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초음파현미경에서 V(z) 곡선을 이용한 세라믹/금속 접합계면의 비파괴평가
박익근,이철구,조동수,김용권,Park Ik-Keun,Lee Chul-Ku,Cho Dong-Su,Kim Yong-Kwon 대한용접접합학회 2005 대한용접·접합학회지 Vol.23 No.2
A leaky surface acoustic wave (LSAW) velocity was measured using a scanning acoustic microscope on the ceramic/metal interface in order to investigate material properties. The inverse Fourier transform (IFFT) of the V(z) curve contains the reflectance function of a liquid-specimen interface. So, the longitudinal, transverse, and Rayleigh wave velocities for each layer are obtained by the inversion of the V(z) curve at the same time. This paper contains mainly the experimental procedure for measurements of the LSAW velocity, and the results obtained for the velocity variation of individual layer after the thermal shock. It is shown that this method is useful in measuring the material properties under external stress.
Comb Transducer를 이용한 파이프 내 유도초음파 모드의 거동에 관한 연구
박익근,김용권,조윤호,안연식,조용상 한국비파괴검사학회 2004 한국비파괴검사학회지 Vol.24 No.2
발전설비의 보수검사에 적용하기 위한 예비 연구로 comb transducer를 이용한 파이프 내에서의 유도초음파 모드의 거동을 실험적으로 검증하였다. 유도초음파의 모드식별은 STFT와 WT에 의한 시간-주파수해석을 통하여 최적의 모드를 선정하였다. 시간-주파수해석과 이론적 해석 방법인 분산 곡선을 비교한 결과 잘 일치함을 알 수 있었으며, pitch-catch법과 선단부로부터 반사된 신호를 모두 분석한 결과 L(0,1) 모두가 다른 모드에 비해 모드변화에 의한 영향이 적었다. 따라서 L(0,1)을 최적의 모드로 선정하고, 결함위치를 추정한 결과 유용함을 알 수 있었다. A preliminary study of the behavior of ultrasonic guided wave mode in a pipe using a comb transducer for maintenance inspection of power plant facilities has been verified experimentally. The mode identification has been carried out in a pipe using the time-frequency analysis methods such as the wavelet transform(WT) and the short time Fourier transform (STFT), compared with theoretically calculated group velocity dispersion curves for longitudinal and flexural modes. The results are in good agreement with analytical predictions and show the effectiveness of using the time-frequency analysis method to identify the individual modes. It was found out that the longitudinal mode(0,l) is less affected by mode conversion compared with the other modes. Therefore, L(0,l) is selected as an optimal mode for the evaluation of the surface defect in a pipe.
박익근,김용권,Park, I.K.,Kim, Y.K. 한국생산제조학회 2010 한국생산제조학회지 Vol.26 No.2
In this paper, study on the mode characteristics analysis of the SH-EMAT (shear horizontal, electromagnetic acoustic transducer) waves for evaluating the thickness reduction in plates such as corrosion and friction is presented. Noncontact methods for ultrasonic wave generation and detection have been a great concern and highly demanded due to their capability of wave generation and reception on surface of high temperature or on rough surface. Mode identification of the SH-EMAT wave is carried out in an aluminum plate with thinning defects using time frequency analysis method such as wavelet transform, compared with theoretically calculated group velocity dispersion curve. The changes of various wave features such as the amplitude and the time-of-flight have been observed and the correlations with the thickness reduction have been investigated. Firstly, experiments have been conducted to confirm that it is possible to selectively generate and receive specific desired SH modes. These modes have then been analyzed to select the parameters that are sensitive to the thickness change. The results show that the mode cutoff and the time-of-flight changes are feasible as key parameters to evaluate the thickness reduction.
박익근,임재생,윤종학,노승남,서성원 한국공작기계학회 2003 한국공작기계학회 추계학술대회논문집 Vol.2003 No.-
본 연구에서는 초음파현미경의 기하학적 원리와 초음파현미경의 특징중 하나인 V(z)곡선의 간섭파형을 시뮬레이션하였고, 실제 초음파현미경의 V(z)곡선법을 이용하여 미소영역에서의 누설탄성표면파 음속을 측정하였다. 초음파현미경을 이용한 V(z)곡선법의음속측정결과가 시뮬레이션 음속값과 큰차이를 보이지 않으므로 미소영역에 초음파현미경의 V(z)곡선법을 적용하여 초음파의 음속측정이 가능함을 확인하였다. 이는 향후 초음파현미경을 이용하여 미세한 재료의 물성평가에 적용할 수 있을 것으로 기대된다.
