• Korean Journal of Materials Research
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• v.27 no.12
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• pp.688-694
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• 2017

Porous materials such as polymeric foam are widely adopted in engineering and biomedical fields. Porous materials often exhibit complex nonlinear behaviors and are sensitive to material and environmental factors including cell size and shape, amount of porosity, and temperature, which are influenced by the type of base materials, reinforcements, method of fabrication, etc. Hence, the material characteristics of porous materials such as compressive stress-strain behavior and void volume fraction according to aforementioned factors should be precisely identified. In this study, unconfined uniaxial compressive test for two types of closed-cell structure polyurethane foam, namely, 0.16 and $0.32g/cm^3$ of densities were carried out. In addition, the void volume fraction of three different domains, namely, center, surface and buckling regions under various compressive strains (10 %, 30 %, 50 % and 70 %) were quantitatively observed using Micro 3D Computed Tomography(micro-CT) scanning system. Based on the experimental results, the relationship between compressive strain and void volume fraction with respect to cell size, density and boundary condition were investigated.

• Journal of The Korean Society of Agricultural Engineers
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• v.48 no.4
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• pp.51-57
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• 2006

This study was carried out to investigate the soil water characteristic curve and prediction of void ratio with net stress and matric suction using the linear elastic and volumetric deformation analysis method on unsaturated silty. The unsaturated soil tests were conducted using a modified oedometer cell and specimens were prepared at water content 2 times of liquid limit and required void ratio. The axis translation technique was used to create the desired matric suctions in the samples. It is shown that soil water characteristic curve and volumetric water content were affected significantly by preconsolidation pressure. As a matric suction increases, the reduction ratio of void ratio was shown to considerably small. Also, the predicted and measured void ratio for unsaturated soils using the linear elastic and volumetric deformation analysis showed good agreement as net stress and matric suction increases.

• Journal of The Korean Society of Agricultural Engineers
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• v.48 no.4
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• pp.67-74
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• 2006

This study was carried out to investigate the liquefaction behaviour of saturated silty sand under monotonic loading conditions. The undrained soil tests were conducted using a modified triaxial cell and specimens were prepared using the moisture tamping method. Undrained triaxial compression tests were performed at different confining pressures, void ratios and overconsolidation ratios and the samples were sheared to axial strains of about 20% to obtain monotonic loading conditions. It is shown that increasing confining pressures, void ratios and overconsoildation ratios increases the deviator stress, but it has no effect on increasing the dilatant tendencies. It is shown that complete static liquefaction was observed regardless of increases in the confining pressure, void ratio and overconsolidation ratio. Therefore, the confining pressure, void ratio and overconsoildation ratio does not provide significant effects on the liquefaction resistance of the silty sand. The presence of fines in the soil was shown to greatly increase the potential for static liquefaction and creates a particle structure with high compressibility for all cases.

• Journal of the Korean Geotechnical Society
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• v.27 no.11
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• pp.83-92
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• 2011

The random and heterogeneous pore structure is a significant factor that dominates physical and mechanical behaviors of soils such as fluid flow and geomechanical responses driven by loading. The characterization method using non-destructive testing such as micro X-ray CT technique which has a high resolution with micrometer unit allows to observe internal structure of soils. However, the application has been limited to qualitatively observe 2D and 3D CT images and to obtain the void ratio at macro-scale although the CT images contain enormous information of materials of interests. In this study, we constructed the 3D particle and pore structures based on sequentially taken 2D images of glass beads and quantitatively defined complex pore structure with void cell and void channel. This approach was enabled by implementing image processing techniques that include coordinate transformation, binarization, Delaunay Triangulation, and Euclidean Distance Transform. It was confirmed that the suggested algorithm allows to quantitatively evaluate the distribution of void cells and their connectivity of heterogeneous pore structures for glass beads.

• Nuclear Engineering and Technology
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• v.51 no.5
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• pp.1241-1250
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• 2019

This study mainly focused on the neutronics modeling of bubbles in bubbly flow in boiling water reactors. The bubble, ring and homogenous models were used for radial void fraction distribution. Effect of the bubble and ring models on the infinite multiplication factor and two-group flux distribution was investigated by comparing with the homogenous model. Square pitch unit cell geometry was used in the calculations. In the bubble model, spherical and non-spherical bubbles at random positions, sizes and shapes were produced by Monte Carlo method. The results show that there are significant differences among the proposed models from the viewpoint of physical interaction mechanism. For the fully-developed bubbly flow, $k_{inf}$ is overestimated in the ring model by about $720{\pm}6pcm$ with respect to homogeneous model whereas underestimated in the bubble model by about $-65{\pm}9pcm$ with a standard deviation of 15 pcm. In addition, the ring model shows that the coolant must be separated into regions to properly represent the radial void distribution. Deviations in flux distributions principally occur in certain regions, such as corners. As a result, the bubble model in modeling the void fraction can be used in nuclear engineering calculations.

