Composite Structures Having Bondlines with Matched Electrical Conductivity
Two composite laminates are joined together by a bondline having portions exposed to the ambient environment. The bondline contains scrim having an electrical conductivity and impedance matched to that of the laminates in order to mitigate effects of lightning strikes.
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1. Field
This disclosure generally relates to techniques for bonding composite structures, and deals more particularly with methods for mitigating the effects of lightning strikes at bondlines.
2. Background
Fiber reinforced composite structures, such as, without limitation, carbon fiber reinforced plastics (CFRP) may be bonded together along a bondline using a structural adhesive. The bondline may be strengthened and reinforced by introducing one or more layers of scrim into the adhesive.
In aircraft applications, areas of composite structures such as fuselage skins are sometimes repaired or reworked by adhesively bonding composite repair patches to the structure. In order to reduce the effects of lightning strikes on the repair patch, it is necessary to provide a continuous electrical path between the repair patch and the structure to which it is bonded in order to dissipate electrical current flow.
In order to provide electrical continuity between a composite repair patch and the composite structure to which it is bonded, an electrically conductive scrim may be placed in the bondline. A problem arises, however, when portions of the bondline are exposed to the ambient environment. A lightning strike may generate an undesirable electrical potential across the bondline. In order to avoid the effects of an undesirable electrical potential across the bondline, the exposed areas of the bondline are covered with an electrically insulating sealant. Although sealants are effective, they increase the weight of the aircraft, and are both time-consuming and labor-intensive, adding to manufacturing costs.
Accordingly, there is a need for a method of joining composite structures along bondlines that mitigate the effects of lightning strikes, and reduce accompanying electrical potentials occurring across exposed bondlines. There is also a need for a method of bonding composite structures together which obviates the need for sealants to cover exposed portions of bondlines between the structures.
SUMMARYThe disclosed methods provide composite structures joined together along bondlines that have electrical conductivities which are matched to the structures which they join. The use of bondlines having conductivities matched to those of the structures reduces an electrical potential across exposed portions of the bondline. The use of sealants to cover exposed portions of bondlines may be reduced or eliminated, thereby reducing aircraft weight and manufacturing costs.
According to one disclosed embodiment, a composite laminate structure is provided comprising first and second fiber reinforced plastic resin laminates each having an electrical impedance, and a structural bondline joining the first and second laminates together. The bondline has an electrical impedance substantially matching the electrical impedance of the first and second laminates. The fiber reinforcement in each of the first and second fiber reinforced plastic resin laminates are carbon fibers, and the bondline includes an adhesively impregnated scrim having an electrical impedance that substantially matches the electrical impedance of the first and second laminates. At least a portion of the bondline is exposed to an ambient environment. The first and second laminates and the bondline may form a T-joint. The first and second laminates may form part of a fuel tank having an open interior, and in which a portion of the bondline is exposed to the open interior of the fuel tank. The bondline includes an adhesively impregnated scrim having an AC (alternating current) conductivity that substantially matches the AC conductivity of the first and second laminates.
According to another embodiment, a composite laminate structure is provided comprising a first carbon fiber reinforced plastic laminate having a first electrical impedance, and a second carbon fiber reinforced plastic laminate having a second electrical impedance substantially matching the first electrical impedance. The laminate structure further includes an adhesive bondline between the first and second laminates. The adhesive bond includes an adhesive and a scrim having a third electrical impedance substantially matching the first and second electrical impedances. The first and second laminates may form part of a fuel tank having an open interior adapted to store fuel, wherein a portion of the adhesive bondline is exposed to the open interior of the fuel tank. The first and second laminates and the adhesive bondline may form a T-joint. Each of the first, second and third electrical impedances include a resistive component and a reactive component. The resistive components are substantially equal, and the reactive components are substantially equal. The scrim may be formed of carbon fibers. The first and second laminates and the bondline have substantially the same AC conductivity.
According to still another embodiment, a composite aircraft fuel tank is provided with lightning protection. The lighting protection comprises at least a first carbon fiber reinforced plastic laminate wall, at least a second carbon fiber reinforced plastic laminate wall, and an adhesive bondline joining the first and second laminate walls, the adhesive bondline including an electrically conductive scrim having an electrical impedance substantially matching the electrical impedance of each of the first and second laminate walls. At least a portion of the adhesive bondline is adapted to be exposed to fuel vapors within the fuel tank.
