WO2009056472A1

WO2009056472A1 - Piezoelectric transducer for the non-destructive testing of a structure comprising a hole

Info

Publication number: WO2009056472A1
Application number: PCT/EP2008/064177
Authority: WO
Inventors: Nicolas Colin; Sylvère BARUT
Original assignee: European Aeronautic Defence And Space Company Eads France
Priority date: 2007-10-30
Filing date: 2008-10-21
Publication date: 2009-05-07
Also published as: FR2923017B1; FR2923017A1; EP2203723A1

Abstract

A piezoelectric transducer (2), for the ultrasonic non-destructive testing of a structure comprising at least one hole, comprises at least one hole (220, 221) and is characterized in that it comprises a first dielectric layer (20) and a second dielectric layer (21), which said first layer and second layer being passed through by at least one hole (220, 221), and at least two elementary transducers (270, 271) located between said first layer and said second layer in the vicinity (230, 231) of at least one hole (220, 221), each elementary transducer (270, 271) essentially being formed by a piezoelectric active component (260a), by a primary electrode (240a - 247a) and by a secondary electrode (250a, 251a). Preferably, for each hole (220, 221), a single secondary electrode (250a, 251a) is shared by the at least two elementary transducers (270, 271). The invention also relates to a structure (7) and a part (8) made of a composite material integrating the piezoelectric transducer (2).

Description

Piezoelectric transducer for non-destructive control of a structure having a hole

The present invention relates to a piezoelectric transducer for non-destructive ultrasonic testing of a structure. More particularly, the present invention relates to a piezoelectric transducer adapted to the non-destructive control of a structure comprising a hole, for locating any defects in an area near the hole.

Non-destructive testing methods, known as CND, are used in many industrial fields to detect defects and / or damage to the surface and / or depth of a structure without degrading it. These methods are used in a production phase of the structure to check the quality of manufacture and / or in a maintenance phase to check whether damage has appeared in said structure.

Numerous CND methods exist, for example, bleeding methods for surface control of the structure, methods using eddy currents for the control of electrically conductive structures, or methods using ultrasound. The CND ultrasonic methods use transducers for transmitting and / or receiving acoustic waves of frequencies generally between 0.1 MHz and 50 MHz, and are used for surface and / or depth control of the structure.

Such methods are particularly used in the field of aeronautics, because of the importance of verifications carried out on structures. Composite materials, among others, are regularly controlled because they are particularly sensitive to damage, for example due to local impacts or overloads, which can induce delamination of said composite materials and reduce their strengths. mechanical.

Some structures of an aircraft to be controlled are difficult to access, and their control requires the prior dismantling of the surrounding structures, the dismantling / reassembly of the various structures increasing the time of immobilization of the aircraft, even the risk of damage.

The transducers used for non-destructive testing must therefore maximize the reliability of said control while minimizing the downtime of the aircraft and the complexity of the non-destructive control operation. In a structure, the zones comprising holes, for example for the passage of a fastening element such as a rivet, are zones in which the mechanical stresses are concentrated and in which preferentially appear defects that may be cause of damage to said structure. The risks associated with the occurrence of defects in an area with a hole are more or less important depending on the positions and sizes of said defects. Accordingly, determining the size and position of each defect in the area having a hole, which requires detailed local control in said area, is essential and leads to frequent checks.

It is known from the French patent application published under number 2874430, to integrate a transducer inside a composite material structure, between folds forming said composite material, in particular a transducer having a hole. The solution described in the French patent application 2874430 however proposes a simple transducer which proves insufficiently discriminating to perform a detailed local control of a zone comprising a hole, and is not able to accurately characterize a detected damage. The present invention relates to a piezoelectric transducer adapted to non-destructive ultrasonic testing of a structure in an area having a hole, allowing detailed local control in said area.

The piezoelectric transducer according to the present invention comprises at least one hole and is characterized in that it comprises a first dielectric layer and a second dielectric layer, which first and second layers are traversed by the at least one hole.

