• Tribology and Lubricants
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• 제25권4호
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• pp.217-224
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• 2009

In this study, friction tests were carried out in order to investigate the friction behavior of textured surface in unlubricated state using ball-on-disk type apparatus. Test specimens were SUJ2 bearing steel ball and SM45C steel disk. Square arrays of circular micro-dimples were created on the surface of disk specimen by Nd:YAG Laser. Friction tests were performed for the disk specimen with various micro-dimple parameters and was also conducted for the variation of normal loads and relative velocities. The results showed that fiction coefficient of textured surface was lower than that of non-textured surface and the deeper depth of micro-dimple was, the lower friction coefficient obtained at the same diameter of micro-dimple in unlubricated state. Area density of micro-dimple had an effect on the friction coefficient. It was also found that friction coefficient generally decreased with the increase of normal load and relative velocity.

• Tribology and Lubricants
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• 제39권2호
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• pp.81-85
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• 2023

This study presents an experimental investigation of the effects of surface roughness on gas foil thrust bearing (GFTB) performance. A high-speed motor with the maximum speed of 80 krpm rotates a thrust runner and a pneumatic cylinder applies static loads to the test GFTB. When the motor speed increases and reaches a specific speed at which a hydrodynamic film pressure generated within the gap between the thrust runner and test GFTB is enough to support the applied static load, the thrust runner lifts off from the test GFTB and the friction mechanism changes from the boundary lubrication to the hydrodynamic lubrication. The experiment shows a series of lift-off test and load-carrying capacity test for two thrust runners with different surface roughnesses. For a constant static load of 15 N, thrust runner A with its lower surface roughness exhibits a higher start-up torque but lower lift-off torque than thrust runner B with a higher surface roughness. The load capacity test at a rotor speed of 60 krpm reveals that runner A results in a higher maximum load capacity than runner B. Runner A also shows a lower drag torque, friction coefficient, and bearing temperature than runner B at constant static loads. The results imply that maintaining a consistent surface roughness for a thrust runner may improve its static GFTB performance.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제30회 추계학술대회
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• pp.35-41
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• 1999

Friction and wear test was performed for nylon, acetal resin, and PTFE(polytetrafluoroethylene) under reciprocating dry sliding conditions against a steel counterpart. Friction coefficient and specific wear rate were analysed as a function of sliding distance and applied load. The worn surfaces of plate and disc specimens were observed using SEM(Scanning Electron Microscopy). The experimental results show that acetal resin exhibited lowest wear rates whereas PTFE possessed lowest friction coefficient. The prominent wear mechanisms found were adhesion and abrasion.

• 동력기계공학회지
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• 제18권6호
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• pp.174-179
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• 2014

The wear behavior of epoxy matrix composites filled with nano sized silica particles is discussed in this paper. Especially, the variation of the coefficient of friction and the specific wear rate under the various applied load and sliding velocity were investigated for these materials. Wear tests of pin-on-disc mode were carried out and followed by scanning electron microscope observations. The presence of silica filler in epoxy composites was demonstrated significant influence on the friction and wear behavior of epoxy nanocomposites. With the incorporation of silica filler into the epoxy matrix, reduction of the coefficient of friction and specific wear rate were identified. Wear mechanism was discussed by analyzing the worn surface by scanning electron microscope as well.

• Tribology and Lubricants
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• 제22권5호
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• pp.282-289
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• 2006

This paper is to investigate the wear behaviors of two type ceramics, $Al_{2}O_{3}\;and\;TiO_{2}$, by coated plasma thermal spray method under the lubricative environment. The lubricative environments are grease fluids, a general hydraulic fluids, and bearing fluids. The wear testing machine used a pin on disk type. Wear characteristics, which were friction force, friction coefficient and the specific wear rate, according to the lubricative environments were obtained at the four kinds of load and sliding velocity is 0.2 m/sec. After the wear experiments, the wear surfaces of the each test specimen were observed by a scanning electronic microscope.

• 한국정밀공학회지
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• 제18권7호
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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.