According to still another embodiment, a method of providing lightning protection for a bond joint between two cured carbon fiber reinforced plastic laminates comprises installing scrim in the bond joint having an electrical impedance that substantially matches the electrical impedance each of the two carbon fiber reinforced plastic laminates. Installing the scrim includes impregnating the scrim with an adhesive. The adhesive may be one of a film adhesive and a paste adhesive. The scrim may be formed of carbon fibers. The laminates and the scrim may possess substantially the same electrical conductivity. Installing the scrim in the bond joint includes assembling the two laminates in a T-shaped configuration, and placing the scrim between an edge of one of the two laminates, and a face of the other of the two laminates.
According to a further embodiment, a method is provided of reducing the electrical potential across an exposed bondline between two, carbon fiber reinforced plastic laminates. The method comprises determining the electrical conductivity of each of the two laminates, selecting a scrim having an electrical conductivity substantially matching the determined electrical conductivity of each of the two laminates, installing the scrim and an adhesive between the two laminates, and curing the adhesive.
According to still further embodiment, a method is provided of fabricating a composite structure having an exposed bond protected against lightning strikes. The method comprises laying up first and second carbon fiber reinforced plastic pre-preg laminates, curing the first and second pre-preg laminates, and joining the first and second cured laminates with a bond joint. Joining the first and second cured laminates with the bond joint may include selecting a scrim having an electrical impedance substantially matching the electrical impedance of each of the first and second laminates, impregnating the scrim with a bonding adhesive, installing the impregnated scrim between the first and second laminates to form a bondline, and curing the adhesive.
The novel features believed characteristic of the illustrative embodiments are set forth in the appended claims. The illustrative embodiments, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment of the present disclosure when read in conjunction with the accompanying drawings, wherein:
Referring first to
The disclosed bondline 22 may be employed to form other types of bonded joints between two laminate structures. For example, referring to
Attention is now directed to
Each of the adhesive layers 34, 36 may comprise an adhesive resin film or an adhesive resin paste which adheres to the CFRP plies of the pre-pregs 24, 26. The scrim 32 may be embedded into and adhere to each of the adhesive layers 34, 36, as by pressing the scrim 32 into the adhesive layers 34, 36. Other techniques for integrating bonding adhesive with the scrim 32 may be possible, including impregnating the scrim 32 with the adhesive. The scrim 32 is configured to provide continuous electrical conductivity throughout the bondline 22 and may also serve as a binding matrix.
As previously mentioned, the scrim 32 possesses an AC conductivity σ1 and an impedance Z1 that substantially match the electrical conductivity σ2 and impedance Z2 of each of the composite pre-pregs joined by the bondline 22. Electrical conductivity σ is a measure of the material's ability to conduct electric current. In the case of a lightning strike causing electrical current to flow through the pre-pregs 24, 26, and through the bondline 22, the current flow is typically not constant, but varies, similar to an alternating current (AC). For example,
The bondline 22 described above having a “matched” electrical conductivity σ1 and a “matched” impedance Z1 may be used in a wide variety of composite laminate structures to mitigate the effects electrical current flows due to lightning strikes. For example, the disclosed bondline 22 may be employed in a composite aircraft fuel tank 42 shown in
Attention is now directed to
Embodiments of the disclosure may find use in a variety of potential applications, particularly in the transportation industry, including for example, aerospace, marine, automotive applications and other application where autoclave curing of composite parts may be used. Thus, referring now to
Each of the processes of method 76 may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on.
As shown in
Systems and methods embodied herein may be employed during any one or more of the stages of the production and service method 76. For example, components or subassemblies corresponding to production process 84 may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft 96 is in service. Also, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during the production stages 84 and 86, for example, by substantially expediting assembly of or reducing the cost of an aircraft 78. Similarly, one or more of apparatus embodiments, method embodiments, or a combination thereof may be utilized while the aircraft 78 is in service, for example and without limitation, to maintenance and service 92.
The description of the different illustrative embodiments has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different illustrative embodiments may provide different advantages as compared to other illustrative embodiments. The embodiment or embodiments selected are chosen and described in order to best explain the principles of the embodiments, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.
Claims
1. A composite laminate structure, comprising:
- first and second fiber reinforced plastic resin laminates each having an electrical impedance; and
- a structural bondline joining the first and second laminates together, the bondline having an electrical impedance substantially matching the electrical impedance of the first and second laminates.
2. The composite laminate structure of claim 1, wherein:
- the fiber reinforcement in each of the first and second fiber reinforced plastic resin laminates are carbon fibers, and
- the structural bondline includes an adhesively impregnated scrim having an electrical impedance that substantially matches the electrical impedance of the first and second laminates.
