• Journal of Industrial Technology
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• v.24 no.B
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• pp.95-105
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• 2004

This paper is an experimental and numerical research works about the effects of the b earing capacity of sloped rubble mound on the density of rubble mound and the position of footing. Centrifuge model tests were performed to investigate the bearing capacity of rubble m ound by changing the density of rubble mound and the location of loading in forms of s trip loading to simulate the caisson. Materials of rubble mound used in the model tests were crushed rocks having similar value of uniformity coefficient to the value in field. Two different relative densities of 80% and 90% were prepared during tests. The dimens ions of centrifuge model were trapezoidal shape of model mound having the bottom wid th of mound, 30cm and height of mound, 10cm. Gravity level applied during the centrif uge test was 50G. Surcharge loading in the forms of strip loading was applied on the t op of the sloped model mound. Tests were carried out by changing the position of loadi ng. The rigid model footing was located in the center of top of the model rubble mound and the edge of model footing was at the crest of mound. Test results were analyzed by using the limit equilibrium methods proposed by Meyer hof(1957) and Bowles(1982) and the numerical approach with FLAC being available com mercially software. For the numerical estimations with FLAC, the rubble mound was si mulated with the constitutive relationship of Mohr-Coulomb elasto-plastic model.

• Journal of the Korean Ceramic Society
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• v.31 no.7
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• pp.695-702
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• 1994

Current study was undertaken to explain the structural evolution and corresponding changes in the properties of calcium aluminate glasses with the variation of SiO2 doping concentration. Calcium aluminate glasses in the compositional ranges of (100-x)(0.6CaO+0.4Al2O3)+xSiO2(where x=0~60) were fabricated. DTA analysis confirmed an anomalous behavior in glass transition temperature (Tg) with the maximum of 887$^{\circ}C$ and minimum of 859$^{\circ}C$ when x=5 and 50, respectively. densities and refractive indices monotonically decreased with increasing SiO2 content and IR transmitting cutoff shifted to shorter wavelength side when the amount of added SiO2 exceeded 5 mole%. IR fundamental vibration absorption peaks showed the change that NBOs were inclined to SiO4 tetrahedron in the low-silica region and NBO per SiO4 tetrahedra changed from 2 to 0 with increasing silica content. Based on the analysis of IR fundamental vibration absorption peaks, the model of the structural change can be proposed in three step: 1) SiO4 scavenged the NBOs located at AlO4-tetrahedra, which resulted in the increased of Tg values, 2) NBOs located in the main network again with a decrease in Tg, and 3) dominated by the decrease in the relative amount of NBOs in the glass system, where Tg re-increased.

• Transactions of the Korean hydrogen and new energy society
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• v.23 no.6
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• pp.573-580
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• 2012

Corrosion resistance and basic physical properties of solid tantalum are not comparable to most of the structural metallic materials. The relative high cost and melting temperature of tantalum are obstacles to be widely applied to general engineering processes. Electrodeposition in molten salt enables compact and uniform tantalum coating. In this study, Ta was coated onto base metal (SUS316L) with different current densities (0.5, 5, $20mA/cm^2$) by using MSE (Molten Salt Electrodeposition). In this study, it showed that deposition efficiency and microstructure of Ta coating layer were strongly depended on current density. In the case of the current density of $5mA/cm^2$, densest microstructure was obtained. The current density above $5mA/cm^2$ caused non-uniform microstructure due to rapid deposition rate. Dense microstructure and intact coating layer contributed to significant corrosion resistance enhancement.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.10
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• pp.1255-1260
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• 2012

The densification behavior of titanium powder in the direct powder rolling process was investigated. An analytical model for the roll-backlash phenomenon during this process was proposed to conduct a realistic finite element analysis. Furthermore, the roll-backlash was quantitatively analyzed, and the relative densities of the greenstrip along the rolling direction were precisely estimated. Finally, the slip and nip phenomena were identified by calculating the contact pressure and shear stress between the titanium powder and the roller in order to understand the densification behavior of the powder during the rolling process.

• Journal of the Korean Vacuum Society
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• v.7 no.4
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• pp.397-402
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• 1998

$SiO_2$ etch characteristics were studied as a function of the basic parameters, such as the main RF power and the operating pressure in a helicon plasma. $SiO_2$ etch characteristics were improved as the main RF power was increased and the operating pressure was decreased. $SiO_2$ etch selectivity over silicon increased from 2.9 to 25.33 when the RF input power increased from 300 W to 2 kW and from 2.3 to 16.21 when the operating pressure decreased from 10 mTorr to 1.5 mTorr with $C_4F_8$ plasma. We used a quadrupole mass spectrometer to measure the relative abundancies of various ionic and radical species to explain the experimental results and found that when the operating pressure is low and the RF input power is high, the highly selective $SiO_2$ etch is achieved as a result of density increment of the densities of various ionic species.

