Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K9/00—Screening of apparatus or components against electric or magnetic fields
  • H05K9/0073—Shielding materials
  • H05K9/0081—Electromagnetic shielding materials, e.g. EMI, RFI shielding
  • H05K9/0086—Electromagnetic shielding materials, e.g. EMI, RFI shielding comprising a single discontinuous metallic layer on an electrically insulating supporting structure, e.g. metal grid, perforated metal foil, film, aggregated flakes, sintering
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B64—AIRCRAFT; AVIATION; COSMONAUTICS
  • B64D—EQUIPMENT FOR FITTING IN OR TO AIRCRAFT; FLIGHT SUITS; PARACHUTES; ARRANGEMENT OR MOUNTING OF POWER PLANTS OR PROPULSION TRANSMISSIONS IN AIRCRAFT
  • B64D45/00—Aircraft indicators or protectors not otherwise provided for
  • B64D45/02—Lightning protectors; Static dischargers
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
  • H05K9/00—Screening of apparatus or components against electric or magnetic fields
  • H05K9/0073—Shielding materials
  • H05K9/0079—Electrostatic discharge protection, e.g. ESD treated surface for rapid dissipation of charges
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T442/00—Fabric [woven, knitted, or nonwoven textile or cloth, etc.]
  • Y10T442/10—Scrim [e.g., open net or mesh, gauze, loose or open weave or knit, etc.]

