Organic matrix layered composite material with integrated damage detection

Abstract

The invention relates to an organic matrix layered composite material (3) with integrated damage detection. The composite material (3) is formed of a stack of layers including at least: - a probe layer (7); and - a conductive layer (9) which is adjacent to the probe layer (7). The probe layer (7) comprises a substrate and an electrical circuit deposited thereon. The electrical circuit has at least two tracks (15) and at least two electrodes (17). The tracks (15) are electrically insulated from the substrate and each connected to a corresponding electrode (17). The electrical circuit is in contact with the conductive layer (9) only via the electrodes (17). The composite material (3) is characterised in that the conductive layer (9) covers the electrodes (17).

Description

[0001] Description

[0002] Title: Organic matrix laminated composite material with integrated damage detection

[0003] This application incorporates by reference the content of French patent application FR 2 411 165 filed on October 15, 2024.

[0004] The field of the invention relates to the detection of damage within an organic matrix laminated composite material.

[0005] A composite material is an assembly of at least two immiscible materials. Such an assembly allows the composite material to possess properties that the materials composing it, taken individually, do not possess.

[0006] A composite material is formed of at least a matrix and a reinforcement.

[0007] The matrix ensures the cohesion of the composite material and gives it the desired shape. The matrix surrounds the reinforcement and transfers mechanical stresses to it. The matrix can be organic, metallic, or ceramic. In the case of an organic matrix composite material, the matrix—then called the "resin"—can be thermosetting, for example, epoxy resin, polyester, or polyimide, or thermoplastic, for example, polypropylene (PP), polyamide (PA), or polyetheretherketone (PEEK).

[0008] The reinforcement forms the backbone of the composite material and gives it most of its mechanical properties. Reinforcement is generally made of fibers such as carbon fibers, glass fibers, aramid fibers, or plant fibers. Reinforcement may also include metallic fillers, carbon fillers, silica fillers, or polymer fillers.

[0009] Due to their characteristics, composite materials have applications in various industrial sectors such as electronics, automotive, rail, aeronautics, and space. For example, it is common in industry to use a carbon / carbon composite – or C / C – made of a graphite matrix reinforced with carbon fibers, or a carbon fiber reinforced polymer (also known by the English acronym CFRP for "carbon fiber reinforced polymer").

[0010] It is known to layer plies of fibers – usually of similar shapes – to form the reinforcement of a composite material. The composite material made from such reinforcement is said to be "laminated".

[0011] Regardless of the application, a laminated composite material is susceptible to damage, for example, from impact or exposure to thermal conditions that the laminated composite material cannot absorb or withstand. Damage to the laminated composite material generally manifests as cracking, delamination, or fiber breakage or rupture.

[0012] It is known to use a sensor embedded in or inserted into the laminated composite material to detect the appearance of potential damage and thus monitor the structural health of the laminated composite material. Such a sensor measures an electrical quantity, variations in which can reveal the presence of damage.

[0013] Chinese patent application CN 1 13752644 A describes an aircraft coating in the form of a laminated composite material in which a damage detection sensor is integrated.

[0014] This sensor comprises a flexible ply, a carbon nanotube film, a protective fiberglass ply, and an insulating fiberglass ply. The flexible ply consists of a copper-clad polyimide substrate onto which an electrical circuit is etched. The electrical circuit has several electrodes around the periphery of the substrate, which together define a space for the carbon nanotube film. The protective fiberglass ply covers the carbon nanotube film and forms the top layer not only of the sensor but also of the laminated composite material. Finally, the insulating fiberglass ply forms the base of the sensor and isolates the flexible ply and the carbon nanotube film from the other layers of the laminated composite material. Such a sensor has several disadvantages.

[0015] Firstly, the electrical contact between the electrodes and the carbon nanotube film is made with a conductive substance, which therefore represents a material cost and a production cost.

[0016] In addition, the sensor is formed of several layers - the flexible ply, the carbon nanotube film, the protective fiberglass ply and the insulating fiberglass ply - which increase the dimensions and mass of the laminated composite material, and this solely for the purpose of damage detection.

