• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2004.11a
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• pp.17-24
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• 2004

Surrface texturing of tribological application is another attractive technology of friction reducing. Also, reduction of friction is therefore considered to be a necessary requirement for improved efficiency of machine. In this paper attempts to investigate the effect of density for micro-scale dimple pattern using photolithography on bearing steel flat mated with pin-on-disk. We demonstrated the lubrication mechanism for a Stribeck curve, which has a relationship between the friction coefficient and a dimensionless parameter for lubrication condition. It is found that friction coefficient is depended on the density of surface pattern. It was thus verified that micro-scale dimple could affect the friction reduction considerably under mixed and hydrodynamic lubrication conditions from based on friction map. Lubrication condition regime has an influence on the friction coefficient induced the density of micro dimple.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.180-184
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• 2004

The tribological behavior of carbon epoxy composites whose surfaces have many small grooves of $100\mu m$ width was experimentally investigated with respect to the sliding direction against groove orientation, surface pressure (P) and velocity (V). The wear mechanism of the composites was observed to calculate the wear volume with respect to the friction coefficient using scanning electron microscopic (SEM). Experimental results show that the abrasive wear is dominant wear mechanism for the grooved composite surface and the friction and wear are greatly reduced when the sliding direction is parallel to the axis of groove because abrasive particles are removed through the grooves effectively.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.3 s.234
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• pp.411-417
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• 2005

Surface texturing of tribological application is another attractive technology of friction reducing. Also, reduction of friction is therefore considered to be a necessary requirement for improved efficiency of machine. In this paper attempts to investigate the effect of density for micro-scale dimple pattern using photolithography on bearing steel flat mated with pin-on-disk. We demonstrated the lubrication mechanism for a Stribeck curve, which has a relationship between the friction coefficient and a dimensionless parameter for lubrication condition. It is found that friction coefficient is depended on the density of surface pattern. It was thus verified that micro-scale dimple could affect the friction reduction considerably under mixed and hydrodynamic lubrication conditions from based on friction map. Lubrication condition regime has an influence on the friction coefficient induced the density of micro dimple.

• Laser Solutions
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• v.18 no.4
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• pp.6-11
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• 2015

Specially designed and 3D printed samples were prepared and joined by a diode laser source. To increase the strength of joining and reliability of samples, the surface was patterned by using a 3D printer. The joining surface was prepared as hemispherical shape with no-patterns, 0.5mm pitch, 0.75mm pitch and 1mm pitch. The optical properties of samples were measured by using an integrated sphere where classical Kubelka-Munk theory and modified Richard-Mudgetts theory for the analysis applied. Scanning speed was set at 500mm/min and laser power was varied between 9 and 10watts for the preliminary joining characteristic analysis.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.338-338
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• 2012

사파이어 ($Al_2O_3$)는 높은 밴드갭 에너지 (~19.5 eV)를 가진 물질로서 우수한 내마모성, 강도, 전기 절연성 및 안정한 화학적 특성을 갖고 발광다이오드 기판, 보석재료 등 각종 산업 및 기술적 분야에서 널리 사용되고 있다. 특히, 플립칩 발광다이오드 구조의 경우 광추출효율을 향상시키기 위해 높은 투과도를 갖는 사파이어 기판이 요구되어 왔으며, 지금까지 건식/습식식각방법을 이용한 사파이어 표면에 마이크로 크기의 심한 거칠기 또는 요철이 형성된 나노크기의 격자구조를 형성시키는 연구가 진행되어 오고 있다. 그 중, 나노 크기의 격자구조는 공기에서 반도체 기판까지 선형적인 유효굴절률 분포를 갖기 때문에 표면에서 생기는 Fresnel 반사 손실을 줄일 수 있다. 이러한 구조를 형성하기 위해서는 식각 마스크가 필요한데, 형성 방법으로 레이저 간섭 리소그래피, 전자빔 리소그래피, 나노임프린트 리소그래피 등이 있으나, 비싼 가격과 복잡한 공정 절차 등의 단점을 지니고 있다. 따라서 본 연구에서는 식각 마스크 패턴을 위해, 보다 저렴하고 간단한 실리카 나노구 및 열적응집 금 나노 입자를 이용하였다. 양면 폴리싱 c-plane 사파이어 기판을 사용하였고, 단일 층의 주기적인 실리카 나노구를 기판 표면에 스핀코팅에 의해 도포한 후 유도결합플라즈마 식각 장비를 이용하여 식각하여 주기적인 패턴을 갖는 렌즈모양의 격자구조를 형성하였다. 그리고 주기적으로 형성된 격자 위에 열 증착기를 이용하여 금 박막을 증착한 후 급속열적어닐닝(rapid thermal annealing)을 이용하여 열처리함으로써 비주기적인 금 나노입자를 형성시켰다. 형성된 금 나노패턴을 이용하여 동일한 조건으로 식각함으로써 광대역 및 전방향성 높은 투과도를 갖는 원뿔 모양의 사파이어 나노구조를 제작하였다. 제작된 샘플의 패턴 및 식각 형상은 전자현미경을 사용하여 관찰하였으며, UV-vis-NIR 분광광도계 (spectrophotometer)를 사용하여 투과율을 측정하였다. 렌즈 모양 표면 위에 원뿔모양의 나노구조를 갖는 사파이어 기판은 일반적인 사파이어 기판보다 향상된 투과율 특성을 보였다.

