• Tribology and Lubricants
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• v.33 no.5
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• pp.220-227
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• 2017

In this work, carbon nanotube and nano-size alumina particle are exploited as additive for lubrication experiment. We used pin-on-disk type tribometer to investigate the tribological characteristics of lubricants with respect to additives and rotational speed. We conducted more than 15 trials of tribotests for two hours for each specimen to obtain stable and accurate frictional force and to create measurable wear track on the substrate. We conducted tests at the boundary/mixed lubrication regime to evaluate the influence of additives on the tribological characteristics. We found that the friction coefficient decreased as the rotational speed increased and as additives were added. In particular, the reduction of friction by adding additives was more significant at low rotational speed than at high rotational speed. We speculate that the additives helped to separate and protect the two contacting surfaces at low speed, while the influence of additives was not significant at high speed since sufficiently thick lubricant film was formed. The wear of the substrate was also reduced by adding additives to the lubricant. However, in contrast to friction, the amount of wear at high rotational speed was less when alumina particles were added to the lubricant than the amount of wear at low speed. We speculate that the increased wear at low rotational speed is as a result of the intermittent abrasive wear caused by alumina particles with uneven shape, while the reduced wear at high speed is as a result of sufficient film thickness which prevented the abrasive wear.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.332-338
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• 1999

A coupled thermal-mechanical analysis has been presented for the thermal distortions of the ventilated disk brakes during IS braking operations. The FEM results show that the bendings and distortions of the disk toward the left side are decreased, but the sinusoidal distortion of the disk rubbing surface along the arc length of the vent hole is highly increased by increasing the convective air cooling effects, which is heavily related to the squeal, wear and micro-thermal crackings at the rubbing surfaces due to uneven dissipation rates of friction heatings.

• Tribology and Lubricants
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• v.15 no.2
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• pp.199-205
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• 1999

Using a coupled thermal-mechanical analysis, the thermal distortion of the ventilated disk brakes has been investigated based on the air cooling effects during 15 braking operations. The FEM results show that the bendings and distortions of the disk toward the left side are decreased, but the sinusoidal distortion of the disk rubbing surface along the arc length of the vent hole is highly increased by increasing the convective air cooling effects, which is heavily related to the squeal, wear and micro-thermal crackings at the rubbing surfaces due to uneven dissipation rates of friction heatings.

• Tribology and Lubricants
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• v.22 no.3
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• pp.149-154
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• 2006

This paper presents the braking friction and wears on the rubbing surfaces of a friction pad-disk brake. In this study, four friction disk specimens are sampled from unused and used disks in which are taken from the disk brake system when the friction induced vibration and noise problems have been occurred during a braking period at a running period of 10,000 km, 20,000 km, and 30,000 km in random. The experimental results indicate that the tribological characteristics of an unused disk brake shows equal and stable as a friction coefficient and temperature distributions during a braking friction/wear test period including a total friction mode from the start to running periods. But the used disk brake shows unstable and uneven friction modes between an outside and inside rubbing surfaces of a disk brake in terms of a friction coefficient and wears. This may lead to a friction induced friction vibration and noise problems of a used disk brake.

• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.6
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• pp.1-8
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• 2004

In this paper we present the effects that valve train design parameters and operating conditions have on the valve rotation properties of a diesel engine. Rotation of intake and exhaust valves are very closely related to the long term durability of diesel engines. of the valves do not rotate even at a rated engine speed, it causes the uneven wear of the valve seat and valve head contact area, which eventually shortens the engine life. Because the rated speed of a diesel engine is relatively lower than that of a gasoline engine, the operating condition of a diesel engine produces tough environment for valve rotation. Therefore, the valve rotation is an important problem which should be solved in the early stage of engine development. In this study, we developed a new technique to measure the valve rotation and shaking motion simultaneously using three proximity sensors. Valve train rotating properties of a diesel engine were measured under various engine operating conditions.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.2
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• pp.184-193
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• 2006

Rotation of intake and exhaust valves are very closely related to the long term durability of automotive engines. If the valves do not rotate even at a rated engine speed, it causes the uneven wear of the valve seat and valve head contact area, which eventually shortens the engine life. A principle of valve rotation mechanism was presumed based on some findings from experiments, and computer programs were developed to simulate the valve rotation phenomena. In this study we investigated the valve rotation mechanism by using the computer simulation models.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.05a
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• pp.886-889
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• 2014

