JP2000287298A - Method and element for acoustic emission detection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable detection of acoustic emission in a wide band and acoustic emission of a high frequency by forming a sensor which receives the acoustic emission by a macromolecular piezoelectric body and detecting the acoustic emission by an electric signal to be obtained from this piezoelectric body. SOLUTION: A sensor 1 is formed by a shield case 2 of a cylindrical shape whose upper face is closed and which has an opening at a lower face, a shield ring 3 of a cylindrical shape, a macromolecular electric film 6 which is virtually circular and to which electrodes 4 and 5 consisting of gold leaves both on the upper and lower sides are stuck respectively, protection films 7 and 8 which are laminated on outer faces of the electrodes 4 and 5, a first lead wire 9, a second lead wire 10, and a transmission cable 11. The transmission cable 11 is combined to an AE signal processor. Thus, an electric signal which can be obtained in accordance with acoustic emission the sensor 1 senses is processed and the acoustic emission is detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for detecting acoustic emission.

[0002]

2. Description of the Related Art Acoustic emission (AE)
Is known as a phenomenon in which energy released due to deformation (including destruction) of a solid propagates as an acoustic pulse. This acoustic pulse may have a high frequency of 10 MHz or more.

For example, “Sensor Technology”, October 1987 (Vol. 7, No. 11), “Principles of Piezoelectric AE Sensors and Application Examples of Ultra-Small Sensors”, or “Measurement Technology” '96 Special Issue 107 -In "Recent Equipment Diagnosis Examples by AE" in Chapter 3 "Equipment Diagnosis Technology and Application Examples" on page 111, a method was developed to grasp the state of the target object by detecting this phenomenon. It is stated that it has been put to practical use and its effects are also considered to have contributed to quality control and have been evaluated.

[0004] On the other hand, as applications have expanded, depending on the acoustic emission to be detected, a sensor having a wide band and / or a high frequency of 20 MHz or more is required, and development of a method for detecting such an acoustic emission has been demanded.

[0005] On the other hand, in a conventional piezoelectric AE sensor developed or put into practical use, its detecting element is made of a ceramic (alumina, PZT, etc.) piezoelectric material, and the upper limit of the detectable frequency is limited. 1MHz to 2M
Hz, which was insufficient to satisfy the above demand.

[0006] Further, as applications have expanded, the surface shape of an object to be detected for acoustic emission has been increasing not only in a flat surface but also in a combination of two or more planes or a curved surface. For example, a sensor having a cylindrical or conical rod-shaped body, or a bowl-shaped convex or concave surface, which can easily cope with an object to be detected is required, and development of a detection element for such an acoustic emission is desired. Began to be.

As described above, the conventional piezoelectric AE sensor is
The detecting element is ceramics (alumina, PZT, etc.)
Since it is made of a piezoelectric material, it is difficult to make the acoustic emission sensing surface of the sensor conform to the curved surface of the object to be detected, which is insufficient to satisfy the above demand.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method and an element for detecting an acoustic emission which solve the above-mentioned conventional problems and satisfy the above-mentioned needs.

[0009]

Means for Solving the Problems The configuration of an acoustic emission detection method according to the present invention for achieving the above object is as follows.

[0010] A polymer piezoelectric film, electrodes provided on both surfaces of the polymer piezoelectric body, lead wires connected to each of these electrodes, and a protective film provided to cover the outer surface of each of the two electrodes. A method for detecting acoustic emission, wherein one of the protective films is made to face an object to be subjected to acoustic emission by using the detection element comprising: and the acoustic emission is detected by the piezoelectric polymer.

According to the present invention, it is possible to detect acoustic emission in a wide band, and it is also possible to detect acoustic emission at a higher frequency than in the prior art.

When the surface of the object to be detected is not a flat surface, in the present invention, the detecting element has a flexible structure as a whole, and the flexibility of the detecting element is utilized by utilizing the flexibility. It is preferable to use in conformity with the surface shape in order to increase the detection accuracy of acoustic emission.

Further, in the present invention, it is preferable that the high-molecular piezoelectric material is a piezoelectric material composed of a copolymer of 65 to 95 mol% of vinylidene fluoride and 35 to 5 mol% of ethylene trifluoride. It is preferable from the viewpoint of increasing the detection accuracy of.

