• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.06a
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• pp.269-275
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• 2000

The fretting wear characteristics of TiN coated Zircaloy-4 tube were investigated experimentally The fretting wear experiment was performed using TiN coated Zircaloy-4 tube as the fuel rod cladding material and uncoated Zircaloy-4 tube as one of grids. TiN coating is probably one of the most frequently and successfully used PVD coatings for the mitigation of fretting wear. In this study, TiN coating by PVD was employed for improvement of Zircaloy-4 tube fretting characteristics. The fretting tester was designed and manufactured for this experiment. TiN coated Zircaloy-4 tube was used as the moving specimen, uncoated ZircaBoy-4 tube as the stationary one. The number of cycles, slip amplitude and normal load were selected as main factors of fretting wear. The results of this research showed that the wear volume of TiN coated Zircaloy-4 tube increased as number of cycles, normal load and slip amplitude increase but the quantity of volume was lower than the case of uncoated Zircaloy-4 tube pairs.

• Journal of Korean Association for Spatial Structures
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• v.15 no.3
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• pp.103-110
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• 2015

Various hybrid dampers have been developed as increasing tall buildings in Korea. To minimize the installment space and cost, the new hybrid friction damper was developed using friction components. It is composed of two one-nodal rotary frictional components and a slotted bolted frictional connection. Because of these components, hybrid friction damper can be activated by building movements due to lateral forces such as a wind and earthquake. In this paper, displacement amplitude dependency tests were carried out to evaluate on the structural performance and the multi-slip mechanism of the hybrid damper. Test results show that the multi-slip mechanism is verified and friction coefficients are increasing as displacement amplitudes are increasing.

• Proceedings of the KSR Conference
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• 2004.06a
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• pp.632-637
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• 2004

In the shrink or press fitted shaft such as railway axle, fretting can occur by cyclic stress and micro-slippage due to local movement between the shaft and the hub. When the fretting occurs in the press fitted shaft, the fatigue strength remarkably decreases compared with that of without fretting. In this paper, the analysis of contact stresses in a press fitted shaft in contact with a hub was conducted by finite element method and the micro-slip according to the bending load was analyzed. It is found that the largest stress concentration and maximum slip amplitude of shrink fitted shaft are found at the edge of the interface and the distribution of contact stresses at the contact edge has largely influenced and coefficient of friction.

• Proceedings of the Korean Nuclear Society Conference
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• 2001.05a
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• pp.329.1-329
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• 2001

• Journal of the Korean Society for Aviation and Aeronautics
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• v.23 no.1
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• pp.62-66
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• 2015

In this paper, a fretting testing machine is developed using ball-on-flat test apparatus. Precise micro-slip motion is produced by a linear stage. A relative displacement between a ball and a flat specimen is measured with a laser displacement sensor. Dry friction tests are conducted with AISI 52100 steel balls and cold-rolled high strength steel plates at room temperature and ambient humidity. The evolution of the kinetic friction coefficient is determined. Comparison between measured friction coefficients and those found in the literature is then carried out. Fretting tests with an electro-deposited coating are employed at an amplitude of 0.05 mm. Slip regime is identified with slip ratio. It is demonstrated that a developed testing machine allows determining the friction coefficient under fretting condition.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.06a
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• pp.89-95
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• 2001

The fretting wear characteristics of Zircaloy-4 tube at room and high temperature were Investigated experimentally. In this study, the number of cycles, slip amplitude and temperature were selected as main factors of fretting wear. The results of this research showed that the wear volume Increased with the Increase of slip amplitudes and the number of cycles but decreased with temperature and the coefficient of friction were observed different tendency between room and high temperature. According to SEM(EDS) only gross slip were observed on the surface of both specimens and compacted oxide were on worn surfaces. XRO patterns showed that the crystallization of ZrO$_2$ were observed on the worn surface at high temperature. The fretting wear were Investigated due to oxidation and accumulation of plastic flow.

• Tribology and Lubricants
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• v.16 no.5
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• pp.389-394
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• 2000

Scanning Probe Microscope (SPM) such as Scanning Tunneling Microscope (STM) and Atomic Force Microscope (AEM) was shown to be the powerful tool for nano-scale characterization of material surfaces. Using this technique, surface morphology of the cyclically deformed Cu or Cu-Al single crystal was observed. The surface became proportionately rough as the number of cycles increased, but after some number of cycles no further change was observed. Slip steps with the heights of 100 to 200 nm and the widths of 1000 to 2000 nm were prevailing at the stage. The slipped distance of one slip system at the surface was not uniform, and formation of the extrusions or intrusions was assumed to occur such place. By comparing the morphological change caused by crystallographic orientation, strain amplitude, number of cycles or stacking fault energy, some interesting results which help to clarify the basic mechanism of fatigue damage were obtained. Furthermore, applicability of the scanning tunneling microscopy to fatigue damage is discussed.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1999.06a
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• pp.67-72
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• 1999

Scanning probe Microscope(SPM) such as Scanning Tunneling Microscope(STM) and Atomic Force Microscope(AFM) was shown to be the powerful tool for nano-scale characterization of material surfaces Using this technique, surface morphology of the cyclically deformed Cu or Cu-Al single crystal was observed. The surface became proportionately rough as the number of cycles increased, but after some number of cycles no further change was observed. Slip steps with the heights of 100 to 200 nm and the widths of 1000 to 2000 nm were prevailing at the stage. The slipped distance of one slip system at the surface was not uniform. and formation of the extrusions or intrusions was assumed to occur such place. By comparing the morphological change caused by crystallographic orientation, strain amplitude, number of cycles or stacking fault energy, some interesting results which help to clarify the basic mechanism of fatigue damage were obtained. Furthermore, applicability of the scanning tunneling microscopy to fatigue damage is discussed.

• The KSFM Journal of Fluid Machinery
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• v.13 no.2
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• pp.5-11
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• 2010

The nanofluidics is characterized by a large surface-to-volume ratio, so that the surface properties strongly affect the flow resistance. We present here the results showing that the effect of wetting properties and the surface roughness may considerably reduce the friction of fluid past the boundaries. For a simple fluid flowing over hydrophilic and hydrophobic surfaces, the influences of surface roughness are investigated by the nonequilibrium molecular dynamics (NEMD) simulations. The fluid slip at near a solid surface highly depends on the wall-fluid interaction. For hydrophobic surfaces, apparent fluid slips are observed on smooth and rough surfaces. The solid wall is modeled as a rough atomic sinusoidal wall. The effects on the boundary condition of the roughness characteristics are given by the period and amplitude of the sinusoidal wall. It was found that the slip velocity for wetting conditions at interface decreases with increasing effects of surface roughness. The results show the surface rougheness and wettability determines the slip or no-slip boundary conditions. The surface roughness geometry shows significant effects on the boundary conditions at the interface.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.6
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• pp.88-98
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• 2014

A moving mass on a skewed linear guideway model to analyze the friction-induced stick-slip behavior of ball-screw-driven slides is proposed. To describe the friction force, a friction coefficient function is modelled as a third-order polynomial of the relative velocity between the slide mass and a guideway. A nonlinear differential equation of motion is derived and an approximate solution is obtained using a perturbation method for the amplitudes and base frequencies of both pure-slip and stick-slip oscillations. The results are presented with time responses, phase plots, and amplitude plots, which are compared adequately with those obtained by Runge Kutta 4th-order numerical integration, as long as the difference between the static and kinematic friction coefficients is small. However, errors in the results by the approximate solution increase and are not negligible if the difference between the friction coefficients exceeds approximately 40% of the static friction coefficient.