[0017] Furthermore, the sensor is positioned on the surface and is electrically isolated from the other plies. Consequently, the sensor cannot distinguish between damage affecting plies of the laminated composite material other than those of the sensor and damage affecting only the sensor itself, such as abrasion or degradation caused by environmental conditions. Moreover, the sensor's detection is only surface-based, as it concerns the carbon nanotube film and not the plies of the laminated composite material other than those of the sensor.

[0018] Finally, there is a high risk of delamination between the carbon nanotube film and, on the one hand, the flexible ply, and, on the other hand, the protective glass fiber ply.

[0019] The present invention improves the situation.

[0020] In this respect, the invention relates to an organic matrix laminated composite material with integrated damage detection. The composite material is formed from a stack of plies comprising at least:

[0021] - a probe fold, and

[0022] - a conductive fold adjacent to the probe fold.

[0023] The probe fold comprises a substrate and an electrical circuit deposited on the substrate. The electrical circuit has at least two tracks and at least two electrodes, the at least two tracks being electrically insulated from the substrate and each connected to a respective electrode of the at least two electrodes. The electrical circuit is in contact with the conductive fold only via the at least two electrodes.

[0024] The conductive fold covers at least two electrodes.

[0025] In one or more embodiments, the stacking of folds includes an additional conductive fold adjacent to the conductive fold.

[0026] In one or more embodiments, the stack of plies includes at least one additional conductive ply, and each electrode is surmounted by an elongated conductive piece, which elongated conductive piece extends from the electrode and pierces at least part of the stack of plies so as to be in contact with at least one additional conductive ply.

[0027] In one or more embodiments, the stack of folds further includes another conductive fold adjacent to the probe fold. The at least two electrodes are distributed on a first and a second face of the substrate, and the conductive fold and the other conductive fold each cover the electrodes of the at least two electrodes on the first and second faces respectively.

[0028] In one or more embodiments, the at least two tracks each have a respective free end and the free ends are brought together on a connection portion of the probe ply accessible from outside the ply stack.

[0029] Typically, the electrical resistance between the free end of one of the at least two tracks and the electrode to which the track is connected is less than 10 Q, and is preferably less than 1 Q.

[0030] In one or more embodiments, the electrical circuit covers less than half of the substrate surface.

[0031] In one or more embodiments, the electrical circuit is formed of a conductive ink, a precursor coating of conductive film or a metal deposited by physical vapor deposition.

[0032] In one or more embodiments, the at least two tracks are electrically insulated from the conductive ply by an insulating film, an insulating ink, or glass fibers. The invention also relates to a damage detection system for an organic matrix laminated composite material, characterized in that it comprises:

[0033] - a composite material as described above, and

[0034] - an excitation and measurement device electrically connected to at least two tracks and arranged to detect damage within the composite material by the power supply and measurement of electrical quantity of the electrical circuit.

[0035] Other features, details, and advantages will become apparent upon reading the detailed description below and analyzing the attached drawings, which illustrate this.

[0036] [Fig. 1] illustrates a damage detection system for organic matrix laminated composite material according to the invention,

[0037] [Fig. 2] illustrates a probe fold of the organic matrix laminated composite material of the system of [Fig. 1], and

[0038] [Fig. 3] illustrates the organic matrix laminated composite material of [Fig. 1],

[0039] Figure 1 illustrates a system 1 for detecting damage to organic matrix laminated composite material.

[0040] System 1 comprises an organic matrix laminated composite material 3 and an excitation and measurement device 5.

[0041] In the following description, the organic matrix laminated composite material 3 is referred to as "composite material 3" for the sake of brevity.

[0042] The organic matrix laminated composite material targeted by damage detection is precisely the one integrated into system 1, i.e. composite material 3.

[0043] Composite material 3 is a laminated composite material and therefore consists of a stack of plies. More specifically, composite material 3 is an assembly of an organic matrix and a reinforcement formed by stacking plies. The organic matrix is ​​referred to as "resin" throughout this description, except in the phrase "organic matrix laminated composite material".

[0044] The resin can be thermosetting, for example epoxy resin, polyester or polyimide, or thermoplastic, for example polypropylene (PP), polyamide (PA) or polyetheretherketone (PEEK).

[0045] The reinforcement's construction offers considerable flexibility. Various types of fibers can be used, including carbon fibers, glass fibers, aramid fibers, and plant fibers. These fibers can be unidirectional, woven, non-woven, or have no particular orientation. Furthermore, the fibers can be pre-impregnated, meaning they are already resin-impregnated, or they can be dry.

