Composite material damage detection system

Abstract

The invention relates to a system (1) for detecting damage to a composite material comprising: - a layer of fibers (3) suitable for integration into a composite material, - a conductive part (5) in contact with the layer of fibers (3), and - a stimulation and measurement device (7) comprising one or more conductive wires (9, 11) each incorporated into the layer of fibers (3) and in contact with the conductive part (5), and a detector (13) arranged to supply power to a conductive wire (9) and to detect, by measuring electrical resistance, an interruption in the flow of current between the supplied conductive wire and the conductive part (5) or, where applicable, between the supplied conductive wire (9) and a third conductive wire (11) electrically connected to each other via the conductive part (5). [Fig. 1]

Description

Title of the invention: Damage detection system for a composite material

[0001] The field of the invention relates to the detection of damage to a composite material, in particular a crack or degradation at the interface with a conductive part.

[0002] A composite material is an assembly of at least two immiscible materials. Such an assembly allows the composite material to possess properties that the individual materials do not possess. Due to their characteristics, composite materials have applications in various industrial sectors such as electronics, automotive, rail, aeronautics, and space.

[0003] A composite material is formed of at least a matrix and a reinforcement.

[0004] The matrix ensures the cohesion of the composite material and allows it to be given the desired shape. The matrix surrounds the reinforcement and transfers mechanical stresses to it. The matrix is ​​typically organic, metallic, or ceramic. In particular, in the case of an organic matrix composite material, the matrix—then called resin—can be thermosetting, for example, epoxy resin, polyester, or polyimide, or thermoplastic, for example, polypropylene (PP), polyamide (PA), or polyetheretherketone (PEEK).

[0005] The reinforcement forms the framework of the composite material and gives it most of its mechanical properties. The reinforcement can increase the strength of the matrix or make it lighter. The reinforcement is generally made of fibers such as carbon fibers, glass fibers, aramid fibers, or even plant fibers. The reinforcement may also include metallic fillers, carbon fillers, silica fillers, or polymer fillers.

[0006] As an example, it is known in the industry to use a carbon / carbon composite - or C / C - formed of a graphite matrix reinforced with carbon fibers or a carbon fiber reinforced polymer (also known by the English acronym CFRP for "carbon filter reinforced polymer").

[0007] Regardless of the field of application, a composite material is susceptible to damage, for example, in the event of impact or exposure to thermal conditions that the composite material is unable to absorb and withstand. Damage to the composite material generally takes the form of a crack or delamination.

[0008] Furthermore, the damage sustained may correspond to degradation at the interface—which may take the form of contact by pressure, bonding, or welding—between the composite material and a part belonging to a structure into which the composite material is integrated. Such a part may, in particular, be a fastener, for example, an insert, a screw, or a rivet, used for assembling the structure and for integrating the composite material.

[0009] It is known that, to detect potential damage, a sensor is used, either embedded in or inserted into the composite material, and its electrical resistance is measured to monitor the condition of the composite material in order to detect possible degradation. Such degradation is then manifested by a change or even a discontinuity in the electrical resistance.

[0010] International application WO 2020 / 245564 A1 describes a sacrificial sensor in the form of a strand integrated into a non-conductive composite material. The sacrificial sensor is in contact with several plies of the composite material such that damage to the latter modifies the electrical properties of the sacrificial sensor, in particular its electrical resistance.

[0011] US patent 9,329,021 B1 relates to monitoring the condition of a composite material using strips of piezoresistive material sandwiched between the plies of the composite material. Each strip is fitted at its ends with electrodes connected to a voltage or current source. A detector, also connected to the electrodes, measures the electrical resistance of the strip to identify any damage.

[0012] European patent application EP 2 950 085 A1 proposes the combined use of a thermal element—for example, a metal wire—and a sensing element contained within separate plies of a composite material. More precisely, the thermal element and the sensing element are electrically insulated and separated from each other by a fiber plies. The thermal element is stimulated to heat the composite material, and then the electrical resistance of the sensing element is continuously measured to determine its thermal profile. This thermal profile is then compared to a reference profile to determine the condition of the composite material and detect the presence of a crack or delamination.

