connote structure by suggesting that the part or component includes structure that performs such one or more tasks during operation. Thus, even if a particular part or component is not operating (e.g., not turned on), the part or component can still be said to be configured to perform that task.

[0025] As used herein, the terms "first," "second," etc. are used merely as markers for the nouns that follow them and do not imply any sort of order (e.g., spatial, temporal, or logical order).

[0026] As used herein, the singular reference to an element or step does not necessarily exclude a plurality of such elements or steps. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. Also, as used herein, the term "combinations thereof" includes combinations with at least one of the associated listed items, where the combination may further include additional items, such as unlisted items.

[0027] As used herein, the phrase "at least one," when used with respect to a list of items, means that various combinations of one or more of the listed items may be used, and that only one of each item in the list may be required. That is, "at least one" means that any number of items from the list may be used in any combination, and not necessarily all of the listed items. An item may be, for example, a particular object, thing, or category.

[0028] 1A-1B, FIG. 1A is a block diagram of an exemplary lightning protection assembly 10 of the present disclosure, and FIG. 1B is a block diagram of an exemplary lightning protection system 12 of the present disclosure, including the lightning protection assembly 10 of FIG. 1A. The blocks in FIGS. 1A-1B represent various elements, and the lines connecting the various blocks do not imply any particular dependency relationships between these elements. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and / or physical connections between the various elements, although alternative or additional functional relationships or physical connections may exist in embodiments disclosed herein. One or more of these blocks may be combined, divided, or combined and then divided into different blocks when implemented in an exemplary embodiment. Furthermore, the illustration of the lightning protection assembly 10 in FIG. 1A and the lightning protection system 12 in FIG. 1B does not impose physical or architectural limitations on the manner in which the exemplary embodiments may be implemented. Other components in addition to or instead of those illustrated may be used. Also, some components may not be necessary.

[0029] 1A illustrates lightning protection assemblies (LSPMA) 10, including uncured lightning protection assembly (LSPMA) 10a, partially cured lightning protection assembly (LSPMA) 10b, and / or cured lightning protection assembly (LSPMA) 10c, at various stages before, during, or after curing 14 (see FIG. 1B) or co-curing 14a (see FIG. 1B). For example, uncured lightning protection assembly 10a is in an uncured stage before curing 14 or co-curing 14a, partially cured lightning protection assembly 10b is in a partially cured stage during curing 14 or co-curing 14a, and cured lightning protection assembly 10c is in a cured stage after curing 14 or co-curing 14a, where co-curing refers to the simultaneous curing of multiple layers. As shown in FIG. 1A, the lightning protection assembly 10 provides lightning protection 11 .

[0030] Preferably, the co-cure 14a or cure 14 performed on the lightning protection assembly 10 is a snap cure process 15 (see FIG. 1B), such as that disclosed in U.S. Pat. No. 11,752,708, which is incorporated herein by reference in its entirety.

[0031] As shown in FIG. 1A, in one exemplary embodiment, lightning strike protection assembly 10 includes a lightning strike expanded metal foil layer 16. Lightning strike expanded metal foil layer 16 includes a lightning strike expanded metal foil 18 (see FIG. 1A). Lightning strike expanded metal foil layer 16 has a first surface 20 (see FIG. 2A), such as an upper surface 20a (see FIG. 2A), and a second surface 22 (see FIG. 2A), such as a lower surface 22a (see FIG. 2A). Lightning strike expanded metal foil layer 16 further includes a metal foil layer body 24 (see FIG. 2A) located between first surface 20 and second surface 22 and between ends 25 (see FIG. 2A) of lightning strike expanded metal foil layer 16.

[0032] As shown in FIG. 1A , the lightning strike expanded metal foil 18 comprises a non-continuous metal foil (MF) 26 that includes one or more of perforated metal foil (MF) 28, expanded metal foil (MF) 29, metal mesh 30, metallized fiber mesh 31, metal screen 32, metallized fiber fabric 33, metal fabric 34, wire mesh 35, metal foam 36, open-cell metal foam 36a, or other suitable non-continuous metal foil 26.

[0033] As shown in Figure 1A, the lightning strike expanded metal foil 18 further includes a metal material 38 or a metal alloy material 40. As further shown in Figure 1A, the metal material 38 includes one or more of copper 38a, aluminum 38b, titanium 38c, nickel 38d, gold 38e, silver 38f, or other suitable metal materials 38. As further shown in Figure 1A, the metal alloy material 40 includes one or more of copper alloy 40a, aluminum alloy 40b, titanium alloy 40c, nickel alloy 40d, gold alloy 40e, silver alloy 40f, bronze 40g, brass 40h, or other suitable metal alloy materials 40.

[0034] 1A, in one exemplary embodiment, lightning strike protection assembly 10 further includes a resin-infused scrim layer 42 laminated to lightning expanded metal foil layer 16. As further shown in FIG. 1A, resin-infused scrim layer 42 includes a non-metallic scrim 44 infused with an infusion resin (IR) 45, also referred to as lightning strike protection resin 46.

[0035] 1A, the non-metallic scrim 44 includes one of a non-metallic scrim mat 44a, a fiberglass scrim mat 44b, a carbon fiber scrim mat 44c, a woven scrim mat 44d, a knitted polyester scrim mat 44e, a non-woven scrim mat 44f, or other suitable non-metallic scrim 44. The non-metallic scrim 44 may further include a woven scrim fabric or carrier having fiberglass or glass fiber reinforcement, carbon fiber or carbon fiber reinforcement, nylon fiber or nylon fiber reinforcement, polyester fiber or polyester fiber reinforcement, or other suitable fiber reinforcement.

[0036] Resin-infused scrim layer 42 has a first surface 48 (see FIG. 2A), such as upper surface 48a (see FIG. 2A), and a second surface 50 (see FIG. 2A), such as lower surface 50a (see FIG. 2A). Resin-infused scrim layer 42 further has a scrim layer body 52 (see FIG. 2A) located between first surface 48 and second surface 50 and between ends 54 (see FIG. 2A) of resin-infused scrim layer 42.

[0037] In some embodiments, the lightning strike protection assembly 10 may further include one or more additional layers over the lightning strike expanded metal foil layer 16. For example, a thin composite prepreg layer, such as a facing film, or other suitable layer may be additionally disposed over the lightning strike expanded metal foil layer 16 to act as a protective or reinforcing layer over the lightning strike expanded metal foil layer 16 and protect the lightning strike expanded metal foil layer 16 during subsequent sanding, painting, polishing, or other post-treatment processes.

[0038] 1A illustrates infusion resin 45, including uncured infusion resin (IR) 45a, partially cured infusion resin (IR) 45b, and / or cured infusion resin (IR) 45c, at various stages before cure 14 (see FIG. 1B) or co-cure 14a (see FIG. 1B), during cure 14 or co-cure 14a, or after cure 14 or co-cure 14a. For example, uncured infusion resin 45a is in an uncured stage before cure 14 or co-cure 14a, partially cured infusion resin 45b is in a partially cured stage during cure 14 or co-cure 14a, and cured infusion resin 45c is in a cured stage after cure 14 or co-cure 14a. When infusion resin 45 is initially heated during cure 14 or co-cure 14a, this initial heating is sufficient to gel the infusion resin 45, such as uncured infusion resin 45a, into a gel 56 (see FIG. 1A), as described in more detail below.

[0039] 1A, the infusion resin 45, such as lightning strike protection resin 46, includes a thermosetting resin 58. As further shown in FIG. 1A, the thermosetting resin 58 includes one or more of adhesive 58a, epoxy 58b, phenolic 58c, polyimide 58d, bismaleimide 58e, polyurethane 58f, fluoropolymer 58g, cyanate ester 58h, or other suitable thermosetting resin 58. The infusion resin 45 may further include a UV-resistant infusion resin, an aliphatic epoxy infusion resin, a flame-retardant infusion resin, or other suitable infusion resin 45.

[0040] 1A, the infusion resin 45 has a viscosity, such as tailored viscosity 60a, a cure profile (CP) 62, such as tailored cure profile (CP) 62a, and a rheology 64, such as tailored rheology 64a. As used herein, "tailored viscosity" refers to the viscosity of a resin, such as the infusion resin in a lightning strike protection assembly, associated with a lightning strike expanded metal foil, that is controlled, adjusted, and selected to be different from the viscosity of a structural resin in a structural assembly, such as a composite laminate assembly, to prevent or minimize intermixing of the infusion resin and structural resin during co-cure or curing.

[0041] As used herein, a "tailored cure profile" refers to a cure profile, such as an optimized cure time and cure temperature, of a resin, such as an infusion resin, in a lightning strike protection assembly, that is controlled, adjusted, and selected to be different from the cure profile of a structural resin in a structural assembly, such as a composite laminate assembly, so that the infusion resin can begin crosslinking at a lower temperature, allowing the viscosity of the infusion resin to increase quickly, and allowing the infusion resin to encapsulate the lightning strike expanded metal foil while maintaining separation and immiscibility between the infusion resin and the structural resin.

[0042] As used herein, "tailored rheology" means a rheology or flow behavior relationship between the viscosity, e.g., gelation and solidification, e.g., upon curing, of a material, such as a resin, including an infusion resin, in a lightning protection assembly, and the temperature of the material, e.g., upon curing, that is controlled, adjusted, and selected to be different from the rheology of a structural resin in a structural assembly, such as a composite laminate assembly, to prevent or minimize intermixing of the infusion resin and the structural resin during co-cure or curing, and to improve thermal moisture cycling microcracking resistance in a co-cured composite structure, such as a co-cured composite laminate structure having a structural element and a lightning protection element.

[0043] The tailored viscosity 60a, tailored cure profile 62a, and tailored rheology 64a of the infusion resin 45 associated with the lightning strike expanded metal foil 18 provide chemical compatibility 66 (see FIG. 1A) and bonding capabilities 68 (see FIG. 1A) between the infusion resin 45 and a structural resin 70 (see FIG. 1B), such as a structural prepreg resin of a structural assembly 71 (see FIG. 1B), such as a composite laminate assembly 72 (see FIG. 1B) that is coupled or bonded to the lightning strike protection assembly 10.