[0046] As illustrated in [Fig. 1], the composite material 3 comprises a succession of plies stacked along a vertical direction Z. This succession of plies includes at least one probe ply 7 and one conductive ply 9.

[0047] The probe ply 7 and the conductive ply 9 are adjacent ply, that is, successive ply in the stack of ply forming the composite material 3.

[0048] The probe fold 7 constitutes, for the device 5, an access to the composite material 3.

[0049] Fig. 2 is a photograph of such a probe fold 7 in top view.

[0050] The probe fold 7 is in the form of a substrate 11 on which an electrical circuit 13 is deposited.

[0051] The substrate 11 supports the electrical circuit 13 and allows it to be in contact - physically and therefore electrically - with the conductive fold 9.

[0052] Typically, substrate 1 1 has a thickness between 10 and 500 micrometers (pm).

[0053] The electrical circuit 13 can be formed from a conductive ink, a conductive film precursor coating, or a metal deposited by physical vapor deposition. Typically, the thickness of the electrical circuit 13 is less than 100 micrometers (pm).

[0054] The electrical circuit 13 has at least two tracks 15 and at least two electrodes 17. Each track 15 is connected to a respective electrode 17. In the example in [Fig. 2], the electrical circuit 13 has sixteen tracks 15 and sixteen electrodes 17.

[0055] In the example of [Fig. 2], the electrical circuit 13 is deposited on only one face of the substrate 11. In other words, the tracks 15 and the electrodes 17 are deposited on the same face of the substrate 11.

[0056] Alternatively, the electrical circuit 13 can be deposited on both faces of the substrate 11. For example, the tracks 15 can be deposited on one face of the substrate 11, while the electrodes 17 are deposited on the other face. Again, as an example, the tracks 15 can be distributed on both faces of the substrate 11, as can the electrodes 17.

[0057] In particular, in the case where a track 15 deposited on one face of the substrate 11 is connected to an electrode 17 deposited on the other face, this track 15 and this electrode 17 are connected to each other through the substrate 11.

[0058] One or more electrodes 17 may also be "doubled". An electrode 17 is doubled when it is formed of two electrodes arranged respectively on the two faces of the substrate 11 and electrically connected to each other through the substrate 11. The two electrodes of a doubled electrode 17 are located one below the other in the vertical direction Z.

[0059] In the example of [Fig. 2], each track 15 has a free end 19 intended to be electrically connected to the device 5.

[0060] Typically, for a given track 15, the electrical resistance between the free end 19 and the electrode 17 is less than 10 ohms (Q), and is preferably less than 1 ohm (Q).

[0061] In the example of [Fig. 2], the respective free ends 19 of the tracks 15 are brought together on a connection portion 21 of the probe ply 7. The connection portion 21 is intended to remain accessible from outside the ply stack when the probe ply 7 is integrated into the composite material 3. The connection portion 21, for example, protrudes from the ply stack forming the composite material 3.

[0062] As an illustration, [Fig. 3], which is a photograph of the composite material 3 as it comes out of an autoclave curing, shows the connection portion 21 protruding from the stack of plies.

[0063] Alternatively, when the probe ply 7 is intended to be positioned on the surface of the composite material 3, the connection portion 21 can be made directly accessible without protruding from the stack of plies.

[0064] Tracks 15 are electrically isolated from substrate 11. Such electrical isolation can be achieved by at least two different methods.

[0065] The first method involves using an insulating—or “non-conductive”—material, that is, a material that impedes the flow of electric current, to create substrate 11. Electrical insulation is thus achieved by the very nature of substrate 11. In the example shown in [Fig. 2], substrate 11 is formed from a ply of glass fibers. Of course, other insulating materials can be used.

[0066] The second method involves treating the areas of the substrate 11 intended to receive the tracks 15 to insulate them. Such insulation can be achieved using various techniques, including the liquid deposition of a resin or dielectric coating, the addition of an insulating layer—for example, an insulating polymer film or a fiberglass ply—or the deposition of an insulating oxide layer. This second method is particularly suitable when the substrate 11 is made from a conductive material; for example, when the substrate 11 is a carbon fiber ply.

