• 한국자동차공학회논문집
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• 제18권3호
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• pp.133-142
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• 2010

The present work focuses on the characterization of material parameters of the Overlay(multilinear hardening) model for analyzing the non-isothermal cyclic deformation. In the previous study, all the parameters were especially based on the Overlay theories, and a simple method was suggested to find out the best material parameters for the isothermal cyclic deformation analysis. Based on the previous research this paper f dther improves the isothermal parameters and suggests how to apply the isothermal parameters to the non-isothermal conditions especially for the description of TMF(Thermo-Mechanical Fatigue) hysteresis behavior. The parameters are determined and calibrated using 400 series stainless steel test data in the reference papers. For the implementation into ABAQUS, a user subroutine is developed by means of ABAQUS/UMAT. The finite element results show good agreement with test for the case of uniaxial non-isothermal cyclic loading, signifying the proposed method can be used in the TMF analysis of the converter-inserted heavy duty muffler system and the stainless steel exhaust-manifold system which are to be done in our future research.

• Journal of Welding and Joining
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• 제19권3호
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• pp.325-333
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• 2001

The effect of base metal grain size on isothermal solidification behavior of Ni-base superalloy, CMSX-2 during transient liquid phase (TLP) bonding was investigated employing MBF-80 insert metal. TLP-bonding of single crystal. coarse-grained and fine-grained CMSX-2 was carried out at 1373∼1548k for various holding time in vacuum. The eutectic width diminished linearly with the square root of holding time during isothermal solidification process for single crystal, coarse-grained and fine-grained base metals. The completion time for isothermal solidification decreased in the order ; single crystal, coarse-grained and fine-grained base metals. The difference of isothermal solidification rates produced when bonding the different base metals could be explained quantitatively by the effect of base metal grain boundaries on the apparent average diffusion coefficient of boron in CMSX-2.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2009년 추계학술발표대회
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• pp.59-59
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• 2009

The influences of B and Si in the filler metals on microstructure and isothermal solidification during transient liquid-phase (TLP) bonding of a nitrogen-containing duplex stainless steel with MBF-30 (Ni-4.5wt.%Si-3.2wt.%B) and MBF-35 (Ni-7.3wt.%Si-2.2wt.%B), were studied at the temperature range of $1030-1090^{\circ}C$ with various times from 60 s to 3600 s under a vacuum of approximately $10^{-5}$ Torr. In case of the former, BN, $Ni_3B$ and $Ni_3Si$ precipitates were formed in the bonding region. BN and $Ni_3Si$ secondary phases were present in the joint for the latter case. The formation of $Ni_3B$ within the joint centerline is dependent on B content. The morphology of $Ni_3Si$ is dominated by Si concentration. A difference between the times for complete isothermal solidification obtained by the experiments and the conventional TLP bonding diffusion model was observed when using MBF-35. According to the simulated results, the isothermal solidification completion time for MBF-35 case was smaller than that in MBF-30. However, this experimental value obtained using MBF-35 was notably larger than that obtained using MBF-30. Isothermal solidification of liquid MBF-30 is controlled by the first isothermal solidification regime dependent on B diffusion model, whereas that of liquid MBF-35 experiences two isothermal solidification regimes and is mainly controlled by the second isothermal solidification dependent on Si diffusion model. In addition, only if Si content exceeds a critical value, the slower 2nd solidification regime will commence.

• 대한기계학회논문집B
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• 제27권7호
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• pp.963-972
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• 2003

Performance characteristics of the planar-type solid oxide fuel cell (SOFC) are investigated by the analysis of flow fields coupled with heat and mass transfer phenomena in anode and cathode channels. For these purposes, performance analysis of the SOFC is conducted based on electrochemical reaction phenomena in electrodes and electrolyte coupled with flow fields in anode and cathode channels. In the present study, the isothermal model adopted in the previous paper prepared by the same authors is extended to the non-isothermal model by solving energy equation additionally with momentum and mass transfer equations using CFD technique. It is found that the difference between isothermal and non-isothermal models come from non-uniform temperature distribution along anode and cathode electrodes by solving energy equation in non-isothermal model. Non-uniform temperature distribution in non-isothermal model contributes to the increase of average temperature of the fuel cell and influences its performance characteristics.

• 열처리공학회지
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• 제25권3호
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• pp.115-120
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• 2012

It has been known that the ferritic stainless steel can be changed to martensitic stainless steel when nitrogen is added. However the high hardness of martensitic stainless steel prevents the plastic deformation. In this study, instead of martensite, the surface microstructure was changed into nitrogen pearlite to increase the plastic deformation easily by isothermal heat treatment after high temperature gas nitriding (HTGN) the AISI 430 ferritic stainless steel. The isothermal treatment was carried out at $780^{\circ}C$ for 4, 6, and 10 hrs, respectively, after HTGN treatment at $1100^{\circ}C$ for 10 hrs. The surface layer of isothermal-treated steel appeared nitrogen pearlite composed with fine chromium nitride and ferrite. Hence, the interior region that was not affected by nitrogen permeation exhibited ferrite phase. When quenching the isothermal treated steel at 1100oC, martensitic phase formed at the surface layer. The hardness of surface layer of isothermal-treated steel and quenched steel measured the value of 150~240 Hv and 630 Hv, respectively.

