Patent Description:
Modem vehicles are becoming more electrified than ever before. Electrification has made it possible to improve performance while reducing greenhouse gas emissions and noise. The emergence of electric cars has illuminated the many possibilities and benefits associated with powering vehicles using electricity. Moreover, like its counterparts in the automotive field, aircraft are also becoming increasingly electrified as systems and monitoring functions have become more sophisticated.

These benefits are accompanied by their own unique technical challenges. Electrical wires are heavy. Each wire must be insulated from the surrounding environment for electrical isolation, corrosion protection, and personnel safety. Each wire must be strong enough to support its own weight in the impact and vibratory environment of an aircraft. Wires may need to be supported at relatively short intervals along its length to avoid abrasion and other destructive factors. Depending on the application, wires may need to be carefully positioned relative to other wires and various electric field sources to avoid electromagnetic interference and coupling.

<CIT> describes a method for forming a structure having lightning strike protection includes receiving at least one structural layer, receiving at least one lightning strike protection strip disposed on at least one reinforcement layer, automatically applying the at least one lightning strike protection strip disposed on the at least one reinforcement layer onto the at least one structural layer, and forming the at least one structural layer, the at least one lightning strike protection strip, and the at least one reinforcement layer, into the structure. The at least one lightning strike protection strip comprises a first material, and the at least one reinforcement layer comprises a second material different from the first material. The automatically applying may include using at least one of fiber placement equipment, tape laying equipment, and similar automated equipment.

<CIT> describes a composite material for use in making a composite structure that is protected against a lightning strike, said composite structure comprising a plurality of electrically conductive fibrous layers that are separated from each other by a resin layer that comprises an cured polymeric resin and a sufficient number of electrically conductive bridges across said resin layer to protect said composite structure from said lightning strike, wherein said electrically conductive bridges comprise electrically conductive particles, said composite material comprising; an electrically conductive fibrous layer; and a resin comprising a polymeric resin and sufficient number of electrically conductive particles having a sufficient size to form said sufficient number of electrically conductive bridges.

<CIT> describes a prepreg includes conductive fibers impregnated with a matrix resin, the prepreg having a conductive region where a conductive material is dispersed in the resin. It is described that a resin layer composed of at least the matrix resin preferably is present on one or both surfaces of a conductive fiber layer composed of at least the conductive fibers, and the conductive region is present at least in the resin layer. In addition, the above-described conductive region preferably is present continuously in the thickness direction. The conductive region preferably is a conductive region where the conductive material is dispersed in the matrix resin, and the resin in the conductive region preferably forms a continuous phase with the matrix resin in other regions. A volume resistivity of the conductive region preferably is <NUM>/<NUM>,<NUM> or less of that of other regions of the matrix resin.

Provided herein are fiber-reinforced composites that embed conductors within the plies of a fiber reinforced plastic composite and function as a conductor of an electrical current to carry signals or distribute power. They can be used to form conductive pathways within the layered material. The pathways could be within a layer (oriented with a layer), on a layer (orientation independent of the layer), through a layer (to function as a via on a circuit board), or with insulating layers within or on the fiber reinforced plastic composite.

Embedding the conductive traces within a fiber-reinforced plastic composite allows the conductor to be fully supported by the composite, require minimal to no additional insulation, require no clamps or brackets for support, and reduces incidental contact with fluids and abrasion. Embedded conductors can also benefit from the natural electromagnetic shielding properties of the surrounding composite and can be easily separated and routed relative to each other for optimum performance.

As another factor, large fiber reinforced plastic composite parts in the aerospace industry are fabricated using automated means, as opposed to manual layups, to reduce manufacturing costs, improve quality, and increase production rates. Advantageously, the provided solution embeds conductors in a fiber-reinforced composite in a configuration that is compatible with automated manufacturing methods.