[0067] The electrodes 17 may or may not be electrically isolated from the substrate 11. When the substrate 11 is made from an insulating material, the electrodes 17 are electrically isolated from the substrate 11 by the very nature of the substrate 11.

[0068] However, when the substrate 11 is made from a conductive material, it may be advantageous not to isolate the electrodes 17 from the substrate 11. The device 5 is then electrically connected not only to the conductive ply 9 but also to the substrate 11, which therefore allows the device 5 to have access to a larger portion of the composite material 3.

[0069] Referring again to [Fig. 1], the conductive fold 9 is suitable for conducting an electric current.

[0070] The conductive ply 9 is, for example, a carbon fiber ply. Of course, other conductive materials can be used to make the conductive ply 9. It is also possible to use a ply whose fibers are insulating but coated with a conductive substance.

[0071] The heart of the invention lies in the contact - and more precisely the electrical contact - between the electrical circuit 13 and the conductive fold 9.

[0072] The probe ply 7 and the conductive ply 9—which are adjacent plies in the sequence of plies of the composite material 3—are shaped and dimensioned such that the conductive ply 9 covers the electrodes 17 of the electrical circuit 13. In other words, when the conductive ply 9 is positioned on the probe ply 7 along the vertical Z direction, the conductive ply 9 comes into contact with the electrodes 17 and conceals them. Put another way, the contact surface of an electrode 17 and the conductive ply 9 is substantially orthogonal to the vertical Z direction. The electrical circuit 13 is positioned opposite the conductive ply 9 along the vertical Z direction.

[0073] Such a contact allows for direct electrical contact between the electrodes 17 and the conductive fold 9. It is therefore not necessary to use a conductive substance to electrically connect the electrodes 17 and the conductive fold 9, as is the case, for example, in the Chinese patent application CN 1 13752644 A mentioned previously.

[0074] Furthermore, as mentioned above, the electrodes 17 can be deposited so as to be distributed over both faces of the substrate 11. In such a case, the stack of folds includes another conductive fold—in addition to the conductive fold 9—adjacent to the probe fold 7. In other words, the probe fold 7 is sandwiched between the conductive fold 9 and this other conductive fold to form a sandwich structure. The conductive fold 9 and this other conductive fold then each cover the electrodes 17 on one of the respective faces of the substrate 11.

[0075] It is possible to increase the dimensions of the electrodes 17 to have a larger contact area between the electrodes 17 and the conductive fold 9. Typically, the electrodes 17 have a diameter greater than 5 millimeters (mm), which is also the case in the example of [Fig. 2]. The electrodes 17 may also not be circular; other shapes are conceivable.

[0076] Furthermore, the arrangement of the electrodes 17 on the substrate 11 can be peripheral; but the electrodes 17 can also be arranged regularly on the substrate 11 so as to form a grid. Other arrangements are conceivable.

[0077] It is also possible, during the manufacture of the probe fold 7, to coat the electrodes 17 with a conductive material, for example a conductive ink or a metallic solder to improve the contact between the electrodes 17 and the conductive fold 9. Alternatively, it is possible to weld, glue or fix a metallic piece at the level of an electrode 17.

[0078] With the aim of further improving contact between electrodes 17 and conductive fold 9, it is also possible to place probe fold 7 and conductive fold 9 under vacuum to obtain pressure contact between electrodes 17 and conductive fold 9.

[0079] To avoid any short circuit, the electrical circuit 13 is in contact with the conductive fold 9 only through the electrodes 17. In other words, there is no direct contact between the rest of the electrical circuit 13, i.e. the tracks 15, and the conductive fold 9.

[0080] To achieve this, an insulating material can be deposited on the tracks 15. Once the probe fold 7 and the conductive fold 9 are aligned, the insulating material is placed between the tracks 15 and the conductive fold 9 so that only the electrodes 17 are in direct contact with the conductive fold 9. Such an insulating material can be a fabric, for example, made of glass fibers. Such a fabric typically has a thickness of less than 500 micrometers (µm). It is also possible to deposit an insulating ink or resin on the tracks 15. Such an insulating ink or resin typically has a thickness of less than 100 micrometers (µm).

