• 한국자동차공학회논문집
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• 제15권5호
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• pp.139-145
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• 2007

Fretting is a kind of surface damage mechanism observed in mechanically jointed components and structures. The initial crack under fretting damage occurs at lower stress amplitude and lower cycles of cyclic loading than that under plain fatigue condition. This can be observed in automobile and railway vehicle, fossil and nuclear power plant, aircraft etc. In the present study, railway axle material RSA1 used for evaluation of fretting fatigue life. Plain and fretting fatigue tests were carried out using rotary bending fatigue tester with proving ring and bridge type contact pad. Through these experiments, it is found that the fretting fatigue limit decreased about 37% compared to the plain fatigue limit. In fretting fatigue, the wear debris is observed on the contact surface, and oblique cracks at an earlier stage are initiated in contact area. These results can be used as useful data in a structural integrity evaluation of railway axle.

• 한국전기전자재료학회논문지
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• 제19권4호
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• pp.398-403
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• 2006

This paper describes the evaluation of the long duration current impulse withstand characteristics of ZnO blocks for high voltage surge arresters. Four ZnO varistors were manufactured with the general ceramic production method and the long duration current impulse withstand test, electrical uniformity evaluation test and microstructure observation were performed. All varistors exhibited high density, which was in the range of $5.42{\sim}5.46g/cm^3$. In the electrical properties, the reference voltage of samples was in the range of $5.11{\sim}5.25\;kV$ and the residual voltage was in the range of $8.314{\sim}8.523\;kV$. In the long duration current impulse withstand test, sample No.2 and No.3 failed at the 2nd and 4th shot of series impulse currents, respectively, but the rest survived 18 shots during the test. Before and after this test, the variation ratio of the residual voltage of samples survived was below 0.5 %, which was in the acceptance range of 5 %. According to the results of the test, it is thought that if the soldering method is improved, ZnO varistors would be possible to apply to the high voltage arresters like the station class and transmission line arresters in the near future.

• 한국초전도ㆍ저온공학회논문지
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• 제19권2호
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• pp.53-57
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• 2017

In superconducting power devices including power cables in which high temperature superconducting (HTS) tapes are utilized, a reliable electrical insulation should be achieved for its maximum performance. For an efficient design of HTS superconducting devices, a comparative evaluation of the mechanical and thermal propperties for various insulation materials at cryogenic temperatures is required. Especially, in the process of the property evaluation of the sheet-shaped insulation materials, anisotropy according to the machining direction should be considered because the mechanical and thermal properties are significantly influenced by the sample orientation. In this study, the cryogenic thermal and mechanical properties of various insulation material sheets such as PPLP, Cryoflex, Teflon, and Kapton were determined considering sample orientation. All samples tested at cryogenic temperature showed significantly higher tensile strength as compared with that of room temperature. The ultimate tensile strength at both temperature conditions significantly depended upon the sample orientation. The thermal properties of the insulation materials exhibited a slight difference among samples depending on the orientation: for the PPLP and Cryoflex, the CD orientation showed larger thermal contraction up to 77 K as compared to the MD one. MD samples in PPLP and Cryoflex showed a lower CTE and thermal contraction which made it more promising as an insulation material due to its comparable CTE with HTS CC tapes.

• 한국의류산업학회지
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• 제4권6호
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• pp.517-523
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• 2002

This study examines whether there are differences in consumer's evaluation price zone on the clothing clue (the type of clothing, brand, time of fashion, place of origin, material. submaterial, place for sale) according to consumer purchasing behavior. Therefore the ultimate goal is to offer help in fixing price when establishing marketing of the clothing industry by grasping the actual price set by consumers under the IMP system. The female consumers of 20s and 30s were chosen as study subjects for their sensitivity to the purchase of clothing. The tests carried out in this research are: SPSSIPC+ is used for frequency Analysis. The Results of this study are showed as the following: It was analyzed that 4 types of consumer are the reasonable consumption oriented consumer, fashion oriented consumer, the no care of fashion consumer and high price oriented consumer Among the several kinds such as the type of clothing, brand, time of fashion, place of origin, material, submaterial, place for sale, only on the type of clothing, there are difference in the type of the consumers, on the time of buying clothes, in the behavior of buying clothes and also on the degree of fashion and the place of origin among such kinds.

• 한국자동차공학회논문집
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• 제18권2호
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• pp.74-82
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• 2010

Fretting damage can be observed in automobile and railway vehicle, fossil and nuclear power plant, aircraft etc. In the present study, railway axle material RSA1 used for evaluation of fretting fatigue life. Plain and fretting fatigue tests were carried out using rotary bending fatigue tester with proving ring and bridge type contact pad. Through these test, the following results are obtained: 1) it is found that the fretting fatigue limit of standard specimen decreased about 37% compared to the plain fatigue limit. 2) The early crack of Shinkansen type specimens initiated in contact area and final fractured below samp=214 MPa. 3) The early crack of all TGV type specimens initiated in rounded area and fractured. 4) Tire tracks and rubbed scars were observed in the oblique crack region and fatigue crack growth region of fracture surface. 5) The wear debris is observed on the contact surface, and oblique cracks at an earlier stage are initiated in contact area. These results can be used as useful data in a structural integrity evaluation of railway axle.