• 한국환경복원기술학회지
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• 제11권3호
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• pp.87-93
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• 2008

In order to manage national environment effectively, one has to understand its ecological traits. The difference of temperature determines ecological traits of each respective region. In other words, temperature differentials on surface make a great impact on botanical structure. Currently, isothermal data-produced by meteorological stations based upon time series analysis-are widely used to plan and manage national environment. Nonetheless, the isothermal data do not reflect real surface temperature of regions. Because of numerous mountainous terrains in the Korean peninsula where temperature varies widely according to altitude, the range of temperature distribution-that reflects altitudinal change-has to be paid special attention. This study aims at expressing in space isothermal distribution that is necessary to plan and manage national environment effectively. In addition, not just South Korea, but also North Korea was included for isothermal distribution. As a result, this study corrected established isothermal lines up to date and demonstrated that altitude, latitude, and distance from coastal lines greatly influence temperature distribution of the Korean peninsula.

• 대한기계학회논문집
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• 제14권1호
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• pp.197-206
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• 1990

본 연구에서는 수평등온평면의 가장자리에 주위물의 온도와 동일한 수평등온 평판을 부착한 모델을 사용하여 수평평면 선단의 하부에서 유체가 상부로 유입되는 것 을 방지함으로서 특별한 가정없이 단열평판의 선단에서의 경계조건을 직접 구할 수 있 었다.그리고 기존 밀도식의 복잡성과 신뢰도를 개선한 Gebhart등의 밀도식을 사용 하여 수치해석결과의 신뢰도를 증진하였다. 유한착분법을 사용하여 수평등온평면 주 위에서 일어나는 자연대류에 대한 기배방정식을 수치계산하여 주위물의 온도변화가 유 선분포, 온도분포, 국소열전달계수 및 평균 Nusselt수에 미치는 영향을 구명하였고, 상향 및 하향 수평등온면 주위에서 일어나는 자연대류의 유동형태와 열전달 특성을 비 교 검토하였다.

• 한국응용과학기술학회지
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• 제24권3호
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• pp.278-286
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• 2007

As a part of enhancing the performance of wood-plastic composites (WPC), polypropylene (PP)/ nanoclay (NC)/ wood flour (WF) nanocomposites were prepared using melt blending and injection molding process to evaluate their thermal stability. Thermogravimetric analysis (TGA) was employed to investigate thermal degradation kinetics of the nanocomposites both dynamic and isothermal conditions. Dynamic scans of the TGA showed an increased thermal stability of the nanocomposites at moderate wood flour concentrations (up to 20 phr, percentage based on hundred percent resin) while it decreased with the addition of 30 phr wood flour. The activation energy $(E_a)$ of thermal degradation of nanocomposites increased when nanoclay was added and the concentration of wood flour increased. Different equations were used to evaluate isothermal degradation kinetics using the rate of thermal degradation of the composites, expressed as weight loss (%) from their isothermal TGA curves. Degradation occurred at faster rate in the initial stages of about 60 min., and then proceeded in a gradual manner. However, nanocomposites with wood flour of 30 phr heated at $300^{\circ}C$ showed a drastic difference in their degradation behavior, and reached almost a complete decomposition after 40 min. of the isothermal heating. The degree of decomposition was greater at higher temperatures, and the residual weight of isothermal degradation of nanocomposites greatly varied from about 10 to 90%, depending on isothermal temperatures. The isothermal degradation of nanocomposites also increased their thermal stability with the addition of 1 phr nanoclay and of wood flour up to 20 phr. But, the degradation of PP100/NC1/MAPP3/WF30 nanocomposites with 30 phr wood flour occurs at a faster rate compared to those of the others, indicating a decrease in their thermal stability.

• 생명과학회지
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• 제24권4호
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• pp.428-436
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• 2014

Loop-mediated isothermal amplification (LAMP)법은 등온에서 DNA 주형을 변성시키지 않고 실시하기 때문에, autocycling 가닥 변위 DNA 합성에 의존한다. 그래서 고가의 PCR 장비를 필요로 하지 않고 등온 유지가 가능한 저가의 장비인 항온 수조, 오븐, 온장고 등에서 증폭이 가능하다. 본 연구진은 Streptococcus parauberis의 random primer중에서 5개를 선정하여, 신장도가 높은 2개의 primer를 이용하여 최적 반응온도 및 최적 반응시간, 최적 반응 조건들을 확립하였다. 그리고 기존의 PCR과 LAMP의 민감도의 비교 분석을 측정한 결과, LAMP의 높은 검출 한계를 확인할 수 있었다. 본 논문에서는 non-target DNA의 영향을 받지 않고 등온 조건 하에서 DNA를 증폭시킬 수 있는 LAMP법과 SYBR-green I를 이용하여 시각화시켰으며, 기존의 PCR과 비교 분석함으로써, S. parauberis에 대한 신속하고 정확한 진단법을 확립하였다.

• 열처리공학회지
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• 제37권5호
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• pp.255-261
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• 2024

To study the effects of patenting temperature and isothermal holding time on the phase transformation and mechanical property changes of SAE 1078 steel, the patenting process was performed at 460℃, 560℃, and 660℃ for isothermal times (30 s, 60 s, 90 s, 120 s, and 150 s) after nitrogen cooling under austenitizing conditions (1000℃, 2 min). In this study, a scanning electron microscope was used to measure the microstructure and interlamellar spacing of pearlite according to process variables, and an X-ray diffraction analyzer was used to calculate the phase fraction. Cooling rate is approximately 18.6℃/s from the austenitizing temperature to the patenting temperature and pearlite transformation begins at 597~602℃. As the patenting temperature increases, the rate of carbon diffusion during isothermal step increases, so a relatively coarse pearlite structure is formed, and the hardness tends to decrease overall. As the isothermal holding time increased, the hardness of the treated specimens converged to 420Hv, 376Hv, and 268Hv, respectively, because the phase transformation was sufficiently completed at 460℃, 560℃, and 660℃. On the other hand, as the isothermal holding time became shorter, sufficient phase transformation did not occur after the isothermal process, so retained austenite existed, resulting in a decrease in hardness.