• Tribology and Lubricants
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• v.29 no.4
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• pp.242-247
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• 2013

This study aims to establish the fundamental basis for the design of materials used in high-speed trains, by using a lab-scale dynamometer to evaluate the characteristic behavior of metallic sintered friction materials in relation to the shape of graphite. The test results clearly demonstrate that when flake graphite and granular graphite are added equivalently, the average coefficient of friction is much lower, and it is less influenced by speed variation; moreover, friction wear is observed to be insignificantly low. Adding flake graphite increases the coefficient of friction, which leads to higher friction wear. In addition, the roughness of the disc surface was equivalent regardless of the shape of the graphite.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.9 s.240
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• pp.1276-1281
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• 2005

Compound semiconductors are the semiconductors composed of more than two chemical elements. Lithium Tantalate$K_I$ wafer is used for several optical devices, especially surface acoustic wave(SAW) device. Because of the lithography in SAW device process, $LiTaO_3$ polishing is needed. In this paper, the commercial slurries $(NALC02371^{TM},\; ILD1300^{TM},\;ceria slurry)$ used for chemical mechanical polishing(CMP) were tested, and the most suitable slurry was selected by measuring material removal rate and average centerline roughness$(R_a)$. From these result, it was proven that $ILD1300^{TM}$ was the most suitable slurry for $LiTaO_3$ wafer CMP due to the chemical reaction between solution in slurry and material.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.205-210
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• 2001

Fatigue crack growth tests were carried out using high manganese cast steel under constant amplitude loading. Average crystal grain sizes of the material are $200{\mu}m$ and $1000{\mu}m$. For this material, ${\Delta}K_{th}$ is about $8MPa{\sqrt{m}}$ which is quiet large as compared to the general structural steels and the crack growth rate is lower than the general structural steels especilly in the low ${\Delta}K$ regsion. The reason of this behavior is crack closure due to fracture surface roughness and fretting oxide. The relationship between da/dN and the ${\Delta}K_{eq}$ was represented by narrow band regardless of the stress ratio.

• Journal of the Semiconductor & Display Technology
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• v.19 no.1
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• pp.93-96
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• 2020

Polyimide thin film was prepared by annealing the polyamic acid that was synthesized through co-deposition of diamine and dianhydride. The polyamic acid and polyimide thin film were characterized with FT-IR and HR FE-SEM. The average roughness of the film surface, evaluated with AFM, were 0.385 nm and 0.299 nm after co-deposition, and annealing at 120 ℃ respectively. OLED was passivated with the polyimide layer of 200 nm thickness. While the inorganic passivation layer enhances the WVTR of OLED, the organic passivation layer gives flexibility to the OLED. The in-situ passivation of OLED with organic thin film layer provides the leading technique to develop flexible OLED Display.

• Transactions on Electrical and Electronic Materials
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• v.10 no.6
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• pp.200-202
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• 2009

Tin oxide thin films were prepared by atomic layer deposition using a tetrakis(ethylmethylamino) tin precursor without any seed layer. The average growth rate of tin oxide film is about 1.2 A/cycle from $50{^{\circ}C}$ to $150{^{\circ}C}$. The rate decreases rapidly at a substrate temperature of $200{^{\circ}C}$. ALD-grown tin oxide thin film was characterized with the use of XRD, AFM and XPS. Due to a thermal annealing effect, the surface roughness and the tin amount in the film composition are slightly increased.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.368-369
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• 2006

By means of magnetic pulsed compaction and sintering of weakly aggregated alumina based nanopowders the jet forming nozzle samples for the hydroabrasive cutting were fabricated. The ceramics was obtained from pure alumina, as well as from alumina, doped by $TiO_2$, MgO and AlMg. It was shown that the samples sintered from AlMg doped $Al_2O_3$ powder have the best mechanical properties and structural characteristics: relative density ${\sim}0.97$, channel microhardness. - 18-20 GPa, channel surface roughness ${\sim}0.7\;{\mu}m$, average crystallite size ${\sim}1\;{\mu}m$.

• Journal of the Korean Society for Precision Engineering
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• v.11 no.2
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• pp.85-94
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• 1994

The cutting mechanism of ultrasonic vibration machining is characterized as two phases, that is, an impact at the cutting edge and a reduction of cutting force due to non-contact interval between tool and workpiece. In this paper, in order to identify cutting dynamics of a system with ultrasonically vibrated cutting tool, an ARMA modeling is performed on experimental cutting force signals which have a dominant effect on cutting dynamics. The aim of this study is, through Dynamic Date System methodology, to find the inherent characteristics of an ultrasonic vibration cutting process by considering natural frequency and damping coefficient. Surface roughness and stability of cutting process under ultrasonic vibration are also considered

• International Journal of Highway Engineering
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• v.19 no.6
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• pp.83-95
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• 2017

PURPOSES : The purpose of this study is to develop a regression model to predict the International Roughness Index(IRI) and Surface Distress(SD) for the estimation of HPCI using Expressway Pavement Management System(PMS). METHODS : To develop an HPCI prediction model, prediction models of IRI and SD were developed in advance. The independent variables considered in the models were pavement age, Annual Average Daily Traffic Volume(AADT), the amount of deicing salt used, the severity of Alkali Silica Reaction(ASR), average temperature, annual temperature difference, number of days of precipitation, number of days of snowfall, number of days below zero temperature, and so on. RESULTS : The present IRI, age, AADT, annual temperature differential, number of days of precipitation and ASR severity were chosen as independent variables for the IRI prediction model. In addition, the present IRI, present SD, amount of deicing chemical used, and annual temperature differential were chosen as independent variables for the SD prediction model. CONCLUSIONS : The models for predicting IRI and SD were developed. The predicted HPCI can be calculated from the HPCI equation using the predicted IRI and SD.

• Journal of Surface Science and Engineering
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• v.40 no.2
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• pp.63-69
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• 2007

Ni-SiC composite coating layers were formed using two kinds of SiC nano-particles by DC electrodeposition in a nickel sulfamate bath containing SiC particles. The effect of stirring rate and SiC particle type on the microstructure and properties of Ni-SiC composite coating layers were investigated. Results revealed that the trend of deposition rate is closely related to the codeposition of SiC and the deposition rate. or nickel, and the codeposition behavior of SiC can be explained by using hydrodynamic effect due to stirring. The average roughness and friction coefficient are closely related to the codeposition of SiC and SiC particle size. It was found that the Victors microhardness of the composite coating layers increased with increasing codeposition of SiC. The composite coating layers containing smaller SiC particle showed higher hardness. This can be explained by using the strengthening mechanism resulting from dispersion hardening. Anti-wear property of the composite coating layers formed using 130 nm-sized SiC nano-particles has been improved by 2,300% compared with pure electroplated-nickel layer.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.12
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• pp.2276-2280
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• 2011

An indium-tin-oxide (ITO) is normally used as a substrate in organic photovoltaic cells. We examined the effects of an oxygen ($O_2$) plasma treatment on the electrical properties of an organic photovoltaic cell. Experiments with four-point probe method and atomic force microscope revealed the lowest surface resistance of 17.64 ${\Omega}$/sq and the lowest average surface roughness of 1.39 nm at the plasma treatment power of 250 W. A device structure of ITO/CuPc/$C_{60}$/BCP/$Cs_2CO_3$/Al was fabricated by thermal evaporation with and without the plasma treated ITO substrate. It was found that the power conversion efficiency of the cell with the plasma treated ITO is 65 % higher than the one without the plasma treated ITO.