[0044] Lightning protection assembly 10 is configured for layup 73 (see FIG. 1B) in a layup process 73a and is laid up on a structural assembly 71 (see FIG. 1B), such as composite layup assembly 72 (see FIG. 1B). The composite layup assembly is, for example, in one embodiment, an uncured composite layup assembly 72a made up of a plurality of structural layers 74 (see FIG. 1B), such as a plurality of structural ply layers 75 (see FIG. 1B), pre-impregnated with structural resin 70. Alternatively, a structural assembly 71, such as composite layup assembly 72, e.g., uncured composite layup assembly 72a, may be laid up on lightning protection assembly 10. 1B, the structural resin 70 has a structural resin viscosity 60b, a structural resin cure profile 62b, and a structural resin rheology 64b that are different from the tailored viscosity 60a, tailored cure profile 62a, and tailored rheology 64a of the infusion resin 45, thereby preventing intermixing of the structural resin 70 and the infusion resin 45 during co-curing 14a or curing 14b, and enabling the infusion resin 45 to effectively encapsulate the lightning strike expanded metal foil 18 via encapsulation 76 (see FIG. 1A) and achieve a defined resin boundary 78 (see FIG. 1B). Additionally, the tailored viscosity 60a of the infusion resin 45 is greater than the structural resin viscosity 60b of the structural resin 70, thereby preventing intermixing of the infusion resin 45 and the structural resin 70 during co-curing 14a or curing 14b.

[0045] The tailored cure profile 62a of the infusion resin 45 initiates crosslinking at a lower temperature 114 (see FIG. 1B), thereby rapidly increasing the tailored viscosity 60a of the infusion resin 45, allowing the infusion resin 45 to effectively encapsulate the lightning-strike expanded metal foil 18 through encapsulation 76 while maintaining separation and immiscibility between the infusion resin 45 and the structural resin 70. Additionally, the initial tailored viscosity 60c (see FIG. 1A) of the infusion resin 45 can be significantly different from the initial structural resin viscosity 60d (see FIG. 1B) of the structural resin 70, thereby minimizing intermixing between the infusion resin 45 and the structural resin 70 during initial cure 14b (see FIG. 1B) or initial co-cure 14c (see FIG. 1B). As used herein, "encapsulation" refers to hardening of the infusion resin, such as a thermosetting resin, around the lightning-strike expanded metal foil, keeping it separated from the structural resin and the composite laminate assembly or structure. For example, during co-cure 14a, the infusion resin 45 in the non-metallic scrim 44 is forced into the openings 130 (see FIG. 2C) in the lightning-strike expanded metal foil 18, such that the infusion resin 45 completely encapsulates or completely surrounds the lightning-strike expanded metal foil 18.

[0046] The tailored viscosity 60a, tailored cure profile 62a, and tailored rheology 64a of the infusion resin 45 are sufficiently different, or for example, significantly different, from the structural resin viscosity 60b, structural resin cure profile 62b, and structural resin rheology 64b of the structural resin 70, thereby enabling the infusion resin 45 to adequately and effectively encapsulate the lightning strike expanded metal foil 18 for in-service protection. The infusion resin 45 has properties associated with thermal humidity cycling that are compatible with the structural resin 70, preventing or minimizing resin intermixing between the infusion resin 45 and the structural resin 70 during co-curing 14a or curing 14b.

[0047] A cured lightning protection (LSP) composite structure 80 (see FIG. 1B), such as co-cured lightning protection (LSP) composite structure 80a (see FIG. 1B), is formed by curing 14 or co-curing 14a of a lightning protection assembly 10, e.g., an uncured lightning protection assembly 10a, with a structural assembly 71 (see FIG. 1B), e.g., a composite layup assembly 72 (see FIG. 1B), such as an uncured composite layup assembly 72a (see FIG. 1B). A cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, is comprised of a cured lightning protection assembly 10c (see FIG. 1A) coupled or bonded to a cured composite layup assembly 72c (see FIG. 1B). The cured lightning protection assembly 10c provides lightning protection 11 (see FIG. 1A) to the underlying cured composite layup assembly 72c. As a result, the hardened lightning protection composite structure 80 has the function of lightning protection 11. In addition, the hardened lightning protection composite structure 80 has the functions of improved microcrack resistance 82 (see FIG. 1B) and degradation resistance 84 (see FIG. 1B).

[0048] The immiscibility of the infusion resin 45 and the structural resin 70 reduces damage to the infusion resin 45 and the structural resin 70 caused by the difference between the coefficient of thermal expansion (CTE) 86a (see FIG. 1A) of the lightning-strike expanded metal foil 18 (see FIG. 1A) and the coefficient of thermal expansion (CTE) 86b (see FIG. 1B) of the composite layup assembly 72. Furthermore, the immiscibility of the infusion resin 45 and the structural resin 70 reduces damage to the infusion resin 45 and the structural resin 70 caused by the difference between the coefficient of hygroscopic expansion (CME) 88a (see FIG. 1A) of the lightning-strike expanded metal foil 18 and the coefficient of hygroscopic expansion (CME) 88b (see FIG. 1B) of the composite layup assembly 72. Typically, during a heat and humidity cycling event, metal expands more than composite materials, for example, in the temperature range of −70° F. to 160° F., potentially resulting in cracks or microcracking. The lightning protection assembly 10 and lightning protection system 12 disclosed herein mitigate the difference between the CTE 86a of the lightning expanded metal foil 18 and the CTE 86b of the composite laminate assembly 72 during a heat and humidity cycling event, thereby reducing or preventing the onset of microcracking or cracking and providing the cured lightning protection composite structure 80 with improved microcracking resistance 82.

[0049] Additionally, the cured lightning protection composite structure 80 has significantly less surface porosity and performs better in heat and humidity cycling events, as evidenced by significantly fewer or no microcracks 83 (see FIG. 2E) or cracks in the cured lightning protection composite structure 80 after exposure to heat and humidity cycling. Additionally, the cured lightning protection composite structure 80 has degradation prevention 84 to prevent degradation, such as microcracks or cracks, from extending into the structural assembly 71, such as the cured composite laminate assembly 72c, and the plurality of structural ply layers 75. Any microcracks 83 (see FIG. 2E) or cracks that may occur will remain within the cured lightning protection assembly 10c and will not extend into the structural assembly 71, such as the cured composite laminate assembly 72c.

[0050] As used herein, "thermo-hygroscopic cycling" or "thermo-hygroscopic cycling event" refers to a process in which a material is exposed to changes in heat and / or moisture, such as endothermic or hygroscopic changes, during use, such as when an aircraft shuttles between a parked position on the ground at ambient or high temperatures and a flight phase in the air at low or freezing temperatures.

[0051] 1B illustrates lightning protection systems (LSPMS) 12, including uncured lightning protection systems (LSPMS) 12a, partially cured lightning protection systems (LSPMS) 12b, and / or cured lightning protection systems (LSPMS) 12c, at various stages before, during, and after curing 14 or co-curing 14a. For example, uncured lightning protection system 12a is in an uncured stage before curing 14 or co-curing 14a, partially cured lightning protection system 12b is in a partially cured stage during curing 14 or co-curing 14a, and cured lightning protection system 12c is in a cured stage after curing 14 or co-curing 14a.

[0052] As shown in Figure 1B, lightning protection system 12 includes lightning protection assembly 10, as described in detail above with respect to Figure 1A. Lightning protection assembly 10 includes lightning expanded metal foil layer 16 (see Figure 1A), which includes lightning expanded metal foil 18 (see Figure 1A). As shown in Figure 1A and as described above, lightning expanded metal foil 18 includes a discontinuous metal foil 26, which may include one or more of perforated metal foil (MF) 28, expanded metal foil (MF) 29, metal mesh 30, metalized fiber mesh 31, metal screen 32, metalized fiber fabric 33, metal fabric 34, wire mesh 35, metal foam 36, open-cell metal foam 36a, or other suitable discontinuous metal foil 26. As further shown in FIG. 1A and as described above, the lightning strike expanded metal foil 18 includes a metal material 38 or a metal alloy material 40, where the metal material 38 includes one or more of copper 38a, aluminum 38b, titanium 38c, nickel 38d, gold 38e, silver 38f, or other suitable metal materials 38, and the metal alloy material 40 includes one or more of copper alloy 40a, aluminum alloy 40b, titanium alloy 40c, nickel alloy 40d, gold alloy 40e, silver alloy 40f, bronze 40g, brass 40h, or other suitable metal alloy materials 40.

[0053] As mentioned above, lightning strike protection assembly 10 further includes a resin-infused scrim layer 42 (see FIG. 1A) laminated to lightning strike expanded metal foil layer 16. Resin-infused scrim layer 42 includes a non-metallic scrim 44 (see FIG. 1A) infused with an infusion resin 45 (see FIG. 1A), also referred to as lightning strike protection resin 46 (see FIG. 1A). As further shown in FIG. 1A, non-metallic scrim 44 includes one of a non-metallic scrim mat 44a, a fiberglass scrim mat 44b, a carbon fiber scrim mat 44c, a woven scrim mat 44d, a knitted polyester scrim mat 44e, a non-woven scrim mat 44f, or other suitable non-metallic scrim 44. 1A, the infusion resin 45 includes a thermosetting resin 58 including one or more of adhesive 58a, epoxy 58b, phenolic 58c, polyimide 58d, bismaleimide 58e, polyurethane 58f, fluoropolymer 58g, cyanate ester 58h, or other suitable thermosetting resin 58. As further shown in FIG. 1A, the infusion resin 45 has a tailored viscosity 60a, a tailored cure profile 62a, and a tailored rheology 64a.

[0054] As shown in FIG. 1B, the lightning protection system 12 further includes a structural assembly 71, such as a composite layup assembly 72. As shown in FIG. 1B, the composite layup assembly 72 has a coefficient of thermal expansion (CTE) 86b and a coefficient of hygroscopic expansion (CME) 88B. As further shown in FIG. 1B, the composite layup assembly (CLA) 72 can include or take the form of an uncured composite layup assembly (CLA) 72a, a partially cured composite layup assembly (CLA) 72b, or a cured composite layup assembly (CLA) 72c. The uncured composite layup assembly (CLA) 72a, the partially cured composite layup assembly (CLA) 72b, and / or the cured composite layup assembly (CLA) 72c exist at various stages before, during, and after curing 14 or co-curing 14a. For example, uncured composite layup assembly 72a is in an uncured stage prior to curing 14 or co-curing 14a, partially cured composite layup assembly 72b is in a partially cured stage during curing 14 or co-curing 14a, and cured composite layup assembly 72c is in a cured stage after curing 14 or co-curing 14a.

[0055] A structural assembly 71, such as a composite layup assembly 72 in the form of an uncured composite layup assembly 72a, a partially cured composite layup assembly 72b, or a cured composite layup assembly 72c, includes a plurality of structural layers 74 (see FIG. 1B), such as a plurality of structural ply layers 75 (see FIG. 1B), pre-impregnated with a structural resin 70 (see FIG. 1B), such as a structural prepreg resin. Each structural ply layer 75 includes a ply 75a (see FIG. 1B), and a plurality of structural ply layers 75 includes a plurality of plies 75a.

