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DESCRIPTION JPH09107599

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DESCRIPTION JPH09107599
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
acoustic emission sensor for detecting acoustic emission and a method of manufacturing the
same.
[0002]
2. Description of the Related Art When a solid breaks or plastically deforms, it releases energy
stored as internal strain as elastic waves (sound and ultrasonic waves). This phenomenon is
called acoustic emission (hereinafter referred to as AE), and the elastic wave is called an AE wave.
[0003]
A method to supplement the precursor of the occurrence of flaws or destruction in the material
by observing AE waves while applying a load to the material, the so-called AE method, “Steel
and Steel Handbook” 3rd Edition, Volume IV, p. 468 As described in, it is applied to fatigue
testing and material research of materials.
[0004]
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An AE sensor that converts an AE wave into an electrical signal is used to detect the AE wave.
An AE sensor using a piezoelectric body is compact and has high sensitivity. For this reason, it is
possible to measure AE waves not only in the laboratory but also at the site where a reactor or
the like is installed.
[0005]
However, with the AE sensor using the above-mentioned piezoelectric material, it is difficult to
detect the displacement of the surface of the object due to the AE wave, even if the occurrence
frequency of the AE wave can be detected, There is a problem that the cause of destruction can
not be analyzed.
[0006]
That is, in the case of an AE sensor using a conventional high sensitivity converter, as shown in
FIG. 7, resonance occurs, so the AE signal becomes a vibration waveform, and the arrival time of
the longitudinal wave can not be measured accurately (in FIG. , P, S indicate the longitudinal and
transverse waves of the AE wave, respectively, and PP and PPP indicate the reflected waves of
the longitudinal wave P).
[0007]
If a condenser type AE sensor (capacitance type converter) is used, the arrival time of the
longitudinal wave can be accurately measured as shown in FIG.
That is, displacement of the surface of the subject due to the AE wave can be accurately detected.
However, the condenser type AE sensor is large, difficult to attach to a subject, and has low
sensitivity, which makes it difficult to measure AE waves in the field.
[0008]
As an AE sensor for solving this problem, Japanese Patent Laid-Open No. 6-341976 is formed on
a columnar piezoelectric body having a substantially conical depression, a bottom of the
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2
columnar piezoelectric body, and a conical surface of a conical depression. An AE sensor is
disclosed which comprises an electrode and a damping material closely fitted in a conical recess.
[0009]
According to this, since the AE wave incident from the bottom of the columnar piezoelectric body
passes through the piezoelectric body and then enters the damping material, the AE wave is
attenuated without being resonated by the piezoelectric body.
Therefore, it is possible to detect the displacement of the surface of the subject due to the AE
wave. Moreover, since the piezoelectric body is used, it is compact and has high sensitivity, and is
easily attached to the subject.
[0010]
However, since it is difficult to closely fit the damping material into the conical depression
provided in the piezoelectric body, it causes a new problem that it is difficult to manufacture an
AE sensor having flat frequency characteristics. .
[0011]
According to the acoustic emission sensor of the first aspect of the present invention, in order to
solve the above problems, a columnar piezoelectric body having a recess and a piezoelectric
member directly cast in the recess of the piezoelectric body are used. And a damping material
closely coupled to the
[0012]
According to the above configuration, since the damping material is in close contact with the
depression of the piezoelectric body, an acoustic emission sensor having flat frequency
characteristics can be easily obtained.
[0013]
In the method of manufacturing an acoustic emission sensor according to the second aspect of
the present invention, in order to solve the above problems, after setting a columnar piezoelectric
body having a recess in a mold, the material of the damping material is melted and the mold is In
this case, the damping material having a predetermined shape is directly formed in the
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depression of the piezoelectric body by injecting the
[0014]
According to the above configuration, even if there is a slight processing error in the
piezoelectric body, it is possible to easily form a damping material that is in close contact with
the recess of the piezoelectric body and has a predetermined shape.
Thereby, an acoustic emission sensor having flat frequency characteristics can be efficiently
manufactured.
[0015]
DESCRIPTION OF THE EMBODIMENTS The following will explain one embodiment of the present
invention in reference to FIGS. 1 to 3. FIG.
[0016]
As shown in FIGS. 1 and 2, the AE sensor according to the present embodiment has a columnar
piezoelectric body 1 having a substantially conical (actually a truncated conical) depression, a
bottom of the piezoelectric body 1, and a conical depression. An electrode (not shown) formed on
the conical surface of the first surface, a damping material 2 directly cast in the conical recess
and in close contact with the piezoelectric body 1, and an alumina plate adhered to the electrode
on the bottom side of the piezoelectric body 1 It consists of three.