[0081] Another possibility for isolating the tracks 15 from the conductive fold 9 is to design the probe fold 7 so that the tracks 15 and the electrodes 17 are not deposited on the same face of the substrate 11. The tracks 15 are then isolated from the conductive fold 9 by the substrate 11 which is interposed between the tracks 15 and the conductive fold 9.

[0082] In the example of [Fig. 1], and similarly to [Fig. 2], the tracks 15 and the electrodes 17 are deposited on the same face of the substrate 11, that is to say the face intended to be in contact with the conductive ply 9 in the composite material 3. This face of the substrate 11 corresponds to the front face in the vertical direction Z.

[0083] With further reference to [Fig. 1], it appears that the stack of plies forming the composite material 3 can include one or more plies in addition to the probe ply 7 and the conductive ply 9. Thus, in the example of [Fig. 1], and for illustrative purposes, the composite material 3 includes an upper ply 23 and a lower ply 25.

[0084] Typically, the composite material 3 is made in such a way that the conductive ply 9 is arranged in the middle of the stack of plies, as is the case in [Fig. 1],

[0085] However, the composite material 3 can also be made in such a way that the conductive ply 9 is the surface ply of the composite material 3, that is to say the highest ply in the vertical direction Z.

[0086] Furthermore, it is also possible that the probe ply 7 is the surface ply of the composite material 3, in which case the electrodes 17 are deposited on the posterior face of the substrate 11, and not on the anterior face, so as to be in contact with the conductive ply 9, which is then located below the probe ply 7, along the vertical Z direction, in the ply stack. The other plies of the composite material 3 can be conductive plies, for example carbon fiber plies, or insulating plies, for example glass fiber plies.

[0087] Advantageously, the composite material 3 includes an additional conductive ply adjacent to the conductive ply 9. In the example of [Fig. 1], such an additional conductive ply is, for example, the upper ply 23. Indeed, due to its contiguity with the conductive ply 9, such an additional conductive ply makes it possible to further extend the detection range of the device 5, which is then able to detect damage such as a crack, delamination, or even a break or rupture of fibers at the level of this additional conductive ply.

[0088] In the same spirit, the conductive fold 9 can be in electrical contact with a succession of additional conductive folds, which are successive in the stacking of folds.

[0089] As explained previously, another variant also consists, when the electrodes 17 are distributed on the two faces of the substrate 11, of placing the probe fold 7 between the conductive fold 9 and another conductive fold - which would correspond to the lower fold 25 on the [Fig. 1] - which then each cover the electrodes 17 of a respective face of the substrate 11.

[0090] With the aim of extending the detection range of device 5, it is also possible to mount an elongated conductive piece across each electrode 17. Such an elongated conductive piece extends from the electrode 17 on which it is mounted and pierces at least part of the stack of folds so as to be in contact with one or more additional conductive folds. Such a conductive piece can be in the form of a metal stud, rod, or punch.

[0091] Such a configuration gives the device 5 access to additional conductive folds that are not directly in contact with the conductive fold 9. For example, an additional conductive fold separated from the conductive fold 9 by one or more insulating fold(s) can thus be reached by each elongated conductive piece extending from an electrode 17. Moreover, it is not necessary for such additional conductive folds, reached by the elongated conductive pieces, to be located above the conductive fold 9 in the vertical direction Z; such conductive folds can instead be below the probe fold 7 in the vertical direction Z.

[0092] Composite material 3 can be manufactured using various known manufacturing processes.

[0093] In particular, composite material 3 can be manufactured using a "wet process" or a "dry process". The "wet process" and the "dry process" are two categories of manufacturing processes that differ from each other in the way in which impregnation is carried out.

[0094] Impregnation involves saturating the reinforcement with resin in a homogeneous manner. A uniform distribution ensures a strong bond between the reinforcement and the resin.

[0095] The wet process encompasses techniques in which the resin impregnates the reinforcement in liquid form. Examples include contact molding, vacuum infusion molding, and resin transfer molding (also known as RTM for "resin transfer molding"), all of which are wet-process manufacturing techniques for organic matrix laminated composite materials.

[0096] The dry process encompasses techniques in which the reinforcement is pre-impregnated. The reinforcement fibers can be coated with resin, resulting in a pre-impregnated material. Examples include automated fiber placement (AFP) and automated tape laying (ATL) for dry composite material manufacturing techniques.

