• Journal of the Korean Society for Nondestructive Testing
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• v.17 no.4
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• pp.278-284
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• 1997

EMAT는 비접촉으로 초음파를 송수신 할 수 있는 탐촉자로서 시험체와 탐촉자간의 접촉을 위한 매개 물질이 필요치 않으므로, 움직이고 있는 물체에 초음파탐상법을 적용하고자 하는 분야와 초음파의 속도를 정밀하게 측정하고자 하는 분야에 주로 응용된다. 구체적으로는 길이가 긴 튜브류의 결함 탐상, 용접중인 재료의 용접상태 감시, 기차바퀴 및 레일의 결함 탐상, 고온상태인 재료의 결함 탐상 등이 비접촉 특성을 이용하여 적용될 수 있는 분야이며, 재료의 집합조직 및 소성이방성의 측정, 재료의 미세조직 및 기계적 강도의 예측, 그리고 잔류응력의 측정 등이 정밀한 초음파속도 및 감쇠의 측정으로부터 적용될 수 있는 분야이다. EMAT가 일반적인 접촉식초음파탐상법에 비하여 특별한 분야에의 응용에 큰 장점을 가지고 있지만, 낮은 에너지 전환효율, 넓은 불감영역, 그리고 사용주파수의 한계 등의 문제를 가지고 있기 때문에 기존의 접촉식 방법의 적용이 용이한 분야에의 적용은 필요하지 않다. 그러나 특별한 목적과 용도에의 적용 필요성이 생길 경우에는 적절한 연구를 통하여 알맞은 탐촉자를 제작하고 탐상 방법을 개발함으로서 본래의 목적에 알맞은 탐상이 수행될 수 있다.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.2
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• pp.132-139
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• 2002

The grain size of aluminum alloy was refined to the submicrometer level by using equal-channel angular pressing(ECAP). The effect of grain size refinement was evaluated by the tensile test, micro-hardness test, microstructure observations, ultrasonic test and acoustic emission test. The strength and the Vickers hardness were increased significantly according to grain size refinement after equal-channel angular pressed. The ultrasonic velocity was faster after equal-channel angular pressed, and the high frequency range appeared. The results of the ultrasonic velocity and the frequency range are expected to be basic data that can prove the grain size refinement

• Journal of the Korean Society for Nondestructive Testing
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• v.17 no.1
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• pp.31-40
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• 1997

원자로 압력용기 재료의 중성자 조사 취화 문제는 원자력발전소의 안전성 및 수명 관리에 가장 중대 한 영향을 미친다. 재료의 조사 취화를 평가하기 위하여 수행하고 있는 충격 및 인장시험 같은 파괴적 시험 결과는 석출물 크기나 분포, 전위 밀도 등, 재료 자체의 조직학적 특성에 좌우되므로 한정된 시편을 이용한 평가에는 많은 불확실성이 존재하게 된다. 따라서 이와 같은 문제점을 해결하기 위하여 비파괴기술을 이용한 조사 취화 평가에 대한 많은 연구가 진행되고 있다. 현재 원자로 압력용기 재료의 조사 취화에 따른 미세 조직 변화를 분석하기 위하여 응용되고 있는 비파괴기술로는 전기, 자기, 전자기, 초음파 및 경도측정법 등이 있으나 비파괴피험 결과와 미세조직의 변화, 기계적 성질 및 취화 정도 등과의 상관 관계를 정립해야만 기존 파괴적 시험의 대체가 가능하게 된다. 따라서 현재까지 수행되고 있는 여러 비파괴기술을 이용한 조사 취화 평가 연구결과를 비교 분석하여 보다 실현 가능성 있는 비파괴기술을 검토하였다.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.1
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• pp.32-38
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• 2001

Although the ultrasonic method has been developed and used widely in the fields, it has been used only for measuring the defect size and thickness loss. In this study, the relationship between surface wave attenuation through micro-crack growth and variation of velocity under repeated cyclic loading has been investigated. The specimens are adopted from 2.25Cr-1Mo steel, which is used for power plant and pipeline system, and have dimensions of $200{\times}40{\times}4mm$. The results of ultrasonic test with a 5MHz transducer show that surface wave velocity gradually decreases from the point of 60% of fatigue life and the crack length of 2mm with the increasing fatigue cycles. From the results of this study, it is found that the technique using the ultrasonic velocity change is one of very useful methods to evaluate the fatigue life nondestructively.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.11
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• pp.29-36
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• 2007

