• 한국자동차공학회논문집
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• 제11권5호
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• pp.112-118
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• 2003

The friction coefficients of the rubber for clutch master cylinder were experimentally measured in this study. The cylindrical rubber samples for primary cup-seal and secondary cup-seal were tested against the aluminum or the steel plates of master cylinder housing under the various conditions of brake oil temperatures and normal loads. Dry sliding friction coefficients were also measured under various load conditions. The test revealed following results. First, the friction coefficient under fluid lubrication condition in general decreases, as the oil temperature or normal load increases. Second, the steel plate of low surface roughness yielded comparatively low friction coefficient on the range of 0.30∼0.67. On the other hand, the aluminum plate of high surface roughness yielded high friction coefficient on the range of 0.31∼1.15. Third, the friction coefficient of dry surface contact decreases as the normal load increases. This is contrary to the general principle of friction coefficient between metal plates.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2014년도 추계학술대회 논문집
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• pp.182-183
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• 2014

Hemispherical dimples with diameter, ø=$60{\mu}m$ and depth, d= $30{\mu}m$ were created on the metal and ceramics surfaces using INYA 10 watt Laser of 1064 nm wavelength. This study reports the influence of dimple pitch on friction and wear behavior rather than dimple size, depth and density. LST was performed on the specimens with dimple pitch and density in the range of 80 to-$200{\mu}m$ and 44 to 7 %, respectively. Surface topography was analyzed by using roughness measurement, scanning electron microscopy (SEM), and optical microscopy. Friction and wear characteristics were analyzed on textured surfaces at lubricating environment to observe the effect of surface texturing on reduction of friction and wear. Reduction on coefficient of friction was achieved by more than 70% due to the dual behavior of dimples as wear (debris) traps and lubricant reservoirs. Wear reduced significantly for the textured surface as compared to the polished surface. Moreover, the friction coefficient of the textured specimens reduced with increasing load and speed which may be attributed to the transition of lubrication regime.

• Tribology and Lubricants
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• 제24권4호
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• pp.163-169
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• 2008

Tribological properties of ceramic brake discs were investigated using a commercial friction material. The discs were manufactured by liquid silicon infiltration (LSI) into a C-C preform. The disc surface was modified by two different methods, producing sliding surfaces with chopped carbon fibers and carbon felt. In addition, the composition of the surface was also changed. Friction characteristics of the discs were examined using a 1/5 scale dynamometer. Results showed that the type and composition of the disc surface significantly affected the level of braking effectiveness and high temperature brake performance. The discs with felt surfaces showed higher friction levels than those with chopped fiber surfaces and SiC tended to increase the friction level while C lowered the friction coefficient. The ceramic disc was more sensitive to the deceleration rate than gray iron, showing high speed sensitivity.

• Tribology and Lubricants
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• 제31권2호
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• pp.62-68
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• 2015

A magnetorheological (MR) fluid is a smart material whose rheological behavior can be controlled by varying the parameters of the applied magnetic field. Because the damping force and shear force of an MR fluid can be controlled using a magnetic field, it is widely employed in many industrial applications, such as in vehicle vibration control, powertrains, high-precision grinding processes, valves, and seals. However, the characteristics of friction caused by iron particles inside the MR fluid need to be understood and improved so that it can be used in practical applications. Surface process technologies such as polytetrafluoroethylene (PTFE) coatings and diamond-like carbon (DLC) coatings are widely used to improve the surface friction properties. This study examines the friction characteristics of an MR fluid with different surface process technologies such as PTFE coatings and DLC coatings, by using a reciprocating friction tester. The coefficients of friction are in the following descending order: MR fluid without any coating, MR fluid with a DLC coating, and MR fluid with a PTFE coating. Scanning electron microscopy is used to observe the worn surfaces before and after the experiment. In addition, energy dispersive X-ray spectroscopy is used to analyze the chemical composition of the worn surface. Through a comparison of the results, the friction characteristics of the MR fluid based on the different coating technologies are analyzed.

• Tribology and Lubricants
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• 제37권5호
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• pp.151-163
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• 2021

Since the discovery of single-layer graphene, exploiting graphene's excellent physical/chemical properties in tribology systems has been a topic of interest in academia over the last few decades. There is no doubt that understanding the underlying friction mechanism of graphite should precede this. Even now, new properties of graphene are being reported in academia, and based on this, studies exploring the origins of graphene's surface properties and friction characteristics in a wide range of scales are also being performed. From the perspective of lubrication engineering, graphene research can be largely divided into studies that 1) reveal its basic friction mechanism at the nanoscale and 2) explore its application in macroscale sliding systems. At the nanoscale, the basic friction mechanism of graphene is mainly due to its atomic thickness. In this paper, the various research on the nanoscale friction and surface characteristics of graphene is reviewed. Graphene surface properties, such as wettability and surface energy and the basic friction mechanisms of graphene attributed to adhesion, electronphonon scattering, bending stiffness, and the underlying substrate, are summarized. Further, we provide the research outcomes on the superlubricity of graphene. Finally, the potential application and challenges of the superlubricity of graphene are highlighted. Through this, we intend to provide summarized information to researchers interested in the tribological properties of graphene and help set the direction of future research.

