• Design & Manufacturing
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• v.17 no.4
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• pp.52-56
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• 2023

In this study, numerical simulation of the thermoforming process of PVC film material was performed using PAMForm. For this purpose, tensile tests were performed at various temperatures and the coefficients of the G'Sell model were obtained and used. As a result of the analysis, it was confirmed that the thickness decreased by up to 55% in the section where the film was in contact with the vertical direction and was greatly stretched. If the thickness is excessively thin, the part may become structurally weak, so in the thermoforming process, numerical simulation of the thickness in advance is expected to be helpful in successfully performing the process.

• Korean Journal of Metals and Materials
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• v.48 no.9
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• pp.856-860
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• 2010

Silver nanoparticles were formed on silica substrates through thin film dewetting at high temperature. The microstructural and morphological evolution of the particles were characterized as a function of processing variables such as initial film thickness, annealing time, and temperature. Silver thin films were deposited onto the silica using a pulsed laser deposition system and annealed in reducing atmosphere to induce agglomeration of the films. The film thicknesses before dewetting were in the range of 5 to 25 nm. A noticeable agglomeration occurs with annealing at temperatures higher than $300^{\circ}C$, and higher annealing temperature increases particle size uniformity for the same film thickness sample. Average particle size linearly correlates to the film thickness, but it does not strongly depend on annealing temperature and time, although threshold temperature for complete dewetting increases with an increase of film thickness. Lower annealing temperature develops faceted surface morphology of the silver particles by enhancing the growth of the low index crystal plane of the particles.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.05a
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• pp.226-234
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• 2002

A systematic study of the role of transfer films on friction properties was performed with various temperatures in the brake system. An NAO friction material specimens containing 9 ingredients were tested using a pad-on-disk type friction tester A new method of measuring the transfer film thickness was developed by considering the electrical resistance of the transfer film using a 4-point probe technique. The properties of transfer film such as surface morphology and film distribution vaied according to the relative amount of graphite and magnesium oxide. By using SEM, it was possible to obtain information about the chemical composition of the transfer film. Results showed that there detected a threshold value of the relative amount of a two active materials to maintain a certiain thickness of a transfer film. Results also showed that formation of friction layer generated on the friction surface was strongly affected by chemical action of two ingredients during sliding due to chemical reaction of solid lubricants at different interface temperature. The results suggested that no apparent relationship between transfer film thickness and the average friction coefficient was founded and friction characteristics were affected more by the property of the solid lubricant and abrasive in the material.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.6
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• pp.947-958
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• 1986

물-증기 역류 성층이상유동에서의 평균 액체층 두께가 여러가지 경사각과 종횡비에 따라 측정되었다. 난류유동에 있어서 전단응력분포의 선형화와 von Karman의 혼합길이 이론을 근거로 평균 액체층의 두께에 대한 관계식이 제시되었으며 실험결과와 잘 일치하였음을 보였다. 접촉면에서의 조파저항이 고려되지 않은 해석결과는, 수평 성층유동의 경우에, 평균 액체층 두께보다는 오히려 파곡까지의 액체층 두께를 예측하고 있는 것으로 나타났다. 또한 평균 액체층 두께에 대한 실험 상관관계식이 계산시 편의를 위해 쉽게 인지할 수 있는 매개변수들의 항들롤 제시되었다.

• Tribology and Lubricants
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• v.34 no.3
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• pp.93-107
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• 2018

The purpose of Part I of this study is to find the potential region of wear scarring on engine journal bearings operating at a constant angular crank shaft velocity under firing conditions. To do this, we calculate the applied loads and eccentricities of a big-end journal bearing installed on a four-stroke and four-cylinder engine at every crank angle. Then, we find potential wear regions, such as a minimum oil film thickness, at every crank angle below most oil film thickness scarring wear (MOFTSW) obtained based on the concept of the centerline average surface roughness. Thus, the wear region is defined as a set of each film thickness below the MOFTSW at every crank angle. In this region, the wear volume changes according to the wear depth and wear angle, depending on the minimum oil film thickness at every crank angle. The total wear volume is the summation during one cycle. Graphical views of the region in the two-dimensional coordinates show the crank angle and bearing angle along the journal center path, indicating the position of the minimum oil film thickness. The results of wear analysis show that the possible wear region is located at a few tens of angles behind the upper center of a big-end bearing at maximum power rpm.

• Tribology and Lubricants
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• v.35 no.4
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• pp.244-266
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• 2019

The purpose of this study is to estimate the wear volumes of engine journal bearings operating at variable angular velocity of a shaft in the beginning of firing start-up cycle. To do this, first we find the potential region of wear scar on engine journal bearings where the applied bearing load and crank shaft velocity are variable. The potential wear regions are discovered by finding minimum oil film thickness at every crank angle existing below most oil film thickness scaring wear (MOFTSW) obtained based on the concept of the centerline average surface roughness. Then we calculate the wear volume from the wear depth and two wear angles decided by the magnitude of each film thickness lower than MOFTSW at every crank angle. The results show that the expected wear region is located at a few bearing angles after and/or behind the upper center of a big-end bearing and the lower center of a main bearing. And the real wear region is similar to the estimated wear region. Further we find that the wear scar on an engine journal bearing may occur at re-starting time after switch-off of a start motor especially under the condition of high oil temperature.

• Proceedings of the Korean Society Of Semiconductor Equipment Technology
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• 2006.05a
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• pp.164-167
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• 2006

In this paper, we prepared Al doped ZnO thin films by using facing targets sputtering method. Al doped ZnO thin film was deposited with different working pressure on flexible substrate. We prepared Al doped ZnO thin film at room temperature, because the flexible substrate has weak thermal resistance. From the results, we could obtain thin film with a resistivity of $8.4{\times}10^{-4}{\Omega}cm$, an average transmittance of over 80% and a film thickness of 200nm.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.88-88
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• 2008

In this study, effect of thickness on structural, electrical and optical properties of B doped ZnO:Ga (GZOB) films was investigated. GZOB films were deposited on glass substrates by DC magnetron sputtering. The thickness range of films were from 100 nm to 600 nm to identified as increasing thickness, stress between substrate and GZOB film. The average transmittance of the films was over 80 % until 500 nm. Then a resistivity of $9.16\times10^{-4}\Omega$-cm was obtained. We presented that a GZOB film of 400 nm was optimization to obtain a high transmittance and conductivity.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.138-138
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• 2008

In this study, effect of thickness on structural, electrical and optical properties of B doped ZnO:Al (AZOB) films was investigated. AZOB films were deposited on PC substrates by DC magnetron sputtering. The thickness range of films were from 300 nm to 800 nm to identified as increasing thickness, stress between substrate and AZOB film. The. average transmittance of the films was over 80 % until 500 nm. Then a resistivity of $1.58\times10^{-3}\Omega$-cm was obtained. We presented that a AZOB film of 500 nm was optimization to obtain a high transmittance and conductivity.

• Journal of the Korean Ceramic Society
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• v.34 no.6
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• pp.611-619
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• 1997

Optimal Mullite sol was synthesized by sol-gel process using Aluminium sec-butoxide(ASB), Tetraethoxysilane(TEOS) and then, Mullite films were dip-coated with various holding time in sol bath and heat-treated at 130$0^{\circ}C$ above for crystallization. The thickness of coated film increased linearly with holding time in sol bath and average pore size was controllable within 20~30$\AA$.