FR2874430A1 - Ultrasound cartography system for monitoring components uses movable and position-coded emitter and receiver of piezoelectric film - Google Patents

Abstract

The ultrasound cartography system consists of an ultrasound emitter (16, 28) and a receiver (14, 26, 36, 38) placed on either side of a component (10, 24) being monitored. It also has an electronic processor (20, 32) for the electrical signals produced by the piezoelectric film when subjected to ultrasound so that the surface of the object can be mapped. The piezoelectric film can be located on a support (6) or placed against one surface of the object while the ultrasound emitter is moved on the opposite surface.

Description

INTEGRATED PIEZOELECTRIC FILM ASSEMBLY FOR

  NON-DESTRUCTIVE CONTROL OF THIS ASSEMBLY

DESCRIPTION TECHNICAL FIELD

  The present invention relates to an assembly of elements, this assembly being provided with means of non-destructive control of the assembly.

  The invention applies in particular to the detection of defects of an assembly of elements and / or the measurement of parameters relating to the state of the constituent material or materials of the assembly.

  The elements of the latter may be of the same nature, for example all electrically conductive, in particular metallic, or all electrically insulating. The assembly may also be composed of elements of different natures, in which case the assembly is composite.

  Let us now indicate that, in the invention, the ultrasound is used for non-destructive testing of the assembly and that one or more piezoelectric films, preferably of PVDF or copolymer type, are used to emit and / or detect ultrasound.

  It is recalled that the acronym PVDF means polyvinylidene fluoride (in English "polyvinylidene fluoride").

  PRIOR ART The emission of acoustic waves and the use of ultrasound in the field of non-destructive testing are well known techniques. These techniques use ceramic or composite sensors whose size is important. The size of these sensors does not allow to integrate them into structures that we want to control.

  Sensors are also known which use materials of the PVDF or copolymer type. But these sensors are bulky.

  The use of PVDF films is also known in the field of intruder alarm systems, a domain that is far removed from non-destructive testing.

  PRESENTATION OF THE INVENTION The subject of the present invention is an assembly of elements, this assembly being provided with means of non-destructive control of the assembly, these means occupying a very small volume and can therefore be integrated into the assembly.

  These means comprise at least one piezoelectric film which is in direct contact with at least one of the elements of the assembly. A layer of glue between the film and the element can be added to attach this film to this element and ensure ultrasound transmission from one to the other. It should be noted that such a layer of glue has a small thickness.

  The non-destructive testing means used in the invention therefore have a very small thickness (thickness of the piezoelectric film plus possible adhesive thickness) and are therefore easily integrable to the assembly to be controlled.

  Precisely, the subject of the present invention is an assembly of elements, this assembly being provided with means of non-destructive control of the assembly, characterized in that these non-destructive inspection means comprise one or a plurality of piezoelectric films which are integrated in this assembly, each piezoelectric film being in direct contact with at least one of the elements, without any layer, with the exception of a possible layer of glue, between this film and this element, each piezoelectric film constituting a ultrasonic transmitter or ultrasonic receiver or both.

  Preferably, each piezoelectric film is of PVDF type or of copolymer type.

  According to a first particular embodiment of the assembly that is the subject of the invention, this assembly comprises at least two piezoelectric films, namely first and second piezoelectric films respectively constituting an ultrasound emitter and an ultrasound receiver.

  These first and second piezoelectric films can be separated by the thickness of at least one of the elements of the assembly.

  Alternatively, the first and second piezoelectric films may be placed on one and the same face of the assembly for the purpose of transmitting and receiving ultrasonic surface waves.

  According to a second particular embodiment of the assembly which is the subject of the invention, this assembly comprises at least one piezoelectric film constituting an ultrasound receiver, the assembly being provided with an ultrasound emitter which is external to this assembly. , when we want to control this one.

  This piezoelectric film can be arranged in the assembly.

  As a variant, this piezoelectric film and the ultrasound emitter may be placed on one and the same face of the assembly, for the purpose of transmitting and receiving ultrasonic surface waves.

