Search Results

You are looking at 1 - 10 of 39 items for

  • Author: Y.S. Kim x
Clear All Modify Search
Open access

K.S. Kim and J.Y. Kim

Abstract

Heat pipes have been recently in use for cooling purposes in various fields, including electronic circuit boards and vehicle parts that generate large amounts of heat. In order to minimize the loss of heat transferred, there is a need to maximize the contact area of the working fluid. This study produced a square tube multi-channel heat pipe to replace the existing circular pipe type to maximize the internal surface area thereof. This expands the surface, allowing the working fluid to come into contact with a wider area and enhancing thermal radiation performance. A mold for the production for such a product was designed, and finite element simulation was performed to determine whether production is possible.

Open access

S.-W. Kim, T.-Y. Ahn, Y.-S. Lim and S.-S. Hwang

Abstract

This work aims to study the stress corrosion crack growth behavior of cold-rolled Alloy 690 in the primary water of a pressurized water reactor. Compared with Alloy 600, which shows typical intergranular cracking along high angle grain boundaries, the cold-rolled Alloy 690, with its heterogeneous microstructure, revealed an abnormal crack growth behavior in mixed mode, that is, in transgranular cracking near a banded region, and in intergranular cracking in a matrix region. From local strain distribution analysis based on local mis-orientation, measured along the crack path using the electron back scattered diffraction method, it was suggested that the abnormal behavior was attributable to a heterogeneity of local strain distribution. In the cold-rolled Alloy 690, the stress corrosion crack grew through a highly strained area formed by a prior cold-rolling process in a direction perpendicular to the maximum principal stress applied during a subsequent stress corrosion cracking test.

Open access

K. S. Kang, C. S. Kim and Y. A. El-Kassaby

Abstract

Acorn production was surveyed for eight consecutive years (2000-2007) in a 94-clone Sawtooth oak (Quercus acutissima) seed orchard established in 1992. Acorn production commenced in 2000 and peaked in 2005 and was characterized by a 3-4 years interval. Sixty out of the orchard’s 94 clones were consistent producers across the study period. Acorn production’s Pearson productmoment and Spearman rank correlation coefficients were significant and consistently positive over the eight years study period. Parental cumulative reproductive output, represented by parental balance curves, slightly varied among mast years and showed steady improvement (less distortion) over years. Effective population size (Np) was high in moderate and good acorn production years; however, departure from clonal equal contribution was observed throughout the study period. Parental effective population size was estimated under various scenarios of male fecundity (pollen production is: 1) proportional to clone size, 2) equal to female contribution, and 3) equal across all clones) resulted in high Np and low group co-ancestry under equal male fecundity scenario while moderate Np size and group co-ancestry were observed when male fecundity was assumed to be proportional to clone size (i.e., ramet number).

Open access

Y.-P. Hong, H.-Y. Kwon, K.-S. Kim, K.-N. Hong and Y.-Y. Kim

Abstract

Level and distribution of genetic diversity in 8 populations of Japanese red pine in Korea were estimated using I-SSR variants. A total of 80 I-SSR variants were observed in the analyzed 150 individuals, which revealed DNA fingerprints-like individual specific amplicon profiles for all of them. Relatively higher level of genetic diversity within populations was observed in 8 populations of Japanese red pine (mean of 0.450) than in other tree species. From the results of AMOVA, majority of genetic diversity was allocated within populations (93.42%) resulting in a moderate degree of population differentiation (ΦST= 0.066). The observed distribution pattern of I-SSR variants among 8 populations was coincided with the typical patterns for the long-lived woody species. Genetic relationships among the populations, reconstructed by UPGMA and Neighbor- Joining methods, revealed 2 genetic groups. The populations of Gangwon-Uljin and Chungnam-Taean turned out to be the most closely related despite a distant location between them. The overall genetic relationships among the 8 populations, reconstructed by both methods, were not coincided with geographic distances. The discrepancy between genetic relationships and geographical distribution among the populations suggests that the analyzed populations might have undergone random changes in genetic composition due to some kinds of disturbances. Results obtained in this study suggests that more careful approach should be made in preparing strategy for gene conservation of Japanese red pine in Korea. More information on countrywide molecular population genetic status of Japanese red pine will be helpful to prepare more reasonable strategy for gene conservation of the species in the country.

Open access

S.Y. Chang, H.S. Jang, Y.H. Yoon, Y.H. Kim, J.Y. Kim, Y.K. Lee and W.H. Lee

Abstract

Electrical discharges using a capacitance of 450 μF at 0.5, 1.0, and 1.5 kJ input energies were applied in a N2 atmosphere to obtain the mechanical alloyed Ti3Al powder without applying any external pressure. A solid bulk of nanostructured Ti3Al was obtained as short as 160 μsec by the Electrical discharge. At the same time, the surface has been modified into the form of Ti and Al nitrides due to the diffusion process of nitrogen to the surface. The input energy was found to be the most important parameter to affect the formation of a solid core and surface chemistry of the compact.

