• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.8
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• pp.1291-1297
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• 1997

Elastic-plastic finite element(FE) simulation was performed for polycrystalline solids subjected to plane strain tensile loading. Using Asaro's double slip crystal plasticity model, the polycrystalline solids were modeled by assigning different initial slip directions to each grain. From the FE calculations, the microscopic deformation characteristics of polycrystalline solids were analyzed. Moreover, the effect of grain size and grain boundaries on the deformation characteristics were clarified.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.2
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• pp.137-143
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• 2000

An automobile clutch diaphragm spring is operating in a closed clutch housing under high temperature and subject to high stress concentration in driving condition, which frequently causes cracks and fracture. The material of spring is required to possess sufficient fatigue strength and tenacity, which depend largely on the condition of tempering heat treatment. In this paper, specimens are made under a number of different tempering temperatures md tested to find the optimal tempering heat treatment condition. The experiments include the verification of microscopic structure, hardness, tensile strength, fatigue crack growth rate, stress intensity factor range and residual stress. Also, decarbonization, which occurs in actual heat treatment process, is measured and allowable decarbonization depth is studied by durability test.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.778-781
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• 2004

As the technique of high-speed end-milling is widely adopted to in machining field. The investigation for microscopic precision of workpiece is necessary for machinability evolution. In this study, cutting force, cutting temperature and microhardness were investigated to evaluate damaged layer in conventional machining and high-speed machining. Damaged layer was measured using optical microscope. The thickness of damaged layer depends on cutting process parameters, specially feed per tooth and radial depth. It is obtained that the characteristics of damaged layer is high-speed machining better than conventional machining.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.36 no.1
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• pp.61-66
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• 2004

Bleached chemithermomechanical pulp (BCTMP) was produced from CTMP of Betula maximowicziana Regel by two staged ozone-hydrogen peroxide bleaching in order to improve the optical properties of high yield pulp. This pulp was used for the evaluation of optical properties improvement, chemical characteristics of lignin in fiber and the relationship between lignin and optical properties in fiber cell wall. Hydrogen peroxide treatment improved the brightness, but the post color number (PC No.). There was little improvement on optical properties by ozone treatment, but this could be improved more by using two staged ozone-hydrogen peroxide bleaching. The hydrogen peroxide treatment did not make any change on chemical characteristics of lignin in cell wall, but by ozone treatment, it was found that the non-aromatic conjugated structure was existed in the surface of cell wall, but this could be removed by hydrogen peroxide treatment in two staged ozone-hydrogen peroxide treatment. Therefore, the optical properties was significantly improved, due to the removal of non-aromatic conjugated structure.

• Journal of ILASS-Korea
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• v.1 no.4
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• pp.32-39
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• 1996

Fuel spray in the MPI gasoline injector and its atomization characteristics are investigated with both macroscopic and microscopic visualization systems. The Bosch injector is inserted into an air-assist spray adapter which is designed to be fabricated and assembled easily. particle motion analysis system is used to measure the SMD of injector, where the assistant air pressure is varied from 0.0 to 1.5bar with fuel pressure 2.8bar. Droplet size decreased with higher air pressure and fine fuel spray with below $60{\mu}m$ of SMD is acquired at the assistant air pressure over 0.5bar.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.1073-1077
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• 1997

In this paper, we have studied internal quality including chemical compositions, microscopic structure and nonmetalic inclusion of test materials. We have analyzed machining characteristics including tensile strength value, impact value, hardness value etcs. Test materials are usd martensitic heat resisting steel, STR11 and STS420J2. The obtined results are as follows : 1. In analyzing internal quality, STR11 and STR420J2 have typical martensite structure and a minute needle-shaped structure. 2. Tensile strength and reduction of area and hardness value are large STR11 than STS420J2. But elongation impact are smaller STR11 than STS420J2. 3. Fracture surface of tensile speciman is ductile in STR11 and STS420J2.

• The Plant Pathology Journal
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• v.24 no.1
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• pp.84-86
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• 2008

Field surveys and specimen collections of the rust fungal pathogen Gymnosporangium were carried out for 15 years from 1985 through 1999 in various locations of Korea. Macroscopic and microscopic examinations of morphological characteristics of aecia from the collected specimens revealed that Gymnosporangium globosum is the causal agent of American hawthorn rust disease on Crataegus pinnatifida and C. pinnatifida varmajor. The host plants are new for this rust fungus. G. globosum was found only in Gyeonggi and Chungbuk provinces, indicating that its distribution in Korea is limited. This is a first full description on morphological characters of aecia of G. globosum in Korea.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.14 no.5
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• pp.49-54
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• 2005

An experimental Investigation was performed to study the characteristics of Electro-Rheological fluid flow in a horizontal rectangular tube with or without D.C electric field control. First, the microscopic behavior of the ER suspension structure between rectangular tube brass electrodes for the stationary ER nut(i and flow of the ER fluid was investigated by flow visualization. The flow of the ER fluid between fluid rectangular tube was solved experimental using the constitutive equation for a Bingham fluid. ER fluid is made silicon oil mixed with $0.2wt\%$ starch having hydrous particles. Velocity distributions of the ER fluids were obtained by particle image velocimetry measuring those of the clusters using an image processing technique.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.7
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• pp.49-54
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• 2010

The cryogenic ball milling was performed on carbon nanotubes (CNTs) at an extremely low temperature to increase the dispersion of CNTs. The effects of milling speed and time on the deagglomeration and structural changes of CNTs were studied. FESEM was used to analyze the dispersion and the change of particle size before and after milling process. Transmission electron microscopic (TEM) analysis was also investigated the effect of cryogenic ball milling on the morphological characteristics of CNTs. The structural changes by the cryogenic ball milling process were further confirmed by x-ray diffraction (XRD) and Raman spectroscopic analysis. The results showed that the agglomeration of CNTs was significantly reduced and amorphous structure was observed at high milling speed. However, the milling time has no great effect on the dispersion property and structural change of CNTs compared with milling speed.

• Tunnel and Underground Space
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• v.19 no.4
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• pp.318-327
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• 2009

Accelerated weathering tests was executed to understand the physical characteristics of rocks in Dokdo. For the tests rock samples including trachytic andestes, andesite dyke and ash tuff were taken in place. Double soxhlet extractor and peristatic pump were used for accelerating the weathering processes. After the tests for 4 months, the variations of superficial structure, microscopic structure and strength of rock samples were observed.