Method for generating a representative map of mechanically altered areas of an adhesive within a bonded assembly of composite materials, corresponding device and computer program

Abstract

Method for generating a representative map of mechanically altered areas of an adhesive within a bonded assembly of composite materials, corresponding device and computer program The invention relates to a method for determining the state of the mechanical properties of a bonded assembly of materials by applying a local thermal source exciting particles included in the adhesive and by studying the consequences of this excitation on the mechanical properties of the adhesive by high-frequency electromagnetic imaging. FIGURE 1A

Description

Title of the invention: Method for generating a representative map of mechanically altered areas of an adhesive within a bonded assembly of composite materials, corresponding device and computer program Field of the invention

[0001] The field of the invention is that of composite materials. More specifically, the invention relates to a solution allowing the detection of mechanical defects within bonded assemblies of composite materials made using an adhesive. Prior art and its drawbacks

[0002] There are many techniques for testing the strength of a multi-material bonded assembly. A bonded assembly is understood to mean an assembly consisting of an adhesive, or glue joint, placed between a first substrate and a second substrate, at least one of said substrates being made of a composite material.

[0003] Such techniques make it possible to detect the presence of visible defects, such as bonding defects, or aging of the bonded assembly of composite materials.

[0004] However, such techniques do not make it possible to determine the presence of defects which induce mechanical weakness within the adhesive joint or detachment at the adhesive joint / substrate interface of the "kiss bonding" type. However, defects of this type are one of the reasons which prevent greater use of the bonding of composite materials, particularly in the aeronautical industry, because there is a lack of methods for detecting defects which locally induce mechanical weakness in the adhesive of a bonded assembly of composite materials.

[0005] The document “NDT-based design of joint material for the detection of bonding defects by infrared thermography”, M. Barus et al., NDT and E International 93 (2018) 157-163, proposes a non-destructive method for detecting mechanical weaknesses in an assembly consisting of an adhesive placed between a first substrate and a second substrate, at least one of said substrates being made of a composite material. Such a method is based on the introduction of additives having a particular infrared signature into the adhesive in order to make it visible to infrared radiation.

[0006] A disadvantage of the method described in this document is that it does not allow the detection of defects such as mechanical weakening of the bonded assembly. This is due in particular to the composite nature of the substrates used. Indeed, substrates made of carbon fiber-based composite materials make it difficult, by their nature, to collect information relating to a deformation field in the adhesive resulting from a local rise in temperature generated by an infrared radiation source, despite the introduction of additives, in high percentage, into the adhesive (due to the similar thermal characteristics between the resin of the substrate and that of the adhesive).

[0007] There is therefore a need for a non-destructive technique for in situ detection of mechanical weaknesses in an assembly consisting of an adhesive placed between a first substrate and a second substrate, at least one of said substrates being made of a composite material not exhibiting all or some of the aforementioned drawbacks. Presentation of the invention

[0008] The invention meets this need by proposing a method for generating a map representative of mechanically altered zones of an assembly, called bonded, consisting of an adhesive comprising particles visible by high-frequency electromagnetic imaging, said adhesive being placed between a first substrate and a second substrate, at least one of said substrates being made of a composite material, said method comprising the following steps:

[0009] - obtaining, by high-frequency electromagnetic imaging, first positions of said particles within the bonded assembly,

[0010] - local thermal excitation of said bonded assembly,

[0011] - obtaining, by high-frequency electromagnetic imaging, second positions of said particles within the bonded assembly,

[0012] - generation of said representative map of mechanically altered zones in associating with at least one area of ​​the bonded assembly a value of at least one parameter representative of a mechanical alteration of the adhesive, said value of said at least one parameter representative of a mechanical alteration of the adhesive and said corresponding area of ​​the bonded assembly being determined as a function of said first positions, said second positions of said particles and reference values.