차량이 도로를 달리는데 있어서 절대적으로 꼭 필요한 타이어의 기능으로는 자동차의 하중을 지탱하고 자동차의 방향 전환 유지와, 노면 충격을 흡수 완화하며, 엔진의 구동력과 브레이킹 시 제동력을 노면에 전달하는 등의 기능이 있다. 이런 기능을 수행함에 있어 타이어의 상태는 안전과 직결된다고 볼 수 있다. 주행 중 운전자가 아무리 운전을 잘한다고 하더라도 타이어의 불량으로 인한 사고를 방지할 수는 없다. 자동차의 주행 안정성을 위한 타이어의 문제 중 타이어의 편마모는 운전자의 운전습관과 휠 얼라이먼트의 이상 등으로 타이어의 특정 부위가 마모되는 증상을 일컫는데, 현재까지 점검 방법으로는 정비사가 타이어를 눈과 손으로 점검하여 판단하고 있어서 점검하는 기준이 주관적이며, 정확하게 검증할 수 없는 것이 현실이다. 이에 본 논문에서는 현실의 애매모호한 주관적인 검증기준의 단점을 보완하고자 타이어의 실제 이미지를 디지털 영상처리 기법을 사용하여 각 타이어의 마모 정도를 체크하여 편마모를 객관적으로 점검할 수 있는 시스템을 설계하고자 한다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.501-504
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• 2014

자동차의 하중을 지탱하고 자동차의 방향 전환 유지와 노면 충격을 흡수 완화하며, 엔진의 구동력과 브레이크 작동 시 제동력을 노면에 전달하는 등의 기능을 수행하는 타이어의 상태는 안전과 직결되어 있다고 볼 수 있다. 주행 중 타이어의 불량으로 인한 사고는 무시할 수 없는 부분을 차지한다. 타이어의 편마모는 주행 안전성을 위한 타이어의 문제 중 하나로 운전자의 운전습관과 휠얼라이먼트의 이상 등으로 타이어의 특정 부위가 마모되는 증상을 말하는데, 객관적으로 정확하게 검증할 수 있는 측정방법이 없는 것이 현실이다. 본 논문에서는 현실의 주관적인 검증기준의 단점을 보완하고 키넥트 센서를 이용하여 각 타이어의 마모 정도를 체크하여 편마모를 객관적으로 검증할 수 있는 시스템을 설계하고자 한다.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.11a
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• pp.52-53
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• 2020

The thermal spray coating process is being used to protect the metals and alloys from wear, abrasion, fatigue, tribology, and corrosion failure. Therefore, in the present study, Al and Zn was deposited by plasma arc thermal spray process onto the steel substrate and their performance was assessed. The bond adhesion result shows that Al coating has higher value attributed to compact, dense, and less porous compared to Zn coating which contain defects/pores and uneven morphology assessed by scanning electron microscopy (SEM). Electrochemical results show that the Al coating exhibited higher impedance value compared to Zn in artificial ocean water solution at prolonged exposure periods. However, both coatings show the increment in polarization resistance with exposure periods which reveal that porosity of coatings is filled by the corrosion products.

• Journal of the Korean Ceramic Society
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• v.35 no.7
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• pp.721-725
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• 1998

In this study solid-phase sintered silicon caribide samples composed of SiC powder having boron and car-bon black as additives were prepared by pressureless sintering at $1950^{\circ}C$. The bending strength the frac-ture toughness and the specific werar rate of the samples were examined and the micro structures of the broken and the worn surface were observed by SEM to understand the relationship between the tri-bological charcteristics and the micro structure. Additionally the relationship between the micro struc-tures and the tribological characteristics of the samples for the frictional opponents SiC and $Al_{2}O_{3}$ pins were investigated Conclusions are as follows ; 1. The specific were rate of the samples for the SiC pin was larger than that for the $Al_{2}O_{3}$ pin. HOwever the specific wear rate for the $Al_{2}O_{3}$ pin was increased about 6,45 times as that for the SiC pin under the load increasing. 2. The specific wear rate of the SiC pin was larger than that of the $Al_{2}O_{3}$ pin. owever the specific wear rate of the $Al_{2}O_{3}$ pin was increased about 4 times as that of the SiC pin under the load increasing 3. The micro stucture of the worn surface showed a flat face without cracks in the case that the frictional opponents has the low friction coefficient but in the case of without cracks in the case that the frictional opponents has the low friction coefficient but in the case of the high friction coefficient the micro structure of the worn surface showed an uneven face having spread-ed cracks. 4. The tribological characteristics of thesolid-phase sintered SiC samples was similar to that of li-quid-phase sintered ones when the pin having the high friction coefficient was used.