• 열처리공학회지
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• 제9권2호
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• pp.147-158
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• 1996

Generally, analytical consideration on the behaviour of metallic structures during quenching process, and analysis on the thermal stress and deformation after heat treatment are very important in presumption of crack and distorsion of quenched material. In this study a set of constitute equations relevant to the analysis of thermo elasto-viscoplastic materials with strain hysteresis during quenching process way presented on the basis of contimuum thermo-dynamics mechanics. The thermal stresses were numerically calculated by finite element technique of weighted residual method and the principle of virtual work. In the calculation process, the temperature depandency of physical and mechaniclal properties of the material in consideration. On the distribution of elasto-viscoplastic thermal stresses according to radial direction, axial and tangential stress are tensile stress(50MPa, 1.5GPa and 300MPa) in surface and compressive stress(-1.2GPa, -1.14GPa and -750MPa) in the inner part on the other hand, radial stress is tensile stress(900MPa) in area of analysis. According to axial direction, tangential stress gradients are average 60MPa/mm on the whole. The reversion of stress takes place at 11.5 to 16.8mm from the center in area of analysing.

• Bulletin of the Korean Chemical Society
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• 제15권8호
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• pp.663-669
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• 1994

Decay kinetics of Ga(5s), Ga(5p) and Ga(4d) atoms in Ar were studied by laser induced fluorescence technique. Theground state gallium atoms in the gas phase were generated by pulsed dc discharge of trimethyl gallium and argon mixtures. Both pulsed discharge and YAG-DYE laser system were controlled by a dual channel pulse generator and the delay time between the end of discharge and laser pulses was set 3.0-6.0 ms. The Ga(5s) and Ga(4d) atoms were generated by single photon excitation from the ground state Ga atoms and radiative lifetimes as well as the total quenching rate constants in Ar were obtained from the pressure dependence of the fluorescence decay rates. The Ga(5p) atoms were populated by a two-photon excitation method and the cascade fluorescence from Ga(5s) atoms were analyzed to extract quenching rate constant of Ga(5p) atoms by Ar in addition to radiative lifetimes of Ga(5p) state. The magnitudes of the quenching rate constants by Ar for the low-lying excited states of Ga atoms are 1.6-3$ {\times}10^{-11}cm^3$ molecul$e^{-1}s^{-1}$, which are much larger than those for alkali, alkaline earth and Group 12 metals. Based on the measured rate constants, kinetic simulations were done to assign state-to-state rate constants.

• Bulletin of the Korean Chemical Society
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• 제27권11호
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• pp.1801-1808
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• 2006

The interaction between whey carrier protein $\beta$-lactoglobulin type A and B (BLG-A and -B) and 2,2'-bipyridin n-hexyl dithiocarbamato Pd(II) nitrate (BPHDC-Pd(II)), a new heavy metal complex designed for anticancer property, was investigated by fluorescence spectroscopy combined with chemometry and circular dichroism (CD) techniques. A strong fluorescence quenching reaction of BPHDC-Pd(II) to BLG-A and -B was observed. Hence, BPHDC-Pd(II) complex can be bound to both BLG-A and -B, and quench the fluorescence spectra of the proteins. The quenching constant was determined using the modified Stern-Volmer equation. The binding parameters were evaluated by fluorescence quenching method. The results of binding study provided evidences presence of two and three sets of binding sites on the BLG-B and -A, respectively, for BPHDC-Pd(II) complex. Using fluorescence spectroscopy and chemometry, the ability of BLG-A and -B to form an intermediate upon interaction with BPHDC-Pd(II) complex was assessed. CD studies displayed that under influence of different concentrations of BPHDC-Pd(II) complex, the regular secondary structure of BLG-B had no significant changes, whereas for BLG-A a transition from $\alpha$-helix to $\beta$-structure was appeared. The results for both of BLG-A and -B displayed that BPHDC-Pd(II) complex can induce a conformational transition from the native form to an intermediate state with a slightly opened conformation, which is detectable with chemometry analyses.

• 멤브레인
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• 제32권6호
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• pp.465-474
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• 2022

역세척이 가능한 평막형 분리막 모듈을 분리막 생물반응기(MBR)에 침지시켜 운전 시간에 따른 흡입 압력을 측정하였다. MLSS 8,000 mg/L 활성 슬러지 수용액에 공칭 세공크기가 0.2 ㎛, 유효막면적이 128 cm² 인 분리막 모듈을 침지시킨 후 투과 유속, quorum qeunching (QQ) 비드를 변화하며 흡입 압력을 확인하였다. Vacant bead (VB), BH4와 DKY-1의 실험군에서 FR과 SFCO 운전방식에 따른 효과를 비교, 분석하였다. 투과 유속 40 L/m² ⋅h 이고 DKY-1 QQ 비드를 주입할 경우 흡입 압력 감소는 가장 효과적이었다. 또한 역세척에 의한 흡입 압력 감소 효과는 DKY-1 QQ 비드의 경우보다 2배 이상 높게 나타났다.

