FR3078162A1 - DEVICE AND METHOD FOR DETECTING DEFECTS OF A STRUCTURE - Google Patents

Abstract

The invention relates to a device for detecting defects of a structure (STR), the device comprising a calculation unit and a plurality of transducers (100) intended to be positioned on or in the structure (STR), - first transducers (E) of the plurality of transducers (100) being able to be in a transmission mode, - second transducers (R) of the plurality of transducers (100) being adapted to be in a reception mode, characterized in that that the first transducers (E) form a hexagonal mesh so as to delimit between them several meshes bordering each other, the second transducers (R) being arranged on respective emission circles of the first transducers (E), each transmission circle a first transducer (E) being centered on the first transducer (E).

Description

TECHNICAL AREA

The invention relates to a device and a method for detecting structural faults.

One field of application of the invention relates to structures used in the field of aeronautics.

STATE OF THE ART

Structural fault detection devices are known, for example from documents US 7,937,248 and US 2015/0308920.

The main objective of airlines is to ensure regular and punctual flights at competitive prices, so as to position themselves favorably against their competitors. As a result, they are attentive to the maintenance costs of their equipment and interested in working with equipment manufacturers who are aware of the issue of the availability and maintainability of a product during its life cycle.

Today, most purely structural elements of aircraft are only visited during the periodic maintenance to which said aircraft are subjected (typically type C inspections, or "C-check" in English terminology), for example every 24 months, or every 10,000 flight hours. More specifically, the maintenance of the IFS type structure (internally fixed structure, or "internai fixed structure" in English terminology,) of a thrust reverser (nacelle) of an aircraft is today hui inspected by an operator who does not have decision-making tools available.

We are looking for two areas for improvement: the first is related to security and the second is related to economic aspects.

The fact that the verification of structural integrity is carried out only during periodic maintenance and by an unassisted human operator, leaves the door open to the possibility of flying with a system not having 100% of its integrity. Here, the safety aspect would like the structural system to be replaced just before the loss of integrity, which implies the need to push preventive maintenance further.

Replacing components during type C inspection also has two major drawbacks: on the one hand, systems are often replaced preventively, while they are still capable of flying; on the other hand, they are sometimes oversized, to meet the scheduled maintenance intervals without compromising safety. As a result, there is a cost to the operator which could be avoided or at least significantly reduced.

We are looking to continuously and / or periodically monitor the evolution of the state of health of aeronautical structures. The objective is to solve the problems mentioned above and at the same time to space, simplify or even reorganize maintenance operations.

Structural diagnostic systems are also known, also called SHM systems (for "Structural Health Monitoring" in English terminology). A SHM system essentially consists of a non-destructive control system which integrates sensors permanently. The data collected makes it possible to detect the appearance, and to follow the evolution, of damage / defects in the structure. Ideally, the SHM system should be able to:

(i) detect the presence of a defect, (ii) locate it, (iii) determine its size, and (iv) provide a prognosis for the life of the structure.

The economic stakes are initially to reduce the downtime of the aircraft, because repairs can be predicted or diagnostics automated. Secondly, the challenge is to replace only the structures or components that really need to be replaced, and therefore to have fewer elements to replace, and therefore to produce.

The instrumentation of the structure makes it possible to obtain measurements, for example measurements of acoustic or guided waves (for example Lamb waves) which must be processed and analyzed in order to define whether or not the structure has a defect.

According to a state of the art, the analysis is today carried out by comparing the measurements which are taken on a structure to be analyzed (said sample under analysis) with respect to those which are taken on a reference structure (said reference sample), which by definition is healthy.

The measurements which are made on the reference structure are often taken in well-defined reference thermal states. This choice implies a constraint, which is that the measurements on the structure to be analyzed cannot be carried out before it has arrived at a thermal state identical to the reference state in which the measurements on the reference structure have been made. .

This problem involves costs linked to delays in the analysis and therefore to delays in the availability of the aircraft.

SUMMARY OF THE INVENTION

The invention aims to obtain a method and a device for detecting defects in a structure, in particular an aeronautical structure, making it possible to carry out an evaluation of the defects without using the reference state, but which is based solely on the information to be its disposition (of the current state) to identify the presence of a fault.

To this end, a first object of the invention is a device for detecting faults in a structure, the device comprising a calculation unit and a plurality of transducers intended to be positioned on or in the structure,

- first transducers of the plurality of transducers being able to be in an emission mode where they emit an excitation signal,

- second transducers of the plurality of transducers being able to be in a reception mode where they receive a reception signal in response to the excitation signal emitted by a first transducer in transmission mode, the excitation signals and the receiving being able to propagate along the structure or in the structure, characterized in that the first transducers form a hexagonal mesh so as to delimit between them several meshes bordering between them, the second transducers being arranged on emission circles respective first transducers, each emission circle of a first transducer being centered on the first transducer.

The device according to the invention may also include the following characteristics, taken alone or in combination:

- the first transducers are piezoelectric sensors, and the second transducers each comprise a Bragg grating of an optical fiber,

- the meshes are equilateral triangular with each vertex corresponding to the position of a first transducer, each emission circle of the first transducer having a radius between 1 and 2 times the distance separating two first transducers within the mesh, the radius being preferably between 1.5 and 2 times this distance, for example 1.73 times this distance.