[0097] It should be noted that some techniques can be implemented using both wet and dry processes, notably filament winding, which consists of winding resin-impregnated fibers onto a mandrel under controlled tension. Specifically, when using thermosetting resin, the fibers are dipped in a resin bath (wet process); and when using thermoplastic resin, the fibers are pre-impregnated and wound directly onto the mandrel (dry process).

[0098] Manufacturing processes can be categorized in ways other than the distinction between "wet process" and "dry process".

[0099] The presence of probe fold 7 may lead to some adaptations with regard to impregnation.

[0100] The main challenge lies in the fact that the electrodes 17 must be in contact with the conductive ply 9, and therefore the stack of plies intended to form the composite material 3 must be impregnated without the resin interposing itself between the electrodes 17 and the conductive ply 9.

[0101] It is possible to use only dry plies, that is, plies that are not yet impregnated. To do this, the plies, and in particular the probe ply 7 and the conductive ply 9, are placed under vacuum to establish pressure contact. A vacuum infusion is then performed to impregnate all the plies. The pressure contact between the probe ply 7 and the conductive ply 9 prevents the resin from getting between the electrodes 17 and the conductive ply 9.

[0102] Another possibility is to create a ply stack in which the plies other than the probe ply 7 and the conductive ply 9 are pre-impregnated. The pre-impregnated plies may have excess resin, which can be used to impregnate the probe ply 7 and the conductive ply 9. For example, the plies are draped and placed under vacuum. The ply stack is then cured in an autoclave. During curing, the resin is distributed evenly throughout all the plies, including the probe ply 7 and the conductive ply 9. If the resin in the pre-impregnated plies is insufficient, the missing amount of resin can be infused under vacuum before curing.

[0103] It is also possible to use a pre-impregnated conductive ply 9. In this case, it is necessary to remove the resin from each area of ​​the conductive ply 9 intended to be in contact with the electrodes 17. As an illustration, [Fig. 3] is a photograph of a composite material 3 after curing in an autoclave.

[0104] In cases where impregnation is required, it is preferable that the electrical circuit 13 cover less than half of the surface of the substrate 11 so as not to obstruct the diffusion of the resin in the stack of plies.

[0105] Device 5 is arranged to probe the composite material 3 in order to detect the presence of any damage such as a crack, delamination or even breakage or rupture of fibers.

[0106] Device 5 includes a power supply 27, a sensor 29, a memory 31 and a processor 33.

[0107] The source 27 is arranged to be connected to a doublet of tracks 15 and to supply the conductive fold 9 with electrical energy via the electrical circuit 13, and more specifically the electrodes 17 connected respectively to the tracks 15 to which the source 27 is connected.

[0108] In the example of [Fig. 1], the source 27 is a current source arranged to apply a desired intensity to the electric current flowing between the two tracks 15 to which the source 27 is connected. These two tracks 15 are in fact electrically connected to each other via their respective electrodes 17 and the conductive fold 9.

[0109] Alternatively, source 27 is a voltage source arranged to apply a voltage between the two tracks 15 to which source 27 is connected.

[0110] The sensor 29 is arranged to be connected to a pair of tracks 15 and to measure an electrical quantity at the level of the electrical circuit 13.

[0111] In the example in [Fig. 1], sensor 29 is a voltage sensor arranged to measure the voltage between the tracks 15 to which sensor 29 is connected. Such a voltage sensor can be a voltmeter-type measuring instrument.

[0112] Alternatively, sensor 29 is a current sensor arranged to measure the intensity of the electric current flowing between the tracks 15 to which sensor 29 is connected. Such a current sensor is, for example, an ammeter. In the example of [Fig. 1], device 5 includes a single source 27 and a single sensor 29.

[0113] Typically, the source 27 and the sensor 29 are both connected to all the tracks 15 by electrical cables. Multiplexers (not shown here) are present and allow selective selection of, on the one hand, the pair of tracks 15 through which the conductive fold 9 is to be supplied with electrical energy and, on the other hand, the pair of tracks 15 by which an electrical quantity is measured at the level of the electrical circuit 13.

[0114] The Applicant described, in French patent FR 3 131 372 B1, an architecture allowing a source - in this case a current source - and a sensor - in this case an analog-to-digital converter - to be connected to electrodes arranged on the periphery of a substrate via multiplexers.

