• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.10
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• pp.1686-1694
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• 2003

The foam-filled tube beams can be used for the front rail and firewall structures to absorb impact energy during frontal or side collision of vehicles. In the case of side collision where bending is involved in the crushing mechanism, the foam filler would be effective in maintaining progressive crushing of the thin-walled structures so that much impact energy could be absorbed. In this study, bending behaviors of the closed-cell-aluminum-alloy-foam-filled stainless steel tube were investigated. The various foam-filled specimens including piecewise fillers were prepared and tested. The aluminum-alloy-foam filling offered the significant increase of bending resistance. Their suppression of the inward fold formation at the compression flange as well as the multiple propagating folds led to the increase of load carrying capacity of specimens. Moreover, the piecewise foams would provide the easier way to fill the thin-walled shell structures without the drawback of strength.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.91-92
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• 2006

Metallic foams have a combination of attractive properties such as high specific mechanical properties and good energy absorption characteristics. This paper presents the properties of steel foam sandwiches produced using powder metallurgy approach. Metallic powder, solid polymeric binder and a foaming agent are dry-mixed and molded into the desired shape. The molded powder mix is then heat-treated to foam, debind and sinter the material. The resulting material has an open cell structure with high porosity. The structure and properties of sandwiches specimens produced with the process are presented and discussed.

• Korean Journal of Materials Research
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• v.29 no.10
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• pp.617-622
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• 2019

In order to develop a process for manufacturing a composite structure of an intermetallic compound foam and a hollow material, the firing and pore form of the Al-Ni precursor in a steel pipe are investigated. When the Al-Ni precursor is foamed in a hollow pipe, if the temperature distribution inside the precursor is uneven, the pore shape distribution becomes uneven. In free foaming, no anisotropy is observed in the foaming direction and the pore shape is isotropic. However, in the hollow pipe, the pipe expands in the pipe axis direction and fills the pipe. The interfacial adhesion between $Al_3Ni$ foam and steel pipe is excellent, and interfacial pore and reaction layer are not observed by SEM. In free foaming, the porosity is 90 %, but it decreases to about 80 % in the foam in the pipe. In the pipe foaming, most of the pore shape appears elongated in the pipe direction in the vicinity of the pipe, and this tendency is more remarkable when the inside pipe diameter is small. It can be seen that the pore size of the foam sample in the pipe is larger than that of free foam, because coarse pores remain after solidification of the foam because the shape of the foam is supported by the pipe. The vertical/horizontal length ratio expands along the pipe axis direction by foaming in the pipe, and therefore circularity is reduced.

• Journal of Korea Foundry Society
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• v.22 no.3
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• pp.137-143
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• 2002

Silica sand, zircon sand, and steel shots were used as mold packing materials in lost foam casting of the aluminum alloy bar. Vibration acceleration in three directions and temperatures in the casting and mold were measured, and packing and cooling characteristics of these materials were investigated. Packing densities increased with increase in vibration magnitude and time, and were $1.41{\sim}1.49g/cm^2$ for silica sand, $2.54{\sim}2.86g/cm^2$ for zircon sand, and $3.92{\sim}4.52g/cm^2$ for steel shots. Sound castings were obtained only without evacuation of the flask during pouring. Solidification time became faster in order of silica sand, zircon sand and steel shot packing because steel shot has the highest cooling capacity of them. Solidification time of steel shot packing was shortened to about 1/2 of silica sand packing. Cooling capacity of sand mold was generally evaluated by heat diffusivity of the mold, however could be simply evaluated with specific heat per unit volume of the packing material in lost foam casting.

• Structural Engineering and Mechanics
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• v.48 no.4
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• pp.569-585
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• 2013

The use of the rigid polyurethane foam (RPF) to strengthen sandwich structures against blast terror has great interests from engineering experts in structural retrofitting. The aim of this study is to use the RPF to strengthen sandwich steel structure under blast load. The sandwich steel structure is assembled to study the RPF as structural retrofitting. The filed blast test is conducted. The finite element analysis (FEA) is also used to model the sandwich steel structure under shock wave. The sandwich steel structure performance is studied based on detonating different TNT explosive charges. There is a good agreement between the results obtained by both the field blast test and the numerical model. The RPF improves the sandwich steel structure performance under the blast wave propagation.