A second object of the invention is a method for detecting defects in a structure, by means of a device as previously described, a mesh consisting of a plurality of meshes and defined by the plurality of transducers having been previously disposed on or in the structure, the method comprising the steps of:

- extraction, as a function of excitation signals emitted by the first transducers, and reception signals received by the second transducers, of a signature for each of the meshes,

- comparison of the signatures between them to identify among the meshes at least one mesh as locating a defect in the structure, called a faulty mesh, when the signature of this mesh is different from several other signatures of several other meshes, the extraction steps and of comparison being implemented by the calculation unit.

The method according to the invention may also include the following characteristics, taken alone or in combination:

- the failing mesh is identified as having a signature which is different from the signatures, which are equal to each other, of at least two other meshes, each independently bordering on the defective mesh,

- a first function for identifying a group defined successively by a first mesh, a second mesh and a third mesh, is further defined by the fact that:

o the first mesh, the second mesh and the third mesh are identified as non-failing meshes, when the signatures of these meshes are equal, o when the signature of the first mesh is different from the signature of the second mesh equal to the signature of the third mesh, the first mesh is identified as failing mesh, o when the signature of the first mesh is equal to the signature of the second mesh and is different from the signature of the third mesh, the first mesh is identified as non-defective mesh and the third mesh is identified as a suspect mesh, o in a first identification sub-step, the first identification function is applied to a first group of three meshes, successively comprising a first mesh, a second mesh, which is bordering to the first stitch, and a third stitch, which borders on the first stitch,

in a second identification sub-step subsequent to the first identification sub-step, the first identification function is applied to another group of cells defined by successively a starting cell formed by the second cell and :

o the first stitch, if the first stitch has been identified as a non-failing stitch, and a fourth stitch, which is bordering on the starting stitch, o a fifth stitch, which is bordering or not bordering on the first stitch, if the first mesh has been identified as a failing mesh, and the fourth mesh, which is bordering on the starting mesh,

- the second identification sub-step is repeated one or more times respectively on one or more other mesh groups,

- the starting grid of each second identification sub-stage is bordering on the starting grid of the second identification sub-stage preceding it,

- the fourth mesh and the fifth mesh are different from the third mesh, which is identified as suspect mesh,

- the meshes of each group are other than a mesh having been identified as a defective mesh,

- for the third mesh, which is identified as a suspect mesh, we apply a second identification function defined by the fact that:

o when the signature of the third stitch is different from the signature of the first stitch equal to the signature of a sixth stitch bordering on the third stitch, the third stitch is identified as failing stitch, o when the signature of the third stitch is different from the signature of the first link different from the signature of the sixth link, the third link is identified as a faulty link and the sixth link is identified as a suspect link, o when the signature of the third link is equal to the signature of the sixth mesh, a first indication signal is sent on a man-machine interface,

- during at least one classification sub-step, the meshes having the same signature are classified in the same respective family:

o the meshes, which are classified in the respective family having the greatest number of meshes, called healthy family, being identified as non-failing meshes, o each mesh, which is classified in a respective family having only one mesh, called respective failing family, being identified as failing mesh,

- to classify the meshes:

o we classify a first mesh having a first signature in a first family, to which we assign a respective reference equal to the first signature, o then successively for each other mesh, different from the first mesh, we iterate the classification sub-step that:

we compare the signature of the other mesh with the respective reference of each family, if the signature of the other mesh is equal to the respective reference of one of the families, then this other mesh is classified in this family, if the signature of the other mesh is not equal to any respective reference of families, then this other mesh is classified in a new family, to which a respective reference is assigned equal to the signature of this other mesh, and

- for each mesh belonging neither to the healthy family, nor to the respective defective family or families, called mesh to be analyzed, a first distance is calculated between the signature of the mesh to be analyzed and the signature of the mesh of the healthy family, and a second respective distance between the signature of the mesh to be analyzed and the signature of the meshes of each respective defective family, for:

o when the first distance is less than each respective second distance, classify the mesh to be analyzed in the healthy family or identify the mesh to be analyzed as a non-failing mesh, o when the first distance is greater than one or more respective second distances, classify the mesh to be analyzed in the failing family having this respective second distance or identify the mesh to be analyzed as a failing mesh.

