Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Corrosion Engineering  

DOI： 10.3323/jcorr.64.78

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

In this study, the method of detecting the formation and the dissociation of gas hydrate using AE method was proposed. In the experiment, gas hydrate was formed on the surface of ice particles, which were placed in a copper container filled by propane gas. During the formation process, elastic waves are emitted due to the volume expansion of the ice/hydrate particles, which causes friction between the particle and wall of the container, and contact among the particles. During the dissociation process, elastic waves are emitted due to the melting of ice and formation of propane gas bubbles in the water, which are formed by the dissociation of the hydrate. As a result, it was confirmed that elastic wave can be measured both in formation and dissociation process. Moreover, it was found that the emission of elastic wave increases as the surface area of the ice/hydrate particles increases and the pressure of propane gas increases, because the mass of formed hydrate increases.

DOI： 10.1299/transjsme.2014tep0374

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Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1088/1742-6596/520/1/012023

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

Waveform simulation techniques are widely used for nondestructive inspections using elastic waves. They are also used for the acoustic emission (AE) technique. Source dynamics can be identified by AE waveform analysis. However, waveforms detected by AE sensors are deformed by the sensor response, and their characteristics depend on the frequency response and sensitivity; thus, accurate AE waveform simulation is difficult because of these problems. In this study, accurate AE waveform simulation involving a sensor response, using a finite-difference time-domain (FDTD) method was developed. The original waveform is calculated by the 2D FDTD method. The sensor response is determined by extraction of the input waves to the AE sensor by a pulse generator and detection by a laser interferometer. To include the sensor width and dispersion of the sensor response, some points of the sensor response on the sensor face are detected. These are convoluted, and the sensor responses of all points are added. After Lamb wave simulation, characteristics of the simulation waveforms were correlated to the artificial AE waveform produced by Hsu-Nielsen sources (pencil lead breaking). AE signals from mode I fracture were simulated next. The fracture was excited by exfoliation between a polyester plate and glass bar embedded in the plate. The characteristics of simulation waveform by developed technique corresponded to the waveform detected by the AE sensor.

DOI： 10.1299/jmmp.7.176

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Corrosion Engineering  

DOI： 10.3323/jcorr.62.449

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s10921-012-0136-x

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

In this study we attempted to evaluate the degree of degradation of an unsaturated polyester resin when it was degraded by exposing it to hot water at 90°C, using the frequency of zero-group-velocity (ZGV) Lamb waves. The energy of ZGV Lamb waves does not propagate while the phase velocity remains finite. We generated ZGV Lamb waves with a Q-switched YAG laser and detected them with a focused air-coupled transducer at the same area of an irradiation point of the YAG laser in con-contact matter. A change in measured frequencies of ZGV Lamb waves decreased with increase of exposed period to hot water and are corresponding to the change in Young's modulus and thickness of the plate near the exposed surface

DOI： 10.1299/jmmp.6.678

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2320/matertrans.I-M2011855

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：THE SESSILE ORGANISMS SOCIETY OF JAPAN  

Clogging of water intake pipes by sessile bivalves is a serious problem hindering the safe operation of industrial and power plants. We developed a system to monitor such clogging by means of an acoustic emission (AE) technique. A sheet-type optical fiber sensor developed in our laboratory was used to monitor AE signals produced by single individuals or colonies of mussel <i>Mytilus galloprovincialis</i> attached by their byssus inside a PMMA pipe. No relation was found between mussel size and peak frequency of AE signal; However, the mussels each had a characteristics frequency, and the scattering of AE signals frequencies corresponded to the number of mussels in a colony. In addition, the AE signal generation rate increased with increasing numbers of mussels in the pipe, but continuous monitoring showed that the signal genera- tion rate also increased when mussels were removed. Continuous monitoring is thus needed if pipe clogging is to be monitored effectively by this AE technique.