  According to a third particular embodiment of the assembly which is the subject of the invention, this assembly comprises at least one piezoelectric film, this piezoelectric film constituting both an ultrasound emitter and an ultrasound receiver.

  According to a fourth particular embodiment of the assembly that is the subject of the invention, this assembly comprises at least one piezoelectric film constituting an acoustic emission receiver, the desired acoustic source being the evolution of a defect in the assembled assembly. under constraints.

BRIEF DESCRIPTION OF THE DRAWINGS

  The present invention will be better understood on reading the description of exemplary embodiments given below, purely by way of indication and in no way limiting, with reference to the appended drawings in which: FIGS. 1 and 2 are diagrammatic views of FIG. Examples of piezoelectric films that can be used in the present invention - Figures 3A and 3B schematically illustrate an example of an assembly according to the invention, which comprises three piezoelectric films and which is seen in longitudinal section in FIG. 3A and in plan view in FIG. 3B; FIG. 4 is a schematic view of another assembly according to the invention, using two piezoelectric films which are fixed on the surface of the assembly to be inspected, FIG. 5 is a schematic view of another example of the invention, using a piezoelectric film integrated in the assembly to be tested and an ultrasonic transmitter which is external. at assembly, and - Figure 6 is a schematic view of another example of the invention, comprising a piezoelectric film, which is attached to the surface of the assembly to be monitored, and an ultrasonic transmitter which is outside this assembly and in contact with this surface, facing the piezoelectric film.

  DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS An object of the present invention is to detect any damage to the elements or parts, of an assembly, or structure, and / or to measure parameters relating to the state of this assembly, when this the last is motionless or, on the contrary, in motion.

  Detection and / or measurement can be applied to one or more elements of the assembly.

  It is generally not easy to control an assembly because of difficulties of access to the area to be controlled but also because of the multiplicity of layers in the assembly, these layers being made of the same material or different materials.

  Indeed, this multiplicity of layers leads to acoustic impedance failures, multiple ultrasound echoes and attenuation of ultrasound at the interfaces of the layers, that a seal or other, such as mastic, is used or not.

  Piezoelectric films are flexible and adaptable - they can be cut to any desired shape - so that they can be integrated into any structure whose integrity is to be controlled.

  Such films can be cut as desired, depending on the application envisaged, and they can be glued or inserted between two elements of an assembly to be tested.

  These films are capable of emitting or detecting ultrasound in a very wide frequency band and can therefore be used for ultrasonic testing irrespective of the nature of the constituent materials of the assembly to be tested.

  Depending on the materials, frequencies in the range of 200 kHz to 50 MHz may be used.

  The ability to emit or detect ultrasound in a very wide frequency band also makes it possible to use piezoelectric films to monitor the behavior of an assembly under stress over time, by acoustic emission, for example in the range of frequencies ranging from 500Hz to 500kHz.

  In addition, piezoelectric films are versatile sensors that make it possible to work with different ultrasound modes.

  After integrating one or more piezoelectric films into an assembly, it can be spot-checked with ultrasound by connecting the film (s) to conventional ultrasound control equipment or other suitable equipment.

  An ultrasonic transmission control technique can be used. In this case, two piezoelectric films can be used, one serving as an ultrasound emitter and the other as an ultrasound receiver. These two films can be integrated in the controlled assembly but one can also fix these two films on the same face of the assembly to control the latter using ultrasonic surface waves.

  It is also possible to implement another ultrasonic transmission control technique, using a piezoelectric film, integrated in the assembly, as an ultrasound receiver, and an ultrasonic transmitter which is external to the assembly to be monitored and generates ultrasound that is detected with the film.

  This external transmitter is for example a conventional ultrasonic probe, operating by contact or immersion, or an ultrasonic transmitter operating by coupling by means of air or an ultrasonic transmitter using a laser source.

