Method for monitoring the manufacturing of an organic matrix composite material

Abstract

The invention relates to a method for monitoring the manufacture of an organic matrix composite material comprising: a) manufacturing (100), by assembling carbon fibers, a conductive layer having a useful portion intended to form a conductive ply of the organic matrix composite material to be manufactured and at least two excess portions protruding from the useful portion, b) inserting (120) electrical connectors, each in at least one excess portion, c) connecting (130) an excitation and measurement device to each electrical connector, d) monitoring (140) one or more manufacturing steps of the organic matrix composite material from the conductive layer by the device by supplying it with electrical energy and measuring an electrical quantity thereof, e) removing (150) each excess portion. [Fig. 1]

Description

Title of the invention: Method for monitoring the manufacturing of an organic matrix composite material

[0001] The field of the invention relates to the monitoring of the manufacture of an organic matrix composite material.

[0002] A composite material is an assembly of at least two immiscible materials. Such an assembly makes it possible to give the composite material properties that the materials composing it, taken in isolation, do not possess.

[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 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).

[0005] The reinforcement forms the framework of the composite material and gives it most of its mechanical properties. 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] Due to their characteristics, composite materials have applications in various industrial fields such as electronics, automotive, railway, aeronautics and space.

[0007] 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 fiber reinforced polymer").

[0008] It is known to layer several plies of fibers to form the reinforcement of a composite material. The plies are generally of similar shapes. Typically, the plies are rectangular, and the resulting reinforcement resembles a rectangular parallelepiped. The composite material made from such a reinforcement is said to be "laminated." It is also possible to use only a single ply to form the reinforcement.

[0009] In order to assess the structural health of a laminated composite material, a conventional approach consists of electrically connecting an excitation and measurement device to one or more conductive plies of the laminated composite material, for example plies of carbon fibers. Such a device allows an electrical signal to circulate in the laminated composite material while measuring an electrical quantity whose evolution can indicate the presence of damage such as a crack or delamination.

[0010] International application WO 2006 / 029642 A1 describes a process for treating a polymer matrix composite material to improve its ability to establish an electrical connection. This process involves a first plasma treatment of the surface of the composite material to remove the polymer, a second plasma treatment to activate the surface, and finally, metallization of the surface.

[0011] European patent application EP 3 314 231 Al proposes to expose a carbon fiber reinforced polymer (CFRP) to pulsed laser radiation to reveal the carbon fibers of a target area and to connect electrodes with low contact resistance.

[0012] Finally, the article “Comparison of Electrical Contacting Techniques to Carbon Fiber Reinforced Plastics for Self-Strain-Sensing Applications” (C 2021, 7(4), 81) by P. Scholle et al. presents various techniques for creating electrical contact with a carbon fiber reinforced polymer in order to detect strain or damage. The article notes that it is possible to remove the resin—which insulates the carbon fibers—with concentrated sulfuric acid or by laser abrasion, and that contact with the carbon fibers can be achieved by electrodeposition or with silver paint.

[0013] Such methods make it possible to establish electrical contact with a composite material and to examine its structure by means of electrical measurements.

[0014] However, these solutions have limited use since they are only implemented after the composite material has been manufactured. Yet, there is a real need to control and monitor the manufacturing stages of a composite material, and not just to assess its structural integrity at the end of the manufacturing process.

[0015] The present invention improves the situation.

[0016] In this respect, the invention relates to a method for monitoring the manufacture of an organic matrix composite material comprising the following operations: a) manufacturing, by assembling carbon fibers, at least one conductive layer having a useful portion intended to form a conductive ply of the organic matrix composite material to be manufactured and at least two excess portions protruding from the useful portion, b) inserting electrical connectors each into at least one excess portion, c) connecting an excitation and measurement device to each electrical connector, the process further comprising, during one or more manufacturing steps of the organic matrix composite material from at least one conductive layer: d) monitor one or more manufacturing steps of the organic matrix composite material by the device by supplying at least one conductive layer with electrical energy and measuring an electrical quantity of at least one conductive layer, and following one or more manufacturing stages of the organic matrix composite material: e) eliminate any excess portion.

[0017] In one or more embodiments, operation a) further comprises: superimposing folds including the respective useful portion of at least one conductive layer so as to form a stack of which at least two respective excess portions of each conductive layer protrude.