The potential applications are significant and diverse. The provided conductor layups can be used to incorporate optical or electrical transmission features, enable composite materials to include energy storage features such as capacitors and/or batteries, incorporate energy harvesting features onto the network, and replace insulating or secondarily conductive elements in the ribbon with semi-conductive voltage-variable resistive constructs to function as a natural overload shunt. In the present invention, a fiber-reinforced composite is provided. The composite comprises: a plurality of prepreg layers, each comprising a polymeric resin and a plurality of fibers disposed therein; and a first electrically-conductive layer in contact with the plurality of prepreg layers, wherein the first electrically-conductive layer is in the form of a first set of ribbons aligned in a first direction, a second electrically-conductive layer in contact with the plurality of prepreg layers, wherein the second electrically-conductive layer is in the form of a second set of ribbons aligned in a second direction, insulating layers lining the major surfaces of the first and second set of ribbons, wherein the first direction is different from the second direction such that the first and second electrically-conductive layers overlap with each other at intersections when viewed from a direction perpendicular to a major surface of the composite, and wherein the insulating layers prevent the first set of electrically-conductive ribbons from being in electrical contact with the second set of electrically-conductive ribbons at the intersections. Specific embodiments of such inventive composite are described in the dependent claims.

An automotive or aircraft part such as an aircraft skin, aircraft fuselage panel, or capacitor may comprise a composite described herein.

Repeated use of reference characters in the specification and drawings is intended to represent the same or analogous features or elements of the disclosure. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the disclosure. The figures may not be drawn to scale.

"Ambient conditions" means at <NUM> and <NUM> kPa pressure.

"Average" means number average, unless otherwise specified.

"Continuous" means extending across a single, unified area along a given layer (a perforated sheet can be continuous);.

"Cure" refers to exposing to radiation in any form, heating, or allowing to undergo a physical or chemical reaction that results in hardening or an increase in viscosity.

"Discontinuous" means extending across a plurality of discrete areas along a given layer, where the discrete areas are spaced apart from each other;.

"Polymer" refers to a molecule having at least one repeating unit and can include copolymers.

"Ribbon" means a construction that is generally constant in width and thickness and available in lengths considerably larger than its width, wherein each length can be conveniently dispensed and/or cut to a desired dimension.

"Size" refers to the longest dimension of a given object or surface.

"Substantially" means to a significant degree, as in an amount of at least <NUM>%, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>%, or <NUM>%.

"Thickness" means the distance between opposing sides of a layer or multilayered article.

As used herein, the terms "preferred" and "preferably" refer to embodiments described herein that can afford certain benefits, under certain circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude other embodiments from the scope of the invention.

As used herein and in the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a" or "the" component may include one or more of the components and equivalents thereof known to those skilled in the art. Further, the term "and/or" means one or all the listed elements or a combination of any two or more of the listed elements.

It is noted that the term "comprises" and variations thereof do not have a limiting meaning where these terms appear in the accompanying description. Moreover, "a," "an," "the," "at least one," and "one or more" are used interchangeably herein. Relative terms such as left, right, forward, rearward, top, bottom, side, upper, lower, horizontal, vertical, and the like may be used herein and, if so, are from the perspective observed in the drawing. These terms are used only to simplify the description, however, and not to limit the scope of the invention in any way.

Reference throughout this specification to "one embodiment," "certain embodiments," "one or more embodiments" or "an embodiment" means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrases such as "in one or more embodiments," "in certain embodiments," "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Where applicable, trade designations are set out in all uppercase letters.

The present disclosure is directed to structural fiber-reinforced composites. The composites include a plurality of layers, and more particularly a plurality of prepreg layers.

A prepreg layer refers to a reinforcing fabric which has been pre-impregnated with a resin system. Commonly the resin system is an epoxy or other thermoset resin and comes pre-mixed with a suitable curing agent. In a manufacturing process, multiple layers of prepreg can be laid down by hand or automated methods onto a shaped mold or tool, and then cured by a combination of pressure and heat.

Prepregs offer several technical advantages, such as the ability to provide high-strength parts, uniformity and repeatability in manufacture, reduced waste, and relatively short curing times. Applications for prepregs include aerospace components, racing, sporting goods, pressure vessels, and commercial products.

A fiber-reinforced composite not according to the claimed invention, but useful in understanding the claimed invention, is shown in <FIG> and hereinafter referred to by the numeral <NUM>. The composite <NUM>, as shown, has a layered structure with two major surfaces. Amongst these layers are prepreg layers 102a, 102b, 102c, as shown.