  In this case, it is also possible to fix the piezoelectric film on one face of the assembly that is to be controlled and also to dispose the external emitter on this face, facing the film, to control the assembly using ultrasonic surface waves.

  In the invention, it is also possible to implement a reflection ultrasound technique using a single piezoelectric film as an ultrasonic transmitter and receiver.

  In the invention, it is also possible to continuously control an assembly using ultrasound, by means of one or more piezoelectric films, to detect and / or locate the primer or the propagation of defects in assembly.

  The foregoing will now be illustrated by examples with reference to Figs. 1-6.

  Figure 1 is a schematic view of a piezoelectric film 2 which is usable in the invention. This film was cut to have the shape of a rectangle. It is provided with an electrical connector 4 for sending an electrical signal in this film, via an electrical conductor 5, for this film to emit ultrasound, and / or the recovery of a signal provided by the film 2 when the latter is excited by ultrasound.

  Figure 2 is a schematic view of another piezoelectric film 6 which is usable in the invention. This film 6 has been cut to have the shape of a square provided with a circular hole 8 at its center. We still see an electrical connector 10 which is provided with the film 6 and which is extended by an electrical conductor 11.

  Figures 3A and 3B schematically illustrate an assembly according to the invention, provided with piezoelectric films that allow control by ultrasound.

  Figure 3A is a longitudinal sectional view of this assembly while Figure 3B is a top view thereof.

  This assembly comprises three layers, or three plates, 12, 14 and 16, the layer 14 being disposed between the layers 12 and 16 and offset relative thereto, as seen in Figures 3A and 3B.

  This assembly is traversed right through by holes 18 which are regularly distributed in three rows 20, 22 and 24.

  The non-destructive inspection means of this assembly comprise three piezoelectric films 26, 28 and 30. These films are respectively provided with electrical connectors 32, 34 and 36 which are respectively extended by electrical conductors 38, 40 and 42.

  In the example shown, the films 26 and 28 are arranged between the rows of holes 20 and 22 while the film 30 is arranged between the rows 22 and 24.

  In addition, the film 26 is disposed between the layers 12 and 14 while the film 28 is disposed between the layers 14 and 16 and the film 30 is, for its part, disposed between the layers 14 and 16.

  To control this assembly according to the invention, an ultrasonic or acoustic emission control device 44 is used, provided with means 46 for displaying the results of the control.

  Depending on the desired control, this unit can be connected to one, two or three of the films 26, 28 and 30.

  This ultrasonic tester is arranged to send electrical excitation signals to the ultrasound emitter film (s), to recover electrical signals from the ultrasound receiver film (s), to process the signals. signals thus recovered and to provide the results of the control which can then be visualized by the display means 46.

  For example, the apparatus can be connected to the films 26 and 28 and use the film 26 as an ultrasound emitter and the film 28 as the ultrasound receiver to control the portion of the layer 14 that is included between these two films.

  In a variant not shown, these films 26 and 28 can be arranged so that they are spaced apart by more than one layer, for example by fixing the film 26 on the surface of the assembly, by means of a layer of glue not shown, and leaving the film 28 between the layers 14 and 16, so as to control the portion of all of these two layers, which is between the films 26 and 28.

  The film 24 can, for its part, be used as an emitter and ultrasound receiver to control part or all of the assembly, which is opposite this film 24.

  In the case where the apparatus 44 is an acoustic emission apparatus, this apparatus can be connected to one or more films 26, 28, 30 in order to detect and / or locate a primer or a fault propagation in the assembled assembly. under constraints. The films are used as acoustic emission receivers, the acoustic source being the evolution of the defect.

  Figure 4 illustrates another example of transmission control. In this other example, to control an assembly 48, two piezoelectric films 50 and 52 are used and these films are fixed on one and the same face of the assembly 48, respectively by adhesive layers 54 and 56 whose thickness can to be very weak, for example equal to 141E.