• 한국재료학회지
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• 제27권1호
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• pp.8-11
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• 2017

Binary Ti-Al alloys containing 50 to 60 atomic percent aluminum are rapidly solidified by hammer anvil method under an argon atmosphere. Constituent phases in each alloy are identified by X-ray diffractometry and microstructures of the alloys are investigated using a transmission electron microscope. In alloys with aluminum content between 50 and 54 percent, a second phase exists besides TiAl(${\gamma}$); this second phase is identified as $Ti_3Al$(${\alpha}2$). The ${\alpha}2$ phase is observed in two types of morphology. One is as fine lamellar alternating with ${\gamma}$ and the other is as a particle. It is concluded that the existence of a metastable phase with the morphologies stated above should arise from a higher quenching rate attained by the hammer anvil method as compared to the conventional roll or splat-quench method. Implications of the above observation are discussed with respect to the phase relations in the Ti-Al binary system; these implications are still controversial in many respects.

• 대한기계학회논문집A
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• 제30권10호
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• pp.1284-1292
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• 2006

Heat treatment is a controlled heating and cooling process to improve the physical and/or mechanical properties of metal products without changing their shapes. Today finite element method is widely used to simulate lots of manufacturing processes including heat treatment and surface hardening processes, which aims to reduce the number of time- and cost-consuming experimental tryouts. In this study we tried, using this method, to simulate the full carburizing process that consists of carburizing, diffusing and quenching, and to predict the distribution of carbon contents, phase fraction and hardness, thermal deformation and other mechanical characteristics as the results. In the finite element analysis deformation, heat transfer, phase transformation and diffusion effects are taken into consideration. The carburizing process of a lock gear, a part of the car seat recliner, that is manufactured by the fine blanking process is adopted as the analysis model. The numerical results are discussed and partly compared with experimental data. And a combination of process parameters that is expected to give the highest surface hardness is proposed on the basis of this discussion.

• 소성∙가공
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• 제22권3호
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• pp.123-132
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• 2013

Hot stamping, which is the hot pressing of special steel sheet using a cold die, can combine ease of shaping with high strength mechanical properties due to the hardening effect of rapid quenching. In this paper, a thermo-mechanical analysis of hot stamping using the finite element method in conjunction with phase transformations was performed in order to investigate the plastic deformation behavior, temperature history, and mechanical properties of the stamped car part. We also conducted a fully coupled thermo-mechanical analysis during the stamping and rapid quenching process to obtain the mechanical properties with the consideration of the effects of plastic deformation and phase transformation on the temperature histories at each point in the part. The finite element analysis could provide key information concerning the temperature histories and the sheet mechanical properties when the phase transformation is properly considered. Such an analysis can also be used to determine the effect of cyclic cooling on the tooling.

• 열처리공학회지
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• 제28권6호
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• pp.300-309
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• 2015

The aim of the present study was to predict the variations in microstructure and deformation occurring during gas carburizing and quenching processes of a SCM420H planetary gear in a real production environment using the finite element method (FEM). The motivation for the present study came from the fact that previous FEM simulations have a limitation of the application to the real heat treatment process because they were performed with material properties provided by commercial programs and heat transfer coefficients (HTC) measured from laboratory conditions. Therefore, for the present simulation, many experimentally measured material properties were employed; phase transformation kinetics, thermal expansion coefficients, heat capacity, heat conductivity and HTC. Particularly, the HTCs were obtained by converting the cooling curves measured with a STS304 gear without phase transformations using an oil bath with an agitator in a real heat treatment factory. The FEM simulation was successfully conducted using the aforementioned material properties and HTC, and then the predicted results were well verified with experimental data, such as the cooling rate, microstructure, hardness profile and distortion.

• 한국추진공학회지
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• 제2권1호
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• pp.31-40
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• 1998

고강도 알루미늄 대형 링롤재의 급냉 및 요소제거 후 발생하는 잔류응력을 2차원 및 3차원 유한요소 해석하였고, 3단계 절단법에 의해 측정된 변형율과 ABAQUS의 요소제거 기능을 이용한 해석값을 직접 비교하였다. 급냉후 잔류응력 해석결과는 2단 과시효후 측정값과 비슷한 경향을 보였으나 그 절대값의 차이가 크게 나타났다. 이는 링 시편의 높이가 작아 측정값이 부정확하였기 때문이며, 링의 높이를 증가시켜 높이방향으로 균일한 응력분포를 갖도록 하면 그 차이가 감소될 것으로 판단된다. 잔류응력을 측정하는 3단계 절단 과정을 모사한 3차원 해석결과와 측정된 변형율을 직접 비교함으로써 실험과 해석의 정확성을 향상시킬 수 있도록 하였다. 이로부터 잔류응력이 내재하고 형상이 복잡한 대형 알루미늄 구조물의 기계가 공에 의한 변형을 정확히 예측할 수 있는 기반을 마련하였다.

• 멤브레인
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• 제28권6호
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• pp.395-405
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• 2018

본 연구에서 Poly(ethylene-co-vinylalcohol) EVOH 중공사막은 열유도상분리(TIPS)법을 이용하여 제조하였다. 다양한 조건에서 제조된 모든 분리막에서 액-액 상분리에 의해 기공이 서로 연결되어 있는 스폰지 구조가 관찰되었다. 글리세롤과 PEG200은 TIPS 방법에서 희석제로 사용하였고, 냉각조에 글리세롤을 혼합한 냉매를 사용하여 중공사 외표면의 기공을 조절하였다. 또한 혼합냉매의 온도를 높여 큰 기공의 형성을 유도하였다. 본 연구에서는 고분자의 농도, 희석제, 냉각조의 영향에 따른 분리막의 구조, 투과도, 기계적 강도에 대해 실험을 통해 알아보고 상호관계에 대해 심도 있게 연구하였다.