QUICK DESCRIPTION OF THE FIGURES

The invention will be better understood on reading the description which follows, given solely by way of nonlimiting example with reference to the appended drawings, in which:

FIG. 1 schematically represents a modular block diagram of a fault detection device according to an embodiment of the invention,

FIG. 2 schematically represents an example of implantation of transducers of the method and of the fault detection device in an area of a structure to be monitored of a first type, according to an embodiment of the invention,

FIG. 3 schematically represents an example of implantation of transducers of the method and of the fault detection device in an area of a structure to be monitored of a second type, according to an embodiment of the invention,

FIG. 4 schematically illustrates the overlap between two emission circles bordering on transducers,

FIG. 5 schematically represents a first example of meshing of a structure by transducers of the method and of the fault detection device according to an embodiment of the invention,

FIG. 6 schematically represents a second example of meshing of a structure by transducers of the method and of the fault detection device according to an embodiment of the invention,

FIG. 7 schematically represents a third example of meshing of a structure by transducers of the method and of the fault detection device according to an embodiment of the invention,

FIG. 8 schematically represents a flow diagram of a first mode of implementation of the method for detecting faults according to the invention,

FIG. 9 schematically represents a flow diagram of a second mode of implementation of the method for detecting faults according to the invention,

FIG. 10 schematically represents the structuring of a measurement matrix, which can be used according to an embodiment of the method for detecting faults according to the invention,

FIG. 11 schematically represents a schematic flow diagram illustrating the principle of calculating a fault indicator, which can be used according to an embodiment of the fault detection method according to the invention,

FIG. 12 schematically represents an example of the result of the detection of faults, indicating on the abscissa a test number, and on the ordinate the value of a fault indicator according to FIG. 11, which can be used according to a setting mode implementation of the fault detection method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In FIGS. 1 to 6, the method for detecting faults in a structure and the device 11 for detecting faults in a structure according to the invention use a plurality of transducers 100 or sensors 100, which are positioned on or in a structure STR, whose aim is to detect and locate any faults. The device 11 according to the invention can be a system for diagnosing the state of the structure. The method according to the invention can be a method of diagnosing the state of the structure. The STR structure can be of any type of material, which can for example be composite (for example composite of monolithic type and / or composite of sandwich type and / or of cells which can be honeycomb or the like). The STR structure may be a part of an aircraft, such as for example a part of airplane turbomachines, such as for example of airplane turbojet or turboprop engines or a part of a thrust reverser (nacelle). The method and the device 11 according to the invention can be used directly on a part of the aircraft itself, the STR structure then being permanently located in the aircraft. The method and the device 11 according to the invention can also be used on a part of the aircraft, having been dismantled from it. The invention can be applied to an IFS type structure (internally fixed structure, or "Internai Fixed Structure" in English terminology) of a nacelle of an aircraft turbomachine or the like, this structure consisting of composite materials of the monolithic and sandwich types, but it can be extended to any other structure of the aircraft.

The transducers 100 can be of any type, for example of the ultrasonic type (for example of the piezoelectric or other type, in particular of the PZT type, ie with lead titano-zirconate) or other, for example of the optical type (for example in comprising one or more Bragg grating (s) of one or more optical fiber (s). In a privileged manner, within the framework of the invention, the plurality of transducers 100 is distributed between first transducers E able to be in an emission mode (also called excitation mode) on the one hand, and on the other hand, second transducers R capable of being in a reception mode. When a transducer 100 is in the emission mode, this first transducer E emits a predetermined excitation signal. When a transducer 100 is in the reception mode, this second transducer R receives a reception signal in response to the excitation signal emitted by a first transducer E. The excitation signals and the reception signals are able to propagate through the STR structure, for example along the STR structure or in the STR structure, for example along an SUR surface of the STR structure. When the excitation signal emitted by a first transducer E does not encounter any faults in the STR structure, the reception signal received by a second transducer R corresponds to this excitation signal or is equal to this excitation signal. When the excitation signal emitted by a first transducer E encounters one or more structural faults STR, the reception signal received by a second transducer R does not correspond to this excitation signal and is disturbed with respect to this signal d 'excitation. Advantageously, the first transducers E are of the ultrasonic type (for example of the piezoelectric or other type, in particular of the PZT type ie lead-zirconate type), and the second transducers R are of the optical type (for example comprising one or more several Bragg grating (s) of one or more optical fiber (s)).

Each transducer 100 may include means 101 for connection to the outside as shown in FIGS. 2 and 3, or wirelessly. It is also provided with the transducers 100 of the power supplies and the electronics necessary for their implementation. These connection means 101 used to send the control signal and the power supply from an outdoor unit 102 to each transducer 100 and to send the reception signals and / or the excitation signals to this outdoor unit 102, as well as is shown in FIG. 1. This outdoor unit 102 is for example an electronic module and is used for the acquisition of the signals emanating from the transducers 100. This outdoor unit 102 can include a supervisor whose purpose is to retrieve the measurements (reception signals and excitation signals) produced by the transducers 100

The transducers 100 have known or predetermined positions relative to the STR structure. The transducers 100 can be arranged for example on the same surface SUR of the STR structure, as shown in FIGS. 2 and 3. FIG. 2 represents transducers 100a, 100b, positioned on the SUR surface of a STR structure formed of a monolithic composite material of the IFS type structure mentioned above. FIG. 3 represents transducers 100a, 100b positioned on the surface SUR of a STR structure formed of a composite material of the honeycomb sandwich type of the structure of the IFS type mentioned above. In FIGS. 2 and 3, the elements 100a correspond to first transducers E of the ultrasonic type (for example of the piezoelectric or other type, in particular of the PZT type ie with lead-zirconate), and the elements 100b to the second optical transducers R which comprise one or more Bragg grating (s) 100b of one or more optical fibers 105. More specifically, as can be seen in these figures, one or more optical fibers ( s) 105 run (s) on, or in, the STR structure, and incorporate (s) a multitude of Bragg networks 100b, which are placed so as to act as second transducers R.