Open access

S.-Y. Kim, M.-H. Lee, T.-S. Kim and B.-S. Kim

Abstract

Porous metallic materials have been widely used in many fields including aerospace, atomic energy, electro chemistry and environmental protection. Their unique structures make them very useful as lightweight structural materials, fluid filters, porous electrodes and catalyst supports. In this study, we fabricated Ni-based porous metallic glasses having uniformly dispersed micro meter pores by the sequential processes of ball-milling and chemical dissolution method. We investigated the application of our porous metal supported for Pt catalyst. The oxidation test was performed in an atmosphere of 1% CO and 3% O2. Microstructure observation was performed by using a scanning electron microscope. Oxidation properties and BET (Brunauer, Emmett, and Teller) were analyzed to understand porous structure developments. The results indicated that CO Oxidation reaction was dependent on the specific surface area.

Open access

S.Y. Chang, Y.W. Cheon, Y.H. Yoon, Y.H. Kim, J.Y. Kim, Y.K. Lee and W.H. Lee

Abstract

Characteristics of electro-discharge-sintering of the Ti-37.5at.% Si powder mixture was investigated as a function of the input energy, capacitance, and discharge time without applying any external pressure. A solid bulk of Ti5Si3 was obtained only after in less than 129 μsec by the EDS process. During a discharge, the heat is generated to liquefy and alloy the particles, and which enhances the pinch pressure can condensate them without allowing a formation of pores. Three step processes for the self-consolidation mechanism during EDS are proposed; (a) a physical breakdown of oxide film on elemental as-received powder particles, (b) alloying and densifying the consolidation of powder particles by the pinch pressure, and (c) diffusion of impurities into the consolidated surface.

Open access

Y.C. Kim, S.S. Kim and J.U. Cho

Abstract

It is indispensable to evaluate fracture energy as the bonding strength of adhesive at composite material with aluminum foam. This specimen is designed with tapered double cantilever beam by British standards (BS 7991 and ISO 11343). 4 kinds of specimens due to m values of 2, 2.5, 3 and 3.5 are manufactured and compared each other with the experimental results. Adhesive fracture energy is calculated from the formulae of British standards. The value of m is the gradient which is denoted as the length and the height of specimen. As m becomes greater at static experimental result, the maximum load becomes higher and the displacement becomes lower. And the critical fracture energy becomes higher. As m becomes less at fatigue experimental result, the displacement becomes higher and the critical fracture energy becomes higher. Fracture behavior of adhesive can be analyzed by this study and these experimental results can be applied into real field effectively. The stability on TDCB structure bonded with aluminum foam composite can be predicted by use of this experimental result. Adhesive fracture energy is calculated from the formulae of British standards. Based on correlations obtained in this study, the fracture behavior of bonded material would possibly be analyzed and aluminum foam material bonded with adhesive would be applied to a composite structure in various fields, thereby analyzing the mechanical and fracture characteristic of the material.

Open access

Y.-K. Jeong, Y.S. Kim and S.-T. Oh

Abstract

An optimum route to fabricate the Cu-based SiC composites with homogeneous microstructure was investigated. Three methods for developing the densified composites with sound interface between Cu and SiC were compared on the basis of the resulting microstructures. Starting with three powder mixtures of elemental Cu and SiC, elemental Cu and PCS coated SiC or PCS and Cunitrate coated SiC was used to obtain Cu-based SiC composites. SEM analysis revealed that the composite fabricated by spark plasma sintering using elemental SiC and Cu powder mixture showed inhomogeneous microstructure. Conversely, dense microstructure with sound interface was observed in the sintered composites using powder mixture of pre-coated PCS and Cu-nitrate onto SiC. The relationship between powder processing and microstructure was discussed based on the role of coating layer for the wettability

Open access

W.H. Lee, Y.H. Yoon, Y.H. Kim, Y.K. Lee, J.Y. Kim and S.Y. Chang

Abstract

A single pulse of 2.0 to 3.5 kJ of input energy from a 450 mF capacitor was applied to a commercially pure Ti rod in a N2 atmosphere. The surface of the Ti rod transformed from TiO2 into titanium nitride in times as short as 159 msec, providing a bimodal morphology of the cross-section. A much higher value of hardness that was observed at the edge of the cross-section was attributed to nitrogen-induced solid-solution hardening that occurred during the electrical discharge process. The activation energy (Ea) for the diffusion process was estimated to be approximately 86.9 kJ/mol. Results show that the electrical discharge process is a possible potential method for the nitriding of Ti; advantages include a short processing time and control of the nitrided layer without dimensional changes.