• Nuclear Engineering and Technology
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• 제48권4호
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• pp.1009-1014
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• 2016

SiC-based ceramic composites are currently being considered for use in fuel cladding tubes in light-water reactors. The joining of SiC ceramics in a hermetic seal is required for the development of ceramic-based fuel cladding tubes. In this study, SiC monoliths were diffusion bonded using a Ti foil interlayer and additional Si powder. In the joining process, a very low uniaxial pressure of ~0.1 MPa was applied, so the process is applicable for joining thin-walled long tubes. The joining strength depended strongly on the type of SiC material. Reaction-bonded SiC (RB-SiC) showed a higher joining strength than sintered SiC because the diffusion reaction of Si was promoted in the former. The joining strength of sintered SiC was increased by the addition of Si at the Ti interlayer to play the role of the free Si in RB-SiC. The maximum joint strength obtained under torsional stress was ~100 MPa. The joint interface consisted of $TiSi_2$, $Ti_3SiC_2$, and SiC phases formed by a diffusion reaction of Ti and Si.

• Nuclear Engineering and Technology
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• 제50권1호
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• pp.116-125
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• 2018

Modified 9Cr-1Mo ferritic steel is a preferred material for steam generators in nuclear power plants for their creep strength and good corrosion resistance. Austenitic stainless steels, such as type 316LN, are used in the high temperature segments such as reactor pressure vessels and primary piping systems. So, the dissimilar joints between these materials are inevitable. In this investigation, dissimilar joints were fabricated by the Shielded Metal Arc Welding (SMAW) process with Inconel 82/182 filler metals. The notch tensile properties and Charpy V-notch impact toughness properties of various regions of dissimilar metal weld joints (DMWJs) were evaluated as per the standards. The microhardness distribution across the DMWJs was recorded. Microstructural features of different regions were characterized by optical and scanning electron microscopy. Inhomogeneous notch tensile properties were observed across the DMWJs. Impact toughness values of various regions of the DMWJs were slightly higher than the prescribed value. Formation of a carbon-enriched hard zone at the interface between the ferritic steel and the buttering material enhanced the notch tensile properties of the heat-affected-zone (HAZ) of P91. The complex microstructure developed at the interfaces of the DMWJs was the reason for inhomogeneous mechanical properties.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 1999년도 춘계학술발표회 초록집
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• pp.5-5
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• 1999

A novel process is proposed to improve oxidation resistance of Ti-Al intermetallic compounds at elevated temperatures by both Cr addition and pre-sulfidation, where TiAl alloys withlor without Cr addition were sulfidized at 1173K for 86.4ks at a 1.3 Pa sulfur partial pressure in a $H_2-H_2S$ gas mixture. The pre-sulfidation treatment formed a thin Cr-Al alloy layer as well as 7~10 micrometer $TiAl_3$ and $TiAl_2$ layer, due to selective sulfidation of Ti. Oxidation resistance of the pre-sulfidation processed TiAl 4Cr alloy was examined under isothermal and heat cycle conditions between room temperature and 1173K in air. Changes in $TiAl_3$ into $TiAl_2$ and then TiAl phases as well as their effect on oxidation behavior were investigated and compared with the oxidation behavior of the TiAl-4Cr alloy as TiAl and pre-sulfidation processed TiAl aHoys. After oxidation for up to 2.7Ms a protective $Al_2O_3$ scale was formed, and the pre-formed $TiAl_3$ changed into $TiAl_2$ and the $Al_2Cr$ phase changed into a CrAlTi phase between the $Al_2O_3$ scale and $TiAl_2$ layer. The pre-sulfidation processed TiAl-4Cr alloy had very good oxidation resistance for longer times, up to 2.7 Ms, in contrast to those observed for the pre-sulfidation processed TiAl alloy where localized oxidation occurred after 81 Oks and both the TiAl and TiAl-4Cr alloys themselves corroded rapidly from the initial stage of oxidation

• 한국구조물진단유지관리공학회 논문집
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• 제9권1호
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• pp.271-281
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• 2005