[0018] In one or more embodiments, several conductive layers are manufactured during operation a).

[0019] In one or more embodiments, at least one of the electrical connectors is inserted into respective excess portions of several conductive layers during operation b).

[0020] In one or more embodiments, at least one conductive layer is manufactured during operation a) by assembling carbon fibers impregnated with organic matrix.

[0021] In one or more embodiments, at least one conductive layer is manufactured during operation a) by assembling dry carbon fibers.

[0022] In one or more embodiments, the electrical connectors are each formed from a conductive material whose melting point at atmospheric pressure is greater than or equal to 1000°C.

[0023] In one or more embodiments, operation b) comprises: inserting at least one self-stripping connector into at least one excess portion, each self-stripping connector forming an electrical connector.

[0024] In one or more embodiments, operation b) comprises: inserting a screw having a head and a threaded shank into at least one excess portion, mounting at least one toothed fan washer on the threaded shank, and tightening a nut on the threaded shank to hold the at least one toothed fan washer between the nut and the head such that the at least one toothed fan washer pierces the at least one excess portion. The screw, the at least one toothed fan washer, and the nut together form an electrical connector.

[0025] In one or more embodiments, operation d) is carried out by electrical impedance tomography.

[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] illustrates a method for monitoring the manufacture of a composite material with an organic matrix according to the invention,

[0028] [Fig.2] illustrates a conductive layer having a useful portion intended to form of a conductive ply of the organic matrix composite material to be manufactured and the excess portions,

[0029] [Fig.3] illustrates a stack of folds including several conductive layers such as that of [Fig.2],

[0030] [Fig.4] illustrates a self-stripping connector,

[0031] [Fig.5] illustrates the stacking of folds of [Fig.3] equipped with several self-stripping connectors such as that of [Fig.4],

[0032] [Fig.6] illustrates an electrical connector including a screw, a toothed fan washer and a nut,

[0033] [Fig.7] illustrates the stacking of folds of [Fig.3] equipped with several connectors electrical such as that of [Fig.6], and

[0034] [Fig.8] illustrates a monitoring system for the manufacture of an organic matrix composite material.

[0035] The present invention relates to the manufacture of a composite material from a reinforcement formed of one or more superimposed layers of fibers and an organic matrix.

[0036] The reinforcement's construction offers a certain degree of flexibility. Various types of fibers can be used, including carbon fibers, glass fibers, aramid fibers, or even plant fibers. Such fibers may be woven or unwoven; in the latter case, the fibers can be unidirectional or multidirectional, for example, to form a mat, that is, a layer of fibers arranged in a disordered or random manner. Furthermore, the fibers can be pre-impregnated, that is, already impregnated with an organic matrix, or, conversely, dry. In addition, the reinforcement can be formed from several plies and thus have a layered structure, or it can be formed from a single ply.

[0037] However, the reinforcement has this constraint: it must contain at least one conductive layer made by assembling carbon fibers. Such a conductive layer will be detailed later in the description, particularly with reference to [Fig. 2].

[0038] The organic matrix is ​​referred to as "resin" in the rest of the description, except in the expression "organic matrix composite material".

[0039] Such a resin can be thermosetting, for example epoxy resin, polyester or polyimide, or thermoplastic, for example polypropylene (PP), polyamide (PA) or polyetheretherketone (PEEK).

[0040] Fig. 1 illustrates a method for monitoring the manufacture of an organic matrix composite material.

[0041] This process takes place in three phases.

[0042] The first phase, corresponding to operations 100, 110, 120 and 130, enables the implementation of a monitoring system for the manufacture of an organic matrix composite material. Such a monitoring system will be detailed later in the description with reference to [Fig. 8].

[0043] The second phase, which corresponds to operation 140, is the monitoring phase itself. This phase is implemented by the monitoring system during the manufacturing of the organic matrix composite material.

[0044] Finally, the third phase, which corresponds to operation 150, is a post-fabrication phase. This phase allows the monitoring system to be dismantled in order to isolate the organic matrix composite material and give it its final shape.

[0045] During operation 100, a conductive layer 1 is manufactured by assembling carbon fibers.

[0046] Carbon fibers can be prepregs, that is, already impregnated with resin. In such a case, the conductive layer 1 then corresponds to a prepreg - or "prepreg" in English - that is, a semi-finished product.