[0013] Such a solution makes it possible to determine, in situ, the state of the mechanical properties of the adhesive joint of a bonded assembly. Indeed, such a solution makes it possible to take a survey of the areas of an adhesive joint of a bonded assembly whose mechanical properties may be altered, although such alterations are not visible and / or detectable by known non-destructive techniques.

[0014] The use of high-frequency electromagnetic radiation, such as X-rays, makes it possible to overcome the absorption constraints associated with substrates made of carbon fibers. Precise and clear images of the particles present in the adhesive are obtained. Such images allow reliable and precise measurement of the positions of the particles.

[0015] It is then possible, from the representative map of mechanically altered areas of a bonded assembly, to carry out targeted repairs of the bonded assembly. It is also possible to implement this method within the framework of regular maintenance operations carried out for example on a fuselage or on any accessible areas of a composite structure benefiting from bonded assemblies.

[0016] In a first implementation of the method which is the subject of the invention, at least one parameter representative of a mechanical alteration of the bonded assembly is a value of the Young's modulus of the adhesive.

[0017] When, for a given area of ​​the bonded assembly, the value of the Young's modulus of the adhesive measured after excitation of the particles is lower than the reference value of the Young's modulus of the adhesive, it is deduced that the mechanical properties of the bonded assembly in this area have been altered. This then appears on the representative map of mechanically altered areas.

[0018] In order to facilitate the determination of the positions of the particles, in a particular embodiment of the method which is the subject of the invention, the bonded assembly comprises a reference grid forming a fixed reference frame for measuring a movement of the excitable particles within the adhesive.

[0019] Such a grid deforms very little under stress, which allows it to be used as a reference for measuring particle displacements in the adhesive. Measurements of particle displacements are also made more accurate by the use of such a reference grid.

[0020] In an exemplary embodiment, the method comprises a preliminary step of determining the reference value of the displacement of a particle during thermal excitation. The generation step thus comprises a sub-step of determining the actual value of displacement of said particles after thermal excitation from the first and second positions, said value of said at least one parameter representative of a mechanical alteration being determined from the comparison between said reference values ​​and said actual values ​​of displacement of the particles.

[0021] The actual displacement of the particles can be determined from the displacement of each particle between its first and second position to be compared with the reference value. The use of a reference value thus makes it possible to easily detect a variation in the mechanical properties from a difference between the actual value of the displacement and the reference value.

[0022] In a first exemplary embodiment of the method for generating a map representative of mechanically altered zones of a bonded assembly which is the subject of the invention, the adhesive comprising magnetic particles, the bonded assembly is thermally excited by the heat generated by the local application of a magnetic field to the magnetic particles.

[0023] In this first embodiment of the invention, the method takes advantage of the use of a local magnetic field to excite magnetic particles capable of generating heat flows, in a very short period of time and locally. Indeed, depending on the material chosen to constitute the magnetic core of the electromagnet used, it is possible to play on the speed of the magnetic field to excite the particles as well as on the location of this excitation in the bonded assembly.

[0024] Preferably, the magnetic particles are particles visible by high frequency electromagnetic imaging.

[0025] Thus, the particles fulfill the dual function of generating heat and providing visibility to high-frequency electromagnetic imaging.

[0026] In a second exemplary embodiment of the method for generating a map representative of mechanically altered zones of a bonded assembly which is the subject of the invention, the bonded assembly is thermally excited by an external heat source.

[0027] In this second embodiment, a heat source external to the adhesive is used, such as a heating finger, which can be moved over a surface of the bonded assembly.

[0028] The invention also relates to a bonded assembly consisting of an adhesive placed between a first substrate and a second substrate, at least one of said substrates being made of a composite material, in such a bonded assembly, the adhesive comprises particles visible by high-frequency electromagnetic imaging allowing the determination of a value of at least one parameter representative of a mechanical alteration of the adhesive when the bonded assembly has been thermally excited.