Each of prepreg layers 102a, 102b, 102c includes a polymeric resin and a plurality of fibers dispersed in the polymeric resin. The plurality of fibers can be provided in the form of a weave that acts as a reinforcing fabric. Non-woven fibers are also possible, in which fiber entanglements enhance web strength along the plane of the layer. Many fibers are available for these purposes, including but not limited to glass fibers, basalt fibers, carbon fibers, and aramid fibers.

If desired, the fibers may be preferentially oriented along certain directions. This can be useful in instances where a given prepreg layer is being laid down in a series of parallel bands (or ribbons) using an automated fiber placement machine. In these cases, it can be preferred for the fibers to be preferentially oriented along the length of the ribbon.

The polymeric resin acts as a matrix and may be made from a thermoset or a thermoplastic resin. Common thermoset resins are epoxy resins, but vinyl ester-based resins, phenolics, bismaleimide, or cyanate ester can also be used. Curatives for these resins are known in the art and can be incorporated into the polymeric resin.

Useful thermoplastic resins include polyurethane, polyvinylidene fluoride, terpolymer of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride (THV), terpolymer of hexafluoropropylene, tetrafluoroethylene and ethylene (HTE), polyetherimide, polyetherether-ketone (PEEK), polyetherketoneketone (PEKK), and combinations thereof.

The prepreg layers 102a, 102b, 102c in this configuration, are electrically-insulating layers. These layers have insulating properties if both the matrix and fibers therein are not electrically-conductive. Insulating properties, at least along certain directions, can also result if any conductive fibers (e.g., carbon fibers) are spatially separated, thus preventing electrical connectivity across the layer. Optionally, one or more of the prepreg layers 102a, 102b, 102c can contain one or more sheets of glass and/or nylon disposed in the polymeric resin along with the plurality of fibers.

The average thickness of the prepreg layers 102a, 102b, 102c can vary significantly based on the application and manufacturing method, but is generally in the range of from <NUM> micrometers to <NUM> micrometers, from <NUM> micrometers to <NUM> micrometers, from <NUM> micrometers to <NUM> micrometers, or in some cases, <NUM> micrometers, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> micrometers.

The composite <NUM> further includes a first electrically-conductive layer <NUM> disposed between the prepreg layers 102a, 102b. By supporting an electric current, the electrically-conductive layer <NUM> is capable of use in widespread applications, including electrical circuits for sensors and actuators and lightning strike protection materials. A pair of electrically-conductive layers separated by an insulating prepreg layer can, for example, act as a parallel plate capacitor.

The first electrically-conductive layer <NUM> can be a continuous or discontinuous layer, and may be strongly or weakly conductive. Its conductivity may be anisotropic (varying by direction). Electrical currents conveyed may be of constant polarity and magnitude, or have variable frequency, variable amplitude, and/or variable polarity.

In this construction, the electrically-conductive layer <NUM> has the shape of a ribbon and traverses certain portions of the adjacent prepreg layers 102a, 102b but not others, as viewed from a direction perpendicular to a major surface of the composite. As a result, the electrically-conductive layer <NUM> can be embedded between the prepreg layers 102a, 102b, a construction in which the prepreg layers 102a, 102b collectively function as an insulator around the first electrically-conductive layer <NUM>.

The electrically-conductive layer <NUM> can be made from any of a number of conductive materials. Suitable conductive materials may be monolithic in nature. Monolithic materials include metal layers of, for example, copper, aluminum, titanium, silver, gold, tin, nickel or their alloys. Metal conductors may be obtained from continuous metal foils. Metal foils may be unperforated or perforated to provide weight savings.

Perforated metal foils, also referred to as foraminous foils, may be made by any known method, including expanding, perforating, cutting, drilling, or plating. Expanded metal foils, for example, are made by slitting a metal foil and then stretching transversely or longitudinally to create a staggered, two-dimensional array of perforations. Foraminous foils need not be characterized by a regularly repeating pattern of holes.

Useful metal layers can an areal density of from <NUM> gsm to <NUM> gsm, <NUM> gsm to <NUM> gsm, <NUM> gsm to <NUM> gsm, or in some cases, less than, equal to, or greater than <NUM> gsm, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> gsm.

