• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.6
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• pp.1753-1761
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• 1996

The wear behaviors of ${Si_3}{N_4}$ under the different sliding conditions were investigated. The cylinder-on-disc wear tester was used. Using the servo-metor, the sliding speed did ot alternate due to the frictional forces. Threekinds of loads and speeds were selected to watch the variation of the wear rates and the frictional forces. Also three kinds of sliding condition under a constant speed were used to see the effects of the oxidationand the abrasion. The contact pressure was more effective than the repeated cycle on the wear behavior of ${Si_3}{N_4}$. With the low loads, the effect of the asperity-failure was more dominant than that of oxidation and abrasion. As increasing the load, the effects of oxidation and abrasion were increased, but the asperity-failure effects were decreased. The wear particles destroyed the ozide layers formed on sliding surfaces. The wear rate could be decreased due to delaying the oxidation. The frictional power and the wear weight per time were usefuel to see the transition of wear.

• Tribology and Lubricants
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• v.12 no.3
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• pp.12-25
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• 1996

The friction and wear behaviors of ceramics against steels with lubricants were investigated and compared with those observed in air. Lubrications wbre done by a water and a commercial engine oil as received. The investigated ceramics were $Al_{2}O_{3}$, SiC, and $Si_{3}N_{4}$. Steels with 0.2 wt.% C were heat treated to obtain tempered structure. A cylinder-on-plate tribometer with rotated sliding motion was used to carry out the experiments. In the experiments reported here, the ranges of different testing speeds and loads were used. It was found that the friction and wear characteristics of tested pairs were significantly influenced by environments. In water and oil environments the wear of ceramics was reduced from 10$^{-6}$ g/s down to 10$^{-8}$ g/s in dry sliding at the same values of the frictional power which are the products of the friction coefficient, the load and the sliding speed. SiC showed excellent wear resistant behavior in water sliding, which was the lowest among tested ceramics, but it was, very poor in oils. In case of $Si_{3}N_{4}$, the wear rates were very low under oil environment, but the highest in water. The wear rates of $Al_{2}O_{3}$ were very low in both lubricating conditions at low values of the frictional power, but high at high values of the frictional power.

• Tribology and Lubricants
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• v.29 no.1
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• pp.46-50
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• 2013

In this study, the frictional behaviors of articular cartilage against a Co-Cr alloy in two types of kinematic motions were compared. Cartilage pins were punched from the femoral condyles of porcine knee joints, and Co-Cr alloy disks were machined from orthopedic-grade rods and polished to a surface roughness ($R_a$) of 0.002. Friction tests were conducted by using a pin-on-disk-type tribotester in phosphate buffered saline (PBS) under pressures of 0.5, 1, and 2 MPa. All tests were performed in the repeat pass rotational (ROT) and the linear reciprocal (RCP) sliding motions with the same sliding distance and speed of 50 mm/s. The coefficients of friction of the cartilage against the Co-Cr alloy increased with the sliding time in both kinematic motions for all contact pressures. The maximum coefficients of friction in RCP motion were 1.08, 2.82, and 1.96 times those in ROT motion for contact pressures of 0.5, 1, and 2 MPa, respectively. As the contact pressure increased, the coefficients of friction gradually increased in RCP motion, whereas they decrease and then increased in ROT motion. The interaction between the directional change of the shear stress and the orientation of collagen fiber in the superficial layer of the cartilage could affect the change in the frictional behaviors of the cartilage. A large difference in the coefficients of friction between the two kinematic motions could be interpreted as differences in the directional change of shear stress at the contact surface.

• Tribology and Lubricants
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• v.6 no.1
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• pp.99-107
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• 1990

Most of machines and structures contain the elements which contact each other directly. When these elements subjected to vibration or repeated load, local relative movement occurs between the elements in contact which results in, a kind of wear. In order to know the factors which govern fretting, we have to analyze the phenomenon of microslip which causes fretting by using a general and efficient method from a viewpoint of contact mechanics. Based on the results of analysis, it is necessary to propose the way of minizing fretting which is one of the most significant surface failure. In this report, a general and efficient algorithm is applied to analyze the contact problem of the bolted joint, which is one of the typical elements damaged by fretting, with ratios of plate thickness, the ratios of Young's moduli, the ratios of the plate thickness to bolt radius varied. Finally, the ways of minizing fretting for the boked joint are suggested.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.255-256
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• 2002

In this paper, the frictional behavior according to the contact geometry was investigated using a micro-tribotester built inside a Scanning Electron Microscope (SEM) and an Atomic Force Microscope (AFM). FFT (Fast Fourier Transform) analysis for friction was conducted as a method to interpret the contact condition. From the experimental results, it could be concluded that the relative dimensions and distribution of contact asperities on the surface could be predicted by the power spectrum and main frequency in the FFT analysis of the friction signal.

• 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.

• Tribology and Lubricants
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• v.10 no.4
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• pp.82-88
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• 1994

This paper deals with a FEM computation as well as measurement of the contact force and distribution of the temperature in rubber lip seals when the sealing interference between the rotating shaft and the lip edge is present. The study of the contact forces and distributions of the temperature and the sealing contact stress has always been one of the basic steps in the process of designing a lip seal. The calculated FEM results indicate that as the sealing interference increases, the contact force moderately increases compared with decreased sealing interference at the seal lip edge and radically increases the contacting width. And the FEM computation of oontact forces including nonlinear problems has been compared with experimental measurements with good agreement. The frictional heat does not dissipate promptly in the rubber seal lip and tends to accumulate at the contacting lip edge especially.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.144-149
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• 2008

A transient finite element simulation is developed for the two-dimensional stationary elastoplastic layer between sliding layers, to investigate thermoelastoplastic instability(TEPI) due to frictional heating in the material. The analysis will show some differences between the case of thermoelastic instability and TEPI, especially according to the contact pressure above yield stress. A transient behavior of contact pressure is captured to explain the behavior of thermoplasticity of contact with different sliding velocity. The instability of contact pressure in the long range of braking time will be explored to understand the generation mechanism of hot spots.

• Journal of the Korean Society of Safety
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• v.26 no.3
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• pp.1-7
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• 2011

Fatigue damage on the train wheel surface was estimated by considering the effect of friction coefficient of rolling on the contact surface between the wheel and rail during operation. From FEM analys, the maximum Tresca stress was 550.7 MPa at a depth of 2.07 mm under the maximum contact pressure ($P_{max}$ = 894.3 MPa) between wheel and rail. The maximum stress continued to increase along with the increase in the frictional coefficient. The fatigue initiation lifetime of the wheel by the rolling contact was predicted using the Smith-Watson-Topper (SWT) equation and the maximum principal strain equation (${\varepsilon}$-N).

• Tribology and Lubricants
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• v.14 no.2
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• pp.49-56
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• 1998

The thermal deformation of the contact seal components has been analyzed using the finite element method. The temperature distributions, the thermal deformations and contact stresses are solved numerically for the contact surface with wear coning effects. The thermal deformation is always shown to distort the sealing surface along the radius of the seal ring. The results show that the deformations of inner radius side are significant compared with those of outer radius. Thus, the thermal deformation due to thermal heatings may promote the coned face wear or wear related thermal cracks at the contacting face of the seal ring component.