• Proceedings of the KSR Conference
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• 2003.10b
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• pp.385-390
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• 2003

Recently, use of Continuous Welded rail(CWR) is increased for structural, economical reason but new problem is caused accordingly and phenomenon that give threat in traveling by ship stability of train is led. According as rail is prolonged, excessive relative displacement and longitudinal force can happen to rail by temperature change and external force. Specially, buckling or fracture of rail can happen in railroad bridges because relative displacement by bridge and properties of matter difference between rail grows and additional axial force happens to rail by behavior of bridge. According to several study, longitudinal force of rail in bridge is influenced with ballast resistance, elongation length, boundary condition, stiffness of framework. Non-linear behavior of ballast acts by the most important factor in interaction between rail and bridge. Therefore, must consider stiffness of bridge construction with non-linear characteristic of ballast and stiffness of base for accuracy with longitudinal force calculation and analyze. In this study, perform material non-linear analysis for longitudinal force of CWR and three dimensional buckling analysis to decide buckling force.

• Corrosion Science and Technology
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• v.6 no.3
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• pp.83-89
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• 2007

It is expected that advanced high strength steels (AHSS) would be widely used for vehicles with better performance in automotive industries. One of distinctive features of AHSS is the high value of carbon equivalent (Ceq), which results in the different properties in formability, weldability and paintability from those of common grade of steel sheets. There is an exponential relation between Ceq and electric resistance, which seems also to have correlation with the thickness of electric deposition (ED) coat. Higher value of Ceq of AHSS lower the thickness of ED coat of AHSS. Some elements of AHSS such as silicon, if it is concentrated on the surface, affect negatively the formation of phosphates. In this case, silicon itself doesn't affect the phosphate, but its oxide does. This phenomenon is shown dramatically in the welding area. Arc welding or laser welding melts the base material. In the process of cooling of AHSS melt, the oxides of Si and Mn are easily concentrated on the surface of boundary between welded and non‐welded area because Si and Mn could be oxidized easier than Fe. More oxide on surface results in poor phosphating and ED coating. This is more distinctive in AHSS than in mild steel. General results on paintability of AHSS would be reported, being compared to those of mild steel.

• Structural Engineering and Mechanics
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• v.4 no.3
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• pp.257-276
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• 1996

In North America, a large number of concrete old slab-on-steel girder bridges, classified noncomposite, were built without any mechanic connections. The stablizing effect due to slab/girder interface contact and friction on the steel girders was totally neglected in practice. Experimental results indicate that this effect can lead to a significant underestimation of the load-carrying capacity of these bridges. In this paper, the two major components-concrete slab and steel girders, are treat as two deformable bodies in contact. A finite element procedure with considering the effect of friction and contact for the analysis of concrete slab-on-steel girder bridges is presented. The interface friction phenomenon and finite element formulation are described using an updated configuration under large deformations to account for the influence of any possible kinematic motions on the interface boundary conditions. The constitutive model for frictional contact are considered as slip work-dependent to account for the irreversible nature of friction forces and degradation of interface shear resistance. The proposed procedure is further validated by experimental bridge models.

• Proceeding of KASS Symposium
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• 2008.05a
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• pp.179-183
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• 2008

Methods of damage detection are used non-destructive test in concrete structures. These are using various sensors, but the most of damage detections are used a visual angle of human. Problems of crack damage detection are occurred to directions and boundary conditions of steel bars using accelerometer in concrete element. In this study, fundamental studies for estimation using 3 axial type of accelerometer and electric resistance property of thermocouple sensors are discussed estimation to effect of arranged steel bars and damage from low strength when they are oscillated elastic wave in concrete specimen.

• Journal of the Korean Ceramic Society
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• v.36 no.9
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• pp.982-990
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• 1999

YSZ/LSM composite cathode was fabricated by dip-coating of YSZ sol on the internal pore surface of a LSM cathode followed by sintering at low temperature (800-100$0^{\circ}C$) The YSZ coating significantly increased the TPB(Triple Phase Boundary) where the gas the electrode and the electrolyte were in contact with each other. Sinter the formation of resistive materials such as La2Zr2O7 or SrZrO3 was prevented due to the low processing temperature and TPB was increased due to the YSZ film coating the electrode resistance (Rel) was reduced about 100 times compared to non-modified cathode. From the analysis of a.c impedance it was shown that microstructural change of the cathode caused by YSZ film coating affected the oxygen reduction reaction. In the case of non-modified cathode the RDS (rate determining step) was electrode reactions rather than mass transfer or the oxygen gas diffusion in the experimental conditions employed in this study ($600^{\circ}C$-100$0^{\circ}C$ and 0,01-1 atm of Po2) for the YSZ film coated cathode however the RDS involved the oxygen diffusion through micropores of YSZ film at high temperature of 950-100$0^{\circ}C$ and low oxygen partial pressure of 0.01-0.03 atm.

