• Composites Research
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• v.13 no.4
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• pp.1-10
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• 2000

SiC particulate reinforced metal matrix composites(MMCs) are emerging as candidate materials for the automobile and aerospace industries due to their significant increase in elastic modulus and strength compared to conventional metallic materials. However, in order to make successful application of MMCs, it is very important to understand micro-failure mechanism under cyclic loading because failure mechanism of MMC is dominated by accumulation of micro-failure due to applied loading. In this study, ultrasonic Lamb wave and acoustic emission(AE) have been used to monitor microscopic damage accumulation under cyclic loading for SiC particulate reinforced metal matrix composite(SiCp/A356). It was found that the change in velocity and attenuation of ultrasonic Lamb wave due to the increase of loading cycles could be characterized by three different stages corresponding to the microscopic fracture processes. The characteristic of AE signal at each stage was analyzed and discussed by comparing with the change of ultrasonic characteristic in MMCs.

• Journal of the Korean Institute of Gas
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• v.10 no.1 s.30
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• pp.32-37
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• 2006

Major components of refinery plants are exposed to various damage mechanisms depending on the operation condition, material selection and kinds of internal fluid. Inspection techniques and damage monitoring methods should be selected considering the damage mechanisms of the components. Hence, it is quite necessary to have an information system with a standardized database on the various damage mechanisms. In this study a damage information system with contents on the damage mechanisms included in API 571 code was developed. Concept of the screening table employed in USA and Japan was also adopted to identify the probable damage mechanisms from the information on operating temperature, internal fluid, metal used for the component and stress condition. This system can be used before the risk based inspection planning to identify key damage mechanisms involved.

• Korean Journal of Materials Research
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• v.10 no.2
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• pp.138-143
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• 2000

화력발전설비의 주요 손상 요인 중의 하나인 응력부식 균열 성장에 대한 확률론적 잔존 수명평가에 대하여 연구하였으며, 손상해석 및 수명평가에 확률해석 기법을 도입한 확률론적 수명평가 프로그램을 개발하였다. 확률론적 수명평가는 재료물성치, 형상, 하중조건, 운전조건 등과 같은 불확실성과 변동 가능성을 고려하여 해석을 수행하며, 일정 시간 운전후 구조물의 손상이 일어날 확률을 예측하는 것이다. 응력부식 균열 성장에 대한 확률론적 잔존 수명평가 연구를 통하여 확률론적 수명평가 기술의 기반을 구축하였으며, 다른 손상기구에 대한 확률론적 수명평가를 수행하여 발전설비에 발생하는 모든 손상에 대하여 확률론적 수명평가가 가능하도록 확대할 계획이다.

• Proceedings of the KSR Conference
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• 2003.05a
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• pp.712-717
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• 2003

지능 재료를 이용한 디바이스는 자연계에 존재하는 생명체와 같이 내.외부 환경 변화에 대응하여 스스로 변하는 능동적 기능을 갖고 있기 때문에 시스템 성능의 극대화 및 유지비용의 최소화를 가져오게 된다. 이러한 지능재료 기술은 지난 10여년 전부터 연구되었는데 대표적인 웅용을 보면, 산업, 항공, 교통, 운송 분야의 능동 소음 및 반능동 진동제어; 복합 재료 손상위치 탐지시스템, 손상구조 건전성 평가시스템, 교량, 저장탱크, 건물, 유조선, 대형 구조물의 건전성 평가 시스템; 초정밀 직진 안내기구, 나노 스테이지, 절삭오차 보정용 엑츄에이터, 초음파 회전모터, 지능유압 서보밸브, 변형 거울 등의 모터/엑츄에이터; 자동차 엔진 성능제어, 흡배기구 압력측정, 가속도 센서, 자이로센서, 에어백 센서, 타이어 센서 등의 지능 MEMS/NEMS 센서; electronic article 정찰, 도서태그, 비접촉 항공 운송물 분류 및 보안시스템, 전자 운전자 식별시스템, 광섬유 건물 보안 시스템, 지능 신경망 형상 인식 시스템 등의 보안 시스템; 지능항공기 구조물, 인공위성안테나, 헬리콥터 회전익 등의 형상제어가 있다. 본 논문에서는 지능재료 기술을 정리하고 차세대 철도차량 기술에 지금까지 적용한 예를 소개하며 향후 적용할 수 있는 분야들을 가능성 및 실용성 면에서 소개하고자 한다.