[0029] Due to the particular constitution of this bonded assembly, it is possible to determine, in situ, the state of the mechanical properties of the adhesive. Indeed, it becomes possible to take a survey of the areas of an adhesive joint of this bonded assembly whose mechanical properties can be altered by irradiating the bonded assembly with high-frequency electromagnetic radiation, such as X-rays.

[0030] Precise and clear images of the particles present in the adhesive are obtained. Such images allow reliable and precise measurement of the positions of the particles.

[0031] Depending on the nature of the particles used, the techniques used to cause local deformation of the adhesive may vary.

[0032] Thus, when the particles introduced into the adhesive have magnetic properties, a local magnetic field is applied to the bonded assembly in order to to excite the particles which then generate a heat flow whose action induces local deformation of the adhesive in a very short period of time.

[0033] When the particles introduced into the adhesive do not have magnetic properties, a heat flow is transmitted, for example locally, to the adhesive to cause deformation of the latter. Such a heat flow can be generated by means of a heating finger which is moved on the surface of the bonded assembly.

[0034] It is then possible to determine the existence of a weakening of the mechanical properties in certain areas of the adhesive.

[0035] In a particular implementation of the bonded assembly which is the subject of the invention, the latter comprises a reference grid forming a fixed reference frame for measuring a displacement of the particles.

[0036] Such a grid deforms very little under stress, which allows it to be used as a reference for measuring the movement of particles in the adhesive.

[0037] The reference grid may be deposited on at least one of said substrates constituting the bonded assembly.

[0038] This embodiment variant cleverly uses the properties of the material constituting the substrate and in particular the fact that the latter deforms very little compared to the adhesive. Such a reference grid is for example deposited on one of the two substrates in the form of plasma.

[0039] Advantageously, in a particular embodiment of the bonded assembly which is the subject of the invention, the adhesive comprises a support comprising said particles.

[0040] Such a support is for example a marquisette, a support used by adhesive manufacturers to calibrate the thickness of adhesive, deposited between the first and second substrate.

[0041] Advantageously, in another particular embodiment of the bonded assembly which is the subject of the invention, the reference grid is the support comprising said particles, said support being embedded in the adhesive.

[0042] This makes it possible to reduce the manufacturing costs of the bonded assembly.

[0043] Another object of the invention is a device for generating a map representative of mechanically altered zones of a bonded assembly consisting of an adhesive comprising particles visible by high-frequency electromagnetic imaging placed between a first substrate and a second substrate, at least one of said substrates being made of a composite material, said device comprising means for:

[0044] - determine, from a first image obtained by electromagnetic imaging at high frequency, of first positions of said particles within the bonded assembly,

[0045] - determine, from a second image obtained by electromagnetic imaging at high frequency, of second positions of said particles within the bonded assembly following the application, to said bonded assembly, of a local thermal excitation,

[0046] - generating said representative map of mechanically altered zones by associating to at least one area of ​​the bonded assembly a value of at least one parameter representative of a mechanical alteration of the adhesive, said value of said at least one parameter representative of a mechanical alteration of the adhesive and said corresponding area of ​​the bonded assembly being determined as a function of said first positions, said second positions of said excitable particles and reference values.

[0047] The invention further relates to a system comprising a device as described previously and a module for moving the device over the bonded assembly in order to scan the entire bonded assembly.

[0048] The thermal stress is carried out locally, which implies a deformation field which, at the border of the heated zone, is discontinuous (due to the differential deformation between the heated zone and the unheated zone). The device detects mechanically altered zones at this discontinuity, the displacement module makes it possible to move this discontinuity over the entire zone to be analyzed in order to generate a map of the bonded assembly.

[0049] The invention finally relates to a computer program product comprising program code instructions for implementing a method as described above, when executed by a processor.

[0050] The invention also relates to a computer-readable recording medium on which is recorded a computer program comprising program code instructions for executing the steps of the method according to the invention as described above.

[0051] On the one hand, such a recording medium may be any entity or device capable of storing the program. For example, the medium may comprise a storage means, such as a ROM, for example a CD ROM or a microelectronic circuit ROM, or a magnetic recording means, for example a USB key or a hard disk.

