• Nuclear Engineering and Technology
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• 제52권1호
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• pp.185-191
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• 2020

Plant-specific analyses of an advanced reactor have been performed to assure the structural integrity of the reactor pressure vessel during transient conditions, which are expected to initiate pressurized thermal shock (PTS) events. The vessel failure probabilities from the probabilistic fracture mechanics analyses are combined with the transient frequencies to generate the through-wall cracking frequencies, which are compared to the acceptance criterion. Several sensitivity analyses are performed, focusing on the orientations and sizes of cracks, the copper content, and a flaw distribution model. The results show that the integrity of the reactor vessel is expected to be maintained for long-term operation beyond the design lifetime from the PTS perspective using the design data of the advanced reactor. Moreover, a fluence level exceeding 9×10¹⁹ n/㎠ is found to be acceptable, generating a sufficient margin beyond the design lifetime.

• 한국재료학회지
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• 제22권10호
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• pp.526-530
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• 2012

Silica-based ceramic-matrix composites have shown promise as advanced materials for many applications such as chemical catalysts, ceramics, pharmaceuticals, and electronics. $SiO_2$-CuO-$CeO_2$ multi-component powders and their thin film, using an oxalic acid template as a chelating agent, have larger surface areas and more uniform pore size distribution than those of inorganic acid catalysts. $SiO_2$-CuO-$CeO_2$ composite powders were synthesized using tetraethylorthosilicate, copper (II) nitrate hemi (pentahydrate), and cerium (III) nitrate hexahydrate with oxalic acid as template or pore-forming agent. The process of thermal evolution, the phase composition, and the surface morphology of these powders were monitored by thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffractometry (XRD), field-emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray spectrometry (EDXS). The mesoporous property of the powders was observed by Brunner-Emmett-Teller surface (BET) analysis. The improved surface area of this powder template with oxalic acid was $371.4m^2/g$. This multi-component thin film on stainless-steel was prepared by sol-gel dip coating with no cracks.

• Corrosion Science and Technology
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• 제20권4호
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• pp.175-182
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• 2021

Magnesium alloy is limited in the industrial field because its standard electrode potential is -2.363 V vs. NHE (Normal Hydrogen Electrode) at 25 ℃. This high electrochemical activity causes magnesium to quickly corrode with oxygen in air; chemical conversion coating prevents corrosion but causes surface defects like cracks and pores. We have examined the anti-corrosion effect of sol-gel coating sealed on the defected conversion coating layer. Sol-gel coatings produced higher voltage current and smaller pore than the chemical conversion coating layer. The conversion coating on magnesium alloy AZ31 was prepared using phosphate-permanganate solution. The sol-gel coating was designed using trimethoxymethylsilane (MTMS) and (3-Glycidyloxypropyl) trimethoxysilane (GPTMS) as precursors, and aluminum acetylacetonate as a ring-opening agent. The thermal shock resistance was tested by exposing specimens at 140 ℃ in a convection oven; the results showed changes in the magnesium alloy AZ31 surface, such as oxidization and cracking. Scanning electron microscope (FE-SEM) analysis confirmed a sealed sol-gel coating layer on magnesium alloy AZ31. Electrochemical impedance spectroscopy (EIS) measured the differences in corrosion protection properties by sol-gel and conversion coatings in 0.35 wt% NaCl solution, and the potentiodynamic polarization test and confirmed conversion coating with the sol-gel coating show significantly improved resistance by crack sealing.

• 생물환경조절학회지
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• 제22권1호
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• pp.73-79
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• 2013

본 연구에서는 온실의 열손실을 최소화할 방안을 모색하기 위하여 경남지역에 있는 시설 농가를 대상으로 열화상 카메라를 이용하여 열손실 사례에 대한 실태조사를 실시하였다. 그 결과를 요약하면 다음과 같다. 치마처리 전 후의 두 실험구간의 온도차는 각각 $2.0{\sim}3.0^{\circ}C$ 및 $1.0{\sim}2.0^{\circ}C$ 정도인 것을 알 수 있다. 열화상 기기에 의해 계측된 온도와 온도 센서에 의해 계측된 온도와는 상관 관계가 큰 것으로 나타났다. 실태조사 지역 간에 큰 차이는 없었지만 보온용 부직포가 1층인 경우와 2층인 경우를 보면, 1층이 2층에 비해 상대적으로 열손실 크게 나타났다. 그리고 전체적으로 온실의 형태와 무관하게 측장부분과 수평보온커튼의 틈새, 측면과 전 후면 보온용 부직포의 이음부분이 완전히 밀폐되지 않아 열손실이 상대적으로 큰 것으로 나타났다. 특히, 파손된 피복재나 출입문, 환기구, 박공, 바닥부근 등에서 틈새가 생겨서 많은 양의 열이 손실되고 있었다.

