• Journal of the Korean Society for Heat Treatment
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• v.6 no.2
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• pp.79-88
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• 1993

The static creep mechanism and behaviour of Al-Zn-Mg alloy have been investigated under condition of constant stress tension creep test in the temperature and stress range of $170-260^{\circ}C$ and 5-12.5 $kg/mm^2$ respectively. The experimental result are follows : The stress exponent value for creep was observed to about 7.3-6.43 and the activation energy for creep deformation was 44-41 kcal/mol. Larson-Miller parameter P for the crept specimens under the creep condition was obtained as P = (T + 460) (log $t_r$ + 8.6). Emperical equation for the creep rate was obtained by the computer simulation as follows. $${\varepsilon}\;=\;\exp[(-5.519{\times}10^{-4}{\sigma}+2.33{\times}10^{-2})T-6.98{\sigma}+18.295]{\times}{\sigma}^{-0.0142+10.18}\exp[\frac{(-6{\sigma}+47.8)1000}{RT}]$$ Fracture was dominated by intergranular mechanism over the experimental range.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.337-342
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• 2007

In this study, molecular dynamics simulation of nano imprint lithography in which patterned stamp is pressed onto amorphous polyethylene(PE) surface are performed to study the behaviour of polymer. Force fields including bond, angle, torsion, and Lennard Jones potential are used to describe the inter-molecular and intra-molecular force of PE molecules and stamp, substrate. Periodic boundary condition is used in horizontal direction and canonical NVT ensemble is used to control the system temperature. As the simulation results, the behaviour of polymer is investigated during the imprinting process. The mechanism of polymer deformation is studied by means of inspecting the surface shape, volume, density, atom distribution. Deformation of the polymer resist was found for various of the stamp geometry and the alignment state of the polymer molecules.

• Journal of Korean Society for Atmospheric Environment
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• v.15 no.5
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• pp.525-544
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• 1999

Polycyclic aromatic hydrocarbons (PAH) were one of the first airborne pollutants to be identified as being carcinogenic. This class of compounds is ubiquitous in the urban atmosphere, and has therefore undergone considerable scrutiny for the last three decades. PAH can be formed in any incomplete combustion or high temperature pyrolytic process involving materials containing carbon and hydrogen, such as fossil fuels. In this paper, the literature on the occurrence, ambient levels, and atmospheric fate and behaviour of airbonrne PAH has been reviewed, with a particular emphasis on the role of automobile sources in PAH emissions. Sampling and analytical techniques for the determination of PAH in air have also been examined. In addition, health implications and legislative aspects of human exposure to airborne PAH have been briefly reviewed. Finally, future requirements for better understanding of the atmospheric behaviour of PAH recommended.

• Tribology and Lubricants
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• v.11 no.3
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• pp.54-58
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• 1995

This paper deals with an experimental study on the dynamic behaviour of rubber oil seals when the interferences between the shaft and the seal lip as well as the dynamic eccentricities are present. The micro-separation of the sealing gap was observed with the aid of an image processing apparatus. The temperature of the seal lip edge, friction torque and the dynamic sealing gap profile are experimentally investigated for the initial interference and the shaft eccentricity. The data was simultaneously measured under the operation conditions. Experimental results show that, as the shaft speed is increased, the leakage of sealed fluids is increasing for a certain range of shaft speeds. The test data indicates that the shaft eccentricity clearly produces the gap separation between the shaft and the seal lip which is unable to follow the radial displacement of shaft as the shaft speed increases.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.919-924
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• 2000

Spray impingement model and fuel film formation model were developed and incorporated into the computational fluid dynamics code, STAR-CD. The spray/wall interaction process were modelled by considering the change of behaviour with surface temperature condition and fuel film formation. We divided behaviour of fuel droplets after impingement into stick, rebound and splash using Weber number and parameter K. Spray impingement model accounts for mass conservation, energy conservation and heat transfer to the impinging droplets. A fuel film formation model was developed by Integrating the continuity, the Navier-Stokes and the energy equations along the direction of fuel film thickness. The validation of the model was conducted using diesel spray experimental data and gasoline spray impingement experiment. In all cases, the prediction compared reasonably well with experimental results. Spray impingement model and fuel film formation model have been applied to a direct injection diesel engine combustion chamber.

• Transactions of Materials Processing
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• v.13 no.2
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• pp.174-179
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• 2004

The effect of grain refinement on the plastic deformation behaviour of nanocrystalline metallic materials is investigated. A phase mixture model in which a single phase material is considered as an effectively two-phase one is discussed. A distinctive feature of the model is that grain boundaries are treated as a separate phase deforming by a diffusion mechanism. For the grain interior phase two concurrent mechanisms are considered: dislocation glide and mass transfer by diffusion. The proposed constitutive model was implemented into a finite element code (DEFORM) using a semicoupled approach. The finite element method was applied to simulating room temperature tensile deformation of Cu down to the nanoscale grain size in order to investigate the pre- and post-necking behaviour.

• Proceedings of the Korean Society of Dyers and Finishers Conference
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• 2006.04a
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• pp.180-181
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• 2006

The hydrolysis of some vinylsulfonyl (VS) typed reactive dyes were investigated at the pH, temperature and other experimental conditions. The hydrolytic behaviour, especially, stability in various pH value, of the water soluble reactive dyes are examined. In neutral and acid condition, mother dyes are a quite stable. Other hand, it was found that dimerization and decomposition for these dyes were estimated in an aqueous alkaline medium. These alkaline hydrolysis behaviour was monitored by the high performance liquid chromatography.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.3
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• pp.547-553
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• 1990

With alumina ceramics to copper brazement of cylindrical shape, the thermal stress analysis was carried out by finite element method. Elastic and plastic behaviour was considered to copper, but only elastic behaviour was considered to alumina. Also material properties of alumina and copper were considered in not constant values but variable functions dependent on temperature. The result of analysis is shown that maximum tensile longitudinal stress is occurred at perimeter of alumina side interface and maximum compressive radial and tangential stresses are occurred at center of alumina side interface. Because of bending effect, tensile raidial and tangential stresses are occurred at near bottom of alumina, far from interface.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.495-496
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• 2006

The kneading process and formulations of feedstock obviously affect the quality of MIM products. In the present work, the rheological behaviour of the composite MIM feedstock, metal matrix (Cu) with few additions of ceramic powders $(Al_2O_3)$, was measured by a self-designed/manufactured simple capillary rheometer. Experimental results show that the distribution between powders and binder is more uniformly when blending time increased. Though high powder loading will increase the feedstock viscosity, the fluidity reveals relatively stable through the load curves of extrusion. Besides, the temperature-dependence of viscosity of the feedstock approximately follows an Arrehnius equation. Basing on Taguchi's method, the kneading optimization conditions and the rheological model of the feedstock were established, respectively.

• Transactions of the Korean Society of Automotive Engineers
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• v.1 no.2
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• pp.89-102
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• 1993

In this experimental investigation, various plasma-sprayed zirconia contained coatings and a kind of alumina-zirconia coating were studied to gain a better understanding of their tribological behaviour under dry contact condition in a reciprocating motion at temperature of 200℃. Particular attention was made for finding appropriate coatings in cylinder liner/piston ring application with an emphasis on the antiwear property. In order to identify the wear mechanism, SEM(Scanning Electron Microscope), optical micrograph, and roughness tester were used. Alumina-zirconia and 8% yttria-zirconia were found to be most appropriate for the application to the cylinder liner/piston ring and, especially, alumina-zirconia exhibited highest wear-resistance and also showed good friction characteristics. Wear mechanisms of ceramic coatings identified.