• Proceedings of the Korean Society of Precision Engineering Conference
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• 1991.04a
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• pp.143-149
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• 1991

기계공업의 발전과 함께 각종의 기계, 장치 및 기기등은 보다 고정도와, 다기능화 및 고품질화가 계속 추구되어 있다. 그러나, 이러한 개선 및 개량이 이루어지기 위해서는 필연적으로이에 들어가는 각종 부품들의 고정도화와 고품질화가 선행되어져아 한다. 본 연구에서는 이러한 제반의 문제점 내지는 결함을 어느정도 해결하고 현장 및 측정실에서도 용이하게 이용할 수 있는 INDEX HEAD를 이용한 절대 진원도의 측정법(일종의 양쎈터 지지법)을 제안하고자 한다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.6
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• pp.1056-1063
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• 1992

Burst pressure of right circular tube is predicted using analytic method, and asymptotic instability pressure of circular tube with roundness defect is found using FEM. Burst tests of nearly right circular tube specimens are carried out and predictions are compared with burst pressures and their accuracy is discussed. It is confirmed that FEM is useful for prediction of burst pressure.

• Journal of the Korean Institute of Gas
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• v.17 no.5
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• pp.64-68
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• 2013

Non destructive testing(NDT) methods of electrofusion(EF) joints of thermoplastics pipes are required for fusion joint safety and for the long term reliability of a pipe system. Electrofusion joints, which are joined at the proper fusion process and procedures, may encounter defects due to the difference of ovality between pipes and coupling, improper fusion process or porosity result from electrofusion joining. These defects can cause the failure of pipeline and by extension, they can be caused the limit to expand the use of plastics pipes. This paper studies inspection results using ultrasonic imaging method for damaged polyethylene electrofusion joints. Gas was leaking from 250mm diameter polyethylene electrofusion joints at February 2004 which was electrofused at December 1994 and operation pressure was 2.45kPa. First, surface inspection was conducted and then in order to find the types of defects examination using ultrasonic imaging method was performed. Lack of fusion and inappropriate inserting for polyethylene pipes into electrofusion coupling were found and causes of the gas leak were judged that misalignment and insert defect. Cutting inspection was performed and each inspection results were compared to. Results of ultrasonic imaging method and cutting inspection were the same.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.12
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• pp.27-34
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• 2005

We have investigated the correlation between the active-layer uniformity and reliability of InGaN/GaN blue LEDs. According to initial characteristics, the devices are classified into two groups: group I devices of uniform light-emission and group II devices of non-uniform light-emission. The group II devices are more dependent on temperature and we have found two degradation mechanisms through reliability test. One is bulk degradation in which the degradation occurred over the entire chip and another one is edge degradation in which the degradation occurred from the edge of the chip. Bulk degradation caused by the nonradiative defects is found to be faster in group II devices while there is no difference in the rate of the much faster edge degradation, where darkening starts from the n-Ohmic contact edge. Therefore, more uniform active layer, more uniform current spreading, and the passivation of the dry-etched side-wall are essential for the high reliability of InGaN/GaN LEDs.