To allow detailed local control in the area of the structure comprising a hole, the piezoelectric transducer comprises between the first and second layers, in the vicinity of the at least one hole, at least two elementary transducers, each elementary transducer being essentially formed by a component piezoelectric active, by a primary electrode and a secondary electrode.

In a preferred embodiment of the invention, for each hole of the piezoelectric transducer, a single piezoelectric active component is shared by the at least two elementary transducers.

For each elementary transducer, the primary electrode and the secondary electrode are advantageously located at a non-zero distance ε from the hole so that they are electrically isolated from an electrically conductive element passing through said hole.

In a particular embodiment of the invention, for each hole of the piezoelectric transducer, a single secondary electrode is shared by the at least two elementary transducers.

In a preferred embodiment, four elementary transducers are located in each active zone, each hole of the piezoelectric transducer is of diameter d0 and, for each hole, the secondary electrode is a concentric ring of said hole, of inner diameter d1 and of diameter outside d2 greater than d1, and each primary electrode is a quarter of a same concentric ring of said hole, inner diameter d1 and outer diameter d2, said crown quarters not being in contact with each other.

To move the primary and secondary electrodes towards a portion of the piezoelectric transducer accessible by an operator when said transducer is positioned on the structure to be controlled, each primary electrode is connected to a primary connection area by a primary conductive track, and each secondary electrode is connected to a secondary connection area by a secondary conductive track, the primary and secondary connection areas being located near an edge of the piezoelectric transducer. In a preferred embodiment of the piezoelectric transducer, the secondary tracks and the secondary connection areas are arranged on an upper face of the second layer, the primary conductive tracks and the primary connection areas are arranged on a lower face of the first layer. , so that the secondary tracks and the secondary connection areas on the one hand and the primary conductive tracks and the primary connection areas on the other hand are not superimposed in the assembled piezoelectric transducer.

Advantageously, a single secondary connection zone is shared by all the secondary electrodes of the piezoelectric transducer.

The piezoelectric active components of the transducer according to the invention are preferably polarized portions of an intermediate layer composed of PVDF or a PVDF-related copolymer. In a particular embodiment of the piezoelectric transducer, the first and second dielectric layers are made of a polymer or polyimide material.

A structure according to the present invention comprises an assembly of at least two parts and at least one piezoelectric transducer, and is characterized in that the at least two parts and the at least one piezoelectric transducer comprise at least one hole for the passage of at least one fixing element, and in that the at least one piezoelectric transducer comprises at least two elementary transducers placed between a first and a second dielectric layer in an area in the vicinity of each hole.

In a particular embodiment of the structure, the at least one piezoelectric transducer is placed at the interface between two parts of the assembly.

A composite material part according to the present invention comprises at least two assembled plies and at least one piezoelectric transducer, and is characterized in that the at least two plies of the composite material part and the at least one piezoelectric transducer comprise at least one hole for the passage of at least one fixing element, and in that the at least one piezoelectric transducer comprises at least two elementary transducers placed between a first and a second dielectric layer in an area in the vicinity of each hole.

The following description of embodiments of the invention is made with reference to the figures which show in a nonlimiting manner:

FIG. 1: a schematic view of a section of a conventional piezoelectric transducer,

FIG. 2: a schematic view of a section of a piezoelectric transducer according to a first embodiment of the invention,

FIG. 3a, FIG. 3b and FIG. 3c: schematic views of a first dielectric layer, a second dielectric layer and an intermediate layer of the piezoelectric transducer of FIG. 2,

FIG. 4a and FIG. 4b are diagrammatic views of the first layer and the second layer of the support of the piezoelectric transducer according to a second embodiment of FIG. the invention,

FIG. 5a and FIG. 5b are diagrammatic views of a section of a structure comprising an assembly of a plurality of parts and the piezoelectric transducer according to two adjacent embodiments,

- Figure 6: an exploded schematic perspective view of an assembly of a plurality of plies of a composite material and the piezoelectric transducer according to the invention.