[0056] Each of the plurality of structural ply layers 75 and plies 75a includes a composite material (COMP.MAT.) 90 (see FIG. 1B) having structural fibers 91, such as composite (COMP.) fibers 92 (see FIG. 1B). As shown in FIG. 1B, the composite material 90 may include one or more of: one or more carbon fiber reinforced polymers (CFRP) 94 or carbon fiber reinforced plastics having carbon fibers 95; one or more glass fiber reinforced polymers (GFRP) 96 or glass fiber reinforced plastics having glass fibers 98 or fiberglass fibers; one or more aramid polymers 100 or aramid plastics (here, "aramid" means aromatic polyamide) having aramid fibers 102; or other suitable composite materials 90 having structural fibers 91, such as composite fibers 92.

[0057] The composite material 90 includes a matrix of structural resin 70 (see FIG. 1B) reinforced with composite fibers 92. Each structural layer 74, such as structural ply layer 75, may include a plurality of structural fibers 91, such as composite fibers 92. These structural fibers may be at least partially or completely encapsulated within the structural resin 70, uncured structural resin (SR) 70a (see FIG. 1B), partially cured structural resin (SR) 70b (see FIG. 1B), and / or cured structural resin (SR) 70c (see FIG. 1B). Examples of the plurality of structural fibers 91, such as composite fibers 92, include a plurality of carbon fibers 95, a plurality of glass fibers 98 or fiberglass fibers, and / or a plurality of aramid fibers 102, or other suitable structural fibers 91. In a preferred example, the structural layers 74 and / or structural fibers 91, such as composite fibers 92, include and / or are disposed in a plurality of structural ply layers 75 having layered plies 75a of composite material 90, the structural ply layers including structural resin 70, such as in the form of uncured structural resin 70a, partially cured structural resin 70b, and / or cured structural resin 70c.

[0058] The plurality of structural layers 74 may include a plurality of structural ply layers 75 formed of a composite material 90 including a structural resin 70, such as uncured structural resin 70a. Each of the plurality of structural layers 74, such as the plurality of structural ply layers 75, may include a plurality of structural fibers 91, such as a plurality of composite fibers 92, at least partially encapsulated in the structural resin 70, such as the uncured structural resin 70a. Each of the plurality of structural layers 74, such as the plurality of structural ply layers 75, may include a plurality of carbon fibers 95, at least partially encapsulated in the structural resin 70, such as the uncured structural resin 70a.

[0059] 1B , in one embodiment, structural resin (SR) 70 comprises a thermosetting structural resin (SR) 104 including one or more of epoxy structural resin (SR) 104a, phenolic structural resin (SR) 104b, polyimide structural resin (SR) 104c, bismaleimide structural resin (SR) 104d, such as a polybismaleimide structural resin, polyurethane structural resin (SR) 104e, fluoropolymer structural resin (SR) 104f, cyanate ester structural resin (SR) 104g, or other suitable thermosetting structural resin 104. In other embodiments, structural resin 70 may comprise any suitable resin that has, defines, and / or may exhibit a structural resin viscosity 60b (see FIG. 1B), such as an initial structural resin viscosity 60d (see FIG. 1B), a structural resin cure profile 62b (see FIG. 1B), a structural resin rheology 64b (see FIG. 1B), a structural resin gel point temperature, and / or a structural resin gel time.

[0060] 1B, the structural resin 70 has a structural resin viscosity 60b, such as an initial structural resin viscosity 60d, a structural resin cure profile 62b, and a structural resin rheology 64b that differ from the tailored viscosity 60a, tailored cure profile 62a, and tailored rheology 64a of the infusion resin 45, thereby preventing intermixing of the structural resin 70 and the infusion resin 45 during co-cure 14a (see FIG. 1B) or cure 14 (see FIG. 1B) and allowing the infusion resin 45 to effectively encapsulate the lightning strike expanded metal foil 18 via encapsulation 76 (see FIG. 1B), achieving a defined resin boundary 78 (see FIG. 1B). This differs from known resin systems in which intermixing occurs between a resin, such as a scrim resin, and the structural laminate resin during co-cure or cure, thereby preventing the formation of a defined or distinct resin boundary.

[0061] 1B, a lightning protection assembly 10, such as uncured lightning protection assembly 10a (see FIG. 1A), is laid up by a layup process 73a onto a composite layup assembly 72, such as uncured composite layup assembly 72a, to form a layup assembly (ASSY.) (LA) 106. As shown in FIG. 1B, the layup assembly (LA) 106 can be in the form of an uncured layup assembly (LA) 106a, a partially cured layup assembly (LA) 106b, and / or a cured layup assembly (LA) 106c, depending on the stage of co-curing 14a or curing 14b, such as before, during, or after co-curing 14a.

[0062] A layup assembly 106, such as uncured layup assembly 106a, including uncured lightning protection assemblies 10a laid up and connected to uncured composite layup assemblies 72a, is placed in a heating device 108 (see FIG. 1B), such as an autoclave 110 (see FIG. 1B) or other suitable heating device 108, for co-curing 14a (see FIG. 1B) or curing 14a (see FIG. 1B). Preferably, the uncured layup assembly 106a, including uncured lightning protection assemblies 10a laid up and connected to uncured composite layup assemblies 72a, is subjected to a snap-cure process 15 (see FIG. 1B), such as that disclosed in U.S. Pat. No. 11,752,708, which is incorporated herein by reference in its entirety.

[0063] During co-curing 14a in a heating device 108, such as an autoclave 110, a layup assembly 106, such as uncured layup assembly 106a, including an uncured lightning protection assembly 10a laid up and coupled to an uncured composite layup assembly 72a, is heated, e.g., initially heated with heat 112 (see FIG. 1B), such as initial heat 112a (see FIG. 1B), to a temperature (TEMP.) 114 (see FIG. 1B), such as initial temperature (TEMP.) 114a (see FIG. 1B), to form a partially cured layup assembly 106b (see FIG. 1B) including a partially cured lightning protection assembly 10b laid up and coupled to a partially cured composite layup assembly 72b (see FIG. 1B). The initial heat 112a and initial temperature 114a from the initial heating are preferably at least 90°C (90 degrees Celsius, 194 degrees Fahrenheit) and at most 140°C (140 degrees Celsius, 284 degrees Fahrenheit). The initial heating includes initial heating for a given heating time 116 (see FIG. 1B), such as an initial heating time 116a (see FIG. 1B) of at least 2 minutes and at most 30 minutes. The initial heating from the initial heat 112a is sufficient to gel the uncured infusion resin 45 into gel 56 (see FIG. 1A), but the initial heating from the initial heat 112a is insufficient to gel the uncured structural resin 70.

[0064] During co-curing 14a in a heating device 108, such as an autoclave 110, the partially cured layup assembly 106b, including the partially cured lightning protection assembly 10b laid up and coupled to the partially cured composite layup assembly 72b, is then post-heated, for example, with a post-heat 112b (see FIG. 1B ), at a desired post-heat temperature (TEMP.) 114b (see FIG. 1B ) until a final temperature (TEMP.) 114c higher than the final heat 112c and the initial temperature 114a is reached, thereby forming a cured layup assembly 106c (see FIG. 1B ) including the cured lightning protection assembly 10c laid up and coupled to the cured composite layup assembly 72c. The combination of the initial, post-heat, and final heat is sufficient to cure, such as fully cure, both the infusion resin 45 and the structural resin 70.

[0065] Post-heating with subsequent heat 112b includes heating for a post-heating time 116b (see FIG. 1B) of at least 15 minutes and at most 120 minutes. The final temperature 114c, such as the final curing temperature, resulting from final heat 112c and final heat is preferably at least 120°C (120°C, 248°F) and at most 260°C (260°C, 500°F). The difference between the final temperature 114c, such as the final curing temperature, and the initial temperature 114a is at least 20°C (20°C, 68°F). Initial heating includes initial heating for initial heating time 116a, and post-heating includes heating for post-heating time 116b, with the difference between post-heating time 116b and initial heating time 116a being at least 10 minutes.

[0066] Co-curing 14a with heat 112 in a heating device 108, such as an autoclave 110, of a layup assembly 106 including an uncured lightning protection assembly 10a laid up and joined to an uncured composite layup assembly 72a further includes applying pressure 118 (see FIG. 1B) to at least one of the uncured composite layup assembly 72a during initial heating with initial heat 112a or the partially cured composite layup assembly 72b during subsequent heating with subsequent heat 112b. In some examples, applying pressure 118 includes applying an elevated air pressure (ATM) 118a of 0 to 150 psi (0 to 150 pounds per square inch) (0 to 10.2 atm) to the uncured composite layup assembly 72a and / or the partially cured composite layup assembly 72b. In some examples, applying pressure 118 includes utilizing a heating device 108, such as an autoclave 110, autoclaving the uncured composite layup assembly 72a during initial heating, and / or autoclaving the partially cured composite layup assembly 72b during post-heating.

[0067] During co-cure 14a, the structural resin 70 and the infusion resin 45 do not mix, and a defined resin boundary 78 (see FIGS. 1B, 2D) is formed between the resin-infused scrim layer 42 (see FIG. 1A) of the lightning strike protection assembly 10 and the top structural ply layer 75b (see FIGS. 2C, 2D), including the top ply 75c (see FIG. 2D) of a composite layup assembly 72, such as in the form of a partially cured composite layup assembly 72b (see FIG. 2C) or a cured composite layup assembly 72c (see FIG. 2D). The infusion resin 45 effectively encapsulates the lightning strike expanded metal foil 16 (see FIGS. 1A and 2D).

[0068] 1B, after co-curing 14a or curing 14 is completed or terminated, for example, after completion of snap-cure process 15, a cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, is obtained. The cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, includes a cured layup assembly 106c (see FIG. 1B) that includes cured lightning protection assembly 10c (see FIG. 1A) co-cured with a structural assembly 71, such as cured composite layup assembly 72c.

[0069] 1B , a cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, may include or be part of a composite (COMP.) structure (STRUC.) (CS) 120, such as aircraft composite structure (CS) 120a, which may be in the form of a panel 122, such as wing panel 122a of wing 204 of aircraft 200a (see FIG. 5), horizontal stabilizer (STABIL.) panel 122b of horizontal stabilizer (STABIL.) 212 of aircraft 200a (see FIG. 5), or fuselage panel 122c of fuselage 202 of aircraft 200a (see FIG. 5). A cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, may also include or be part of any other suitable composite structure 120 or other suitable aircraft composite structure 120a.

[0070] As shown in FIG. 1B, a hardened lightning protection composite structure 80, such as a co-hardened lightning protection composite structure 80a, provides lightning protection (LSP) 11 and also provides enhanced micro-crack resistance 82 and degradation resistance 84.