Altematively, the electrically-conductive layer <NUM> can be made by dispersing electrically-conductive particles in a matrix resin. Conductive particles can be in the form of spheres, chopped fibers, or flakes. The matrix resin, which is generally not electrically-conductive, can be composed of any of the polymeric resins described previously for the prepreg layers 102a, 102b, 102c.

The conductive particles or sheets are not particularly limited and can be comprised of electrically-conductive particles or sheets of carbon, glass and/or nylon. Suitable sheets include papers or weaves of electrically-conductive fibers. Carbon fiber is, by itself, weakly conductive. Nonconductive particles and sheets can be made conductive by coating with an electrically-conductive metal-usually silver, gold, tin, copper, nickel or alloys thereof. Examples of these include metallized glass or metallized nylon. If desired, conductive fibers and particles can both be incorporated into the same layer within the ribbon.

The matrix resin is preferably loaded with conductive particles or sheets at sufficient amounts to impart substantial electrical conductivity along the length of the ribbon. The loading of the conductive particles or sheets in the matrix resin can be from <NUM>% to <NUM>%, from <NUM>% to <NUM>%, from <NUM>% to <NUM>%, or in some cases, less than, equal to, or greater than <NUM>%, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>% by weight relative to the overall weight of the electrically-conductive layer <NUM>.

As a further option, the electrically-conductive layer <NUM> could have a hybrid construction in which a monolithic conductor such as a perforated or unperforated metal foil is used in combination with a matrix resin containing electrically-conductive particles or sheets.

The ribbon can be made flat and quite thin to preserve flexibility of the layer, while retaining its capacity to carry an electrical current with much less current loss or much less loss of signal clarity than is capable by the surrounding fiber-reinforced composite. Depending on the particulars of the application and other dimensions of the ribbon, the average thickness of the ribbon can be from <NUM> micrometers to <NUM> micrometers, from <NUM> micrometers to <NUM> micrometers, from <NUM> micrometers to <NUM> micrometers, or in some cases, <NUM> micrometers, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> micrometers.

Referring again to <FIG>, the composite <NUM> further includes second and third conductive layers <NUM>, <NUM>, which have similar characteristics to the conductive layer <NUM>. The conductive layers <NUM>, <NUM> are separated by a prepreg layer 102d but are connected along one area by an electrically-conductive via <NUM>. Unlike the conductive layer <NUM>, the conductive layer <NUM> and via <NUM> are coplanar with a prepreg layer-for example, the conductive layer <NUM> is coplanar with the prepreg layer 102c and the via <NUM> is coplanar with the prepreg layer 102d. The second conductive layer <NUM> and via <NUM> also have peripheral edges that contact respective peripheral edges of the prepreg layers 102c, 102d.

The electrically-conductive via <NUM> is a discontinuous, electrically-conductive layer that provides an electrically-conductive pathway along the z-axis of the composite <NUM>-i.e., the direction perpendicular to its major surface. Advantageously, the via <NUM> provides a confined, pre-determined area where electrical conductivity is available through an opening (e.g., window) in the prepreg layer 102d. Potentially, this opening can enable communication between opposing sides of the prepreg layer 102d not only with respect to electrical conduction but also thermal conduction, electric permittivity, and magnetic permeability. Openings in a prepreg layer can allow electrically-conductive layers on opposite sides of the prepreg layer to contact each other through the opening.

<FIG> shows a composite ribbon <NUM> in which an electrically-conductive layer <NUM> is provided in a sandwich construction between two adjacent layers that are insulating layers. In this three-layer configuration, the electrically-conductive layer <NUM> is comprised of a matrix resin containing electrically-conductive particles. Extending across and directly contacting the electrically-conductive layer <NUM> are a pair of prepreg layers <NUM>, <NUM> symmetrically disposed on its opposing major surfaces.

Advantageously, the composite ribbon <NUM> has a configuration that is thin while providing significant tensile strength, making it suitable for use in automated fiber placement (AFP) and automated tape layup (ATL) manufacturing equipment. Here, tensile strength of the composite ribbon <NUM> is attributable, to a large degree, by the plurality of fibers embedded in the prepreg layers <NUM>, <NUM>.

