• Computers and Concrete
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• 제20권3호
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• pp.257-262
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• 2017

This study aims to develop a signal processing scheme to accurately predict the thickness of concrete slab using air-coupled impact-echo. Air-coupled impact-echo has been applied to concrete non-destructive tests (NDT); however, it is often difficult to obtain thickness mode frequency due to noise components. Furthermore, apparent velocity in concrete is a usually unknown parameter in the field and the thickness of the concrete slab often cannot be accurately measured. This study proposes a signal processing scheme using guided wave analysis, wherein dispersion curves are drawn in both frequency-wave number (f-k) and phase velocity-frequency ($V_{cp}-f$) domains. The theoretical and experimental results demonstrate that thickness mode frequency and apparent velocity in concrete are clearly obtained from the f-k and $V_{cp}-f$ domains, respectively. The proposed method has great potential with regard to the application of air-coupled impact-echo in the field.

• 제어로봇시스템학회논문지
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• 제11권7호
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• pp.595-601
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• 2005

A mobile robot system utilizing NDT (Non-Destructive Testing) method is designed and fabricated f3r automatic integrity evaluation of large sized industrial reservoirs and pipelines. The developed mobile robot can crawl over the outer surface of the industrial facilities even though the shape of the structures is various and unsymmetric. The robot detects defects such as pinholes, cracks and thickness reduction at the wall of the facilities using EMAT (Electro-Magnetic Acoustic Transducer). Image processing technology for weld line detection at the surface of the target and host programs including defect detecting algorithms are also developed. Automation of defect detection for these kinds of large facilities using mobile robots is helpful to prevent significant troubles of the structures without danger of human beings under harmful environment.

• 대한전자공학회논문지
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• 제26권2호
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• pp.163-168
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• 1989

본 연구에서는 Rayleigh 임계각 근처에서 발생하는 후방산란신호를 검출 함으로써 탄성매질에서 Rayleigh 파의 속도를 측정하였다. Rayleigh 각을 측정하기 위한 회전시스템을 제작하였으며 스테인레스, 황동, 알루미늄, 구리샘플에 대해서 측정된 속도는 이론값과 좋은 일치를 보였다. 후방산란신호에 의한 비파괴검사 방법을 제시하였으며 IC 샘플내부에 대한 c-scan 음향이미지를 나타내었다.

• E2M - 전기 전자와 첨단 소재
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• 제7권1호
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• pp.42-48
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• 1994

The preventive diagnosis technique for power system is being highlighted as a research area for deterioration of insulation in machinery because of high-voltage power system. We make efforts to develop not only diagnosis of aging state but also detection of defects in the initial stage from preventive diagnosis technique. Especially, partial discharge is actively studied as a non-destructive diagnosis technique and very useful because partial discharge measurement reduces damage than conventional diagnosis technique. The loaded stress during this test is smaller than that of other diagnosis techniques. But the continuous research for various complicated analysis method is required because partial discharge has very small signals and its signals have complex forms. In this paper, the measurement of partial discharge was investigated and studied on many specimens with void. We made samples having artificial voids and measured partial discharge. In order to use as a practical diagnosis technique, we studied ways of measurement, measured illustrations and types of partial discharge which could be used in order to diagnose defects of power machinery.

• 한국압력기기공학회 논문집
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• 제4권2호
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• pp.29-33
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• 2008

As the measures of nuclear power plant utilities and manufacturers to reduce the defects of tube expansion region during manufacturing steam generators, many types of NDEs(Non-Destructive Examinations) are conducted to inspect the expansion region. The expansion region of tube is subject to degrade because of stress concentration induced by tube expansion, sludge pile and high temperature. So the inspections for tube expansion region have been reinforced. Liquid penetrant test, helium leak test, Bobbin profile test and hydraulic test are performed to confirm the integrity of tube expanded by hydraulic expansion method. Liquid penetrant test and helium leak test are used to inspect seal weld region on tubesheet end part. Bobbin Profile test is used to inspect fully the expanded region of steam generator tube. Hydraulic test finally verifies the integrity of seal weld region on tubesheet end part.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1988년도 전기.전자공학 학술대회 논문집
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• pp.47-50
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• 1988

In this paper, Rayleigh wave velocity has been measured by detecting the backscattered signal generating near the Rayleigh critical angle in the elastic medium. The rotating system has been made for the measurment of Rayleigh angle. It has been shown that the measured results has been good agreement with the theoretical value. The method of non-destructive evaluation using backscattering signal has been presented and the internal of IC sample has been displayed acoustic image with good contrast.