[0047] Conversely, carbon fibers can be dry, in which case impregnation will be necessary during the manufacturing process of the organic matrix composite material.

[0048] Typically, such carbon fibers are raw, meaning that they have not yet been subjected to the cooking process which, in the manufacturing process of the organic matrix composite material, can be used to promote the chemical reaction responsible for hardening the resin, particularly when the latter is a sand thermosetting resin.

[0049] Figure [Fig. 2] illustrates a conductive layer 1 in top view.

[0050] The conductive layer 1 has a useful portion 3 and at least two excess portions 5. In the example of [Fig.2], the conductive layer 1 has four excess portions 5.

[0051] The useful portion 3 is intended to form a conductive ply of the organic matrix composite material to be manufactured.

[0052] In the case where the organic matrix composite material to be manufactured, and more precisely its reinforcement, comprises several plies, the useful portion 3 of the The conductive layer 1 has a shape similar to that of the other folds. In the example of [Fig.2], the useful portion 3 has a rectangular shape.

[0053] The excess portions 5 protrude from the useful portion 3.

[0054] The manufacturing process of the conductive layer 1 by assembling carbon fibers is unique in that the useful portion 3 is intentionally augmented by excess portions 5, which will be used to monitor the manufacturing of the organic matrix composite material. The carbon fibers are deposited in such a way as to extend beyond the contour corresponding to the desired ply—here, the useful portion 3—to obtain the excess portions 5. The conductive layer 1 is thus a preliminary conductive ply, and the excess portions 5 are intended to be removed once the monitoring of the manufacturing of the organic matrix composite material is complete.

[0055] It should be noted that several conductive layers 1 such as that illustrated in [Fig.2] can be made during operation 100 for the manufacture of the organic matrix composite material.

[0056] In the case where the organic matrix composite material to be manufactured, and more precisely its reinforcement, comprises only one ply, this ply then corresponds to the useful portion 3 of the single conductive layer 1 manufactured. In such a case, operation 100 is directly followed by operation 120 detailed below.

[0057] However, in the example of [Fig.1] developed here, operation 100 is followed by operation 110.

[0058] In the following description, and without loss of generality, it is assumed that this operation 110 is implemented, and therefore that the organic matrix composite material to be manufactured comprises several plies.

[0059] During operation 110, folds are superimposed in a stacking direction so as to form a stack 7. Among these folds is the respective useful portion 3 of each conductive layer 1 produced during operation 100.

[0060] Fig. 3 is a photograph of such a stack 7 in top view.

[0061] In the example of [Fig.3], several conductive layers 1 are present. In particular, the upper fold, that is to say the last fold of the stack 7 according to the stacking direction is formed by the useful portion 3 of one of the conductive layers 1. Multiple excess portions 5 of different conductive layers 1 are visible and protrude from the stack 7.

[0062] The presence of several conductive layers 1 allows for more precise monitoring of the stacking 7.

[0063] The stacking 7 corresponds to a volume formed by the folds, including the respective useful portions 3 of the conductive layers 1, and each of the excess portions 5 protrudes from this volume. Here, such a volume takes the general form of a rectangular parallelepiped.

[0064] During operation 120, electrical connectors 9 are each inserted into at least one excess portion 5.

[0065] Each electrical connector 9 must have a plug portion adapted to insert into one or more excess portions 5 and must be formed from a conductive material. In particular, when the carbon fibers of the conductive layer 1 are already impregnated with resin, the plug portion is adapted to penetrate at least the resin to make contact with the carbon fibers. For example, the plug portion may be adapted to pierce one or more excess portions 5.

[0066] An electrical connector 9 is arranged to give each conductive layer 1 having an excess portion 5 into which it is plugged the ability to establish an electrical connection.

[0067] Furthermore, monitoring the manufacturing process of the organic matrix composite material may involve, among other things, baking, and the electrical connectors 9 may, on this occasion, be subjected to high temperatures. Therefore, advantageously, an electrical connector 9 is formed from a metal whose melting point—also called the "melting temperature"—at atmospheric pressure is greater than or equal to 1000°C. Such a metal is, for example, copper (Cu) or iron (Fe). Alternatively, an electrical connector 9 is formed from a non-metallic conductive material whose melting point at atmospheric pressure is greater than or equal to 1000°C, such as carbon (C).