[0115] Alternatively, source 27 may denote a set of power supply sources, each arranged to be connected to a respective pair of tracks 15; and sensor 29 may denote a set of sensors, each arranged to be connected to a respective pair of tracks 15.

[0116] Memory 31 is arranged to store instructions whose implementation by the processor 33 results in the operation of device 5.

[0117] Memory 31 can also be arranged to store a record of measurements from sensor 29.

[0118] Memory 31 can refer to any data storage medium designed to receive and retain digital data, for example, a hard drive, a solid-state drive (SSD), or more generally, any computer hardware that allows data storage on flash memory. Memory 31 can also be random access memory (RAM) or a magneto-optical disk. A combination of several storage media is also possible. The processor 33 is designed to detect, based on measurements taken by the sensor 29, the presence of damage such as a crack, delamination, or breakage or rupture of fibers within the composite material 3.

[0119] The processor 33 can be configured to operate the device 5 in different modes. For example, the device 5 can operate in a continuous monitoring mode in which the source 27 continuously supplies the electrical circuit 13 with electrical energy and in which the sensor 29 performs continuous measurements. The device 5 can also operate in a discrete monitoring mode in which the source 27 supplies the electrical circuit 13 with electrical energy at regular intervals and in which the sensor 29 performs measurements at regular intervals.

[0120] The processor 33 can be implemented in any known form, for example, as a microprocessor, a programmable logic device (PLD), a dedicated chip such as an FPGA (Field Programmable Gate Array) or SoC (System on Chip), a computing resource grid, a microcontroller, or any other proprietary form with the computing power necessary for damage detection. One or more of these elements can also be implemented as specialized electronic circuits such as ASICs (Application-Specific Integrated Circuits). A combination of processors and electronic circuits is also possible.

[0121] The principle of damage detection is as follows: the source 27 excites a doublet of tracks 15 to supply electrical energy to the conductive ply 9. This supply results in the appearance of an electrical signal, that is, a movement of electrical charge carriers. Such an electrical signal is characterized, at a given instant, by an intensity and a voltage. The source 27 can be a current source, in which case the intensity of the electrical signal is controlled, or a voltage source, in which case the voltage of the electrical signal is controlled. The sensor 29 measures an electrical quantity, and more precisely an intensity or a voltage, at the level of the electrical circuit 13. The processor 33 receives the measurements taken by the sensor 29 and detects, if necessary, the presence of damage such as a crack, delamination, or even a break or rupture of fibers.

[0122] Such damage manifests itself, in the measurements taken by sensor 29, as an unusual variation or even a discontinuity in the values ​​of the electrical quantity. It should be noted that the analysis performed by processor 33 may involve monitoring the electrical resistance of the probe fold 7, which can be calculated from the electrical quantity measured by sensor 29, whether this electrical quantity is the voltage or the current intensity, and with regard to the current or voltage applied by source 27.

[0123] In such a configuration, the detection carried out by the device 5, and more precisely by the processor 33, is binary since the information generated from the measurements carried out by the sensor 29 indicates the presence or absence of damage within the composite material 3. However, such detection can be more precise and allow not only the detection of the presence of possible damage but also, if necessary, the location of such damage to be known.

[0124] To this end, device 5 can implement electrical impedance tomography (EIT).

[0125] Electrical impedance tomography (EIT) is an imaging technique used to determine the electrical properties of a material by measuring the voltage of electrode pairs typically—but not necessarily—placed on the surface of the material. These voltage measurements are used to map the electrical charge density or electrical conductivity of the material.

[0126] In the present case, the material can refer to all conductive plies such as the conductive ply 9 which are capable of carrying an electric current through the probe ply 7.

[0127] According to the general principle of TIE, electrode doublets 17 are supplied with electrical energy by the source 27, and the voltage between the two electrodes 17 of different electrode pairs is measured. Several processes have been developed based on this principle and differ in their injection pattern—that is, the way in which the electrode doublets 17 to be excited are formed.

[0128] The most commonly used injection pattern is the adjacent pattern - or "adjacent pattern" - described by DC Barber and BH Brown in the article "Applied potential tomography" (Journal of Physics E: Scientific Instruments, vol. 17, no. 9, 1984) and which consists, in this case, of supplying each pair of electrodes 17 formed of two neighboring electrodes 17 and then measuring the voltage at each pair of electrodes 17 also formed of two neighboring electrodes 17.