[0071] As discussed above, a cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, has significantly less surface porosity and improved performance in heat and humidity cycling events, as evidenced by a significantly reduced or limited number of microcracks 83 (see FIG. 2E ) or cracks in a cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, after exposure to heat and humidity cycling. Additionally, a cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, has degradation prevention 84 to prevent degradation, such as microcracks or cracks, from extending into a structural assembly 71, such as cured composite laminate assembly 72c, and multiple structural ply layers 75. Any microcracks 83 (see FIG. 2E ) or cracks that may occur remain within the cured lightning protection assembly 10c and do not extend into a structural assembly 71, such as cured composite laminate assembly 72c.

[0072] 2A, which is a cross-sectional front view of an exemplary lightning protection assembly 10 of the present disclosure, such as uncured lightning protection assembly 10a, prior to co-curing 14a (see FIG. 1B) or curing 14 (see FIG. 1B), such as by a snap-cure process 15 (see FIG. 1B). As shown in FIG. 2A, a lightning protection assembly 10, such as uncured lightning protection assembly 10a, includes a lightning expanded metal foil layer 16 comprised of a lightning expanded metal foil 18. As further shown in FIG. 2A, the lightning expanded metal foil layer 16 has a first surface 20, such as an upper surface 20a, a second surface 22, such as a lower surface 22a, and a metal foil layer body 24 located between the first surface 20 and the second surface 22 and between the ends 25 of the lightning expanded metal foil layer 16.

[0073] 2A, in one embodiment, lightning protection assembly 10, such as uncured lightning protection assembly 10a, includes a discontinuous metal foil 26, including perforated metal foil 28. In other embodiments, discontinuous metal foil 26 includes expanded metal foil 29, metal mesh 30, metalized fiber mesh 31, metal screen 32, metalized fiber fabric 33, metal fabric 34, wire mesh 35, metal foam 36, open-cell metal foam 36a, or other suitable discontinuous metal foil 26, as shown in FIG.

[0074] 2A, lightning protection assembly 10, such as uncured lightning protection assembly 10a, includes a resin-infused scrim layer 42 laminated to lightning expanded metal foil layer 16. As further shown in FIG. 2A, resin-infused scrim layer 42 includes a non-metallic scrim 44 infused with infusion resin 45.

[0075] In one embodiment, the non-metallic scrim 44 comprises a non-metallic scrim mat 44a, as shown in Figure 2A. In other embodiments, the non-metallic scrim 44 comprises a fiberglass scrim mat 44b, a carbon fiber scrim mat 44c, a woven scrim mat 44d, a knitted polyester scrim mat 44e, a non-woven scrim mat 44f, or other suitable non-metallic scrim 44, as shown in Figure 1A.

[0076] 2A, in one embodiment, the infusion resin 45 comprises an uncured infusion resin 45a that includes a thermosetting resin 58, such as adhesive 58a. In other embodiments, the thermosetting resin 58 includes an epoxy 58b, a phenolic 58c, a polyimide 58d, a bismaleimide 58e, a polyurethane 58f, a fluoropolymer 58g, a cyanate ester 58h, or other suitable thermosetting resin 58, as shown in FIG. 1A.

[0077] 2A, resin-infused scrim layer 42 has a first side 48, such as upper side 48a, a second side 50, such as lower side 50a, and a scrim layer body 52 located between first side 48 and second side 50 and between ends 54 of resin-infused scrim layer 42. As further shown in FIG. 2A, second side 22, such as lower side 22a, of lightning-strike expanded metal foil layer 16 is disposed directly on, joined to, and in continuous contact with first side 48, such as upper side 48a, of resin-infused scrim layer 42.

[0078] Referring now to FIG. 2B, FIG. 2B is a cross-sectional front view of an exemplary lightning protection system 12 of the present disclosure, such as uncured lightning protection system 12a, showing the lightning protection assembly 10 of FIG. 2A, such as uncured lightning protection assembly 10a, laid up and placed on a structural assembly 71, such as a composite layup assembly 72, e.g., uncured composite layup assembly 72a, prior to co-curing 14a (see FIG. 1B) or curing 14 (see FIG. 1B) to form a layup assembly 106, such as uncured layup assembly 106a.

[0079] As shown in Figure 2B, a lightning protection assembly 10, such as uncured lightning protection assembly 10a, includes a lightning expanded metal foil layer 16 constructed from lightning expanded metal foil 18 and further includes a resin-infused scrim layer 42 laminated to lightning expanded metal foil layer 16. As shown in Figure 2B, resin-infused scrim layer 42 includes a non-metallic scrim 44, such as a non-metallic scrim mat 44a, infused with an infusion resin 45, such as an uncured infusion resin 45a, e.g., a thermosetting resin 58 in the form of an adhesive 58a. Figure 2B also shows a first side 20, e.g., upper side 20a, of lightning expanded metal foil layer 16 and a second side 50, e.g., lower side 50a, of resin-infused scrim layer 42.

[0080] FIG. 2B further illustrates a structural assembly 71, such as a composite layup assembly 72 in the form of an uncured composite layup assembly 72a, having a plurality of structural layers 74, such as a plurality of structural ply layers 75, each pre-impregnated with structural resin 70, such as in the form of uncured structural resin 70a. In one embodiment, as shown in FIG. 2B, a structural assembly 71, such as a composite layup assembly 72, has four structural layers 74, such as four structural ply layers 75, each including a ply 75a, and a plurality of structural ply layers 75 including a plurality of plies 75a. In other embodiments, a structural assembly 71, such as a composite layup assembly 72, may have fewer or more than four structural layers 74, such as a top ply 75c. FIG. 2B also illustrates a bottom ply 75d and an intermediate ply 75e laminated between the bottom ply 75d and the top ply 75c. As shown in FIG. 2B, each of the top ply 75c, bottom ply 75d, and middle ply 75e has a first surface 124, such as upper surface 124a, and a second surface 126, such as lower surface 126a.

[0081] As shown in FIG. 2B , the second surface 50, such as the lower surface 50a, of the resin-infused scrim layer 42 of a lightning protection assembly 10, such as uncured lightning protection assembly 10a, is laid up, directly disposed, coupled to, and in continuous contact with the first surface 124, such as the upper surface 124a, of the top ply 75c of the plurality of structural ply layers 75 of a structural assembly 71, such as composite laminate assembly 72.

[0082] 2B, structural ply layer 75 and ply 75a each include a composite material 90 having structural fibers 91, such as composite fibers 92. As shown in FIG. 1B, composite material 90 may include one or more of one or more carbon fiber reinforced polymers 94 or plastics having carbon fibers 95, one or more glass fiber reinforced polymers 96 or plastics having glass fibers 98 or fiberglass fibers, one or more aramid polymers 100 or plastics having aramid fibers 102, or other suitable composite materials 90 having structural fibers 91, such as composite fibers 92.

[0083] 2B, in one embodiment, the structural resin 70 comprises a thermosetting structural resin 104 comprising an epoxy structural resin 104a. In other embodiments, as shown in FIG. 1B, the thermosetting structural resin 104 comprises a phenolic structural resin 104b, a polyimide structural resin 104c, a bismaleimide structural resin 104d, such as a polybismaleimide structural resin, a polyurethane structural resin 104e, a fluoropolymer structural resin 104f, a cyanate ester structural resin 104g, or other suitable thermosetting structural resin 104.

[0084] 2C, which is a cross-sectional front view of the lightning protection system 12 of FIG. 2B in the form of a partially cured lightning protection system 12b inside a heating apparatus 108, such as an autoclave 110, during co-curing 14a. FIG. 2C shows a layup assembly 106, such as in the form of a partially cured layup assembly 106b, during co-curing 14a, which includes a lightning protection assembly 10, such as in the form of a partially cured lightning protection assembly 10b, laid up and arranged in a structural assembly 71, such as a composite layup assembly 72 in the form of a partially cured composite layup assembly 72b.

[0085] Figure 2C illustrates lightning protection assembly 10, such as in the form of partially cured lightning protection assembly 10b, with lightning expanded metal foil layer 16 comprised of lightning expanded metal foil 18. Figure 2C also illustrates lightning protection assembly 10, such as in the form of partially cured lightning protection assembly 10b, with resin-infused scrim layer 42 comprised of non-metallic scrim 44, which is a non-metallic scrim mat 44a infused with infusion resin 45, such as in the form of partially cured infusion resin 45b.

[0086] FIG. 2C further illustrates a structural assembly 71, such as a composite layup assembly 72 in the form of a partially cured composite layup assembly 72b, having a plurality of structural layers 74, such as a plurality of structural ply layers 75, each of which is pre-impregnated with a structural resin 70, such as in the form of a partially cured structural resin 70b.

[0087] During co-cure 14a, the infusion resin 45, such as in the form of partially cured infusion resin 45b within the non-metallic scrim 44, is forced into the openings 130 (see FIG. 2C) in the lightning-strike expanded metal foil 18, thereby completely encapsulating or surrounding the lightning-strike expanded metal foil 18. The infusion resin 45 effectively encapsulates the lightning-strike expanded metal foil 18 via encapsulation 76 (see FIG. 2C), minimizing intermixing of the infusion resin 45 with the structural resin 70 during initial cure 14b (see FIG. 1B) and co-cure 14a. The adjusted viscosity 60a (see FIG. 1A) of the infusion resin 45 can be significantly different from the structural resin viscosity 60b (see FIG. 1B) of the structural resin 70, thereby preventing intermixing of the infusion resin 45 with the structural resin 70 during initial cure 14b (see FIG. 1B) or co-cure 14a. The tailored cure profile 62a (FIG. 1A) of the infusion resin 45 initiates crosslinking at a lower temperature, which allows the tailored viscosity 60a to increase quickly, allowing the infusion resin to effectively encapsulate the lightning-strike expanded metal foil 18 while maintaining separation and immiscibility between the structural resin 70 and the infusion resin 45 within the multiple structural ply layers 75 of the composite layup assembly 72. The infusion resin 45 with the tailored viscosity 60a and tailored cure profile 62a associated with the lightning-strike expanded metal foil 18 achieves chemical compatibility 66 (see FIG. 1A) and bonding capability 68 (see FIG. 1A) with the structural resin 70.

[0088] 2C further illustrates a defined resin boundary 78 beginning to form between the resin-infused scrim layer 42 of the lightning strike protection assembly 10 and the top structural ply layer 75b, including the top ply 75c, of the composite laminate assembly 72. This defined resin boundary 78 helps prevent or minimize intermixing of the infusion resin 45 and the structural resin 70 during co-cure 14a.

[0089] Referring now to Figure 2D, Figure 2D is a cross-sectional front view of an exemplary cured lightning protection composite structure 80 of the present disclosure, such as co-cured lightning protection composite structure 80a. As shown in Figure 2D, cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, includes a layup assembly 106, such as in the form of cured layup assembly 106c, which includes a lightning protection assembly 10, such as in the form of cured lightning protection assembly 10c, co-cured and bonded with a structural assembly 71, such as a composite layup assembly 72, such as in the form of cured composite layup assembly 72c. Figure 2D also shows lightning protection system 12 in the form of cured lightning protection system 12c after co-curing 14a (see Figure 2C).

