• 한국군사과학기술학회지
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• 제2권1호
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• pp.183-193
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• 1999

환원분위기 소결조건에서 반도성 (Sr0.85Ca0.15)TiO3 소결체를 제조한후, 금속 양이온(Na, K)을 소결체 입계를 통해 확산시켜 확산시간과 확산량에 따른 소결체의 전기적 특성 변화를 고찰하였다. K이온과 Na 이온을 입계확산시킨 경우 반도성 소결체는 바리스터 특성을 나타내며, 확산시간과 확산량이 증가함에 따라 문턱전압이 증가하였다. 이들 소결체의 입계전위장벽은 0.01 ~ 2.89 eV이며 입계저항은 2.2 ~ 120.4 $M{\Omega}$ 값을 나타냈다 투과전자현미경을 이용하여 입계의 구조를 관측하였으며 이들 결과와 소결체의 전기적 특성과의 상관관계를 고찰하였다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.250-254
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• 2002

Intergranular corrosion of austenitic stainless steels is a conventional and momentous problem during welding and high temperature use. One of the major reasons for such intergranular corrosion is so-called sensitization, i.e., chromium depletion due to chromium carbide precipitation at grain boundaries. Conventional methods for preventing sensitization of austenitic stainless steels include reduction of carbon content in the material, stabilization of carbon atoms as non-chromium carbides by the addition of titanium, niobium or zirconium, local solution-heat-treatment by laser beam, etc. These methods, however, are not without drawbacks. Recent grain boundary structure studies have demonstrated that grain boundary phenomena strongly depend on the crystallographic nature and atomic structure of the grain boundary, and that grain boundaries with coincidence site lattices are immune to intergranular corrosion. The concept of "grain boundary design and control", which involves a desirable grain boundary character distribution, has been developed as grain boundary engineering. The feasibility of grain boundary engineering has been demonstrated mainly by thermomechanical treatments. In the present study, a thermomechanical treatment was tried to improve the resistance to the sensitization by grain boundary engineering. A type 304 austenitic stainless steel was pre-strained and heat-treated, and then sensitized, varying the parameters (pre-strain, temperature, time, etc.) during the thermomechanical treatment. The grain boundary character distribution was examined by orientation imaging microscopy. The intergranular corrosion resistance was evaluated by electrochemical potentiokinetic reactivation and ferric sulfate-sulfuric acid tests. The sensitivity to intergranular corrosion was reduced by the thermomechanical treatment and indicated a minimum at a small roll-reduction. The frequency of coincidence-site-lattice boundaries indicated a maximum at a small strain. The ferric sulfate-sulfuric acid test showed much smaller corrosion rate in the thermomechanically-treated specimen than in the base material. An excellent intergranular corrosion resistance was obtained by a small strain annealing at a relatively low temperature for long time. The optimum parameters created a uniform distribution of a high frequency of coincidence site lattice boundaries in the specimen where corrosive random boundaries were isolated. The results suggest that the thermomechanical treatment can introduce low energy segments in the grain boundary network by annealing twins and can arrest the percolation of intergranular corrosion from the surface.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2014년도 추계 학술논문 발표대회
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• pp.167-168
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• 2014

Building destruction can be occurred by decreasing of structural stability and deformation according to fire. Especially, a structural behavior of beam can be shown a slightly difference by beam types. In this paper, an evaluation of the structural stability of beam made of ordinary structural steel designed by fixed and simple boundary condition was done by an analytic method using mechanical properties of SS 400 and an heat transfer theory.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 추계학술대회 논문집 Vol.19
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• pp.235-236
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• 2006

The contact resistance and grain boundary potential barrier of ceramic $BaTiO_3$ PTCR were investigated. The electroless plated Ni, evaporated Al, and Ag paste were chosen as electrode materials of PTCR device for comparison analysis before and after heat treatment. The contact resistance of electrode were measured by electrometer (dc), digital multimeter (dc), and LCR meter (ac). In the case of Al electroded samples, the heat treatment and protective oxide layer had high resistance and effect on the stability of PTCR effect against contact resistance degradation, but the Ag-paste had comparably high contact resistance before heat treatment and decreased after heat treatment with safe. On the other hand, the samples with electroless plated Ni electrode had good properties of contact resistance against aging.