3. The composite laminate structure of claim 1, wherein at least a portion of the structural bondline is exposed to an ambient environment.
4. The composite laminate structure of claim 1, wherein the first and second laminates and the structural bondline form a T-joint.
5. The composite laminate structure of claim 1, wherein:
- the first and second laminates form part of a fuel tank having an open interior, and
- a portion of the structural bondline is exposed to the open interior of the fuel tank.
6. The composite laminate structure of claim 1, wherein the structural bondline includes an adhesively impregnated scrim having an AC conductivity that substantially matches the AC conductivity of the first and second laminates.
7. A composite laminate structure, comprising:
- a first carbon fiber reinforced plastic laminate having a first electrical impedance;
- a second carbon fiber reinforced plastic laminate having a second electrical impedance substantially matching the first electrical impedance; and
- an adhesive bondline between the first and second laminates, the adhesive bond including an adhesive and a scrim having a third electrical impedance substantially matching the first and second electrical impedances.
8. The composite laminate structure of claim 7, wherein:
- the first and second laminates form part of a fuel tank having an open interior adapted to store fuel, and
- a portion of the adhesive bondline is exposed to the open interior of the fuel tank.
9. The composite laminate structure of claim 7, wherein the first and second laminates and the adhesive bondline form a T-joint.
10. The composite laminate structure of claim 7, wherein:
- each of the first, second and third electrical impedances include a resistive component and a reactive component,
- the resistive components are substantially equal, and
- the reactive components are substantially equal.
11. The composite laminate structure of claim 7, wherein the scrim is formed of carbon fibers.
12. The composite laminate structure of claim 7, wherein the first and second laminates and the bondline have substantially the same AC conductivity.
13. A composite aircraft fuel tank having lightning protection, comprising:
- at least a first carbon fiber reinforced plastic laminate wall;
- at least a second carbon fiber reinforced plastic laminate wall;
- an adhesive bondline joining the first and second laminate walls, the adhesive bondline including an electrically conductive scrim having an electrical impedance substantially matching the electrical impedance of each of the first and second laminate walls.
14. The composite aircraft fuel tank of claim 13, wherein at least a portion of the adhesive bondline is adapted to be exposed to fuel vapors within the fuel tank.
15. A method of providing lightning protection of for a bond joint between two cured carbon fiber reinforced plastic laminates, comprising:
- installing scrim in the bond joint having an electrical impedance that substantially matches the electrical impedance each of the two carbon fiber reinforced plastic laminates.
16. The method of claim 15, wherein installing the scrim includes impregnating the scrim with an adhesive.
17. The method of claim 16, wherein the adhesive is one of a film adhesive and a paste adhesive.
18. The method of claim 15 wherein the scrim is formed of carbon fibers.
19. The method of claim 15, wherein the laminates and the scrim possess substantially the same electrical conductivity.
20. The method of claim 16, wherein installing the scrim in the bond joint includes:
- assembling the two laminates in a T-shaped configuration, and
- placing the scrim between an edge of one of the two laminates, and a face of the other of the two laminates.
21. An aircraft fuel tank having a exposed bond joint produced by the method of claim 15.
22. A method of reducing the electrical potential across an exposed bondline between two carbon fiber reinforced plastic laminates, comprising:
- determining the electrical conductivity of each of the two laminates;
- selecting a scrim having an electrical conductivity substantially matching the determined electrical conductivity of each of the two laminates;
- installing the scrim and an adhesive between the two laminates;
- curing the adhesive.
23. A method of fabricating a composite structure having an exposed bond protected against lightning strikes, comprising:
- laying up first and second carbon fiber reinforced plastic pre-preg laminates;
- curing the first and second pre-preg laminates;
- joining the first and second cured laminates with a bond joint, including selecting a scrim having an electrical impedance substantially matching the electrical impedance of each of the first and second laminates, impregnating the scrim with a bonding adhesive, installing the impregnated scrim between the first and second laminates to form a bondline, and curing the adhesive.
Type: Application
Filed: Oct 30, 2012
Publication Date: May 1, 2014
Applicant: THE BOEING COMPANY (Chicago, IL)
Inventor: The Boeing Company
Application Number: 13/663,543
International Classification: B32B 1/02 (20060101); B32B 37/12 (20060101); B32B 7/02 (20060101); F16B 12/04 (20060101); B60K 15/03 (20060101); B23P 11/00 (20060101);