[0090] As a result of co-curing 14a (see FIG. 2C), as shown in FIG. 2D, infusion resin 45, such as in the form of cured infusion resin 45c, completely encapsulates or completely surrounds lightning-strike expanded metal foil 18 of lightning-strike expanded metal foil layer 16 by encapsulation 76, resulting in encapsulated lightning-strike expanded metal foil 18a. As shown in FIG. 2D, infusion resin 45, such as in the form of cured infusion resin 45c, is present within openings 130 in lightning-strike expanded metal foil 18 and also within resin-infused scrim layer 42.

[0091] 2D further illustrates a defined resin boundary 78 formed between the second surface 50, e.g., bottom surface 50a, of the resin-infused scrim layer 42 of the lightning strike protection assembly 10 and the first surface 124, e.g., top surface 124a, of the top structural ply layer 75b, including the top ply 75c of a composite layup assembly 72, such as cured composite layup assembly 72c. This is different from known resin systems in which a defined or distinct resin boundary is not formed due to intermixing of the resin, such as the scrim resin, with the structural laminate resin during co-curing or curing.

[0092] As shown in FIG. 2D, a composite layup assembly 72, such as cured composite layup assembly 72c, has a plurality of structural layers 74, such as a plurality of structural ply layers 75, having a structural resin 70, such as in the form of cured structural resin 70c.

[0093] A cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, provides lightning protection (LSP) 11 (see FIG. 1B) and also provides enhanced micro-crack resistance 82 (see FIG. 1B) and degradation resistance 84 (see FIG. 1B). A cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, with the lightning protection assembly 10 and lightning protection system 12 disclosed herein mitigates the difference between the CTE 86a (see FIG. 1A) of the lightning expanded metal foil 18 and the CTE 86b (see FIG. 1B) of the composite laminate assembly 72 during a heat-humidity cycling event, thereby reducing or preventing the occurrence of micro-cracking or cracking and providing the cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, with enhanced micro-crack resistance 82.

[0094] Referring now to FIG. 2E, FIG. 2E is a cross-sectional front view of the cured lightning protection composite structure 80 of FIG. 2D, such as co-cured lightning protection composite structure 80a, incorporated into a composite structure 120, such as panel 122, illustrating microcracks 83 formed through the lightning expanded metal foil layer 16, including the lightning expanded metal foil 18, and through the resin-infused scrim layer 42 in a lightning protection assembly 10, such as in the form of cured lightning protection assembly 10c.

[0095] As shown in FIG. 2E , a defined resin boundary 78 formed between the second surface 50, e.g., lower surface 50a, of the resin-infused scrim layer 42 of the lightning protection assembly 10 and the first surface 124, e.g., upper surface 124a, of the uppermost structural ply layer 75b, including the top ply 75c of a composite layup assembly 72, such as cured composite layup assembly 72c, prevents microcracks 83 from extending into a structural assembly 71, such as a composite layup assembly 72 in the form of cured composite layup assembly 72c. The defined resin boundary 78 acts as a barrier to prevent microcracks 83 from extending into the cured composite layup assembly 72c. In this manner, a cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, provides degradation protection 84 (see FIG. 1B ) to prevent degradation, such as microcracks 83 or cracks, from extending into the structural assembly 71, such as cured composite layup assembly 72c, and the plurality of structural ply layers 75. Any microcracks 83 (see FIG. 2E) or cracks that may occur will remain within the cured lightning strike protection assembly 10c and will not extend into the structural assembly 71, such as the cured composite laminate assembly 72c.

[0096] Additionally, the cured lightning protection composite structure 80, such as the co-cured lightning protection composite structure 80a, has improved microcrack resistance 82 (see FIG. 1B ), which mitigates, minimizes, or prevents the formation of microcracks 83 within the cured lightning protection composite structure 80, such as the co-cured lightning protection composite structure 80a. FIG. 2E shows a single microcrack 83. The microcrack 83 may be observed during thermocycling, temperature changes, tensile loading, or fatigue loading. As discussed above, the cured lightning protection composite structure 80, such as the co-cured lightning protection composite structure 80a, has significantly less surface porosity and improved performance in heat-humidity cycling events, as evidenced by significantly fewer or fewer microcracks 83 (see FIG. 2E ) or cracks within the cured lightning protection composite structure 80, such as the co-cured lightning protection composite structure 80a, after exposure to heat-humidity cycling.

[0097] Compared to a cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, with a lightning protection assembly 10, such as cured lightning protection assembly 10c, known composite structures with known resin systems in which a resin, such as a scrim resin, is mixed with a structural laminate resin during co-curing or curing may have more microcracks, such as multiple microcracks, less resistance to microcracks, and the microcracks that may extend into the structural plies of the composite structure, increasing degradation of the composite structure. Thus, a cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, may minimize degradation that may occur during use of a lightning protection assembly 10, such as cured lightning protection assembly 10c, and provide desired benefits.

[0098] As further shown in Figure 2E, a cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, includes a layup assembly 106, such as in the form of cured layup assembly 106c, which includes a lightning protection assembly 10, such as in the form of cured lightning protection assembly 10c, co-cured and bonded with a structural assembly 71, such as a composite layup assembly 72, such as in the form of cured composite layup assembly 72c. Figure 2E also shows a lightning protection system 12 in the form of cured lightning protection system 12c after co-curing 14a (see Figure 2C).

[0099] As further shown in Figure 2E, infusion resin 45, such as in the form of cured infusion resin 45c, encapsulates lightning-strike expanded metal foil 18 and is also within resin-infused scrim layer 42. As further shown in Figure 2E, composite layup assembly 72, such as cured composite layup assembly 72c, has a plurality of structural layers 74, such as a plurality of structural ply layers 75, having structural resin 70, such as in the form of cured structural resin 70c.

[0100] 3A, which illustrates a graph 132 showing viscosity 60 or thickness along y-axis 134 and temperature 114 along x-axis 136 during curing or co-curing of an exemplary lightning protection system 12 (see FIG. 1B) of the present disclosure, where the lightning protection system 12 includes an infusion resin 45 (see FIG. 1A) and a structural resin 70 (see FIG. 1B). In graph 132, viscosity 60 decreases from top to bottom along y-axis 134, and temperature 114 increases from left to right along x-axis 136.

[0101] 3A shows an infusion resin plot 138 and a structural resin plot 140. The infusion resin plot 138 represents the infusion resin 45 having a tailored viscosity 60a (see FIG. 1A), a tailored cure profile 62a (see FIG. 1A), and a tailored rheology 64a (see FIG. 1A), and is subjected to a snap-cure process 15 (see FIG. 1B). The structural resin plot 140 represents the structural resin 70 (see FIG. 1B) having a structural resin viscosity 60b (see FIG. 1B), a structural resin cure profile 62b (see FIG. 1B), and a structural resin rheology 64b (see FIG. 1B) that differs from the tailored viscosity 60a, tailored cure profile 62a, and tailored rheology 64a of the infusion resin 45.

[0102] As shown in Figure 3A, the infusion resin plot 138 has a starting point 142, where the viscosity 60 or thickness is high or thick. As further shown in Figure 3A, as the temperature 114 increases, the viscosity 60 or thickness initially decreases to a midpoint 144, where, as the temperature 114 continues to increase, the viscosity 60 now begins to steadily increase from the midpoint 144 to an end point 146, where, as the curing or co-curing continues, the infusion resin 45 cures or co-cures to a solid or solid state. As shown in Figure 3A, the infusion resin plot 138 has a U-shape 148.

[0103] As further shown in Figure 3A, the structural resin plot 140 has a starting point 150, where the viscosity 60 or thickness is high or thick. As further shown in Figure 3A, as the temperature 114 increases, the viscosity 60 or thickness decreases to a midpoint 152, where the viscosity 60 continues to decrease slightly as the temperature 114 continues to increase, leveling off from the midpoint 152 to an end point 154, where the structural resin cures or co-cures to a hardened or solid state as the curing or co-curing continues. As further shown in Figure 3A, the infusion resin plot 138 has a generally downward sloping curve 155.

[0104] 3A, there is a large viscosity difference 156 between the viscosity 60 at the end point 146 of the infusion resin plot 138 and the viscosity 60 at the leveling point 158 ​​on the structural resin plot 140. This large viscosity difference 156 during curing or co-curing prevents or minimizes intermixing of the infusion resin 45 and the structural resin 70.

[0105] 3B, which illustrates a graph 160 showing viscosity 60 or thickness along y-axis 134 and temperature 114 along x-axis 136 during cure or co-cure of a conventional known resin system for lightning strike protection, where the known resin system includes a known resin without tailored viscosity, tailored cure profile, or tailored rheology, and a known structural laminate resin. In graph 160, viscosity 60 decreases from top to bottom along y-axis 134, and temperature 114 increases from left to right along x-axis 136.

[0106] 3B shows a resin plot 162 and a structural laminate resin plot 164. Resin plot 162 represents a known resin that does not have a tailored viscosity, tailored cure profile, and / or tailored rheology like infusion resin 45 (see FIG. 1A), which has a viscosity, cure profile, and rheology that is no different from a known structural laminate resin, and is not subjected to the snap cure process 15 (see FIG. 1B). Structural laminate resin plot 164 represents a known structural laminate resin.

[0107] As shown in Figure 3B, resin plot 162 has a starting point 166, where the viscosity 60 or thickness is high or thick. As further shown in Figure 3B, as the temperature 114 increases, the viscosity 60 or thickness decreases to a midpoint 168, where the viscosity 60 continues to decrease slightly as the temperature 114 continues to increase, leveling off from midpoint 168 to an end point 170, where the curing or co-curing continues as the structural resin cures or co-cures to a hardened or solid state. As shown in Figure 3B, resin plot 162 has a generally downward sloping curve 155a.

[0108] As further shown in Figure 3B, the structural laminate resin plot 164 has a starting point 172, where the viscosity 60 or thickness is high or thick. As further shown in Figure 3B, as the temperature 114 increases, the viscosity 60 or thickness decreases until midpoint 174, at which point the viscosity 60 continues to decrease slightly as the temperature 114 continues to increase, leveling off from midpoint 174 to end point 176, where the curing or co-curing continues as the structural laminate resin cures or co-cures to a hardened or solid state. As shown in Figure 3B, the structural laminate resin plot 164 has a generally downward sloping curve 155b.

[0109] 3B, there is a small viscosity difference 178 between the viscosity 60 at point 180 near endpoint 170 of resin plot 162 and the viscosity 60 at point 182 near endpoint 176 of structural laminate resin plot 164. This small viscosity difference 178 upon curing or co-curing facilitates mixing of known resins with known structural laminate resins.

