• Polymer(Korea)
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• v.24 no.4
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• pp.538-544
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• 2000

The characteristics of cell growth and foamed cell structures of PP were investigated by a continuous foaming process. The operating parameters were the contents of blowing agent and nucleating agent, nucleating agent contents, die temperatures and die dimensions. The foaming cells grew without collapse at less than 14.5 wt% of blowing agent, isopentane. But the cells were collapsed when the blowing agent content was more than 14.5 wt%. The foam density dramatically decreased when a very small amount of the nucleating agent, 1 wt%, was added. After the nucleating agent was added, the cell's weight plummeted to one-seventh of its previous weight. Stable foam cell structures were formed at the die temperature of 17$0^{\circ}C$. However, the effects of the pressure drop rate on the cell morphology were not serious.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.6
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• pp.222-229
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• 2003

The purpose of this study is to evaluate the mechanical properties of 6061 Al foams, which were fabricated by P/M and multi-step induction heating method, and to build the database, which is needed for computer aided modeling or foam components design. Aluminium foams, consisting of solid aluminium and large quantities of porosities, is widely used in automotive, aerospace, naval as well as functional applications because of its high stiffness at very low density, high impact energy absorption, heat and fire resistance, and greater thermal stability than any organic material. In this study, 6061 Al foams were fabricated for variation of fraction of porosities (%) according to porosities (%)-final heating temperature ( $T_{a3}$) curves. Mechanical properties such as compressive strength, energy absorption capacity, and efficiency were investigated to evaluate the feasibility of foams as crash energy absorbing components. Moreover, effect of the surface skin thickness on plateau stress and strain sensitivity of the 6061 Al foams with low porosities (%) were studied.d.

• Journal of computational fluids engineering
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• v.22 no.1
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• pp.95-102
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• 2017

Debris flow is a composition of solid objects of various sizes, suspension and water, which occurs frequently as the results of landslide following heavy rainfall. This often causes extensive damage in the form of socio-economic losses and casualties as witnessed during the incident around Mt. Umyeon, Seoul in 2011. There have been numerous investigation to mitigate the impacts from debris flow; however, the estimation as preparedness measure has not been successful due to nonlinear and multiphase characteristics of phenomena both in material and process inherent in the debris flow. This study presents a numerical approach to simulate the debris flow using open source code of computational fluid dynamics, OpenFOAM with non-Newtonian viscosity model for three phase material modeling. In order to validate the proposed numerical method, the quantitative evaluations were made by comparisons with experimental results and qualitative analysis for the dispersion characteristics was carried for the case of debris flow in the actual incident from Mt. Umyeon.

• Journal of Korea Foundry Society
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• v.25 no.5
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• pp.203-208
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• 2005

The main emphasis of this study is to optimize the process variables for manufacturing aluminum foam materials by direct foaming of remelted aluminum scraps. Aluminum foams were fabricated from two different raw materials, pure aluminum and used beverage cans. For both cases, $TiH_{2}$ was used as a foaming agent. Calcium was added as a thickener for the foaming of pure aluminum and no thickener was added for that of used beverage Cans because the pre-existing oxides of the used beverage cans are used as a thickener. Calcium and $TiH_{2}$ content varies from 0.5wt.% to 2.0wt.% and from 0.5wt.% to 1.5wt.%, respectively. The processing conditions, such as the effect of calcium on the melt viscosity, foaming temperature, and the optimum amount of the foaming agent with regard to the melt viscosity were discussed.

• Journal of Korea Foundry Society
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• v.36 no.6
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• pp.208-214
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• 2016

Casting defects, which are closely related to entrapped air bubbles and metallic oxides, occur very frequently in the casting process. Many researchers have shown that these defects can be reduced by adopting an appropriate gating system design. But, it is difficult for field engineers to identify a specific gating system that is more appropriate for their products. In this study, we tried to draw a comparison of gating system designs with and without ceramic foam filters. A ceramic foam filter was added to the horizontal runner just after the sprue to prevent air bubble generation and to reduce turbulence without change of the gating system design. To verify the effects of initial pouring velocity, the experiment was conducted with four different amounts of water volume in the reservoir. Results of the water modeling experiment applying the filter showed remarkably changed flow characteristics. Although the study confirmed that use of the filter may change the flow characteristics, it needs to be noted that only filter use alone cannot solve all the problems caused by a poorly designed gating system.