[0013] However, none of the existing solutions takes advantage of the environment in which the composite material is used, i.e., the structure or technical system into which the composite material is integrated. Indeed, as explained previously, the composite material is likely to come into contact with a part, for example, a fastener, and the potential damage may therefore concern the contact between the composite material and the part. Yet, the solutions described above focus on the composite material as such and do not take into account taking into account its possible interactions with the structure or technical system of which it is a part.

[0014] The present invention improves the situation.

[0015] In this respect, the invention relates to a damage detection system for a composite material comprising: - a layer of fibers suitable for integration into a composite material, and - a conductive part in contact with the layer of fibers.

[0016] The system further includes a stimulation and measurement device comprising one or more conductive wires each incorporated into the fiber layer and in contact with the conductive part and a detector arranged to supply a conductive wire and to detect, by measuring electrical resistance, an interruption of the flow of current between the supplied conductive wire and the conductive part or, where appropriate, between the supplied conductive wire and a third conductive wire electrically connected to each other via the conductive part.

[0017] The fiber layer is, for example, composed of glass fibers.

[0018] Alternatively, the fiber layer is composed of carbon fibers, and each conductive wire is electrically insulated from the fiber layer.

[0019] In one or more embodiments, at least one conducting thread is a textile thread.

[0020] In one or more embodiments, at least one conducting wire is made of carbon.

[0021] In one or more embodiments, the detector includes a voltage source arranged to apply a voltage between the powered conductive wire and the conductive part or, where applicable, between the powered conductive wire and the third conductive wire, and a current sensor arranged to measure the intensity of the current flowing between the powered conductive wire and the conductive part or, where applicable, between the powered conductive wire and the third conductive wire.

[0022] Alternatively, the detector includes a current source arranged to circulate a current between the powered conductive wire and the conductive part or, where applicable, between the powered conductive wire and the third conductive wire, and a voltage sensor arranged to measure the voltage between the powered conductive wire and the conductive part or, where applicable, between the powered conductive wire and the third conductive wire.

[0023] In one or more embodiments, at least one conducting yarn is incorporated into the fibre layer by weaving, knitting, braiding or gluing.

[0024] In one or more embodiments, at least one conductive wire is in contact with the conductive part by pressure, gluing or welding.

[0025] The invention also relates to a composite material comprising a plurality of plies and the system described above, one of the plies being formed by the fiber layer of the system.

[0026] Other features, details and advantages will become apparent upon reading the detailed description below, and upon analysis of the accompanying drawings on which:

[0027] [Fig. 1] schematically illustrates a first embodiment of a damage detection system for a composite material according to the invention comprising a layer of fibers, a conductive part and a stimulation and measurement device with at least one pair of conductive wires,

[0028] [Fig.2] is a photograph of part of the system, namely a conductive part and two pairs of conductive wires,

[0029] [Fig.3] illustrates the variations in the electrical resistance of a pair of conducting wires of the stimulation and measurement device of the system of [Fig.1], and

[0030] [Fig.4] schematically illustrates a second embodiment of a damage detection system for a composite material according to the invention comprising a layer of fibers, a conductive part and a stimulation and measurement device with a single conductive wire.

[0031] Fig. 1 illustrates a system 1 for detecting damage to a composite material.

[0032] A composite material is an assembly of at least two immiscible materials: a matrix and a reinforcement. The matrix can be organic, metallic, or ceramic—in which case they are referred to, respectively, as an organic matrix composite (OMC), a metal matrix composite (MMC), and a ceramic matrix composite (CMC). The reinforcement is generally made of fibers, for example, carbon fibers, glass fibers, aramid fibers, or plant fibers. The reinforcement may also include fillers such as metallic fillers, carbon fillers, silica fillers, or polymer fillers.

[0033] The composite material can be assembled by stacking several layers—called plies—each corresponding to the matrix or the reinforcement. For example, it is known to arrange the plies so as to alternate those corresponding to the matrix and those corresponding to the reinforcement. It is also possible to form the matrix by molding and embed the reinforcements within it.