As illustrated in FIG. 1, a conventional piezoelectric transducer 1 is essentially formed by a piezoelectric active component 10 and by two electrodes 11 and 12 in contact with said piezoelectric active component. The piezoelectric active component 10 converts an electrical signal at the electrodes 11 and 12 into an ultrasonic acoustic wave and vice versa. FIG. 2 represents a piezoelectric transducer 2 according to a first embodiment of the invention, which comprises a first dielectric layer 20 having a lower face 200 and a second dielectric layer 21 having an upper face 210. An intermediate layer 26 is located between said lower face and said upper face, with which said intermediate layer is in contact.

The first and second layers 20 and 21 are preferably made of a polymeric material, for example a polyimide such as Kapton®, which has the advantage of being adapted to the production of flexible and resistant layers of small thickness and geomethes. varied. The piezoelectric transducer 2 comprises a hole 220, passing through the two dielectric layers 20 and 21 and the intermediate layer 26, of diameter adapted for the passage of a fastener mounted on a structure to be controlled. The structure also comprises a hole, for the passage of said fixing element, in the vicinity of which the control is carried out. The piezoelectric transducer 2 also comprises, in an active zone 230 in a vicinity of the hole 220, between the upper face 210 and the lower face 200, a plurality of elementary transducers of which two are visible in FIG. 2, identified by the references 270 and 271. each elementary transducer having two electrodes 240a, 250a and 241a, 250a and a piezoelectric active component 260a.

The description of the arrangement of said elementary transducers in the active zone 230 is made with reference to FIGS. 3a, 3b and 3c which respectively represent a view of the lower face 200 of the first layer 20, a view of the upper face 210 of FIG. the second layer 21 and a view of the intermediate layer 26 before an assembly operation during which said intermediate layer is interposed between said lower face and said upper face, said three layers being preferably bonded, to obtain the assembled transducer 2 shown in FIG. 2. The first layer 20 comprises four primary electrodes 240a -

243a which are distributed around the hole 220 in the active zone 230, on a surface of the peripheral lower face 200 of said hole.

The first layer 20 is of any shape, advantageously a simple shape, as illustrated in FIG. 3a, for moving the four primary electrodes 240a - 243a towards four primary electrical connection zones 240c - 243c, which are also electrically conductive and which are placed in a portion of the transducer that is accessible when said transducer is positioned on the structure to be controlled.

For example, the first layer 20 is of rectangular shape and the four primary connection areas 240c - 243c are located near an edge of said first layer, for example an edge located on a side furthest from the hole 220.

Each primary electrode 240a - 243a is connected to a primary connection zone 240c - 243c respectively by a primary conductive track 240b - 243b, respectively. advantageously, said primary conductor tracks and said primary connection areas are arranged in pairs so that a fifth conductive track and a fifth connection area can be interposed respectively between the primary conductor tracks 240b, 241b on the one hand and 242b, 243b d on the other hand, and between the primary connection areas

240c, 241c and 242c, 243c.

The second layer 21, shown in FIG. 3b, is preferably of shape and dimensions substantially identical to those of the first layer 20. The second layer 21 comprises a secondary electrode 250a in the active zone 230, which covers a surface of the upper face 210 peripheral of the hole 220.

In a neighboring embodiment of the piezoelectric transducer

2, the second layer 21 has a plurality of secondary electrodes, for example four secondary electrodes. The example of Figure 3b is a preferred mode from a complexity reduction point of view of the manufacture of said transducer.

The second layer 21 also comprises a secondary conductive track 250b and a secondary connection zone 250c situated in an accessible part of the transducer, preferably close to the primary connection zones 240c-243c in the piezoelectric transducer.

2 assembled close to an edge on one side farthest from hole 220.

The secondary electrode 250a is connected by the secondary conductive track 250b to the secondary connection zone 250c. The intermediate layer 26, shown in FIG. 3c, is preferably of shape and dimensions substantially identical to those of the first and second layers 20 and 21.

The intermediate layer 26 has in the active zone 230 an active component 260a which surrounds the hole 220. In a similar embodiment, the intermediate layer 26 comprises a plurality of piezoelectric active components, for example four piezoelectric active components of shapes and dimensions substantially identical to those of the primary electrodes 240a-243a.