The transducers 100 can also be arranged in the STR structure, for example by belonging to a SUR surface embedded inside the STR structure. The surface SUR can be immaterial, in that it constitutes the geometrical place gathering all the positions of the transducers 100. The surface SUR can also be material, for example be made up of an attached film (for example by gluing) on STR structure, or embedded inside the STR structure. Alternatively, this material SUR surface can form a sheet disposed between two successive sheets of composite materials, before or after the baking of said materials. In any event, the SUR surface may not constitute a two-dimensional plane, for example when the SUR surface matches the particular shape of the STR structure. However, it is always possible to project the surface SUR, on a horizontal two-dimensional plane. In fact, when the SUR surface is material, the transducers 100 are first positioned on this flat surface (i.e. two-dimensional), before being integrated into the STR structure. The particular positioning of the transducers 100 within the framework of the invention, which will now be described, must therefore be understood as positioning on the horizontal plane in two dimensions, regardless of the position of the surface SUR in space afterwards. during its integration into the STR structure.

The network formed by the plurality of transducers 100 makes it possible to have optimal analysis coverage of the STR structure, while using a minimum number of transducers 100. The propagation of the excitation signals from a first transducer E is wave propagation type in free field and omnidirectional. In addition, in the context of the invention, it is assumed that this propagation is concentric with respect to the first transducers E. Each first transducer E emitting a mechanical wave which propagates in a uniform manner, the second transducers R are therefore arranged so as to be reachable by at least one transducer 100 in transmission mode. There is thus an overlap between two bordering emission circles, as visible in FIG. 4. In order to guarantee optimal analysis coverage with a minimum number of transducers 100, in a preferred embodiment of the detection device 11 according to l invention, the SUR surface is covered with a minimum number of emission circles E while guaranteeing a minimum overlap between two adjacent emission circles E.

In this respect, as visible in FIG. 5, the first transducers E are arranged to delimit between them several meshes M, according to a hexagonal mesh. The first transducers E are therefore not all aligned with one another. The meshes M are bordering between them. The meshes M have known positions with respect to the STR structure. The corners of the meshes M are formed by the first transducers E. Each mesh M surrounds an area situated between three first non-aligned transducers E or more than three first non-aligned transducers E. As visible in FIG. 5, each mesh M is delimited by three first non-aligned transducers E and is therefore triangular. Each mesh M can have one, two, three meshes, or more than three meshes which are adjacent thereto. The meshes M are, in a preferred embodiment, equilateral triangular, so as to form the hexagonal mesh. Each vertex of the equilateral triangular meshes M thus corresponds to the position of a first transducer E. For example, in FIG. 5, the fictional meshes 1, 2, 3 are shown by fictitious solid lines between the first transducers E, 4, 5, 6, 7, 8, 9, 10, which are equilateral and bordering one after the other, and which are delimited by a first row R1 of three first transducers E aligned, a second row R2 of first four transducers E aligned with one another and not aligned with row R1 and a third row R3 with three first transducers E aligned with each other and not aligned with rows R1 and R3.

From this hexagonal mesh of the plurality of first transducers E, various embodiments for positioning the plurality of second transducers R, have been illustrated in FIGS. 6 and 7. In FIG. 6, each first transducer E is surrounded by three second transducers R arranged on an emission circle centered on the first transducer E. In FIG. 7, there are six second transducers R by first transducer E.

Advantageously, the radius of the emission circle is between 1 and 2 times the distance separating two first transducers E, preferably between 1.5 and 2 times this distance, for example 1.73 times this distance.

According to one embodiment of the invention, in a first step E1 of measurement acquisition, each first transducer E emits an excitation signal, and the second transducers R which surround it on its emission circle acquire signals reception.

In a second calculation step E2, subsequent to the first measurement acquisition step E1, a signature is extracted or determined from the excitation signals of the first transducers 100 E and the reception signals of the second transducers R S for each of the meshes M, for example by a calculation unit 103, connected to the acquisition unit 102. The S signatures can for example be calculated by a signal processing and multivariate analysis tool, by the fact that the S signatures are extracted from measurement matrices, calculated as a function of the excitation signals and of the reception signals. In addition, this calculation unit 103 implements the algorithm described below and can be an algorithmic fault detection module. The calculation unit 103 is automatic, such as for example one or more calculator (s) and / or one or more computer (s), and / or one or more processor (s) and / or one or more server (s) ) and / or one or more machine (s), which can be programmed in advance by a pre-recorded computer program. The meshes M and / or the position of the meshes M with respect to the structure STR and / or the position of the transducers 100 and / or the membership of the transducers 100 to the meshes M are calculated and / or recorded and / or prerecorded in the calculation unit 103.

In a third step E3 of defect identification, subsequent to the second step E2 of calculation, the signatures S are compared with one another. One or more meshes M are identified among the meshes M as locating a defect in the structure STR, called a faulty mesh (mesh in the damaged state), when the signature S of this or these meshes is different from several other signatures of several others sts.

