• Journal of Welding and Joining
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• 제18권2호
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• pp.227-227
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• 2000

Pressure vessels usually consist of main body and pipes which are connected with the main body. And as joining method of such main body and pipes, welding is carried out. After welding, welding residual stresses inevitably occur around welded joints. As residual stresses act harmfully on fatigue strength, corrosion and buckling strength of structure, PWHT is carried out for the purpose of removing the residual stress. But, during PWHT process, 2 ¼Cr-1Mo steels are frequently apt to generate reheat crack. For this reason, it is strongly needed to analyze and examine the mechanical behavior of welded joints before and after PWHT process. So, in this study, welded nozzle parts of pressure vessel where reheat cracks frequently occur are selected for examining the mechanism of crack-occurrence. (Received December 2, 1999)

• Journal of Welding and Joining
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• 제18권2호
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• pp.100-104
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• 2000

Pressure vessels usually consist of main body and pipes which are connected with the main body. And as joining method of such main body and pipes, welding is carried out. After welding, welding residual stresses inevitably occur around welded joints. As residual stresses act harmfully on fatigue strength, corrosion and buckling strength of structure, PWHT is carried out for the purpose of removing the residual stress. But, during PWHT process, $2\frac{1}{4}Cr-1Mo$ steels are frequently apt to generate reheat crack. For this reason, it is strongly needed to analyze and examine the mechanical behavior of welded joints before and after PWHT process. So, in this study, welded nozzle parts of pressure vessel where reheat cracks frequently occur are selected for examining the mechanism of crack-occurrence.

• 열처리공학회지
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• 제33권6호
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• pp.284-289
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• 2020

Since the dissimilar bonded interface usually consists of intermetallic compounds (IMCs) layer and cracks, their mechanical and electrical properties can be influenced by microstructure at interface between two different metals. In this study, the friction welded Cu-Al busbar, which is widely used to connect a secondary battery and their component, is selected to analyze the influence of interfacial characteristic on their tensile strength and electric conductivity. Then, the electrical characteristics of Cu busbar and Cu-Al busbar were investigated by thermal flow analysis and temperature rise test. In addition, the relationship between the maximum saturation temperature and the electrical conductivity were discussed in terms of interfacial characteristics of the friction welded Cu-Al busbar.

• KEPCO Journal on Electric Power and Energy
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• 제8권2호
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• pp.93-96
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• 2022

The boiler tubes of thermal power plants are exposed to harsh environment of high temperature and high pressure, and the deterioration state of materials rapidly increases. In particular, parent material and welds of the materials used are subjected to a temperature change and various constraints, resulting in deformation and its growth, resulting in frequent leakage accidents caused by tube failure. The power plant checks the integrity of boiler tubes through non-destructive testing as it may act as huge costs loss and limitation of power supply during power station shutdown period due to boiler tube leakage. However, the current non-destructive testing is extremely limited in the field to detect micro cracks. In this study, the ability of metal magnetic memory technique to detect flaws of size that are difficult to inspect by the visual or general non-destructive methods was verified in the early stage of their occurrence.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2002년도 춘계학술발표회 초록집
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• pp.37-37
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• 2002

Diamoncl/Mo/Ni multi-layers on SKH-51 steel substrate was prepared to improve the abrasive wear resistance of a tool and die by a commercial chemical vapor deposition unit and electro-plating. The diamond after 7 hour deposition had cuba-octahedral structure with 2~5$\mu\textrm{m}$ grains. The existence of non-ferrous metals such as chromium, nickel and molybdenum between diamond and SKH-51 substrate results in forming higher quality of diamond layer by retarding carbon diffusion in the diamond layer during deposition, and also improving hardness and wear resistance. Surface cracks on the film was sometimes observed by the difference of by the thermal expansion coefficients between the steel substrate and the deposited layers during cooling.

• Nuclear Engineering and Technology
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• 제55권2호
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• pp.408-420
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• 2023

Beryllium oxide (BeO) is being re-emphasized and utilized in Micro Modular Reactors (MMR) because of its prominent nuclear and high temperature properties in recent years. The implications of the research about effects of neutron irradiation on the microstructure and properties of BeO are significant. This article comprehensively reviews the effects of neutron irradiation on BeO and proposes the maximum permissible neutron doses at different temperatures for BeO without cracks in appearance according to the data in the previous literature. This maximum permissible neutron dose value has important reference significance for the experimental study of BeO. The effects of neutron irradiation on the thermal conductivity and flexural strength of BeO are also discussed. In addition, microstructure evolution of irradiated BeO during post-irradiation annealing is summarized. This review article has important implications for the application of BeO in MMR.