[0129] In the field of electrical energy theory (IET), inverse problem theory is commonly used to determine the electrical properties of a material. The principle of this approach is to identify the cause—in this case, the distribution of electrical charge density or electrical conductivity—from the effects—in this case, the voltage measurements between the two electrodes of electrode pairs. Indeed, any change in the distribution of electrical conductivity leads to changes in the potential distribution and, consequently, to changes in the voltage between the electrodes.

[0130] An inverse TIE problem is a nonlinear and ill-posed problem. In particular, this inverse problem does not depend continuously on voltage measurements. As recalled by SR Kupis in the publication "Methods for the Electrical Impedance Tomography Inverse Problem: Deep Learning and Regularization with Wavelets" (All Theses, 2021), it is possible to use a MIRGN-type Gauss-Newton algorithm (modified iteratively regularized Gauss-Newton) or a Tikhonov regularization to solve an inverse TIE problem.

[0131] Furthermore, solvers currently exist that can reconstruct the distribution of electrical charge density or electrical conductivity from voltage measurements. For example, the open-source software EIDORS, which runs under MATLAB (registered trademark), can be used to solve an inverse problem. Memory 31 and processor 33 can thus be configured to solve an inverse problem of the TIE (Thermal Impulse Efficiency) from measurements collected by sensor 29.

Claims

Demands

1. An organic matrix laminated composite material (3) with integrated damage detection, wherein the composite material (3) is formed of a stack of plies comprising at least: - a probe fold (7), and - a conductive ply (9) adjacent to said probe ply (7), which probe ply (7) comprises a substrate (11) and an electrical circuit (13) deposited on said substrate (11), said electrical circuit (13) having at least two tracks (15) and at least two electrodes (17), said at least two tracks (15) being electrically insulated from said substrate (11) and each connected to an electrode (17) respective to said at least two electrodes (17), said electrical circuit (13) being in contact with the conductive ply (9) only through said at least two electrodes (17), said composite material (3) being characterized in that the conductive ply (9) covers the at least two electrodes (17).

2. Composite material (3) according to claim 1, characterized in that the ply stack includes an additional conductive ply adjacent to the conductive ply (9).

3. Composite material (3) according to claim 1 or 2, characterized in that the ply stack includes at least one additional conductive ply, and each electrode (17) is surmounted by an elongated conductive piece, which elongated conductive piece extends from said electrode (17) and pierces at least a part of the ply stack so as to be in contact with said at least one additional conductive ply.

4. Composite material (3) according to any one of the preceding claims, characterized in that the ply stack further includes another conductive ply adjacent to the probe ply (7), the at least two electrodes (17) are distributed on a first and a second face of the substrate (11), and the conductive ply (9) and said other conductive ply each cover the electrodes of said at least two electrodes (17) of the first and second faces respectively.

5. Composite material (3) according to any one of the preceding claims, characterized in that the at least two tracks (15) each have a respective free end (19) and said free ends (19) are gathered on a connection portion (21) of the probe ply (7) accessible from outside the ply stack.

6. Composite material (3) according to claim 5, characterized in that the electrical resistance between the free end (19) of a track (15) of the at least two tracks (15) and the electrode (17) to which said track (15) is connected is less than 10 Q, and is preferably less than 1 Q.

7. Composite material (3) according to any one of the preceding claims, characterized in that the electrical circuit (13) covers less than half of the surface of the substrate (11).

8. Composite material (3) according to any one of the preceding claims, characterized in that the electrical circuit (13) is formed of a conductive ink, a conductive film precursor coating or a metal deposited by physical vapor deposition.

9. Composite material (3) according to any one of the preceding claims, characterized in that the at least two tracks (15) are electrically insulated from the conductive ply (9) by an insulating film, an insulating ink or glass fibers.

10. System (1) for detecting damage to organic matrix laminated composite material characterized in that it comprises: - a composite material (3) according to any one of the preceding claims, and - an excitation and measurement device (5) electrically connected to at least two tracks (15) and arranged to detect damage within said composite material (3) by the power supply and measurement of electrical quantity of the electrical circuit (13).

Images