• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.10
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• pp.907-911
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• 2007

This paper dealt with the frequency spectrum analysis of acoustic signal produced by partial discharge (PD) in insulation oil and the positioning of PD occurrence to apply in diagnosis of oil insulated transformers. Three types of electrode system ; the needle-plane, the plane-plane, and the wire-wire structure were assembled to simulate partial discharges in oil insulated transformers. A low-noise amplifier and a decoupling circuit were designed to detect acoustic signal with high sensitivity The frequency spectrum of the acoustic signal were 50 kHz ${\sim}$ 260 kHz in the needle-plane, 50 kHz ${\sim}$ 250 kHz in the plane-plane, and 45 kHz${\sim}$195 kHz in the wire-wire electrode system. Their peak frequencies were 145 kHz, 130 kHz and 114 kHz, respectively The position of PD occurrence was calculated by the time difference of arrival (TOA) using three acoustic emission (AE) sensors, and we could find the position within the error of 1 % in the experimental apparatus.

• Tunnel and Underground Space
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• v.27 no.3
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• pp.121-131
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• 2017

We studied the time-dependent behaviors of rock and concrete materials by conducting the static and dynamic long-term strength tests. In particular, acoustic emission(AE) signals generated while the tests were analyzed and used for the long-term stability evaluation. In the static subcritical crack growth test, the long-term behavior and AE characteristics of Mode I and Mode II were investigated. In the dynamic long-term strength test, the fatigue limit and characteristics of generation of AE were analyzed through cyclic four points bending test. The graph of the cumulative AE hits versus time showed a shape similar to that of the creep curve with the first, second and third stages. The possibility for evaluating the static and dynamic long-term stability of rock and concrete is presented from the log - log relationship between the slope of the secondary stage of cumulative AE hits curve and the delayed failure time.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.6
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• pp.490-500
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• 2000

A new technique for the source location of acoustic emission (AE) in plates whose thichness are close to or thinner than the wavelength has been studied by introducing wavelet transform de-noising technique. The detected AE signals were pre-processed using wavelet transform to be decomposed into the low-frequency, high-amplitude flexural components and the high-frequency, low-amplitude extensional components. If the wavelet transform de-noising was employed, we could successfully filter out the extensional wave component, one of the critical errors of source location in plates by arrival time difference method. The accuracy of source location appeared to be significantly improved and independent of the setting of gain and threshold, plate thickness, sensor-to-sensor distance, and the relative position of source to sensors. Since the method utilizes the flexural component of relatively high amplitude, it could be applied to very large, thin-walled structures in practice.

• Geomechanics and Engineering
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• v.36 no.5
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• pp.511-525
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• 2024

Underground openings significantly affect the mechanical stability of underground spaces and create damaged zones. This study investigated the acoustic emission (AE) characteristics associated with the formation of damaged zones around circular openings. Uniaxial compression experiments were conducted on three types of rock specimens, namely, granite (GN-1 and GN-2), gabbro (GB), and slate (SL), containing a circular opening. AE and digital image correlation (DIC) techniques were used to monitor and evaluate the damaged zones near the circular openings. The AE characteristics were evaluated using AE parameters, including count, energy, amplitude, average frequency, and RA value. The DIC results revealed that the estimated diameters of the damaged zones of GN-1, GN-2, GB, and SL were 1.66D, 1.53D, 1.49D, and 1.9D, respectively. The average displacements at the surface of the damaged zones for these specimens were 0.814, 0.786, 0.661, and 0.673 mm, respectively, thus demonstrating a strong correlation with Young's modulus. The AE analysis with DIC revealed that tensile failure occurred in the direction parallel to the maximum compression axis as the load increased. Thus, this study provides fundamental data for a comprehensive analysis of damaged zones in underground openings and will facilitate the optimization of rock engineering projects and safety assessments thereof.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.4
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• pp.46-53
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• 1997

This paper presents a method of detection localized defects on tapered roller bearing in main spindle of machine tool system. The feature vectors, i.e. statistical parameters, in time-domain analysis technique have been calculated to extract useful features from acoustic emission signals. These feature vectors are used as the input feature of an neural network to classify and detect bearing defects. As a results, the detection of bearing defect conditions could be sucessfully performed by using an neural network with statistical parameters of acoustic emission signals.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.05a
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• pp.68-74
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• 2002