• Journal of Korea Foundry Society
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• v.39 no.5
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• pp.87-93
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• 2019

The effects of mold materials on the microstructure and tensile properties were investigated to develop a mass production technique of aluminum alloy parts with excellent mechanical properties using a lost foam casting method. The microstructures of the plate-shaped cast alloy showed a tendency to be finer in proportion to the thickness of the plate, and a remarkably fine structure was obtained by applying a steel chill or a ball as a mold material compared to general sand. When a steel ball was used, it was observed that the larger the ball, the finer the cast structure and the better the tensile properties. The microstructure and tensile properties of the cast parts with complex shapes were greatly affected by the gating system, but the positive effects of the steel chill and the steel ball as a mold material were clear.

• Polymer(Korea)
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• v.27 no.4
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• pp.340-348
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• 2003

A previous stud-pull test was modified to measure the bond strength of polyurethane foam to carbon steel substrate. This test was appropriate in that the specimen foamed on Zn phosphated steel (0.95 kN) was broken at higher load than that of smooth galvanizing treated steel (0.38 kN). Among the samples foamed on the substrate atvarious preheating temperatures, the polyurethane foam to the steel held over 60$^{\circ}C$ exhibited very high bond strength. The samples were exposed at water vapor absorption, and, then, their bond strengths were measured. The adhesion was significantly reduced in the samples foamed on the steel at temperatures below 40$^{\circ}C$ and above 70$^{\circ}C$. For the polyurethane foams formulated with two blowing gases, the adhesion was higher by 0.03 kN in the samples with HCFC-l4lb than that with HFC-245fa. When the these samples were exposed at water vapor soaking, the reduction of the bond strength for the HFC-245fa blown sample was negligible due to smaller area fraction of void area filled with gas at interfacial area. Consequently, it was found that adhesion of polyurethane foam to metal substrate was determined by variation of microstructural features with substrate preheating, surface treatment type of blowing agent.

• Steel and Composite Structures
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• v.29 no.3
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• pp.301-308
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• 2018

Properties of AFS vary with the changes in the face-sheet materials. Hence, the performance of AFS can be optimized by selecting face-sheet materials. In this work, three types of face-sheet materials representing elastic-perfectly plastic, elastic-plastic strain hardening and purely elastic materials were employed to study their effects on the flexural behavior and failure mechanism of AFS systematically. Result showed face-sheet materials affected the failure mechanism and energy absorption ability of AFS significantly. When the foam cores were sandwiched by aluminum alloy 6061, the AFS failed by face-sheet yielding and crack without collapse of the foam core, there was no clear plastic platform in the Load-Displacement curve. When the foam cores were sandwiched by stainless steel 304 and carbon fiber fabric, there were no face-sheet crack and the sandwich structure failed by core shear and collapse, plastic platform appeared. Energy absorption abilities of steel and carbon fiber reinforced AFS were much higher than aluminum alloy reinforced one. Carbon fiber was suggested as the best choice for AFS for its light weight and high performance. The versus strength ratio of face sheet to core was suggested to be a significant value for AFS structure design which may determine the failure mechanism of a certain AFS structure.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.199-200
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• 2023

This paper presents a study on the selection of optimal mix proportions for producing lightweight pre-foam concrete as a substitute for Autoclaved Lightweight Concrete (ALC) without the accelerated curing. The study was conducted using a rapid hardening binder made from by-products of the steel industry as the primary raw material. The experimental results established the optimal mix proportions, which included retarder content, water/binder ratio, foam content, and fiber inclusion amount, for the production of lightweight foam concrete. The optimal mix proportion was determined to have a retarder content at the minimum amount required to secure the working time, W/B of 35%, a foam content limited to 65% or less, and a fiber inclusion amount of 0.05% or less.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.10a
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• pp.427-428
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• 2009

In the manufacture process of refrigerator cabinet, polyurethane(PU) liquid firstly is injected between outer plate and inner case in high temperature about $40^{\circ}C$, and PU foam is generated and solidified to the room temperature. There will be great residual stress in the PU foam, especially at the corners after the whole refrigerator is completely assembled. The stress condition will become more complicated under operating condition because of the large temperature difference between the freezing room and outer plate. And also, there are great differences of properties for plastic and steel which would cause different deformation under temperature gradient. The steel outer plate would expand compared to the PU foam or ABS material under operation condition, which induces a thermally bowing deformation in the refrigerator cabinet. The objective of this paper is to design an optimum bead structure or to use reinforcement in the refrigerator except for improving material properties in order to decrease the deformation.