[0068] A person skilled in the art understands that different types of electrical connectors 9 can be used. Accordingly, two examples of electrical connectors 9 are detailed below: a first example with reference to [Fig.4] and [Fig.5]; and a second example with reference to [Fig.6] and [Fig.7].

[0069] Fig. 4 is a photograph of a self-stripping connector (better known by the English acronym IDC for "insulation-displacement contact") marketed by the company RS Pro and which can be used as an electrical connector 9.

[0070] The self-stripping connector has a portion of the plug 11 formed of blades (or punches).

[0071] The blades (or punches) are arranged to pierce an excess portion 5 and thus establish electrical contact with the corresponding conductive layer 1. Such blades (or punches) are capable of simultaneously piercing several excess portions 5.

[0072] These blades (or punches) not only have the advantage of being able to be fixedly inserted into an excess portion 5 but also of coming into contact with the carbon fibers even when the latter are impregnated with resin.

[0073] Figure 5 is a photograph of stacking 7 of Figure 3 in a mode of realization in which each electrical connector 9 is a self-stripping connector such as that of [Fig.4].

[0074] It appears that the respective excess portions 5 of the different conductive layers 1 have been grouped together in such a way that twenty electrical connectors 9 are sufficient.

[0075] More particularly, each electrical connector 9, therefore each self-stripping connector, is plugged into several excess portions 5 each belonging to a different conductive layer 1.

[0076] Figure 6 is a photograph of an electrical connector 9 other than the connector self-stripping.

[0077] In this photograph, the electrical connector 9 is inserted into an excess portion 5.

[0078] In the example of [Fig.6], the electrical connector 9 includes a screw 13, a first toothed fan washer 15, a second toothed fan washer 17 and a nut 19.

[0079] The screw 13 has a head 21 and a threaded shank 23.

[0080] The threaded rod 23 is the plug portion of the electrical connector 9.

[0081] The threaded rod 23 is arranged to pierce an excess portion 5 and thus establish electrical contact with the corresponding conductive layer 1. Such a threaded rod 23 is capable of simultaneously piercing several excess portions 5.

[0082] The first toothed fan washer 15 and the second toothed fan washer 17 are arranged to be mounted on the screw 13, and more specifically on the threaded rod 23. The first toothed fan washer 15 and the second toothed fan washer 17 each have a central orifice through which the threaded rod 23 passes to mount the first toothed fan washer 15 and the second toothed fan washer 17 onto the screw 13.

[0083] The first fan washer with teeth 15 and the second fan washer with teeth 17 each have teeth arranged to pierce the excess portion 5 and thus improve electrical contact with the corresponding conductive layer 1. Such teeth are capable of simultaneously piercing several excess portions 5.

[0084] These teeth not only have the advantage of being able to be fixedly inserted into an excess portion 5 but also of coming into contact with the carbon fibers even when the latter are impregnated with resin.

[0085] The nut 19 is arranged to be tightened onto the screw 13 such that the first toothed fan washer 15 and the second toothed fan washer 17 are held between nut 19 and head 21. Nut 19 has a threaded cylindrical hole into which the threaded rod 23 fits exactly.

[0086] More particularly, the first toothed fan washer 15 is interposed between the nut 19 and the excess portion 5, and the second toothed fan washer 17 is interposed between the excess portion 5 and the head 21.

[0087] In the example of [Fig.6], the electrical connector 9 includes the first toothed fan washer 15 and the second toothed fan washer 17. However, the electrical connector 9 may also include only the first toothed fan washer 15 or only the second toothed fan washer 17.

[0088] [Fig.7] is a photograph of the stack 7 of [Fig.3] in an embodiment in which each electrical connector 9 is such as that shown in [Fig.6].

[0089] As in [Fig.5], the excess portions 5 have been grouped together in such a way that twenty electrical connectors 9 are sufficient.

[0090] Here too, each electrical connector 9 is plugged into several excess portions 5, each belonging to a different conductive layer 1.

[0091] During operation 130, an excitation and measurement device 25 is connected to each electrical connector 9.

[0092] For this purpose, electrical cables can be used. Such electrical cables are also visible, although not referenced, in the photograph in [Fig.5].

[0093] Fig. 8 illustrates a monitoring system 27 for the manufacture of the organic matrix composite material obtained at the end of operation 130.