[0110] Referring now to FIG. 4, FIG. 4 illustrates a flowchart of an exemplary embodiment of a method 190 of the present disclosure. In another embodiment of the present disclosure, a method 190 is provided for imparting improved microcrack resistance 82 (see FIG. 1B) and degradation prevention 84 (see FIG. 1B) to a cured lightning protection composite structure 80 (see FIG. 1B) using the lightning protection system 12 (see FIG. 1B) described above. The blocks in FIG. 4 represent steps and / or portions thereof or elements, and the lines connecting the various blocks do not imply any particular order or dependency of these steps or portions thereof. The disclosure of the steps of method 190 in FIG. 4 and herein does not necessarily dictate the order in which these steps are performed. Rather, one exemplary order is shown, but the order of steps can be varied as appropriate. Thus, certain operations may be performed in a different order or simultaneously.

[0111] 4, method 190 includes step 192 of providing lightning protection system 12. As described in detail above, lightning protection system 12 includes lightning protection assembly 10 (see FIG. 1A). As described in detail above, lightning protection assembly 10 includes lightning expanded metal foil layer 16 (see FIGS. 1A, 2A) which includes lightning expanded metal foil 18 (see FIGS. 1A, 2A).

[0112] Step 192 of providing lightning protection system 12 further includes providing a lightning protection system having lightning protection assembly 10, where lightning expanded metal foil 18 includes a discontinuous metal foil 26 including one or more of perforated metal foil 28, expanded metal foil 29, metal mesh 30, metalized fiber mesh 31, metal screen 32, metalized fiber fabric 33, metal fabric 34, wire mesh 35, metal foam 36, open-cell metal foam 36a, or other suitable discontinuous metal foil 26, as shown in FIG. 1A .

[0113] Additionally, step 192 of providing a lightning protection system 12 further includes providing a lightning protection system 12 having a lightning protection assembly 10, wherein the lightning expanded metal foil 18 further includes a metal material 38 including one or more of copper 38a, aluminum 38b, titanium 38c, nickel 38d, gold 38e, silver 38f, or other suitable metal materials 38, as shown in FIG. 1A, or a metal alloy material 40 including one or more of copper alloy 40a, aluminum alloy 40b, titanium alloy 40c, nickel alloy 40d, gold alloy 40e, silver alloy 40f, bronze 40g, brass 40h, or other suitable metal alloy materials, as shown in FIG. 1A.

[0114] As described above, lightning strike protection assembly 10 further includes a resin-infused scrim layer 42 (see FIGS. 1A and 2A) laminated to lightning expanded metal foil layer 16. Resin-infused scrim layer 42 includes a non-metallic scrim 44 (see FIG. 1A) infused with an infusion resin 45 (see FIG. 1A). Infusion resin 45 has a viscosity 60 (see FIG. 1A), such as tailored viscosity 60a (see FIG. 1A), a cure profile 62 (see FIG. 1A), such as tailored cure profile 62a (see FIG. 1A), and a rheology 64 (see FIG. 1A), such as tailored rheology 64a (see FIG. 1A).

[0115] The step 192 of providing the lightning protection system 12 further includes providing the lightning protection system 12 having the lightning protection assembly 10, wherein the infusion resin 45 comprises a thermosetting resin 58 including one or more of adhesive 58a, epoxy 58b, phenolic 58c, polyimide 58d, bismaleimide 58e, polyurethane 58f, fluoropolymer 58g, cyanate ester 58h, or other suitable thermosetting resin 58, as shown in FIG. 1A.

[0116] As detailed above, lightning protection system 12 further includes a composite layup assembly 72 (see FIGS. 1B, 2B), such as uncured composite layup assembly 72a (see FIGS. 1B, 2B), comprised of a plurality of structural layers 74 (see FIG. 1B), such as a plurality of structural ply layers 75 (see FIG. 1B), pre-impregnated with structural resin 70 (see FIG. 1B). As shown in FIG. 1B, structural resin 70 has a structural resin viscosity 60b, a structural resin cure profile 62b, and a structural resin rheology 64b that differ from the tailored viscosity 60a, tailored cure profile 62a, and tailored rheology 64a of infusion resin 45.

[0117] Each of the plurality of structural ply layers 75 includes a composite material 90 (see FIG. 1B) including one or more carbon fiber reinforced polymers (CFRP) 94 or plastics, one or more glass fiber reinforced polymers (GFRP) 96 or plastics, one or more aramid polymers 100 (see FIG. 1B), or other suitable composite material 90, as shown in FIG. 1B. The composite material 90 includes composite fibers 92 (see FIG. 1B), such as carbon fibers 95 (see FIG. 1B), glass fibers 98 (see FIG. 1B), aramid fibers 102 (see FIG. 1B), or other suitable composite fibers 92. As shown in FIG. 1B , the structural resin 70 includes a thermosetting structural resin 104 including one or more of an epoxy structural resin 104a, a phenolic structural resin 104b, a polyimide structural resin 104c, a bismaleimide structural resin 104d, a polyurethane structural resin 104e, a fluoropolymer structural resin 104f, a cyanate ester structural resin 104g, or other suitable thermosetting structural resin 104.

[0118] As shown in FIG. 4, the method 190 further includes a step 194 of laying up 73 (see FIG. 1B) the lightning strike protection assembly 10 (see FIGS. 1A, 2B) onto the uncured composite layup assembly 72a (see FIGS. 1B, 2B) by a layup process 73a (see FIG. 1B).

[0119] As shown in FIG. 4, the method 190 further includes a step 196 of co-curing 14a or curing 14 of the uncured composite laminate assembly 72a (see FIG. 2C) and the lightning strike protection assembly 10 (see FIG. 2C) thereon using heat 112 in a heating device 108 (see FIG. 2C), such as an autoclave 110 (see FIG. 2C), wherein during the co-curing 14a or curing 14, the structural resin 70 (see FIGS. 1B, 2C) and the infusion resin 45 (see FIGS. 1A, 2C) do not mix but achieve a defined resin boundary 78 (see FIG. 2C), and the infusion resin 45 effectively encapsulates the lightning strike expanded metal foil 18 (see FIG. 2C).

[0120] Preferably, the co-cure 14a or cure 14 performed on the lightning protection assembly 10, such as uncured lightning protection assembly 10a, and the composite layup assembly 72, such as uncured composite layup assembly 72a (see FIG. 1B), is a snap cure process 15 (see FIG. 1B) as disclosed in U.S. Pat. No. 11,752,708, which is incorporated herein by reference in its entirety.

[0121] The step 196 of co-curing 14a or curing 14b of the uncured composite layup assembly 72a and the lightning protection assembly 10 thereon using heat 112 in the autoclave 110 further includes initially heating the uncured composite layup assembly 72a to a temperature 114 (see FIG. 1B), such as an initial temperature 114a (see FIG. 1B), sufficient to gel the uncured infusion resin 45 but insufficient to gel the uncured structural resin 70, to form a partially cured composite layup assembly 72b (see FIG. 1B), and post-heating the partially cured composite layup assembly 72b to a final temperature 114c (see FIG. 1B), higher than the initial temperature 114a, to form the cured lightning protection composite structure 80 (see FIGS. 1B, 2D), the combination of the initial and post-heating being sufficient to fully cure both the infusion resin 45 and the structural resin 70.

[0122] Step 196 of co-curing 14a or curing 14b the uncured composite layup assembly 72a and the lightning protection assembly 10 thereon using heat 112 in the autoclave 110 further includes applying pressure 118 (see FIG. 1B) to at least one of the uncured composite layup assembly 72a during initial heating or the partially cured composite layup assembly 72b during post-heating.

[0123] As shown in FIG. 4 , the method 190 further includes a step 198 of obtaining a cured lightning protection composite structure 80 (see FIGS. 1B and 2D), such as a co-cured lightning protection composite structure 80a (see FIG. 1B), formed by co-curing 14a or 14b of a lightning protection assembly 10 (see FIGS. 1A and 2A), such as an uncured lightning protection assembly 10a (see FIGS. 1A and 2A), and a composite layup assembly 72, such as an uncured composite layup assembly 72a (see FIGS. 1B and 2B), and using the lightning protection system 12 to impart improved micro-crack resistance 82, degradation prevention 84, and lightning protection 11 to the cured lightning protection composite structure 80, such as the co-cured lightning protection composite structure 80a.

[0124] Step 198 of obtaining a cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, further includes obtaining a cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, including a composite structure 120 (see FIG. 1B), such as aircraft composite structure 120a (see FIG. 1B), including, for example, a panel 122 (see FIG. 1B), such as one of wing panel 122a (see FIGS. 1B and 5) of wing 204 (see FIGS. 1B and 5) of aircraft 200a (see FIG. 5), horizontal stabilizer panel 122b (see FIG. 1B) of horizontal stabilizer 212 (see FIGS. 1B and 5) of aircraft 200a (see FIG. 5), or fuselage panel 122c (see FIG. 1B) of fuselage 202 (see FIGS. 1B and 5) of aircraft 200a (see FIG. 5), or any other suitable aircraft panel or structure.

[0125] Referring now to Figure 5, Figure 5 is a perspective view of a vehicle 200, such as an aircraft 200a, incorporating an exemplary cured lightning protection composite structure 80 (see Figures 1B, 2D, and 2E), e.g., exemplary co-cured lightning protection composite structure 80a (see Figures 1B, 2D, and 2E), having a lightning protection system 12 (see Figures 1B and 2B) of the present disclosure and disposed within a composite structure 120, such as aircraft composite structure 120a. As shown in Figure 5, the vehicle 200, such as the aircraft 200a, includes a fuselage 202, wings 204, an engine 206, and a tail section 208. As shown in Figure 5, the tail section 208 includes a vertical stabilizer 210 and a horizontal stabilizer 212.

[0126] 5, a cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, may include or be a part of a composite structure 120, such as aircraft composite structure 120a, which is in the form of a panel 122, such as wing panel 122a of wing 204 of aircraft 200a. A cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, may include or be a part of a composite structure 120, such as aircraft composite structure 120a, which is in the form of a panel 122, such as horizontal stabilizer panel 122b (see FIG. 1B) of horizontal stabilizer 212 (see FIG. 5) of aircraft 200a (see FIG. 5), fuselage panel 122c (see FIG. 1B) of fuselage 202 (see FIG. 5) of aircraft 200a (see FIG. 5), or any other suitable composite structure 120 or other suitable aircraft composite structure 120a.

