COMPOSITE STRUCTURE

Abstract

A composite structure (10) comprising one or more electrically conductive pathways (12) and one or more isolators for isolating the pathways (12) from the bulk of the structure (10).

Claims

1. A composite structure comprising one or more electrically conductive pathways and one or more isolators for isolating the pathways from the bulk of the composite structure.

2. A composite structure according to claim 1 wherein the composite structure comprises fibre reinforcement and a reinforcement resin matrix, said electrically conductive pathways being formed from said fibre reinforcement and said reinforcement resin matrix.

3. A composite structure according to claim 2 wherein the electrically conductive pathways are formed from the same fibre reinforcement and the same resin matrix as the bulk of the composite structure.

4. A composite structure according to claim 1 wherein the electrically conductive pathways are discrete.

5. A composite structure according to claim 1 wherein the isolators are formed by an isolator resin matrix.

6. A composite structure according to claim 5 wherein the isolator resin matrix comprises the reinforcement resin matrix.

7. A composite structure according to claim 2 wherein the composite structure comprises multiple ply layers of fibre reinforcement, the isolator extending across at least two ply layers.

8. A composite structure according to claim 1 wherein the length of the isolator is n times the critical fibre length wherein n=1 to 10.

9. A composite structure according to claim 1 wherein the electrically conductive pathways are formed by unidirectional carbon fibre.

10. A composite structure according to claim 9, wherein the carbon fibre is coated with a metal.

11. A method of controlling current paths in a composite structure comprising providing one or more electrically conductive pathways in the structure and isolating the pathways from the bulk of the structure.

12. A method according to claim 11, wherein the electrically conductive pathway is isolated from the composite structure by means of isolators.

13. A method according to claim 11 wherein the composite structure is prepared from a lay-up of resin preimpregnated fibrous reinforcement material layers, the layers being arranged to connect metallic elements directly to the electrically conductive pathways of the structure.

14. A method according to claim 11 wherein one or more discontinuities are introduced in one or more layers to ensure that the electrically conductive pathway is isolated.

15. A method according to claim 11 wherein the composite structure has resin filled discontinuities or isolators.

Description

SPECIFIC DESCRIPTION

[0036] Specific embodiments of the invention will now be described by way of Example only and with reference to the accompanying drawings in which:

[0037] FIG. 1 presents a diagrammatic plan view of a structure not according to an embodiment of the invention; and

[0038] FIG. 2 presents a diagrammatic plan view of another structure according to an embodiment of the invention.

[0039] The present invention provides a composite structure comprising pathways for connecting connecting metallic elements to one another. The pathways are isolated from the bulk of the composite structure by means of isolators. These isolators are preferably formed by the reinforcement resin of the structure.

[0040] In aircraft, pathways may preferably be provided between mechanical fasteners and/or framing and/or LSP surface structures and/or engines and/or other metallic elements such as bond straps.

[0041] The pathways may be formed from conductive reinforcement fibers such as carbon fiber.

[0042] Alternatively, metallized fabrics and/or metallized fibers may be used. Examples of such fibers and/or fabrics will now be briefly disclosed. Diamond Fiber Composites (Cincinnati, Ohio) coats carbon fibers with a wide variety of metals including nickel, copper, silver, gold, palladium, platinum and metal hybrids (multilayer coatings) using a chemically based coating process that provides a uniform coating. These coated fibers may be obtained as continuous fiber lengths, chopped fibers, woven fabrics and nonwoven veils/mats.

[0043] Electro Fiber Technologies (Stratford, Conn.) offers single or dual metal hybrids coated onto carbon, graphite, glass, polyester and other synthetic fibers. The company supplies chopped fibers (down to 1 mm/0.04 inch in length) and continuous tows from 3K to 80K as well as nonwoven veils and mats.

[0044] Technical Fibre Products (Newburgh, N.Y.) supplies electrically conductive nonwoven mats and veils using carbon, nickel-coated carbon, aluminized glass, silicon carbide, stainless steel and nickel fibers.

[0045] Textile Products Inc. (Anaheim, Calif.) supplies a Style #4607 216 g/m2 carbon/aluminum hybrid fabric made with A54-3K carbon fiber and aluminum wire. It also supplies a Style #4608 218 g/m2 hybrid with T650/35-3K carbon fiber and aluminum wire. Both are plain weaves, 14 mils thick and 107 cm/42 inches wide.

[0046] Varinit (Greenville, S.C.) supplies electrically conductive reinforcing fabrics, developing and manufacturing products to meet customer specifications.

[0047] An embodiment of the invention is illustrated with respect to FIGS. 1 and 2. FIG. 1 shows a composite structure 10 which consists of a lay-up of multiple unidirectional carbon fiber reinforcement layers 12,14,18 which are impregnated with a resin matrix to form prepregs. The prepreg layers consist of prepreg without a conducting surface material 12, prepreg with a conducting surface material in the form of an expanded copper foil (ECF) 14 and a prepreg with a continuous conducting layer 18 in the form of carbon fiber tows. A bolt hole 16 is drilled into the composite structure and is arranged such that a mechanical fastener inserted in the hole 16 is in direct contact with the layer 18. This allows currents due to a lightning strike on or near the fastener to be conducted away from the fastener.

[0048] In FIG. 2, the reference numerals correspond to the same parts of FIG. 1. Isolators 20 in the form of cuts of the carbon fiber tows 18 are present to control the direction of conduction of currents away from the fastener to a desired location in the composite structure to a point via which the current can be removed from the structure following a lightning strike.

[0049] The composite structure of FIG. 2 may be formed by providing cuts into the reinforcement fiber tows. The cuts or discontinuities are introduced by laser cutting during the lay-up phase of the structure. Following lay-up as the resin cures, it flows into the gap and cures thereby forming a resilient insulative barrier to electrical charges and currents.

[0050] Several fibre discontinuites can be introduced per layer to either increase the efficacy of protection or to ensure that a safe zone is created which will accommodate tolerances in position of the discontinuities relative to the protected surface introduced through tolerances in manufacturing due to trimming and drilling operations.

[0051] The isolating discontinuities are several times the critical fiber length to ensure that the mechanical performance of the composite structure is not reduced.

[0052] The resin matrix as hereinbefore described may comprise any suitable resin including thermosets, thermoplastics or mixtures of the two. Preferably the resin is free from conductive ingredients which may accumulate in the fibre discontinuity and would reduce its isolating properties.

[0053] There is thus provided a structure and a method which enables effective control of electrical charges and/or currents in composite structures, particularly but not exclusively in composite aircraft or wind energy structures.