• 한국해양공학회지
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• 제32권6호
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• pp.492-501
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• 2018

The following results were obtained from a series of studies to accumulate data to reduce the coefficient of friction for press dies by performing tribological tests before and after the UNSM treatment of SM45C. The UNSM-treated material had a nano-size surface texture, high surface hardness, and large and deep compressive residual stress formation. Even when the load was doubled, the small amount of abrasion, small weight of the abrasion, and width and depth of the abrasion did not increase as much as those for untreated materials. When loads of 5 N, 7.5 N, and 10 N were applied to the untreated material of SM45C, the coefficient of friction was approximately 0.76-0.78. With the large specimen, a value of 0.72-0.78 was maintained at a load of 50 N despite the differences in the size of the wear specimen and working load. Tribological tests of large specimens of SM45C treated with UNSM under tribological conditions of 100 N and 50 N showed that the frictional coefficient and time constant stably converged between 0.7 and 0.8. The friction coefficients of the small specimens treated with UNSM showed values between 0.78 and 0.75 under 5 N, 7.5 N, and 10 N. The friction coefficients of the SM45C treated with UNSM were comparable to each other.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.159-160
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• 2002

To investigate the humidity effect on tribological behaviors of Si-DLC/DLC multi-layers, the samples were prepared using a system consisted of an ion-gun for deposition DLC films and a balanced magnetron sputter for introducing silicon atoms to Si-DLC films. The Si-DLC/DLC multi-layers were composed of pure DLC films and Si-incorporated DLC films alternatively and had different bilayer numbers. Hardness and residual stress were drastically decreased through the formation of Si-DLC/DLC multi-layers compared to those of the pure and Si-incorporated DLC films. Wear results obtained under the various humidity conditions (<10%, $40{\sim}50%$, and >85%) showed that the pure DLC film was largely depended on the humidity while the Si-DLC and the Si-DLC/DLC multi-layers were little affected by the environmental humidity. Although friction coefficients of all samples were increased with the relative humidity, the multi-layer films showed relatively lower friction coefficients that those of the single films.

• 한국정밀공학회지
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• 제25권11호
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• pp.119-125
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• 2008

The objective of this study was to compare micro-scale friction coefficients with and without synovial fluid, and micro-scale measurements were performed using atomic force microscopy (AFM) with a $5{\mu}m$ spherical probe. Four cylindrical cartilage specimens were harvested from two fresh bovine humeral heads (4-6 months old). $Average{\pm}standard$ deviation values of the micro-scale AFM frictional coefficients calculated from the liner fit of friction versus normal force was $0.177{\pm}0.012$ and $0.130{\pm}0.010$ with and without synovial fluid coating on AFM probe respectively, showing its reduction by ${\sim}27%$ with synovial fluid. To the best of our knowledge, this experimental study investigates the first such comparisons of frictional response of articular cartilage with and without synovial fluid coating on AFM probe, and provides significant insights into the role of synovial fluid in the articular cartilage friction and lubrication independently of the confounding effect of fluid pressurization in the articular cartilage.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2003년도 학술대회지
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• pp.164-180
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• 2003

A series of cooperative interlaboratory tests (round robins) was conducted in 1997, 1998, 1999, 2000, 2001, 2002 and 2003 by the DIN 51834 Working Group on Tribological Tests in Translatory Oscillation Apparatus. The statistical analysis of these test results shows the influence of cleaning solvent, machine model and evaluation criteria on the tribological properties of the lubricants tested. Coefficients of friction and wear results are ranked according to the effects of ten different cleaning solvents, where isopropanol gave the lowest values and isoparaffin solvents the highest. The effect of machine model on coefficients of friction varied from about $0.2\%\;to\;0.9\%$ of the mean. Wear results were not affected. The tests also showed that the seizure criteria and methods of measuring wear required for in the test procedure do not provide a suitable measure of the tribological properties of some lubricants. The precision was Improved by introducing a grease apply caliper as well as an increased stroke to 1,5 mm and running-in. The temperature does not affect the precision of the oil test procedure.

• 로봇학회논문지
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• 제13권3호
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• pp.174-181
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• 2018

For a mobile robot that travels along a terrain consisting of various geology, information on tire force and friction coefficient between ground and wheel is an important factor. In order to estimate the lateral force between ground and wheel, a lot of information about the model and the surrounding environment of the vehicle is required in conventional method. Therefore, in this paper, we are going to estimate lateral force through simple model (Minimal Argument Lateral Slip Curve, MALSC) using only minimum data with high estimation accuracy and to improve estimation reliability of the friction coefficient by using the estimated lateral force data. Simulation is carried out to analyze the correlation between the longitudinal and transverse friction coefficients and slip angles to design the simplified lateral force estimation model by analysing simulation data and to apply it to the actual field environment. In order to verify the validity of the equation, estimation results are compared with the conventional method through simulation. Also, the results of the lateral force and friction coefficient estimation are compared from both the conventional method and the proposed model through the actual robot running experiments.

