• 대한기계학회논문집A
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• 제41권6호
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• pp.483-489
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• 2017

본 연구에서는 초음파 기법을 이용하여 메가헤르츠 대역에서 작동하는 마이크로 캔틸레버의 공진 주파수를 측정하였다. 고출력 초음파 펄스 발생기와 탐촉자를 이용하여 실리콘 재질의 마이크로 캔틸레버를 가진하였으며, 532 nm 연속파장(continuous wave) 레이저를 광원으로 하는 마이켈슨 간섭계를 사용하여 자유진동하는 마이크로 캔틸레버의 시간영역 파형을 획득하였다. 고속 푸리에 변환(fast Fourier transform)을 통한 주파수 응답 특성으로부터 마이크로 캔틸레버의 고유진동수를 평가할 수 있었으며, 유한요소법을 이용한 수치해석을 통하여 그 타당성을 검증하였다. 본 연구는 기존 원자현미경 기반의 측정기술과 대비하여 민감도를 향상시킬 수 있는 특성평가 기법을 제시한다.

• Nuclear Engineering and Technology
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• 제53권1호
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• pp.234-243
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• 2021

In the research or project planning for the decommissioning of a nuclear power plant, one of several preparations will be the establishment of a list of potential radionuclides to be considered at the time of characterization or final status surveys. Reliable data for selection of potential radionuclides during the transition period to prepare for decommissioning will depend heavily on historical data at the site or, where possible, sampling analysis. However, during the transition period, direct sampling can be challenging, depending on the circumstances of the site or national regulation. A methodology of selecting potential radionuclides for nuclear facility sites which largely consists of three major processes: production of initial list of radionuclides, selection of the insignificant radionuclide that will be eliminated, and consideration of site characterization or sampling. For developing a preliminary list of potential radionuclides for Kori Unit 1 decommissioning, the list of initial radionuclides was made referring to the technical documents applied at decommissioned NPPs in the U.S and additional reference materials applied until the operation of NPPs in Korea. For the screening of insignificant radionuclides, we applied criterion of less than 0.1% of the amount of radioactivity inventory and confirmed the dose fraction using the RESRAD code. The final suit of radionuclides was established, which should be supplemented by reflecting site characterization and sampling process in the future. Thus, the methodology and results for the selection of potential radionuclides suggested in this paper can give an insight as a future reference to deriving DCGLs in relation to site remediation of decommissioning nuclear plants.

• Journal of Mechanical Science and Technology
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• 제16권11호
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• pp.1477-1484
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• 2002

Various characteristics of a thin liquid film in its vapor-phase are investigated using the molecular dynamics technique. Local distributions of the temperature, density, normal and tangential pressure components, and stress are calculated for various film thicknesses and temperature levels. Distributions of local stresses change considerably with respect to film thicknesses, and interracial regions on both sides of the film start to overlap with each other as the film becomes thinner. Integration of the local stresses, i.e., the surface tension, however, does not vary much regardless of the interfacial overlap. The minimum thickness of a liquid film before rupturing is estimated with respect to the calculation domain sizes and is compared with a simple theoretical relation.

• Geomechanics and Engineering
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• 제15권3호
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• pp.899-910
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• 2018

Terrace deposits are often encountered in portal areas and tunnels with low overburden. They are challenging to excavate considering their great mechanical and spatial heterogeneity and a very high stiffness contrast within the ground. Terrace deposits are difficult to characterize, considering that samples for laboratory testing are almost unfeasible to obtain, and laboratory tests may not be representative due to scale effects. This paper presents the approach taken for their characterization during the design stage and their posterior validation performed during construction. Lessons learned from several tunnels excavated on terrace deposits on the Bogota-Villavicencio road (central-east Colombia), suggest that based on numerical simulations, laboratory testing and tunnel system behaviour monitoring, an observational approach allows engineers to optimize the excavation and support methods for the encountered ground conditions, resulting in a more economic and safe construction.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.409-412
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• 2004