• Journal of Mechanical Science and Technology
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• 제14권1호
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• pp.30-38
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• 2000

This paper presents a framework how to estimate crack driving forces in terms of crack-tip opening displacement and J-integral for mismatched dissimilar joints with interface cracks. The mismatch in elastic, thermal, and plastic hardening properties is not considered, but the mismatch in plastic yield strengths is emphasized here. The main outcome of the present work is that the existing methods to estimate crack driving forces for homogeneous materials can be used with slight modification. Such modification includes (i) mismatch- corrected limit load solutions, and (ii) evaluating the contribution of each material in dissimilar joints to the total crack driving force, which depends on the strength mismatch of the dissimilar joints.

• 대한기계학회논문집A
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• 제22권3호
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• pp.695-703
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• 1998

The crack problem of continuous casting slab due to the thermal stresses during the reheating process is analyzed using FEM. In this study, the C(t)-integral is calculated. As a result, the values of the C(t)-integral decrease by increasing the initial temperature of the slab and decreasing total heat flux. And those decrease by decreasing the heat flux of pre-heating zone and increasing the heat flux of heating zone.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 추계학술대회 논문집
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• pp.117-120
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• 2003

Joining or welding of dissimilar metallic materials is very difficult problem because material properties like heat conductivity, melting points, coefficient of thermal expansion, etc. are different each other and cracks are occurred easily due to formation of intermetallic compounds. Nevertheless, deep attention from great industrial demands and trials to joining dissimilar materials has been increased steadily. In this study, TIG welding of Cu to Al is tried and tensile test, SEM and EDX analysis are carried out.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1995년도 봄 학술발표회 논문집
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• pp.274-279
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• 1995

The heat of hyderation of cement causes the internal temperature rise and volume change at early age, paticular in massive concrete structures. As the results of the temperature rise and extenal restraint conditions, the themal stress may induce cracks in concrete. Therefore various techenuques of the themal stress control of the mass concrete has been widely used. One of these techniques is pipe-cooling which is considered in this study. The objective of this paper is to develop finite element program which is capable of simulating the temperature history and the thermal stress considering pipe-cooling, creep and the modified elastic modulus dud to maturity effect.

• 동력기계공학회지
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• 제7권2호
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• pp.73-79
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• 2003

The present study was aimed at analysing the damage of a used gas turbine bucket after 39,500h of total service. Microstructures and cracks of service-induced bucket were observed. The crack might have initiated from the coating in the bucket surface by thermal fatigue and propagated into the GTD111 base metal. Maximum depth of penetration was 2.7 mm(full penetration) at the leading edge. Crack contains a lot of Cr-,Ti-,Al-oxide which will prohibit filling and wetting of insert metal. Depth and propagation direction of crack were accorded with centrifugal force and temperature distribution in turbine bucket. Present result will provide basic data for repair bonding process.

• 소성∙가공
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• 제13권3호
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• pp.268-272
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• 2004

Transparent materials such as fused silica are widely utilized in optical and optoelectronics field because of its outstanding properties, such as transparency in a wide wavelength range, strong damage resistance for laser irradiation, and high thermal and chemical stability. In this study, we made a few micro patterns on the surface of fused silica plate using laser induced wet etching. KrF excimer laser was used as a light source. There were no burrs and micro cracks on the etched surface of fused silica and the flatness of the etched surface was fairly good. We investigated the influence of etchant upon the etch rate and quality in laser induced wet etching. Pyrene-acetone solution and toluene were used as etchant. In the side of etch rate, toluene solution was better than pyrene-acetone solution. But we made in wider range of energy density using pyrene-acetone solution. But pyrene-acetone solution gave us wider window of energy density for successful micro patterning.