• 한국세라믹학회지
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• 제41권9호
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• pp.677-683
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• 2004

레이저 모체재료용 Nd:LLM (Nd:LiLa(MoO$_4$)$_2$) 단결정을 쵸크랄스키법으로 성장시켰다 성장된 Nd:LLM 단결정은 균열 등이 쉽게 발생하였는데, 균열의 원인은 상전이, 불합치용융, 구성성분의 화학적 불균질, 열적구조의 불균형 및 성장방향 등이 있다. 성장된 단결정의 TG-DTA 열분석 결과 상전이는 없었으며, XRD 회절분석에 의해 합치 용융체임을 확인하였다. Li$_2$O 성분의 휘발은 화학적 불균질에 중요한 원인이었다. 자체 제작된 저항발열로의 온도프로파일은 도가니 높이로 조절하였다 또한, Nd:LLM 결정은 성장방향에 따라 단결정의 성장에 영향을 받았으며, (101)의 방향의 성장에서 단결정의 품질이 가장 우수하였다. 성장된 단결정의 N$d^{3+}$ 이온의 분포 및 유효편석계수은 PIXE분석에 의해 수행되었다.

• Composites Research
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• 제27권4호
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• pp.174-181
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• 2014

본 연구에서는 탄소섬유 강화 복합재의 점탄성 성질을 적용한 유한요소 해석에 대해서 기술하였다. 고온의 성형과정에서 발생하는 가장 중요한 문제 중 하나는 잔류응력의 발생이다. 잔류응력으로 인해 성형이 끝난 후 뒤틀림, 균열이 일어 날 수 있으며 이는 완성품에 심각한 결함을 가져올 수 있다. 잔류응력의 주요 원인은 점탄성이며 고온의 성형과정에서 열팽창계수의 차이와 수지의 시간 및 온도에 대한 물성의 변화로 인해 발생하는 탄소섬유 강화 복합재의 특징이다. 화학 수축도 잔류응력에 많은 영향을 주며 이를 고려한 뒤틀림 예측에서 오차를 줄일 수 있는 중요한 요소이다. 본 연구는 복합재 성형에 사용된 온도변화에 대한 경화도와 점탄성 효과, 화학수축을 유한요소 해석으로 수행하기 위한 기법을 연구하고, 점탄성의 영향성을 연구하였다. 기존에 연구되어 있는 논문을 참고하여 서브루틴의 타당성을 검증한 후 나아가 복합재의 적층각의 변화에 따른 응력과 변형을 해석해 봄으로써 실제 복합재의 성형 시 발생하는 휨 현상에 대한 예측방법을 제시하였다.

• Carbon letters
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• 제12권2호
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• pp.95-101
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• 2011

To investigate new applications for illite as an additive for carbon-based composites, the composites were prepared with and without illite at different heat-treatment temperatures. The effects of the heat-treatment temperature on the chemical structure, microstructure, and thermal oxidation properties of the resulting composites were studied. As the heat-treatment temperature was increased, silicon carbide SiC formation via carbothermal reduction increased until all the added illite was consumed in the case of the samples heat-treated at $2,300^{\circ}C$. This is attributed to the intimate contact between the $SiO_2$ in the illite and the phenol carbon precursor or the carbon fibers of the preform. Among composites prepared at all temperatures, those with illite addition exhibited fewer pores, voids, and interfacial cracks, resulting in larger bulk densities and lower porosities. A delay of oxidation was not observed in the illite-containing composites prepared at $2,300^{\circ}C$, suggesting that the illite itself absorbed energy for exfoliation or other physical changes. Therefore, if the illite-containing C/C composites can reach a density generally comparable to that of other C/C composites, illite may find application as a filler for C/C composites. However, in this study, the illite-containing C/C composites exhibited low density, even when prepared at a high heat-treatment temperature of $2300^{\circ}C$, although the thermal oxidation of the resulting composites was improved.

• Nuclear Engineering and Technology
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• 제45권5호
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• pp.683-688
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• 2013

Candidate coating materials for re-usable metallic nuclear fuel crucibles, TaC, TiC, ZrC, $ZrO_2$, and $Y_2O_3$, were plasmasprayed onto a niobium substrate. The microstructure of the plasma-sprayed coatings and thermal cycling behavior were characterized, and U-Zr melt interaction studies were carried out. The TaC and $Y_2O_3$ coating layers had a uniform thickness, and high density with only a few small closed pores showing good consolidation, while the ZrC, TiC, and $ZrO_2$ coatings were not well consolidated with a considerable amount of porosity. Thermal cycling tests showed that the adhesion of the TiC, ZrC, and $ZrO_2$ coating layers with niobium was relatively weak compared to the TaC and $Y_2O_3$ coatings. The TaC and $Y_2O_3$ coatings had better cycling characteristics with no interconnected cracks. In the interaction studies, ZrC and $ZrO_2$ coated rods showed significant degradations after exposure to U-10 wt.% Zr melt at $1600^{\circ}C$ for 15 min., but TaC, TiC, and $Y_2O_3$ coatings showed good compatibility with U-Zr melt.