[0052] On the other hand, such a recording medium may be a transmissible medium such as an electrical or optical signal, which may be conveyed via an electrical or optical cable, by radio or by other means, so that the computer program it contains is remotely executable. The program according to the invention may in particular be downloaded over a network, for example the Internet.

[0053] Alternatively, the recording medium may be an integrated circuit in which the program is incorporated, the circuit being adapted to execute or to be used in the execution of the method which is the subject of the aforementioned invention. List of figures

[0054] Other aims, characteristics and advantages of the invention will appear more clearly on reading the following description, given as a simple illustrative, and non-limiting, example, in relation to the figures, among which:

[0055] [Fig.lA]: this figure represents a glued assembly according to a first exemplary embodiment of the invention,

[0056] [Fig.lB]: this figure represents a glued assembly according to a second exemplary embodiment of the invention,

[0057] [Fig.2]: this figure represents the different stages of a generation process of a representative map of mechanically altered areas of an adhesive according to the invention,

[0058] [Fig.3]: this figure represents an image of the bonded assembly obtained by irradiating the assembly bonded by means of high-frequency electromagnetic radiation,

[0059] [Fig.4A]: this figure represents a particle included in the adhesive,

[0060] [Fig.4B]: this figure represents the same particle as [Fig.4A] following the application of local thermal excitation,

[0061] [Fig.5]: this figure represents a device for generating a representative map of mechanically altered areas of a bonded assembly according to the invention.

[0062] Detailed description of exemplary embodiments of the invention

[0063] The general principle of the invention is based on the introduction of particles visible by high-frequency electromagnetic imaging into an adhesive deposited between a first substrate and a second substrate, at least one of the two substrates being a composite material. These particles are subject to excitation (and are therefore called excitable particles). The presence of these excitable particles within the adhesive makes it possible to determine non-destructively and in situ the state of certain mechanical properties of the adhesive. Thus, it becomes possible to regularly check, during maintenance operations, the state of certain mechanical properties of objects comprising such a bonded assembly, such as for example aircraft fuselages, but also other parts comprising bonded assemblies. An object of the present technique is to carry out a mapping of the force flows passing through an adhesive placed between two substrates.These two substrates can, for example, be made of composite materials comprising, for example, a matrix (thermosetting or thermoplastic) and reinforcing fibers (carbon, glass, aramid, etc.).

[0064] According to the present technique, in relation to [Fig. 1A], an example of such a bonded assembly 1 according to a first exemplary embodiment of the invention is presented. Such a bonded assembly 1 comprises: a first substrate 10 and a second substrate 11 bonded together by means of an adhesive layer 12. At least one of the substrates 10, 11 is a substrate made of composite material, for example based on carbon fibers, or glass fibers. The resin of at least one of the substrates 10, 11 is a resin made of polymer material, for example a thermosetting resin, in particular an epoxy resin, or a thermoplastic or elastomeric resin. The adhesive 12 is made of a resin similar to the resin of the substrates 10, 11. It is the use of the same type of resin for the substrates and the adhesive that makes the visibility of the bonded assembly complex and for which the invention proposes a solution.Particles 13 visible by high-frequency electromagnetic imaging, such as X-ray imaging, such as for example metal particles or particles having magnetic properties, are introduced into the adhesive 12, for example during the manufacture of the epoxy resin in a variable quantity depending on the nature of the particles 13, the substrates 10, 11 and the adhesive 12. For example, particles of stainless steel of the 316L type can be introduced into the adhesive 12.

[0065] An example of such a bonded assembly 1 according to a second embodiment of the invention is presented in relation to [Fig. 1B]. Such a bonded assembly 1 comprises: a first substrate 10 and a second substrate 11 bonded together by means of a layer of adhesive 12. At least one of the substrates 10, 11 is a substrate made of composite material, for example based on carbon fibers. The adhesive 12 comprises a resin, for example epoxy. The adhesive 12 may further comprise a support 14, such as a marquisette, making it possible to calibrate the thickness of the adhesive joint 12. This support 14 is embedded in the resin. Particles 13 are introduced into the adhesive 12, for example during the manufacture of the epoxy resin in a variable quantity depending on the nature of the particles 13, the substrates 10, 11 and the adhesive 12.