DOI： 10.4282/sosj.29.11

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/kikaia.78.1610

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

Lithium ion batteries are widely used for electrical devices. However, their degradation causes serious accidents such as fires or explosions. In order to detect the degradation of a lithium ion battery during charging and discharging in real time, an acoustic emission (AE) technique was applied and a clustering method was developed to extract AE signals caused by battery degradation. In this study, highly oriented pyrolytic graphite (HOPG) and a lithium metal were used as working and counter electrodes, respectively, and a glass fiber sheet was used as a separator. An ethylene carbonate / diethyl carbonate (EC/DEC) solution, which was used as the electrolyte solution, was sealed in a metallic shell. Degradation of this type of battery mainly occurred by gas evolution and fracture or exfoliation of the graphite electrode. During the first charging and discharging cycle, 499 AE signals were detected. AE signals were clustered by a method that was developed based on the waveform polarity, power spectrum, and enveloped waveform. These features were first clustered by correlation coefficients. AE signals which the Euclidean distance of each feature was close were clustered into the same cluster. AE signals were clustered into 43 clusters by this method. In order to characterize clustered AE signals from a degrading battery, the clustered signals were compared to artificial AE signals created by simulating degradation behavior in the battery. Gas evolution on an electrode in the battery was simulated by electrolysis of water. AE signals due to graphite fracture were simulated by mechanically fracturing the graphite in a Vickers indentation test. As a result, AE signals characterizing gas evolution were detected continuously during the cycle. This result constituted gas evolution phenomena in the battery. Fracture-related AE signals due to graphite electrode exfoliation tended to occur when the lithium intercalation rate changed. Thus, fracture or exfoliation of graphite was attributed to the formation of a solid electrolyte interface (SEI) or volume expansion/contraction due to lithium intercalation, respectively. Other classes AE signals were also discussed, of which some were attributed to the distortion of graphite.

DOI： 10.1299/jmmp.5.678

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society for Non-Destructive Inspection  

In order to detect degradation and damage in lithium ion batteries, the acoustic emission (AE) technique was applied. The AE signals generated in the battery during the charge - discharge cycles were monitored at three different charging and discharging rates. Highly oriented pyrolytic graphite (HOPG) and lithium metal were used as working and counter electrodes, respectively. AE signals were mainly detected during the first charge and the AE event rate increased near the potential plateau that appears during changing a phase of the graphite depending on the degree of intercalation of the lithium. Source of these signals were assumed to be the formation of solid electrolyte interface (SEI) on the graphite surface. AE signals from the graphite fracture were also mainly detected during charging. However, when a short in the battery occurred, AE signals induced by the fracture were detected even during discharging. The charge - discharge cycle tests were next studied. The AE generation rate decreased as the cycle number increased. Its tendency did not depend on the charging rate. The AE generation rate increased just before a short circuit in the battery occurred.

DOI： 10.11396/jjsndi.60.665

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s10921-011-0090-z

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Society of Sea Water Science, Japan  

This study aims to detect and monitor the initiation and progression of corrosion that occurs at a flange connection using an acoustic emission technique, and to investigate the correlation between acoustic emission parameters such as hit rate and frequency component of AE and the corrosion progression. We first monitor AE from the corrosion in a crevice of an assembled flange under corrosion potential control in order to investigate the feasibility of AE monitoring for corrosion detection. Many burst type AE waves were detected during testing and most of the AE source locations agreed fairly with the corrosion area. Next, AE monitoring for corrosion at a flange connection under a continuous flow of artificial concentrated sea water was performed with four PZT-type AE sensors. The AE generation rate during testing equaled 10 to 30 events / hour. Peak frequency of detected AE shifted higher to 300 kHz with the progression of corrosion. Using an optical fiber AE monitoring system developed in-house, the AE from corrosion in a crevice was also monitored. This system can monitor AE for three flanges with one optical fiber. These sensors detected AE from corrosion at an individual flange under continuous flow test. As a result, it was found that the AE method is a potential tool for monitoring corrosion at a flange connection in salt product plants.

DOI： 10.11457/swsj.65.105

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Other Link： https://jlc.jst.go.jp/DN/JALC/00368093751?from=CiNii

Language：Japanese   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1299/kikaia.77.1056

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society for Non-Destructive Inspection  

An acoustic emission (AE) monitoring system with real time noise reduction function using a spectral subtraction (SS) process was developed, in order to monitor AE in a noisy environment. To evaluate the noise reduction performance of the SS, we monitored artificial AE signals in various noise environments. The S/N ratio of the AE signal in background noise, which includes electrical noise of a pre-amp and/or an A/D converter, was improved by 18.4dB using the SS process. Periodic noise was reduced and the S/N ratio increased to 40dB. We also reduced the noise with wide frequency band and the S/N ratio increased by 8-10dB. We then monitored the cylinder wave AE signals produced by a pencil lead breaking in the noise generated by the air flow in the pipe. The system improved the S/N ratio of the AE signal by 9.2dB and was able to detect AE signals.