• Journal of the korean academy of Pediatric Dentistry
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• v.41 no.2
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• pp.125-133
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• 2014

The purpose of this study was to investigate the effect of various surface treatment methods on the shear bond strength of orthodontic brackets in vitro. Ninety six specimens, 6 mm in diameter and 5 mm in height, were made with composite resin ($Filtek^{TM}$ Z350 XT, 3M ESPE, USA) and treated with an aging procedure. After aging, the specimens were randomly separated in six groups: (1) control with no surface treatment, (2) 37% phosphoric acid gel, (3) 4% hydrofluoric acid gel, (4) sodium bicarbonate particle abrasion, (5) diamond bur, and (6) 1 W carbon dioxide laser for 5s. The metal brackets were bonded to composite surfaces by means of an orthodontic adhesive (Transbond XT, 3M Unitek, USA). Shear bond strength values were evaluated with a universal testing machine (R&B Inc., Korea). Analysis of variance showed a significant difference between the groups. Group 5 had the highest mean shear bond strength (11.9 MPa), followed by group 6 (11.1 MPa). Among the experimental groups, group 2 resulted in the weakest mean shear bond strength (5.22 MPa). The results of this study suggest that the repair shear bond strength of the aged composite resin was acceptable by surface treatment with a carbon dioxide laser.

• Journal of the Korean Society for Railway
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• v.20 no.2
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• pp.234-240
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• 2017

In this study, the influences of rail surface roughness on dynamic wheel-rail forces currently employed in conventional lines were assessed by performing field measurements according to grinding of rail surface roughness. The influence of the grinding effect was evaluated using a previous empirical prediction model for dynamic wheel-rail forces; model includes first-order derivatives of QI (Quality Index) and vehicle velocity. The theoretical dynamic wheel-rail force determined using the previous prediction equation was analyzed using the QI, which decreased due to rail grinding as determined through field measurements. At a constant track support stiffness, an increase in the QI caused an increase in dynamic wheel-rail forces. Further, it can be inferred that the results of dynamic wheel-rail analysis obtained using the measured data, such as the variation of QI due to rail grinding, can be used to predict the peak dynamic forces. Therefore, it is obvious that the optimum amount of rail grinding can be determined by considering the QI, that was regarding an operation characteristics of the target track (vehicle velocity and wheel load).

• Journal of dental hygiene science
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• v.11 no.5
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• pp.405-410
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• 2011

The aim of this study was to evaluate antibacterial effect of Cl coated titanium. To coat the Cl on the titanium, first, the titanium was modified by blasting treatment with hydroxyapatite and alumina powder. Anodization process was completed using electrolyte solution of 0.04 M ${\beta}$-glycerol phosphate disodium salt n-hydrate, 0.4 M calcium acetate n-hydrate and 1 M NaCl on the condition of 250 voltages for 3 min. Surface morphology and elements' observation were performed with scanning electron microscopy and energy dispersive spectroscopy and surface profiler was used to analyze the surface roughness. Antibacterial effect was evaluated by film adhesion method. The anodized titanium after blasting showed dimpled surface contained the Cl. Surface average roughness of these surfaces had significantly higher compared to polished titanium. Result of antibacterial test showed that anodized titanium after blasting had an enhanced antibacterial effect compared to the polished titanium. Therefore, these results suggested that titanium contained Cl by anodization after blasting had a rough surface as well as antibacterial effect.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.8
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• pp.1051-1057
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• 2013

In this study, an automatic surface-strain measurement system called "ASIAS-bio" has been developed. This system can be used even in cases in which it is very difficult to apply a regular grid pattern necessary for measuring surface-strain, such as curved or uneven surfaces; surfaces damaged by corrosion or contamination; or soft materials such as rubber, foam, and biological tissues. This system works independently of the measurement conditions including the material and its surface condition, grid pattern and size, grid marking method, and degree of deformation. A comparison between the strain distributions of the sheet metal parts measured by using this system and those obtained by a commercial system showed that this system was sufficiently reliable. In addition, the deformation of the swine joint capsule and human knee skin was measured by using this system to demonstrate its usefulness.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.47.2-47.2
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• 2010

For reducing outer reflection in mono-crystalline silicon solar cell, wet texturing process has been adapted for long period of time. Nowadays mixed solution with potassium hydroxide and isopropyl alcohol is used in silicon surface texturing by most manufacturers. In the process of silicon texturing, etch rate is very critical for effective texturing. Several parameters influence the result of texturing. Most of all, temperature, process time and concentration of potassium hydroxide can be classified as important factors. In this paper, temperature, process time and concentration of potassium hydroxide were set as major parameters and 3-level test matrix was created by using robust design for the optimized condition. The process optimization in terms of lowest reflection and stable etch rate can be traced by using robust design method.