• Journal of the Korean Society for Nondestructive Testing
• /
• v.13 no.1
• /
• pp.15-20
• /
• 1993

This study describes ultrasonic reflection at a water/fiber reinforced polymer composite/water interface. Theoretical predictions of reflected beam amplitudes are also presented. Four different polymer composite laminates are investigated : T300/5208 graphite/epoxy $[0]_{31T},\;[45/90/-45/0]_{3S},\;[45/-45]_{2S}$, and S-2 glass/epoxy $[0/90]_{4S}$. The analytical leaky plate wave dispersion curves for the unidirectional laminate and other three laminates can be obtained by searching for the minimum magnitude of the reflection coefficient.

• Bulletin of the Korean Mathematical Society
• /
• v.32 no.1
• /
• pp.45-56
• /
• 1995

D. H. Gottlieb [1, 2] studied the subgroups $G_n(X)$ of homotopy groups $\pi_n(X)$. In [5, 7, 10], the authors introduced subgroups $G_n(X, A)$ and $G_n^{Rel}(X, A) of \pi_n(X)$ and $\pi_n(X, A)$ respectively and showed that they fit together into a sequence $$ \cdots \to G_n(A) \longrightarrow^{i_*} G_n(X, A) \longrightarrow^{j_*} G_n^{Rel}(X, A) \longrightarrow^\partial $$ $$ \cdots \to G_1^{Rel}(X, A) \to G_0(A) \ to G_0(X, A) $$ where $i_*, j_*$ and \partial$ are restrictions of the usual homomorphisms of the homotopy sequence $$ \cdot \to^\partial \pi_n(A) \longrightarrow^{i_*} \pi_n(X) \longrightarrow^{j_*} \pi_n(X, A) \to \cdot \to \pi_0(A) \to \pi_0(X) $$.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2006.05a
• /
• pp.300-303
• /
• 2006

Sandwich panel with inner structure is expected to find many applications because of high stiffness to mass ratio. However, low resistance to the pressure in the thickness direction may become a weak point in the forming process. Two pyramid type designs for inner structure are considered. For the resistance characteristics in the thickness direction, finite element simulations are carried out. For one design, experimental results are provided. It is shown that simulation can give a reasonable agreement with experiment. The reasons for the discrepancy are discussed mainly in the geometrical viewpoint. It is observed that most of deformation depends on bending mode. Two designs are compared using simulation.

• Elastomers and Composites
• /
• v.32 no.3
• /
• pp.166-172
• /
• 1997

The objective in this study was investigated temperature susceptibility and low temperature fracture of rubber modified asphalt. A chlorinated polyethylene elastomer, Tyrin CM0730, was added to 200/300 grade asphalt with 3.0 and 5.0wt% to improve campatibility. The elastomer modified asphalts were analyzed for temperature susceptibility relating to penetration index(PI) and penetration-viscosity number(PVN) as well as low temperature fracture relating to fracture energy $(G_{IC})$. These indices were obtained from the measurements of penetration, viscosity, failure load and modulus. The addition of small amounts of elastomer to the asphalt resulted in a significant increase of both the PI and PVN over an unmodified asphalt. Also, the fracture energy increased with the addition of elastomer to asphalt. These significant improvement at both the high and low temperature result in enhanced performance.

• Proceedings of the KIEE Conference
• /
• 1996.07c
• /
• pp.1639-1641
• /
• 1996

Polyirnide thin films were fabricated an using vapor deposition polymerization apparatus, and their FT-IR and TGA characteristics were investigated. The peaks of $720cm^{-1}$ and $1380cm^{-1}$ show C=O stretch mode and C-N stretch mode, and that of the cured polyimide at $300^{\circ}C$ were saturated. TGI(Thormogravi metric index) was showed at $459^{\circ}C$ from reaserch of thermal resistivity characteristics by TGA.

• Proceedings of the KIEE Conference
• /
• 1995.11a
• /
• pp.606-608
• /
• 1995

A thermally actuated micro-relay using a mercury-contact has been designed and fabricated. The mercury actuation was achieved by external nitrogen pressure and the mercury-contact was moved by actuation pressure of 110torr in the 100${\mu}m$ wide microchannel. The Injection pressure of mercury was 300torr in the 60${\mu}m$ wide microchannel of the micro relay structure.

• 한국전산유체공학회:학술대회논문집
• /
• 2008.03b
• /
• pp.300-303
• /
• 2008

In the present study, the simple form of the heat transfer equation were suggested to estimate the temperature variation inside the oil pipe in order to determine the thickness of the insulating materials to retain the working oils below the critical temperature. The conservation of the thermal energy at arbitrary time were modeled to one dimensional unsteady equation with the empirical formula or data. The calculating results for non-insulation case showed that the temperature were very sensitive to the thermal convection by the velocity of the external wind. For insulation case, the insulation material which has higher density and specific heat, lower thermal conductivity should be chosen with more brighter coloring outside the pipe in order to retain the working oils below the critical temperature.

• Journal of Power System Engineering
• /
• v.14 no.3
• /
• pp.19-24
• /
• 2010

The purpose of this study is to develop a snow melting system using the pulsating heat pipe(PHP). The experimental apparatus is consisted of a PHP, a concrete structure, a constant water thermostatic bath and a flowmeter. The experiment was performed at the outdoor air temperature of $-8^{\circ}C$ and inlet temperature of hot water of $75^{\circ}C$. PHP is the closed and non-loop type heat exchanger which is charging R-410A as an operating fluid. As experimental results, the temperature profile of vertical and horizontal orientation of concrete structure was measured with operating time. The heat flux of the snow melting was required more than 300 $W/m^2$. We confirmed that the snow melting system using the PHP was useful for anti-freezing road.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2006.05a
• /
• pp.661-662
• /
• 2006

This research is on a laser soldering using the micro solder-balls used in flip chip packaging process. A laser source used in laser soldering is Nd:YAG laser(250W and 60W). Solder-balls of 100, 300, $500{\mu}m$ size are used in experiments. The laser head to deliver a laser beam and the nozzle to transfer solder-balls are manufactured to bump solder-balls. After soldering solder-balls the shear test is carried out to determine the wetting at the interface between the surface and a solder-balls With the results of solder bumping tests a laminated molding is accomplished for manufacturing the three dimensional molding.

• Bulletin of the Korean Chemical Society
• /
• v.29 no.4
• /
• pp.758-760
• /
• 2008

Nanoporous AAO (Anodic Aluminum Oxide) membranes have many advantages as a template for variety of magnetic materials. Materials can be embedded into the pores by electrodeposition, sputtering or magnetic-field-assisted infiltration of magnetic nanoparticles. This work focuses on the fabrication of the magnetic structures in the AAO templates by electrodeposition. Our method allows the controlled growth of Co nanostructures within the porous alumina membrane in the form of dots, rods and long wires. The shape of Co nanostructures has been investigated by field emission scanning electron microscope (FESEM). The magnetic hysteresis loops of Co nanostructures were measured using SQUID at 5 K and 300 K. The magnetic properties of the Co nanostructures are proportional to their aspect ratios and can be controlled by changing the aspect ratios.