Definitions

• the present invention belongs to the field of structures made with composite materials. More particularly, the invention relates to structures made of composite materials that are non-electrically conductive or weakly conductive and that may be subjected during their use to lightning strikes.
• the invention relates in particular to composite material structures for aircraft.
• the family of composites comprising fibers of a mineral material (glass, silica, carbon %) or organic (aramid, Kevlar® ”) held in a hard organic matrix (polyester, epoxy %) is widely used for the realization of structures because of their mechanical performance, in particular their resistance to mass, and or because of their ability to produce complex shapes.
• a first known technique is to place on the surface of the composite material part of the conductive bands more or less spaced connected by at least one of their ends to a general mass of the aircraft.
• surge arresters is advantageously implemented on aircraft radomes but its construction is delicate and has the defect of not protecting the entire surface of the part, particularly when the radio transparency is not sought.
• a second known technique is to cover the entire surface to be protected from the composite material structure by a mesh made of an electrically conductive metallic material.
• a mesh made of an electrically conductive metallic material.
• Such a grid is most often made of bronze or copper, in particular because of the electrical conductivity characteristics of these materials and for reasons of resistance to corrosion, either by a conventional method of weaving wires or by a method of drawing from a plate prepared to obtain a grid by deployment.
• These grids are deposited on the surface of the part according to various techniques, for example deposited on the surface of the part being produced before a curing cure by polymerization of the matrix of the composite material.
• the gratings Due to the intensities associated with lightning strikes, particularly near the point of the structure at which the impact occurs, the gratings must have sufficient conducting sections which lead to heavy fences (generally 150 at 300 g / m2 on an aircraft structure, ie of the order of 1000 kg for the protection of a fuselage of a long-haul aircraft) and secondly that deteriorate the surface state of the aircraft. structure thus treated whose aerodynamic appearance and aesthetic appearance require to be preserved a primer layer of sufficient thickness and a layer of paint finish of about 100 microns (E10-4 m) sources of penalties in terms of costs and mass.
• the present invention specifically aims to define a structure of composite material effectively protected against the effects of lightning, and which avoids accumulations of electrical charges on its surface, with a reduced mass penalty compared to known performance solutions at least equivalent to protection against the effects of lightning strikes.
• the protected part comprises a structural part of electrically insulating or weakly conductive composite material such as parts made from mineral or organic fibers, for example glass fibers, aramid fibers or carbon fibers, maintained in a hard organic matrix, epoxy for example.
• electrically insulating or weakly conductive composite material such as parts made from mineral or organic fibers, for example glass fibers, aramid fibers or carbon fibers, maintained in a hard organic matrix, epoxy for example.
• the part On the surface of the structural part, at least on the side of the part likely to be subjected to accumulations of electric charges or to lightning strikes, the part is covered, at least in the areas to be protected, by a network made with an electrically conductive material, fixed directly on the surface of the structural part, and comprises a layer of electrically conductive paint deposited in such a way that the network is situated between the structural part made of composite material and the layer of electrically conductive paint.
• the paint forms a continuous conductive layer that disperses the foot of the arc during a lightning strike and ensures the passage of lightning current in the conductor network with decreased current densities compared to a situation in which lightning strikes directly the conductive network, even through a layer of insulating paint covering the conductive network. It is thus possible to reduce the areal density of the network of electrically conductive material compared with conventional metallization using this type of network.
• the part comprises, if necessary, between the network and the layer of electrically conductive paint, a layer of primer and or protective primer of the network, this layer of primer filling in particular hollow volumes that may remain between the conductive parts of the network after laying the network on the structural part.
• the grating is advantageously made by means of a metal grid made of bronze, copper or a copper-based alloy, or else aluminum or an aluminum alloy. aluminum-based alloy.
• the implementation of the invention limits the amount of metal used to form the conductive network.
• the composite structure is satisfactorily protected against the effects of lightning with a surface density of the conducting network of between 30 and 100 g / m 2 and preferably a surface density of 70 ⁇ 10 g / m2, or on average a mass penalty dedicated to the metallization of composite structures two to three times lower for metallization performance equivalent or less. Effective protection is achieved particularly when the electrical conductivity of the electrically conductive paint layer is at least 0.0001 Siemens / m.
• the protected surface is covered with a layer of paint finish whose thickness is preferably 20 ⁇ 5 microns on average.
• FIG. 2a a photograph of a section of a test specimen (micro-section) of FIG. 2a showing the different layers on the side of a protected surface of the following composite material the invention;
• FIG. 2b a photograph of the protected surface of the test specimen having undergone a lightning strike.
• a component 1 of composite material structure according to the invention mainly comprises a structural portion 2 of Es structural thickness comprising inorganic or organic fibers held in an organic hard matrix.
• Figure 1 shows a locally flat part for illustration without this character being limiting of the invention.
• Such a structure is known in particular in aeronautical applications for which a structural strength to favorable structural mass ratio is sought.
• a structure comprises stacked folds of glass fibers, kevlar® or carbon, woven or unidirectional, held in a matrix of a polymeric material such as an aramid.
• the structure comprises in its thickness Es a cellular structure, foam or honeycomb for example, between two coatings made by fibers held in a matrix, such a structure having externally similar properties screws to electrical problems related to lightning that a composite material structure without alveolar core.
• the structure is shaped according to the shape of the part during a forming process before curing by polymerization of the matrix material, in the case of so-called thermosetting matrices, or during a forming process at a time. temperature for which the matrix is in a plastic state, in the case of thermoplastic matrices.
• a part comprises metal parts (not shown) and or bores (not shown), in particular for Fixing needs of the part 1.
• such a part is for example a so-called structural part subjected to significant efforts, of the same order under conditions of use as the structural strength of the part, for example an aircraft fuselage or wing panel, or a so-called secondary part such as a fairing, for example a connecting fairing between the wing and the fuselage of an aircraft.