The tensile tests to identify the statistical tensile properties and the acoustic emission characteristics were conducted for STS304 stainless steel at $600^{\circ}C,\;700^{\circ}C$. From tensile tests performed by constant cross head speed controls with 1mm/min, rates at each elevated temperature, the scatters were observed in tensile strength, reduction of area, elongation and the acoustic emission parameters. The effect of temperature on the scatter of tensile behavior was larger at $700^{\circ}C$. The distributions of tensile properties was well followed in 3-parameter Weibull. The AE counts and energy of the $700^{\circ}C$ specimens were smaller than the $600^{\circ}C$.

• Proceedings of the Acoustical Society of Korea Conference
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• 1992.06a
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• pp.87-90
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• 1992

Detecting acoustic emission (AE) provides an appropriate method to diagonize on-line transformers, since acoustic signal is not influenced by strong electric field. Then AE versus AE signal processing method is investigated. But this processing is difficult that decision of starting point of AE wave with acoustic noise. This problem is sloved by correlation which calculate time interval between two signals eactly. This paper presents a technique locating the eact position of the partial discharge (PD) in a power transformer by the correlation of the AE signals from two ultrasonic sensors. And PD position is displayed on monitor. Laboratory tests confirmed that the proposed method can be used for locating the PD in power transformer.

• Composites Research
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• v.36 no.6
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• pp.429-434
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• 2023

In this study, aimed at improving the existing acoustic emission sensor for real time monitoring, a macro-fiber composite (MFC) transducer was employed as the acoustic emission sensor in the gas leak detection system. Prior to implementation, structural analysis was conducted to optimize the MFC's design. Consequently, the flexibility of the MFC facilitated excellent adherence to curved pipes, enabling the reception of acoustic emission (AE) signals without complications. Analysis of AE signals revealed substantial variations in parameter values for both high-pressure and low-pressure leaks. Notably, in the parameters of the Fast Fourier Transform (FFT) graph, the change amounted to 120% to 626% for high-pressure leaks compared to the case without leaks, and approximately 9% to 22% for low-pressure leaks. Furthermore, depending on the distance from the leak site, the magnitude of change in parameters tended to decrease as the distance increased. As the results, in the future, not only will it be possible to detect a leak by detecting the amount of parameter change in the future, but it will also be possible to identify the location of the leak from the amount of change.

• Journal of Ocean Engineering and Technology
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• v.13 no.3 s.33
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• pp.77-82
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• 1999

The compleete joining method for dissimilar hot die punch materials and its real-time evaluation method are not available at present. Brazing method has been used for joining them, but it is known that the welded joint by the brazing has the lower bonding efficiency and reliability than the diffusion welding. The friction wleding with a diffusion mechanism in bonding was applied in this study. So, this work was carried out to determine the optimal friction welding conditions and to analyze mechanical properties of friction welded joints of hot die punch materials (STD61 for the blade part of hot die punch) to alloy steel (SCM440 for the shank park of hot die punch) such as plunger. In addition, acoustic emission test was carried out during friction welding to evaluate the weld quality.

• Composites Research
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• v.27 no.4
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• pp.152-157
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• 2014

Non-destructive testing methods of composite materials are very important for improving material reliability and safety. AE measurement is based on the detection of microscopic surface movements from stress waves in a material during the fracture process. The examination of AE is a useful tool for the sensitive detection and location of active damage in polymer and composite materials. FBG (Fiber Bragg Grating) sensors have attracted much interest owing to the important advantages of optical fiber sensing. Compared to conventional electronic sensors, fiber-optical sensors are known for their high resolution and high accuracy. Furthermore, they offer important advantages such as immunity to electromagnetic interference, and electrically passive operation. In this paper, the crack detection capability of AE (Acoustic Emission) measurement was compared with that of an FBG sensor under tensile testing and buckling test of composite materials. The AE signals of the PVDF sensor were measured and an AE signal analyzer, which had a low pass filter and a resonance filter, was designed and fabricated. Also, the wavelength variation of the FBG sensor was measured and its strain was calculated. Calculated strains were compared with those determined by finite element analysis.