• Elastomers and Composites
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• v.36 no.2
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• pp.121-129
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• 2001

The friction characteristics of natural rubber plates under various conditions including sliding speed, normal force, hardness, lubrication conditions and thickness of plate are analyzed experimentally. The frictional force and normal force are measured by a tester pin and a load ceil with strain gages. Experimental results suggest that the coefficient of friction decreases with increasing the hardness of rubber and decreasing the thickness of plate. The effect of sliding speed is not significant over the speed range employed. The coefficient of friction is found to be about 0.1 under oil lubrication condition and varies from 0.9 to 3.9 under no lubrication condition.

• Tribology and Lubricants
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• v.38 no.6
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• pp.261-266
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• 2022

Notably, laser surface patterning facilitates tribological applications under lubricated sliding contacts. Consequently, a special pattern that can reduce the coefficient of friction under contact is considered necessary for improved machine efficiency. However, inappropriate pattern designs produce higher friction coefficients and cannot reduce friction. In this study, we use cast iron pins as specimens to investigate their friction and wear characteristics. Moreover, we experimentally investigate the correlation between the friction reduction effect and the design of groove crosshatch patterns fabricated with various angles and widths. We conduct a friction test using a pin-on-disc type tribometer under grease lubrication to study the friction reduction effect of the specimens, and we observe that the average coefficient of friction changes with the crosshatch angle and width. The experiment reveals that grooved crosshatch specimens with a crosshatch angle of 135°maximize friction reduction. The coefficient of friction of the groove specimens with a width of 120 ㎛ is lower than that of the specimens with a width of 200?. The friction reduction effect of the width of the groove is attributed to the density of the groove pattern. Thus, grooved crosshatch patterns can be designed to maximize friction reduction, and the friction property of a grooved crosshatch pattern is found to be related to its width and angle.

• Tribology and Lubricants
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• v.39 no.4
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• pp.148-153
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• 2023

Laser surface dimple patterning is a method of laser surface texturing to reduce lubrication sliding friction. The dimple pattern improves friction properties by reserving lubricant and trapping worn particles. This surface texturing technology can reduce coefficients of friction and extend the service life by applying a uniform load to the surface of the material. This study investigates the friction properties using PMMA, a highly compatible polymer material, as a specimen. We observe the friction properties of untextured specimens by processing specimens with dimple pattern densities of 5 and 10 on the surface area using laser. Dimple pattern density affects the coefficient of friction. We present the following friction property results using a pin-on-disc sliding friction test under saline lubrication. The coefficients of friction for the dimple patterned specimens are lower than those for the untextured specimens. As the normal load and sliding speed increase, the coefficients of friction of the dimple pattern specimens decrease differently from those of the untextured specimens. The specimen with a dimple pattern density of 5 at a normal load of 24.5 N and a sliding speed of 0.22 m/s has the best friction properties. Notably, different friction properties are exhibited depending on the dimple pattern densities.

• Journal of the Korean Society for Advanced Composite Structures
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• v.3 no.1
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• pp.8-15
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• 2012

The initial clamping forces of high strength bolts depending on different faying surface conditions drop within 1,000 hours regardless of loading, any other external force or loosening of the nut. This study is focused on an expectation model for relaxation of high strength bolt, which is confined to creep on coated faying surfaces after initial clamping. The range of this experiment is limited to estimate the relaxation of bolted joints coated by inorganic zinc primer. The candidate bolts were dacro-coated tension control bolts. The parameters of coated thickness for the faying surface were 96, 168,and $226{\mu}m$ respectively. From experiments, it exhibited that the logarithmic function for creep strain was derived due to the parameter of coating thickness. By using the creep strain, subsequently the quantitative model for estimating long term relaxation of high strength bolt can be taken with the elapsed time. The experimental results showed that the relaxation after the initial clamping of high strength bolt rose to a much higher range from 10% to 18% due to creep of the coating as the coating thickness was increased. This study showed that the clamping force reflecting relaxation after the elapse of constant time can be calculated from the initial clamping force of high strength bolt.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.10a
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• pp.159-163
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• 2001

마찰구동은 다른 구동방식에 비하여 구조가 간단하고, 기계적인 정도를 얻기 쉬우며, 백래쉬 등에 기인하는 비선형 요소인 로스트모션이 없고 관성이 작아 구동력이 작은 이점이 있다. 그 반면에 접촉부에서 미끄럼이 발생하여 큰 구동력을 얻기 어렵고 마찰저항에 의하여 마멸이 생기는 결점이 지적되고 있다. 본 연구에서는 초정밀가공기용 위치결정기구로 마찰구동기구를 사용하기 위하여 위치 결정도에 관한 설계, 구동력의 설계 및 재료의 선택에 관하 여 분석하고 시작품을 제작하여 특성을 연구하였다.

