• Journal of the Earthquake Engineering Society of Korea
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• v.27 no.4
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• pp.181-186
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• 2023

In this study, considering the expansion/contraction behavior of the upper structure at all times and the abnormal behavior of the receiving friction elements that allow horizontal movement during earthquakes, a port receiving test body simulating the protrusion of the friction elements was created and the modulus performance was evaluated. In order to confirm the influence of the friction element's projection, the friction element's degree of separation was divided into four stages, and the shear behavior of the test specimen and the friction coefficient were confirmed. As a result of the experiment, it was found that the friction load increases as the protrusion degree of the friction element increases. On the other hand, as the degree of protrusion of the coefficient of friction increases, the coefficient of friction also increases. It was confirmed that damage to the friction elements during use increases the coefficient of friction, hinders smooth expansion and contraction of the upper structure, and causes stress concentration at the fixed-end support.

• Geotechnical Engineering
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• v.8 no.3
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• pp.13-22
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• 1992

Model pile tests using calibration chamber are performed in !his paper in order to clarify the effect of the fundamental differences between the newly developed SPLT(Simple Pile Loading Test)and the conventional pile loading test on the pile bearing capacity. They are : (1) the direction of the applied load to mobilize the skin friction ; and (2) the use of reduced sifted sliding core. The conclusions obtained from the model pile tests are as follows : (1) The skin friction in tension loading is found to be somewhat smaller than that in compression loading. The average ration is 0.73 with the coefficient of variation (COV) of 0.18. (2) The ratio of the tip resistance rosin연 the reduced sized sliding core to that using the whole shoe shows wide scattering ; its average is 0.99 and the COV is 0.28. The aver - age of 0.99 means that there is no considerable difference in the tip resistance whether the reduced sized sliding core or the whole shoe is used, on condition that penetration depth ratio is larger than 4 : if the boundary effect of the chamber test is considered, the resistance of the whole shoe might be even larger.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.09a
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• pp.287-294
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• 2001

Dynamic responses of multi-span simply supported bridges are investigated to examine the effect of damaged bearings under seismic excitations. The damaged bearings are modeled as sliding elements with friction between the super-structure and the pier top. Various values of the friction coefficients for damaged bearings are examined with increasing magnitudes of peak ground accelerations. It is found that the g1oba1 seismic behaviors are significantly influenced by the occurrence of bearing damage. It should be noticed that the most possible location of unseating failure of superstructures differs with that in the model without consideration of the bearing damage. It can be concluded that the bearing damage may play the major role in the unseating failure of a bridge system, so that the damage of bearings should be included to achieve more rational seismic safety evaluation.

• Smart Structures and Systems
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• v.20 no.1
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• pp.23-33
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• 2017

Variable Curvature Friction Pendulum (VCFP) bearing is one of the alternatives to control excessive induced responses of isolated structures subjected to near-fault ground motions. The curvature of sliding surface in this isolator is varying with displacement and its function is non-spherical. Selecting the most appropriate function for the sliding surface depends on the design objectives and ground motion characteristics. To date, few polynomial functions have been experimentally tested for VCFP however it needs comprehensive parametric study to find out which one provides the most effective behavior. Herein, seismic performance of the isolated structure mounted on VCFP is investigated with two different polynomial functions of the sliding surface (Order 4 and 6). By variation of the constants in these functions through changing design parameters, 120 cases of isolators are evaluated and the most proper function is explored to minimize floor acceleration and/or isolator displacement under different hazard levels. Beside representing the desire sliding surface with adaptive behavior, it was shown that the polynomial function with order 6 has least possible floor acceleration under seven near-field ground motions in different levels.

• Tribology and Lubricants
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• v.23 no.6
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• pp.306-311
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• 2007

This paper presents the friction characteristics of pb-fres pin bushing bearings for an automotive gasoline engine. The external load is 100 N to 600 N and the speed of the pin bushing bearing is 1000 rpm to 3000 rpm against the rubbing surfaces. And the contact modes of rubbing surfaces between a piston pin and a pb-free pin bushing specimen are a dry friction, an oil lubricated friction and a mixed friction that is starved by a lack of engine oil. Two influential factors of a contact rubbing modes and a material property are very important parameters on the tribological performance of a friction characteristic between a piston pin and a pb-free pin bushing. The experimental result shows that the pin bushing speed of 2000 rpm shows a typical oil film lubricated sliding contact mode in which means that as the applied load is increased, the friction loss is increasing. But other contact mode depending on the speed and the load may affect to the fiction coefficient without a regular and uniform trend. In summary, the oil lubricated rubbing surface definitely decreases a running-in period in short and increase oil film stiffness, and this may leads the reduction of a friction loss.

