• 비파괴검사학회지
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• 제25권3호
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• pp.157-162
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• 2005

In order to evaluate the corrosion of reinforcing steel-bars (rebar) in concrete, a nondestructive evaluation by the half-cell potential method is currently applied. In this study, potentials measured on a concrete surface are compensated into those on the concrete-rebar interface by the inverse boundary element method (IBEM). Because these potentials are obtained three-dimensionally (3-D), 3-D visualization is desirable. To this end, a visualization system has been developed by using VRML (Virtual Reality Modeling Language). As an application, results of a reinforced concrete (RC) slab with corroded rebars are visualized and discussed.

• 비파괴검사학회지
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• 제26권6호
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• pp.403-410
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• 2006

Eddy current testing (ECT) signals produced by a differential bobbin coil probe vary according to probe design parameters such as the number of turns, geometry and coil gap size. In the present study, the characteristics of a differential bobbin coil probe signals are investigated by numerical simulation in order to determine the optimum coil gap. For verification of numerical simulation accuracy, a specially designed bobbin probe of which the coil gap can be adjusted is fabricated and a series of experiments to acquire signals from two kinds of standard tubes with the variation in coil gap is performed. Then, the experimental signals are compared to the simulation results. Based on this investigation, a decision on the optimum range of coil gap is made. The theoretically predicted signals agree very well to the experimental signals. In fact, this excellent agreement demonstrates a high potential of the simulation as a design optimization tool for ECT bobbin probes.

• 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.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.130.1-130.1
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• 2005

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 2004년도 High Temperature Superconductivity Vol.XIV
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• pp.4-4
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• 2004

• 비파괴검사학회지
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• 제18권4호
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• pp.304-312
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• 1998

비파괴검사중의 하나인 초음파 탐상검사는 교량, 발전설비 및 석유화학플랜트 등의 각종 다양한 구조물들의 안전성 확보를 위한 내부결함 및 손상평가를 위하여 일반적으로 폭넓게 사용되고 있다. 초음파를 이용한 데 파괴 평가 기술은 각종 구조물에 존재하는 내부결함에 의한 산란신호를 통해 건전성을 평가하는 기법이므로 결함의 신뢰성 녹은 정량적 평가를 위해서는 결함으로부터의 초음파 산란산호특성에 대한 기본적 이해가 필수적이며 따라서 이를 위한 모델링 수치해석 연구가 요구된다. 본 연구에서는 동탄성 경계요소법을 이용하여 무한체내에 존재하는 다중기공 결함에 의한 초음파 수평횡파의 근거리 산란특성에 대하여 결함의 형상과 결함사이의 상호작용을 고려하여 해석하였다. 본 연구에서 얻어진 결과들은 결함검출 민감도의 개선 및 역변환 해석에 의한 정량적 비파괴 평가에 큰 도움을 줄 수 있다.

• 비파괴검사학회지
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• 제32권6호
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• pp.686-695
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• 2012

This paper proposes a noncontact thermography technique for fatigue crack evaluation under a cyclic tensile loading. The proposed technique identifies and localizes an invisible fatigue crack without scanning, thus making it possible to instantaneously evaluate an incipient fatigue crack. Based on a thermoelastic theory, a new fatigue crack evaluation algorithm is proposed for the fatigue crack-tip localization. The performance of the proposed algorithm is experimentally validated. To achieve this, the cyclic tensile loading is applied to a dog-bone shape aluminum specimen using a universal testing machine, and the corresponding thermal responses induced by thermoelastic effects are captured by an infrared camera. The test results confirm that the fatigue crack is well identified and localized by comparing with its microscopic images.

• 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.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.1830-1835
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• 2005

It is important to estimate the distribution of intensity of a magnetic field for application of magnetic method to industrial nondestructive evaluation. Magnetic camera provides the distribution of a quantitative magnetic field with homogeneous lift-off and same spatial resolution. And it is possible to interpret the distribution of the magnetic field when the dipole model is introduced. This study introduces the numerical and experimental considering of the quantitative evaluation of several size and shapes of the cracks using the magnetic field images of the scan type magnetic camera.

• 한국신뢰성학회:학술대회논문집
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• 한국신뢰성학회 2001년도 정기학술대회
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• pp.235-238
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• 2001

It is well known that the reliability of materials of mechanical products is becoming more and more important not only for assurance of quality, but for international competition of products. In order to assure the reliability of materials or mechanical products nondestructive evaluation (NDE) techniques are playing more important roles. The existence of Internal defects in materials or mechanical parts is served as crack initiation site during the various loading condition. Historically, nondestructive evaluation (NDE) technique has been used almost exclusively for detecting microscopic discontinuities In materials or mechanical parts after they have been in service to expand the role of the NDE to include all aspects of materials production and application. Research efforts are being directed at developing and perfecting NDE techniques capable of monitoring (1) materials production processes (2) material integrity following transport, storage and fabrication and (3) the amount and rate of degradation during service. In addition, efforts are underway to develop technique capable of quantitative discontinuity sizing, permitting determination of response using fracture mechanics analysis, as well as techniques for quantitative materials characterization to replace the qualitative techniques used in the past. In this paper, the important role of NDE technology for reliability assurance of materials/mechanical parts is introduced.