JPH0812180B2 - Acoustic emission sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention is directed to acoustic emission (Acoust).
ic emission) for an acoustic emission sensor.

[Conventional technology]

When a solid is destroyed or plastically deformed, the energy stored as internal strain is released as elastic waves (sound waves and ultrasonic waves). This phenomenon is called acoustic emission (hereinafter abbreviated as AE). , The elastic wave is called AE wave. Then, by observing this AE wave while applying a load to the material, a method of supplementing the precursor of the occurrence of damage or destruction of the material,
The so-called AE method has been applied to material fatigue tests and material research, as described in Iron and Steel Handbook, 3rd edition, Vol. IV, page 468.

A piezoelectric element as an ultrasonic receiving element is usually used in an AE sensor for detecting AE waves.
As disclosed in Japanese Unexamined Patent Publication No. 890, the contact portion between the piezoelectric element and the subject is made of an electrically insulating material, and the piezoelectric elements are stacked in two stages. A balanced AE sensor has been proposed in which a phase difference is less likely to occur between AE signals detected by a piezoelectric element.

[Problems to be Solved by the Invention] When ultrasonic waves propagate in an object, longitudinal waves propagate faster than transverse waves. Therefore, if only the longitudinal wave in the AE wave is detected, it is possible to faithfully detect the change in the AE generation intensity in the AE generation source, but in the above conventional configuration, not only the longitudinal wave but also the transverse wave is detected. Have a point.

Therefore, in order to detect only the longitudinal wave (longitudinal vibration mode) in the AE wave, a prismatic ceramic piezoelectric body is polarized in the height direction, and a synthetic resin-ceramic composite piezoelectric element arrayed in a synthetic resin matrix is used. It can be used for AE sensor. However, since the ceramic piezoelectric element with high detection sensitivity for AE waves has a combined vibration mode of longitudinal vibration and lateral vibration, it is affected by lateral vibration, and this effect is affected by the angle at which AE is received (incident angle). It was difficult to detect only the longitudinal vibration because of the overlap.

[Means for solving the problem]

In order to solve the above-mentioned problems, the acoustic emission sensor of the present invention has a plurality of cylindrical ceramic piezoelectric bodies that are polarized in the axial direction and are placed in a synthetic resin matrix so that their axial directions are substantially parallel to each other. It is characterized in that an array of synthetic resin-ceramics composite piezoelectric elements is provided.

[Action]

According to the above configuration, a synthetic resin-ceramic composite piezoelectric element is provided in which a plurality of cylindrical ceramics piezoelectric bodies that are polarized in the axial direction are arranged in a synthetic resin matrix so that their axial directions are substantially parallel to each other. Therefore, the transverse vibration mode is damped, and in the AE wave propagating in the axial direction, the synthetic resin-ceramic composite piezoelectric element produces a potential difference on both end faces only for the longitudinal vibration mode. For this reason,
Only the longitudinal vibration mode is detected. In addition, since the cylindrical ceramic piezoelectric body has no radial anisotropy, the axial vibration induced by the AE wave is dissipated by the synthetic resin damper. Therefore, the lateral vibration mode does not occur as a voltage.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

The acoustic emission sensor (hereinafter abbreviated as AE sensor) of the present invention, as shown in FIG.
The wave receiving plate 2 for receiving the AE wave from the subject, a synthetic resin-ceramic composite piezoelectric element 7 provided on the wave receiving plate 3 for converting the AE wave into an electric signal, and a metal ring 8 are mainly constituted.

As shown in the longitudinal sectional view of FIG. 1 and the transverse sectional view of FIG. 2, the synthetic resin-ceramics composite piezoelectric element 7 has cylindrical ceramic piezoelectric bodies 1 ... Array in the synthetic resin matrix 2
The electrodes 4 and 5 are provided on both end faces thereof, and the electrode 5 at the lower end covers about half the side surface of the synthetic resin matrix 2. In each of the cylindrical ceramic piezoelectric bodies 1, the crystal axes of the piezoelectric crystal grains are arranged in the height direction (first
It is oriented in the vertical direction in the figure) and polarized in that direction.

The wave receiving plate 3 is fixed to the electrode 5 at the lower end of the synthetic resin-ceramic composite piezoelectric element 7 with an adhesive.
Further, the metal binder 8 is fitted in close contact so as to be electrically connected to the side surface portion of the electrode 5. A pair of lead wires 6 for extracting the AE signal are soldered to the metal ring 8 and the electrode 4 as shown in FIG.

In the above configuration, when the wave receiving plate 3 is brought into close contact with the surface of the subject, the AE wave generated inside the subject propagates in the subject and reaches the surface, and passes through the wave receiving plate 3 and the electrode 5. Is transmitted to the synthetic resin-ceramics composite piezoelectric element 7, and the cylindrical ceramics piezoelectric body 1 expands and contracts in the height direction. Then, due to this expansion and contraction, a potential difference is generated at both ends of the cylindrical ceramic piezoelectric body 1, and this results in the lead wire 6 as an AE signal.
Taken out from 6.