[0066] The introduction of the particles 13 into the adhesive 12 makes it possible to functionalize the adhesive 12 by making it interrogable by the method which will be described later.

[0067] According to an alternative embodiment not shown in the figures, the particles 13 are not introduced into the resin of the adhesive 12 but into the support 14, for example during the manufacture of the latter. Thus, the composition of the resin is not modified, which is advantageous in fields, such as aeronautics, requiring long and costly campaigns of certification of the materials for each modification.

[0068] The bonded assembly 1 may further comprise a reference grid forming a fixed reference frame for measuring a movement of the particles within the adhesive 12. The reference grid may be deposited on at least one of said substrates 10, 11 constituting the bonded assembly 1. The material constituting the substrate 10, 11 being slightly deformable, the dimensions and positioning of the reference grid remain stable. over time, thus ensuring the reliability of the measurements carried out during the life of the bonded assembly 1. Such a reference grid is for example deposited on one of the two substrates 10, 11 in the form of plasma.

[0069] In another example of embodiment of the glued assembly 1 which is the subject of the invention, the reference grid is the support 14 of the adhesive 12.

[0070] Such a bonded assembly 1 is used in a method for generating a representative map of mechanically altered zones of a bonded assembly, the different steps of which are described with reference to [Fig.2].

[0071] In a preliminary step, a reference value of the particle displacement is determined. This reference value corresponds to the theoretical displacement of a particle in an assembly not exhibiting mechanical alteration following thermal excitation. Such a reference value can be determined numerically from a finite element calculation for which the input data are the mechanical characteristics of the assembly.

[0072] During a step E1, a first image of the bonded assembly 1 is obtained by irradiating the bonded assembly 1 by means of high-frequency electromagnetic radiation, such as for example X-ray radiation.

[0073] [Fig. 3] represents such a first image. Each dark spot represents a particle present in the adhesive 12. Indeed, the particles introduced into the adhesive 12 have the property of reacting to the high-frequency electromagnetic radiation applied to the bonded assembly 1 so that they appear in the first image.

[0074] From this first image, it is possible to determine for all the particles visible on this first image, first positions in the glued assembly 1. The determination of these first positions is for example facilitated by the presence, in the glued assembly 1, of the reference grid.

[0075] In a step E2, a local mechanical stress of a thermomechanical nature is applied to the bonded assembly 1. Such a local mechanical stress takes the form of a local thermal excitation applied to the bonded assembly 1.

[0076] This local stress involves a deformation field which, at the boundary of the heated zone, is discontinuous (due to the differential deformation between the heated zone and the unheated zone). It is this discontinuity which is used by the present invention to determine whether the boundary zone is mechanically altered.

[0077] In a first embodiment of the invention, the bonded assembly 1 is thermally excited by an external heat source. Such an external heat source is for example an electrical resistance which may be in the form of a heating finger which can be moved over the entire surface of the bonded assembly 1 in order to move the boundary zone which is studied.

[0078] In a second exemplary embodiment of the invention, particles (which may be distinct from the particles 12) having magnetic properties are introduced into the adhesive 12. In this second exemplary embodiment, the local thermal excitation is obtained by applying an alternating magnetic field to the bonded assembly 1. The application of this alternating magnetic field excites the magnetic particles which then generate heat. For example, certain magnetic particles can produce temperature variations of the order of several tens of degrees in the space of a millisecond when they are excited by a suitable magnetic field. Just as in the first exemplary embodiment, the source of the alternating magnetic field can be moved over the entire surface of the bonded assembly 1.