DOI： 10.11396/jjsndi.58.549

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

We quantitatively estimated the location and area fraction of a model blockage inside a pipe utilizing guided waves propagating in a liquid inside a pipe. The guided wave was excited and detected by film-type PZT elements wounded around an external pipe surface. Location of the blockage can be estimated from an arrival time of the wave reflected by the blockage and measured propagation velocity. The blocking ratio can be also estimated by comparing the measured amplitude to the predicted one when the profile of the blockage was roughly evaluated prior to the measurement. We also discussed the effect of the flow rate on the amplitude of the reflected wave.

DOI： 10.1299/jmmp.3.278

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Corrosion Engineering  

We developed a new heat-resistant optical fiber AE sensor and a homodyne Mach-Zender type laser interferometer to monitor the acoustic emission (AE) from hot members. The optical fiber coated with copper was used as a heat resistant sensor, and AEs from hot pipes were measured up to 600°C for 108 ks. The sensor was found to monitor the longitudinal mode cylinder wave which conventional PZT sensor can not monitor, when the sensing fiber was wound on the pipe. The system was utilized for monitoring AEs from crack and exfoliation of non-protective scales produced by catastrophic oxidation of Type 304 stainless steel pipe at 700°C. The cylindrical AEs were classified into two fracture types, i.e., Mode-I fracture with a crack opening vector in the circumferential direction (scale fracture) and in the radial directions (exfoliation). A number of AEs detected during cooling was found to be produced by Mode-I crack of the scales. Their sources were located using arrival time differences of L(0,2) and F(1,1) modes at 80 kHz and found to be in the zone with non-protective scales.

DOI： 10.3323/jcorr.56.560

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Other Link： https://jlc.jst.go.jp/DN/JALC/00304306464?from=CiNii

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.3323/jcorr.56.321

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DOI： 10.2320/matertrans.I-MRA2007843

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DOI： 10.2320/matertrans.I-MRA2007848

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

We developed an advanced multi-sensing optical fiber AE monitoring system with both a feed back and polarization controller. Optical fiber was wound on the horizontal hollow pipes with different diameters. The fiber between the plate and pipe first detected the in-plane motion of AE as the Lamb wave and then the resonant wave with resonance frequencies of the pipes. The resonance wave was found to be excited by the out-of-plane motion of the Ao mode wave arriving at the velocity of the frequency equivalent to the resonance frequency of the pipe. We studied source dynamics and source location of artificial sources such as Mode-I fracture. For the study of the source dynamics, we simulated waveform of first arrival So-mode Lamb wave utilizing the experimental overall transfer function of the second kind. Location of Lamb wave AEs on an isotropic (aluminum) plate were successfully estimated by suing unique location scheme

DOI： 10.1299/kikaia.72.1895

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Other Link： https://jlc.jst.go.jp/DN/JALC/00289043941?from=CiNii

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japanese Society for Non-Destructive Inspection  

We developed a noble multi-sensing optical fiber acoustic emission (AE) monitoring system. The system is essentially the same as that reported previously, i.e, a phase compensation Mach-Zehnder laser homodyne interferometer; but a long sensing fiber was divided into many AE sensors with different frequency characteristics. This unique system can measure the arrival times of AEs and estimate the source location of AE. Multi-sensing was achieved by winding the sensing fiber over small cylindrical rods (sensor holders) with different diameters. Thus each optical fiber sensor can detect the AE with resonance frequency of the rod. Here, the resonance frequency of each sensor can be optionally controlled by the diameter and density of the rod. Utility of this system was demonstrated by the source location of pencil lead breaking on a steel plate and piping connected by socket and elbow. A long sensing fiber of 10 m was divided into three sensors with resonance frequencies of 83 kHz, 103 kHz and 123 kHz by using aluminum rods of 40, 30 and 20 mm diameter. AE signals were monitored by a single sensing fiber and divided into three packets using the wavelet transform. AE sources could be located within distance error of less than 7% for the Lamb wave AE through the steel plate. This system also makes the identification of the connected pipe with the AE source possible.