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.6
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• pp.598-606
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• 2001

Recently, semiconductor packages trend to be thinner, which makes difficult to detect defects therein. A preconditioning test is generally performed to evaluate the reliability of semiconductor packages. The test procedure includes two scanning acoustic microscope (SAM) tests at the beginning and end of the entire test, in order to help detect physical defects such as delaminations and package cracks. In particular, of primary concern are package cracks and delaminations caused by moisture absorbed under ambient conditions. This paper discusses the failure mechanism associated with the moisture absorbed and encapsulated in semiconductors, and the use SAM to detect failures such as tracks and delaminations grown during the preconditioning test.

• Journal of the Korean Society for Nondestructive Testing
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• v.36 no.5
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• pp.353-362
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• 2016

Thermal barrier coating (TBC) is an essential element consisting of a super-alloy base and ceramic coating designed to achieve long operational time under a high temperature and pressure environment. However, the top coat of TBC can be delaminated at certain temperatures with long operation time. As the delamination of TBC is directly related to the blade damage, the coupling status of the TBC should be assured for reliable operation. Conventional studies of nondestructive evaluation have been made for detecting generation of thermally grown oxide (TGO) or qualitatively evaluating delamination in TBC. In this study, the ultrasonic C-scan method was developed to obtain the damage map inside TBC by estimating the delamination in a quantitative way. All specimens were isothermally degraded at $1,100^{\circ}C$ with different time, having different partial delamination area. To detect partial delamination in TBC, the C-scan was performed by a single transducer using pulse-echo method with normal incidence. Partial delamination coefficients of 1 mm to 6 mm were derived by the proportion of the surface reflection signal and flaw signal which were theoretical signals using Rogers-Van Buren and Kim's equations. Using the partial delamination coefficients, the partial delamination maps were obtained. Regardless of the partial delamination coefficient, partial delamination area was increased when degradation time was increased in TBC. In addition, a decrease in partial delamination area in each TBC specimen was observed when the partial delamination coefficient was increased. From the portion of the partial delamination maps, the criterion for delamination was derived.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.1
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• pp.12-17
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• 2006

A steam generator of nuclear power plant has thousands of thin tubes. These tubes play an important role in maintaining the pressure boundary between the primary and secondary side of nuclear power plant. The steam generator tube is easy to be damaged because of the severe operating conditions such as the high temperature and pressure. Therefore, tremendous efforts are made to assess the structural integrity of the steam generator tubes. The eddy current test is the most popular non-destructive test to assess the integrity of the tubes. However, the eddy current test has the limitation to size the flaw accurately because the eddy current signal behavior depends on the total volume of flaw. This paper shows the possibility that the ultrasonic test method can be applied to detect the flaws in the steam generator tubes and to measure them quantitatively. From the test results, it is expected that if the ultrasonic test is put to practical use in the steam generator tube inspection, the inspection results will be improved.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.1
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• pp.15-20
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• 2009

The results of crack evaluation by conventional UT(Ultrasonic Test)is highly depend on the inspector's experience or knowledge of ultrasound. Phased array UT system and its application methods for small crack length evaluation will be a good alternative method which overcome present UT weakness. This study was aimed at checking the accuracy of crack length evaluation method by electronic scanning and discuss about characteristics of electronic scanning for crack length evaluation. Especially ultrasonic phased array with electronic scan technique was used in carrying out both sizing and detect ability of crack as its length changes. The response of ultrasonic phased array was analyzed to obtain the special method of determining crack length without moving the transducer and detect-ability of crack minimal length and depth from the material. A method of crack length determining by electronic scanning for the small crack is very real method which has it's accuracy and verify the effectiveness of method compared to a conventional crack length determination.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.10a
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• pp.257-262
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• 2004

As optical connectors dominate the performance of optical transmitters or receivers, they need an ultra-precise processing and are composed of optical fibers, ferrule and optical glass lenses. Therefore, this study suggests a nondestructive evaluation technique or a system using resonant ultrasound spectroscopy to evaluate flaws in a optical glass lens. It also conducted a nondestructive evaluation for flaws that are commonly found in a optical glass lens and reviewed the results.