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부명환,박영철,광뢰행웅,Boo, Myung-Hwan,Park, Young-Chul,Hirose, Yukio 대한기계학회 1999 大韓機械學會論文集A Vol.23 No.7
In X-ray stress measurements for uni-directionally deformed surfaces such as grinding, a strongly curved $sin^2{\Psi} diagram, so called $\Psi-splitter, has been observed recently. It has been known that this is caused by the residual shear stress induced in the deformed layer by external forces. In this case it is necessary to consider this enough for ceramics and composite materials with tri-axial stress analysis. However, sufficient studies have not been done about the tri-axial stress analysis of the macro stress and micro. stress on each phase of the composite materials. The result of obtaining is as follows. 1. $\Psi-splitter does not appear in the vertical direction though $\Psi-splitter appears in grinding direction in WC-Co cemented carbides. The reversal of $\Psi-splitter to each phase does not appear. 2. $\Psi-splitter caused in WC-Co cemented carbides has a close relation in dislocation which accumulates in WC phase and phase transformation caused in Co phase. 3. The residual stress on the surface of grinding of each phase is in the state of the compression stress.
부명환,이경수,오창균,김현수,Boo, Myung Hwan,Lee, Kyoung Soo,Oh, Chang Kyun,Kim, Hyun Su 한국압력기기공학회 2017 한국압력기기공학회 논문집 Vol.13 No.2
세계적으로 원자력발전소의 안정적 운영 및 안전성 확보를 위해 수명기간 중 주요 기기 및 배관의 실제 운전 과도상태를 체계적으로 관리하고, 피로 손상의 정량적 평가 및 관리를 위한 체계적인 시스템이 요구되고 있는 실정이다. 이에 본 논문에서는 원자력발전소의 안전등급 1 설비에 대한 피로 평가요건을 분석하였고, 피로 감시방법 및 절차와 웹 기반으로 개발된 피로 감시 시스템인 NuFMS 개발 및 검증 내용을 기술하였다. NuFMS는 설계 시 고려한 과도상태 발생 횟수 대 비발전소의 특정 운전 시점에서의 실제 발생 횟수를 비교하여 안전 여유도의 정량적 확인이 가능하며, 누적피로사용계수 도출을 통해 정확한 피로영향 분석뿐만 아니라 손상 관리가 가능하다. 이와 같이 NuFMS의 적용을 통해 원자력발전소 기기 및 배관의 피로 건전성을 확인하고 운영 신뢰도를 향상시킬 수 있으며, 발전소의 안전성 유지 및 운영비용 절감 등의 효과를 기대할 수 있다. 따라서 향후 국내 전 원전에 NuFMS를 확대 적용할 예정이며, 이러한 기술의 해외 수출을 적극 추진 중이다. Metal fatigue is an important aging mechanism that material characteristics can be deteriorated when even a small load is applied repeatedly. An accurate fatigue evaluation is very important for component structural integrity and reliability. In the design stage of a nuclear power plant, the fatigue evaluations of the Class 1 components have to be performed. However, operating experience shows that the design evaluation can be very conservative due to conservatism in the transient severity and number of occurrence. Therefore, the fatigue monitoring system has been considered as a practical mean to ensure safe operation of the nuclear power plants. The fatigue monitoring system can quantify accumulated fatigue damage up to date for various plant conditions. The purpose of this paper is to describe the fatigue monitoring procedure and to introduce the fatigue monitoring program developed by the authors. The feasibility of the fatigue monitoring program is demonstrated by comparing with the actual operating data and finite element analysis results.
부명환(Myung-Hwan Boo),박치용(Chi-Yong Park),김진원(Jin-Weon Kim),이선학(Seon-Hak Lee),정재경(Jai-Kyung Jung) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.8
In heavy industrial fields such as power plant and chemical plant, it is often necessary to restore a damaged part of large machinery or structure which is installed in the hazard working place. In this paper, to estimate residual stresses during the process of damaging and restoring of cylindrical beam structure, a finite element technique has been used. The variations of residual stresses on the process of damaging and restoring for surfaces and cross-sections have been examined. The results show that the maximum von Mises stresses occur outer cylinder surfaces of boundary between cylindrical beam support and cylindrical beam when deformation procedure and restoring force is applied. The maximum residual stress remain 158.6㎫ in the inner wall and this value correspond to 53% of yield stress when deformation and restoration procedure is finished.
부명환(Myung-Hwan BOO),조충형,김상재(Sang-Jai KIM),임경수,김영석(Young-Suk KIM),Dong-Jun OH,Sung-Soo KIM 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3
The aim of this study is to investigate fracture toughness of a Zr-2.5Nb pressure tube with temperature. The tensile and fracture toughness tests were performed at temperatures ranging from room temperature to 300℃ on tensile and curved compact tension, CCT specimens. The CCT specimens were directly cut from the tube retaining original curvature using wire cutting machine. The Zr-2.5Nb tube had a decrease in yield and tensile strengths with increasing temperature. However, its elongation had a maximum at 150℃ followed by a decrease with increasing temperatures. The loss of ductility which was stricking in the temperature range of 200~250℃ determined the fracture toughness resistance, dJ/da of the Zr-2.5Nb tube with temperature, resulting in the maximum in the range of 100~150℃. The temperature dependence of the fracture toughness for the Zr-2.5Nb tube is discussed fracture in association with the formation of secondary crack on the fractured surfaces.
부명환(Myung-Hwan BOO),오동준(Dong-Jun OH),안창윤(Chang-Yun AN),김성수(Sung-Soo KIM),김영석(Young-Suk KIM) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.8
The aim of his study is to investigate the effect of hydrogen embrittlement of Zr-2.5Nb CANDU pressure tube. The tests were performed at various of hydrogen contents for CCT specimens. The specimens were directly machined from the tube retaining original curvature using electric discharge machine. From the fracture toughness test, it was found that fracture toughness dJ/da was decreased with speedily increasing hydrogen content. And it observed constant value about 70-80ppm of hydrogen content. In fractography by SEM, we observed dimple fracture in AR materials, dimple and short fissure in 30ppm, and quesi-cleavage and large fissure in 80ppm. The decrease of fracture toughness with the addition of hydrogen is due the distribution of hydride and habit plane(10.7) of zirconium grain.
WC-Co합금의 X선 응력측정에 의한 탄성변형거동의 연구
夫明煥(Myung-Hwan Boo),吳世旭(Sae-Wook Oh),朴榮哲(Young-Chul Park),廣瀨幸雄(Yukio Hirose) 한국해양공학회 1994 韓國海洋工學會誌 Vol.8 No.2
Cemented carbides are composed of the dispersing phase of WC and biding phase of Co, which are very different from each other in mechanical properties. When the alloys are deformed uniformly in the macroscopic scale, each phase may be deformed differently under their own stress state. Therefore, in order to clarify the deformation characteristics and strengthening mechanism of the alloys, it is necessary to investigate microscopic deformation and fracture mechanism of each phase.<br/> In the present study, each phase of the X-ray elastic constant and the stress constant of the dispersing phase of WC and binding phase of Co, were measured by X-ray diffraction method during applied tensile elastic defromation. The phase stress of WC phase and Co phase within a WC-Co alloy was determined for diffraction from WC(112) plane and Co(311) plane. The phase stress was discussed on the basis of the law of mixture.