• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.1865-1867
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• 2002

In this paper, frequency spectra of AE signals detected from respective the insulation deterioration were analysed to under ac high-voltage application using epoxy resin sample and insulation oil. Also, frequency spectra of AE signals generated from the load currents in the actual operating transformer of 500[kVA] under distribution system of 22.9[kVJ] were also analysed to distinguish the AE signals due to void discharges from the magnetic circuit noises in transformer. As the experimental results, we could distinguish the AE signals whether those signals were caused due to the void discharges or due to the magnetic circuit noises by analyzing the frequency spectrum of AE signals.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 1999.11a
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• pp.127-131
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• 1999

In this paper, using a wide-band AE sensor with the frequency range from 100[kHz], the frequency spectra of AE signals generated from the corona discharges of the needle-plane electrode was analyzed to determine the proper ultrasonic sensor. We also examined the relationship between the magnitude of corona discharge and the magnitude of AE signals in peak-to-peak value under the application of 60[Hz] AC high-voltage in oil. From these results, the main frequency spectra of AE signals emitted from the corona discharges of the needle-plane gap were found to be 130[kHz] by the fast fourier transform. The magnitude of AE signals was proportional to the magnitude of corona discharge and discharge current pulse with increasing the applied voltages. Also the detection of corona discharge point location by AE signals was found to be possible by using two sensors.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.1223-1228
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• 2005

A lot of PSC railway bridges have been constructed in countries and, they are considered as cost-effective and less maintenance-demanded structures. However, recently several collapse of PSC bridges happened in Europe show that PSC bridges have some serious maintenance problems related to tendon corrosion and wire fractures. Furthermore, any reliable NDT method is not presented until recently. In this paper, AE techniques are investigated for detection of wire fractures in PSC beam. Using long-term monitoring AE techniques, two acoustic signals of wire fractures in a PSC beam are obtained. These data are compared to other noise signals. Based on the test results, the characteristics of the AE signals are classified and wire fracture signals are figured out among the other AE signals. As a result, AE techniques are certainly exposed to tendon fracture sound, and application of AE techniques are better than any other non-destructive method.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.330-333
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• 2006

In this paper experimental tests were performed to evaluate velocities of the acoustic waves through prestressed concrete beam and source locations using AE technique. Seven AE sensors are mounted on the surface of 5m length test beam with equal spacing and using Schmidt Hammer AE events are made 18 locations. The velocities of AE signals are evaluated using the time differences of arrival times and the distances between the AE source loactions and the AE sensor locations. In addition, using the Least Square Method, the AE source locations are re-evaluated reversely using both of the arrival times and the velocities of AE signals. Test results show the average velocity of the AE signals is about 4,000m/sec and the velocity decreased with the increase of the trevalling times due to the effect of attenuation. Based on the estimation of the source locations, it is observed that the accuracy of source location is increased when the velocity of each AE sensor used rather than the average velocity.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.678-682
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• 1996

Acoustic emission(AE) is monitored during end milling with a sensor attached to the cutting fluid discharge nozzle. Cutting forces are also measured and compared with the AE signals to examine the reliability of the AE signals. It is demonstrated that the AE signals provide reliable informations about the cutting processes and tool states. Moreover, edge chipping and fracture of tools can be successfully detected using both the AE signals and cutting forces.

• Geomechanics and Engineering
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• v.15 no.5
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• pp.1125-1133
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• 2018

Real-time characterization of the rock thermal deformation and fracture process provides guidance for detecting and evaluating thermal stability of rocks. In this paper, time -frequency characteristics of acoustic emission (AE) and electromagnetic radiation (EMR) signals were studied by conducting experiments during rock continuous heating. The coupling correlation between AE and EMR during rock thermal deformation and failure was analyzed, and the microcosmic mechanism of AE and EMR was theoretically analyzed. During rock continuous heating process, rocks simultaneously produce significant AE and EMR signals. These AE and EMR signals are, however, not completely synchronized, with the AE signals showing obvious fluctuation and the EMR signals increasing gradually. The sliding friction between the cracks is the main mechanism of EMR during the rock thermal deformation and fracture, and the AE is produced while the thermal cracks expanding. Both the EMR and AE monitoring methods can be applied to evaluate the thermal stability of rock in underground mines, although the mechanisms by which these signals generated are different.

• Proceedings of the KIEE Conference
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• 1999.07e
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• pp.2335-2337
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• 1999

In this paper, using AE (Acoustic Emission) sensor the electrical and emitted-sound signals are measured by treeing breakdown in the epoxy resin, and the corresponding frequency spectrum of the AE signals are analyzed. We also examined the relationship between partial discharge magnitude and pulse number of AE signals to diagnose the deterioration of the electrical insulation due to treeing breakdown. From these results, a frequency band of AE signals through treeing breakdown was set to about 230 [kHz], and it appeared that pulse number of AE signal was proportional to partial discharge magnitude.

• Smart Structures and Systems
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• v.8 no.4
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• pp.385-398
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• 2011

This paper discusses the applicability of Acoustic Emission (AE) to assess the damage in reinforced concrete (RC) structures subjected to complex dynamic loadings such as those induced by earthquakes. The AE signals recorded during this type of event can be complicated due to the arbitrary and random nature of seismicity and the fact that the signals are highly contaminated by many spurious sources of noise. This paper demonstrates that by properly filtering the AE signals, a very good correlation can be found between AE and damage on the RC structure. The basic experimental data used for this research are the results of fourteen seismic simulations conducted with a shake table on an RC slab supported on four steel columns. The AE signals were recorded by several low-frequency piezoelectric sensors located on the bottom surface of the slab. The evolution of damage under increasing values of peak acceleration applied to the shake table was monitored in terms of AE and dissipated plastic strain energy. A strong correlation was found between the energy dissipated by the concrete through plastic deformations and the AE energy calculated after properly filtering the signals. For this reason, a procedure is proposed to analyze the AE measured in a RC structure during a seismic event so that it can be used for damage assessment.

• Journal of Power System Engineering
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• v.13 no.4
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• pp.43-48
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• 2009

The purpose of this study is to show how to eliminate the noises and to obtain the data related with the relationship between AE signal characteristics and mechanical behaviors for the pressure vessel steel. Various kinds of noises are introduced into the AE data in the course of experiments. Accordingly, real AE data have to be obtained after tests. AE test was carried out under four point bending load. Among AE signals, counts and signal strength are used to find out the differences of AE characteristics between the basemetal and weldment. After tests, this paper shows the procedures of filtering the noises against basemetal of the pressure vessel steel to obtain the real data around crack tip. Relationships between plastic zone size and cumulative AE counts are shown also. AE signals were absent within an elastic region, regardless of the specimens. Most of AE signals are produced in the process of plastic deformation. The deformation and fracture modes of basemetal and weldment are quiet different.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.243-246
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• 2005

Using long-tenn monitoring AE techniques, two acoustic signals of wire fractures in a PSC beam are obtained. These data are compared to other noise signals. Based on the test results, the characteristics of the AE signals are classified and wire fracture signals are figured out among the other AE signals.