According to one embodiment, the mesh or meshes having been identified faulty meshes and their known position with respect to the STR structure are sent in an indication signal to a man-machine interface 104 to be restored to a user, during 'a fourth step E4 of indication, subsequent to the third step E3 of identification of faults. The user is thus provided with their known position of the faulty meshes with respect to the STR structure and therefore the location of the defects thus detected. The 104 machine interface allows for example the use by maintenance teams. The man-machine interface 104 is for example connected to the computing unit 103.

The device 11 for detecting faults in the STR structure includes, for example, the transducers 100, the calculation unit 103, the acquisition unit 102 and the man-machine interface 104. The detection device 11 implements the method for detecting defects in the STR structure, in particular thanks to the calculation unit 103 which implements the extraction steps E2 and comparison E3.

A first embodiment, known as a majority vote, of this comparison is described below during the third step E3 of identifying faults, with reference to FIG. 8. The faulty mesh is identified as having a signature S which is different from the signatures S, which are equal to or similar to each other, by at least two other meshes. There are at least two other meshes, independently of one another, each bordering on the defective mesh, for reasons of thermal inertia. The comparison is for example made in several groups of three meshes or more than three meshes, each group being different from the other groups by at least one mesh. Each group comprises for example an odd number of meshes.

According to one embodiment, we consider below groups of three meshes M. According to one embodiment, an identification of the failing meshes is thus applied according to a majority criterion 2 out of 3. It is considered that the probability of having two stitches with the same defect in the same places is very small. Of course, each group of cells could have more than three cells M, in particular an odd number of cells. The meshes of each group are bordering between them.

Each group is defined successively by a first mesh, a second mesh and a third mesh bordering them. Each group therefore has a starting stitch, which is the first stitch. For example, the case of a group of meshes bordering between them is the first group G1 of three meshes, defined successively by the first mesh 1, the second mesh 2, which is bordering on the first mesh 1, and the third mesh 6 , which is bordering on the first mesh 1 in FIG. 4 or on the second mesh.

A first function for identifying any group of cells defined successively by a first cell, a second cell and a third cell, which are adjacent to each other, is defined below, taking the example of the first group G1 below. The identification function can be applied to the first group G1 and to any group of cells other than the first group G1, and therefore to any group of cells which may be other than cell 1 and / or than cell 2 and / or that stitch 6 of the first group G1.

By the first identification function, the first mesh 1, the second mesh 2 and the third mesh 6 are identified as meshes 1, 2, 6 not failing, when the signatures S of these meshes 1, 2, 6 are equal.

By the first identification function, when the signature S of the first mesh 1 is different from the signature S of the second mesh 2 equal to the signature S of the third mesh 6, the first mesh 1 is identified as a faulty mesh.

By the first identification function, when the signature S of the first mesh 1 is equal to the signature S of the second mesh 2 and is different from the signature S of the third mesh 6, the first mesh 1 is identified as non-mesh damaged (or healthy mesh) and the third mesh 6 is identified as a suspect mesh.

The third identification step E3 may include one or more first identification sub-step (s) E31 and one or more second identification sub-step (s) E32.

Thus, in the first identification sub-step E31, the first identification function is applied to the first group G1 of successively meshes 1, 2 and 6. This first identification sub-step E31 is therefore carried out for the first group G1 having as starting mesh cell 1.

According to one embodiment, in the second identification sub-step E32, subsequent to the first identification sub-step E31, the first identification function is applied to another group G2 of cells having as cell of start the second stitch 2.

For example, this other group G2 of meshes is defined successively by the second mesh 2,

- then the first mesh 1, if the first mesh 1 has been identified as a non-failing mesh, and a fourth mesh 3, which is bordering on the starting mesh (mesh 2 in this case),

- then a fifth mesh, which is bordering or not bordering on the first mesh 1, if the first mesh 1 has been identified as failing mesh, and the fourth mesh 3, which is bordering on the starting mesh (mesh 2 in this case ).

According to one embodiment, the fourth mesh 3 and the fifth mesh 7 are different from the third mesh 6, which is identified as a suspect mesh. For example, the first mesh 1, the second mesh 2, third mesh 6, the fourth mesh 3 and the fifth mesh 7 are distinct from each other. For example, the fifth mesh, in the case where it is not bordering on the first mesh 1, may be mesh 7.

According to one embodiment, the second substep E32 of identification is reiterated one or more times on one or more other mesh groups respectively. The starting stitches of the second successive identification sub-steps E32 may be different from each other.

According to one embodiment, the starting cell of each second identification sub-step E32 is bordering on the starting cell of the second identification sub-step E32 preceding it. Identification is thus carried out on groups step by step.

According to one embodiment, the meshes of each group are other than a mesh having been identified as a defective mesh.

According to one embodiment, for example, the first identification function is applied to another group G3 of cells having as starting cell the fourth cell 3, bordering on the second cell 2.

