• 한국산업융합학회 논문집
• /
• 제22권2호
• /
• pp.191-199
• /
• 2019

In this paper, dissimilar friction welding were produced using 15 mm diameter solid bar in chrome molybedenum steel(SCM440) to stainless steel(STS316L) to investigate their mechanical properties. Consequently, optimal welding conditions were n=2000 rpm, HP=70 MPa, UP=140 MPa, HT=10 sec and UT=10 sec when the metal loss(Mo) is 8.6 mm. In addition, an acoustic emission technique was applied to evaluate the optimal friction welding condition. AE parameters including the cumulative count, amplitude and energy showed a various changes according to the friction condition. A continuous type waveforms and low frequency spectrum was presented in friction time. On the other hand, a burst type waveform and high frequency spectrum was exhibited in pressing time.

• 말소리와 음성과학
• /
• 제5권4호
• /
• pp.3-15
• /
• 2013

The acoustic analysis of diadochokinesis(DDK) has been used to evaluate dysarthria. However, there has not been an automatic method to evaluate dysarthria. The aim of this study was to introduce a new automated program to measure DDK tasks and to apply this to clinical patients with idiopathic Parkinson's disease(IPD). Fourty-seven patients with IPD and a healthy control group of twenty participants were selected with every DDK task recorded three times. Twenty-five acoustic parameters in the program were developed. The relevant parameters were times of DDK, pitch related parameters, intensity parameters which were analyzed by 2-way ANOVA. Significant differences between the groups were found in the times of DDK, pitch related parameters, and intensity parameters. The findings indicated that the pitch of control group was more stable than that of the IPD. Even though the patients with IPD had a higher intensity value, this phenomenon was caused by the weakness of the IPD group who could not control their speech with a breath.

• 비파괴검사학회지
• /
• 제29권5호
• /
• pp.466-472
• /
• 2009

고온, 고압의 원자력 배관 누설 판별을 위해 음향방출기법(AE)을 이용한 누설감지 시스템인 ALMS 기법이 적용되고 있다. 이 시스템은 단지 AE 센서로 전해진 신호의 RMS값을 이용하여 누설의 유무만을 판단할 뿐, 누설 발생시 누설부의 크기나 형태를 평가하는 것에는 어려움이 있었다. 따라서 본 논문에서는 이러한 문제를 해결하기 위하여 AE센서와 가속도센서를 동시에 이용한 이중 센서 시스템을 제안하였다. 빠른 학습 속도와 정확성을 위해 Levenberg-Marquardt 학습 알고리즘을 이용한 인공신경회로망을 적용시키고, 이를 통해 신뢰성 있는 분석 결과를 얻을 수 있다. 배관내 압력과 누설부의 크기와 모양에 따른 실험신호들을 학습시키고 그 판별 정확성을 확인하였다. 추가적으로 배관 두께에 따라 발생하는 파(wave)의 종류와 특성이 달라지는 것을 이론과 실험을 통하여 알아보았다.

• 대한기계학회논문집A
• /
• 제26권9호
• /
• pp.1787-1794
• /
• 2002

TiNi alloy fiber was used to solve the problem of the tensile residual stress as the reinforced material. TiNi alloy fiber improves the tensile strength of composite by occurring compressive residual stress in the matrix using shape memory effect. In order to generate compressive residual stress in TiNi/Al6061 shape memory alloy(SMA) composite, 1, 3 and 5% pre-strains were applied to the composite in advance. It was also evaluated the effect of compressive residual stress corresponding to the pre-strain variation and the volume fraction of TiNi alloy. AE technique was used to clarify the microscopic damage behavior at high temperature and the effect of pre-strain in TiNi/Al6061 SMA composite. The results of the microscopic damage evaluation of TiNi/Al6061 SMA composite under various pre-strain using AE technique can be divided into three stage corresponding to the AE signals. AE counts and events were useful parameters to evaluate the fracture mechanism according to the variation of pre-strain. In addition, two dimensional AE source location technique was applied for monitoring the crack initiation and propagation in composite.

