• Transactions of Materials Processing
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• v.12 no.6
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• pp.566-571
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• 2003

The metal forming behavior and defect formation in Ti-6Al-4V tube during hot backward extrusion were investigated. Dynamic material model(DMM) including Ziegler's instability criterion was employed to predict the forming defects such as shear band, inner and/or surface cracks. This approach was coupled to the internal variables generated from FE analysis. The simulation results fur the backward extrusion were compared with the experimental observation. The chilling effect and friction indicated a great influence on the deformation mode of the tube and the formation of surface cracks. The formation of forming defects in the extruded tube was attributed to non-uniform distribution of strain, strain rate and temperatures in the extruded tubes for the given test conditions.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.463-463
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• 2013

This paper reports the synthesis and characterization of ZnO:Ga nano-structures deposited on Au/SiNx/Si(001) by radio-frequency sputtering. The effect of the temperature on the microstructure of the as-grown ZnO:Ga thin films was examined. The growth mode of ZnO:Ga nano-structures can be explained by the profile coating, i.e. the ZnO nano-structures were formed with a morphological replica of Au seeds. Initially, the ZnO:Ga nano-structures were overgrown on top of Au nano-crystals. Small ZnO:Ga nano-dots were then nucleated on hexagonal ZnO:Ga discs.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.964-965
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• 2006

The injection molded Fe sintered bodies were fabricated using two kinds of nano Fe powders, $Fe-5%vol.ZrO_2$ and $Fe-10vol.%ZrO_2$ powders. The relationship between microstructure and mechanical properties depending on the $ZrO_2$ contents and sintering temperature were characterized by SEM and TEM techniques. In the wear test, the $Fe-0vol%ZrO_2$ sintered bodies showed mainly adhesive wear, but in the Fe-5%vol. $ZrO_2$ and Fe-10vol. % $ZrO_2$ composites the main wear behavior showed abrasive wear mode.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1159-1160
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• 2006

For pure Molybdenum carburized in mixed gases of argon and carbon monoxide, microstructural observations were carried out. X-ray diffraction analysis for carburized specimens revealed that brittle ${\alpha}-Mo_2C$- layer hardly formed in the case of low carbon monoxide concentration. Fracture strength of the specimen carburized at 1673 K for 16 h is about 550 MPa higher than that of the un-carburized specimen. SEM observation revealed that with increasing carburizing temperature, the region demonstrating a transgranular fracture mode progressed towards the center of specimen. This result means that the grain boundaries were strengthened by the grain boundary diffusion of carbon and the strength of grain boundaries exceeded that of grain itself.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.13 no.1
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• pp.84-91
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• 2017

This paper is proposed to select the optimal finite element type in finite element analysis. Based on the NUREG reports, static analyses were performed using a commercial analysis program, $ABAQUS^{TM}$. In this study, we used a nonlinear kinematic hardening model proposed by Chaboche. The analysis result of solid elements by inputting the same material constants was different from the results of the NUREG report. This is resulted from the difference between shell element and solid element. Therefore, the material constants that have similar result to the experimental result were determined and compared according to element type. In case of using solid element for efficient finite element analysis, we confirmed that the use of C3D8I element type(incompatible mode 8-node linear brick element) leads the accurate result while reducing the analysis time.

• Journal of KSNVE
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• v.4 no.2
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• pp.239-248
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• 1994

Wind tunnel tests and analyses of the response of the concrete pylon for the Seo Han Grand Bridge were conducted using aeroelastic model technique. A 1/250 scale aeroelastic model was used to measure the responses of the pylon at the several critical locations and to find any possible vibrational behavior. In order to confirm the model design and fabrication, natural frequencies and mode shapes measured from the model were compared with those from the calculation. Tests were conducted under the various angles ranging from $0^{\circ}$ to $90^{\circ}$ to find the critical angle of the wind. In order to evaluate the sensitivity of the response to changes in structural damping, a series of tests were conducted with two different values of structural damping such as 0.2% and 1.0% of critical. Additional tests were also conducted considering construction sequence.

• ETRI Journal
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• v.33 no.3
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• pp.355-365
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• 2011

IPTV broadcast channels and video content distribution are increasingly saturating network paths. New solutions based on inter-domain multicast protocols could contribute to the enhancement of multimedia content distribution over the Internet. The aim of this paper is to propose new capabilities for an existing inter-domain multicast protocol, the Protocol Independent Multicast-Sparse Mode. We describe the modified protocol and analyze its behavior using newly developed tools based on an open-source software simulator. The resulting protocol does not require topology information, which is advantageous for easier deployment. In addition, the adopted solution avoids inherent problems with inter-domain multicast routing, such as multiple paths and path asymmetries.

• Journal of ILASS-Korea
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• v.22 no.1
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• pp.36-41
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• 2017

The present study investigates the evaporation heat transfer characteristics of nanofluid droplet for different nanoparticle sizes. Also, the heat transfer coefficient was measured at different nanoparticle concentrations during evaporation. From the experimental results, it is found that the evaporation behavior of sessile droplet can be considered as constant radius mode due to pinning effect. The total evaporation time of sessile droplet decreases with nanoparticle size up to 7.9% for 0.10 vol% nanofluid droplet. As nanoparticle concentration increases, the clear difference in heat transfer coefficient is observed, showing that the size effect should be examined. This result would be helpful in designing the correlation between the nanoparticle size and the heat transfer characteristics for various applications.

• Bulletin of the Korean Chemical Society
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• v.30 no.8
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• pp.1743-1748
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• 2009

Novel 2-aminothiazolinium based tripodal receptors were designed and synthesized. The binding property of these receptors toward various anions was investigated by the isothermal titration calorimetry (ITC) method. Receptor 4 recognized the acetate anion with 1:1 stoichiometry, whereas it bound the other oxoanions such as sulfate and phosphate in complex modes. By modifying the phenyl groups at the 4-position of the thiazoline rings of the tripodal receptor 4 to induce a mutual aromatic stacking interaction among the three ligands, receptor 10 showed totally different binding behavior, which gave rise to the 1:1 binding mode for the sulfate anion. This result was confirmed by ESI MS spectrometry.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.833-838
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• 1998

This paper is aimed to investigate structural performance of flexural members enlarged with epoxy mortar at soffit. Main test variables are steel ratio and interface treatment method and six test beams are tested to investigate the effect of each test variables on maximum load capacity, load-deflection and moment-curvature relationship, interface behavior and failure mode. Test results show that section enlarged beams can carry almost same load of the monolithic beams with same size and the flexural stiffness and cracking moments are increased about 2.5 times and 50 to 70%of failure moment in comparison with same sized control beam, respectively. However, deflections and curvatures are decreased at the same load and interface fractures are not discovered at the ultimate load.