In the assembled piezoelectric transducer 2, shown in FIG. 2, the piezoelectric active component 260a is located between the four primary electrodes 240a - 243a and the secondary electrode 250a, with which said active component is in contact, forming four elementary transducers i) 240a, 260a, 250a, ii) 241a, 260a, 250a, iii) 242a, 260a, 250a and iv) 243a, 260a, 250a. In a particular embodiment of the active component 260a, the intermediate layer 26 is for example a film composed of a polyvinylidene fluoride called PVDF, or a PVDF-related copolymer (such as a copolymer of vinylidene fluoride and trifluoroethylene) , having a polarized portion in the active area around the hole forming said piezoelectric active component, and a non-polarized portion 260b elsewhere. The PVDF or related copolymer is particularly suitable for the production of thin active components and complex geometries, and also has the advantage of producing broadband active components from 20OkHz to 50MHz. In another embodiment, the unpolarized portion 260b does not exist and the intermediate layer is limited to the polarized portion 260a in the active area 230.

In a preferred embodiment, the primary electrodes 240a-243a and the secondary electrodes 250a are not located immediately at the edge of the hole 220, but are at least at a distance ε from said hole. The distance ε is preferably small so that the control is performed in an immediate vicinity of said hole, and not zero so that said electrodes and a fixing element, generally electrically conductive, passing through said hole, are not in contact. The distance ε is for example 0.5mm. In the embodiment shown in FIGS. 3a and 3b, the section of the hole 220 is a disc of diameter d0, the secondary electrode 250a is a concentric ring of said turn, of internal diameter d1 equal to dO + ε and outside diameter d2 greater than d1, and the four primary electrodes 240a - 243a are quarters of the same ring, also concentric of said hole and inner diameter d1 and outer d2. For example, the diameters d0, d1 and d2 are respectively equal to 6.5mm, 7mm and 9mm, and the quarter crowns are spaced 0.5mm apart.

In the assembled piezoelectric transducer 2, the secondary conductive track 250b and the secondary connection zone 250c on the one hand and the primary conductive tracks 240b-243b and the primary connection zones 240c-243c on the other hand do not overlap, of so that said primary and secondary tracks, said primary and secondary connection areas and the intermediate layer 26 do not create a capacitive effect in said assembled piezoelectric transducer. In the case where the intermediate layer 26 does not comprise the unpolarized portion 260b, the secondary conductive track 250b on the one hand and the secondary connection zone 250c on the other hand are respectively interposed between the primary conductive tracks 241b and 242b , and between the primary connection areas 241c and 242c, so that the conductive tracks and the connection areas present on the two dielectric layers 20 and 21 are not in contact with each other.

Thanks to the arrangement of the elementary transducers (240a, 260a, 250a to 243a, 260a, 250a) in the active zone 230 around the hole 220, it is possible to locate defects in the area of the structure to be controlled comprising a hole and to determine the size of said defects.

The number of elementary transducers in the active zone around the hole is, in the present invention, greater than or equal to two. In the particular case described of four elementary transducers, said transducers have dimensions that allow them to emit or receive enough energy to detect defects of small size. The first and second layers 20 and 21 further provide protection and electrical insulation of the conductive elements (i.e. the electrodes, the conductive tracks and the connection areas) of the piezoelectric transducer 2, particularly in the non-destructive testing of an electrically non-insulating material such as a metallic material, a carbon composite material or a hybrid composite material having metal pleats, with which said transducer is to be contacted.

In a second embodiment of the invention, the piezoelectric transducer 2 comprises two or more active zones.

Figures 4a and 4b show respectively the lower face

200 of the first layer 20 and the upper face 210 of the second layer 21 of the piezoelectric transducer 2 in the case where said transducer comprises a second active zone 231 around a second hole 221.