• Journal of the Korean Ceramic Society
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• v.44 no.12
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• pp.727-732
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• 2007

In order to fabricate a highly performing cathode for low-temperature type solid oxide fuel cells working at below $700^{\circ}C$, electrode microstructure control and electrode polarization measurement were performed with an electronic conductor, $La_{0.8}Sr_{0.2}MnO_3$ (LSM) and a mixed conductor, $La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_3$(LSCF). For both cathode materials, when $Sm_{0.2}Ce_{0.8}O_2$ (SDC) buffer layer was formed between the cathode and yttria-stabilized zirconia (YSZ) electrolyte, interfacial reaction products were effectively prevented at the high temperature of cathode sintering and the electrode polarization was also reduced. Moreover, cathode polarization was greatly reduced by applying the SDC sol-gel coating on the cathode pore surface, which can increase triple phase boundary from the electrolyte interface to the electrode surface. For the LSCF cathode with the SDC buffer layer and modified by the SDC sol-gel coating on the cathode pore surface, the cathode resistance was as low as 0.11 ${\Omega}{\cdot}cm^2$ measured at $700^{\circ}C$ in air atmosphere.

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.4
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• pp.370-377
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• 2018

Ball valve has been widely used in the field of high-pressure gas pipeline as an important component because of its low flow resistance and good leakage performance. The present paper focuses on the flow nature at the downstream of the ball valve used for gas pipelines according to valve opening rates. Steady 3-D RANS equations, SC/Tetra, have been introduced to analyze the flow characteristics inside the ball valve. Numerical boundary conditions at the inlet and outlet of the valve system are imposed by mass flow-rate and pressure, respectively. Velocity distributions obtained by numerical simulation are compared with respect to the valve opening rates of 30, 50, and 70%. Cavity distributions, asymmetry flow velocity and the flow stabilization point at each opening rate are also compared. When the valve opening rates are 30 and 50%, the flow stabilization requires the sufficient length of 10D or more due to the influence of the recirculation flow at the downstream of the valve.

• Electrical & Electronic Materials
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• v.9 no.6
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• pp.572-577
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• 1996

Alternating current and direct current of pure, ball milled, and $Al_{2}$O$_{3}$ added ZnO were investigated by means of complex impedance measurement and voltage-current source measurement unit. The electrical conductivity of A1$_{2}$O$_{3}$ added ZnO samples increases when the content of A1$_{2}$O$_{3}$ is used within 1 at% and decreases when it's used more than that. The increase and decrease of electrical conductivity seem to be the donor effect of $Al_{2}$O$_{3}$ and the increase of the number of ZnO grains, respectively. Impedance spectrum seems to be one semircicle. The size of semicircle increase with increasing the A1$_{2}$O$_{3}$ contents. The calculated dielectric constant(at 50.deg. C) were about 70-140 at the peak of the semicircle. The semicircles seem not to be the resistance of ZnO grain as compared to that of 10 for pure ZnO.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.1
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• pp.51-56
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• 2012

This paper reports the generation efficiency and the thermal performance of a thermoelectric generator (TEG) harvesting energy from the waste heat of high power electronic components. A thermoelectric (TE) model containing thermal boundary resistances is used to predict generation efficiency and junction temperature of a high power electronic component. The predicted results are verified with measured values, and the discrepancy between prediction and measurement is seen to be moderate. The verified TE model predicts generation efficiencies, junction temperatures of the component, and temperature differences across a TEG at various source heat flows associated with various electrical load resistances. This study explores effects of the load resistance on the generation efficiency, the temperature difference across a TEG, and the junction temperature.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.16 no.5
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• pp.151-156
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• 2007

In this paper, the creep characteristics of lead and lead-free solder joint were investigated using the QFP(Quad Flat Package) creep test. Two kind of solder pastes(Sn-3Ag-0.5Cu, Sn-0.2Sb-0.4Ag-37.4Pb) were applied to the QFP solder joints and each specimen was checked the external and internal failures(i.e., wetting failure, void, pin hole, poor-heel fillet) by digital microscope and X-ray inspection. The creep test was conducted at the temperatures of $100^{\circ}C$ and $130^{\circ}C$ under the load of 15$\sim$20% of average pull strength in solder joints. The creep characteristics of each solder joints were compared using the creep strain-time curve and creep strain rate-stress curves. Through the comparison, the Sn-3Ag-0.5Cu solder joints have higher creep resistance than that of Sn-0.3Sb-0.4Ag-37.4Pb. Also, the grain boundary sliding in the fracture surface and the necking of solder joint were observed by FE-SEM.