[0094] The monitoring system 27 includes the stack 7, the electrical connectors 9 and the device 25.

[0095] In the example of [Fig. 8], the stack 7 comprises, among the superimposed folds of which it is formed, the useful portion 3 of a single conductive layer 1, which corresponds to the conductive layer 1 of [Fig. 2]. The useful portion 3, concealed among the superimposed folds, is not visible in [Fig. 8]. On the other hand, the excess portions 5 protrude from the stack 7 and are therefore visible.

[0096] Each excess portion 5 constitutes, for the device 25, an access to the stack 7. It is therefore advantageous to have several conductive layers 1 to multiply the accesses to the stack 7 and to achieve the most precise possible monitoring of the manufacture of the organic matrix composite material.

[0097] Advantageously, one or more plies of the stack 7 other than the useful portion(s) 3 are also formed of carbon fibers and are electrically in contact with the useful portion(s) 3, in which case even more complete monitoring of the stack 7 can be achieved. It is also possible, based on this principle, that all the plies of the stack 7 other than the useful portion(s) 3 are formed of carbon fibers, which then allows monitoring of the stack 7 in its entirety.

[0098] As mentioned previously, the carbon fibers of the conductive layer 1 may already be impregnated with resin, and the same may be true of all the plies of the stack 7.

[0099] Conversely, the stack 7 can be dry, that is to say, not yet impregnated with resin.

[0100] The device 25 is arranged to probe the stack 7 in order to collect information relating to the manufacture of the organic matrix composite material. Such information will be detailed later in the description.

[0101] As explained previously, it is considered here that the organic matrix composite material to be manufactured comprises several plies, which form the stack 7. However, it must be kept in mind that the organic matrix composite material to be manufactured may also comprise only one ply, which then necessarily corresponds to the useful portion 3 of the single conductive layer 1.

[0102] The device 25 includes a power supply 29, a sensor 31, a memory 33 and a processor 35.

[0103] As mentioned previously, [Fig.8] represents a simplified configuration in which only one conductive layer 1 is present; and each electrical connector 9 is plugged into a single excess portion 5 of this conductive layer 1. The following description of the device 25 can, however, be easily extended to the case in which several conductive layers 1 are present and in which each electrical connector 9 is plugged into several excess portions 5, each belonging to a different conductive layer 1.

[0104] The source 29 is arranged to be connected to a doublet of electrical connectors 9 and to supply the conductive layer 1 with electrical energy via the excess portions 5 into which the electrical connectors 9 forming the aforementioned doublet are inserted.

[0105] In the example of [Fig. 8], the source 29 is a current source arranged to apply a desired intensity to the electric current flowing between the electrical connectors 9 to which the source 29 is connected. These electrical connectors 9 are in fact electrically connected to each other via the excess portions 5 into which they are respectively inserted and via the useful portion 3.

[0106] Alternatively, the source 29 is a voltage source arranged to apply a desired voltage between the two electrical connectors 9 to which the source 29 is connected.

[0107] The sensor 31 is arranged to be connected to a pair of electrical connectors 9 and to measure an electrical quantity at the level of the conductive layer 1.

[0108] In the example of [Fig. 8], the sensor 31 is a voltage sensor arranged to measure the voltage between the electrical connectors 9 to which the sensor 31 is connected. Such a voltage sensor may be a voltmeter-type measuring instrument.

[0109] Alternatively, the sensor 31 is a current sensor arranged to measure the intensity of the electric current flowing between the electrical connectors 9 to which the sensor 31 is connected. Such a current sensor is, for example, an ammeter-type measuring instrument.

[0110] In the example of [Fig.8], the device 25 includes a single source 29 and a single sensor 31.

[0111] Typically, the source 29 and the sensor 31 are both connected to all the electrical connectors 9 by electrical cables. Multiplexers (not shown here) are present and allow selective selection of, on the one hand, the pair of electrical connectors 9 through which the conductive layer 1 is to be supplied with electrical energy and, on the other hand, the pair of electrical connectors 9 by means of which an electrical quantity is measured at the level of the conductive layer 1.

[0112] The Applicant described, in French patent FR 3 131 272B1, 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.

[0113] Alternatively, the source 29 may designate a set of electrical power sources, each arranged to be connected to a respective pair of electrical connectors 9; and the sensor 31 may designate a set of sensors, each arranged to be connected to a respective pair of electrical connectors 9.