• Tribology and Lubricants
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• 제23권4호
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• pp.170-174
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• 2007

Wear and scuffing tests were conducted using friction and wear measurement of piston rings and cylinder blocks in low friction diesel engine. The frictional forces, wear amounts and cycles to scuffing in boundary lubricated sliding condition were measured using the reciprocating wear tester. The cylinder blocks were used as reciprocating specimens, and the piston rings with several coatings were used as fixed pin. Several coatings were used such as DLC, TiN, Cr-ceramic and TiAlN in order to improve the tribological characteristics. From the tests wear volume of piston ring surfaces applied various coatings were compared. During the tests coefficients of friction were monitored. Test results showed that DLC coatings showed good tribological properties. TiN and Cr-ceramic coated rings showed good wear resistance properties but produced high friction.

• Journal of Advanced Marine Engineering and Technology
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• 제38권10호
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• pp.1237-1243
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• 2014

The aim of the present paper is to analyze the friction and mass flow in a rough microchannel using Lattice Boltzmann Method (LBM). The LBM is a kinetic method based on the particle distribution function, so it can be fruitfully used to study the flow dependence on Knudsen number including slip velocity, pressure drop in rough microchannel. The surface roughness elements are taken to be considered as a series of circular shaped riblets throughout the channel with relative roughness height up to a maximum 10% of the channel height. The friction coefficients in terms of Poiseuille number (Pn), mass flow rate and the flow behaviors have been discussed in order to study the effect of surface roughness in the slip flow regime at Knudsen number (Kn), ranging from 0.01 to 0.10. It is seen that the friction factor and the flow behaviors in a rough microchannel strongly depend on the rarefaction effect and the relative roughness height. The friction factor in a rough microchannel is higher than that in smooth channel but the mass flow rate is lower than that of smooth channel. Moreover, it is seen that the friction factor increased with relative roughness height but decreased with increasing the Kundsen number (Kn) whereas the mass flow rate is decreased with increasing both of surface roughness height and Knudsen number.

• Tribology and Lubricants
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• 제11권4호
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• pp.28-34
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• 1995

PTFE has good mechanical and chemical stability at wide temperature range, and more over, shows a low value of friction coefficient. On the other hand, it shows cold flow and high wear rate. However, these short comings can be overcome by adding various fillers. In this experiment, PTFE and polyimide powder were mixed into composite and its tribological characteristics was investigated. 100% polyimide was also tested for comparison. The countefface material was a stainless steel (SUS304). Friction and wear tester of ring-on-block type was used at room temperature and under atmosphere. After the wear test, the worn surfaces were examined by optical microscope. The test results show that PTFE-polyimide composite generates. the wear transfer film on both sides of the friction surfaces, and, the friction coefficient and the wear rates are relatively low. 100% polyimide generated little wear transfer films, showed high friction and wear rates, and also showed some problems of vibration and noise. It even damaged the stainless steel countefface. It was concluded that 100% polyimide does not generate transfer film well because its shear resistanbe is high and it stickslips, thus, friction coefficients and wear rates are high. In case of PTFE-polyimide composite, on the other hand, transfer film containing sufficient PTFE adheres and remains on both wear surfaces well enough because PTFE has low shear resistance. Polyimide particles in the composite were proved to be able to bear normal load and does not show stick-slip because they are covered with transfer film containing much PTFE.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제29회 춘계학술대회
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• pp.7-13
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• 1999

An experimental study was performed to discover the effect of silver coating on the frictional behavior of SM45C steel at sliding surfaces. Pure silver was coated the SM45C disk surfaces by a thermal evaporation method. Experiments using a pin-on-disk test-rig was performed under dry air and various humidity conditions. Friction coefficients increased to a high and unstable value after failure of coating, and friction coefficients increased with increasing the thickness of silver coated layer. But optimum coating thickness was not observed.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.163-164
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• 2002

This paper describes a new carbon film that afford superlubricity (i.e, friction coefficients of 0.001- 0.005) and superlow wear rates (i.e., $10^{-11}-10^{-10}mm^3/N.m$) to sliding metallic and ceramic surfaces, when tested in inert test environments. The wear life of these films are more than 1000 km even under very high contact pressures (i.e., 1-3 GPa) and at a wide range of sliding velocities (i.e., 0.1 to 2 m/s). They are produced in a plasma enhanced chemical vapor deposition system at room temperature using highly hydrogenated gas discharge plasmas. Extensive research has shown that films grown in highly hydrogenated gas discharge plasmas (i.e., hydrogen-to-carbon ratio of 6 and above) provide superlow friction and wear coefficients. In full paper, specific conditions under which superlubricity can be achieved in carbon films will be discussed.and a mechanistic model will be proposed to explain the superlubricity of new carbon films.