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JPH06341976

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DESCRIPTION JPH06341976
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
acoustic emission sensor for detecting an acoustic emission.
[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. As described in, it is applied to fatigue testing
and material research of materials.
[0004]
An AE sensor that converts an AE wave into an electrical signal is used to detect the AE wave.
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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]
If a condenser type AE sensor (capacitance type converter) is used, as shown in FIG. 5, it is
possible to accurately detect the displacement of the surface of the subject due to the AE wave
(in the figure, P and S respectively represent the vertical length of the AE wave (Waves indicate
transverse waves, PP and PPP indicate reflected waves of longitudinal waves P).
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.
[0007]
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an acoustic
emission sensor according to the present invention comprises a pillar-shaped piezoelectric body
having a substantially conical depression, and a bottom surface and a conical shape of the pillarshaped piezoelectric body. And a damping material closely fitted in the conical recess.
[0008]
According to the above configuration, 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.
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2
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.
[0009]
DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will
be described below with reference to FIGS.
[0010]
As shown in FIG. 1, the AE sensor of the present embodiment includes a cylindrical piezoelectric
body 1 having a substantially conical depression, and an electrode formed on the bottom surface
of the piezoelectric body 1 and the conical surface of the conical depression. And the damping
material 2 closely fitted into the conical recess.
As the damping material 2, metals such as stainless steel and lead are suitable.
[0011]
Specifically, the piezoelectric body 1 is made of, for example, cylindrical PZT (lead zirconate
titanate) having a diameter of 10 mm and a height of 6 mm, and the upper base has a diameter
of 8 mm, the lower base has a diameter of 1 mm, and the height is 5. It has a 5 mm inverted
frusto-conical depression. The cylindrical axis of the piezoelectric body 1 substantially coincides
with the axis of the inverted truncated cone.
[0012]
An electrode (not shown) is formed on the bottom surface 1a of the piezoelectric body 1 and the
conical surface 1b of the recess by applying a silver conductive adhesive. Lead wires (not shown)
are taken out of the electrodes, respectively.
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3
[0013]
The damping material 2 is made of SUS304 having an inverted truncated conical shape with a
lower base of 1 mm and an upper base of 40 mm. The damping material 2 is fitted into the
recess of the piezoelectric body 1 and is bonded with a silver conductive adhesive.
[0014]
In order to confirm the performance of the above AE sensor, 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.
[0015]
Fig. 2 shows the schematic configuration of the measurement system.
[0016]
The measurement system is obtained by the aluminum plate 10 (aluminum alloy 2034, size 600
mm × 600 mm × 60 mm) as a transmission medium, the above-mentioned AE sensor 5 closely
attached to the surface of the aluminum plate 10 with vacuum grease, and the AE sensor 5
Digital oscilloscope 8 (Yokogawa Electric Co., Ltd., DL1200E) for monitoring the signal and a
personal computer 9 (PC-9801VX, manufactured by NEC Corporation) that controls the digital
oscilloscope 8 and records data obtained by the digital oscilloscope 8 It consists of
[0017]
The AE sensor 5 and the digital oscilloscope 8 are directly connected by a 1.5 m cable, and the
digital oscilloscope 8 and the personal computer 9 are connected by GP-IB (general-purpose
interface bus).
[0018]
As the AE sensor 6 for comparison, a high sensitivity converter (manufactured by Fuji Ceramics
Co., Ltd., 3φ × 3t) was used.
The signal obtained by the AE sensor 6 for comparison was amplified by the preamplifier 7
(NF9913S manufactured by NF Circuit Design Block Co., Ltd., gain 20 dB), and then input to the
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digital oscilloscope 8.
[0019]
In the above configuration, the pencil core is compressed on the back surface of the aluminum
plate 10 to generate a pseudo AE wave, and the pseudo AE wave is received by the AE sensor 5
or 6 attached to the surface of the aluminum plate 10.
[0020]
The trigger mode of the digital oscilloscope 8 is set to single shot, and the waveforms obtained
by the AE sensors 5 and 6 are shown in FIGS. 3 and 4, respectively.
[0021]
In the AE sensor 5 of this 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 resonating in the piezoelectric body 1.
Therefore, near the time when the longitudinal wave P reaches the surface of the aluminum plate
10, as shown in FIG. 3, a waveform similar to the waveform obtained by the condenser type AE
sensor (see FIG. 5) is obtained.
That is, it is possible to detect the displacement of the surface of the aluminum plate 10 due to
the pseudo AE wave (in particular, the longitudinal wave P).
Moreover, since the AE sensor 5 of the present embodiment uses the piezoelectric body 1, it is
compact and highly sensitive, and the attachment to the aluminum plate 10 is easy.
[0022]
On the other hand, when a conventional high sensitivity converter is used, as shown in FIG. 4,
resonance occurs due to the pseudo AE wave, so it becomes a vibration waveform, and the
displacement of the surface of the aluminum plate 10 due to the pseudo AE wave is detected. Can
not do it.
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5
[0023]
As described above, according to the AE sensor 5 of the present embodiment, since the damping
material 2 is provided, resonance does not occur.
Therefore, the displacement of the surface of the subject can be detected.
Moreover, since the piezoelectric body 1 is used, the sensitivity is high.
For this reason, the preamplifier 7 can be omitted.
[0024]
The acoustic emission sensor corresponding to the present invention includes a columnar
piezoelectric body 1 having a substantially conical depression, an electrode formed on the
bottom surface of the columnar piezoelectric body 1 and the conical surface of the conical
depression, and a conical shape. It is the structure which consists of the damping material 2
closely_contact | adhered to the hollow and fitted.
[0025]
According to this, the AE wave incident from the bottom surface of the columnar piezoelectric
body 1 passes through the piezoelectric body 1 and then enters the damping material 2, so the
AE wave is attenuated without being resonated by the piezoelectric body 1.
Therefore, it is possible to detect the displacement of the surface of the subject due to the AE
wave. Moreover, since the AE sensor 5 of the present embodiment uses the piezoelectric body 1,
it is compact and has high sensitivity, and it is easy to attach to the subject. This makes it
possible to analyze the cause of the destruction inside the subject.
[0026]
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As described above, the acoustic emission sensor according to the present invention is formed on
the columnar piezoelectric body having the substantially conical depression, the bottom of the
columnar piezoelectric body, and the conical surface of the conical depression. Since it consists
of a damping electrode closely fitted to the conical electrode and the conical electrode, the AE
wave incident from the bottom of the columnar piezoelectric body passes through the
piezoelectric body and is then incident on the damping material. Attenuates without resonance in
the piezoelectric body. Therefore, it is possible to detect the displacement of the surface of the
subject due to the AE wave. In addition, since the AE sensor of the present embodiment uses a
piezoelectric body, it has the effect of being small and having high sensitivity and being easy to
attach to the object.
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