• 전기학회논문지
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• 제62권2호
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• pp.284-287
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• 2013

In this work, we have fabricated TiC films by using unbalanced magnetron sputtering method with graphite and Ti targets for contact strip application of electric railway. TiC films were deposited with various substrate temperatures. We investigated various properties of TiC films prepared with various substrate temperatures, such as the hardness, surface roughness, friction coefficient, resistivity, FESEM (Field Emission Scanning Electron Microscopy), HRTEM (High Resolution Transmission Electron Microscopy) and XPS (X-ray Photoelectron Spectroscopy). The hardness and friction coefficient properties of TiC films were improved with increasing substrate temperature. These results indicate that the improvement of hardness and resistivity is related to the increase of sp2 clusters in TiC films. And also, the resistivity value of TiC films were decreased with increasing substrate temperature.

• 한국세라믹학회지
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• 제35권9호
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• pp.974-980
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• 1998

This study is concerned with the production of carbon fiber reinforced carbon(C/C) with polyaromatic mesophase pitch as matrix precursor and with the investigation of friction-wear characteristics in ambient air using a constant speed type of friction tester. The main problem in using the polyaromatic mesophase as the matrix precursor is the high viscosity which may limit the complete impregnation of the fiber preform in the vacuum. To solve these problems two dimensional carbon fiber fabrics were infiltrated with meso-phase pitch in the pitch impregnator. After the impregnation and the heat treatment process. C/C com-posites were characterized by density porosity to monitor the influence of high pressure and temperature. It showed that the bulk density was increased and the apparent porosity and the density increasing rate was reduced as repeating the impregnation the carbonization and the heat treatment. The friction-wear charac-teristics of C/C composites were investigated by measuring the average friction coefficient and the specific wear rate as functions friction speed and friction pressure using a constant speed type of friction tester. C/C composite4s showed the average friction coefficient to be reduced as increasing the friction speed and the friction pressure.

• Tribology and Lubricants
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• 제25권1호
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• pp.61-65
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• 2009

Tribological properties of the semi-metallic friction materials containing different solid lubricants (graphite, $WS_2$, $MoS_2$) were investigated. The friction materials were fabricated with an experimental formulation and tested with gray cast iron disks. Results showed that graphite contributed to stabilize the friction coefficient during run-in processes. Also, graphite provided better fade resistance than that of $WS_2$ and $MoS_2$. At intermediate temperature ranges, however, friction materials with $WS_2$ or $MoS_2$ maintained higher friction effectiveness than that of graphite. On the other hand, friction materials containing $MoS_2$ showed increased wear rates than that with graphite or $WS_2$. Friction materials with proper combinations of two solid lubricants showed better friction and wear properties than that of the friction materials containing single solid lubricant.

• Tribology and Lubricants
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• 제39권3호
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• pp.87-93
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• 2023

Nanofluids are dispersions of particles smaller than 100 nm (nanoparticles) in base fluids. They exhibit high thermal conductivity and are mainly applied in cooling applications. Nanolubricants use nanoparticles in base oils as lubricant additives, and have recently started gathering increased attention owing to their potential to improve the tribological and thermal performances of various machinery. Nanolubricants reduce friction and wear, mainly by the action of nanoparticles; however, only a few studies have considered the rheological properties of lubricants. In this study, we adopt a parallel slider bearing model that does not generate geometrical wedge effects, and conduct thermohydrodynamic (THD) analyses to evaluate the effect of higher thermal conductivity and viscosity, which are the main rheological properties of nanolubricants, on the lubrication performances. We use a commercial computational fluid dynamics code, FLUENT, to numerically analyze the continuity, Navier-Stokes, energy equations with temperature-viscosity-density relations, and thermal conductivity and viscosity models of the nanolubricant. The results show the temperature and pressure distributions, load-carrying capacity (LCC), and friction force for three film-temperature boundary conditions (FTBCs). The effects of the higher thermal conductivity and viscosity of the nanolubricant on the LCC and friction force differ significantly, according to the FTBC. The thermal conductivity increases with temperature, improving the cooling performance, reducing LCC, and slightly increasing the friction. The increase in viscosity increases both the LCC and friction. The analysis method in this study can be applied to develop nanolubricants that can improve the tribological and cooling performances of various equipment; however, additional research is required on this topic.

• Journal of Advanced Marine Engineering and Technology
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• 제25권3호
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• pp.552-562
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• 2001

Measurement of average of heat transfer and friction coefficients were obtained with air flowing through electrically heated ducts having square, rectangular(aspect ration, 5), and triangular cross section for range of surface temperature from $540^{\circ}$to $1780^{\circ}$ R and Reynolds number from 1000 to 330,000. The results indicates that the effect of heat flux on correlations of the average heat transfer and friction coefficients is similar to that obtained for circular tubes in previous investigation and was nearly eliminated by evaluating the physical properties and density of the air a film temperature halfway between the average surface and fluid bulk temperatures, With the Nusselt and Reynolds numbers on the hydraulic diameter of the ducts, the data for the noncircular ducts could be represented by the same equations obtained in the previous investigation for circular tubes. Correlation of the average difference between the surface corner and midwall temperatures for the square duct was in agreement with predicted values from a previous analysis. However, for the rectangular and triangular ducts, the measured corner temperature was greater by approximately 20 and 35 percent, respectively, than the values predicted by analysis.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.972-975
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• 2002

