• Journal of the Korean Ceramic Society
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• v.36 no.11
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• pp.1261-1265
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• 1999

Effect of SiC particle size of the densification of Al2O3-SiC composite during pressureless sintering was investigated. Two types of SiC powders having average particle size of 0.15${\mu}{\textrm}{m}$ and 3${\mu}{\textrm}{m}$ were used. Densification rate of the specimen containing 0.15${\mu}{\textrm}{m}$ SiC particles was slower than that of the specimen containg 3${\mu}{\textrm}{m}$ SiC particles. Although the relative density of the specimen containing 0.15${\mu}{\textrm}{m}$ SiC particles was below 90% of theoretical density after sintering at 155$0^{\circ}C$ the complete closure of open pores occurred. Therefore full densification could be obtained by subsequent HIP. On the other hand in the specimen containing 3${\mu}{\textrm}{m}$ SiC particles the complete closed pore was observed at 95% of theoretical density. Such a fast pore closure in the specimen containing 0.15${\mu}{\textrm}{m}$ SiC particles is likely to occur as a result of dense reaction layer formation on the specimen surface which is attributed to the high reactivity of small size particles with sintering atmosphere.

• Journal of Korea Foundry Society
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• v.25 no.1
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• pp.16-22
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• 2005

This study aims to investigate the effects of the microstructures and nodule type on the fatigue characteristics of cast iron. Fatigue tests were carried out in tension-tension mode using a servo-hydraulic testing machine with load control mode operating at a frequency of 15 Hz. The tests were conducted at stress ratio R=Kmin/Kmax, of 0.1. Initial crack ${\Dalta}K$ values were highly performed with increase in tensile strength of DCI fatigue specimens. ${\Dalta}K_{th}$ region, fatigue crack propagation was primarily advanced through cell boundary and in periphery of near nodule. Fatigue crack propagation rate of D2 consisted with 2Phase(Ferrite+Pearlite) was slow due to crack closure enhanced by crack deflection and occurred crack branching. The generation of crack branch was occurred due to interaction of crack-nodule. At Threshold and Paris zone, the fractographs of the fatigue fracture surface for DCI show typical striations of a ductile fracture and isolated cleavage planes near graphite. The effect of microstructure on fatigue crack propagation of GC strongly depends on the type of flake. The generation of crack branch occurred due to interaction of crack-nodule. The fractographs of the fatigue fracture surface for GC show cleavage plane along the flake graphite.

• Korean Journal of Soil Science and Fertilizer
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• v.24 no.3
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• pp.177-182
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• 1991

This study was carried out to clarify the effects of grassland afforestation on some chemical properties of the Japanese ceder(Cryptomeria japonica) forest soil in Cheju Island. The following results were obtained in this study ; 1. T-C, T-N, exch. cations and base saturation in the surface soil(0~10cm) decreased sharply from planting to crown closure. However, after crown closure, exch. Ca and Mg increased considerably. On the other hand, there were no definit changes below surface soil. 2. In vertical distribution of chemical properties, T-C, T-N, exchangeable acidity and exch. cations decreased with soil depth. Especially, exch. Ca and Mg of surface soil in closed stand show a higher value than that in open stand, but there were no variation below surface soil. 3. In closed stand, the amounts of exch. Ca, Mg and K were 1.8 times, 1.6 times and 1.5 times greater than those in open stand. There was no significant difference between open and closed stand in T-C and T-N. 4. The ratios of the amounts of nutrients in surface soil to those in mineral horizons(ha, 50cm) between the open and closed stand showed 30% and 50% for exch. Ca, 30% and 40% for exch. Mg, 38% and 38% for exch. K, respectively.

• 한국해양학회지
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• v.27 no.4
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• pp.311-323
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• 1992

The study of ocean surface mixed layer modelling has three different approaches: integral models. diffusive models including K theory and higher turbulence closure scheme, and transilient models. None of them is suitable for all occasions because each model has its specific merits and defects. In the present paper, these three types mixed layer models are described, and their relative advantages and applicabilities are discussed in order to guide the researchers who initiate ocean mixed layer study.