• 제어로봇시스템학회:학술대회논문집
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• 1988.10a
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• pp.315-320
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• 1988

This paper considers modelling and control of ABS(Anti-skid Brake System) which avoids dangerous wheel locking due to excessive brake pressure during the vehicle braking. The brake pressure is controlled by on and off's of solenoid valves via the variation of the wheel circumferential deceleration measured using tacho-sensors. The dynamic model between the brake pressure and the wheel acceleration of a vehicle is mathematically derived. The computer simulation shows that the threshold value of the on-off control is critical to the performance of the ABS.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1992.04a
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• pp.335-340
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• 1992

유압 시스템(System)은 원동기의 기계적 에너지를 유압펌프가 작동유를 압력 에너지의 형태로변환 시켜 이것을 유합 실린더(Cylinder)등의 엑츄에이터(Actuator)가 다시 기계적 에너지로 변환시켜 부하 를 구동하게한다. 상용차(NT-1, KH 등)용 파워스티어링(Power Steering)에 장착되는 Vane Type Oil Pump (이하 VOP)가 바로 이와같은 역할을 담당하고 있다. 본 연구에서는 VOP의 성능과 관련되어지는 주요 제원(Parameter)인 미끄럼부에서의 틈새, 작동유점도, 압력변화, 회전수 등을 다양하게 변화시키는 모의실험(Simulation)을 통하여각각의 조건하에서얻어지는 누설 유량과 체적효율을 수치적 으로 예측하고 이것을 주요제원을 고려하여 해석해서 정량적인 값을 얻는 것을 목적으로한다.

• Tribology and Lubricants
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• v.15 no.2
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• pp.178-183
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• 1999

This paper presents friction and wear related results of thermite and gas pressure welded rails under various environmental contact conditions. A welded rail which was fabricated by thermite welding and gas pressure one has been tested over full range of test conditions in a pin-on-disk wear testing machine. The results show that the friction coefficient and wear rates of a welded rail are heavily dependent on the contact pressures and sliding environments for two welding methods such as thermite and gas pressure weldings.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.133-136
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• 2008

The cost of repairing the deterioration of concrete structures due to corrosion of the reinforcement steel has been the prominent figure in the maintenacne of the reinforced-concrete infrastructures. As an alternative material to steel reinforcement, the use of Glass Fiber Reinforced Polymer (GFRP) bar in concrete is being actively studied for the high resistance of chemical environment and high strength to weight ratio properties of GFRP. However, there remain various aspects of GFRP properties that still need to be studied before the standard design criteria can be established. One of the imminent issues is the bond between GFRP and concrete. In this study, the bond-behavior of GFRP bars in concrete is investigated via the pullout test with varying parameters: surface condition of GFRP bars and concrete compression strength. And the local bond-stress model of GFRP rabars with applying monotonc load was also derived from the present test.

• Applied Chemistry for Engineering
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• v.5 no.6
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• pp.990-997
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• 1994

The vulcanized NR and blend films were prepared with mixing of natural rubber latex (NRL) and methyl methacrylated grafted latex(MGL) with various additives by dipping process. It was investigated the basic properties of vulcanized NR films that is optimum condition of the mature time, swelling degree, cure time at $110^{\circ}C$, and measured the mechanical properties of tensile strength and elongation of its condition. In order to identify the surface structure and the slip properties of blend films contact angles and static and kinetic friction coefficient were measured. Contact angles were decreased with increment of blend ratio of MGL, and static and kinetic friction coefficient were decreased rapidly for the NR/MG and NR-d-MG films than for the NR films. From the results, NR/MG and NR-d-MG films has slip's reinforcement in skin contact surface with increased of blend ratio of MGL.