• Tribology and Lubricants
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• v.16 no.6
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• pp.477-483
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• 2000

Rolling contact fatigue (RCF) tests were performed for two kinds of commercial silicon nitride balls using 4-Ball rolling contact fatigue life tester under EHL condition (Λ=8.9) and boundary lubrication condition (Λ=0.2). All the test balls were finished up to the dimensional accuracy of Grade 5 defined in KS B 2001 (Steel Balls for Ball Bearings) with a size of 8.731 mm. RCF tests were then conducted under the initial theoretical maximum contact stress 6.63 GPa and the spindle speed 10,000 rpm. All the test balls were not failed until 3.75 $\times$ 107 contact cycles and wear tracks of test balls were not conspicuous under EHL condition (Λ= 8.9). In the operations of low lambda regime (Λ= 0.2), all the test balls were surface damaged and high rolling wear resistance was achievable in fully densified using MgO 1 wt% and HIPed balls. Rolling wear of silicon nitride balls under boundary lubrication condition depend mainly on grain size and intergranular phase content of silicon nitride balls.

• Korean Journal of Materials Research
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• v.12 no.8
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• pp.669-675
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• 2002

CrN film coated by AIP method, improved the mechanical properties (Hardness, Roughness, wear and fatigue) of Ti-6Al-4V alloy. The properties were studied using GXRD, XPS, Hardness, Roughness, wear and fatigue testers. CrN thin film thickness was about 7.5$\mu\textrm{m}$ and grew with (111) orientation. Hardness of CrN thin film was very high (Hv 1390) and roughness of the surface layer was greatly improved (Ra=0.063$\mu\textrm{m}$) compared with matrix alloy (Ra=0.321$\mu\textrm{m}$). Such changes of hardness and roughness could be contributed to improving the wear resistance and fatigue life. Striation like pattern with dimples and voids, a typical fatigue fracture mode, was observed throughout the specimen.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1996.04a
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• pp.122-127
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• 1996

In this paper, the effects of the film tinckness, pre-treatment and testing load on. the tribological characteristics have been studied. During the "Ring on-Disk" testing period silica-gel was used to remove the effect of humidity. As a result, increasing the film thickness revealed prolonged wear life, in the case or reasl the testing loads the dynamic friction coefficient was decreased gradually but in regarding the wear life, an intermideate contact pressure (4kgf/mm${2}$) revealed the maximum value. In regarding the surface protuberance friction an intermediate value of area fraction (60%) revealed maximum wear life. In this paper, the qualitative model in regarding the variation of the friction coefficient andworn depth was presented.presented.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.1109-1112
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• 2001

In the grinding process, the edge of shape is very important to evaluate the surface roughness and the precision of dimension. To keep precision of product, parameters with respect to the amount of wheel wear have to limit by grinding condition. In this paper, we measured variation of grinding force to seek the grinding characteristics by the amount of wheel wear in surface grinding. Also, we find out that how these condition give influence to wheel life.

• Journal of the Korean Society of Costume
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• v.25
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• pp.183-199
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• 1995

Among many different approaches of study of history of Kokuryo clothing culture, this study attempted to understand the costume by including political , militarial , economical , cultural , and religious aspects of Kokuryo society. It also included pictures in mural tumbs and old studies in Kokuryo costume. Clothing culture related to political life clearly differenciated social status by restricting styles and colors of clothes according to peoples social status. Generally people in high social status wore clothes with detailed decorations invariety of colors, and also used more fabrics than people in low social status. Costume was also affected by military life style that needed to meet the vigorous physical activities. High rank worriors wore iron scaled shielded clothes with red decoration on it which identified different ranks of the worriors. Economy also contributed it role to affect the clothing styles in Kokuryo. Based on old studies of costume, this study focused on people's life styles that included hunting and weaving . Hunting clothes were differentiated by decorating wit feathers . Jowoguan(조우관) is one of the examples. Since weaving was a major economic power or factor, silk and flax were very popular. People even used those fabrics to pay tax. Regarding cultural aspect , this study emphasized on song and dance wear along with active wear. Song and dance wear specially decorated with poka dots, however men and women wear were claryly distinguished. Unlike other clothes that were restricted in colors and styles, song and dance wear were decorated in variety of colors. Lastly this study presents religious aspects of Kokuryo costume . Monks wore black clothing (내의) that was influenced from China and the Western Regions(서역). To emphasize their religious power, Gods in the pictures of mural tumbs wore clothes with wings and feathers. God of fire and agriculture wore simple dresses without much decorations which represented simple life style of working class.