In the AE sensor of the present invention, the cylindrical ceramic piezoelectric body 1 has a structure in which the crystal axis is oriented in the height direction and is polarized in that direction, so that only when it is expanded and contracted in the height direction, Positive and negative charges are generated, but even if expanded and contracted in other directions, for example, in a direction orthogonal to the height direction, no charges are generated at both ends thereof. That is, only the longitudinal vibration component is detected in the AE wave reaching the surface from the inside of the subject.

As a result, longitudinal waves and transverse waves caused by AE that are temporally and spatially different have different propagation velocities, so even if they arrive at the AE sensor at the same time, only the longitudinal waves are detected and generated inside the subject. The intensity of AE and its change can be detected faithfully.

By the way, the potential difference generated between the electrodes 4 and 5 of the synthetic resin-ceramic composite piezoelectric element 7 by the AE wave is unique to the material and shape of the cylindrical ceramic piezoelectric body 1. Therefore, in a preliminary experiment, ultrasonic waves of known intensity are received, and at that time, the electrodes 4 and 5 are received.
If the relationship of the potential difference that occurs between the electrodes is obtained, the intensity of the AE wave can be calculated from the measured potential difference between the electrodes 4 and 5 using this relationship.

Further, since the cylindrical ceramic piezoelectric body 1 forming the synthetic resin-ceramic composite piezoelectric element 7 has no radial anisotropy, the axial vibration induced by the AE wave is different from that in the prismatic case. And is easily combined with the radial synthetic resin and dissipated. Therefore, the vertical vibration component is detected.

As the material of the cylindrical piezoelectric ceramic body 1, specifically, for example, a barium titanate sintered body, a lead titanate sintered body, a PZT (lead zirconate titanate) sintered body, or the like can be used. Although it is preferable in terms of AE detection sensitivity, any material can be used as long as it has piezoelectric characteristics and is polarized in the height direction. Further, it is preferable that the shape is a columnar shape, and the ratio of the height to the length of one side of the bottom surface is 2 or more from the viewpoint of AE detection sensitivity. It is more preferable to have. In addition, the elastic modulus of the ceramic piezoelectric body 1 is preferably 6000 kgf / mm ² or more in terms of AE detection sensitivity.

Any synthetic resin may be used as the synthetic resin matrix 2 as long as it can be combined with and integrated with the cylindrical ceramic piezoelectric body 1. Specifically, for example, silicone rubber, urethane rubber, butadiene rubber, nitrile rubber, ethylene-propylene rubber, chloroprene rubber, fluororubber, ethylene-acrylic rubber, polyester elastomer, epichlorohydrin rubber, acrylic rubber, or chlorinated ethylene rubber is used. However, it is preferable to use silicone rubber, urethane rubber, or butadiene rubber for damping lateral vibration. The elastic modulus of the synthetic resin is 1 to 50 kgf / mm ² , and it is preferable to match the acoustic impedance in terms of damping.

Further, in the synthetic resin-ceramics composite piezoelectric element 7, the ratio of the total volume of the columnar ceramics piezoelectric bodies 1 ... to the volume of the synthetic resin matrix 2 is in the range of 8/92 to 40/60. It is preferable in terms of detection sensitivity.

Hereinafter, a urethane rubber-PZT (lead zirconate titanate) composite piezoelectric element will be given as a specific example of the synthetic resin-ceramics composite piezoelectric element 7, and its manufacturing method and the performance of an AE sensor using the same will be described.

As a material for the cylindrical piezoelectric ceramic body 1, a cylindrical (φ10 mm × 10 mm) polarized PZT sintered body (manufactured by Honda Electronics Co., Ltd., model number HC-50GS) is used, and processed into φ1 mm.
Cylinders of × 5mm are placed on a PZT disk with a thickness of 5mm at a pitch of 1.5mm.
An upright PZT microfabricated product with 32 regular arrangements was obtained. For the above processing, an ultrasonic processing device (made by JEOL Ltd.) equipped with a tool made of S45C (structural carbon steel)
Was used.

The PZT microfabricated product thus obtained was fitted into a silicon mold, and the synthetic resin matrix 2 was placed in the mold.
Filled with urethane rubber for electrical insulation as a material of (San-yu-Resin Co., trade name SU-2153-9, hardness 52, black),
After left at room temperature for 1 day, the urethane rubber was cured at 60 ° C for 5 hours in a dryer to cure the urethane rubber, and the urethane rubber-PZT was formed on the PZT disk by taking it out from the mold. A urethane rubber-PZT composite was prepared.

Next, the PZT disk portion of the urethane rubber-PZT composite was cut off with a diamond blade (Malteau crystal cutter) to form a urethane rubber matrix,
32 cylinders of φ1 mm × 4 mm made of PZT are regularly arranged to prepare urethane rubber-PZT composite piezoelectric body,
Both end faces were polished with sandpaper.