[0079] The local rise in temperature caused by the thermal excitation induces local mechanical stresses within the adhesive joint 12. Such mechanical stresses make it possible to reveal the existence of a weakening of certain mechanical properties of the adhesive 12 in certain areas of the bonded assembly 1.

[0080] In a step E3, a second image of the bonded assembly 1 is obtained by irradiating the bonded assembly 1 by means of high-frequency electromagnetic radiation, such as for example X-ray radiation.

[0081] From this second image, it is possible to determine for all the particles visible on this second image, second positions in the glued assembly 1. The determination of these second positions is for example facilitated by the presence, in the glued assembly 1, of the reference grid.

[0082] Steps E1 and E3 are implemented, for example, by a portable radiography device. The images acquired by such a device are then transmitted, for example, to a computer capable of implementing steps E4 and E5 described below.

[0083] [Fig.4A] and [Fig.4B] respectively represent a particle in first positions and the same particle in second positions following the application of a local thermal excitation during step E2. Knowing the first positions and the second positions of the particle, a real displacement value of the particles in the adhesive 12 (displacement field) representative of a weakening of certain mechanical properties of the adhesive 12 in certain zones of the bonded assembly is deduced therefrom during a step E4. From this real displacement value of a particle and the reference value, a value of at least one parameter representative of a mechanical alteration of the bonded assembly 1 is determined.

[0084] Such a parameter representative of a mechanical alteration of the bonded assembly 1 may in particular be a value of the deformation, obtained by derivation of the values ​​of displacement of the particles.

[0085] To do this, the deformation values ​​(linked to Young's modulus) of the assembly are calculated from the difference between the reference value and the actual displacement value of each particle. When this difference exceeds a tolerance threshold, a mechanical alteration is detected at the particle level. In other words, a difference between the actual displacement value and the reference value is representative of an alteration of the mechanical properties of the adhesive 12.

[0086] The value of the parameter representing a mechanical alteration is then determined from the difference between these reference values ​​and these real values. In practice, it is the deformation fields, obtained by derivation of the displacement fields, which are compared.

[0087] Step E4 is implemented for all the particles identifiable in the first image and the second image.

[0088] In a step E5, a map representative of mechanically altered zones of the bonded assembly 1 is generated, for example in the form of a map by color level.

[0089] Such a map representative of mechanically altered zones of the bonded assembly 1 is for example obtained by associating with at least one zone of the bonded assembly 1, the coordinates of which in a given reference frame, for example the reference frame of the reference grid, are known, one or more values ​​of the parameter representative of a mechanical alteration of the adhesive 12 obtained during step E4, corresponding to one or more particles located in the zone of the bonded assembly 1 considered.

[0090] The representative map of mechanically altered zones of the bonded assembly 1 thus obtained can be stored with a view to being transmitted to remote equipment for processing.

[0091] [Fig.5] represents a device for generating a map representative of mechanically altered zones of a bonded assembly according to the invention.

[0092] A device for generating a map representative of mechanically altered areas of a bonded assembly may comprise at least one hardware processor 51, a storage unit 52, a first communication interface 53 and a second communication interface 54 which are connected to each other via a bus 55. Of course, the constituent elements of the device for generating a map representative of mechanically altered areas of a bonded assembly may be connected by means of a connection other than a bus.

[0093] The processor 51 controls the operations of the device for generating a map representative of mechanically altered areas of a bonded assembly. The unit of storage 52 stores at least one program for implementing the method according to an exemplary embodiment to be executed by the processor 51, and various data, such as parameters used for calculations performed by the processor 51, intermediate data of calculations performed by the processor 51, etc. The processor 51 may be formed by any known and suitable hardware or software, or by a combination of hardware and software. For example, the processor 51 may be formed by dedicated hardware such as a processing circuit, or by a programmable processing unit such as a central processing unit (Central Processing Unit) which executes a program stored in a memory thereof.