• Tribology and Lubricants
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• v.30 no.5
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• pp.303-310
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• 2014

In order to reduce friction and improve reliability, researchers have applied various surface texturing methods to highly sliding machine elements such as mechanical seals and piston rings. Despite extensive theoretical research on surface texturing, previous numerical results are only applicable to isothermal and iso-viscous conditions. Because the lubricant flow pattern of textured bearing surfaces is much more complicated than that for non-textured bearings, the Navier?Stokes equation is more suitable than the Reynolds equation for the former. This study carries out a thermohydrodynamic (THD) lubrication analysis to investigate the lubrication characteristics of a single micro-dimpled parallel thrust bearing cell. The analysis involves using the continuity, Navier?Stokes, energy, temperature?viscosity relation, and heat conduction equations with the commercial computational fluid dynamics (CFD) code FLUENT. This study discretizes these equations using the finite volume method and solves them using the SIMPLE algorithm. The results include finding the streamlines, pressure and temperature distributions, and variations in the friction force and leakage for various dimple radii and depths. Increasing the dimple radius and decreasing the depth causes a recirculation flow to form because of a strong vortex, and the oil temperature greatly increases compared with the non-textured case. The present numerical scheme and results are applicable to THD analysis of various surface-textured sliding bearings and can lead to further study.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.173-174
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• 2002

To study the effects of mating materials on the tribological properties of DLC films. we used a ball-on-plate reciprocating friction tester in dry air and mating materials of martensite stainless steel (hardened, annealed SUS440C), austenite stainless steels (SUS304), and bearing steel (hardened, annealed SUJ2). At a light load of 0.6 N, the friction coefficient always exceeded ${\mu}>0.3$. Tribological properties of DLC film were still excellent above 0.6 N, except in sliding against annealed SUJ2. Analysis using micro-laser Raman spectroscopy showed that the difference between annealed SUJ2 and others materials appears mainly due to structural change in film.

• Tribology and Lubricants
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• v.11 no.1
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• pp.27-36
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• 1995

Maximum allowable PV values of oilless composite bearing materials (70% epoxy-resin/30% Graphite) were measured and compared at various types of test rigs that have different contact geometry and the operating conditions. Test results showed that material failure was mainly characterized by the sharp increase in both coefficient of friction and surface temperature, and different PV values were measured under different Contact geometry. The discrepancy in measurement of PV values was analyzed in the light of theoretical frictional heating analysis. Results show that surface temperature rise depends on its contact geometry, and PV values could be overestimated in the testing conditions of high sliding velocity. Test data of different contact geometry were normalized by using a normalized contact pressure and sliding velocity; it showed a good correlation. This work suggests that normalized PV values could be more effective in evaluating bearing materials than conventional PV values for a design parameter of journal bearings.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.05a
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• pp.152-155
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• 2004

Effects of sliding speed, applied load, counterpart radius and thickness of PMMA (Poly Methyl Methacrylate) coating layers on their dry sliding frictional and wear behavior were investigated. Sliding wear tests were carried out using a pin-on-disk wear tester. The PMMA layer was coated on Si wafer by a sol-gel technique with two different thicknesses, $1.5{\mu}m\;and\;0.8{\mu}m$. AISI 52100 bearing steel balls were used as a counterpart of the PMMA coating during the wear. Normal applied load and sliding speed were varied. Wear mechanisms were investigated by examining worn surfaces by an SEM. Under most of sliding test conditions, the thicker layer with the thickness of $1.5{\mu}m$ showed lower fiction coefficient than the thinner layer. Effects of sliding speed and counterpart's radius on the frictional behavior were varied depending on the thickness of the coating layer.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.5
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• pp.19-27
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• 2002

Dynamic responses of a multi-span simply supported bridge are investigated to examine the effect of bearing damage under seismic excitations. The damaged bearings are modeled as sliding elements with friction between the superstructure and the top of the pier. Various values of the friction coefficients are examined to figure out the effect of damaged bearings with various levels of peak ground accelerations. It is found that the global seismic behaviors are significantly influenced by the occurrence of bearing damage. It should be noticed that the most possible location of unseating failure of superstructures differs from that in the bridge model without considering the bearing damage. It can be concluded that the bearing damage may play the major role in the unseating failure of a bridge system, so that the damage of bearings should be included to achieve more rational seismic safety evaluation.