• The Journal of the Acoustical Society of Korea
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• v.30 no.1
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• pp.17-21
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• 2011

The effects of screening hydrophones with open-cell foams for reduction of the infrasonic self-noise induced by the flow around hydrophones are investigated by at-sea experiment. Test results of the 10 ppi polyurethane open-cell foams with different thickness show that the foams of 1 cm and 3 cm thickness reduce the flow-induced self-noises up to 20 dB and 28 dB at the frequency band of 2-10 Hz, respectively.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.4
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• pp.363-370
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• 2016

Lightweight geopolymers are more readily produced and give higher fire resistant performance than foam cement concrete. Lowering the density of solid geopolymers can be achieved by inducing chemical reactions that entrain gases to foam the geopolymer structure. This paper reports on the effects of adding different concentrations of aluminum powder on the properties of cellular structured geopolymers. The apparent density of lightweight geopolymers has a range from 0.7 to $1.2g/m^3$ with 0.025, 0.05 and 0.10 wt% of a foaming agent concentration, which corresponds to about 37~60 % of the apparent density, $1.96g/cm^3$, of solid geopolymers. The compressive strength of cellular structured geopolymers decreased to 6~18 % of the compressive strength, 45 MPa of solid geopolymers. The microstructure of geopolymers gel was equivalent for both solid and cellular structured geopolymers. The workability of geopolymers with polyprophylene fibers needs to be improved as in fiber-reinforced cement concrete. The lightweight geopolymers could be used as indoor wall tile or board due to fire resistance and incombustibility of geopolymers.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.4
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• pp.182-189
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• 2021

Porous ceramics were manufactured using the foaming method for the development of inorganic insulating materials. Silica fume and SiO₂ were used as main raw materials, and bentonite was used as a rapid setting agent for uniform structure formation of porous ceramics. The porous ceramics were sintered at 1200℃, and porosity, density, compressive strength, microstructure and thermal conductivity were analyzed. As the content of silica fume to SiO₂ of the porous ceramics increased 70 to 90 %, the specific gravity increased from 0.63 to 0.69, and the compressive strength increased from 9.41 Mpa to 12.86 Mpa. But, the porosity showed a tendency to decrease from 72.07 % to 70.82 %, contrary to the specific gravity. As a result of measuring the thermal conductivity, the porous ceramic with a silica fume content of 70 % showed a thermal conductivity of 0.75 to 0.72 W/m·K at 25 to 800℃, respectively, and, another that a silica fume content of 90 % showed a 0.66~0.86 W/m·K. So the lower the silica f ume content, the lower the thermal conductivity, which was conf irmed to be consistent with porosity result. As a result of microstructure analysis using SEM (Scanning Electron Microscope), pores in the range of tens to hundreds ㎛ were observed inside and outside the porous ceramic, and it was confirmed that the pore distribution was relatively uniform.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.19-24
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• 2003

Potential applications of foam-filled section are the automotive structures. A foam-filled section can be used for the front rail and firewall structures to absorb impact energy during frontal or side collision. In the case of side collision where bending is involved in the crushing mechanics, the foam filler will be significant in maintaining progressive crushing of the thin-walled structures so that more impact energy can be absorbed. In this study, the manufacturing process of closed cell aluminum alloy foam filled stainless steel tube was studied, and the various foam filled specimens including piecewise fillers were prepared, tested and discussed about the bending behaviors.