Optionally, one or more additional carrier layers may be incorporated into the ribbon <NUM> to further enhance tensile strength along the length of the ribbon. Examples of useful carrier layers are described in co-pending International Application Publication No. <CIT>).

Variants are also possible. Instead of using the prepreg layers <NUM>, <NUM> in this instance, either or both layers could be replaced with a different insulating layer such as a glass or nylon layer.

Alternatively, or in combination, the electrically-conductive layer <NUM> could include a metallic conductive layer, such as an expanded metal mesh. Electrical conductors with down-web oriented strands are described for this purpose in International Application Publication No. <CIT>).

<FIG> shows in cross-section a conductive fiber-reinforced composite laminate <NUM> that could be prepared from the composite ribbon <NUM> of <FIG>. The composite laminate <NUM> includes a plurality of prepreg layers <NUM>. Embedded within the plurality of prepreg layers <NUM> are a plurality of electrically-conductive ribbons 304a, 304b. The electrically-conductive ribbons 304a are oriented in one direction (in <FIG>, parallel to the plane of the page) while the electrically-conductive ribbons 304b, 304c are oriented perpendicular to that direction (in <FIG>, perpendicular to the plane of the page).

The electrically-conductive ribbons 304a, 304b are stacked in a manner that enables electrical contact from one layer to another. More particularly, the ribbons 304a stand in electrical contact with each other because of a conductive pathway passing through the ribbons 304b, which act as vias between the ribbons 304a. By contrast, the ribbon 304c electrically isolated from the remaining ribbons 304a, 304b because of the surrounding prepreg layers <NUM>, which are electrically-insulating.

<FIG> shows a composite laminate <NUM> as viewed from a direction perpendicular to its major surface. The laminate <NUM> includes a prepreg layer <NUM>, and crisscrossing conductive bands disposed thereon provided by electrically-conductive ribbons 404a, 404b. The ribbons 404a, 404b cross each other at intersections <NUM>.

In this embodiment, the major surfaces of the ribbons 404a, 404b are lined with insulating layers as described in <FIG>. As a result, the ribbons 404a, 404b each have excellent electrical conductivity along their length but are not in electrical contact at the intersections <NUM> because the insulating layers separate the overlapping conductive ribbons from each other.

Useful methods for making the provided electrically-conductive composite laminates may be manual, automated, or a combination thereof.

In a hand layup method, individual prepreg and electrically-conductive layers, or combinations thereof, can be assembled from their constituent individual layers. In one embodiment, layers of polymeric resin are first coated from a solution onto a release liner and then dried to provide a solidified resin layer. The resin layer can then be incorporated into a stack along with any other fibrous and/or conductive metal layers, followed by vacuum lamination to consolidate the layers. Lamination can be facilitated using a vacuum table, which may be flat or have curved contours. The consolidated layers can then be cured into a finished composite laminate by autoclaving in a vacuum bag.

AFP and ATL machines can be configured to lay down composite layers onto a substrate according to a pre-determined pattern. The substrate may be a manufacturing tool which can have either a flat or curved surface. The pre-determined pattern can be represented by digital data customized according to the user application. Based on the digital data, the AFP or ATL machine can use a computer programmed to control movement of an automated fiber placement head to fabricate, layer-by-layer, a fiber-reinforced composite laminate.

To fabricate layers that extend across significant areas, the automated fiber placement head can lay down material in a series of successive parallel and contiguous bands. The layered structure of the composite makes it possible for electrically-conductive layers to overlap one another and even cross each other along directions non-parallel relative to each other, enabling three-dimensional electrical circuits. Applications for such electrical circuits include power distribution and storage, data bus, antennae, sensors, and health monitoring networks. Conductors having a configuration distributed across the skin of an aircraft can be useful in lightning strike protection.

In an exemplary method, an automated fiber placement head is moved over a substrate while laying down a first layer, which may be either a prepreg layer or electrically-conductive layer, onto the substrate. The fiber placement head is then used to lay down a second layer, which may be a prepreg layer or electrically-conductive layer, onto the substrate and/or the first layer. This process can continue for any number of layers. For greater coverage, an electrically-conductive layer can include a plurality of electrically-conductive layers that are laid down to overlap each other as viewed from a direction perpendicular to a major surface of the composite.

