• 한국자동차공학회논문집
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• 제10권3호
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• pp.77-84
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• 2002

Measurements of NO and NOx emission of laminar partially premixed LPG/air flames with and without acoustic excitation are reported. The NOx emission at the tailpipe of a combustion chamber is determined by chemiluminescent analyser. The NOx measurements are taken in flames with several different center tube equivalance ratio( ø$\sub$o/), and overall equivalace ratio(ø$\sub$o/) for a fixed fuel flowrate. The NOx emission decrease to reach a minimum value at an optimum ø$\sub$c/ 2. Theø$\sub$c/ 2 flame gives a compromise of thermal NO and prompt NO mechanism. In the case of excitation. the visual shape of the flame is changed from laminar flame to turbulent-like flame. With increasing levels of excitation amplitude, an optimum value of the NO and NOx emission exists. A shorter flame caused by the enhanced upstream mixing due to acoustic excitation results in the reduction of NO and NOx emission in the present flames. The reduction of flame length affects the shorter residence time of center tube mixture, and significantly influences the NOx reduction.

• 비파괴검사학회지
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• 제23권5호
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• pp.488-496
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• 2003

본 연구에서는 금속재 연소관내부에 단열고무/내열복합재로 구성된 연소관 조립체의 품질평가에 적용 가능한 음향방출 비파괴 시험 평가 기법을 정립하기 위하여 그간 수행되었던 시험결과를 종합하여 실제 생산에 적용 가능한 평가 기법을 정립하였다. 유한요소 code를 사용하여 연소관 조립체 구조 해석한 결과를 바탕으로 내열복합재에 절개선이 있는 연소관 표면의 스트레인과 절개선이 없는 연소관 표면의 스트레인 값을 비교하였다 해석결과는 공압시험 중 연소관 표면에 부착된 스트레인 값과 음향방출센서로부터 측정된 신호와 비교함으로써 연소관과 단열고무 접착성이 확인되었다. 음향방출법을 이용하여 금속재 연소관과 단열고무와의 접착성을 평가하는 방법으로서 실제 생산과정에 적용 가능함을 확인하였다.

• 대한기계학회논문집A
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• 제24권4호
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• pp.858-865
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• 2000

It is well recently recognized that quench is one of the serious problems for the integrity of superconducting magnets, which is mainly attribute to the rapid temperature rising in the magnet due to some extrinsic factors such as conductor motion, crack initiation etc. In order to apply acoustic emission(AE)echnique effectively to monitor and diagnose superconducting magnets, it is essential to identify the sources of acoustic emission. In this paper, an acoustic emission technique has been used to monitor and diagnose quenching phenomenon in racetrack shaped superconducting magnets at cryogenic environment of 4.2K. For these purposes special attention was paid to detect AE signals associated with the quench of superconducting magnets. The characteristics of AE parameters have been analyzed by correlating with quench number, winding tension of superconducting coil and charge rate by transport current. In addition, the source location of quench in superconducting magnet was also discussed on the basis of correlation between magnet voltage and AE energy.

• 한국측량학회지
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• 제24권3호
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• pp.271-279
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• 2006

음향방출(AE: Acoustic Emission) 기법은 구조물 내부에서 발생하는 균열을 연속적으로 모니터링 할 수 있는 효과적인 비파괴검사법이다. 본 논문에서는 AE센서을 이용하여 PSC 보에서의 파원위치를 결정하기 위한 수학적 모델을 제시하고 실험을 통해 제시된 모델을 평가하였다. 실험을 위해 제작된 5m-PSC보의 표면에서 인위적으로 쉬미트해머의 타격에 의해 탄성파를 발생시켰으며 1m 간격으로 선형으로 배치된 7개의 AE센서에 의해 탄성파의 도달시간이 측정되었다. 최소제곱법에 의해 측정된 도달시간의 잔차의 제곱합이 최소가 되도록 파원의 위치를 구한 후, 실제 타격위치와 비교하여 추정된 위치결정방법의 정확도를 평가하였다. 54개의 타격실험을 통해 얻어진 파원위치의 평균제곱근 오차는 약 2cm 이었다.

• 소성∙가공
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• 제29권1호
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• pp.20-26
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• 2020

In the design of the metal forming processes, various types of ductile fracture criteria are used to predict crack initiation and to fabricate metallic products without any defects. However, the quantitative measurement method for determination of crack initiation is insufficient. It is very difficult to detect crack initiation in ductile metals with excellent deformability because no significant load drop is observed due to crack generation. In this study, the applicability of acoustic emission sensors, which are commonly used in facility diagnostics, to measure crack initiation during the metal forming process was analyzed. Cylindrical notch specimens were designed using the finite element method to induce a premature crack on the surface of pre heat-treated steel (ESW90) material. In addition, specimens with various notch angles and heights were prepared and compression tests were carried out. During the compression tests, acoustic emission signal on the dies and images of the surface of the notch specimen were recorded using an optical camera in real time. The experimental results revealed that the acoustic emission sensor can be used to detect crack initiation in ductile metals due to severe plastic deformation.