The structure of the acoustic emission detecting element according to the present invention for achieving the above object is as follows.

A polymer piezoelectric film, thin-layer electrodes provided on both sides of the polymer piezoelectric film, lead wires respectively connected to one ends of these electrodes, and an outer surface of each of the two electrodes. A thin protective film provided, and a flexible thin shield member made of a conductive material provided to cover one outer surface of these protective films, and the other of the protective films is made of acoustic emission. An acoustic emission detection element having flexibility as a receiving surface.

According to the present invention, it is possible to detect acoustic emission in a wide band, to detect acoustic emission at a higher frequency than in the prior art, and to further flatten the surface of the object to be detected. Even if it is not a surface, it is possible to detect acoustic emission with high accuracy.

Further, in the present invention, it is preferable that the polymer piezoelectric material is a piezoelectric material composed of a copolymer of 65 to 95 mol% of vinylidene fluoride and 35 to 5 mol% of ethylene trifluoride. It is preferable from the viewpoint of increasing the detection accuracy of.

Incidentally, the piezoelectric material itself made of this copolymer is disclosed in Japanese Patent Publication No. 63-18869.
Also, the piezoelectric body itself consisting of a single crystal film of this copolymer is:
It is disclosed in JP-A-8-36917.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of an acoustic emission detection method and a detection element according to the present invention will be described with reference to the drawings.

FIG. 1 is a longitudinal sectional view of an example of a sensor used to carry out the present invention, and FIG. 2 is a bottom view of the sensor shown in FIG.

1 and 2, a sensor 1 has a cylindrical shield case 2 having a closed upper surface and an opening on a lower surface, a cylindrical shield ring 3, and electrodes 4 and 5 made of gold foil on both upper and lower surfaces. A protective film 7, 8, a first lead wire 9, a second lead wire 10, which are respectively adhered to the outer surfaces of the substantially circular polymer piezoelectric film 6, the electrodes 4, 5,
The transmission cable 11 is formed.

The polymer piezoelectric film 6 includes upper and lower protective films 7,
The protective films 7 and 8 are sealed outside, and the outer peripheral end of the joint is attached to the lower end surface of the shield ring 3. Thus, the opening on the lower surface of the shield case 2 is closed by the polymer piezoelectric film 6.

Shield case 2 and shield ring 3
A communication portion (cable insertion hole or connector mounting hole) 12 with which the transmission cable 11 communicates is provided between the outer peripheral surface of the case 2 and the inner peripheral surface of the ring 3.

An air flow hole 13 penetrating between the outer peripheral surface of the case 2 and the inner peripheral surface of the ring 3 is provided in a part of the shield case 2 and the shield ring 3.

Further, a part of the shield case 2 includes a cavity 1.
4 is bored, and below the cavity 14 is a shield case 2
Is open to the outside at the lower surface thereof, and the upper part thereof is open to the air circulation hole 13. The cavity 14 is a space having a semicircular cross section surrounded by the inner wall of the shield case 2 and the outer wall of the shield ring 3.

The first lead wire 9 has one end joined to the electrode 5, passes through the joint between the protective films 7 and 8, extends from the end into the cavity 14 of the shield case 2, and further has the air circulation hole 1.
3, it enters the lumen 15 of the shield case 2, and is joined to the inner surface of the shield case 2 at the other end.

One end of the second lead wire 10 is connected to the electrode 4.
In the same manner as the first lead wire 9, enters the lumen 15 of the shield case 2, and reaches the communication end 12 of the shield case 2 at the other end, and directly or via a connector from the coaxial cable. The transmission cable 11 is connected to a signal line. The shield case 2 and the ground line of the transmission cable 11 are connected by a connection line 16.

This transmission cable 11 is coupled to a known AE signal processor (not shown),
An electric signal obtained in accordance with the acoustic emission sensed by the sensor 1 is processed, and the acoustic emission is detected.

In the embodiment shown in FIG. 1, the polymer piezoelectric film 6
This is driven in the λ / 2 mode. Although not shown, an appropriate absorbing material or a reflecting plate is located on the back surface of the polymer piezoelectric film 6 so that the polymer piezoelectric film 6 has a λ /
It is also possible to drive in four modes.

FIG. 3 is a longitudinal sectional view of an example of a sensor used to carry out the present invention, and FIG. 4 is a top view of the sensor shown in FIG.