Multiple layers can be laid down adjacent one another within a single layer or stacked on top of one another. For electrically-conductive layers, this can be an effective way to increase the cross-section of the conductor, thereby increasing its capacity to carry an electric current.

Machine-dispensable prepreg ribbons can have any suitable width to accommodate continuous dispensers. AFP machines typically dispense ribbons having widths in the range of from <NUM> millimeters (<NUM> inches) to <NUM> millimeters (<NUM> inches), with even greater widths possible. The narrow dispensing widths of AFP machines make them suitable for depositing prepreg layers onto surfaces with compound curvatures while avoiding wrinkles.

ATL machines can increase throughput by dispensing ribbons having significantly greater widths. While these machines tend to be limited to planar surfaces, they can lay down ribbons at nominal widths of <NUM> centimeters (<NUM> inches), <NUM> centimeters (<NUM> inches), <NUM> centimeters (<NUM> inches) and more. Overall, the average width of the ribbon can be from <NUM> millimeters to <NUM> millimeters, from <NUM> millimeters to <NUM> millimeters, from <NUM> millimeters to <NUM> millimeters, or in some embodiments, less than, equal to, or greater than <NUM> millimeters, <NUM>, <NUM>, <NUM>, or <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> millimeters.

Objects and advantages of this disclosure are further illustrated by the following non-limiting examples.

At a temperature of <NUM> (<NUM>°F), <NUM> grams DER-<NUM>, <NUM> grams SD-<NUM>, <NUM> grams PG-<NUM>, <NUM> grams R-<NUM>, <NUM> grams CG-<NUM> and <NUM> grams U-<NUM> were charged into a plastic cup designed for use in a planetary mill, model "SPEED MIXER DA <NUM> FV", available from Synergy Devices Limited, Buckinghamshire, United Kingdom. The cup was placed into a planetary mixer and mixed at <NUM> rpm for two minutes. The mixture was milled in a three-roll mill for three passes and then set aside.

At a temperature of <NUM> (<NUM>°F), <NUM> grams DER-<NUM> and <NUM> grams EPON SU-<NUM> were manually crushed with a pestle and mortar and charged into another plastic cup designed for use in the planetary mill. <NUM> grams MEK and <NUM> grams MPK were added to the cup, which was then secured to the mill and rotated at <NUM>,<NUM> rpm until the mixture was dissolved (approximately fifteen minutes).

<NUM> grams MX-<NUM>, <NUM> grams MY-<NUM>, <NUM> grams DF-<NUM>, <NUM> grams RA-<NUM>, <NUM> grams TS-<NUM>, <NUM> grams of the mill base, and <NUM> grams PCDI were added to the cup. The mixture was returned to the planetary mixer and mixing continued for another one minute at <NUM>,<NUM> rpm. The mixture was manually scraped and returned to the planetary mill until all components were homogeneously dispersed (approximately one minute).

Quantities of conductive particles, MEK, and the adhesive composition (AC) were combined in a cup as represented in Table <NUM> and mixed in the planetary mixer for one minute at <NUM> rpm. The sides of the cup were manually scraped, and the mixture was returned to the planetary mixer until all components were homogeneously dispersed (approximately one minute).

The resin compositions represented in Table <NUM> were subsequently notch bar coated, at approximately <NUM> x <NUM> (<NUM> inch by <NUM> inch), onto a bleached silicone coated release liner, type "<NUM><NUM># BL KFT H/HP 4D/<NUM> MH", obtained from Loparex, Inc. , Iowa City, IA. United States, at bar gaps of <NUM> micrometers (<NUM> mil). The resin compositions were dried for at least twelve hours at approximately <NUM> (<NUM>°F). A sheet of <NUM> gsm ECF was laid between two sheets of the dried resin coating. This assembly was then placed in a layup tool and a vacuum of <NUM> kPa (<NUM> psi) applied for approximately five to ten minutes. The consolidated conductors were then slit into <NUM> (¼ inch) ribbons.