• Polymer(Korea)
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• v.25 no.4
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• pp.528-535
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• 2001

Polyurethane specimens were mainly composed of polyol, MDI, silicone surfactant, and water. The effects of ethylene glycol on the cell size, forming magnification, cream time, gel time, take free time, final free rising height, and reactive temperature were investigated. The cyclopentane was used for PU foam as a physical blowing agent. The components were hand-mixed at about 5000 rpm within 4 seconds at room temperature. The mixtures with various ethylene glycol contents were foamed in the wood mold. When the index of isocyanate was fixed, as the amount of ethylene glycol increased, cell size and thermal conductivity were decreased by about 5.1% and 14%, respectively.

• Journal of the Korea Institute of Military Science and Technology
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• v.19 no.5
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• pp.559-566
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• 2016

Cables for Towed Array Sonar System(TASS) were developed. In order to verify the performance of cables, environmental and operational conditions as well as functional requirements were investigated during design stage. Double armored high and low voltage integrated cable for towed body and two kinds of cables, armored and light weight power and optic hybrid cables for towed array sensor system were developed by modeling and simulation. Customized manufacturing process and test method, such as foam extrusion and dynamic fatigue test were applied to this development. In conclusion, underwater towed hybrid cable with high tensile strength and compact structure were developed.

• KSBB Journal
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• v.9 no.4
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• pp.406-411
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• 1994

An extractive fermentation process was developed to produce citric acid from g1ucose. Citric acid is a strong inhibitor to this fermentation. A mixture of tertiary amine and oleyl alcohol was used to selectively extract citric acid from the fermentation broth, hence enhancing the productivity by over 200%. Although the toxicity of the solvent was significant in the range of higher than 30% of amine, immobilization in polyurethane foam was useful to protect the cells from the toxicity of the solvent.

• Steel and Composite Structures
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• v.31 no.2
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• pp.133-148
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• 2019

This paper reports on the energy absorption characteristics of a lattice-web reinforced composite sandwich cylinder (LRCSC) which is composed of glass fiber reinforced polymer (GFRP) face sheets, GFRP lattice webs, polyurethane (PU) foam and ceramsite filler. Quasi-static compression experiments on the LRCSC manufactured by a vacuum assisted resin infusion process (VARIP) were performed to demonstrate the feasibility of the proposed cylinders. Compared with the cylinders without lattice webs, a maximum increase in the ultimate elastic load of the lattice-web reinforced cylinders of approximately 928% can be obtained. Moreover, due to the use of ceramsite filler, the energy absorption was increased by 662%. Several numerical simulations using ANSYS/LS-DYNA were conducted to parametrically investigate the effects of the number of longitudinal lattice webs, the number of transverse lattice webs, and the thickness of the transverse lattice web and GFRP face sheet. The effectiveness and feasibility of the numerical model were verified by a series of experimental results. The numerical results demonstrated that a larger number of thicker transverse lattice webs can significantly enhance the ultimate elastic load and initial stiffness. Moreover, the ultimate elastic load and initial stiffness were hardly affected by the number of longitudinal lattice webs.

• Journal of Auto-vehicle Safety Association
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• v.14 no.4
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• pp.27-34
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• 2022

In the development of automated driving, interest in the interior parts of vehicle is to become more significant in terms of the occupant safety and comfort. This study proposed an optimal design of front seat according to the design requirements for frame stiffness and seat comfort. For the seat comfort, the appropriate foam thickness was obtained using the structural analysis under reclined occupant loadings. While the strength and stiffness analyses were performed to evaluate the seat frame structure. Topology optimization was carried out based on the simulation results and the derived optimal model and baseline seat design was updated. The conceptual seat design for the autonomous vehicle in this study showed that the model development process is appropriate for the design parameters in both frame stiffness and seat comfort.