외부유체를 유한요소화 할 경우 경계조건을 만족시키도록 무한반경까지를 모델링 할 수 없으므로 이를 보정하기 위하여 유한경계에서의 경계조건으로 발산경계조건을 사용하였다. 외부유체의 모델링에서 적용한 수치모델은 쉘 요소 및 유체요소를 축대칭 구조물의 특성을 이용한 링요소로 모델화하여 자오방향 모우드와 주변방향의 파형 모우드를 변수분리함으로써 지진하중 등의 해석에서도 수십 개의 링요소에 의해 정해에 근사한 값을 얻을 수 있도록 하였다. 축대칭 쉘 구조물과 유체-구조물의 상호관계는 접촉면에서 구조물의 가속도와 유체의 압력관계를 이용한 부가질량을 유체를 비점성, 비압축 및 비회전으로 가정하여 유한요소법에 의해 구하였다. 이에 따라 구조물의 변형에 따른 외부유체 효과를 고려한 부가질량매트릭스를 얻을 수 있었으며, 이에 대한 수치해석을 통하여 고유진동해석 및 지진하중을 주하중으로 한 동적해석을 실시하였다.

• 대한치과기공학회지
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• 제23권1호
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• pp.31-43
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• 2001

This study was performed to observe the micro-structure change of surface, behavior of oxide change of element, the component transformation of the alloy and the bonding strength between the porcelain interface in order to investigate effects of indium, tin on interfacial properties of porcelain fused to low gold alloy. Hardness of castings was measured with a micro-Vicker's hardness tester. The compositional change of the surface of heat-treated specimen was analyzed with an EDS and an EPMA. The interfacial shear bonding strength between alloy specimen and fused porcelain was measured with a mechanical testing system(MTS 858.20). The results were as follows: 1) The hardness value of alloy increased as increasing amount of indium addition. 2) The formation of oxidation increased as increasing indium and tin contents after heat treatment. 3) Diffusion of indium and tin elements increased as increasing indium and tin contents in metal-porcelain surface after porcelain fused to metal firing. 4) The most interfacial shear bonding strength was increased as increasing a composition of adding elements, and a heat-treatment time, and an oxygen partial pressure. From the results of this study it was found that the addition of alloying elements such as indium and tin increase hardness of as-cast alloy, produce surface oxide layer of adding elements by heat-treatment which may improve interfacial bonding strength between alloy and porcelain.

• 한국세라믹학회지
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• 제36권1호
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• pp.61-68
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• 1999

층상구조를 이루는 재료의 소결시 형성되는 다양한 결함 및 잔류응력을 고찰하기 위해 TZP-SUS계 및 ZT/SUS계다층재료와 porcelain/alumina 및 porcelain/Y-TZP 이층재료를 소결법으로 제조하였다. 상압소결로 제조한 다층재료에서는 층간의 소결수축율 차이에 의해 warping, splitting, 균열 등의 소결결함이 관찰되었으며, 중간층수 및 두께의 조절과 출발물질의 제어를 통해 이러한 소결결함이 완화됨을 알 수 있었다. Tape casting법으로 제조한 다층재료에서는 소결시 가한 압력에 의해 소결결함, 특히 warping이 제어됨을 확인할 수 있었다. 이층재료에서 형성되는 잔류응력은 vickers 압입법으로 관찰하였다. Porcelain/alumina에서는 porcelain 측의 계면에 작은 인장응력이, porcelain/Y-TZP에서는 압축응력이 형성됨을 확인할 수 있었으며, 이러한 잔류응력은 이층재료의 강도에도 영향을 미침을 알수 있었다. 결국 다층재료의 소결결함 및 잔류응력은 재료설계와 출발물질 상수에 영향을 받는다는 것을 알 수 있었다.

• 한국전기전자재료학회논문지
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• 제24권4호
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• pp.303-308
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• 2011

The Gallium-doped ZnO(GZO) film deposited at a temperature of $200^{\circ}C$ and a pressure of 10 mtorr has an optical transmittance of 89.0% and a resistivity of $2.0\;m{\Omega}{\cdot}cm$ because of its high crystallinity. Effect of $Al_2O_3$ oxide buffer layers on the optical and electrical properties of sputtered ZnO films were intensively investigated for developing the electrodes of opto-electronic devices which demanded high optical transmittance and low resistivity. The use of $Al_2O_3$ buffer layer could increase optical transmittance of GZO film to 90.7% at a wavelength of 550 nm by controlling optical spectrum. Resistivity of deposited GZO films were much dependent on the deposition condition of $O_2/(Ar+O_2)$ flow rate ratio during the buffer layer deposition. It is considered that the $Al_2O_3$ buffer layer could increase the carrier concentration of the GZO films by doping effect of diffused Al atoms through the rough interface.