DOI： 10.11396/jjsndi.55.295

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.stam.2005.11.010

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Language：Japanese   Publishing type：Research paper (scientific journal)  

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Language：English   Publisher：The Japan Society of Mechanical Engineers  

We quantitatively estimated the location and area fraction of a model blockage inside a pipe utilizing guided waves propagating in a liquid inside a pipe. The guided wave was excited and detected by film-type PZT elements wounded around an external pipe surface. Location of the blockage can be estimated from an arrival time of the wave reflected by the blockage and measured propagation velocity. The blocking ratio can be also estimated by comparing the measured amplitude to the predicted one when the profile of the blockage was roughly evaluated prior to the measurement. We also discussed the effect of the flow rate on the amplitude of the reflected wave.

DOI： 10.1299/jmmp.3.278

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DOI： 10.3323/jcorr.56.321

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DOI： 10.2320/matertrans.I-MRA2007843

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DOI： 10.2320/matertrans.I-MRA2007848

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Language：Japanese   Publisher：Japan Society of Corrosion Engineering  

We developed a new heat-resistant optical fiber AE sensor and a homodyne Mach-Zender type laser interferometer to monitor the acoustic emission (AE) from hot members. The optical fiber coated with copper was used as a heat resistant sensor, and AEs from hot pipes were measured up to 600°C for 108 ks. The sensor was found to monitor the longitudinal mode cylinder wave which conventional PZT sensor can not monitor, when the sensing fiber was wound on the pipe. The system was utilized for monitoring AEs from crack and exfoliation of non-protective scales produced by catastrophic oxidation of Type 304 stainless steel pipe at 700°C. The cylindrical AEs were classified into two fracture types, i.e., Mode-I fracture with a crack opening vector in the circumferential direction (scale fracture) and in the radial directions (exfoliation). A number of AEs detected during cooling was found to be produced by Mode-I crack of the scales. Their sources were located using arrival time differences of L(0,2) and F(1,1) modes at 80 kHz and found to be in the zone with non-protective scales.

DOI： 10.3323/jcorr.56.560

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Other Link： https://jlc.jst.go.jp/DN/JALC/00304306464?from=CiNii

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Language：English  

DOI： 10.1016/j.stam.2005.11.010

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Web of Science

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

We developed an advanced multi-sensing optical fiber AE monitoring system with both a feed back and polarization controller. Optical fiber was wound on the horizontal hollow pipes with different diameters. The fiber between the plate and pipe first detected the in-plane motion of AE as the Lamb wave and then the resonant wave with resonance frequencies of the pipes. The resonance wave was found to be excited by the out-of-plane motion of the Ao mode wave arriving at the velocity of the frequency equivalent to the resonance frequency of the pipe. We studied source dynamics and source location of artificial sources such as Mode-I fracture. For the study of the source dynamics, we simulated waveform of first arrival So-mode Lamb wave utilizing the experimental overall transfer function of the second kind. Location of Lamb wave AEs on an isotropic (aluminum) plate were successfully estimated by suing unique location scheme

DOI： 10.1299/kikaia.72.1895

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Other Link： https://jlc.jst.go.jp/DN/JALC/00289043941?from=CiNii

Language：Japanese   Publisher：The Japanese Society for Non-Destructive Inspection  

We developed a noble multi-sensing optical fiber acoustic emission (AE) monitoring system. The system is essentially the same as that reported previously, i.e, a phase compensation Mach-Zehnder laser homodyne interferometer; but a long sensing fiber was divided into many AE sensors with different frequency characteristics. This unique system can measure the arrival times of AEs and estimate the source location of AE. Multi-sensing was achieved by winding the sensing fiber over small cylindrical rods (sensor holders) with different diameters. Thus each optical fiber sensor can detect the AE with resonance frequency of the rod. Here, the resonance frequency of each sensor can be optionally controlled by the diameter and density of the rod. Utility of this system was demonstrated by the source location of pencil lead breaking on a steel plate and piping connected by socket and elbow. A long sensing fiber of 10 m was divided into three sensors with resonance frequencies of 83 kHz, 103 kHz and 123 kHz by using aluminum rods of 40, 30 and 20 mm diameter. AE signals were monitored by a single sensing fiber and divided into three packets using the wavelet transform. AE sources could be located within distance error of less than 7% for the Lamb wave AE through the steel plate. This system also makes the identification of the connected pipe with the AE source possible.

DOI： 10.11396/jjsndi.55.295

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Language：Japanese   Publisher：日本工業出版  

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