• Tunnel and Underground Space
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• v.23 no.5
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• pp.401-412
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• 2013

Multi-stage shear test has been performed using joint specimens of gneiss, granite and shale to investigate the influence of micro-scale asperity change on the shear strength of joint plane. For each shear test asperity degradation characteristics of joint specimens of different joint surface strength have been analyzed by utilizing the optimum asperity parameter which can reflect the sequential asperity degradation. Elevation of joint surface profile has been measured and both the changes of asperity parameters and micro-scale asperity distribution have been investigated. Two distinctive variation modes of cohesion and friction angle have been delineated and major cause of shear strength parameter change has been analyzed by considering the micro-scale asperity angle change resulting from the abrasion, fracturing and regeneration of micro-scale asperities. Effects of micro-scale asperity variation on the joint shear strength have been also investigated.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1997.10a
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• pp.173-182
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• 1997

In many practical lubricated contacts such as a rough concentrated contact on the sliding of nominally flat surfaces, the fluid may be of molecular (nanometer) scale owing to the asperity interactions on the surfaces. Under this condition, there is insufficient lubricant on the concentrated contact spot to maintain a realistic continuum. Rheological behavior for this kind of concentrated contact was studied to know whether the application of viscous fluid model is appropriate. The interaction of two rough surfaces is simplified as perfectly flat-rough surfaces contact under certain conditions by "composite topography" and for a nanometer scale fluid film, three kinds of rheological fluid behavior are analyzed in elastohydrodynamic asperity point contact.t contact.

• Tribology and Lubricants
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• v.23 no.6
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• pp.255-260
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• 2007

This paper presents the contact pressure distribution of pin bushing bearings for various lubrication friction modes such as oil film and elastohydrodynamic lubrication contacts, a mixed lubrication contact, a boundary contact, and a dry contact. During a sliding contact of a plain bearing, the boundary and dry rubbing contacts are dominated between a piston pin and a pin bushing bearing. This may come from a micro-scale clearance, an explosive impact pressures from the piston head, and an oscillatory motion of a pin bearing. The computed results show that as the oil film parameter $h/{\sigma}$ is increased from the dry rubbing contact to the oil film lubrication friction, the maximum oil film pressure is radically increased due to an increased viscous friction with a thin oil film thickness and the maximum asperity contact pressure is reduced due to a decreased asperity contact of the rubbing surfaces.

• 전자공학회논문지 IE
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• v.44 no.3
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• pp.42-50
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• 2007

In this paper, elastic and plastic adhesion index was very important in deciding adhesive characteristics and varying elastic and plastic index, dimensionless load and pull-off force were analyzed and simulated. Finally, using AFM, experimental surface roughness parameters of substrates and pull-off force between tip and substrates were produced. Using these values, pull-off forces were calculated and were compared with experimental pull-off forces. Through simulation and experiment, it was found that interaction of asperity also had very important influence on adhesive contact.

• Tunnel and Underground Space
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• v.16 no.2 s.61
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• pp.166-178
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• 2006

Recently, the frequency of occurring dynamic events such as earthquakes, explosives blasting and other types of vibration has been increasing. Besides, the chances of exposure for rock discontinuities to free faces get higher as the scale of rock mass structures become larger. For that reason, the frictional behavior of rock joints under dynamic conditions needs to be investigated. In this study, artificially fractured rock joint specimens were prepared in order to examine the dynamic frictional behavior of rough rock joint. Roughness of each specimen was characterized by measuring surface topography using a laser profilometer and a series of shaking table tests was carried out. For mated joints, the static friction angle back-calculated ken the yield acceleration was $2.7^{\circ}$ lower than the tilt angle on average. The averaged dynamic friction angle for unmated joints was $1.8^{\circ}$ lower than the tilt angle. Displacement patterns of sliding block were classified into 4 types and proved to be related to the first order asperity of rock joint. The tilt angle and the static friction angle for mated joints seem to be correlated to micro average inclination angle which represents the second order asperity. The tilt angle and the dynamic friction angle for unmated Joints, however, have no correlation with roughness parameters. Friction angles obtained by shaking table test were lower than those by direct shear test.