[0017]
Lead wires 4a and 4b for AE signal output are connected to the upper and lower electrodes of the
piezoelectric body 1, respectively.
If the damping material 2 has electrical conductivity, it is not necessary to form an electrode in
the conical recess, and the lead wire 4a may be connected to the top of the damping material 2
as shown in the figure.
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[0018]
Next, a method of directly casting the damping material 2 in the depression of the piezoelectric
body 1 will be described based on FIGS. 3 (a) to 3 (h).
[0019]
First, as shown in FIG. 3A, a gypsum mold 11 (mold) having a cavity 12 a in the shape of the
damping material 2 is prepared.
At the bottom of the cavity 12a, a recess 12b in which the piezoelectric body 1 can be fitted is
formed.
[0020]
The piezoelectric body 1 is fitted into the recess 12b (FIG. 6 (b)).
Then, the melted material of the damping material 2 is injected into the cavity 12a (FIG. 6C).
At this time, the depression of the piezoelectric body 1 is filled with the melting material without
any gap.
Then, the molten material is cooled and solidified (the same figure (d)).
After the material of the damping material 2 is sufficiently cured, it is demolded (FIG. 3E). And
the unnecessary part of the material of the damping material 2 is cut (the figure (f)), and a cut
surface is polished with a polish board (the figure (g)). Thereby, the damping material 2 directly
cast in the depression of the piezoelectric body 1 is obtained. Thereafter, the alumina plate 3 is
attached to the bottom of the piezoelectric body 1 with an adhesive to complete the AE sensor
(FIG. 6H).
[0021]
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In the AE sensor manufactured in this manner, since the molten material is injected using a mold
such as gypsum mold 11 or the like, the damping which is in close contact with the recess of the
piezoelectric body 1 more than before and which has a predetermined shape The material 2 can
be easily formed. This makes it possible to efficiently manufacture an AE sensor having a flat
frequency characteristic than that of the prior art.
[0022]
As the damping material 2, a metal such as silver, lead, tin or an alloy of these is suitable. In
particular, a low melting point alloy such as solder having a melting point of 250 ° C. or less
hardly degrades the piezoelectric performance of the piezoelectric body 1 at the time of casting
of the damping material 2 and is easy to cast. It is.
[0023]
DESCRIPTION OF THE PREFERRED EMBODIMENTS The following description will explain an
embodiment of the present invention, while referring to FIGS.
[0024]
Specifically, the piezoelectric body 1 for AE sensor is made of, for example, cylindrical PZT (lead
zirconate titanate) having a diameter of 3 mm and a height of 3 mm, and the upper bottom
diameter is 2 mm and the lower bottom diameter is 1 mm, It has an inverted truncated coneshaped depression with a height of 2.8 mm.
The cylindrical axis of the piezoelectric body 1 substantially coincides with the axis of the
inverted truncated cone.
[0025]
Furthermore, in the wall portion surrounding the depression, there are formed in the four places
(axial direction: depth 2.8 mm, width 0.2 mm) radially extending slit-like grooves having
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substantially the same depth as the depression (axial direction) When seen from the cross, the
groove is formed). Thereby, unnecessary radial vibration in the piezoelectric body 1 can be
prevented. In addition, this groove also has a secondary effect of preventing cracking of the
piezoelectric body 1 when the damping material 2 is cast.
[0026]
Specifically, the damping material 2 is made of, for example, a solder containing about 60% tin
and about 40% lead as a main component and a small amount of silver added, and the height
measured from the connection with PZT is 14.5 mm It is in the shape of an inverted cone
(diameter of the end face is 20 mm).
[0027]
The frequency characteristics obtained by the above-mentioned AE sensor are shown in FIG.
Further, for comparison, the frequency characteristics obtained by the AE sensor for comparison
are shown in FIG. The AE sensor for comparison is a piezoelectric material made of the same PZT
as the above, with the damping material obtained by processing the metal to a diameter of 20
mm, a height of 14.5 mm, a tip height of 2.8 mm, and a tip diameter of 1 mm Manufactured by
fitting into body 1.