[0094] The storage unit 52 may be formed by any suitable means capable of storing the program(s) and data in a computer-readable manner. Examples of the storage unit 52 include non-transitory computer-readable storage media such as semiconductor memory devices, and magnetic, optical, or magneto-optical recording media loaded into a read-write unit.

[0095] The first communication interface 53 provides a connection between the device for generating a map representative of mechanically altered areas of a bonded assembly and the portable radiography device.

[0096] The second communication interface 54 provides a connection between the device for generating a map representative of mechanically altered areas of a bonded assembly and remote equipment to which a map representative of mechanically altered areas of a bonded assembly can be transmitted.

Claims

Claims

1. Method for generating a map representative of mechanically altered areas of an assembly, called bonded, consisting of an adhesive comprising particles visible by high-frequency electromagnetic imaging, said adhesive being placed between a first substrate and a second substrate, at least one of said substrates being made of a composite material, said method comprising the following steps: - obtaining, by high-frequency electromagnetic imaging, first positions of said particles within the bonded assembly, - local thermal excitation of said bonded assembly, - obtaining, by high-frequency electromagnetic imaging, second positions of said particles within the bonded assembly, - generation of said map representative of mechanically altered areas by associating with at least one area of ​​the bonded assembly a value of at least one parameter representative of a mechanical alteration of the adhesive,said value of said at least one parameter representative of a mechanical alteration of the adhesive and said zone of the corresponding bonded assembly being determined as a function of said first positions, said second positions of said particles and at least one reference value of the displacement of a particle during thermal excitation.,

2. Method for generating a map representative of mechanically altered areas of a bonded assembly according to claim 1 in which said at least one parameter representative of a mechanical alteration of the bonded assembly is a value of the Young's modulus of the adhesive.

3. Method for generating a map representative of mechanically altered areas of a bonded assembly according to claim 1 in which the bonded assembly comprises a reference grid forming a fixed reference frame for measuring a movement of the particles within the adhesive.

4. Method for generating a map representative of mechanically altered zones of a bonded assembly according to claim 1 comprising a preliminary step of determining said at least one reference value of the displacement of a particle during of a thermal excitation, and in which the generation step comprises a sub-step of determining a real value of displacement of said particles after thermal excitation from the first and second positions, said value of said at least one parameter representative of a mechanical alteration being determined from the comparison between said reference value and said real value of displacement of the particles.

5. A method of generating a representative map of mechanically altered areas of a bonded assembly according to claim 1 wherein the adhesive comprises magnetic particles and the bonded assembly is thermally excited by heat generated by the local application of a magnetic field to the magnetic particles.

6. A method according to the preceding claim, wherein the magnetic particles are particles visible by high-frequency electromagnetic imaging.

7. A method of generating a map representative of mechanically altered areas of a bonded assembly according to claim 1 wherein the bonded assembly is thermally excited by an external heat source.

8. System for generating a map representative of mechanically altered areas of a bonded assembly consisting of an adhesive comprising particles visible by high-frequency electromagnetic imaging placed between a first substrate and a second substrate, at least one of said substrates being made of a composite material, said system comprising: - at least one high-frequency electromagnetic imaging device, - means for applying local thermal excitation, - at least one device for generating a map representative of mechanically altered areas comprising means for: - receiving a first image of said bonded assembly obtained by said imaging device and at least one second image of said bonded assembly also obtained by said imaging device following the application, to said bonded assembly,of a local thermal excitation by said means of applying a local thermal excitation, - determining, from said first image, first positions of said particles within the bonded assembly, - determining, from said second image, second positions of said particles within the bonded assembly, - generating said map representing mechanically altered zones by associating with at least one zone of the bonded assembly a value of at least one parameter representative of a mechanical alteration of the adhesive, said value of said at least one parameter representative of a mechanical alteration of the adhesive and said corresponding zone of the bonded assembly being determined as a function of said first positions, said second positions of said excitable particles and reference values, - at least one module for moving the device on the bonded assembly in order to scan the entire bonded assembly.

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