[0127] A composite structure 120, such as an aircraft composite structure 120a, including a wing panel 122a, a horizontal stabilizer panel 122b, a fuselage panel 122c, or other suitable aircraft panel, may include a composite structure 120, such as an aircraft composite structure 120a, formed from a composite material 90 (see FIG. 1B), such as a carbon fiber reinforced polymer (CFRP) 94 (see FIG. 1B) or carbon fiber reinforced plastic, a glass fiber reinforced polymer (GFRP) 96 (see FIG. 1B) or glass fiber reinforced plastic, or an aramid polymer 100 (see FIG. 1B), or other type of composite material 90. The use of a cured lightning protection composite structure 80, such as a co-cured lightning protection composite structure 80a with a lightning protection material system 12 (FIGS. 1B and 2D), on aerosurfaces such as wings 204, horizontal stabilizers 212, fuselage 202, and other aerosurface regions of aircraft 200a provides improved micro-crack resistance 82 (see FIG. 1B), degradation resistance 84 (see FIG. 1B), and lightning protection 11 (see FIG. 1B).

[0128] FIG. 5 further illustrates a lightning strike 214 striking wing 204 and a cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, having a lightning protection system 12 (see FIG. 1B) in which a lightning protection assembly 10 (see FIG. 1B) is part of or includes a composite structure 120, such as aircraft composite structure 120a, providing lightning protection 11 (see FIG. 1B) to an underlying structural assembly 71 (see FIG. 1B), such as a composite laminate assembly 72 (see FIG. 1B).

[0129] 5 generally represents a commercial passenger aircraft having one or more aircraft composite structures 120a, the teachings of the disclosed embodiments of the lightning protection assembly 10 (see FIG. 1A), the lightning protection system 12 (see FIG. 1B), and the method 190 (see FIG. 4) may also be applied to aircraft composite structures 120a of other passenger aircraft. The teachings of the disclosed embodiments of the lightning protection assembly 10 (see FIG. 1A), the lightning protection system 12, and the method 190 may also be applied to aircraft composite structures 120a of cargo aircraft, military aircraft, rotorcraft, and other types of aircraft or air vehicles, as well as aerospace vehicles such as spacecraft, satellites, space launch vehicles, rockets, and other aerospace vehicles. Additionally, the teachings of the disclosed embodiments of the lightning protection assembly 10 (see FIG. 1A), the lightning protection system 12, and the method 190 may also be applied to a composite structure 120, such as a watercraft, an automobile, a train, a building structure, or other suitable vehicle or structure.

[0130] 6 and 7, FIG. 6 is a flowchart of an exemplary aircraft production and service method 300, and FIG. 7 is an exemplary block diagram of an aircraft 316. With reference to FIG. 6 and 7, aspects of the disclosure may be described in conjunction with aircraft production and service method 300 as shown in FIG. 6 and aircraft 316 as shown in FIG.

[0131] During pre-production, exemplary aircraft manufacturing and service method 300 includes specification and design 302 of the aircraft 316 and material procurement 304. During production, component and subassembly manufacturing 306 and system integration 308 of the aircraft 316 occurs. The aircraft 316 then undergoes certification and delivery 310 and enters service 312. While in customer service 312, the aircraft 316 may be scheduled for routine maintenance and service 314, which may include modifications, reconfigurations, refurbishments, and other suitable maintenance.

[0132] Each step of aircraft production and service method 300 may be performed or carried out by a system integrator, a third party, and / or an operator (e.g., a customer). A system integrator may include, for example, but is not limited to, any number of aircraft manufacturers and major system subcontractors. A third party may include, for example, any number of vendors, subcontractors, and suppliers. An operator may include, for example, an airline, a leasing company, a military entity, a service organization, or any other suitable operator.

[0133] 7 , an aircraft 316 produced by exemplary aircraft manufacturing and service method 300 may include an airframe 318 having a number of systems 320 and an interior 322. Examples of the number of systems 320 include one or more of a propulsion system 324, an electrical system 326, a hydraulic system 328, and an environmental system 330, as well as any number of other systems. Additionally, while described as being used in the aerospace industry, the principles of the present disclosure may be applied to other industries, such as the automotive industry.

[0134] Apparatus and systems embodied herein may be employed in any one or more steps of aircraft manufacturing and service method 300. For example, parts or subassemblies corresponding to part and subassembly manufacturing 306 may be similarly manufactured or produced as parts or subassemblies produced during in-service 312 of aircraft 316. Additionally, one or more apparatus embodiments, method embodiments, or a combination thereof may be employed during part and subassembly manufacturing 306 and system integration 308, for example, to substantially increase the speed or reduce the cost of assembly of aircraft 316. Similarly, one or more apparatus embodiments, method embodiments, or a combination thereof may be employed during in-service 312 of aircraft 316, for example, without limitation, during maintenance and service 314.

[0135] Disclosed embodiments of the lightning protection assembly 10 (see FIG. 1A), the lightning protection system 12 (see FIG. 1B), and the method 190 (see FIG. 4) prevent the infusion resin 45 (see FIG. 1A) or the lightning protection resin 46 (see FIG. 1A) from intermixing with the structural resin 70 (see FIG. 1B) of an underlying structural assembly 71 (see FIG. 1B), such as a composite laminate assembly 72 (see FIG. 1B), during co-curing 14a (see FIG. 1B) or curing 14 (see FIG. 1B), avoiding areas where the two dissimilar materials are in close proximity to each other, and provide sufficient infusion resin 45 (see FIG. 1A) or the lightning protection resin 46 (see FIG. 1A) during co-curing 14a (see FIG. 1B) or curing 14 (see FIG. 1B) to effectively encapsulate the lightning expanded metal foil 18 (see FIG. 1A) of the lightning expanded metal foil layer 16 (see FIG. 1A).

[0136] Additionally, disclosed embodiments of lightning protection assembly 10 (see FIG. 1A), lightning protection system 12 (see FIG. 1B), and method 190 (see FIG. 4) mitigate, minimize, and / or prevent microcracking, microcracking 83 (see FIG. 2E), have improved microcrack resistance 82 (see FIG. 1B), and provide degradation protection 84 (see FIG. 1B) to prevent damage to underlying composite layup assemblies 72, such as cured composite layup assembly 72c (see FIG. 1B), thereby avoiding costly repairs and rework.

[0137] Additionally, disclosed aspects of the lightning strike protection assembly 10 (see FIG. 1A), the lightning strike protection system 12 (see FIG. 1B), and the method 190 (see FIG. 4) provide a novel infusion resin 45, such as a thermosetting resin 58 (see FIG. 1A), having a controlled or tailored resin viscosity 60a (see FIG. 1A), a controlled or tailored cure profile 62a (see FIG. 1A), and a tailored rheology 64a (see FIG. 1A) associated with the lightning strike expanded metal foil 18 (see FIG. 1A), while achieving chemical compatibility 66 (see FIG. 1A) and bonding capability 68 (see FIG. 1A) between the structural resin 70 and the infusion resin 45 or lightning strike protection resin 46 (see FIG. 1A). Furthermore, the tailored viscosity 60a, tailored cure profile 62a, and tailored rheology 64a of the infusion resin 45 are different from the structural resin viscosity 60b (see FIG. 1B), structural resin cure profile 62b (see FIG. 1B), and structural resin rheology 64b (see FIG. 1B) of the structural resin 70, thereby preventing mixing of the structural resin 70 with the infusion resin 45 or the lightning protection resin 46 (see FIG. 1A). A cured lightning protection composite structure 80 (see FIG. 1B), such as a co-cured lightning protection composite structure 80a (see FIG. 1B) comprising the lightning protection assembly 10 (see FIG. 1A) and lightning protection system 12 (see FIG. 1B) disclosed herein, improves micro-cracking resistance during heat-humidity cycling in a co-cured laminate having a structural element and a lightning protection element, for example, a cured lightning protection composite structure 80, such as the co-cured lightning protection composite structure 80a.

[0138] The infusion resin 45 is laminated to the lightning expanded metal foil 18 (see FIG. 1A) using a non-metallic scrim 44 (see FIG. 1A). A composite layup assembly 72 (see FIG. 1B) includes a plurality of structural layers 74 (see FIG. 1B), such as a plurality of structural ply layers 75 (see FIG. 1B), formed of a composite material 90 (see FIG. 1B), such as a carbon fiber reinforced polymer (CFRP) 94 (see FIG. 1B) or carbon fiber reinforced plastic, a glass fiber reinforced polymer (GFRP) 96 (see FIG. 1B) or glass fiber reinforced plastic, or an aramid polymer 100 (see FIG. 1B), and pre-impregnated with a structural resin 70 (see FIG. 1B), and the composite layup assembly is co-cured or cured with the lightning protection assembly 10 (see FIG. 1A) to form a composite structure 120, such as a cured lightning protection composite structure 80 (see FIG. 1B), e.g., a co-cured lightning protection composite structure 80a (see FIG. 1B). Additionally, the initial adjusted viscosity 60c (see FIG. 1A) of the infusion resin 45 can be significantly different from the initial structural resin viscosity 60d (see FIG. 1B) of the structural resin 70, thereby minimizing intermixing of the infusion resin 45 and the structural resin 70 during the initial cure 14b (see FIG. 1B) or initial co-cure 14c (see FIG. 1B). For example, during the co-cure 14a, the infusion resin 45 in the non-metallic scrim 44 is forced into the openings 130 (see FIG. 2C) in the lightning-strike expanded metal foil 18, thereby completely encapsulating or surrounding the lightning-strike expanded metal foil 18. The tailored cure profile 62a of the infusion resin 45 initiates crosslinking at a lower temperature 114 (see FIG. 1B), which allows the tailored viscosity 60a of the infusion resin 45 to increase quickly, effectively encapsulating the lightning expanded metal foil 18 through encapsulation 76 (see FIG. 1B) while maintaining separation and immiscibility between the infusion resin 45 and the structural resin 70. This difference prevents mixing of the two resins, i.e., the infusion resin 45 and the structural resin 70, during curing or co-curing, resulting in distinct, separate resin layers and defined resin boundaries 78 (see FIGS. 1B, 2D) in a co-cured panel, such as the cured lightning protection composite structure 80, e.g., the co-cured lightning protection composite structure 80a.This results in significantly less surface porosity and improved performance in heat and humidity cycling events, as evidenced by fewer microcracks 83 (see FIG. 2E) in cured lightning protection composite structure 80, such as co-cured lightning protection composite structure 80a, after exposure to heat and humidity cycling. The immiscibility of the two resins, i.e., infusion resin 45 and structural resin 70, reduces damage to the two resins, i.e., infusion resin 45 and structural resin 70, caused by different coefficients of thermal expansion (CTE) 86a, 86b and different coefficients of hygroscopic expansion (CME) 88a, 88b of the two resins, i.e., infusion resin 45 and structural resin 70.

