• The korean journal of orthodontics
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• v.28 no.1 s.66
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• pp.123-133
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• 1998

The effectiveness of TiN ion-plating was examined with TiN ion-plated Co-Cr wires(.016“, .016”x.022“) on three different types of bracket(TiN ion-plated metal bracket ceramic bracket and plastic bracket). Maximum static frictional forces and characteristic curves obtained from the frictional characteristic graph, were compared and surface roughness of wires and bracket slots before and after friction experiment was observed by SEM. The obtained results were as follows $\cdot$The frictional forces of TiN ion-plated wires were significantly lower than those of non ion-plated wires(p<0.05). $\cdot$On the effect of wire shape, the frictional forces of round wires were significantly lower than those of rectangular wires(p<0.05) $\cdot$As the result of the SEM observation on the wires and bracket slots after the friction experiment the surface of non ion-plated wires was rougher than that of TiN ion-plated ones. $\cdot$The difference between the static frictional forces and the kinetic frictional forces was not significant in case of the TiN ion-plated round ins, but the static frictional forces were a little higher than the kinetic frictional forces in the TiN ion-plated rectangular wires. $\cdot$The static frictional forces were much higher than the kinetic frictional forces in the case of non ion-plated wires.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1992.10a
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• pp.68-72
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• 1992

자동차 및 각종 판재 성형시 성형율을 향상시키는 방법에는 신소재 개발, 금형기술개발, 접촉부의 마찰을 줄여 주기 위한 윤활 등등이 있겠으나 손쉽게 공구다이 상하에 비드를 설치하여 판재를 성형할 경우 미끄럼 저항의 균형을 이루어 주름 억제와 두께분포가 보다 균일해지며 스프링백 현상 등으로 인한 성형 후 치수 불량 등을 주어 판재성형율을 향상시키는데 기여할 수 있다. 본 연구에서는 펀치가 판재를 성형하기 위해 진행됨에 따라 공구다이와 펀치간의 접촉각도가 변하게 되는 점을 고려하여 인출 각도변화에 따른 인출특성 및 마찰계수 변화등을 알아보고자 하며 원형 형태의 환저비드, 단일원형비드, 이중원형 비드의 종류와 크기변화 및 비드좌우 모서리 변화, 공구다이모서리변화, 블랭크가압력 변화, 비드 전진깊이 변화, 비드통 과 후 재료의 기계적 성질 변화등 인출 특성에 영향을 미치는 인자들을 변화시켜나가며 이에 따르는 인출특성을 Data Bank화 시켜 비드 종류나 형상에 따른 금형설계의 기초자료를 제공하고자 한다.

• Water for future
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• v.28 no.2
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• pp.155-168
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• 1995

The present paper discusses the traditional empirical equations of friction factor or cross-sectional mean velocity of open channel flow and suggests the new form of friction factor equation. Dimensional analysis is conducted for the possible forms of traditional empirical equations in order to satisfy the dimensional equality, and new forms of empirical equations are presented with introducing equivalent roughness height. Considering the distribution of friction factor against Reynolds number which has a similar characteristics to that of smooth turbulent flow in circular pipe, the friction factor equation of rectangular open channel flow is developed by modifying the friction factor equation of circular pipe flow for the region of smooth turbulent flow. The equations including the dimensionally-corrected empirical equations are tested against Bazin's laboratory experiments.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.6
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• pp.491-498
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• 2011

The structural vibration due to earthquake or outside impact causes serious problem for building safety. A dynamic model of a friction damper which can be constructed and installed easily is needed to reduce the vibration of the building. In this paper, the experimental equation of a circular friction damper is derived and designed for reduction of a earthquake vibration of a building. The developed experimental equation is defined to simply design the capacity on design of the circular friction damper based on the results of the performance test. Finally this experimental equation can be used for the design of a circular friction damper.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.5
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• pp.165-172
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• 1993

On the basis of Nikuradse laboratory experiments conducted in circular pipe with uniform roughness, five flow regimes are defined with respect to the characteristics of boundary layer such as laminar, transition laminar, smooth turbulent, transition turbulent and rough turbulent flows. Two cases are found for the transition laminar flow: one for the transition between laminar flow and smooth turbulent flow and the other for the one between laminar flow and rough turbulent flow. They all can be clearly determined by the relative roughness or the ratio of pipe diameter to the roughness. Explicit functions are developed for the estimation of pipe friction factor for the various flow conditions including turbulent flow regimes, which have excellent agreement with the Nikuradse laboratory data.

