• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.425-430
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• 2008

To verify the system performance of portable AE leak diagnosis system which can measure with moving conditions, AE activities such as RMS voltage level, AE signal trend, leak rate degree according to AE database, FFT spectrum were measured during operation on total 11 valves of the secondary system in nuclear power plant. AE activities were recorded and analyzed from various operating conditions including different temperature, type of valve, pressure difference, valve size and fluid. The results of this field study are utilized to select the type of sensors, the frequency band for filtering and thereby to improve the signal-to-noise ratio for diagnosis for diagnosis or monitoring of valves in operation. As the final result of application study above, portable type leak diagnosis system by AE was developed. The outcome of the study can be definitely applied as a means of the diagnosis or monitoring system for energy saving and prevention of accident for power plant valve. The purpose of this study is to verify availability of the acoustic emission in-situ monitoring method to the internal leak and operating conditions of the major valves at nuclear power plants. In this study, acoustic emission tests are performed when the pressurized temperature water and steam flowed through glove valve(main steam dump valve) and check valve(main steam outlet pump check valve) on the normal size of 12 and 18 ". The valve internal leak monitoring system for practical field was designed. The acoustic emission method was applied to the valves at the site, and the background noise was measured for the abnormal plant condition. To improve the reliability, a judgment of leak on the system was used various factors which are AE parameters, trend analysis, frequency analysis, voltage analysis and amplitude analysis of acoustic signal emitted from the valve operating condition internal leak.

• 한국안전학회지
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• 제12권4호
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• pp.214-219
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• 1997

미캐니컬 씰은 회전축에 장착되는 밀봉장치의 하나로써 많은 산업 현장에서 사용되고 있다. 산업발전과 더불어 미캐니컬 씰의 고장 즉, 밀봉장치에서의 누설, 크랙, 파손, 과대마멸 등과 같은 이상 상태는 대규모 공장의 생산라인을 정지시키거나 심각한 환경오염을 유발시키는 등 경제, 사회적 문제를 야기시키고 있다. 미캐니컬 씰 밀봉면의 미끄럼 운동상태를 인지하고, 미캐니컬 씰의 고장에 대한 감시인자를 도출하기 위하여 미끄럼 마멸실험을 수행하였다. 미캐니컬 씰의 회전속도를 1750 rpm 으로 하여, 매 10 분 마다 미캐니컬 씰 밀봉면의 마멸상태를 광학현미경으로 관찰하였고, 실험동안에 미캐니컬 씰의 미끄럼 운동면에서의 음향방출(AE : Acoustic Emission), 토크, 온도, 등을 측정하였으며, 실시간으로 토크 신호의 주파수 분석을 실시하였다. 각 실험의 초기를 제외하고는 전 구간에서 음향방출 신호의 크기와 토크 값의 변화 경향이 대체로 유사한 경향을 보였다. 정상상태에서는 음향방출, 토크 및 온도가 안정된 상태를 유지하였으나, 이상상태에서는 음향방출의 크기와 토크값이 안정된 상태를 유지하지 못하였으며, 온도는 이상상태 때 급상승하는 경향을 보였다. 토크 값과 온도의 변화가 미캐니컬 씰의 고장에 대한 장기적 감시인자로 적절하다고 생각되며, 미캐니컬 씰의 순간적인 이상상태를 확인하거나 미캐니컬 씰의 운동상태를 인지하는 데는 실효치 전압 상태의 음향방출 신호가 적당하다고 생각된다. 온도는 이상상태 감시 시스템에서 시스템의 신뢰도를 증진시키는 병렬요소로써 활용될 수 있을 것이다.장 큰 결합활성도(binding activity)를 나타내며, 또한 Hyphantria cunea와 같은 나비목의 다른 종의 lipophorin도 인식하는 것으로 나타났다. 따라서 리포포린에 결합하는 수용체의 구조적 또는 기능적 요소는 같은 목내의 종간에 보존되는 것으로 생각된다.과 성충의 생존율은 온도에 따른 계통간 차이는 없었다. 내적자연증가율( $r_{m}$ )은 S계통이 $R_{L}$, $R_{F}$계통보다 $25^{\circ}C$에서는 낮았지만 2$0^{\circ}C$와 3$0^{\circ}C$에서는 높았다. 특히 3$0^{\circ}C$에서는 S계통이 현저히 높았다. 결론적으로 dicofol 저항성계통( $R_{L}$, $R_{F}$)은 저온(2$0^{\circ}C$)과 고온(3$0^{\circ}C$)에서 감수성계통에 비해 생물학적 적응력이 떨어질 것으로 생각된다.력이 떨어질 것으로 생각된다.력이 떨어질 것으로 생각된다.해도 될 것이다. 쐐기 투과율을 정하는 위치가 d$_{max}$ 나 공기중이라면 민조사변에 대한 출력계수를 적용할 수 있지만 다른 깊이에서는 쐐기필터 각각에 대한 출력계수를 또는 조사면크기에 따른 쐐기투과율을 적용해야 할 것이다. 39.2%가 이유 설명 후 사주지 않는 것으로 나타났으며 23.2%가 다음으로 미룬다, 무조건