In addition to the characteristics already described, the piezoelectric transducer 2 comprises on the lower face 200 of the first layer 20:

four primary electrodes 244a-247a on a peripheral surface of the hole 221,

four primary conductive tracks 244b-247b and four primary connection zones 244c-247c, each primary conductive track connecting a primary electrode and a primary connection zone. The piezoelectric transducer 2 also has on the upper face 210 of the second layer 21:

a secondary electrode 251a covering a peripheral surface of the hole 221,

a secondary conductive track 251b connecting the two secondary electrodes 250a and 251a, connecting indirectly the secondary electrode 251a to the secondary connection zone 250c via the secondary track 250b. In the active zone 231, the intermediate layer 26 also comprises a second piezoelectric active component which surrounds the hole 221, similar to the piezoelectric active component 260a surrounding the hole 220. In the assembled piezoelectric transducer 2, the second active component is located between the electrodes primary 244a-247a and the secondary electrode 251a to form four elementary transducers in the active zone 231 around the hole 221. The primary conductive tracks 240b-247b and secondary 250b,

251 b, the primary connection areas 240c - 247c and secondary 250c are arranged so that they are not superimposed in the assembled piezoelectric transducer 2.

In a particular embodiment of the conductive elements of the piezoelectric transducer 2, the combination of a connection zone, a contact zone and a conducting track connecting them is formed by a single conductive circuit.

The elementary transducers are used simultaneously or sequentially, in transmission or reception or transmission / reception. In the case where an elementary transducer is used at least in transmission, it is connected, via the connection zones, to a not shown electric pulse generator.

The piezoelectric transducer 2 is essentially used according to the following three modes: 1) each elementary transducer is used in reception, and an external ultrasonic source is used to emit an ultrasonic wave received by the elementary transducer,

2) at least one elementary transducer is used in transmission and at least one elementary transducer is used in reception to detect an ultrasonic wave emitted by the at least one elementary transducer used in emission, 3) each elementary transducer is used in transmission and reception, that is to say that it emits an ultrasonic wave and detects the echoes generated inter alia by the defects of the structure. Electrical connection means, not shown, for connecting the connection areas 240c - 247c, 250c to viewing and / or recording means, and / or to an electrical pulse generator. The connection means are for example local taps, or remote in the case of a concentration of connection means from a plurality of piezoelectric transducers.

A piezoelectric transducer 2 according to the invention is preferably permanently installed in a structure comprising an assembly of parts or inside a composite material forming for example part of an aircraft. FIGS. 5a and 5b show two neighboring embodiments of a structure comprising an assembly incorporating a piezoelectric transducer 2 comprising a single hole 220.

FIG. 5a shows a first embodiment of a structure 7 according to the invention, comprising an assembly of an upper part 70 and a lower part 71. The upper part 70 and the lower part 71 respectively comprise a hole 700 and a hole 710 for the passage of a third piece 72, for example a fastening element such as a rivet.

The piezoelectric transducer 2 is placed on one side of the upper part 70 not in contact with the lower part 71, and so that the fixing element 72 passes through said piezoelectric transducer (220), said upper and lower parts ( 700 and 710), and holds them together.

Preferably, the piezoelectric transducer 2 is bonded to the upper part 70 to adapt the acoustic impedances of said transducer and said upper piece.

FIG. 5b shows a variant of the structure 7 of FIG. 5a, in which the piezoelectric transducer 2 is placed between the upper part 70 and the lower part 71. FIG. 6 represents a part 8 made of composite material inside which the piezoelectric transducer 2 is placed permanently between folds 80 and 81 of said part. Each fold forming the piece of composite material has a hole opposite that of said transducer, so that once the various folds and said transducer assembled, a fastener can pass through said folds and said transducer.

The piezoelectric transducer according to the invention makes it possible to carry out a detailed local control of a structure in a zone comprising a hole, and to determine more precisely the necessary frequency of the controls, the repairs which must be carried out and / or the parts of the structure that must be replaced to optimize the downtime of said structure.