[0028]
Although resonance peaks are observed around 200 kHz and 700 kHz in the spectrum of the AE
sensor for comparison, no noticeable resonance peak is seen in the spectrum of the AE sensor of
this example, and the spectrum is almost flat up to 1 MHz. For this reason, the AE sensor of the
present embodiment can detect displacement of the surface of the object due to the AE wave
more accurately than in the related art.
[0029]
In order to confirm this, a pencil core of φ 0.5 mm and HB was crushed to generate a pseudo AE
wave, which was received by the above AE sensor.
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[0030]
The measurement system observes the signals obtained by the aluminum plate (aluminum alloy
2034, size 600 mm × 600 mm × 60 mm) as a transmission medium, the above-mentioned AE
sensor closely attached to the surface of the aluminum plate with vacuum grease, and the AE
sensor And a personal computer (PC-9801VX, manufactured by NEC Corporation) that controls
the digital oscilloscope and records data obtained by the digital oscilloscope 8.
[0031]
The AE sensor and the digital oscilloscope are directly connected by a 1.5 m cable, and the digital
oscilloscope and the personal computer are connected by a GP-IB (general-purpose interface
bus).
[0032]
In the above configuration, the pencil core was compressed on the back surface of the aluminum
plate to generate a pseudo AE wave, and the pseudo AE wave was received by an AE sensor
attached to the surface of the aluminum plate.
[0033]
The waveform obtained by setting the trigger mode of the digital oscilloscope to single shot is
shown in FIG.
[0034]
In the AE sensor of the present embodiment, the pseudo AE wave incident from the bottom
surface of the piezoelectric body 1 passes through the piezoelectric body 1 and then enters the
damping material 2 and is attenuated without being resonated by the piezoelectric body 1.
Therefore, in the vicinity of the time when the longitudinal wave P reaches the surface of the
aluminum plate, a waveform substantially similar to the waveform obtained by the conventional
condenser type AE sensor (see FIG. 8 shown in the prior art) is obtained.
That is, the displacement of the surface of the aluminum plate due to the pseudo-AE wave (in
particular, the longitudinal wave P) can be accurately detected.
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[0035]
Moreover, since the AE sensor of the present embodiment uses the piezoelectric body 1, it is
compact and has high sensitivity, and is easy to attach to the subject.
In addition, because of high sensitivity, it is possible to omit a preamplifier that is required for a
condenser type AE sensor.
[0036]
As described above, the acoustic emission sensor according to the first aspect of the present
invention comprises: a columnar piezoelectric body having a recess; and a damping material
which is directly cast in the recess of the piezoelectric body and closely coupled to the
piezoelectric body. It is the composition which consists of.
[0037]
According to this, since the damping material is in close contact with the depression of the
piezoelectric body, it is possible to easily obtain an acoustic emission sensor having flat
frequency characteristics.
[0038]
In the method of manufacturing an acoustic emission sensor according to the second aspect of
the present invention, as described above, after the columnar piezoelectric body having a recess
is set in the mold, the material of the damping material is melted and injected into the mold.
Thus, the damping material having a predetermined shape is directly formed in the depression of
the piezoelectric body.
[0039]
According to this, even if there is a slight processing error in the piezoelectric body, it is possible
to easily form a damping material that is in close contact with the depression of the piezoelectric
body and has a predetermined shape.
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Therefore, there is an effect that an acoustic emission sensor having flat frequency
characteristics can be efficiently manufactured.
[0040]
Brief description of the drawings
[0041]
1 is a front view showing a configuration of an AE sensor according to an embodiment of the
present invention.
[0042]
2 is a longitudinal sectional view of the AE sensor of FIG.
[0043]
3 is an explanatory view showing a manufacturing method of the AE sensor of FIG. 1, (a) to (h) is
an explanatory view showing each process.
[0044]
4 is a spectrum diagram showing an embodiment of the present invention, showing the
frequency characteristics of the AE sensor.
[0045]
5 is a spectrum diagram showing the frequency characteristics of the AE sensor for comparison.
[0046]
6 is a waveform diagram obtained when the pseudo AE wave is received by the AE sensor
according to the present invention.
[0047]
7 is a signal waveform diagram obtained when the pseudo AE wave is received by the AE sensor
using the conventional high sensitivity converter.
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[0048]
8 is a signal waveform diagram obtained when the pseudo AE wave is received by the AE sensor
using the conventional capacitive transducer.
[0049]
Explanation of sign
[0050]
Reference Signs List 1 piezoelectric body 2 damping material 3 alumina plate 4a lead wire 4b
lead wire 11 plaster mold (mold) 12a cavity
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