• Journal of the Korean Ceramic Society
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• v.25 no.3
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• pp.231-236
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• 1988

In order to investigate the effect of second phase on $Al_2O_3$ matrix, SiC particles were dispersed in $Al_2O_3$ matrix as a second phase over the content range of 5 vol.% to 20 vol.%. To this mixture, $Y_2O_3$ or $TiO_2$ powders were added as a sintering additive before isostatically pressing and pressurelessly sintering at 180$0^{\circ}C$ for 90 min in $N_2$ atmosphere. With increasing SiC content, relative densities of composites were decreased but mechanical properties of composites were improvjed. In the case of adding $Y_2O_3$ as a sintering additive, maximum values of flexural strength, hardness and fracture toughness were 525 MPa, 17.1 GPa, 4.1 MPa.m1/2 respectively. In the case of adding X$TiO_2$ as a sintering additive, maximum values of flexural strength, hardness were 285 MPa, 12.1 GPa respectively. Improved mechanical properties were found to be the results of grain growth control of $Al_2O_3$ matrix and crack deflection by the second phase SiC particles.

• Journal of the Korean Ceramic Society
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• v.27 no.2
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• pp.201-210
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• 1990

The mullite-15v/o ZrO2 composites were prepared by dispersing ZrO2-3m/o Y2O3 powders into the mullite matrix in order to improve the mechanical properties of the mullite. The densification and retention of t-ZrO2 in the matrix of synthetic mullite were also investigated. From IR spectroscopic analysis, the obtained amorphous SiO2-Al2O3 powder was observed to have Si-O-Al chemical bond in its structure which might result in the homogeneous mullite composition. The lattice parameter of the mullite powder calcined above 130$0^{\circ}C$ (a0=7.5468$\AA$) is nearly close to the value of stoichiometric mullite (71.8wt% Al2O3, a0=7.5456$\AA$). The sintering behavior, microstructure, flexural strength and fracture toughness of the mullite and mullite-15v/o ZrO2 composites have been studied. The mullite-15v/o ZrO2(+3m/o Y2O3) ceramics with relative densities of 96% were obtained when sintered at 1$600^{\circ}C$. The flexural strength and fractrue toughness of the composites sintered at 1$600^{\circ}C$(calcination temperature of mullite powders ; 125$0^{\circ}C$) had maximum values of 307MPa and 2.50MPa.m1/2, respectively. The fracture toughness improvement in the mullite-ZrO2 cmoposite is assumed to be resulted from the combined effect of the stress-induced phase transformation of tetragonal ZrO2 and the crack deflection due to microcracking by the monoclinic ZrO2 formation.

• Journal of the Korean Geotechnical Society
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• v.20 no.8
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• pp.159-166
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• 2004

In this study, experiments on the SWCC were performed in order to find out the characteristics of unsaturated soil and to analyze the stability of unsaturated weathered slopes with rainfall-induced wetting. Several soil types classified by mixture portion of clay (CH) in the weathered soil (SW) were used in experimental tests. To achieve the SWCC, the filter paper method was used on SW with varying clay contents. A tensiometer test was used for measuring wetting front suction of the soils in a laboratory with varying relative densities. Based on the experimental results, it is shown that the wetting front suction increases as clay contest of mixture soil increases : in particular, the wetting front suction increases sharply as the clay contents increase. It is also found that wetting front suction affects the initial wetting band depth and stability of the slope.

• Journal of the Korean Geotechnical Society
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• v.28 no.10
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• pp.27-40
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• 2012

In the design of a piled raft, the axial resistance is offered by the raft and group piles acting on the same supporting ground soils. As a consequence, pile - soil - raft and pile - soil interactions, occurring by stress and displacement duplication with pile and raft loading conditions, act as a key element changing resistances of the raft and group piles. In this study, a series of centrifuge model tests have been performed to compare the axial behavior of group pile and raft with that of a piled raft (having 16 component piles with an array of $4{\times}4$) in sands with different relative densities. The test results revealed that the increase of settlement resistance occurs separately with settlement by group pile - soil interactions. The axial resistance of group piles (at piled raft) increases by group pile - raft (pile cap) interactions and that of raft (at piled raft) decreases by group pile - raft (pile cap) interactions.

• Transactions of the Korean hydrogen and new energy society
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• v.21 no.1
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• pp.1-11
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• 2010

Current distribution measurement technique based on a segmented bipolar plate (BP) has been widely adopted to visualize the distribution of current density in a polymer electrolyte membrane. However, a concern is raised how closely the current density of a segmented BP can approach that of a corresponding non-segmented membrane. Therefore, in this paper, the accuracy of the measurement technique is numerically evaluated by applying a three-dimensional, two-phase fuel cell model to a $100\;cm^2$ area fuel cell geometry in which segmented BPs and non-segmented membrane are combined together. The simulation results reveal that the errors between the current densities of the segmented BPs and non-segmented membrane indeed exist, predicting the maximum relative error of 33% near the U-turn regions of the flow-field. The numerical study further illustrates that the erroneous result originates from the BPs segmented non-symmetrically based on the flow channels that allows some currents bypassing flow channels to flow into its neighboring segment. Finally, this paper suggests the optimal way for bipolar plate segmentation that can minimize the deviation of current measured in a segmented BP from that of a corresponding membrane region.