  For the control of the assembly 48, another suitable apparatus 58 is used, provided with display means 60. This apparatus makes it possible to excite the film 50 by an electrical signal. This film 50 then emits ultrasound, in particular surface ultrasonic waves which are deduced by the film 52. The latter then provides an electrical signal which is received and processed by the apparatus 58, thus making it possible to control the surface area of the film. assembly between the films 50 and 52.

  In the example of FIG. 5, it is desired to control an assembly 62 which is a stack of three plates 64, 66 and 68. A piezoelectric film 70 is integrated in the assembly 62, between the plates 64 and 66. This film serves of ultrasound receiver.

  For the control of the assembly by means of a suitable apparatus 72 provided with display means 74, an external ultrasonic transmitter 76 is used. This emitter is placed opposite one face of the assembly 62, opposite the film 70, and sends ultrasound towards this film.

  In the example, these ultrasounds are transmitted via the plate 64, which makes it possible to control the latter in the zone opposite which the film 70 is located.

  The ultrasonic transmitter 76 and the assembly 62 may be placed in the water to perform immersion testing. Alternatively, the transmitter 76 may be placed in contact with the assembly 62 to perform a contact check.

  In another variant, the transmitter and the assembly can be separated by air which then serves as coupling means between the transmitter 76 and the assembly 62.

  In the example of FIG. 6, an assembly 78 is controlled by surface ultrasonic waves. A piezoelectric film 80 is fixed to the surface of the assembly 78 by a layer of adhesive 82 whose thickness may be very small, for example equal to 10 m.

  To control the assembly 78, the latter is provided with an external ultrasonic emitter 84 which is placed against the same face as the film 80.

  An appropriate ultrasonic tester 86 with display means 88 is used and the transmitter 84 is excited by electrical signals. This emitter then emits ultrasonic signals, in particular surface ultrasonic waves, and these waves are detected by the film 80.

  The latter then emits electrical signals which are recovered and processed by the apparatus 86, thus allowing control of the assembly in the superficial zone between the emitter 84 and the film 80.

Claims (10)

  1. Assembly of elements, said assembly being provided with means of non-destructive testing of the assembly, characterized in that said non-destructive inspection means comprise one or a plurality of piezoelectric films (26, 28, 30; 52; 70; 80) which are integrated in this assembly, each piezoelectric film being in direct contact with at least one of the elements (12, 14, 16; 64, 66, 68), without any layer, except a possible adhesive layer (54, 56; 82) between this film and this element, each piezoelectric film constituting an ultrasound emitter or an ultrasound receiver or both.   An assembly according to claim 1, wherein each piezoelectric film (26, 28, 30; 50, 52; 70; 80) is PVDF or copolymer type.   3. An assembly according to any one of claims 1 and 2, comprising at least two piezoelectric films, namely first and second piezoelectric films (26, 28, 50, 52) respectively constituting an ultrasound emitter and a piezoelectric receiver. ultrasound.   An assembly according to claim 3, wherein the first and second piezoelectric films (26, 28) are separated by the thickness of at least one of the elements (14) of the assembly.   5. The assembly of claim 3, wherein the first and second piezoelectric films (50, 52) are placed on the same face of the assembly, for the emission and reception of surface ultrasonic waves.   An assembly according to any one of claims 1 and 2, comprising at least one piezoelectric film (70; 80) constituting an ultrasonic receiver, the assembly being provided with an ultrasonic transmitter (76; 84) which is external to this assembly, when one wants to control it.   The assembly of claim 6, wherein the piezoelectric film (70) is disposed in the assembly.   8. An assembly according to claim 6, wherein the piezoelectric film (80) and the ultrasound emitter (84) are placed on the same face of the assembly, for transmitting and receiving waves. ultrasonic surface.   9. An assembly according to any one of claims 1 and 2, comprising at least one piezoelectric film (30), said piezoelectric film constituting both an ultrasonic transmitter and an ultrasonic receiver.   10. An assembly according to any one of claims 1 and 2, comprising at least one piezoelectric film, this or these piezoelectric films constituting acoustic emission receivers.