Claims

1 - Piezoelectric transducer (2) for the non-destructive ultrasonic testing of a structure comprising at least one hole, said piezoelectric transducer comprising at least one hole (220, 211) and characterized in that it comprises a first layer (20 dielectric and a second layer (21) dielectric, which said first layer and second layer being traversed by the at least one hole (220,221), and at least two elementary transducers (270,271) located between said first layer and said second layer at a neighborhood (230, 231) of the at least one hole (220, 211), each elementary transducer (270, 271) being substantially formed by a piezoelectric active component (260a), by a primary electrode

(240a - 247a) and by a secondary electrode (250a, 251a).

2 - piezoelectric transducer (2) according to claim 1, wherein for each hole (220,221) a single piezoelectric active component (260a) is shared by the at least two elementary transducers

(270,271).

3 - piezoelectric transducer (2) according to claim 1 or 2, wherein for each elementary transducer (270,271) the primary electrode (240a - 247a) and the secondary electrode (250a, 251 a) are located at a distance ε no zero of the hole (220,221).

4 - piezoelectric transducer (2) according to one of the preceding claims, wherein for each hole (220,221) a single secondary electrode (250a, 251 a) is shared by the at least two elementary transducers (270,271). 5 - piezoelectric transducer (2) according to claim 4, wherein four elementary transducers (270,271) are located in the vicinity (230,231) of each hole (220,221), and wherein for each hole (220,221), the secondary electrode (250a , 251 a) is a crown concentric of said hole, of inner diameter d1 and outer diameter d2 greater than d1, and each primary electrode (240a-247a) is a quarter of a same concentric ring of said hole, of inner diameter d1 and outside diameter d2, said quarters of crown not being in contact with each other.

6 - piezoelectric transducer (2) according to one of the preceding claims, wherein each primary electrode (240a - 247a) is connected to a primary connection area (240c - 247c) by a primary conductive track (240b - 247b), and each secondary electrode (250a, 251a) is connected to a secondary connection area (250c) by a secondary conductive track (250b, 251b), said primary connection areas and said secondary connection areas being located near a edge of the piezoelectric transducer (2). 7 - piezoelectric transducer (2) according to claim 6, wherein the secondary tracks (250b, 251b) and the secondary connection areas (250c) are arranged on an upper face (210) of the second layer (21), the primary conductive tracks (240b - 247b) and the primary connection areas (240c - 247c) are arranged on a lower face (200) of the first layer (20), so that said secondary tracks and said secondary connection areas of one side and said primary conductive tracks and said primary connection areas on the other hand are not superimposed. 8 - piezoelectric transducer (2) according to claim 6 or 7, wherein a single secondary connection area (250c) is shared by the secondary electrodes (250a, 251a).

9 - piezoelectric transducer (2) according to one of the preceding claims, wherein each piezoelectric active component (260a) is a polarized portion of an intermediate layer (26) composed of PVDF or PVDF-related copolymer. - Piezoelectric transducer (2) according to one of the preceding claims, wherein the first layer (20) and the second layer (21) are made of a polymer material or polyimide. - Structure (7) comprising an assembly of at least two parts (70,71) and at least one piezoelectric transducer (2), characterized in that the at least two parts (70,71) and the at least one piezoelectric transducer (2) comprise at least one hole (700, 710, 220) for the passage of at least one fastening element (72), and in that the at least one piezoelectric transducer (2) comprises at least two transducers elementals (270,271) placed between a first layer

(20) dielectric and a second dielectric layer (21) in an area adjacent to (230) each hole (220). - Structure (7) according to claim 11, wherein the at least one piezoelectric transducer (2) is placed at the interface between two parts

(70, 71) of the assembly. - Part (8) of composite material comprising at least two folds (80 - 81) assembled and at least one piezoelectric transducer (2), characterized in that the at least two folds of said piece and the at least one piezoelectric transducer ( 2) have at least one hole

(800, 810, 220) for the passage of at least one fixing element, and in that the at least one piezoelectric transducer (2) comprises at least two elementary transducers (270, 271) placed between a first dielectric layer (20) and a second dielectric layer (21) in an area in the vicinity (230) of each hole (220).