• Journal of the Korean Geotechnical Society
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• v.24 no.8
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• pp.25-34
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• 2008

A new hybrid oedometer cell is designed and manufactured to investigate a behavior of soft soils by using elastic and electromagnetic waves during consolidation test. Bender elements, which generate and detect shear waves, are placed in the top cap and the bottom plate and mounted on the oedometer wall. Double wedge type electrical resistance probe, which measures local void ratio change, is positioned onto the top cap of the oedometer cell. The bender elements and the electrical resistance probe are anchored into a nylon set screw with epoxy resin. The nylon set screw with epoxy resin minimizes directly transmited elastic waves through the oedometer cell due to impedence mismatch and allows for easy replacement of defected bender elements and electrical resistance probe. Primary consolidation time can be estimated from the slope of electrical resistance versus log time curve and the evolution of shear wave velocity. The shear wave velocity can be used to assess inherent anisotropy when disturbance effects are minimized because particle alignment affects the shear wave velocity. The void ratios evaluated by the electrical resistance probe are similar to those by the settlement during consolidation. This study suggests that the shear wave velocity and the electrical resistance can provide complementary imformations to understand consolidation characteristics such as primary consolidation, anisotropy, and void ratio.

• Microbiology and Biotechnology Letters
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• v.13 no.3
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• pp.209-212
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• 1985

The cell density and packing characteristics of Escherichia coli immobilized in a dual hollow fiber bioreactor consisting of outer silicone membrane for oxygen transport and three inner isotropic polypropylene hollow fibers for substrate transport were investigated. The cells have grown forming the layer like animal tissue in a nearly 100％ packing density. The dry biomass density was 550g/liter of void volume for cell growth, which was the highest among the biomass densities ever reported.

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.829-834
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• 2005

A series of reinforced G109 type specimens was fabricated and pended with a 15 weight percent NaCl solution. Mix design variables included 1) two cement alkalinities (equivalent alkalinities of 0.32 and 1.08), 2) w/c 0.50 and 3) two rebar surface conditions (as-received and wire-brushed). Potential and macro-cell current between top and bottom bars were monitored to determine corrosion initiation time. Once corrosion was initiated, the specimen was ultimately autopsied to perform visual inspection, and the procedure included determination of the number and size of air voids along the top half of the upper steel surface. This size determination was based upon a diameter measurement assuming the air voids to be half spheres or ellipse. The followings were reached based upon the visual inspection of G109 specimens that were autopsied to date. First, voids at the steel-concrete interface facilitated passive film breakdown and onset of localized corrosion. Based upon this, the initiation mechanism probably involved a concentration cell with contiguous concrete coated and bare steel serving as cathodes and anodes, respectively. Second, the corrosion tended to initiate at relatively large voids. Third, specimens with wire-brushed steel had a lower number of voids at the interface for both cement alkalinities, suggesting that air voids preferentially formed on the rough as-received surface compared to the smooth wire brushed one.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.4
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• pp.319-326
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• 2008

In this study, we investigate the deformation behavior of F.C.C. single crystals containing micro- or submicron-sized voids by using three dimensional finite element methods. The locally homogeneous constitutive model for the rate-dependent crystal plasticity is integrated based on the backward Euler method and implemented into a finite element program (ABAQUS) by means of user-defined subroutine (UMAT). The unit cell analysis has been investigated to study the effect of stress triaxiality and crystallographic orientations on the growth and coalescence of voids in F.C.C. single crystals.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.2
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• pp.225-236
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• 2014

Shear wave velocity was used to estimate the geotechnical characteristics (void ratio and shear strength) of ground near an underground rainfall storage facility. An oedometer cell was utilized to measure the shear wave velocity and the displacement of specimens. Shear strengths were obtained by direct shear tests. The relationships along the shear wave velocity, void ratio, and shear strength were verified and used to infer the shear strength profile with the depth. In addition, changes in shear strength due to the construction of the underground rainfall storage system were estimated using the suggested method. The results show that the in-situ shear strength deduced from the shear wave velocity-void ratio-shear strength relationship is in good agreement with that obtained from an in-situ investigation (SPT).