• 대한기계학회논문집
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• 제19권1호
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• pp.193-201
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• 1995

The role of thermal contact resistance between a casting and a metal mold as well as natural convection in the melt during solidification of a pure metal is numerically studied. Numerical simulation is performed for a rectangular cavity using the coordinate transformation by boundary-fitted coordinate and pure aluminum is used as the phase- change material. The influences of thermal contact resistance on the interface shape and position, solidified volume fraction, temperature field and local heat transfer are investigated.

• 공업화학
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• 제9권5호
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• pp.698-703
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• 1998

실리콘고무 (polydimethylsiloxane, PDMS)막에 의한 trichloroethylene (TCE)과 chlorobenzene (CB)수용액의 투과증발실험을 수행하고 농도분극이 분리특성에 미치는 영향을 연구하였다. 경계층저항은 직렬저항모델을 사용하여 설명하였으며, 수용액으로부터 미량의 유기염화물을 제거하는 투과증발에서는 농도분극현상이 투과거동에 중요한 영향을 미치고 있음을 확인할 수 있었다. 같은 막두께에서, 막에 대한 친화력이나 선택투과성이 더 큰 TCE가 CB수용액보다 경계층저항의 영향이 더 크게 나타났다. 막두께가 증가할수록 경계층저항의 영향은 감소하고 막저항이 지배적이 되며, 겉보기분리계수는 증가하여 막의 고유분리계수에 가까워졌다.

• 대한조선학회논문집
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• 제57권5호
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• pp.278-286
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• 2020

Reynolds-averaged Navier-Stokes simulations have been performed to investigate an effect of numerical region with high resolution for Kelvin wave around KRISO container ship on its resistance. In the present study, 13 millions cells were used to describe wave profile along the ship hull and Kelvin wave patterns. In order to control a size of numerical region with high resolution for waves around the hull, we employed relaxation zones from a side boundary of numerical domain in which Kelvin wave was suppressed. When the far-field Kelvin wave was not precisely resolved due to the relaxation zone, the instantaneous history of ship resistance was affected although the time average of ship resistance showed -1.15~2.1 % errors. Especially, the damping characteristics of ship resistance in time history was significant when using a large relaxation zone in the side boundary.

• 한국화재소방학회논문지
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• 제28권1호
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• pp.20-25
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• 2014

강구조 건축물의 기둥부재 내화성능은 접합부의 경계조건과 기둥부재의 길이에 따라 변화되지만, 내화성능 평가는 실험장비의 제약과 기술적 요인으로 인하여 힌지단과 3500 mm 길이 조건으로 이루어지고 있다. 그러나 실제 강구조물에 적용되는 기둥부재는 부지조건과 설계조건에 따라 다양한 경계조건과 길이의 변화를 가져올 수 있으며, 이에 대한 내화성능의 평가는 대상으로 고온 시의 재료특성과 해석적 이론을 바탕으로 고온 시 구조적 성능을 평가하여, 경계조건과 길이 변화에 따른 내화성능의 기본 자료를 도출하였다.

• 한국세라믹학회지
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• 제35권9호
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• pp.917-922
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• 1998

YSZ와 계면반응하지 않는 ${(La_{0.75}Sr_{0.25})}_{0.95}Mn_{0.8 }Co_{0.2}O_3$에 전해질 물질인 YSZ를 첨가하여 양극의 분극특성을 고찰하였다. LSMC에 YSZ를 첨가함에 따라 삼상계면(Three Phase Boundary)이 증가하고, 분극저항이 감소하여 60 : 40wt% 비에서 최소값을 나타내었다. LSMC-YSZ composite 전극은 $1200^{\circ}C$ 에서 소결하여 최소의 분극저항을 나타내었고, 정전용량의 값은 소결온도의 증가에 따라 증가하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1382-1387
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• 2004

From the viewpoint of a macro state, there is no thermal boundary resistance (TBR) at an interface if both surfaces at an interface are perfectly contacted. However, recent molecular dynamics (MD) studies reported that there still exists the TDR at the interface in an ideal epitaxial superlttice. Our previous studies suggested the model to predict the TBR not only quantitatively also qualitatively in superlattices. The suggested model was based on the classical theory of a wave reflection, and provided highly satisfactory results for an engineering purpose. However, it was not the complete model because our previous model was derived by considering only the effects from a mass ratio and a potential ratio of two species. The interaction of two species presented by the Lennard-Jones (L-J) potential is governed by the mutual ratio of the masses, the potential well depths, and the diameters. In this study, we performed the preliminary simulations to investigate the effect resulting from the diameter ratio of two species for the completion of our model and confirmed that it was also a ruling factor to the TBR at an interface in superlattices.