For example, this other group G3 of meshes is defined successively by the fourth mesh 3,

- a seventh stitch, which is bordering or not bordering on the starting stitch and which has not been identified as failing stitch, and an eighth stitch, which is bordering or not bordering on the starting stitch,

- a seventh mesh, which is bordering or not bordering on the starting mesh, if the second mesh (2) has been identified as non-failing mesh, and an eighth mesh, which is bordering or not bordering on the starting mesh.

The seventh mesh may be bordering on the starting mesh (fourth mesh 3) and may be mesh 4 or mesh 2, if mesh 2 has not been identified as a defective mesh. The eighth mesh can be bordering on the starting mesh (fourth mesh 3) and be mesh 8 or mesh 2. One way of making this choice can be that of choosing the two meshes which were least used at the time of the analysis, in order to limit the risk of error.

According to one embodiment, for the third mesh 6 or each mesh, which is identified as a suspect mesh, a second identification function is applied, defined as follows.

When the signature of the third mesh 6 or suspect mesh is different from the signature of the first mesh 1 equal to the signature of a sixth mesh 7 bordering on the third mesh 6 or suspect mesh, the third mesh 6 or suspect mesh is identified as a defective mesh.

When the signature of the third mesh 6 or suspect mesh is different from the signature of the first mesh 1 different from the signature of the sixth mesh 7, the third mesh 6 or suspect mesh is identified as a failing mesh and the sixth mesh Ί is identified as a suspect mesh.

When the signature of the third mesh 6 or suspect mesh is equal to the signature of the sixth mesh 7, a second indication signal is sent to the man-machine interface 104, for example to request a decision from the user, however, this case rarely occurs.

When the suspect mesh (for example 6) is bordering on a mesh identified as a faulty mesh (for example 1), the second identification sub-step E32, the first identification sub-step E31 and / or the second function d are applied. 'identification with another mesh (for example 7) bordering on the suspect mesh.

According to one embodiment, the second identification sub-step E32 is applied, the first identification function and / or the second identification function so that the starting stitch is in turn each of the stitches, without being a mesh having been identified as a defective mesh.

A second embodiment, known as population classification, of this comparison is described below during the third step E3 of identification of faults, with reference to FIG. 9.

The third identification step E3 may include one or more third classification sub-step (s) E33 and one or more fourth classification sub-step (s) E34.

During the third (s) sub-step (s) E33 of classification, the meshes M having the same signature are classified in the same respective family F.

The meshes M, which are classified in the respective family F having the greatest number of meshes, called healthy family, are identified as non-failing meshes.

Each mesh M, which is classified in a respective family F having only one mesh M, called the respective failing family, is identified as a failing mesh.

It is unlikely to have the same type of defect on several meshes, and it is therefore considered that the population with the most individuals is a population of meshes in good condition, while we consider that all the populations having no only one individual are failing mesh populations.

According to one embodiment, in the population construction phase, we classify each mesh of the structure in a family so that we can then analyze the families and deduce if there are families that are failing. Each population is defined by a reference.

According to one embodiment, to classify the meshes, a first mesh 1 having a first signature S1 is classified in a first family F1, to which a respective reference is assigned equal to the first signature S1. We thus define the reference for the first population, whose number of individuals is equal to 1 (for the first mesh 1).

Then successively for each other mesh k (for example mesh 2, 3, 4, 5, 6, 7, 8, 9, 10), different from the first mesh 1, the fourth substep E34 of classification described below is iterated.

The signature S2 of the other cell k is compared to the respective reference of each family F (including the family F1), for example by successively comparing the signature S2 of the other cell k to the respective reference of the families Fj one after another.

If the signature S2 of the other mesh k is equal to the respective reference of one Fj of the families F, then this other mesh k is classified in this family Fj. Thus, in this case, the number of individuals of the family Fj is incremented by 1. If the signature S2 of the other mesh k is not equal to the respective reference of the family Fj, then the comparison is carried out from the signature S2 of the other mesh k to the respective reference of the following family Fj, with j incremented by 1.

If the signature S2 of the other mesh is not equal to any respective reference of the families F, Fj, then this other mesh k is classified in a new family F2, to which a respective reference is assigned equal to the signature of this other mesh k. Thus, in this case, the number of individuals of new family F2 is equal to 1.

We then go to the next mesh, on which we perform the fourth substep E34 of classification.

This iteration is carried out, as long as there is one or more meshes not yet classified in a family F.

According to one embodiment, it is determined, by calculation of distances, whether the family being analyzed is closer to the healthy family or to a failing family.

According to one embodiment, each mesh belonging to neither the healthy family, nor to the respective failing family or families, called mesh to be analyzed, is classified into a family to be analyzed.

According to one embodiment, for each mesh to be analyzed of the family to be analyzed, a first distance is calculated between the signature of the mesh to be analyzed and the signature of the meshes of the healthy family, and a second respective distance between the signature of the mesh to analyze and the signature of the meshes of each respective failing family.

When the first distance is less than each respective second distance, the mesh to be analyzed is classified in the healthy family or the mesh to be analyzed is identified as a non-failing mesh.

When the first distance is greater than one or more respective second distances, the mesh to be analyzed is classified in the failing family having this respective second distance or the mesh to be analyzed is identified as a failed mesh.