[0034] In the context of the invention, the composite material is part of a structure or technical system in an industrial field such as electronics, automotive, rail, aeronautics, or space. The composite material is thus susceptible to mechanical stresses or exposure to external conditions, for example, temperature and pressure, which can cause failures such as cracking or delamination.

[0035] The system 1 comprises a layer of fibers 3, a conductive part 5 and a stimulation and measurement device 7.

[0036] The fiber layer 3 is suitable for integration into a composite material, and more specifically here the composite material whose system 1 is designed to detect any damage. The fiber layer 3 then forms a reinforcement within the composite material.

[0037] The fiber layer 3 may advantageously be composed of non-conductive fibers, i.e., fibers that impede the flow of current, such as glass fibers. Alternatively, the fiber layer 3 may be composed of conductive fibers, i.e., fibers that conduct current, such as carbon fibers, subject to adjustments to the device 7, which are explained later in the description.

[0038] The fibre layer 3 here refers to a conventional reinforcement ply, the manufacture of which is well known to those skilled in the art.

[0039] By way of example, a conventional process for manufacturing glass fibers consists of heating a glass composition to approximately 1500 °C and then forming molten glass filaments by drawing them out. A sizing is then applied to the filaments to bind them together into a thread, protect them against the risk of abrasion that can occur during ply formation, increase the rigidity of the filaments, and facilitate subsequent impregnation by the matrix. The glass fiber reinforcement ply is then formed by weaving.

[0040] Generally speaking, the fiber layer 3 can be formed by weaving, knitting, braiding or gluing.

[0041] The distinctive feature of system 1 is that it utilizes the environment of the composite material. The conductive part 5 is thus part of the structure or technical system within which the composite material is used. For example, the conductive part 5 may be a fastener such as an insert, screw, or rivet used for assembling the structure or technical system and for integrating the composite material. More specifically, the conductive part 5 is in contact with the fiber layer 3. Such contact may result from pressure, i.e., mechanical stress, or be achieved by bonding.

[0042] The conductive part 5 may be made of metal, for example copper, aluminum, tin, zinc, or iron. The conductive part 5 may also be a metal alloy, for example steel. Again, by way of example, the conductive part 5 may also be made of carbon.

[0043] The device 7 is arranged to be installed on the composite material, and more generally on the structure or technical system of which the composite material is part, in order to detect any damage.

[0044] Damage refers in particular to a crack or loss of contact between the fibre layer 3 and the conductive part 5.

[0045] The device 7 includes at least one conductive wire and a detector 13.

[0046] In the embodiment illustrated in [Fig. 1], the device 7 comprises a pair of conductive wires 9 and 11.

[0047] Each conductive wire 9, 11 is incorporated into the fiber layer 3. The incorporation of the pairs of conductive wires 9 and 11 into the fiber layer 3 can be carried out during its formation, for example by weaving, knitting, braiding, or gluing. Alternatively, the conductive wires 9 and 11 can be incorporated into the fiber layer 3 after its formation, and more specifically during the integration of the conductive part 5.

[0048] The conductive wires 9 and 11 are also electrically connected to each other via the conductive part 5 with which they are in direct contact, by pressure, gluing or welding.

[0049] The conductive wires 9 and 11 can be textile yarns and thus be formed by spinning, that is, the joining or agglutination of textile fibers. Furthermore, the ability of the conductive wires 9 and 11 to conduct current can be conferred by the material from which they are composed, for example, carbon. The conductive wires 9 and 11 can also be made of copper or an alloy. Alternatively, such an ability can be achieved by means of a conductive coating, for example, a metallic coating.

[0050] Advantageously, the conducting wires 9 and 11 have a breaking strength - also called "strain to fail" in the English-language literature - less than or equal to that of the fiber layer 3. Such a characteristic makes it possible to increase the probability that a crack propagating in the fiber layer 3 will cause the breakage of at least one of the conducting wires 9 and 11.

