• 한국정밀공학회지
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• 제22권3호
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• pp.130-136
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• 2005

The nondestructive evaluation system consisted of a ball indentation tester and a ultrasonic tester was developed to evaluate material properties. The relations between the parameters from test results using the system and the results of tensile and fracture toughness tests were investigated. The fracture toughness and tensile properties could be determined using the system. Some metallic materials were experimented to predict the fracture toughness and tensile properties and verify the relations between them. The predicted fracture toughness and tensile properties show a good agreement with the results obtained by conventional tests. It is found that the material properties and the material degradation can be evaluated using the nondestructive evaluation system.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.280-285
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• 2000

It is very important to evaluate the surface or subsurface microstructure because of their influences on mechanical properties of materials. Surface SH-wave which is horizontally polarized shear wave traveling along near surface and subsurface layer is an attractive technique for material evaluation. The destructive method is widely used for the estimation of material degradation but it has a great difficulty in preparing specimens from in-service industrial facilities. In this study, nondestructive evaluation for degraded structural materials used at high temperature though surface SH-wave method is discussed. 2.25Cr-1Mo steel specimens which were prepared by the isothermal aging heat treatment at $650^{\circ}$ were evaluated though ultrasonic nondestructive evaluation techniques investigating the change of sound velocity, attenuation coefficient and amplitude spectra. In addition, it has verified experimentally the frequency-dependence of attenuation coefficient though wavelet analysis method.

• 한국공작기계학회논문집
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• 제14권3호
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• pp.38-46
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• 2005

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 estimation of degraded structural materials used at high temperature by nondestructive evaluation such as electric resistance method, replica method, Barkhausen noise method, electro-chemical method and ultrasonic method are strongly desired. In this study, various nondestructive evaluation(NDE) parameters of the Barkhausen noise method, such as MPA(Maximum Peak Amplitude), RMS, IABNS(Internal Area of Barkhausen Noise on Signal) and average amplitude of frequency spectrum are investigated and correlated with thermal damage level of 2.25cr-1.0Mo steel using wavelet analysis. Those parameters tend to increase while thermal degradation proceeds. It also turns out that the wavelet technique can help to reduce experimental false call in data analysis.

• 비파괴검사학회지
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• 제15권2호
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• pp.364-370
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• 1995

본 논문은 초음파법을 이용하여 소결 재료의 비파괴적인 평가 방법을 확립하는데 목적을 두고 있다. 소결 재료의 밀도는 소결체로 제작되는 동안 금형과 분말사이의 마찰 때문에 부분적으로 불균질한 분포를 가지고 있으며 이 불균질성은 에너지 감쇠 계수 및 초음파 반사 에코의 주파수 스펙트럼에 있어 중심 주파수의 변화량에 의해 조사되었다. 초음파의 속도, 탄성계수, 포와송 비는 소결 재료의 밀도와 비례 관계에 있었으며 저면 반사파의 중심 주파수는 초음파의 전파 거리의 증가 및 밀도의 감소에 따라 저주파수 쪽으로 이동하였으나 에너지 감쇠 계수는 밀도의 증가에 따라 감소하고 있었다. 본 논문에서는 반사파의 주파수 스펙트럼에 있어 중심 주파수의 변화가 소결 재료의 비파괴적인 평가 방법으로써의 가능성을 보여주고 있다.

• 연구논문집
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• 통권28호
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• pp.229-238
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• 1998

비파괴평가의 대상이 되는 소재나 부품은 관련 표준시험편을 이용하여 평가되고, 표준시험편은 평가대상과 동일 또는 유사한 재질로 제작되어야 한다고 규정하고 있다. 따라서 비파괴평가가 요구되는 소재나 부품을 생산, 외국에 수출하기 위해서는 반드시 공인된 설비와 품질관리 체계로부터의 인증이 선행되어야 한다. 본 논문에서는 초음파를 이용한 항공기용 Udimet 720Li 디스크의 비파괴평가를 위하여 ASTM에 규정되어 있는 4340강 초음파 표준시험편의 적용타당성을 제시하였다. 현미경 시험을 통하여 Udimet 720Li 합금의 미세조직을 규명하고, 고출력 초음파 분석시스템을 이용한 펄스의 위상값을 측정하는 방법으로 4340강 표준시험편 및 Udimet 720Li 합금의 초음파 속도와 감쇠값을 구하였다. 결론적으로 4340강 초음파 표준시험편이 Udimet 720Li 디스크의 평가를 위한 표준시험편으로 사용될수 있음을 증명하였다.