3 and 4, the sensor 21 has a lower electrode 23 made of a gold foil adhered to the lower surface of a substantially circular polymer piezoelectric film 22, and a lower thin electrode formed on the lower surface of the electrode 23. A protective film 24 is adhered, an upper thin-layer electrode 25 made of gold foil is adhered on the upper surface of the polymer piezoelectric film 22, and an upper thin-layer protective film 26 is adhered on the upper surface of the electrode 25. A flexible thin shield member 27 made of a conductive material is provided so as to cover the upper surface of the upper thin protective film 26, and a first lead wire 28 is coupled to one end of the lower electrode 23; A second lead wire 29 is connected to one end of the upper electrode 25.
Are formed by bonding.

The first lead 28 and the second lead 29 are coupled to a known AE signal processor (not shown), so that they are obtained according to the acoustic emission detected by the sensor 21. The electrical signal is processed and acoustic emission is detected.

In the sensor 21 having this structure, the total thickness of the polymer piezoelectric film 22, the lower and upper electrodes 23 and 25, and the lower and upper protective films 24 and 26
It can be designed to be 0.5 mm or less.

The flexible thin shield member 27 made of a conductive material is formed of a thin metal wire, for example, a thin tin-plated copper wire having a wire diameter of about 0.05 mm to 0.5 mm. A flexible mesh type sheet made of a knitted fabric, a woven fabric, or a nonwoven fabric is preferably used.

According to this structure, since the sensor 21 has flexibility as a whole, even if the surface of the object to be detected is not flat, the sensor 21 can take advantage of this flexibility.
Can be positioned along the surface of the object to be detected.

In conventional acoustic emission detection using a ceramic piezoelectric body, this is difficult except when the ceramic piezoelectric body is previously formed in accordance with the surface shape of the object to be detected. Was.

[0037]

EXAMPLES Next, examples of the method for detecting acoustic emission according to the present invention and comparative examples will be described.

Example A sensor 1 having the same structure as the sensor 1 shown in FIG. 1 was manufactured based on the following requirements.

The shield case 2 is made of brass, has an outer diameter of 22 mm, a height from the lower surface to the upper surface of 10 mm, an inner diameter of 16 mm, and a height of the inner cavity 15 of 8 mm.
2, an air flow hole 13 and a cavity 14 are provided.

The shield ring 3 is made of brass, has an outer diameter of 16 mm, an inner diameter of 15 mm, and a height of 8 mm, and is provided with a connecting portion 12 and an air flow hole 13.

Polymer piezoelectric film 6: polyvinylidene fluoride 8
Eight 60 μm-thick polymer piezoelectric films formed of a copolymer of 0 mol% and 20 mol% of ethylene trifluoride are laminated via an adhesive (epoxy resin), and are laminated on the upper and lower surfaces thereof. And electrodes 4 and 5 made of gold each having a thickness of 1000 angstroms. The diameter of the polymer piezoelectric film 6 was 12.4 mm. By reducing the number of laminated polymer piezoelectric films, an AE sensor capable of detecting a high frequency of 20 MHz or more can be manufactured.

Protective films 7, 8: A polyimide film having a thickness of 12.50 μm. The protective films 7 and 8 were attached to the outer surfaces of the electrodes 4 and 5, respectively. The outer diameter of these protective films 7 and 8 was substantially the same as the outer diameter of the shield ring 3 of 16 mm. The outer peripheral portion where the protective films 7 and 8 were joined and integrated was joined to the lower end surface of the shield ring 3 via an adhesive (epoxy resin).

Transmission cable 11: 1 m long and 2.2 diameter
mm, 50Ω series coaxial cable was used, one end was electrically connected to the first lead wire 9 and the second lead wire 10, and the other end was fitted with a connector (not shown).

A frequency response analyzer (Frequency Response A)
nalyzer) (5090FRA) is used, and the sensor 1 is mounted on the reference device of the analyzer so that the polymer piezoelectric film 6 side of the sensor 1 is in contact with the upper surface of the reference device, and the reference device is driven. The signal output from the sensor 1 was recorded.

The recorded result is shown in the chart of FIG.