• Composites Research
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• 제36권6호
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• pp.429-434
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• 2023

본 연구에서는 기존 배관 가스 누출 감지에 사용되던 음향방출 센서가 실시간 모니터링에 적용될 때 발생할 수 있는 문제들을 개선하기 위해, Macro-fiber composite (MFC) 트랜스듀서를 음향방출 센서로 사용하여 가스 누출 감지 시스템에 적용하였다. 적용 전 MFC의 구조를 최적화하기 위해 구조해석을 진행하여 제작하였고, 그 결과 MFC가 가지는 유연성으로 굴곡진 배관에 잘 밀착되어 AE 신호를 문제없이 수신할 수 있었다. AE 신호 분석 결과 고압 누출, 저압 누출 모두 파라미터 값 변화에 유의미한 결과를 보였으며, 특히, FFT 그래프의 파라미터에서 고압 누출의 경우 누출이 없는 경우 대비 120~626%의 변화량, 저압 누출의 경우 9~22%의 변화량을 보였다. 또한, 누출 발생 부위에서의 거리에 따라, 거리가 멀수록 이러한 파라미터 변화량이 줄어드는 경향을 보여, 추후 파라미터 변화량 감지를 통해 누출 감지가 가능할 뿐만 아니라, 변화량으로부터 누출 발생 위치를 파악할 수 있을 것으로 보인다.

• 한국공작기계학회논문집
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• 제15권5호
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• pp.104-113
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• 2006

The main objective of this study is to investigate the effect of compounded welding by using acoustic emission (AE) signals and doing a source location for weld heat affected zone (HAZ) through tensile testing. This study was carried out an SWS 490A high strength steel for electric shield metal arc welding, SMAW; $CO_2$ gas metal arc welding, GMAW($CO_2$); and gas tungsten arc welding, GTAW/TIG. Data displays are based on the measured parameters of the AE signals, along with environmental variables such as time and load. For instance, Gutenberg-Richter magnitude-frequency relationship (G-R MFR) offers useful b-value in data analysis. Namely event identification, source location gives the X- and Y-coordinates of the AE source. And K-means clustering analysis by Euclidean distance confirmed that was powerful to source location. Generally, strength of welded metal zone was stronger than strength of base metal. As the result, confirmed certainly that fracture is produced in HAZ instead of welded metal zone from source location.

• 한국항공운항학회지
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• 제18권4호
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• pp.51-58
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• 2010

Recently, aerospace structures have lightweight trend in order to reduce the cost of fuel and system, Carbon Fiber Reinforced Plastic (CFRP) can give the ability to reduce weight at 20~50% as the substitution of metal alloy, and there are advantages such as high Non-rigid, specific strength and anti-corrosion, but it is difficult to prove its destruction properties due to heterogeneous structure and anisotropy. In this study we designed specimen, inducing distinguishing destructions of material (for example, matrix crack, fiber breakage, and delamination) by using the Carbon Fiber Reinforced Plastic (CFRP) which is used in a real aircraft, to apply acoustic emission technique to aerospace structures. And we gained data via tensile testing and acoustic emission technique, from which each fault signal was classified respectively by using AE parameters and waveform.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 1999년도 추계학술발표대회 논문집
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• pp.28-31
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• 1999

Carbon fiber/epoxy composites using electrodeposited monomeric and polymeric coupling agents were compared with the dipping and the untreated cases. Treating conditions such as time, concentration and temperature were optimized. Four-fibers embedded micro-composites were prepared for fragmentation test. Interfacial properties of four-fiber composites with different surface treatments were investigated with simultaneous acoustic emission (AE) monitoring. The microfailure mechanisms occurring from fiber break, matrix and interlayer crackings were examined by AE parameters and an optical microscope. It was found that interfacial shear strength (IFSS) of electrodeposited carbon fibers was much higher than the other cases under dry and wet conditions. Well separated and different-shaped AE groups occurs for the untreated and ED treated case, respectively.