An understanding of tribological behavior in CMP(Chemical Mechanical Polishing) is one of the most important things to reveal the mechanism of material removal. In CMP, the contact type is thought to be semi-direct, elastohydrodynamic contact type from the Stribeck diagram, which is a combination of solid-solid direct contact and hydrodynamic lubrication with thin liquid film. This study is focused on the decay of friction force during CMP from two points of view, one of which is change of the real contact area and the other is the decrease of the elastic modulus of the pad caused by the increase of the temperature during CMP Experiments are implemented with elastic modulus measuring system and tool dynamometer. Results show that the decay of friction force during CMP results from the decrease of the real contact pressure working on an abrasive, which is induced by the decrease of elastic modulus of pad caused by the increase of temperature. And, the phenomenon is thought to be happen specially in the case that the weight concentration of abrasive in slurry is small enough.

• Journal of Welding and Joining
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• 제35권3호
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• pp.44-51
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• 2017

In the present study, AA 5083-O plates are joined by friction stir welding technique. A universal milling machine was used to perform the welding process of the work-pieces which were fixed on the proper position by a vice. The joints were friction stir welded by two tools with different pin profiles; cylindrical threaded pin and tapered smooth one at different rotational speed values; 400 rpm and 630 rpm, and different welding speed values; 100 mm/min and 160 mm/min. During FSW of each joint, the temperature was measured by infra-red thermal image camera. The welded joints were inspected by visually as well as by the macro- and microstructure evolutions. Furthermore, the joints were tested for measuring the hardness and the tensile strength to study the effect of changing the FSW parameters on the mechanical properties. The results show that increasing the rotational speed results in increasing the peak temperature, while increasing the welding speed results in decreasing the peak temperature for the same tool pin profile. Defect free welds were obtained at lower rotational speed by the threaded tool profile. Moreover, the threaded tool pin profile gives superior mechanical properties at lower rotational speed.

• 소성∙가공
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• 제32권4호
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• pp.215-220
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• 2023

In this study, the correction process of stress-strain curves obtained from hot compression test is introduced since the barreling induced by friction and adiabatic heat generation induced by plastic work occur under high strain rate. A shear friction factor was quantitatively estimated by measuring the dimension of barreling and temperature rise due to adiabatic heat generation was directly measured during compression test. Thereafter, the stress-strain curves were re-evaluated by introducing several equations to correct the effects of the friction and temperature rise. It was found that adiabatic factor at strain rate of 10/s is in the range of about 0.5 to 0.75 for Nimonic 80A and decreases as the assigned temperature increases.

• Tribology and Lubricants
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• 제38권6호
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• pp.267-273
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• 2022

Surface texturing is the latest technology for processing grooves or dimples on the friction surface of a machine. When appropriately applied, it can reduce friction and significantly increase durability. Despite many studies over the past 20 years, most are isothermal (ISO) analyses in which the viscosity of the lubricant is constant. In practice, the viscosity changes significantly owing to the heat generated by the viscous shear of the lubricant and film-temperature boundary condition (FTBC). Although many thermohydrodynamic (THD) analyses have been performed on various sliding bearings, only few results for surface-textured bearings have been reported. This study investigates the effects of the FTBC and groove number on the THD lubrication characteristics of a surface-textured parallel thrust bearing with multiple rectangular grooves. The continuity, Navier-Stokes, and energy equations with temperature-viscosity-density relations are numerically analyzed using a commercial computational fluid dynamics code, FLUENT. The results show the pressure and temperature distributions, variations of load-carrying capacity (LCC), and friction force with four FTBCs. The FTBCs greatly influence the lubrication characteristics of surface-textured parallel thrust bearings. A groove number that maximizes the LCC exists, which depends on the FTBC. ISO analysis overestimates the LCC but underestimates friction reduction. Additional analysis of various temperature boundary conditions is required for practical applications.

• Tribology and Lubricants
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• 제30권3호
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• pp.189-198
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• 2014

This paper presents the results of an experimental investigation of the correlation between the lubrication characteristics of an engine and its fuel economy. Improving the lubrication characteristics of the engine oil is one of the most efficient ways to improve a car's fuel economy. The methods to accomplish this include lowering the viscosity, adding a friction modifier and optimizing the shear stability index of a viscosity index improver. In addition, it is necessary to use different methods to reduce the friction to individual lubrication areas, because different lubrication regimes are used for different engine parts. The experimental investigation in this study is based on design of experiments ; this paper presents the results of a modified Sequence VID test, which is an ASTM standard test used to measure the effects of automotive engine oils on the fuel economy of passenger cars. The results demonstrate the effects of the following lubrication factors on the fuel economy : the low temperature cranking viscosity, high-temperature high shear (HTHS) viscosity, friction modifier, polymer type and shear stability index of the viscosity index improver. Moreover, this study involves an analysis of variance based on design of experiments. The test results show that the HTHS viscosity, friction modifier and shear stability index of the viscosity index improver are more effective than the other factors. Therefore, lowering the viscosity, adding a friction modifier and optimizing the shear stability index of a viscosity index improver should be considered to improve fuel economy.