• Transactions of Materials Processing
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• v.4 no.1
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• pp.48-58
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• 1995

In this study, a contact algorithm for the finite element analysis of free surface contact problem in materials forming is presented. The proposed contact algorithm consists of two parts. The first is the contact searching part, and the second, the constraint part. The contact searching algorithm does not require any a priori knowledge of the pairs of contact nodes or segments and the impenetrability constraint is satisfied using the penalty function scheme. void colsure in open-die forging was simulated to verify the accuracy and capability of the currently developed contact algorithm. The simulation results, obtained from ABAQUS simulation, were compared well to the experimental data available in the literature.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.81-86
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• 2001

Interfacial pressure jump terms based on the physics of phasic interface and bubble dynamics are introduced into the momentum equations of the two-fluid model for bubbly flow. The pressure discontinuity across the phasic interface due to the surface tension force is expressed as the function of fluid bulk moduli and bubble radius. The consequence is that we obtain from the system of equations the real eigenvalues representing the void-fraction propagation speed and the pressure wave speed in terms of the bubble diameter. Inversely, we obtain an analytic closure relation for the radius of bubbles in the bubbly flow by using the kinematic wave speed given empirically in the literature. It is remarkable to see that the present mechanistic model using this practical bubble radius can indeed represent both the mathematical well-posedness and the physical wave speeds in the bubbly flow.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.8 s.227
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• pp.929-936
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• 2004

In the present work, shape of the mixing vane in Plus7 fuel assembly has been optimized numerically using three-dimensional Reynolds-averaged Navier-Stokes analysis of flow and heat transfer. Standard $k-{\epsilon}$ model is used as a turbulence closure. The Response surface method is employed as an optimization technique. The objective function is defined as a combination of heat transfer rate and inverse of friction loss. Bend angle and base length of mixing vane are selected as design variables. Thermal-hydraulic performances for different shapes of mixing vane have been discussed, and optimum shape has been obtained as a function of weighting factor in the objective function.

• Journal of Veterinary Clinics
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• v.16 no.1
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• pp.189-192
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• 1999

Tarsorrhaphy is widely used to protect the cornea, reduce evaporation of tears, and facilitate reepithelialization of the ocular surface. However, a dilemma ensues in patients when frequent neurological evaluations and postoperative examinations are needed. The modified temporary tarsorrhaphy in this study was simple to perform, provided stable eyelid closure, and could be opened and closed as needed. It could be easily reversed with minimal complications of the eyelid and it allowed the surgeon to control traction of the bolsters in all of 45 dogs with corneal epithelial defects. Also, The globe could be examined without further anesthesia, sutures, and pain at any time after surgery. It was concluded that this modified method might be effective for evaluation of the corneal healing process and useful for ocular surface reconstruction clinically.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.7
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• pp.91-97
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• 2001

When a body including a crack inside is subjected to the compressive forces, the crack is closed and sliding occurs on the crack surfaces. In this work, a subsurface crack subjected to a static compressive load is analyzed with the finite element method considering friction on the crack surface. The friction on the crack surface is assumed to follow the Coulomb friction law, and a numerical method based on the finite element method and iterative method is applied in this work. The result is compared with those of ANSYS and references.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.8 s.251
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• pp.715-721
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• 2006

In the present work, nozzle shape of a jet fan is optimized numerically using three-dimensional Reynolds-averaged Navier-Stokes analysis. Standard $k-{\epsilon}$ model is used as a turbulence closure. Response surface method is employed as an optimization technique. The objective function is defined as maximum throw distance. Three geometric variables, i.e., length and angle of nozzle, and interval between two nozzles, are selected as design variables. As the main result of the optimization, the throw distance has been improved effectively.