• 한국공작기계학회논문집
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• 제14권1호
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• pp.30-36
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• 2005

This study is to investigate a damage estimation of single edge notched tensile specimens as a function of acoustic emission(AE) according to the uni-directionally oriented carbon fiber/epoxy composites, CFRP In fiber reinforced composite materials, AE signals due to several types of failure mechanisms are typically observed. These are due to fiber breakage, fiber pull-out matrix cracking, delamination, and splitting or fiber bundle breaking. And these are usually discriminated on the basis of amplitude distribution, event counts, and energy related parameters. In this case, AE signals were analyzed and classified 3 regions by AE event counts, energy and amplitude for corresponding applied load. Bath-tub curve shows 3 distinct periods during the lifetime of a single-edge-notch(SEN) specimen. The characterization of AE generated from CFRP during SEN tensile test is becoming an useful tool f3r the prediction of damage failure or/and failure mode analysis.

• Nuclear Engineering and Technology
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• 제47권4호
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• pp.454-460
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• 2015

Acoustic emission (AE) is one of the promising methods for detecting the formation of stress corrosion cracks (SCCs) in laboratory tests. This method has the advantage of online inspection. Some studies have been conducted to investigate the characteristics of AE parameters during SCC propagation. However, it is difficult to classify the distinct features of SCC behavior. Because the previous studies were performed on slow strain rate test or compact tension specimens, it is difficult to make certain correlations between AE signals and actual SCC behavior in real tube-type specimens. In this study, the specimen was a AISI 304 stainless steel tube widely applied in the nuclear industry, and an accelerated test was conducted at high temperature and pressure with a corrosive environmental condition. The study result indicated that intense AE signals were mainly detected in the elastic deformation region, and a good correlation was observed between AE activity and crack growth. By contrast, the behavior of accumulated counts was divided into four regions. According to the waveform analysis, a specific waveform pattern was observed during SCC development. It is suggested that AE can be used to detect and monitor SCC initiation and propagation in actual tubes.

• 대한기계학회논문집A
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• 제31권8호
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• pp.870-879
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• 2007

In this study, various damage modes in bending unimorph piezoelectric composite actuators with a thin sandwiched PZT plate during bending fracture tests have been evaluated by monitoring acoustic emission (AE) signals in terms of waveform and peak frequency as well as AE parameters. Three kinds of actuator specimens consisting of woven fabric fiber skin layers and a PZT ceramic core layer are loaded with a roller and an AE activity from the specimen is monitored during the entire loading using an AE transducer mounted on the specimen. AE characteristics from a monolithic PZT ceramic with a thickness of $250{\mu}m$ are examined first in order to distinguish different AE signals from various possible damage modes in piezoelectric composite actuators. Post-failure observations and stress analyses in the respective layers of the specimens are conducted to identify particular features in the acoustic emission signal that correspond to specific types of damage modes. As a result, the signal classification based on waveform and peak frequency analyses successfully describes the failure process of the bending piezoelectric composite actuator exhibiting diverse failure mechanisms. Furthermore, it is elucidated that when the PZT ceramic embedded actuators are loaded mechanical bending loads, the failure process of actuator specimens with different lay-up configurations is almost same irrespective of their lay-up configurations.

• 한국해양공학회지
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• 제17권3호
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• pp.46-51
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• 2003

Acoustic emission (AE) signals, emanated during local failure of aluminum alloys, have been the subject of numerous investigations. It is well known that the characteristics of AE are strongly influenced by the previous thermal and mechanical treatment of the sample. Possible sources of AE during deformation have been suggested as the avalanche motion of dislocations, fracture of brittle particles, and debonding of these particles from the alloy matrix. The goal of the present study is to determine if AE occurring as the result of fatigue crack propagation could be evaluated by the joint time-frequency analysis method, short time Fourier transform (STFT), and Wigner-Ville distribution (WVD). The time-frequency analysis methods can be used to analyze non-stationary AE more effectively than conventional techniques. STFT is more effective than WVD in analyzing AE signals. Noise and frequency characteristics of crack openings and closures could be separated using STFT. The influence of various fatigue parameters on the frequency characteristics of AE signals was investigated.