• 동력기계공학회지
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• 제3권4호
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• pp.51-56
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• 1999

The ultrasonic method, which is well known as nondestructive test method, is widely used to evaluate the material damage due to degradation. However, this method is just used for measuring the crack size and the thickness loss of the tube. The purpose of this study is to investigate the applicability of the ultrasonic technique for the evaluation of marine diesel engine exhaust valve and to suggest the correlations between the ultrasonic characteristics and valve degradation. From the evaluation of the results obtained, the technique of using the ultrasonic property was founds to be a efficient method to evaluate the degree of marine diesel engine exhaust valve by nondestructive test.

• 비파괴검사학회지
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• 제20권6호
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• pp.501-510
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• 2000

초음파 에코파형의 시간-주파수해석법으로 Wigner 분포와 웨이브렛 변환 등과 같은 새로운 신호처리 기법이 비파괴평가 분야에 널리 응용되고 있다. 본 연구에서는 웨이브렛 변환(wavelet transform)에 의한 음속과 감쇠계수의 주파수의존성과 초음파 결함신호의 잡음제거의 유용성 유무를 실험적으로 검증하였다. Gabor 함수를 웨이브렛의 기본함수로 사용하였다. 초음파의 에코파형에 포함된 각 주파수성분의 속도와 감쇠계수의 주파수의존성을 추정할 수 있었으며, 초음파탐상에서 결함의 검출능 향상과 결함크기 산정의 정량화에 접근하기 위해 웨이브렛 변환에 의한 S/N비 신호처리 시뮬레이션 결과를 오스테나이트강 스테인레스 용접부에 가공한 EDM 노치의 초음파 결함신호에 적용한 결과 임상에코를 저감하고 S/N비를 개선하는 것이 가능하였다.

• 대한기계학회논문집
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• 제19권5호
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• pp.1202-1210
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• 1995

Aiming at nondestructive evaluation of defect with high accuracy and resolution, ICFPD(Induced Current Focusing Potential Drop) technique was newly developed. This technique can be applied for locating and sizing of defects in components with not only simple shape such as plain surface but also more complex shape and geometry such as curved surface and dissimilar joing. This paper describes the principle of ICFPD technique and also the results of 2-dimensional surface crack in ferromagnetic metal(A508 Cl. III steel) and paramagnetic metal (pure aluminum and stainless 304 steel) measured by this technique. Results are that surface defects in each specimen are detected with the difference of potential drop, and potential drops are distributed a similar shape for each metal and each depth. The normalized potential drop ( $V_{\delta}$2/$^{t}$ / $V_{{\delta} 2}$$^{-1}$) max. in the vicinity of defect is varied with the depth of defect. Therefore, ICFPD technique can be used for the evaluation of defect not only in ferromagnetic metal but also in paramagnetic steel..

• Journal of Mechanical Science and Technology
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• 제16권2호
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• pp.147-154
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• 2002

The objective of this paper is to develop a nondestructive method for estimating the fracture toughness (K$\_$IC/) of CrMoV steels used as the rotor material of steam turbines in power plants. To achieve this objective, a number of CrMoV steel samples were heat-treated, and the fracture appearance transition temperature (FATT) was determined as a function of aging time. Nonlinear ultrasonics was employed as the theoretical basis to explain the harmonic generation in a damaged material, and the nonlinearity parameter of the second harmonic wave was the experimental measure used to be correlated to the fracture toughness of the rotor steel. The nondestructive procedure for estimating the 7c consists of two steps. First, the correlations between the nonlinearity parameter and the FATT are sought. The FATT values are then used to estimate K$\_$IC/, using the K$\_$IC/ versus excess temperature (i.e., T-FATT) correlation that is available in the literature for CrMoV rotor steel.

• 비파괴검사학회지
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• 제7권2호
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• pp.52-57
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• 1988

This article presents a newly developed equipment system for computer-aided, magneto-inductive testing of metals for material properties. The advantages of ultramodern computer technology over conventional test mothods are illustrated, in particular the greatly simplified equipment adjustment and the extended possibilities of test data evaluation. The characterisitics of the new system of equipment are demonstrated by way of practical testing examples.