• Composites Research
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• v.12 no.4
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• pp.62-70
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• 1999

It was well recognized that damages associated mainly with the aging of civil infrastructrues were one of very serious problems for assurance of safety and reliability. In recent, carbon fiber sheet(CFS) has been widely used for reinforcement and rehabitation of damaged concrete beam. However, the fundamental mechanism of load transfer and its load-resistant for carbon fiber sheet reinforced concrete are not fully understood. In this study, three point bend test has been carried out to understand the damage progress and micro-failure mechanism of CFS reinforced concretes. For these purposes, four kinds of specimens are used, that is, concrete, respectively. Acoustic Emission(AE) technique was used to evaluate the characteristics of damage progress and failure mechanism of specimens. In addititon, two-dimensional AE source location was also performed to monitor crack initiation and propagation processes for four types of these specimens.

• Composites Research
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• v.15 no.5
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• pp.1-6
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• 2002

When compared to other composite materials such as FRP and MMC, hybrid composite material is more attractive one due to the high specific strength and the resistance to fatigue. However, the fracture mechanism of hybrid composite material is extremely complicated because of the bonding structure of metals and FRP. Recently, nondestructive technique has been used to evaluate the fracture mechanism of these composite materials. In this study. AE technique has been used to clarify the fracture mechanism and the degree of damage for Al 7075/CFRP hybrid composite material. It was found that AE event, energy and amplitude among AE parameters were effective to evaluate fracture process of Al 7075/CFRP composite material. In addition, the relationship between the AE signal and the characteristics of failure surface using optical microscope was discussed.

• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.4
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• pp.380-385
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• 2010

The integrity of components and piping of operating nuclear power plants has been identified by in-service inspection(ISI) requirements and activities commensurate with standards and codes such as KEPIC MI or ASME Code Section XI. However, the other various degradation mechanisms not considered during design stage of nuclear power plants have been checked by enhanced ISI. The requirements of enhanced ISI have been voluntarily developed by the industry itself or strickly issued by regulatory body. Even though the requirements were developed by the industry, they should be reviewed by regulatory body for their application in nuclear power plants. The enhanced ISI activities and requirements of non-destructive examination(NDE) which reflect the degradation issues in nuclear power industry will be primarily discussed in this paper.

• Composites Research
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• v.17 no.1
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• pp.47-54
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• 2004

Vacuum hot pressing has been used for the development of titanium metal matrix composites using foil-fiber-foil technique. Subsequent micro-mechanical characteristics of the composites are then investigated by means of several experimental methods. The levels of consolidation, together with mechanism based failure processes of the materials have been analyzed by employing a thermo-acoustic emission technique. As shown by the results, fiber strength degradation occurs during the consolidation, and particularly residual stresses results from the thermal expansion mismatch between fiber and matrix materials during cooling process are incorporated in the changes of mechanical properties of the finished products. In industrial applications, both qualitative and quantitative evaluations of the material-mechanical characteristics are particularly important, and therefore must be included in process development. The present paper represents a methodology by which this can be achieved.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.2
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• pp.59-64
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• 2001

The purpose of this work is to investigate the static strength, the stress distribution, and the failure process of quasi-isotropic composite laminates made of two different matrices when loading directions are changed. We carried out static tests of $[0/-60/+60]_s$ and $[+30/-30/90]_s$ laminates. Two types of matrices used are AS4/epoxy and AS4/PEEK. The damage mechanisms of the quasi-isotropic laminate, $[0/-60/+60]_s$, strongly depend on the load direction applied to the laminate.

• Journal of the KSME
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• v.33 no.5
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• pp.393-404
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• 1993

원자로 압력용기의 수명 및 건전성을 결정짓는 중성자 조사취화현상에 대해 손상과정, 기구, 영 향인자, 예측 및 평가방법을 소개하였다. 용기재료의 현상, 특성과 설계, 제조, 운전시의 건전성 확보를 위한 활동 및 방법도 함께 살펴보았다. 설계시는 물론 수명기간 동안 건전성을 유지하 면서 운전하고 나아가 수명연장 운전을 위해서는 용기의 상태(파괴인성치, 결함, 작용응력)를 정확히 진단, 예측, 평가해야 하고, 이들이 건전성에 미치는 영향평가와 건전성 평가방법을 통한 수명예측 기술의 확보가 매우 중요하다. 특히, 고리 1호기가 가동된지 15년이 되어 계속적인 감 시가 요구되고 수명연장 타당성 연구를 추진중에 있으며, 영광 3, 4호기를 시작으로 앞으로 건 설되는 원자로가 국내에서 제작 . 설치되고, 설계 및 소재의 국산화율을 높이고자 하는 우리나 라에서는 더욱 그러하다. 미소시험법 및 시편재활용 기술개발을 통한 시험자료의 확충과 국내 원자로에 대한 데이터베이스 구축 및 각 발전소 특유의 경향곡선 확립 . 적용이 필요하며, 조사 손상 기구 및 모델링 관련연구가 계속되어야 한다. 조사효과에 대한 기초 및 응용연구는 1994년 한국원자력연구소의 다목적연구용원자로(MRR ; multipurpose research reactor) 가동과 더불어 더욱 활발해질 것이다.