• 한국구조물진단유지관리공학회 논문집
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• 제5권3호
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• pp.123-130
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• 2001

The purpose of this study is to suggest the non-destructive equation for the estimation of concrete strength by ultrasonic pulse velocity at the Age of 28day compressive strength of $600{\sim}1000kg/cm^2$. For this purpose, selected test variables were water-hinder ratio, replacement ratio of silica fume, binder content, maximum size of coarse aggregate and sand-aggregate ratio. From the results, the average increase or decrease of ultrasonic pulse velocity is 61m/sec for each 1% of moisture content. And the correlation equation between the ultrasonic pulse velocity and the compressive strength of concrete is as follows. $F_c=896.3V_p-3514$ ($R^2$ = 0.81) where, $F_c$ : compressive strength($kgf/cm^2$), $V_p$ : ultrasonic velocity(km/sec).

• 한국지반공학회논문집
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• 제24권8호
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• pp.13-23
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• 2008

다양한 토목 건축 구조물의 하부구조로 많이 사용되는 콘크리트 말뚝기초는 상부 토목 건축 구조물의 안전에 있어 매우 중요한 요소이다. 본 논문에서는 이러한 말뚝의 비파괴적인 건전성 평가를 위하여, 범용적인 파의 위상 그룹속도 결정법인 HWAW(Harmonic Wavelet Analysis of Wave)방법을 말뚝의 비파괴 시험에 적용하였다. 제안된 방법은 말뚝자체의 건전성 평가와 선단지지말뚝의 거동에 매우 중요한 말뚝 선단부 상태(경계조건)를 자동적으로 결정할 수 있다. 제안된 방법을 검증하기 위하여 ABAQUS를 사용한 수치모의 실험을 수행하였으며, 실제 모형말뚝을 제작하여 공기중 실험과 실제 지반조건을 모사하기 위한 토조내 실험을 수행하였다. 이러한 수치모의 실험과 실제 모의 실험을 통하여 말뚝의 비파괴 건전성 평가에 있어서의 제안된 방법의 타당성을 확인하였다.

• International Journal of Railway
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• 제1권1호
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• pp.1-5
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• 2008

The railway system requires safety and reliability of service of all railway vehicles. Suitable technical systems and working methods adapted to it, which meet the requirements on safety and good order of traffic, should be maintained. For detection of defects, non-destructive testing methods-which should be quick, reliable and cost-effective - are most often used. Since failure in railway wheelset can cause a disaster, regular inspection of defects in wheels and axles are mandatory. Ultrasonic testing, acoustic emission and eddy current testing method and so on regularly check railway wheelset in service. However, it is difficult to detect a crack initiation clearly with ultrasonic testing due to noise echoes. It is necessary to develop a non-destructive technique that is superior to conventional NDT techniques in order to ensure the safety of railway wheelset. In the present paper, the new NDT technique is applied to the detection of surface defects for railway wheelset. To detect the defects for railway wheelset, the sensor for defect detection is optimized and the tests are carried out with respect to surface and internal defects each other. The results show that the surface crack depth of 1.5 mm in press fitted axle and internal crack in wheel could be detected by using the new method. The ICFPD method is useful to detect the defect that initiated in railway wheelset.

• 한국철도학회논문집
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• 제10권1호
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• pp.1-6
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• 2007

Railway wheels in service are regularly checked by ultrasonic testing, acoustic emission and eddy current testing method and so on. However, ultrasonic testing is sometimes inadequate for sensitively detecting the cracks in railway wheel which is mainly because of the fact of crack closure. Recently, many researchers have actively fried to improve precision for defect detection of railway wheel. The development of a nondestructive measurement tool for wheel defects and its use for the maintenance of railway wheels would be useful to prevent wheel failure. The induced current focusing potential drop(ICFPD) technique is a new non-destructive tasting technique that can detect defects in railway wheels by applying on electro-magnetic field and potential drops variation. In the present paper, the ICFPD technique is applied to the detection of surface and internal defects for railway wheels. To defect the defects for railway wheels, the sensor for ICFPD is optimized and the tests are carried out with respect to 4 surface defects and 6 internal defects each other. The results show that the surface crack depth of 0.5 mm and internal crack depth of 0.7 mm in wheel tread could be detected by using this method. The ICFPB method is useful to detect the defect that initiated in the tread of railway wheels