• Proceedings of the Korean Fiber Society Conference
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• 1998.10a
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• pp.260-263
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• 1998

섬유단면이 원형이 아닌 L, T, H, W, Y, I 등과 같은 모양을 가지는 이형단면 섬유(shaped fiber)는 그 모양으로 인해 원형단면 섬유와는 다른 광택, 마찰계수, 촉감, 굽힘강도 등을 가지고 여러 가지 용도로 쓰이고 있다. 이형단면 섬유의 용융방사시 같은 면적을 가진 원형단면 섬유와 비교해 증가된 표면적은 열과 물질 전달을 증가시키고 고화를 촉진한다. (중략)

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.10a
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• pp.130-131
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• 2010

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.3
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• pp.291-299
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• 2010

Aspect-ratio-based numerical analysis is carried out to investigate the air-side convective heat transfer characteristics in compact heat exchangers with circular tubes and flat tubes-plate fins. The RNG $k-{\varepsilon}$ model is adopted for turbulence analysis. The numerical analysis is carried out for aspect ratios ranging from 3.06 to 5.44 and for Reynolds numbers ranging from 1,000 to 10,000. The calculated results indicate a correlation between the friction factor and Colburn j factor in the compact heat exchanger system for the range of aspect ratios under consideration. The results obtained for circular tubes and flat tubes-plate fins in this study can be utilized to realize the optimal design of an air conditioning system.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.4
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• pp.658-666
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• 1992

In developing computer-aided design technology for optimization of stamping die design, it has been an important issue to treat the frictional constraint acting on the blank holder surface. The main goal of this work is to establish database of draw bead restraint force and clarify friction characteristic for various automotive sheet steels, which is essential in developing friction algorithm that can be used for CAD of stamping die design. Draw bead friction tester is used to evaluate the various parameters that affect the draw restraint force and the coefficient of friction for the cold rolled and the coated sheet steels such as drawing rate, lubricant type, surface property of material, etc.

• The korean journal of orthodontics
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• v.30 no.5 s.82
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• pp.613-623
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• 2000

The purpose of this study was to amount of the frictional forces with the brackets and wires, ligation methods, dry/wet, offsets, interbracket distances, velocity and to compare them each other by different conditions. This study tested 0.018'x0.025' slot sized 8 types of orthodontic bracket systems and 0.016', 0.016'x0.022' sized stainless steel, NiTi, Cu-NiTi orthodontic wires. One cuspid bracket were positioned on the slide glass and archwire was engaged into bracket and ligated with elastomeric modules. The values of frictional forces were measured with the instron universal testing machine. The results were as follows; 1. Polycrystalline ceramic bracket had the highest mean frictional forces and followed and by ceramic reinforced plastic bracket, metal bracket, plastic bracket with metal slot, monocrystalline ceramic bracket, single bracket, self-ligating bracket, friction free bracket in descending order. The self-ligating bracket showed low frictional forces in the round wires and high frictional forces in the rectangular wires. 2. Stainless steel wires had the least frictional forces and followed by NiTi, Cu-NiTi wires in descending order. Round wires had lower frictional forces then that of rectangular wires. 3. The stainless steel ligation method had significantly greater mean frictional forces them the elastomeric module ligation method. 4. Artificial saliva statistically increased the frictional forces in stainless steel wire, NiTi wire and Cu-NiTi wire. 5. There was a statistically significant difference with offset change 6. There was no statistically significant difference with interbracket distance in stainless steel wires but a significant difference in NiTi wires as the interbracket was decreased. 7 There was no statistically significant difference with velocity change. From the above findings, self-ligating bracket, stainless steel wires and the elastomeric module ligation method might be effective than any other materials to reduce the frictional forces in the orthodontic treatment and can be correlated to clinical situations seen in orthodontic patient care.