[0051] It is also important that no current can flow between the pair of conducting wires 9 and 11 and the fiber layer 3. To achieve this, the fiber layer 3 can simply be composed of non-conductive fibers—typically glass fibers—in which case electrical insulation is achieved by the very nature of the fiber layer 3, which cannot conduct current. However, as mentioned previously, it is also possible for the fiber layer 3 to be composed of conductive fibers—typically carbon fibers—in which case it is necessary to electrically insulate the conducting wires 9 and 11 from the fiber layer 3. The conducting wires 9 and 11 can be insulated using an insulating sheath or coating, for example, a polymer insulator such as polyurethane, polyvinyl chloride (better known by its English acronym PVC for "polyvinyl chloride"), or polytetrafluoroethylene (PTFE).

[0052] In the example of [Fig.1], the device 7 comprises a single pair of conductive wires 9 and 11. However, it must be understood here that the device 7 can comprise a plurality of pairs of conductive wires such as the pair of conductive wires 9 and 11.

[0053] By way of illustration, [Fig.2] is a photograph of system 1, and more precisely of a part of system 1 in an embodiment in which the device 7 comprises, in addition to the pair of conducting wires 9 and 11, an additional pair of conducting wires 15 and 17.

[0054] In [Fig.2], the conductive part 5 is an instrumented metallic part whose visible face - in contact with the pair of conductive wires 9 and 11 as well as with the pair of conductive wires 15 and 17 - is intended to form an interface with the fiber layer 3 (not shown in the photograph) of the system 1.

[0055] The use of several pairs of conductive wires increases the chances of detecting damage to the fiber layer 3 or degradation at the interface between the fiber layer 3 and the conductive part 5, which manifests itself as a progressive loss of contact.

[0056] Furthermore, as explained in the rest of the description with reference to [Fig.4], the device 7 can also comprise a single conducting wire or several conducting wires each treated individually.

[0057] When the device 7 includes several conductive wires - typically several pairs of conductive wires -, the device 7 may further include one or more multiplexers (not shown in the figures) in order to be able to use the same electronic resources, in particular the same detector 13 described below, for all the conductive wires.

[0058] The detector 13 is arranged to detect an interruption of the current flow within the pair of conductive wires 9 and 11 by measuring electrical resistance.

[0059] With further reference to [Fig.1], the detector 13 comprises a power supply 19, a sensor 21, a memory 23, a processor 25 and a communication module 27.

[0060] The source 19 is arranged to be connected to the pair of conductive wires 9 and 11. More particularly, the source 19 is arranged to supply the pair of conductive wires 9 and 11.

[0061] Source 19 can be a voltage source, in which case source 19 applies a voltage between the conductive wires 9 and 11. Alternatively, source 19 is a current source, in which case source 19 generates a current which flows from one conductive wire to the other of the pair of conductive wires 9 and 11.

[0062] The sensor 21 is arranged to be connected to the pair of conductive wires 9 and 11. More specifically, the sensor 21 is arranged to measure an electrical quantity, namely the intensity of the current flowing in the pair of conducting wires 9 and 11 or the voltage between the conducting wires 9 and 11. The measurement may correspond to the determination of the value of the electrical quantity or simply to the detection of the crossing of a threshold.

[0063] Several embodiments are therefore conceivable.

[0064] In the embodiment illustrated in [Fig. 1], the source 19 is a voltage source and the sensor 21 is a current sensor - for example an ammeter-type measuring instrument - arranged to measure the intensity of the current flowing in the pair of conducting wires 9 and 11. The detector 13 is then arranged to determine the value of the electrical resistance from the measured current intensity and the voltage imposed by the source 19.

[0065] Alternatively, the source 19 is a current source and the sensor 21 is a voltage sensor - for example a voltmeter-type measuring instrument - arranged to measure the voltage between the conducting wires 9 and 11. The detector 13 is then arranged to determine the value of the electrical resistance from the measured voltage and the current intensity imposed by the source 19. Such a configuration is also illustrated in [Fig. 4] described below.

[0066] As mentioned previously, damage to the composite material can result in a crack in the fiber layer 3 or in a loss of contact between the fiber layer 3 and the conductive part 5. Damage to the fiber layer 3 is likely to have an impact on the pair of conductive wires 9 and 11 and on the conductive part 5.

[0067] Thus, the propagation of a crack can lead to the breakage of at least one of the conductive wires 9 and 11. The conductive wires 9 and 11 are then no longer electrically connected and current no longer flows from one to the other. The interruption of the current flow is manifested by an increase in electrical resistance detected by the detector 13.