• Journal of Convergence for Information Technology
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• v.9 no.5
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• pp.158-164
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• 2019

Recently many studies to reduce the noise of dental hand piece which generate inevitably mechanical sound to offend to the ear of a patient have been spotlighted. Generally, methods of adding a sound absorbing material inside the exhaust valve, air pump of machine or automobile are widely reported as optimal way to reduce the mechanical noise. In this paper we studied a new UV laser aided manufacturing of micro-porous structure of EPP substrate and applied dental hand piece to improve the efficiency of sound absorption. A lot of micro-sized pores were fabricated with UV laser processing on the surface of sliced EPP substrate. From fundamental experiments, more high-performance of micro-porous EPP substrate has finally demonstrated for sound-absorbing structure of the micro muffler inside dental hand piece, which actually has the excellent potential to apply a lot of potable machine.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.1
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• pp.75-82
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• 2016

As spreading of train concrete ballast leads to the increase resounding friction noise, an porous sound absorbing block is applied in urban train tunnel as a counterparts against the friction noise. Three steps of major variables tests for an optimal mix design of the block are conducted to pursue the light weight of the block. Pilot property tests of the block for the cases of the fly-ash only as lightweight aggregates are carried satisfying KRT(Korean Rail Transit) and new KRS(Korean Railway Standards). Based on the results of pilot tests, required structural strength and admixture effects are evaluated. Additionally, typical lightweight aggregates are replaced so that lightweight and strength are improved for serviceability of poor working conditions and proper maintenance in urban train tunnel.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.5
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• pp.543-551
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• 2015

Polyurethane Foam(PUF), a outstanding thermal insulation material, is used for various structures as being composed with other materials. These days, PUF composed with glass fiber, Reinforced PUF(R-PUF), is used for a insulation system of LNG Carrier and performs function of not only the thermal insulation but also a structural member for compressive loads like a sloshing load. As PUF is a porous material made by mixing and foaming, mechanical properties depend on volume fraction of voids which is a dominant parameter on density. Thus, In this study, density is considered as the effect parameter on mechanical properties of Polyurethane Foam, and mechanical behavior for compression of the material is described by using modified Gurson damage model.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.21 no.1
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• pp.47-53
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• 2011

The artificial aggregates (AAs) were manufactured from the parent batch powders consisting of bottom ash containing excess unburned carbon and dredged soil, 7 : 3 weight ratio by direct sintering method and those physical properties were evaluated. Especially, the effects of waste glass or frit (NWG) which was made by addition of 5 wt% $Na_2O$ to the waste glass upon the bloating phenomenon of AAs were analyzed. The AAs manufactured from the parent batch powders showed a lower specific gravity than that of specimens containing waste glass or NWG due to excess u$Na_2O$nburned carbon which usually obstructs a sintering process. But, the waste glass added on parent batch powders promoted the sintering and densification thus increased the specific gravity of AAs. Also the specific gravity of AAs added with 5 wt% NWG, was lowered compared to that of AAs added with as-received waste glass. This is because of bloating of shell which captures gases owing to the lowered viscosity of liquid formed at the specimen surface caused by $Na_2O$ addition. In conclusion, the AAs sintered at above $1100^{\circ}C$ in this study showed characters of lightweight aggregate of specific gravity 1.15~1.34 and water absorption 11~19 %, and the bloating phenomenon of AAs was occurred at the shell rather black core part.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.43 no.1
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• pp.27-33
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• 2017

Up to now, better convenience and portability were important factors in the development of the cosmetics and achieved by immersing low viscosity makeup water-in-oil (W/O) emulsion into the impregnation material. Conventionally, polyurethane sponges having porous network structures and hard textures have been dominantly used. It has an advantage of easy to manufacture because of its good impregnation property due to its structural characteristics. However, it releases emulsion too much at first use, and shows unexpected dramatic decline during the period of usage. In this study, we studied on makeup W/O emulsion with various features and developed the new foaming sponge, which showed excellent formability and proper absorption and discharge ability of cosmetic composition through the combination of natural rubber (NR) and styrene butadiene rubber (SBR). This impregnation material is characterized by the softness of elasticity like a rubber, high elongation and uniform output. We confirmed that this material can be used to develop makeup products using various oils depending on polarity and controlling the viscosity of the makeup W/O emulsion. Thus, it is concluded that these results provide valuable information in developing new cosmetics impregnation materials.