• Journal of the Korean Society of Costume
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• v.25
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• pp.185-199
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• 1995

Among many different approches of study of history of Kokuryo clothing culture, this study attempted to understand the costume by in-cluding political, militarial, economical, cul-tural, and religious aspects of Kokuryo society. It also included pictures in mural tumbs and old studies in Kokuryo costume. Clothing culture related to political life clearly differenciated social status by restricting styles and colors of clothes accord-ing to peoples social status. Generally people in high social status wore clothes with detailed decorations in variety of colors, and also used more fabrics than people in low social status. Costume was also affected by military life style that needed to meet the vigorous physi-cal activities. High rank worriors wore iron scaled shielded clothes with red decoration on it which identified different ranks of the worriors. Economy also contributed its role to affect the clothing styles in Kokuryo. Baseed on old studies of costume, this study focused on people's life styles that included hunting and weaving. Hunting clothes were differentiated by decorating with feathers. Jowoguan is one of the exemples. Since weaving was a major economic power or factor, silk and flax were very popular. People even used those fabrics to pay tax. Regarding cultural aspect, this study emphasized on song and dance wear along with active wear. Song and dance wear specially decorated with poka dots, however means and womens wear were claryly dis-tinguished. Unlike other clothes that were re-stricted in colors and styles, song and dance wear were decorated in variety of colors. Lastly this study presents religious aspects of Kokuryo costume. Monks wore black cloth-ing that was influenced from China and the Western Regions. To emphasize their religious power. Gods in the pictures of mural tumbs wore clothes with wings and feathers. God of five and agriculture wore simple dresses without much decorations which represented simple life style of working class.

• Tribology and Lubricants
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• v.30 no.5
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• pp.271-277
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• 2014

Hydraulic reciprocating seals have been widely used to prevent fluid leakage and to provide lubricant film on counter surface in various hydraulic system. The degradation of the seal may cause the catastrophic failure of the hydraulic system. To assess the durability of the seals and the compatibility with counter surface, accelerated life testing (ALT) has been typically employed from industry. However, ALT often takes up to a few months to cause a failure of the seals, and therefore, there is a need to develop more efficient ALT methods. In this work, the degradation characteristics of polyurethane (PU) seals from field test are investigated and they are compared to those from the component and bench tests, with an aim to contribute to the development of ALT method. From the comparison of the cross-sectional profiles of the sealing surface of the PU specimens before and after the tests, both wear and compression set are found to be responsible for degradation of the PU seals. It is also shown that the major wear mechanisms of the PU seals from the field is abrasive wear and formation of pits. The component and bench tests performed in this work are shown to reproduce such wear mechanisms, and therefore, those test methods can be used as an ALT method for PU seals. In particular, the bench test proposed in this work may be effectively utilized to assess the durability and the compatibility of the seals with the counter surface. The results of this work are expected to aid in the design of ALT for PU seal.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.560-567
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• 2011

Wheel and rail wear is a fundamental and complicate problem in railway field. The life of railway is usually limited by wear. The wheel surface is subjected to high normal and tangential contact stress. The removal of material from the surface by wear is function of the sliding and contact stress. In the present paper, the wear characteristic depended on slip rate, contact pressure and temperature are investigated and is used to twin disc tester. The result shows that the wear in wheel-rail interface is remarkably depended on slip rate and contact pressure.

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.1000-1007
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• 2011

Wheel and rail wear is a fundamental and complicate problem in railway field. The life of railway is usually limited by wear. The wheel surface is subjected to high normal and tangential contact stress. The removal of material from the surface by wear is function of the sliding and contact stress. In the present paper, the wear characteristic depended on slip rate, contact pressure and temperature are investigated and is used to twin disc tester. The result shows that the wear in wheel-rail interface is remarkably depended on slip rate and contact pressure.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.05a
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• pp.355-358
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• 2003

Recently, micro forming process technology have been developed since the size of machine parts become the crucial factor for minimizing of products in general electronic products. Most small machine parts consist of gear and rotation axis and the wear by mechanical contact is known as the primary factor for life reduction of high precision machine part. Lots of studies for mechanical wear and friction have been reported and many researches of MEMS technology have been studied recently. But just few studies for wear of micro or milli sized machine part have teen implemented. In this research, the wear equation is suggested according to the contact shape of axial part in micro or milli sized machine part. And wear analysis model which can predict the magnitude of wear through this suggested equation with numerical analysis program.