Microstructures and mechanical properties of microalloyed cold forging steel and cold forged prototype automobile part are characterized. The work hardening according to the increase of plastic strain plays a major role in increasing the tensile strength of microalloyed cold forging steel during cold forming. On the other hand, inhomogeneous distribution of plastic strain causes variations in microstructure and mechanical properties. The relation between inhomogeneous distribution of plastic strain and variations in microstructure and mechanical properties is discussed. The variation of mechanical property in cold forged automobile part is analyzed using quantitative evaluation of plastic strain from finite element method.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1692-1696
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• 2008

In this paper, we characterize the mechanical properties of PCL strand which is made by oscillating nozzle for tissue engineering scaffold. In order to increase the mechanical properties of the PCL strand, we designed an oscillating nozzle system for the 3D plotting system. First, we check the effect of the nozzle speed (3 to 8 mm/sec), frequency (0 or 300 Hz) and the oscillating amplitude (0 or 100 V) on the diameter of the PCL strand. Second, we observe the effect of the frequency (0, 100, 200 and 300 Hz) and the oscillating amplitude (0, 50 and 100 V) on the mechanical property of PCL strand. The mechanical properties and surface morphology of PCL strand made by oscillating nozzle are compared with the PCL strand made by normal nozzle using Nano-UTM and SEM.

• 동력기계공학회지
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• 제17권5호
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• pp.23-29
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• 2013

The activation process is the key to graphene's practical application. In this study, the effect of grinding speed in planetary ball mill on structural integrity of graphene has been studied at various grinding speed such as 100 rpm, 200 rpm, 300 rpm, 400 rpm and 500 rpm. The morphology and structure of pristine graphene and ground graphenes were studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy respectively. According to these results, structural properties of graphene were improved when grinding speed was increased.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
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• pp.57-58
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• 2006

Chemical-mechanical planarization (CMP) of Cu has used currently in semiconductor process for multilevel metallization system. This process requires the application of a considerable down-pressure to the sample in the polishing, because porous low-k films used in the Cu-multilevel interconnects of 65nm technology node are often damaged by mechanical process. Also, it make possible to reduce scratches and contaminations of wafer. Electrochemical mechanical planarization (ECMP) is an emerging extension of CMP. In this study, the electrochemical mechanical polisher was manufactured. And the static and dynamic potentiodynamic curve of Cu were measured in KOH based electrolyte and then the suitable potential was found.

• Journal of Electrochemical Science and Technology
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• 제13권4호
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• pp.486-496
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• 2022

The effect of solution-treated on the self-corrosion performance and discharge performance of AZ91 magnesium alloy as anode material was analyzed by microscopic characterization, immersion tests, electrochemical measurements, and discharge performance tests. The study shows that the β-phase in the AZ91 magnesium alloy gradually dissolved in the matrix with the increase of the solution temperature, and the electrochemical activity of the magnesium alloy anode was significantly improved. Through the comparison of three different solution-treated processes, it is found that the AZ91 magnesium alloy has the most vigorous activity and better discharge performance after solution-treated of 415℃+12 h. In addition, the proportion and distribution of β-phase AZ91 magnesium alloy have a direct impact on its discharge performance as an anode material.

• 한국분말재료학회지
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• 제27권1호
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• pp.52-57
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• 2020

In this study, we report the microstructure and characterization of Ta₂₀Nb₂₀V₂₀W₂₀Ti₂₀ high-entropy alloy powders and sintered samples. The effects of milling time on the microstructure and mechanical properties were investigated in detail. Microstructure and structural characterization were performed by scanning electron microscopy and X-ray diffraction. The mechanical properties of the sintered samples were analyzed through a compressive test at room temperature with a strain rate of 1 × 10^-4 s^-1. The microstructure of sintered Ta₂₀Nb₂₀V₂₀W₂₀Ti₂₀ high-entropy alloy is composed of a BCC phase and a TiO phase. A better combination of compressive strength and strain was achieved by using prealloyed Ta₂₀Nb₂₀V₂₀W₂₀Ti₂₀ powder with low oxygen content. The results suggest that the oxide formed during the sintering process affects the mechanical properties of Ta₂₀Nb₂₀V₂₀W₂₀Ti₂₀ high-entropy alloys, which are related to the interfacial stability between the BCC matrix and TiO phase.