• 동력기계공학회지
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• 제6권2호
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• pp.48-53
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• 2002

Plunger (piston rod) materials are used in high-pressure condition. So STD11 is the essential material to build this plunger. However, it costs more to make a plunger by using only STD11 than using the welding of STD11 to SCM440 and other dissimilar material. And it has been difficult to weld this sort of dissimilar materials. They could be unstable in the quality by the conventional arc welding. And also they have a lot of technical problems in manufacturing. But, by the friction welding technique, it will be able to be made without such problems. And then, on account of such reasons, we need a new approach of study on real-time quality evaluation by acoustic emission (AE) techniques as well as a domestic development of the plunger by friction welding. So that, the purpose of this study for such developments is the development of a plunger by optimizing of friction welding with more reliability and more applicability. Then, this study aimed not only to develop the optimization of friction welding of dissimilar plunger steels of STD11 to SCM440, but also to develop the application technique of the acoustic emission to accomplish an in-process real-time quality evaluation during friction welding of the plunger materials by the AE technique.

• 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.

• 전산구조공학
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• 제9권2호
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• pp.153-161
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• 1996

본 논문에서는 가압열충격의 파괴역학적 해석에 필요한 이론을 조사하였고 원자로용기의 구조건전성을 평가하기 위하여 해석과정을 전산화하였다. 우선 사고 transient에 대하여 원자로용기내의 압력과 주입되는 냉각재의 온도변화가 주어지면 이들로 부터 시간에 따른 용기에서의 온도와 응력분포를 구하고, 중성자 조사량과 용기 재질의 화학성분으로 부터 기준무연성천이온도의 분포가 구해지며 이로부터 파괴인성치 K/sub IA/와 K/sub IC/의 분포가 얻어진다. 또한 응력분포로 부터 균열의 크기 및 형상에 따라 응력확대계수 K/sub I/이 구해지므로 이를 K/sub IA/및 K/sub IC/와 비교함으로써 균열의 성장거동을 예측할 수 있다. 지금까지 보고된 가압열충격을 유발할 수 있는 대표적인 사고 transient가 국내 발전소에 발생할 경우를 가정하여 해석을 수행하였고 그 결과에 대하여 검토하였다.

• 한국공간구조학회논문집
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• 제9권4호
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• pp.73-80
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• 2009

성능에 기초한 내진설계에서 구조물의 지진에 대한 성능평가를 위하여 구조물의 비탄성 지진거동을 정확하게 예측하는 젓이 중요하다. 정확한 시스템의 연성능력 평가를 위해서는 각부재의 하중과 변형의 관계를 보다 실제적으로 규정하는 것이 중요하다. 비선형 해석에 의한 구조물의 비탄성 거동 파악을 위해서 단순화된 부재의 하중-변형 관계 모델을 적용한다면 구조물의 실제적이고 정확한 거동을 예측하기에는 어려움이 있다. 본 논문에서는 하중-변형 관계를 Backbone 이력모델을 적용하여 단순화된 하중-변형 관계를 적용한 모델과 시스템연성능력 및 층연성능력을 비교, 평가하였다. 해석결과로 이선형 이력모델의 경우에 시스템 및 층 연성도의 과소평가는 실제구조물의 소성거동을 과소평가하는 곁과를 초래하며 보다 정착한 비선형해석을 위하여 부재의 이력모델은 Backbone 이력모델을 사용하는 것이 바람직하다.

• Steel and Composite Structures
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• 제12권6호
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• pp.523-540
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• 2012

It was clear from the former researches on reinforced concrete filled tubular steel (RCFT) structures that RCFT structures have different performance than concrete filled steel tubular (CFT) structures. However, despite of that, load-sharing ratio of RCFT is evaluating by the formula and range of CFT given by JSCE. Therefore, the aim of this investigation is to study the load-sharing ratio of RCFT columns subjected to axial compressive load by performing numerical simulations of RCFT columns with the nonlinear finite element analysis (FEA) program - ADINA. To achieve this goal, firstly proper material constitutive models for concrete, steel tube and reinforcement are proposed. Then axial compression tests of concrete, RC, CFT, and RCFT columns are carried out to verify proposed material constitutive models. Finally, by the plenty of numerical analysis with small-sized and big-sized columns, load-sharing ratio of RCFT columns was studied, the evaluation formulas and range were proposed, application of the formula was demonstrated, and following conclusions were drawn: The FEA model introduced in this paper can be applied to nonlinear analysis of RCFT columns with reliable results; the load-sharing ratio evaluation formula and range of CFT should not be applied to RCFT; The lower limit for the range of load-sharing ratio of RCFT can be smaller than that of CFT; the proposed formulas for load-sharing ratio of RCFT have practical mean in design of RCFT columns.