• 한국산학기술학회논문지
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• 제18권1호
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• pp.585-591
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• 2017

본 연구에서는 터보과급기의 성능을 저해하는 주요 인자 중 하나인 마찰손실에 대한 연구를 수행하였다. 실제 엔진에서 빈번하게 사용되는 저속 구간에서의 승용차용 터보과급기의 마찰손실 측정 장치를 개발하고, 30,000~90,000rpm의 저속 영역에서 작동하는 터보과급기의 마찰손실을 측정하였다. 플로팅 베어링 타입의 승용차용 터보과급기를 실험 대상으로 선정하였으며, 마찰손실 측정 장치는 구동 모터, 오일 공급 시스템, 커플링으로 구성되었다. 실제 차량의 저속 운전 상황을 모사할 수 있도록 설계, 제작되었고, 회전속도, 오일 온도 및 압력을 실험 변수로 선정하였다. 또한, 마찰손실 측정 장치는 로드셀을 사용하여 발생하는 마찰 토크를 직접 측정하여 마찰손실을 산출하였으며, 마그네틱 커플링을 통해 구동 모터의 동력을 터보과급기 축에 전달하고, 오일 공급 시스템을 오일 온도 및 압력을 조절하였다. 온도 $60^{\circ}C$와 $90^{\circ}C$, 압력 4bar의 오일을 공급하는 상태에서 터보과급기가 회전수 30,000~90,000rpm으로 작동할 때 터보과급기 회전속도 증가할 때 마찰손실은 증가하며, 대략적으로 과급기 회전속도의 1.4~1.8 지수승에 비례함을 보이고 있다. 또한 오일온도가 $60^{\circ}C$에서 $90^{\circ}C$로 증가할 때 마찰손실은 최소 41%, 최대 63% 감소하였다.

• 반도체디스플레이기술학회지
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• 제18권1호
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• pp.25-31
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• 2019

In this study, a new adhesion evaluating equipment and data processing methods were developed to overcome some limitations of existing evaluating equipment. Nano-diamond coated tool is a specimen of experiment. When applying frictional force and shear force on the specimen by a rotating polishing pad, delamination occurs at a moment. During each experiment, the vibration, load, and torque is obtained by accelerometer, loadcell and torque s+ kpensor. Frictional force and coefficient of friction are obtained by calculating torque and load. Based on FFT transformation, acceleration is processed and analyzed. As a result, the moment of delamination and the load at that time can be detected by the new developed equipment and measurement system. Finally, we call this load as an Adhesion force.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 하계학술대회 논문집 Vol.5 No.2
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• pp.1312-1315
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• 2004

Chemical Mechanical Polishing is referred to as a three body tribological system, because it includes two solids in relative motion and the slurry. On the assumption that the abrasives between the pad and the wafer could be a major reason of not only the friction force but also material removal during polishing. The friction force generated by the abrasives was inspected with the change of abrasive size and concentration in this paper. The variation of coefficient of friction with abrasive concentration and size could result from the condition of contact and load balance between wafer and abrasives carried by pad asperity. The simulation was performed in this paper and compared with the result of experiment. The material removal rate also estimated with abrasive concentration and size increasement.

• Tribology and Lubricants
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• 제31권4호
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• pp.183-188
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• 2015

This paper presents the experimental effects of lubricant with nanodiamond particles in sliding friction. In order to improve the performance of lubricants many additives are used, such as MoS₂, cadmium chloride, indium, sulfides, and phosphides. These additives are harmful to human health and to the environment, so alternatives are necessary. One such alternative is nanodiamond powder, which has a large surface area. In order to investigate the effect of nanodiamonds in lubricants under sliding friction, they are dispersed in the lubricant at a variety of concentrations (0 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%, and 1 wt%) using the matrix synthesis method. Friction and wear tests are performed according to the ASTM G99 method using a pin-on-disc tester at room temperature. The specimens used in this experiment are AISI 52100 ball bearings and AISI 1020 steel discs. During the test, lubricant mixed with nanodiamond is supplied constantly to keep the two bodies separated by a lubricant film. To maintain boundary lubrication, the speed is set to 0.18 m/s and a load of 294 N is applied to the disc through the pin. Results are recorded by using workbench software over the test duration of 10 minutes. Experimental results show that when the concentration of nanodiamond increases, the coefficient of friction decreases. However, above a nanodiamond concentration of 0.5 wt%, both the coefficient of friction and wear volume increase. From this experiment, the optimum concentration of nanodiamond showing a minimum coefficient of friction of 0.09 and minimum wear volume of 0.82 nm² was 0.5 wt%.