Four sheets approximately <NUM> x <NUM> (<NUM> inch by <NUM> inch) of P2353U prepreg were laid on a vacuum table, orientated at <NUM>/<NUM>/<NUM>/<NUM> degrees, and a vacuum of <NUM> kPa (<NUM> psi) was applied for approximately five to ten minutes to secure the sheets. Strips of the <NUM> (¼ inch) electrically-conductive ribbons (505a, 505b) were applied to the prepreg to form a finished panel layup represented in <FIG>. The finished panel layup was placed in an autoclave and a vacuum of approximately <NUM> kPa (<NUM> psi) was applied to the inside of the bag for ten to fifteen minutes at <NUM> (<NUM>°F). External pressure was gradually increased to <NUM> kPa (<NUM> psi). The vacuum inside the bag was maintained at <NUM> kPa (<NUM> psi) and the temperature was increased at a rate of <NUM> (<NUM>°F) per minute until reaching <NUM> (<NUM>°F). This temperature was held for two hours and then the temperature was returned to <NUM> (<NUM>°F). The pressure was released, and the cured composite article was removed from the vacuum bag.

After curing, a Model <NUM> CNC router obtained from Shopsaber of Lakeville, MN. United States was used to sever the electrically-conductive ribbons 505a, 505b in four locations represented in <FIG> as <NUM>. A hand grinder was used to expose the electrically-conductive ribbons at eight locations 525a, 535a, 545a, 545a, 525b, 535b, 545b, and 555b as represented in <FIG>. Resistance was measured with a Fluke multimeter across pairs (525a-to-525b, 535a-to-535b, 545a-to-545b, and 555a-to-555b) of exposed conductors and the results were recorded (as an average of three measurements) in Table <NUM>. The resistance between exposed ends of unconnected ribbons was beyond measurable.

Adhesive composition (AC) was knife coated onto a paper liner using a <NUM> micrometer (<NUM> mil) gap. The adhesive composition dried into a film for twelve hours at room temperature. Two sheets of the film <NUM>, four sheets of <NUM> gsm Cu-Ni-Carbon fiber paper <NUM> obtained from Technical Fibers of Schenectady, NY. United States, and a <NUM> gsm ECF expanded copper foil <NUM> were arranged as represented in <FIG>. The layers were vacuum laminated together at room temperature and <NUM> kPa (<NUM> psi) for one hour to produce a construct as illustrated in <FIG>. The construct was then slit into <NUM> (¼ inch) wide strips assembling conductive ribbons with z-axis conductivity.

Adhesive composition (AC) was knife coated onto a paper liner using a <NUM> micrometer (<NUM> mil) gap. The adhesive composition dried into a film for twelve hours at room temperature. Two sheets of the film <NUM>, two sheets of <NUM> gsm glass fiber paper <NUM> obtained from Technical Fibers of Schenectady, NY. United States, and a <NUM> gsm ECF expanded copper foil <NUM> were arranged as represented in <FIG>. The layers were vacuum laminated together at room temperature and <NUM> kPa (<NUM> psi) for one hour to produce a construct as illustrated in <FIG>. The construct was then slit into <NUM> (¼ inch) wide strips assembling conductive ribbons without z-axis conductivity.

Two sheets of approximately <NUM> x <NUM> (<NUM>-inch x <NUM> inch) <NUM> glass fabric prepreg were placed on a vacuum table, orientated at <NUM>/<NUM> degrees, and a vacuum of <NUM> kPa (<NUM> psi) was applied for approximately five to ten minutes to secure the sheets as Sequence <NUM> illustrated in <FIG>. Two ribbons prepared in Preparatory Example <NUM> were placed on the consolidated prepreg, one straight and one curved (represented as Sequence <NUM> in <FIG>). A vacuum of <NUM> kPa (<NUM> psi) was applied for approximately five to ten minutes to secure the ribbons.