• the part 1 further comprises, on a surface 21, said outer surface, the structural portion 2 on one side of said part on which electrical charges are likely to accumulate and or an electric arc, particularly related to lightning , is likely to occur, a layer 3 of so-called metallization surface.
• the surface, or part of the surface, of the part 1 on the side of which is said metallization layer 3 is said protected surface.
• it corresponds in particular to the surface of the part of an outer side of the aircraft, that is to say the surface subject to aerodynamic flow.
• the metallization layer 3 itself comprises on the one hand a first conductive layer 31 formed by an electrically conductive network covering the outer surface 21 of the protected structural part of the workpiece and fixed directly on said outer surface and on the other hand a second conductive layer 32 formed by an electrically conductive paint covering the first conductive layer 31.
• the outer surface 21 is not necessarily completely covered by the metallization, certain area not or little exposed to the risk of lightning that may not be metallized or metallized by other means, the description being limited to a portion of the outer surface 21 metallized according to the principle of the invention.
• Electrically conductive paints are generally known and consist for example of paints loaded with conductive particles.
• the second layer 32 of conductive paint does not guarantee sufficient conduction to dissipate lightning currents in the event of a lightning strike, but said second conductive paint layer due to its low local surface resistance ensures a dispersion of arc of the lightning around the point of impact sufficient to distribute the current on a surface such that surface densities of current are reduced on the protected surface.
• an electrically conductive paint having electrical conductivity equal to or greater than 0.0001 Siemens / m is selected.
• the lightning current is able to be efficiently dispersed by the first conductive layer 31 without the need to produce an electrically conductive network as dense as in conventional protection, the network electrically conductive, the role of which is to discharge the electric charges and to conduct the electric currents generated by the lightning arc, being consequently no longer subject to the current densities as high as in the conventional metallization principles implementing a conductive network.
• the network is lightened by being made with finer electrically conductive wires and or with a network mesh less tight.
• the network is for example made by weaving conductive son or by a process of stretching and deployment of a conductive sheet in which have previously been made notches.
• the network is made of conductive metal with a surface density of between 30 and 100 g / m 2, preferably 70 ⁇ 10 g / m 2, a density as low as 30 g / m 2 having been demonstrated to be effective.
• the network of the first conductive layer 31 is attached directly to the outer surface 21 of the structural layer 2 without the use of an intermediate separator such as a sheet material, similarly to the bronze screens used for metallizing the composite panel surfaces in the aeronautical manufactures.
• One method consists, when the structure of the composite material part has been made, to bond the network on the outer surface 21 by means of a resin compatible with the composite material of the part 1. This method adds a step during the production of the piece, a step that is performed on a hard piece and shaped close to its final shape.
• Another method is to place the network during a step of producing the part by considering the network as an outer fold of the composite material structure placed at the outer surface 21. If the part is made with a resin cured during a heat polymerization step (a firing of the thermosetting matrix), the network is deposited on the piece on the side of the outer surface before the firing step and is fixed on the outer surface of the piece during the firing step in which the folds of the composite material are compressed in known manner against each other.
• the network is placed on the part, before or after forming, on the outer surface 21 and adheres to the part on said outer surface under the effect of a pressure applied when the
• the temperature of the resin corresponds to the temperature at which the resin is brought into a plastic state either simultaneously with a step of forming and compacting the thermoplastic plies, or during a subsequent separate step.
• a primer layer 33 is deposited on the first electrically conductive layer 31 to prepare the bonding of the conductive paint layer 32 and especially when the protected surface is visible, an outer topcoat 34 by a conventional paint provides protection of the electrically conductive paint, an improved final surface finish and decoration of the structure.
• the thickness of the layer 34 of exterior finishing paint is reduced to a minimum, advantageously of the order of 20 ⁇ m, typically 20 ⁇ 5 ⁇ m on average, which is made possible by the layer of electrically conductive paint 32 which also has the physico-chemical behavior of a paint.
• the layer 34 of finishing paint can be insulating, said layer being traversed by the lightning currents near the point of impact of the lightning and, because its small thickness has reduced strength compared to a conventional paint of the order of five times thicker.
• the cumulative thicknesses of the second conductive paint layer 32 and the outer finish paint layer 34 are less than or substantially equal to the thickness of a conventional paint protection and finishing layer, ie approximately 100 ⁇ 20 ⁇ m on average.
• Figures 2a and 2b illustrate the effectiveness of the invention which has been demonstrated in lightning tests on specimens.
• FIG. 2a which is a photograph with a large magnification of a micro-section of the specimen on the side of the protected surface of the composite material
• the network of electrically conductive material 31 appears in section as a discontinuous layer (in clear on micro-cutting), and it can it is easy to identify the conductive paint 32 and the finishing paint 34, as well as the plies of the composite material 2 closest to the considered surface, well differentiated on the micro-cut due to the different orientation of the fibers of each fold.
• Figure 2b shows the surface of the specimen representative of the piece
• the conductive material of the network 32 has traces of evaporation on a reduced surface and the conductive paint layer 32 is evaporated about 200 mm, the diameter of the area 41 surrounded by a dashed circle in Figure 2a.
• the protection is implemented by conventional techniques of laying metal networks on a composite structure and of paints without the need to resort to complex protection arrangements using intermediate layers of little interest. vis of their effect on lightning currents.

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• Engineering & Computer Science (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Aviation & Aerospace Engineering (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Laminated Bodies (AREA)
• Elimination Of Static Electricity (AREA)

Applications Claiming Priority (2)

Publications (1)

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• 2008
  • 2008-12-15 FR FR0858580A patent/FR2939954B1/fr not_active Expired - Fee Related
• 2009
  • 2009-12-15 WO PCT/EP2009/067154 patent/WO2010069944A1/fr not_active Ceased
  • 2009-12-15 US US13/139,633 patent/US20110318981A1/en not_active Abandoned
  • 2009-12-15 EP EP09771378A patent/EP2377380A1/de not_active Withdrawn

Patent Citations (1)

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