[0068] Furthermore, the loss of contact between the fiber layer 3 and the conductive part 5 also interrupts the flow of current between the conductive wires 9 and 11 since these are electrically connected via the conductive part 5. Here again, the increase in electrical resistance is detected by the detector 13.

[0069] A record of electrical resistance measurements taken by detector 13 is illustrated in [Fig. 3]. The curve shown illustrates more precisely the percentage change in electrical resistance as a function of time, expressed in seconds (s).

[0070] Analysis of this curve allows us to observe the effects of a loss of contact - in this case a detachment - between the layer of fibers 3 and the conductive part 5 on the electrical resistance of a pair of conductive wires such as the pair of conductive wires 9 and 11.

[0071] In particular, the absence of any change in electrical resistance from 0 to 320 seconds indicates the absence of damage. The gradual increase in electrical resistance from 320 to 675 seconds corresponds to the beginning of the delamination of the fiber layer 3. The abrupt increase in electrical resistance from 675 to 750 seconds corresponds to the end of the delamination, i.e., the total loss of contact between the fiber layer 3 and the conductive part 5.

[0072] The memory 23 is arranged to store instructions whose implementation by the processor 25 results in the operation of the detector 13.

[0073] The memory 23 can also be arranged to store a record of electrical resistance measurements - or equivalent values ​​obtained by processing electrical resistance measurements - and / or to keep a history of damage suffered by the composite material, and more specifically here by the fiber layer 3. Such a history can be used in real time to prevent damage and / or later for the purposes of maintenance, consolidation or reinforcement of the structure or technical system of which the analyzed composite material is a part.

[0074] Memory 23 can refer to any data storage medium designed to receive and store 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 23 can also be random access memory (RAM) or a magneto-optical disk. A combination of several storage media can also be considered.

[0075] The processor 25 can be arranged to operate the detector 13 in different modes. For example, the detector 13 can operate in a continuous monitoring mode in which the source 19 continuously supplies the pair of conductive wires 9 and 11 and in which the sensor 21 continuously measures, as appropriate, the current flowing through the pair of conductive wires 9 and 11 or the voltage between the conductive wires 9 and 11. The detector 13 can also operate in a discrete monitoring mode in which the source 19 supplies the pair of conductive wires 9 and 11 at regular intervals and in which the sensor 21 measures, at regular intervals as appropriate, the current flowing through the pair of conductive wires 9 and 11 or the voltage between the conductive wires 9 and 11.

[0076] The processor 25 can be implemented in any known way, for example in the form of a microprocessor, a programmable logic device (PLD) or a dedicated chip of the FPGA (Field Programmable Gate Array) or SoC (System on Chip) type, a resource grid computer systems, a microcontroller, or any other proprietary device with the computing power necessary to detect damage to the composite material on which system 1 is installed. One or more of these elements can also be implemented as specialized electronic circuits of the ASIC type (Application-Specific Integrated Circuit). A combination of processors and electronic circuits can also be considered.

[0077] The communication module 27 is arranged to transmit data stored in memory 23, for example the reading of electrical resistance measurements or the history of damage suffered by the composite material, to the terminal of an operator.

[0078] Fig. 4 illustrates an embodiment in which the device 7 comprises a single conductive wire 29. In this embodiment, the detector 13 is arranged to detect an interruption of the current flow between the conductive wire 29 and the conductive part 5 by measuring electrical resistance.

[0079] It may be noted that the shape of the conductive part 5 on [Fig.4] is different from that on [Fig.1], which has no effect on the general operation of the device 7.

[0080] The source 19 is then arranged to be connected to the conductor wire 29 and to the conductive part 5. More specifically, the source 19 is arranged to supply the conductor wire 29. Furthermore, the conductive part 5 can be connected to ground.

[0081] Similarly, the sensor 21 is arranged to be connected to the conductive wire 29 and the conductive part 5. More particularly, the sensor 21 is arranged to measure the intensity of the current flowing between the conductive wire 29 and the conductive part 5 or the voltage between the conductive wire 29 and the conductive part 5.