[0114] Memory 33 is arranged to store instructions whose execution by the processor 35 results in the operation of device 25.

[0115] The memory 33 can be further arranged to store a record of measurements from the sensor 31.

[0116] Memory 33 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 33 can also be random access memory (RAM) or a magneto-optical disk. A combination of several storage media can also be considered.

[0117] The processor 35 is arranged to collect, from the measurements made by the sensor 31, information relating to the manufacture of the organic matrix composite material.

[0118] The processor 35 can be arranged to operate the device 25 in different modes. For example, the device 25 can operate in a continuous monitoring mode in which the source 29 continuously supplies the conductive layer 1 with electrical energy and in which the sensor 31 performs continuous measurements. The device 25 can also operate in a discrete monitoring mode in which the source 29 supplies the conductive layer 1 with electrical energy at regular, predefined intervals and in which the sensor 31 performs measurements at these regular, predefined intervals.

[0119] The processor 35 can be implemented in any known form, for example as a microprocessor, a programmable logic device (PLD), a dedicated chip such as a field-programmable gate array (FPGA) or system-on-chip (SoC), a computing resource grid, a microcontroller, or any other proprietary form with sufficient computing power to monitor the manufacturing of the organic matrix composite material. One or more of these elements can also be implemented as specialized electronic circuits such as application-specific integrated circuits (ASICs). A combination of processors and electronic circuits is also possible.

[0120] The manufacture of the organic matrix composite material is implemented from stacking 7.

[0121] As mentioned above, the organic matrix composite material to be manufactured may also comprise only one ply, in which case the manufacture of the organic matrix composite material is implemented from the conductive layer 1, which is therefore unique.

[0122] During operation 140, the monitoring system 27 implements the monitoring of one or more manufacturing steps of the organic matrix composite material.

[0123] It should be noted that, for the sake of simplicity, a "manufacturing step" here refers to a step subsequent to the implementation of the monitoring system 27, and therefore a manufacturing step that can be monitored. However, this distinction is specific to the present invention since, strictly speaking, the manufacture of one or more conductive layers 1 during operation 100 can be considered a manufacturing step, given that the useful portion 3 of each conductive layer 1 is intended to form part of the organic matrix composite material to be manufactured.

[0124] A "manufacturing step" may refer to any treatment, reaction or operation involving the stacking 7 or, where appropriate, a single conductive layer 1 for the purpose of manufacturing the organic matrix composite material.

[0125] The monitoring system 27 is compatible with different manufacturing processes for organic matrix composite material.

[0126] The method for monitoring the manufacture of the organic matrix composite material can be implemented within the framework of a manufacturing process that falls under the category of the "wet process" or the "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.

[0127] Impregnation consists of saturating the reinforcement with resin in a homogeneous manner. A uniform distribution ensures a strong bond between the reinforcement and the resin.

[0128] 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 by the English acronym RTM for "resin transfer molding"), which are wet-process manufacturing techniques for organic matrix composite materials.

[0129] The dry process encompasses techniques in which the reinforcement is pre-impregnated. The reinforcement fibers can thus be coated with resin, resulting in a pre-impregnated material. For example, automated fiber placement (AFP) and automated tape laying (ATL) are dry-process composite material manufacturing techniques.

[0130] It should be noted that certain techniques can be implemented using both wet and dry methods, notably filament winding, which consists of winding resin-impregnated fibers onto a mandrel under controlled tension. In particular, when the resin used is thermosetting, the fibers are dipped in a resin bath (wet method); and, when the resin used is thermoplastic, the fibers are pre-impregnated and wound directly onto the mandrel (dry method).

[0131] The manufacturing processes for organic matrix composite materials can be categorized in ways other than the distinction between the "wet process" and the "dry process".

[0132] It is understood from the above that, beyond impregnation, other aspects of the manufacture of the organic matrix composite material may be monitored, including shaping and curing.

[0133] Shaping refers to a set of techniques that allow the stack 7 to be given the desired shape. Shaping generally relies on heating, which makes the stack 7 more malleable, and on shaping itself, which may involve the use of a mold and / or a press.

