• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2004년도 춘계 학술발표대회 개요집
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• pp.305-307
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• 2004

One set of rotor coils is required per each large generator rotor assembly, Rotors consist of two directly opposing poles. Each pole requires from 5 to 9 coils. Each coil is made up of two halves identified on the connection end. These coil halves will be joined together by butt brazing process during subsequent rotor assembly. Each half coil is made up of typically 4 to 9 layers of copper conductors. Because of Generator rotor is rotated very high speed with 3,600RPM, the quality soundness of brazed joints is very important at each coil. But, it is very difficult to be optimized non-destructive evaluation, because c-coil has the long shape and evaluation is to be done assembled condition. In this paper introduce newly developed inspection process and acceptance standards for the ultrasonic inspection of " C" coil butt braze. This inspection system is a semi-automatic ultrasonic flaw detector with data acquisition and retention capable of assessing the relative lack of bond of brazed butt joints

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.348-352
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• 1995

In the conventional linear elasticity, ultrasonic velocity is determined by elastic modulus and density of te medium which ultrasonic wave propagates through. But, practical ultrsonic wave depends on the stress acting in the medium, and as the stress increases such dependency becomes nonlinear. This nonlinear dependencyof ultrasonic velocity on stress can be identified by using nonlinear elastic modulus up to 4th order. In thid paper, with the above background relationships between nonlinear elastic modulus and the internalstatus of materials, normal, plastic deformed or heat stressed, are discussed. For this purpose, a new type of measuring system extended from the general nondestructive UT(ultrasonic test) equipment is constructed.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2006년도 춘계학술발표논문집
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• pp.209-213
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• 2006

In this paper describes image enhancement technique using deconvolution processing for ultrasonic nondestructive testing. . When flaws are detected for B-scan or C-scan, blurring effect which is caused by the moving intervals of transducer degrades the quality of images. In addition, acquisited images suffer form speckle noise which is caused by the ultrasonic components reflected from the grain boundary of material [1,2]. The deconvolution technique can restore sharp peak value or clean image from blurring signal or image. This processing is applied to C-scan image obtained from known specimen. Experimental results show that the deconvolution processing contributes to get improved the quality of C-scan images.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2006년도 춘계학술발표논문집
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• pp.217-222
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• 2006

This paper describes a development of ultrasonic examination analysis software to analyze steam generator of nuclear power plant. The developed software includes classical analysis method such as A, B, C and D-scan images. This software provides the information of shape, depth, size and position of flaws. To do such, we obtain raw data from specimens and/or real pipeline of power plants and, modify the obtained ultrasonic 1-dimensional data according to prepared software design schedule. The developed analysis software is applied to specimens containing various flaws with known dimensions. The results of applications showed that the developed software provided accurate and enhanced images of flaws on various specimens.

• 한국해양공학회지
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• 제14권4호
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• pp.68-72
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• 2000

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 application of the ultrasonic technique for the evaluation of marine diesel engine exhaust valve and to suggest the correlation 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 degree of marine diesel engine exhaust valve by nondestructive test.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2015년도 춘계 학술논문 발표대회
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• pp.78-79
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• 2015

For estimating compressive strength of concrete, non-destructive test has conducted generally. It used experimental equation to calculate compressive strength from construction. This study investigated experiment to apply non-destructive test, based on fresh property, compressive strength and ultrasonic pulse velocity of high performance concrete. And it conducted to compare various proposed equation.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.290-295
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• 2004

In this study, the pressure vessel piping with corrosion used during long term were investigated from the time-frequency analysis method. The damage of piping could be evaluated the attenuation factor by ultrasonic parameters such as center frequency and echo waveform. Based on NDE analysis by time-frequency analysis method, it should also be possible to evaluate from various damages and defects in piping members.

• 동력기계공학회지
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• 제10권1호
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• pp.77-82
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• 2006

In this study, dissimilar friction welding were produced using 15mm diameter solid bar in chrome molybedenum steel(SCM440) to carbon steel(S45C) to investigate their mechanical properties and the relationship between the weld parameters and the nondestructive coefficients, such as AE counts and ultrasonic attenuation coefficient. The main friction welding parameters were selected to endure good quality welds on the basis of visual examination, tensile tests, Vickers hardness surveys of the bond of area and heat affected zone. The specimens were tested as-welded and post weld heat treated(PWHT). The tensile strength of the friction welded steel bars was increased up to 100％ of the S45C base metal under the condition of all heating time. The ductility of PWHT specimens is higher than as-welded.

• 한국정밀공학회지
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• 제20권3호
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• pp.157-164
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• 2003

The pulse-echo method is one of the most widely used ultrasonic techniques for application of nondestructive evaluation. Particularly, quantitative nondestructive evaluation of defects has been considered more important to assure the reliability and the safety of structure. Frequency energy in adhesive joints is based on the ultrasonic wave analysis. The attenuation coefficient upon wave amplitude and the frequency energy that is expressed in the term of wave pressure amplitude were utilized for the primary wave experiment. By means of a control experiment, it was confirmed that the variation of the frequency energy in adhesive joints depends on transition by stress variation. In this paper, the ultrasonic characteristics were measured for single lap joint and Double Cantilever Beam specimen with different fracture modes that was subjected to stress. Consequently, the data that was obtained from the adhesive specimen was analytically compared to the fracture mechanics parameter

• 한국정밀공학회지
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• 제13권4호
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• pp.53-60
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• 1996

In the conventional linear elasticity, sound speed is determined by only elastic modulus and density of the medium. In actual, however, sound speed depends on the stress and this dependency becomes nonlinear as the stress increases. These phenomena can be introducing nonlinear elastic modulus. In this paper, relationships between nonlinear elastic modulus up to 4th order and the internal status of materials are discussed through computer simulations and experiments. For the measurement of sound speed, a new type of measurement system using ultrasonic wave is proposed on the basis of ultrasonic pulse echo method which has been generally used in nondestructive ultrasonic test equipment. In order to confirm the stress dependency of sound speed, several experiments are carried out for alumina specimen.