Then, silver paste (manufactured by Degussa Co., trade name DEMETRON 629) is provided on one end face and the side face close to the other end face.
0-0275) was applied and baking treatment was carried out at 120 ° C. for 30 minutes to form the electrode 4 as a silver electrode and the side surface portion of the electrode 5. Further, a gold electrode as an end face portion of the electrode 5 was formed on the remaining end face portion by a sputtering method so as to be electrically connected to the silver electrode on the side face portion. And
On this gold electrode surface, a 0.2 mm-thick alumina thin plate (made by Mitsubishi Mining Cement Co., model number MAB-L201K-10 as the wave-receiving plate 3) was used.
φ) was adhered with an adhesive.

Then, a metal ring 8 made of copper with a diameter of 10 mm x 3 mm is closely fitted to the side surface of the electrode 5, and the electrode 4 and the metal ring 8 are attached.
Lead wire 6 is soldered to the urethane rubber-PZT
An AE sensor using a composite piezoelectric element was obtained.

The piezoelectric constant was measured in order to investigate the piezoelectric characteristics of this AE sensor. For comparison, a comparative AE sensor in which the 32 PZTs have a prismatic shape (1 mm × 1 mm × 4 mm) was prepared by using the same material and manufacturing method as above, and the piezoelectric constants thereof were also measured. For the measurement, an impedance meter (Yokogawa Hewlett-Packard, Model No. 4194A) was used to measure the resonance characteristic, and the piezoelectric constant was determined from this.

Also, in order to confirm the response of the AE sensor, φ0.5mm
The pencil replacement core (hardness H) was crushed to generate a pseudo AE wave, which was received by the AE sensor and the rising time thereof was measured. At this time, the detection sensitivity and the mechanical quality factor Q _M were also measured. For comparison, the rise time of the pseudo AE wave in the comparative AE sensor was also measured. For this measurement, 400 mm × 400 mm × as a transmission medium
A 60 mm aluminum plate was used to detect a pseudo AE wave with an AE sensor. For detection and recording of AE signals, digital storage oscilloscope (manufactured by Hewlett Packard, model number HP-54201D / printer: 6bit / 2
00MHz) was used, and a 1m long coaxial cable (5D2V equivalent) was used for connection with the AE sensor.

As a result, as shown in Table 1, the AE sensor of the present invention using the cylindrical ceramic piezoelectric body 1 has a mechanical quality factor Q _M that is higher than that of the rectangular piezoelectric ceramic body 1. Is 1/3. This indicates that the reverberant sound within the synthetic resin-ceramic composite piezoelectric element 7 is rapidly attenuated, and the AE signal separation characteristic is clearly improved. Moreover, piezoelectric constant g ₃₃ , rise time (time from the start of receiving the pseudo AE wave to the peak)
Also, the AE detection sensitivity has almost the same characteristics as the comparative AE sensor. That is, the AE sensor of the present invention can improve the AE signal separation characteristic without lowering the AE detection sensitivity.

Further, in the AE sensor of the present invention, since the synthetic resin-ceramics composite piezoelectric element 7 having excellent piezoelectric characteristics is used, it is small and has high detection sensitivity. Further, instead of directly connecting the lead wire 6 to the electrode 5 on the wave receiving plate 3 side, the metal ring 8
The lead wire 6 can be connected easily and surely.

Further, the AE sensor of the present invention can be used not only for detecting not only AE waves but also all elastic waves propagating in gas, liquid, solid, and conversely, by applying an AC voltage from the outside, It can also generate waves.

〔The invention's effect〕

As described above, the acoustic emission sensor of the present invention is a synthetic resin in which a plurality of cylindrical ceramic piezoelectric bodies that are polarized in the axial direction are arranged in a synthetic resin matrix so that their axial directions are substantially parallel to each other. -Because the ceramic composite piezoelectric element is provided, a potential difference is generated at both end surfaces of the synthetic resin-ceramic composite piezoelectric element only for the longitudinal vibration component in the AE wave propagating in the axial direction. Therefore, only the vertical vibration component is detected. As a result, it is possible to obtain an acoustic emission sensor having high detection sensitivity and excellent AE signal separation characteristics.

[Brief description of drawings]

1 to 3 show an embodiment of the present invention. FIG. 1 is a vertical sectional view of an acoustic emission sensor according to the present invention. FIG. 2 is a cross-sectional view of the acoustic emission sensor according to the present invention. FIG. 3 is a front view of the acoustic emission sensor according to the present invention. 1 is a ceramic piezoelectric body, 2 is a synthetic resin matrix,
3 is a wave receiving plate, 4 and 5 are electrodes, 6 is a lead wire, 7 is a synthetic resin-ceramic composite piezoelectric element, and 8 is a metal ring.

Claims (1)

[Claims] 1. A synthetic resin-ceramic composite piezoelectric element comprising a plurality of cylindrical ceramics piezoelectric bodies which are polarized in the axial direction and arranged in a synthetic resin matrix so that their axial directions are substantially parallel to each other. Acoustic emission sensor characterized by being