[0082] Unlike the example in [Fig. 1] in which source 19 is a voltage source and sensor 21 is a current sensor, [Fig. 4] illustrates an example in which source 19 is a current source and sensor 21 is a voltage sensor. It is understood that, as with the embodiment of [Fig. 1], it is also possible to use a voltage source for source 19 and a current sensor for sensor 21.

[0083] Here again, damage to the composite material can result in a crack, the propagation of which can lead to the breakage of the conductive wire 29 or to a loss of contact between the conductive wire 29 and the conductive part 5. Indeed, in either case, the conductive wire 29 is no longer electrically connected to the conductive part 5, and current no longer flows between the two. The interruption of current flow is manifested by an increase in electrical resistance detected by the detector 13.

[0084] It should be noted that the device 7 may comprise several conductive wires, each treated individually in the same way as the conductive wire 29 shown in [Fig. 4]. Generally, the device 7 may comprise one or more pairs of conductive wires such as the pair of conductive wires 9 and 11 and / or one or more individual conductive wires such as the conductive wire 29.

[0085] The respective functions of the other components of the detector 13, in particular the memory 23, the processor 25 and the communication module 27, are similar to those described previously with reference to [Fig.1].

Claims

Demands

1. A system (1) for detecting damage to a composite material comprising: - a layer of fibers (3) suitable for integration into a composite material, and - a conductive part (5) in contact with said layer of fibers (3), the conductive part (5) being part of a structure or technical system within which the composite material is used, said system (1) being characterized in that it further comprises a stimulation and measurement device (7) comprising one or more conductive wires (9, 11, 15, 17, 29) each incorporated into said layer of fibers (3) and in contact with the conductive part (5), and a detector (13) arranged to supply power to a conductive wire (9, 15, 29) and to detect, by measuring electrical resistance, an interruption in the flow of current between said supplied conductive wire (29) and the conductive part (5) or, where applicable, between said supplied conductive wire (9, 15) and a conductive wire (11,17) third parties electrically connected to each other via the conductive part (5).

2. System (1) according to claim 1, characterized in that the fibre layer (3) is composed of glass fibres.

3. System (1) according to claim 1, characterized in that the fibre layer (3) is composed of carbon fibres, and in that each conducting wire (9, 11, 15, 17, 29) is electrically insulated from said fibre layer (3).

4. System (1) according to any one of the preceding claims, characterized in that at least one conducting wire (9, 11, 15, 17, 29) is a textile wire.

5. System (1) according to any one of the preceding claims, characterized in that at least one conducting wire (9, 11, 15, 17, 29) is made of carbon.

6. System (1) according to any one of the preceding claims, characterized in that the detector (13) comprises a voltage source (19) arranged to apply a voltage between the energized conductive wire (29) and the conductive part (5) or, where applicable, between the energized conductive wire (9, 15) and the third conductive wire (11, 17), and a current sensor (21) arranged to measure the intensity of the current flowing between the energized conductive wire (29) and the conductive part (5) or, where appropriate, between the energized conductor (9, 15) and the third conductor (11, 17).

7. System (1) according to any one of claims 1 to 5, characterized in that the detector (13) comprises a current source (19) arranged to carry a current between the energized conductor wire (29) and the conductive part (5) or, where applicable, between the energized conductor wire (9, 15) and the third conductor wire (11, 17), and a voltage sensor (21) arranged to measure the voltage between the energized conductor wire (29) and the conductive part (5) or, where applicable, between the energized conductor wire (9, 15) and the third conductor wire (11, 17).

8. System (1) according to any one of the preceding claims, characterized in that at least one conducting yarn (9, 11, 15, 17, 29) is incorporated into the fibre layer (3) by weaving, knitting, braiding or gluing.

9. System (1) according to any one of the preceding claims, characterized in that at least one conductive wire (9, 11, 15, 17, 29) is in contact with the conductive part (5) by pressure, gluing or welding.

10. Composite material comprising a plurality of plies and the system (1) according to any one of the preceding claims, characterized in that one of the plies is formed by the layer of fibers (3) of said system (1).

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