• 한국컴퓨터정보학회논문지
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• 제16권7호
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• pp.77-84
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• 2011

B$\'{e}$k$\'{e}$sy 청력검사는 피검자의 청력 역치를 결정할 수있을 뿐만 아니라 누가현상을 추정 할 수 있고 난청의 병변위치를 규명하는데도 도움을 주는 청력검사 방법이다. 본 논문은 가격 경쟁력을 제공하기 위한 방법으로 PC 사운드카드를 사용하여 ANSI 표준을 준수하는 B$\'{e}$k$\'{e}$sy 청력검사 시스템의 개발에 대해 기술한다. 본 시스템은 동적으로 검사 신호를 생성하며, 실시간으로 검사 결과를 확인할 수 있는 인터페이스를 제공한다. 또한 표준에서 요구하는 최대 청력 레벨을 지원하기 위해 증폭기를 구현한다. 그리고 구현된 시스템이 ANSI 표준을 준수하는지 검증한다.

• Corrosion Science and Technology
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• 제5권5호
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• pp.168-172
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• 2006

Alloy 600 having a superior resistance to a corrosion is used as a steam generator tubing in nuclear power plants. In spite of its high corrosion resistance, there are many tubings which experience corrosion problems such as a SCC under the high temperature and high pressure environments of nuclear power plants. The Alloy 600 tubing can be repaired by using a Ni electroplating having an excellent SCC resistance. In order to carry out a successful Ni electrodeposition inside a steam generator tubing, the effects of various parameters on the material properties of the electrodeposit should be elucidated. Hence this work deals with the effects of an applied current density, duty cycle($T_{on}/(T_{on}+T_{off})$) of a pulse current, bath temperature and solution pH on the material properties of Ni electrodeposit obtained from a Ni sulphamate bath by analyzing the current efficiency, potentiodynamic curve, hardness and stress-strain curve. Hardness, YS(yield strength) and TS(tensile strength) decreased whereas the elongation increased as the applied current density increased. This was thought to be by a concentration depletion at the interface of the electrodeposit/solution, and a fractional decrease of the hydrogen reduction reaction. As the duty cycle increased, the hardness, YS and TS decreased while the elongation increased. During an off time at a high duty cycle, the concentration depletion could not be recovered sufficiently enough to induce a coarse grain sized electrodeposit. With an increase of the solution temperature and pH, the YS and TS increased while the elongation decreased. The experimental results of the hardness and the stress-strain curves can be supplemented by the results of the potentiodynamic curve.

• Smart Structures and Systems
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• 제17권1호
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• pp.149-165
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• 2016

Floods have been known to be one of the main causes of bridge collapse. Contrary to earthquakes, flood events tend to occur repeatedly and more frequently in rainfall areas; flood-induced damage and collapse account for a significant portion of disasters in many countries. Nevertheless, in contrast to extensive research on the seismic fragility analysis for civil infrastructure, relatively little attention has been devoted to the flood-related fragility. The present study proposes a novel methodology for deriving flood fragility curves for bridges. Fragility curves are generally derived by means of structural reliability analysis, and structural failure modes are defined as excessive demands of the displacement ductility of a bridge under increased water pressure resulting from debris accumulation and structural deterioration, which are known to be the primary causes of bridge failures during flood events. Since these bridge failure modes need to be analyzed through sophisticated structural analysis, flood fragility curve derivation that would require repeated finite element analyses may take a long time. To calculate the probability of flood-induced failure of bridges efficiently, in the proposed framework, the first order reliability method (FORM) is employed for reducing the required number of finite element analyses. In addition, two software packages specialized for reliability analysis and finite element analysis, FERUM (Finite Element Reliability Using MATLAB) and ABAQUS, are coupled so that they can exchange their inputs and outputs during structural reliability analysis, and a Python-based interface for FERUM and ABAQUS is newly developed to effectively coordinate the fragility analysis. The proposed framework of flood fragility analysis is applied to an actual reinforced concrete bridge in South Korea to demonstrate the detailed procedure of the approach.