A rectangular slot <NUM> (¼ inch) by <NUM> (<NUM> inch) was trimmed into two sheets of approximately <NUM> x <NUM> (<NUM> by <NUM> inch) <NUM> glass fabric prepreg that were positioned over the straight ribbon created in Sequence <NUM>. This process is represented as Sequence 3A in <FIG> (Note: dashed lines in <FIG> indicate ribbon shape and positioning underneath subsequently stacked layers). A <NUM> (<NUM> inch) long ribbon assembled in Preparatory Example <NUM> was positioned to fill the rectangular opening cut into each prepreg sheet to form Sequence 3B illustrated in <FIG>. The glass fabric prepreg was laid on the consolidated prepreg, orientated at <NUM>/<NUM> degrees with the ribbon in place and a vacuum of <NUM> kPa (<NUM> psi) was applied for approximately five to ten minutes to secure the sequence.

Sequence <NUM> (represented in <FIG>) positioned a ribbon prepared in Preparatory Example <NUM> onto the consolidated prepreg such that it intersected the segment of the ribbon prepared in Preparatory Example <NUM> in Sequence <NUM> (refer to <FIG>) without intersecting the projection of the curved ribbon of Sequence <NUM>. A vacuum of <NUM> kPa (<NUM> psi) was applied for approximately five to ten minutes to secure the ribbon.

Two sheets of approximately <NUM> x <NUM> (<NUM>-inch x <NUM> inch) <NUM> glass fabric prepreg were then placed on the consolidated prepreg, orientated at <NUM>/<NUM> degrees and a vacuum of <NUM> kPa (<NUM> psi) was applied for approximately five to ten minutes to secure the sheets as Sequence <NUM> illustrated in <FIG>.

The finished panel was placed in an autoclave and a vacuum of <NUM> kPa (<NUM> psi) was applied to the inside of the bag for ten to fifteen minutes at <NUM> (<NUM>°F). External pressure was gradually increased to <NUM> kPa (<NUM> psi). The vacuum inside the bag was maintained at <NUM> kPa (<NUM> psi) and the temperature was increased at a rate of <NUM> (<NUM>°F) per minute until reaching <NUM> (<NUM>°F). This temperature was held for two hours and then the temperature was returned to <NUM> (<NUM>°F). The pressure was released, and the cured composite article was removed from the vacuum bag.

A panel was fabricated identically as Example <NUM> except that the ribbon assembled in Preparatory Example <NUM> was used in place of the ribbon prepared by Preparatory Example <NUM>.

A panel was fabricated identically as Example <NUM> except that <NUM>/PWC carbon fabric prepreg was used instead of the <NUM> glass fabric prepreg.

A panel was fabricated identically as Example <NUM> except that <NUM>/PWC carbon fabric prepreg was used instead of the <NUM> glass fabric prepreg and the ribbon assembled in Preparatory Example <NUM> was used in place of the ribbon prepared by Preparatory Example <NUM>.

After curing, Examples <NUM>-<NUM> were abraded to expose the conductors at sites A, B, and C as illustrated in <FIG>. Resistance measurements were taken at sites A-to-A, B-to-B, and C-to-C with a Fluke multimeter to verify conduction along each ribbon. Resistance measurements were recorded A-to-B to determine how the prepreg conducts between non-intersecting ribbons sandwiched between the same prepreg layers. Resistance measurements were recorded A-to-C to determine how the prepreg conducts between non-intersecting ribbons separated by two prepreg layers. Resistance measurements were recorded B-to-C to determine how the prepreg conducts between non-intersecting ribbons connected by a via constructed of ribbons. Resistance measurements were averaged and are reported in Table <NUM> (N/A represents the condition where resistance was too high and conductivity was too low to obtain a measurement).

Claim 1:
A structural fiber-reinforced composite comprising:
a plurality of prepreg layers, each comprising a polymeric resin and a plurality of fibers disposed therein; and
a first electrically-conductive layer in contact with the plurality of prepreg layers wherein the first electrically-conductive layer is in the form of a first set of ribbons aligned in a first direction,
a second electrically-conductive layer in contact with the plurality of prepreg layers wherein the second electrically-conductive layer is in the form of a second set of ribbons aligned in a second direction,
insulating layers lining the major surfaces of the first and second set of ribbons,
wherein the first direction is different from the second direction such that the first and second electrically-conductive layers overlap with each other at intersections when viewed from a direction perpendicular to a major surface of the composite, and
wherein the insulating layers prevent the first set of electrically-conductive ribbons from being in electrical contact with the second set of electrically-conductive ribbons at the intersections.