According to one embodiment, in SHM, the calculated distances are called fault indicators. According to one embodiment, the proposed indicator is calculated by means of an extraction method based on multivariate analysis. The details of the calculation of this indicator are described later in this document.

For example, for all families with 2 or more individuals (meshes), but which are not the population with the most meshes, an indicator is calculated between the main populations and that with a single individual.

Then carry out the indication step E4, described above.

Compared to the first embodiment, this second embodiment makes it possible to have a limited number of meshes having the same defect and therefore to overcome the problem of the majority vote 2 out of 3 with 2 defective meshes and one non-defective mesh.

According to one embodiment, an interrogation wavelength (of the excitation signal) is less than the distance between the transducers of the same mesh.

An embodiment of the feature extraction is described below.

Let ^e | _a matrix emanating from a structural zone considered without failure (cf. Figure 10, representing the structuring of the measurement matrix):

'711 yu yiiïy ymi .Jwi vMI

or :

ⁿ y is the number of sensors or transducers C1, C2, ... Ck, Ck + 1, ... Cny instrumented on the area,

W is the number of acquisitions established to interrogate the area, k is the discrete time.

The definition of the faultless zone is in our case linked either to the majority vote or to a higher population density, according to the algorithms described above.

The extraction of health status characteristics is established through a multivariate analysis method, for example, principal component analysis (PCA). This method makes it possible to transform variables linked to one another (called correlated) into new variables decorrelated from each other, for example according to the document [1] Tibaduiza, D.A et al (2015). “Structural damage detection using principal component analysis and damage indices”. Journal of Intelligent Material Systems and Structures.

Mathematically speaking, PCA is based on a decomposition into eigenvectors and vectors of the measurement matrix (cf. equation 1), thus making it possible to obtain a main and residual space, defined by the following equations:

Λ =

P - [? Ivrxn _r PAfxOn-nr)] (2) (3) where:

The matrices Λ, P _SO are called matrices of eigenvalues, eigenvectors, associated with the main space.

The matrices ^Λ »Ρ are called matrices of eigenvalues, eigenvectors, associated with the residual space.

An embodiment of the fault indicator is described below.

Let us now consider the matrix emanating from another structural zone considered suspect, and associate with this zone, a matrix of measures denoted ^Y ", constructed in the same way as the diagram in Figure 10 and according to equation (1).

An area considered suspect is an area with an indicator different from that of the area considered healthy.

To establish the defect indicator necessary for making a decision on the state of health, the matrix ^Y u is projected into the PCA model (according to equations (2) and (3)) established on the zone considered without failure. The fault indicator denoted DI is defined by the following equation:

E = [Y „(fc) (l - PP ^T ) JW

DI, = E, Ef < ⁵ >

where i corresponds to the acquisition number established to query the structure.

Figure 11 illustrates a block diagram of the calculation of the fault indicator.

Figure 12 illustrates the application of majority voting to the flaw indicator. By comparison, we can see that the indicator from the area

N ° 3 is more important than that from zone N ° 1 and N ° 2, thus indicating that a fault is present in zone N ° 3.

Of course, the above embodiments, characteristics and examples can be combined with one another or be selected independently of one another.

Claims (15)