[0139] Additionally, disclosed embodiments of lightning protection assembly 10 (see FIG. 1A), lightning protection system 12 (see FIG. 1B), and method 190 (see FIG. 4) provide environmental protection to structural composites or composite structures 120 (see FIG. 1B) that provide lightning protection, such as cured lightning protection composite structures 80, such as co-cured lightning protection composite structure 80a. Disclosed embodiments of lightning protection assembly 10 (see FIG. 1A), lightning protection system 12 (see FIG. 1B), and method 190 (see FIG. 4) prevent premature damage due to heat and humidity cycling to products such as cured lightning protection composite structures 80, such as co-cured lightning protection composite structure 80a, achieving degradation-free and degradation-resistant 84 (see FIG. 1B) for lightning protection assembly 10 and lightning protection system 12. Additionally, disclosed embodiments of the lightning protection assembly 10 (see FIG. 1A), the lightning protection system 12 (see FIG. 1B), and the method 190 (see FIG. 4) may increase the interval between paint maintenance for in-service products and reduce the potential for damage to composites equipped with lightning protection due to heat-humidity cycles during use. Depending on the resin composition of the infusion resin 45, the infusion resin 45 may have useful structural, adhesive, or electrical properties. Furthermore, disclosed embodiments of the lightning protection assembly 10 (see FIG. 1A), the lightning protection system 12 (see FIG. 1B), and the method 190 (see FIG. 4) may shorten the evaluation cycle for new proposed systems, thereby enabling new and improved systems to be implemented more quickly and minimizing production and use issues.

[0140] Many modifications and other embodiments of the present disclosure will come to mind to one skilled in the art to which this disclosure pertains having the benefit of the teachings of the foregoing descriptions and the associated drawings. The embodiments described herein are illustrative and not intended to be limiting or comprehensive. Although specific terms are employed herein, these terms are used in a generic and descriptive sense only and not for purposes of limitation. Functionally equivalent methods and apparatuses within the scope of the present disclosure, in addition to those enumerated herein, are possible from the foregoing description. All such modifications and variations are intended to be included within the scope of the appended claims. The present disclosure is limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled.

Claims

1. a lightning-strike expanded metal foil layer including a lightning-strike expanded metal foil; a resin-infused scrim layer laminated to the lightning-strike expanded metal foil layer, the resin-infused scrim layer comprising a non-metallic scrim infused with an infusion resin having a controlled viscosity and a controlled cure profile, the lightning strike protection assembly is configured to be laid up on and co-cured with an uncured composite layup assembly comprised of a plurality of structural ply layers pre-impregnated with a structural resin, the structural resin having a structural resin viscosity and a structural resin cure profile that is different from the tailored viscosity and tailored cure profile of the infusion resin, thereby preventing intermixing of the structural resin and the infusion resin during co-curing and allowing the infusion resin to effectively encapsulate the lightning strike expanded metal foil while providing a defined resin boundary; The lightning protection assembly and the uncured composite laminate assembly are co-cured to form a cured lightning protection composite structure, which provides lightning protection as well as improved micro-cracking resistance and degradation resistance.

2. 10. The lightning strike protection assembly of claim 1, wherein the lightning expanded metal foil comprises a discontinuous metal foil comprising one or more of perforated metal foil, expanded metal foil, metal mesh, metallized fiber mesh, metal screen, metallized fiber fabric, metal fabric, wire mesh, metal foam, and open-cell metal foam.

3. The lightning-strike expanded metal foil is a metallic material including one or more of copper, aluminum, titanium, nickel, gold, and silver; or 10. The lightning strike protection assembly of claim 1, comprising a metal alloy material comprising one or more of a copper alloy, an aluminum alloy, a titanium alloy, a nickel alloy, a gold alloy, a silver alloy, bronze, and brass.

4. 10. The lightning strike protection assembly of claim 1, wherein the non-metallic scrim comprises one of a non-metallic scrim mat, a fiberglass scrim mat, a carbon fiber scrim mat, a woven scrim mat, a knitted polyester scrim mat, or a non-woven scrim mat.

5. 10. The lightning strike protection assembly of claim 1, wherein the infusion resin comprises a thermoset resin including one or more of adhesives, epoxies, phenolics, polyimides, bismaleimides, polyurethanes, fluoropolymers, and cyanate esters.

6. 2. The lightning strike protection assembly of claim 1, wherein the tailored viscosity and tailored cure profile of the infusion resin are associated with the lightning strike expanded metal foil to provide chemical compatibility and bonding capabilities between the infusion resin and the structural resin.

7. 1. A lightning protection system comprising a lightning protection assembly and an uncured composite layup assembly, The lightning protection assembly comprises: a lightning-strike expanded metal foil layer including a lightning-strike expanded metal foil; a resin-infused scrim layer laminated to the lightning-strike expanded metal foil layer, the resin-infused scrim layer comprising a non-metallic scrim infused with an infusion resin having a controlled viscosity and a controlled cure profile; the uncured composite layup assembly is comprised of a plurality of structural ply layers pre-impregnated with a structural resin, the structural resin having a structural resin viscosity and a structural resin cure profile that is different from the tailored viscosity and the tailored cure profile of the infusion resin; the lightning strike protection assembly is laid up on and co-cured with the uncured composite layup assembly, wherein upon co-curing, the structural resin and the infusion resin do not intermix to provide a defined resin boundary, and the infusion resin effectively encapsulates the lightning strike expanded metal foil; A lightning protection system, wherein the lightning protection assembly and the uncured composite laminate assembly are co-cured to form a cured lightning protection composite structure, which provides lightning protection as well as improved micro-crack resistance and degradation resistance.

8. 8. The lightning strike protection system of claim 7, wherein the lightning expanded metal foil comprises a discontinuous metal foil comprising one or more of perforated metal foil, expanded metal foil, metal mesh, metalized fiber mesh, metal screen, metalized fiber fabric, metal fabric, wire mesh, metal foam, and open-cell metal foam.

9. The lightning-strike expanded metal foil is a metallic material including one or more of copper, aluminum, titanium, nickel, gold, and silver; or 8. The lightning strike protection system of claim 7, comprising a metal alloy material comprising one or more of a copper alloy, an aluminum alloy, a titanium alloy, a nickel alloy, a gold alloy, a silver alloy, a bronze, and a brass.

10. 8. The lightning strike protection system of claim 7, wherein the non-metallic scrim comprises one of a non-metallic scrim mat, a fiberglass scrim mat, a carbon fiber scrim mat, a woven scrim mat, a knitted polyester scrim mat, or a non-woven scrim mat.

11. 8. The lightning strike protection system of claim 7, wherein the infusion resin comprises a thermoset resin including one or more of adhesives, epoxies, phenolics, polyimides, bismaleimides, polyurethanes, fluoropolymers, and cyanate esters.

12. 8. The lightning strike protection system of claim 7, wherein each of the plurality of structural ply layers comprises a composite material including one of one of: one or more carbon fiber reinforced polymers, one or more glass fiber reinforced polymers, or one or more aramid polymers.

13. 8. The lightning strike protection system of claim 7, wherein the structural resin comprises a thermosetting structural resin including one or more of an epoxy structural resin, a phenolic structural resin, a polyimide structural resin, a bismaleimide structural resin, a polyurethane structural resin, a fluoropolymer structural resin, and a cyanate ester structural resin.

14. The hardened lightning strike protection composite structure comprises: Aircraft wing panels, A horizontal stabilizer panel of an aircraft horizontal stabilizer, and The lightning strike protection system of claim 7 , comprising one or more fuselage panels of an aircraft fuselage.

15. 1. A method of providing improved microcracking resistance and degradation resistance to a cured lightning protection composite structure using a lightning protection material system, comprising: providing the lightning protection system, the lightning protection system comprising: a lightning strike protection assembly; and an uncured composite laminate assembly, the lightning strike protection assembly comprising: a lightning-strike expanded metal foil layer including a lightning-strike expanded metal foil; a resin-infused scrim layer laminated to the lightning-strike expanded metal foil layer, the resin-infused scrim layer comprising a non-metallic scrim infused with an infusion resin, the infusion resin having a tailored viscosity and a tailored cure profile; the uncured composite layup assembly is comprised of a plurality of structural ply layers pre-impregnated with a structural resin, the structural resin having a structural resin viscosity and a structural resin cure profile that is different from the tailored viscosity and the tailored cure profile of the infusion resin; The method includes laying up the lightning strike protection assembly to the uncured composite layup assembly; and co-curing the uncured composite laminate assembly and the lightning strike protection assembly thereon using heat in an autoclave, wherein during co-curing, the structural resin and the infusion resin do not intermix to achieve a defined resin boundary, and the infusion resin effectively encapsulates the lightning strike expanded metal foil; obtaining the cured lightning protection composite structure formed by co-curing the lightning protection material assembly and the uncured composite layup assembly, and using the lightning protection material system to impart the improved micro-cracking resistance, the degradation prevention capabilities, and the lightning protection capabilities to the cured lightning protection composite structure.

16. The step of providing the lightning protection system further includes providing the lightning protection system with the lightning protection assembly, wherein the lightning expanded metal foil comprises: discontinuous metal foils including one or more of perforated metal foil, expanded metal foil, metal mesh, metallized fiber mesh, metal screen, metallized fiber fabric, metal fabric, wire mesh, metal foam, and open-cell metal foam; Furthermore, the lightning expanded metal foil is a metallic material including one or more of copper, aluminum, titanium, nickel, gold, and silver; or 16. The method of claim 15, comprising a metal alloy material comprising one or more of a copper alloy, an aluminum alloy, a titanium alloy, a nickel alloy, a gold alloy, a silver alloy, a bronze, and a brass.

17. 16. The method of claim 15, wherein the step of providing the lightning protection system further comprises providing the lightning protection system with the lightning protection assembly, wherein the infusion resin comprises a thermoset resin including one or more of adhesives, epoxies, phenolics, polyimides, bismaleimides, polyurethanes, fluoropolymers, and cyanate esters.

18. co-curing the uncured composite laminate assembly and the lightning strike protection assembly thereon using heat in the autoclave, initially heating the uncured composite layup assembly to an initial temperature to form a partially cured composite layup assembly, the initial heating being sufficient to gel the uncured infusion resin but insufficient to gel the uncured structural resin; 16. The method of claim 15, further comprising post-heating the partially cured composite layup assembly to a final temperature that is higher than the initial temperature to form the cured lightning strike protection composite structure, the combination of the initial heating and the post-heating being sufficient to fully cure both the infusion resin and the structural resin.

19. co-curing the uncured composite laminate assembly and the lightning strike protection assembly thereon using heat in the autoclave, the uncured composite layup assembly during the initial heating; and The method of claim 18 further comprising applying pressure to at least one of the partially cured composite layup assemblies during the post-heating.

20. The step of obtaining the hardened lightning strike protection composite structure comprises: Aircraft wing panels, a horizontal stabilizer panel of the horizontal stabilizer of the aircraft; or The method of claim 15 , further comprising obtaining the hardened lightning strike protected composite structure comprising one of a fuselage panel of a fuselage of the aircraft.

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