Here, in the case of a conventional AE sensor using a ceramic piezoelectric body, the sensor is mounted on the upper surface of a reference device,
Unless it is firmly attached using a magnet or a strong adhesive, accurate vibration transmission cannot be achieved. However, an AE using the polymer piezoelectric substance according to the present invention
In the case of a sensor, the sensor can be used as an appropriately driven AE sensor simply by placing the sensor on the top of the standard and simply holding it with an adhesive tape (gum tape).
This is an advantage not seen in the AE sensor using the conventional ceramic piezoelectric material. Further, in the case of the AE sensor using the polymer piezoelectric substance according to the present invention, the AE sensor itself is much more flexible than the conventional ceramic piezoelectric substance. By interposing the acoustic couplant, it is possible to reduce the contact pressure on the acoustic transmission surface.

Comparative Example An AE sensor (AE) in which a piezoelectric material generally commercially available as a broadband type is made of ceramics
-900F2) was used, and the signal output from this sensor was recorded in the same manner as in the example.

The recorded result is shown in the chart of FIG.

From the comparison of the respective waveforms in the charts of FIGS. 5 and 6, according to the method for detecting acoustic emission according to the present invention, an acoustic emission having a flat waveform over an extremely wide band, which cannot be achieved by the prior art. Can be detected.

[0050]

According to the present invention, it is possible to detect an acoustic emission having a flat waveform over an extremely wide band, which cannot be achieved by the prior art. Also, by selecting the thickness of the polymer piezoelectric body, by selecting the number of laminated films,
It is possible to detect the acoustic emission in a high frequency range of 20 MHz or more after the preparation. Also, the detection element is
Since it has flexibility as a whole, even when the surface of the object to be detected is not a flat surface, the detection element can be mounted along the surface, so that the detection accuracy of acoustic emission is guaranteed.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an example of a sensor made of a polymer piezoelectric material that is preferably used in an acoustic emission detection method according to the present invention.

FIG. 2 is a bottom view of the sensor shown in FIG. 1;

FIG. 3 is a longitudinal sectional view of an example of a flexible acoustic emission detection element according to the present invention.

FIG. 4 is a top view of the sensor shown in FIG. 3;

FIG. 5 is a chart showing characteristics of a sensor according to the embodiment.

FIG. 6 is a chart showing characteristics of a sensor according to the embodiment.

[Explanation of symbols]

 1: Sensor 2: Shield Case 3: Shield Ring 4: Electrode 5: Electrode 6: Polymer Piezoelectric Film 7: Protective Film 8: Protective Film 9: First Lead Wire 10: Second Lead Wire 11: Transmission Cable 12 : Connection part 13: Air flow hole 14: Cavity 15: Lumen 16: Connection line 21: Sensor 22: Polymer piezoelectric film 23: Lower thin layer electrode 24: Lower thin layer protective film 25: Upper thin layer electrode 26: Upper Thin protective film 27: Thin shield member 28: First lead wire 29: Second lead wire

Claims (5)

[Claims] 1. A polymer piezoelectric film, electrodes provided on both surfaces of the polymer piezoelectric body, lead wires connected to each of these electrodes, and an outer surface of each of the two electrodes. A method for detecting acoustic emission, wherein a detection element comprising a protective film is used, one of the protective films is opposed to a target to be subjected to acoustic emission, and the acoustic emission is detected by the polymer piezoelectric material. 2. The detection device according to claim 1, wherein the detection element has flexibility as a whole, and the detection element is used along the surface shape of the object to be detected by utilizing the flexibility. Acoustic emission detection method. 3. The acoustic material according to claim 1, wherein the polymer piezoelectric material is a piezoelectric material comprising a copolymer of 65 to 95 mol% of vinylidene fluoride and 35 to 5 mol% of ethylene trifluoride. Emission detection method. 4. A polymer piezoelectric film, thin-layer electrodes provided on both surfaces of the polymer piezoelectric film, lead wires respectively connected to one ends of these electrodes, and an outer surface of each of the two electrodes. A thin protective film provided over the protective film and a flexible thin shield member made of a conductive material provided over one outer surface of the protective film. Acoustic emission detection element having flexibility as a receiving surface of an application. 5. The acoustic emission according to claim 4, wherein the polymer piezoelectric film is a piezoelectric film made of a copolymer of 65 to 95 mol% of vinylidene fluoride and 35 to 5 mol% of ethylene trifluoride. Detection element.