1. Device (11) for detecting faults in a structure (STR), the device (11) comprising a calculation unit (103) and a plurality of transducers (100) intended to be positioned on or in the structure (STR ) - first transducers (E) of the plurality of transducers (100) being able to be in an emission mode where they emit an excitation signal, - second transducers (R) of the plurality of transducers (100) being able to be in a reception mode where they receive a reception signal in response to the excitation signal emitted by a first transducer (E) in transmission mode, the excitation signals and the reception signals being able to propagate along the structure (STR) or in the structure (STR), characterized in that the first transducers (E) form a hexagonal mesh so as to delimit between them several meshes (M) bordering them, the second transducers (R) being arranged on respective emission circles of the first transducers (E), each emission circle of a first transducer (E) being centered on the first transducer (E). 2. Device (11) according to claim 1, in which the first transducers (E) are piezoelectric sensors (110a), and the second transducers (R) each comprise a Bragg grating (100b) of an optical fiber (105 ). 3. Device (11) according to one of claims 1 or 2, in which the meshes (M) are equilateral triangular whose each vertex corresponds to the position of a first transducer (E), each emission circle of the first transducer (E) having a radius between 1 and 2 times the distance separating two first transducers (E) within the mesh, the radius preferably being between 1.5 and 2 times this distance, for example 1.73 times this distance . 4. Method for detecting defects in a structure (STR), by means of a device (11) according to one of claims 1 to 3, a mesh consisting of a plurality of meshes (M) and defined by the plurality of transducers (100) having been previously disposed on or in the structure (STR), the method comprising the steps of: - extraction, (E2) as a function of excitation signals emitted (E1) by the first transducers (E), and reception signals received (E1) by the second transducers (R), of a signature (S) for each of the meshes (M), - comparison (E3) of the signatures (S) with one another to identify among the meshes (M) at least one mesh as locating a defect in the structure (STR), called a defective mesh, when the signature (5) of this mesh (M ) is different from several other signatures (S) by several other meshes (M), the extraction (E2) and comparison (E3) steps being implemented by the calculation unit (103). 5. Method for detecting defects in a structure (STR) according to claim 4, in which the faulty mesh is identified as having a signature which is different from the signatures, which are equal to each other, of at least two other meshes ( M), each independently bordering on the faulty mesh. 6. Method for detecting defects in a structure (STR) according to claim 4 or 5, in which a first function for identifying a group defined successively by a first mesh (1), a second mesh (2) and a third mesh (6) is further defined by the fact that: - the first mesh (1), the second mesh (2) and the third mesh (6) are identified as non-faulty meshes (1, 2, 6), when the signatures of these meshes (1, 2, 6) are equal , - when the signature of the first link (1) is different from the signature of the second link (2) equal to the signature of the third link (6), the first link (1) is identified as a faulty link, - when the signature of the first stitch (1) is equal to the signature of the second stitch (2) and is different from the signature of the third stitch (6), the first stitch (1) is identified as a non-failing stitch and the third mesh (6) is identified as a suspect mesh, - in a first identification sub-step (E31), the first identification function is applied to a first group of three meshes (1, 2, 6), successively comprising a first mesh (1), a second mesh ( 2), which is bordering on the first mesh (1), and a third mesh (6), which is bordering on the first mesh (1). 7. A method for detecting defects in a structure (STR) according to claim 6, in which, in a second identification sub-step (E32) subsequent to the first identification sub-step (E31), the the first identification function is applied to another group of cells defined successively by a starting cell formed by the second cell (2) and: - the first mesh (1), if the first mesh (1) has been identified as a non-failing mesh, and a fourth mesh (3), which is bordering on the starting mesh, - a fifth mesh (7), which is bordering or not bordering on the first mesh (1), if the first mesh (1) has been identified as failing mesh, and the fourth mesh (3), which is bordering on the mesh of departure. 8. Method for detecting defects in a structure (STR) according to claim 7, in which the second sub-step (E32) of identification is repeated once or several times on one or more other mesh groups respectively. 9. Method for detecting defects in a structure (STR) according to claim 8, in which the starting mesh of each second identification sub-step (E32) is bordering on the starting mesh of the second sub-step (E32 ) of identification preceding it. 10. A method of detecting defects in a structure (STR) according to any one of claims 7 to 9, in which the fourth mesh (3) and the fifth mesh (7) are different from the third mesh (6), which is identified as a suspect mesh. 11. Method for detecting defects in a structure (STR) according to any one of claims 6 to 10, in which the meshes of each group are other than a mesh having been identified as a defective mesh. 12. Method for detecting defects in a structure (STR) according to any one of claims 6 to 11, in which, for the third mesh (6), which is identified as suspect mesh, a second function of identification defined by the fact that: - when the signature of the third stitch (6) is different from the signature of the first stitch (1) equal to the signature of a sixth stitch (7) bordering on the third stitch (6), the third stitch (6) is identified as a faulty mesh, - when the signature of the third link (6) is different from the signature of the first link (1) different from the signature of the sixth link (7), the third link (6) is identified as a faulty link and the sixth link (7) is identified as a suspect mesh, - when the signature of the third mesh (6) is equal to the signature of the sixth mesh (7), a first indication signal is sent to a man-machine interface (104). 13. Method for detecting defects in a structure (STR) according to claim 4, in which, during at least one classification sub-step (E33, E34), the meshes (M) having the same classification are classified signature in the same respective family: - the meshes (M), which are classified in the respective family having the greatest number of meshes, called healthy family, being identified as non-failing meshes, - each mesh (M), which is classified in a respective family having only one mesh, called the respective failing family, being identified as a failing mesh. 14. Method for detecting defects in a structure (STR) according to claim 13, in which to classify the meshes (M): a first mesh (1) having a first signature (S1) is classified in a first family (F1), to which a respective reference equal to the first signature (S1) is assigned, - then successively for each other mesh (k), different from the first mesh (1), the classification sub-step (E34) is iterated according to which o the signature (S2) of the other mesh (k) is compared to the respective reference of each family (F1), o if the signature (S2) of the other mesh (k) is equal to the respective reference of one (Fj) of the families (F), then this other mesh (k ) is classified in this family (Fj), o if the signature (S2) of the other mesh (k) is not equal to any respective reference of the families (F), then this other mesh (k) is classified in a new family (F2), to which one assigns a respective reference equal to the signature (S2) of this other mesh (k). 15. Method for detecting defects in a structure (STR) according to claim 13 or 14, in which: - for each mesh belonging neither to the healthy family, nor to the respective defective family or families, called mesh to be analyzed, a first distance is calculated between the signature of the mesh to be analyzed and the signature of the mesh of the healthy family, and a second respective distance between the signature of the mesh to be analyzed and the signature of the meshes of each respective defective family, for: o when the first distance is less than each respective second distance, classify the mesh to be analyzed in the healthy family or identify the mesh to be analyzed as a non-failing mesh, o when the first distance is greater than one or more respective second distances, classify the mesh to be analyzed in the failing family having this respective second distance 5 or identify the mesh to be analyzed as a failing mesh.