[0134] For example, stamping generally involves heating a prepreg, placing it in a mold, and then applying high pressure to force the prepreg to conform to the mold's contours. Furthermore, if a thermosetting resin is used, the prepreg is baked to allow the resin to harden. Conversely, if a thermoplastic resin is used, the prepreg is cooled to allow it to harden.

[0135] As another example, thermocompression generally involves placing a prepreg in a heated press and then applying high pressure to give the prepreg the desired shape. Here again, curing is used to harden the resin when it is a thermosetting resin, while the prepreg is cooled under pressure to harden the resin when it is a thermoplastic resin.

[0136] These are of course only examples, and it is not necessary to use prepregs; impregnation can be carried out prior to or during shaping, for example by vacuum infusion.

[0137] It is also understood that, depending on the manufacturing process, impregnation, shaping and / or hardening may be intertwined or, conversely, correspond to distinct and independent steps.

[0138] Regarding hardening, it can be noted that this is achieved by baking in the case of a thermosetting resin, and that this baking results in polymerization or cross-linking. It is also known to perform such baking in an autoclave. As mentioned previously, for monitoring the baking process, it is preferable that each electrical connector 9 be formed from a conductive material, metallic or non-metallic, with a melting point at atmospheric pressure greater than or equal to 1000°C to guarantee their integrity, and therefore the reliability of the measurements, throughout the entire baking process.

[0139] In the case of a thermoplastic resin, such hardening is obtained by cooling after applying the heat which makes it possible to soften it for shaping purposes.

[0140] The use of the device 25 can be extended until an industrial part is formed from the manufactured organic matrix composite material. Furthermore, the hardening process increases the adhesion of an electrical connector 9 to the excess portion(s) 5 into which it is inserted.

[0141] Device 25 collects, during operation 140, information relating to the manufacture of the organic matrix composite material.

[0142] This information may relate to the impregnation, shaping and / or hardening of the stack 7.

[0143] This information may also correspond to the detection of stresses or deformations undergone by the stack 7.

[0144] In the example of [Fig. 1], operation 110, in which the stack 7 is formed by superimposing plies along the stacking direction, is carried out prior to operations 120, 130 and 140. However, the formation of the stack 7 can be considered as a manufacturing step of the organic matrix composite material and, as such, be subject to monitoring.

[0145] To do this, it is sufficient to carry out operations 120 and 130 directly after operation 100, and then, during operation 140, to monitor the superposition of the plies and the formation of the stack 7 as a manufacturing step of the organic matrix composite material.

[0146] This information can also reveal the presence of damage such as a crack, delamination or even breakage or rupture of fibers in a ply.

[0147] The principle of the device 25 is as follows: the source 29 excites a pair of electrical connectors 9 to supply the corresponding conductive layer(s) 1 with electrical energy. This supply results in the appearance of an electrical signal, that is, a movement of electric charge carriers. Such an electrical signal is characterized, at a given instant, by a current and a voltage. The source 29 can be a current source, in which case the current of the electrical signal is controlled, or a voltage source, in which case the voltage of the electrical signal is controlled. The sensor 31 measures an electrical quantity, and more precisely a current or a voltage, at the level of the conductive layer(s) 1 via a pair of electrical connectors 9.The processor 35 receives the measurements taken by the sensor 31 and determines, from these measurements and with regard to the intensity or voltage applied by the source 29, information relating to the manufacture of the organic matrix composite material such as those mentioned above.

[0148] More specifically, device 25 can implement electrical impedance tomography (EIT).

[0149] Electrical impedance tomography (EIT) is an imaging technique used to determine the electrical properties of a substrate by measuring the voltage of electrode pairs, usually—but not necessarily—arranged at the periphery of the substrate. The voltage measurements are used to map the electrical charge density or electrical conductivity of the substrate.

[0150] In the present case, each conductive layer 1 can act as a substrate and each electrical connector 9 can be used as an electrode. By virtue of their respective positions, namely at the level of the excess portions 5, the electrical connectors 9 are in fact arranged at the periphery of the conductive layer(s) 1.

[0151] According to the general principle of the TIE, pairs of electrical connectors 9 are supplied with electrical energy by the source 29 and the voltage between the two electrical connectors 9 of different pairs of electrical connectors 9 is measured. Several processes have been developed on this principle and differ in their injection pattern – that is, the way in which the pairs of electrical connectors 9 to be excited are formed.