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

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2011년도 정기 학술대회
• /
• pp.419-423
• /
• 2011

AE는 다른 비파괴 검사방법과 달리 가동 상태에서 구조물의 결함이 발생 및 성장을 검출 할 수 있으며, 연속 검사가 가능하다는 장점으로 인하여 대형 구조물의 안정성 평가에 널리 이용되고 있다. 하지만 AE는 20kHz부터 20MHz 사이에 발생하는 음파를 감지하기 위해 센서를 사용하며, 이 센서의 감도에 따라 결과가 달라질 가능성이 존재한다. 이에 본 연구에서는 STS 304와 SS400 강재에 인장실험을 실시하여, 강재의 균열 신호를 탐지하고자 한다. 인장실험에는 스테인리스강 및 탄소강 시편을 준비하였고, 감도가 다른 센서를 이용하여 동일한 인장실험을 실시하였다. 그리고 균열이 발생하는 13개의 신호 파라미터에 대해 군집분석을 실시하여 4가지 종류의 군집으로 분류하였다. 또한 기무가설을 이용한 통계분석을 통해 두 시험편이 다르지 않다는 것을 증명하였다. 이 결과를 바탕으로 본 실험에서 얻은 Waveform이 재료의 균열신호라는 신뢰성을 확인할 수 있었다.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 1998년도 Proceedings ICPE 98 1998 International Conference on Power Electronics
• /
• pp.961-965
• /
• 1998

The rapid development of small-scale (1-10 MJ) Superconducting Magnetic Energy Storage Systems (SMES) can be explained by real perspective of practical implementation of these devices in electro power nets. However the serious problem of all high mechanically stressed superconducting coils-problem of training and degradation (decreasing) of operating current still exists. Moreover for SMES systems this problems is more dangerous because of pulsed origin of mechanical stresses-one of the major sources of local heat disturbances in superconducting coils. We investigated acoustic emission (AE) phenomenon on model and 0.5 MJ SMES coils taking into account close correlation of AE and local heat disturbances. Two-coils 0.5 MJ SMES system was developed, manufactured and tested at Russian Research Center in the frames of cooperation with Korean Electrical Engineering Company (KEPCO) [1]. The two-coil SMES operates with the stored energy transmitted between coils in the course of a single cycle with 2 seconds energy transfer time. Maximum operating current 1.55 kA corresponds to 0.5 MF in each coil. The Nb-Ti-based conductor was designed and used for SMES manufacturing. It represents transposed cable made of Nb-Ti strands in copper matrix, several cooper strands and several stainless steel strands. The coils are wound onto fiberglass cylindrical bobbins. To make AE event information more useful a real time instrumentation system was used. Two main measured and computer processed AE parameters were considered: the energy of AE events (E) and the accumulated energy of AE events (E ). Influence of current value in 0.5 MJ coils on E and E was studied. The sensors were installed onto the bobbin and the external surface of magnets. Three levels of initial current were examined: 600A, 1000A, 2450 A. An extraordinary strong dependence of the current level on E and E was observed. The specific features of AE from model coils, operated in sinusoidal vibration current changing mode were investigated. Three current frequency modes were examined: 0.012 Hz, 0.03 Hz and 0.12 Hz. In all modes maximum amplitude 1200 A was realized.

• 한국해양공학회지
• /
• 제22권5호
• /
• pp.100-105
• /
• 2008

A106 Carbon Steel has recently been used as the material for pipes, nozzles, and tank shells in nuclear power plants. Its corrosion resistance gives the steel many advantages for use in structures under high temperature and high pressure. This steel is also expected to be used as a structural material in the shipbuilding industry for applications involving severe conditions, such as high temperature and pressure. In this study, the mechanical properties of A106 carbon steel were evaluated in regard to its corrosion times. The tensile and yielding strengths decreased as the corrosion time increased. In particular, the tensile strength was influenced by corrosion. In addition, an acoustic emission (AE) technique was used to clarify the microscopic damage to specimens that had undergone corrosion for a certain period. It was found that AE parameters, such as events, energy, duration time, and amplitude were useful for evaluating the degree of damage and remaining life of the corroded specimen. Various properties of the waveform and frequency range were also seen, based on the degree of damage to the specimen from the corrosion time.

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

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2005년도 춘계학술대회 논문집
• /
• pp.108-113
• /
• 2005

In this study, rotary type diamond dressing system for ultra-precision centerless grinding for ferrule was developed at the first time and experiments were conducted with AE sensor and hall sensor system to verify the optimum dressing condition for ultra-precision centerless grinding for ferrule. The correlations with the condition of dressing are evaluated by AE signal analysis with root mean square (RMS) and frequency analysis. And current signals from hall sensor are also studied as a factor of dressing optimum condition selection. Dressing process was conducted to investigate the effects of depth of cut, rotating speed, and the number of overlap to select the optimum condition of rotary dressing system of ultra-precision centerless grinding machine for ferrule fabrication. In order to verify the optimum condition of dressing, AE and current signals were compared with the surface quality of dressing wheel and grinding wheel for ultra-precision ferrule grinding. All of these experiments were completed by Taguchi Methodology to reduce experimental time. Hence, the optimum condition of rotary dressing system for ultra-precision centerless grinding for ferrule fabrication can be selected following to the experiment result from signals of AE and hall sensor.