• 한국기계가공학회지
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• 제16권2호
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• pp.63-68
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• 2017

Friction occurs when surfaces that are in contact move relatively between solid surfaces, fluid layers, and materials slide against one another. This friction force causes wear on the contact surface, generates unwanted heat and leads to performance degradation. Thus, much research has been performed to avoid friction reduction. Among these studies, a textured surface that has micro patterns on the surface has drawn attention for its ability to reduce friction. A mathematical model is developed in this study to examine friction reduction due to the texture of a surface. Numerical simulations are carried out with respect to various factors such as the shape aspect ratio and texture depth of a diamond-shaped texture in the hydrodynamic lubrication regime. As a result, a shape aspect ratio of 1 is best for friction reduction.

• 한국기계가공학회지
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• 제19권5호
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• pp.38-44
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• 2020

Surface texturing of micro-dimples has been used in many manufacturing industries to reduce friction between two sliding contacted surfaces. Surface texturing decreases the frictional force owing to minimizing of the sliding contact area. In this paper, micro-dimples have been fabricated on an Al6061-T6 surface using a two-frequency elliptical vibration texturing (TFEVT) method. A high-frequency of 18 kHz and low-frequency of 250 Hz were applied to an elliptically-vibrated tool holder. The Stribeck curve was plotted to analyze the friction coefficient trends. Furthermore, the representative wetting index, such as the water contact angle (WCA), was measured by considering the friction coefficient. WCA is associated with micro-dimple density and associated parameters. Consequently, the dimpled surfaces with a low friction coefficient exhibited a relatively high WCA in the feed direction. According to the Stribeck curve, the dimpled surfaces demonstrate superior friction performance for mixed-film lubrication compared to the non-textured surface.

• Journal of Welding and Joining
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• 제24권1호
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• pp.43-49
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• 2006

This paper describes the friction surface modification which has been successfully developed with the friction stir welding recently There are several problems including just position control and backlash in conventional friction surface modification system. Therefore it has been developed the friction surface modification system which has been controlled precisely both position and force by driving hydraulic cylinder in this paper. The mechtrode rotation speed(N) and feeding speed(Vz), travel speed(Vx,y) are of critical importance for the width and thickness of the coating in friction surfacing process. But there is no theoretical method of determining interrelations between process parameters affect the coating width and thickness. As a result of DOE(design of experiment) with developed system, the coating thickness and width seemed to decrease according to increase the mechtrode rotation speed(N) and traveling speed(Vx,y), to decrease feeding speed(Vz) apparently. However as the result of regression analysis the main effect was only the mechtrode rotation speed in the coating thickness.

• 대한조선학회논문집
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• 제56권6호
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• pp.532-540
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• 2019

This study describes a test method for evaluating the ice friction and abrasion performance of polar coatings. The evaluation methods of physical properties of general coatings for ocean-going vessels and polar coatings for ice-going vessels were investigated and their limitations were analyzed. We have also reviewed previous researches related to the development of polar paints and confirmed the necessity of developing test techniques. A flat steel plate was coated with several types of commercial coating, and cold model ice was used to cause ice friction and abrasion events between coated surface and ice. For evaluation of ice friction and abrasion performances, test procedures such as measurement of coating surface roughness, measurement of frictional force using model ice, implementation of ice abrasion and drying of coating surface were developed. The friction and abrasion characteristics of each coating are analyzed and summarized through the change of friction force and roughness data according to the progress of ice abrasion.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2006년도 추계학술대회
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• pp.515-518
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• 2006

This paper presents the friction and wear characteristics of contact type sealing unit for a water turbine of a small hydro-power generation, which Is to stop a leakage of a circulating water from a outside of an impeller to an inside of a rolling bearing. The surface wear strongly affect to the seal life of a mechanical face seal. In this study, the hardness of a stainless steel in which is a heat-treated is 892.8 in Vickers hardness and the hardness of silicone carbide of SiC is 714.1 in Vickers hardness. The surface hardness of a heat-treated stainless steel is 25% high compared with that of a ceramic material of SiC. The contact modes of rubbing surfaces aye a dry friction a water film friction and a mixed friction that is contaminated by a dust, silt and moistures, etc. These two factors of a contact rubbing modes and a material property are very important parameters on the tribological performance such as a friction and wear between a seal ring and a seal seat. The experimental result shows that the surface hardness of a seal material is very important on the friction coefficient and a wear volume. Thus, the results recommend higher hardness of a seal material, which may reduce a friction loss and increase a wear life of primary seal components