유도초음파를 이용한 2.25Cr-1Mo재의 열화도 평가
박익근,박은수,이상용,권숙인,조윤호,윤승현 한국비파괴검사학회 2001 한국비파괴검사학회지 Vol.21 No.4
고온에서 장시간 사용으로 인하여 발생되는 경년열화 평가에는 파괴적인 방법이 신뢰성이 높지만 시험편 채취의 어려움이 있다. 그러므로 비파괴적인 방법에 의한 열화도 평가가 바람직하다. 본 연구에서는 2.25Cr-1Mo강에 대하여 장시간 등온열처리로 모의 열화시험편을 제작하여 고온설비부재에서 발생되는 탄화물의 석출 및 조대화, 불순물의 입계편석 등 금속학적 미세조직을 관찰하고, 미세조직의 변화와 유도 초음파의 전파특성과의 상관관계를 규명하고, 파괴시험치와 그 결과를 비교하여 초음파 비파괴평가에 의한 고온부재의 열화도 평가의 가능성을 실험적으로 검증하고자 한다. The destructive method is reliable and widely used for the estimation of material degradation but, it have time-consuming and a great difficulty in preparing specimens from in-service industrial facilities. Therefore, the etimation of degraded structural materials by nondestructive evaluation is strongly desired. In this paper, the use of guided wave was suggested for the evaluation of thermally damaged 2.25Cr-1Mo steel as an alternative way to compensate for limitations of fracture tests. The observation of microstructure variations of the material including carbide precipitation increase and spheroidization near gain boundary was conducted and the correlation with the guided wave features such as energy loss ratio and group velocity changes was investigated. Through this study the feasibility of ultrasonic guided wave evaluation for thermally damaged materials was explored.
초음파에 의한 필렛 용접힐부의 표면결함 검출능에 관한 실험적 검증
박익근,이철구 대한용접접합학회 2000 대한용접·접합학회지 Vol.18 No.1
Ultrasonic nondestructive evaluation (UNDE) technique is commonly used for detecting inner defects in the materials. Recently, new methods are trying to apply for detecting surface and subsurface flaws using Rayleigh wave or creeping wave. These techniques, however, have following problems. Echo amplitude is remarkably affected by the surface conditions and discrimination of echo pattern is usually difficult because shear wave propagate in the material at the same time. We can apply surface SH-wave(which is horizontally polarized shear wave traveling along near surface layer) technique to detect surface flaws. In this paper, directivity, distance amplitude characteristics and detectability of surface flaws at fillet weld hills of the 5 MHz and 2 MHz surface flaws at fillet weld hills of the 5 MHz and 2 MHz surface Sh-wave are experimentally investigated. As a result of the study, it was found out that these techniques are valuable for the detection of fatigue cracks at fillet weld heels which can not be detected by other ultrasonic techniques such as angle beam technique and which are inaccessible for non-destructive testings e.g. MT(magnetic particle testing) or PT(liquid penetrant testing).
박익근,김용권,김현묵,송원준,조용상,안연식,Park, Ik-Keun,Kim, Yong-Kwon,Kim, Hyun-Mook,Song, Won-Joon,Cho, Yong-Sang,Ahn, Yeon-Shik 대한용접접합학회 2005 대한용접·접합학회지 Vol.23 No.5
Conventional non-destructive techniques for inspection of the weld in pipelines require significant test time and high cost. Ultrasonic guided waves have been widely studied and successfully applied to various non-destructive tests with advantage of the long-range inspection. In this paper, a study on the application of ultrasonic guided waves to the long-range inspection of the pipeline is presented using a long-range guided wave inspection system, Wavemaker SE16, GUL. The characteristics and setup of the long-range guided wave inspection system and experimental results in pipes of with various diameter are introduced. The experimental results in mock-up pipes with cluster type detects show that the minimum detectable wall thickness reduction with this guided wave system is $2\~3\%$ in the pipe cross section area. And the wall thickness reduction of $5\%$ in cross section area can be detected when actual detection level is used. Therefore, the applicability of the guided wave systeme to long-range inspection of wall thickness reduction in pipes is verified.