• Journal of the Korean Geotechnical Society
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• v.30 no.2
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• pp.77-85
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• 2014

The paper presents comparison between numerical and experimental results to verify finite element algorithm of air diffusion in three-phase porous media. The theory of two-phase flow in partially saturated soil is a fundamental study to predict the safety for $CO_2$ sequestration. Geotechnical engineering problems exposed to atmospheric pressure generally assume that air pressure is equal to zero in three-phase porous media, but the geotechnical engineering problem at a depth of about over 1 km needs to be considered in connection with deformable solid skeleton due to air pressure. Therefore, the objective of this study is to validate the numerical algorithm by comparing with results obtained from measurement of air diffusion and dissipation through drainage test.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.2 s.173
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• pp.472-480
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• 2000

A macroscopic yield criterion for porous solids with pressure-sensitive matrices modeled by Coulomb's yield criterion was obtained by generalizing Gurson's yield criterion with consideration of the hydrostatic yield stresses for a spherical thick-walled shell and by fitting the finite element results of a voided cube. The macroscopic yield criterion is valid for negative mean normal stresses as well as for positive mean normal stresses. From the yield criterion, a plastic potential function for the porous solids was derived either for plastic normality flow or for plastic non-normality flow of pressure- sensitive matrices. In addition, the elastic relation, an evolution equation of the plastic flow stress of the matrices and an evolution equation of the void volume fraction were presented to complete a set of constitutive relations. The set of constitutive relations was implemented into a finite element code ABAQUS to analyze the material behavior of rubber-toughened epoxies. The cavitation and the deformation behavior were analyzed around a crack tip under three-point bending and around notch tips under four-point bending. In the numerical analyses, the cavitation of rubber particles was considered via a stress-controlled nucleation model. The numerical results indicate that a reasonable cavitation zone can be obtained with void nucleation controlled by the macroscopic mean normal stress, and a plastic zone is smaller around a notch tip under compression than under tension. These numerical results agree well with corresponding experimental results on the cavitation and plastic zones.

• Journal of Powder Materials
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• v.23 no.1
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• pp.49-53
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• 2016

The present study demonstrates the effect of freezing conditions on the pore structure of porous Cu-10 wt.% Sn prepared by freeze drying of $CuO-SnO_2$/camphene slurry. Mixtures of CuO and $SnO_2$ powders are prepared by ball milling for 10 h. Camphene slurries with 10 vol.% of $CuO-SnO_2$ are unidirectionally frozen in a mold maintained at a temperature of $-30^{\circ}C$ for 1 and 24 h, respectively. Pores are generated by the sublimation of camphene at room temperature. After hydrogen reduction and sintering at $650^{\circ}C$ for 2 h, the green body of the $CuO-SnO_2$ is completely converted into porous Cu-Sn alloy. Microstructural observation reveals that the sintered samples have large pores which are aligned parallel to the camphene growth direction. The size of the large pores increases from 150 to $300{\mu}m$ with an increase in the holding time. Also, the internal walls of the large pores contain relatively small pores whose size increases with the holding time. The change in pore structure is explained by the growth behavior of the camphene crystals and rearrangement of the solid particles during the freezing process.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.6
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• pp.491-497
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• 2017

In recent years, 3D printing has received increasing attention due to its potential for direct fabrication beyond the traditional rapid prototyping. 3D printing has the advantage of being able to manufacture complicated shapes that were thought impossible to produce by traditional manufacturing processes. This advantage has driven applications of 3D printing to direct manufacturing of functional parts, such as lightweight structures and component integration. In this study, a porous shell structure is designed for the purpose of weight reduction and ventilation. Finite element (FE) analyses are performed to compare the effective stiffness of the porous structure with the conventional solid structure. Structural reinforcements are also considered in order to make up the stiffness reduction due to the porosity, and the relevant FE analyses are performed to investigate the effect of the reinforcement design on the bending stiffness. The optimized reinforced structure is then proposed through response surface analysis.