• 한국암반공학회:학술대회논문집
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• 한국암반공학회 2006년도 춘계학술발표회 논문집
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• pp.79-93
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• 2006

It is well known that acoustic emission (AE) is indicator of rock fracturing or damage as rock is brought to failure under the uniaxial compressive loads. In this paper, an experimental study on the source location of acoustic emission on the cylindrical specimens of granite under uniaxial compression test was made. The AE source location was made by measuring the six channel AE data. Comparing to this experiment, the numerical method is applied to model the initiation and propagation of fracture by AE using a numerical code, RFPA (Realistic Failure Process Analysis). This code incorporates the mesoscopic heterogeneity in Young's modulus and rock strength characteristic of rock masses. In the numerical models, values of Young's modulus and rock strength are realized according to a Weibull distribution in which the distribution parameters represent the level of heterogeneity of the medium. The results of the simulations show that RFPA can be used not only to produce acoustic emission similar to those measurements in our experiments, but also to predict fracturing patterns under uniaxial loading condition.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제28권1호
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• pp.16-23
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• 2002

To understand the micro-mechanical changes and the effects of the fluoride on rat's femur after administration of sodium fluoride, the three-point bending test, acoustic emission analysis during the three-point bending test and scanning electron microscopy were performed. The obtained results were as follows: 1. Bone strength increased in the rats given 1, 5, 10 and 20 ppm of fluoride but, there were no statistical significances (p>0.05). 2. With increasing the concentration of fluoride, most AE events released rapidly just before the maximum load and smaller events were recorded than the control group's. The average of cumulative AE event counts until maximum load of the femur in 20 ppm group were significantly small with respect to the control group's (p<0.05). 3. Fracture surfaces were well coincide with the results of acoustic emission behavior. Analyses of fracture surfaces indicated that, consistent with its the highest load, rat femur in 20 ppm fluoride group displays the roughest surface.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.213-219
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• 2003

Acoustic emission behavior during fatigue crack growth test was investigated under various loading condition. To describe the acoustic emission activity, counts rate (d/dn) was related with SIFR (stress intensity factor range, K). Results indicated that SIFR could be divided into two parts according to its relationship with counts rate. For $K<25_{MPa\sqrt{m}}$, counts rate was increased as the SIFR increased. However, for values greater than $25_{MPa\sqrt{m}}$ , decreasing behavior was shown. This behavior of counts rate corresponding SIFR was keeping the same trend regardless of load range or crack length. Acoustic emission response to the single overload was sudden drop and slow recovery in counts rate like crack growth retardation. Under variable loading condition, counts rate of each loading block was same as that of constant amplitude loading. Overall experimental data was somewhat scattered since sensitive characteristics of acoustic emission method. However, these empirical relations indicated that counts rate was uniquely correlate with single parameter, SIFR.

• 비파괴검사학회지
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• 제31권1호
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• pp.53-61
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• 2011

본 연구는 편측 노치가 삽입된 A16061-T6 알루미늄 합금 평판 시편에 대해 유리섬유강화플라스틱(GFRP) 복합재 패치의 적층수를 변수로 하여 보수히고, 인장 하중에 따른 시편의 손상 과정을 음향방출법(acoustic emission, AE)으로 실시간 분석하였다. AE 에너지 발생률(AE energy rate), hit 발생률(hit rate), AE 진폭(AE amplitude) 거통과 파형 및 1차 중심주파수(1st peak frequency)의 대역을 조사하여, 시편 파괴시 알루미늄 크랙(Al cracking), 섬유 파단(fiber breakage), 수지 균열(resin cracking), 층간 분리(delamination)로 분류하였다. 시편의 변위를 음향방출 특성에 따라 구간(region) I, II, III으로 나눌 수 있었으며, 패치 자체가 실제 파괴되는 구간인 구간 II를 세부적으로 분석하여 패치의 적층수에 따른 AE 특성 차이를 구하였다.

• 동력기계공학회지
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• 제9권1호
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• pp.5-13
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• 2005

Acoustic emission(AE) is defined as the transient elastic waves thar are generated by the rapid release of energy. The advantage of AE is that very early crack growth can be detected well before a highly stressed component may fail. At present, an exact diagnosis is the most reliable means for determining the soundness of structures during power plant operations. AE monitoring has been applied successfully in power plants to determine mechanical problems, pressure vessel integrity and external valves leaks, vacuum leaks, the onset of cavitation in pumps and valves, the presence of flow(or no flow) in piping and heat exchange equipment, etc. Acoustic emission(AE) technology has recently strengthened its application base, and practitioners' understanding of the technique's fundamentals. This paper introduces the methods of a survey and assessment on AE monitoring applications in nuclear, fossil and hydraulic power plant. The main objective of this paper was to obtain information on various applications of AE technology in power plant.