[0152] 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 the case here, of supplying each doublet of electrical connectors 9 formed of two neighboring electrical connectors 9 and then measuring the voltage at each pair of electrical connectors 9 also formed of two neighboring electrical connectors 9.

[0153] In the field of electrical energy transfer (IET), it is known to use inverse problem theory to determine the electrical properties of a substrate. The principle of this approach is to determine the cause—here, the distribution of the electric charge density or electrical conductivity—from the effects—here, the voltage measurements between the two electrical connectors 9 of the pairs of electrical connectors 9. Indeed, each change in the distribution of electrical conductivity leads to changes in the potential distribution and, consequently, to changes in the voltage between the electrical connectors 9.

[0154] An inverse TIE problem is a nonlinear and ill-posed problem. In particular, this inverse problem does not depend continuously on the voltage measurements. As recalled by SR Kupis in the publication "Methods for the Electrical Impedance Tomography Inverse Problem: Deep Leaming 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.

[0155] Furthermore, solvers currently exist that can reconstruct the distribution of electric charge density or electrical conductivity from voltage measurements. For example, the free software EIDORS, which runs under MATLAB (registered trademark), can be used to solve an inverse problem.

[0156] The memory 33 and the processor 35 can thus be configured for solving an inverse TIE problem from the measurements collected by the sensor 31.

[0157] Finally, during operation 150, the excess portions 5 can be eliminated to isolate the organic matrix composite material and give it its final shape, i.e. without the excess portions 5 protruding from it.

[0158] In other words, only the useful portion 3 of each conductive layer 1 remains in the manufactured organic matrix composite material and then fully plays its role as a ply.

Claims

Demands

1. A method for monitoring the manufacture of an organic matrix composite material comprising the following steps: a) manufacturing (100), by assembling carbon fibers, at least one conductive layer (1) having a useful portion (3) intended to form a conductive ply of the organic matrix composite material to be manufactured and at least two excess portions (5) projecting from said useful portion (3), b) inserting (120) electrical connectors (9) each into at least one excess portion (5), c) connecting (130) an excitation and measurement device (25) to each electrical connector (9), said method further comprising,during one or more manufacturing steps of the organic matrix composite material from at least one conductive layer (1): d) monitor (140) said one or more manufacturing steps of the organic matrix composite material by the device (25) by supplying the at least one conductive layer (1) with electrical energy and measuring an electrical quantity of the at least one conductive layer (1), and at the end of said one or more manufacturing steps of the organic matrix composite material: e) remove (150) each excess portion (5).

2. A method according to claim 1, wherein operation a) further comprises: superimposing (110) folds including the respective useful portion (3) of at least one conductive layer (1) so as to form a stack (7) of which at least two respective excess portions (5) of each conductive layer (1) protrude.

3. A method according to claim 1 or 2, wherein, during operation a), several conductive layers (1) are manufactured.

4. A method according to claim 3, wherein, during operation b), at least one of the electrical connectors (9) is inserted into respective excess portions (5) of several conductive layers (1).

5. A method according to any one of the preceding claims, wherein, during operation a), at least one conductive layer (1) is manufactured by assembling carbon fibers impregnated with an organic matrix.

6. A method according to any one of claims 1 to 4, wherein, during operation a), at least one conductive layer (1) is manufactured by assembling dry carbon fibers.

7. A method according to any one of the preceding claims, wherein the electrical connectors (9) are each formed from a conductive material having a melting point at atmospheric pressure greater than or equal to 1000°C.

8. A method according to any one of the preceding claims, wherein operation b) comprises: inserting at least one self-stripping connector into at least one excess portion (5), each self-stripping connector forming an electrical connector (9).

9. A method according to any one of the preceding claims, wherein operation b) comprises: inserting a screw (13) having a head (21) and a threaded shank (23) into at least one excess portion (5), mounting at least one toothed fan washer (15, 17) on said threaded shank (23), and tightening a nut (19) on the threaded shank (23) to retain said at least one toothed fan washer (15, 17) between said nut (19) and said head (21) such that the at least one toothed fan washer (15, 17) pierces said at least one excess portion (5), the screw (13), the at least one toothed fan washer (15, 17) and the nut (19) together forming an electrical connector (9).

10. A method according to any one of the preceding claims, wherein operation d) is carried out by electrical impedance tomography.

Images