• Korean Journal of Materials Research
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• v.25 no.1
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• pp.27-31
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• 2015

This paper proposes a novel way of fabricating aligned porous Sn by freeze-drying of camphene slurry with stannic oxide ($SnO_2$) coated Sn powders. The $SnO_2$ coated Sn powders were prepared by surface oxidation of the initial and ball-milled Sn powders, as well as heat treatment of tin chloride coated Cu powders. Camphene slurries with 10 vol% solid powders were prepared by mixing at $50^{\circ}C$ with a small amount of oligomeric polyester dispersant. Freezing the slurry was done in a Teflon cylinder attached to a copper bottom plate cooled at $-25^{\circ}C$. Improved dispersion stability of camphene slurry and the homogeneous frozen body was achieved using the oxidized Sn powder at $670^{\circ}C$ in air after ball milling. The porous Sn specimen, prepared by freeze-drying of the camphene slurry with oxidized Sn powder from the heat-treated Sn/tin chloride mixture and sintering at $1100^{\circ}C$ for 1 h in a hydrogen atmosphere, showed large pores of about $200{\mu}m$, which were aligned parallel to the camphene growth direction, and small pores in their internal walls. However, $100{\mu}m$ spherical particles were observed in the bottom part of the specimen due to the melting of the Sn powder during sintering of the green compact.

• Journal of Wetlands Research
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• v.12 no.2
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• pp.67-73
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• 2010

This study was performed to figure out what would be effective to maintain good water quality in the retention pond which was badly polluted before. In order to keep the good water quality of the retention pond it is necessary to prevent outer non-point source pollutants from flowing into the pond. In this study, we proposed to use porous slag as a blockage of the inflow into the pond from external non-point sources. We experimented with porous slag nets to see how the water is effected. With the results of the experiments, we found out there is a close correlation($r^2=0.9765$) between contact time and the removal rate of phosphorus, therefore we can conclude that contact time affects removal rate greatly. Synthetic wastewater, activated sludge effluent, and sewage were passed through a porous slag packed bed, both phosphorus and the suspended solid in water were removed highly. With the results of these tests, we proposed to set up a porous slag packed bed inside of the retention pond and revetment to prevent external non-point source pollutants flowing into the retention pond.

• Nuclear Engineering and Technology
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• v.26 no.4
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• pp.453-460
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• 1994

The migration equation is modified for a three-member decay chain in the fracture and porous matrix Analytical solutions are obtained by utilizing Laplace transform the initial conditions of Delta function and Bateman equation. The concentrations for each nuclide of Np$^{237}$ -U$^{233}$ -Th$^{229}$ and U$^{234}$ -Th$^{230}$ -Ra$^{226}$ chains selected from the 4n＋1 and 4n＋2 chains are plotted by utilizing analytical solutions in the fracture. Retardation coefficient of the nuclides are obtained using those of the granite. The results indicate that the daughter nuclides such as U$^{233}$ , Th$^{229}$ , Th$^{230}$ and Ra$^{226}$ become important at the far field from the repository though there is very small initial inventory in the waste solid or spent fuel, for they are produced by the mother nuclides decayed in the fracture and porous matrix.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1093-1094
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• 1995

A porous electrode substrate of Ni-YSZ cermet anode was used as a support for YSZ film fabrication. The purpose of this research is to investigate characteristics for tubular solid oxide fuel cell.

• Journal of the Korean Ceramic Society
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• v.46 no.3
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• pp.249-252
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• 2009

Nanocrystalline ceria particles were prepared by using the ultrasonic spray pyrolysis method. The prepared ceria particles were found to be spherical and non-agglomerated by the SEM and TEM analyses. It was found that carrier gas influences the size and morphology. It was found that the air stream of carrier gas results in porous agglomerated structure of ceria abrasives, whereas solid nano-sphere can be obtained in a more oxidizing atmosphere.

• Journal of Industrial Technology
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• v.4
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• pp.43-46
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• 1984

In process of water removing safely from plastic clay, an electric field applied to a wet, porous solid such as day usually causes the rapid dehydration. The water-bearing positive ions move to negative electrode under the d. c. electrical stress or field. Therefore application of electro-osmosis to wet clay could include drying thick and large-scale ceramic body quickly and evenly. The d. c. power supply unit to 60 volts is necessary for safe practice. Also wider contact area and shorter distance between electrodes accelerate effectively the removal of water.