• Journal of the Korean Society for Precision Engineering
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• v.19 no.10
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• pp.163-170
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• 2002

The dynamic model of a high-speed vacuum circuit breaker mechanism with spring-actuated cam and linkage is derived to simulate the high-speed closing and opening operations. Its validation for an analysis of high-speed motion behavior is checked through experiments. The characteristics of the friction on the camshaft are investigated using the nonlinear pendulum experiment. The parameters of the friction model are estimated using the optimization technique. The analysis exhibits that the friction of the pendulum depends on stick-slip, Stribeck effect and viscous damping. Comparing simulation results with actual responses using a high-speed camera, the appropriateness of derived dynamic models for the rapid closing and opening operations is shown. The spring motion, which has much influence on the closing responses, is observed.

• Fibers and Polymers
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• v.5 no.4
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• pp.259-263
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• 2004

Rubber-modified epoxy resins have been employed as adhesive and matrix materials for glass and corbon-fiber composites. The behavior of fracture around a crack tip for rubber-modified epoxy resin is investigated through the acoustic emission (AE) analysis of compact tension specimens. Damage zone and rubber particles distributed around a crack tip were observed by a polarized optical microscope and an atomic force microscope (AFM). The damage zone in front of pre-crack tip in rubber-modified specimen $(15wt\%\; rubber)$ began to form at about $13\%$ level of the fracture load and grew in size until $57\%$ load level. After that, the crack propagated in a stick-slip manner. Based on time-frequency analysis of AE signals and microscopic observation of damage zone, it was thought that AE signals with frequency bands of 0.15-0.20 MHz and 0.20­0.30 MHz were generated from cavitation in the damage zone and crack propagation, respectively.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.23 no.2
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• pp.199-208
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• 2010

A friction damper installed at a building shows nonlinear behavior since its stick and slip states are occurred repeatedly depending on the amplitude of external loadings to dissipate input energy. Friction damping is existed for the building with a friction damper. In additionally viscous one is inherently included. Therefore, the building installed in such combined damping is quite involved to find the analytical solution. In this study, first, displacement and acceleration characteristics are identified based on the exact solution for a single-degree-freedom building with a friction damper having both friction and viscous damping. Second, in free vibration, the equivalent viscous damping ratio is obtained by the energy dissipation. Third, numerical analysis is carried out to find response configuration with various friction force ratios. Fourth, corresponding equivalent viscous damping ratio is derived with the finding that the response reaches into steady-state for both friction and viscous damped structure. It is deduced using balance of input external energy and output dissipation energy for steady-state response. Finally, the equivalent viscous damping ratios of free or harmonic vibration are verified through nonlinear analysis.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.11
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• pp.1228-1235
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• 2012

A refrigerator has many components which are made from diverse materials such as metal, polymer, plastic, and rubber. So, it generally requires much time and efforts to build up an analysis model in finite element analysis. In this work, to reduce the computational time and efforts a simplified modeling method was proposed for the analysis of a refrigerator. Occasionally, a stick-slip noise occurs in a refrigerator due to relative slip between shelf and inner-case. When we solve the problem by a FE analysis, we should model the structures with detail for considering the contact conditions; by this reason, too many efforts are consumed in the conventional analysis method. Through this work, we shows the concept of simplifying approach and a good agreement with the results of a real model analysis. And also, the evaluation of the proposed method and the application of contact analysis using the simplified model are discussed.

• Journal of the Korean Society for Railway
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• v.19 no.1
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• pp.20-28
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• 2016

Curved squeal noise may result when railway vehicles run on curved tracks. Contact between the wheels and the rails causes a stick-slip phenomenon, which generates squeal noise. In order to identify the mechanism of the squeal noise systematically, a scaled test rig has been fabricated. Knowledge of the contact forces between the wheels and the rail rollers is essential for investigating the squeal noise characteristics; however, it is difficult to measure there contact force. In this study, contact forces have been calculated indirectly according to the modal behavior of the subframe that supports the rail roller and the responses at specific positions of that subframe. In order to verify the estimated contact forces, the displacements at the contact points between the wheels and rail rollers have been calculated from the estimated forces; the resulting values have been compared with the measured displacement values. The SPL at the specific location has been calculated using the estimated contact forces and this also has been compared with the SPL, measured in a semi-anechoic chamber. The comparisons in displacements and SPLs show good correlation.

• Tribology and Lubricants
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• v.17 no.5
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• pp.351-357
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• 2001

Tribological behavior of NAO type brake linings containing different volume ratios of graphite and Sb$_2$S$_3$ was investigated using a scale dynamometer. Three different test modes consisting of stop, drag, and fade tests were employed to elucidate the effect of the solid lubricants on brake performance. Results of this work showed that the two solid lubricants, graphite and Sb$_2$S$_3$, significantly affected friction characteristics at various braking situations. Compared with the brake linings containing a single lubricant, the brake linings containing both solid lubricants showed better friction stability due to the synergistic effect of the two disparate lubricants during the stop and the drag test. In particular, in the case of containing two solid lubricants, the brake lining with higher contents of graphite showed better fade resistance than others.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.5
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• pp.572-577
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• 2011

Curve squealing of inter-city railway vehicle is a noise with high acoustic pressure and rather narrow frequency spectra. This noise turns out to be very annoying for the people living in the neighborhood of locations and the passenger in railway vehicle where this phenomenon occurs. Squealing is caused by a self-exited stick-slip oscillation in the wheel-rail contact. Curve squeal noise of railway vehicles that passed by a factor of the speed limit, so to overcome in order to improve running performance is one of the largest technology. In the present paper, characteristic of squeal noise behavior at the Hanvit-200 tilting train test-site. Curve squealing of railway wheels/rail contact occurs in R400~ R800 curves with a frequency range of about 4~11 kHz. If the curve is less than the radius of wheel frail contact due to |left-right| noise level difference (dBA) shows a significant effect of squeal noise were more likely.

• Tribology and Lubricants
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• v.29 no.3
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• pp.167-170
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• 2013

The friction behavior of human skin is determined by the complex interplay of the material and surface properties of the skin, as well as the contacting material, and strongly depends on the contact parameters (e.g., pressure and sliding velocity) and the presence of substances such as water, sweat, or skin surface lipids at the interface. Including a study on the effect of a surface's physical roughness for skin sliding over the surface, various studies have been conducted to understand human tactile sensibility. However, to investigate products in relation to human tactile sensibility, more objective research is needed. This study performed sliding experiments between the skin and the surfaces of phone cases to understand how the texture, friction, and stick-slip characteristics are related. Eight phone case surfaces with different topologies and chemical (or mechanical) compatibilities with skin were prepared and tested multiple times.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.06a
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• pp.55-63
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• 2001

Friction and wear properties of brake friction materials containing different metal fibers (Al, Cu or Steel fibers) were investigated using a pad-on-disk type friction tester. Two different materials(gray iron and Al-MMC)) were used for disks rubbing against the friction materials. Results from ambient temperature tests revealed that the friction material containing Cu fibers sliding against cast iron disk showed a distinct negative ${\mu}$-ν (friction coefficient vs. sliding velocity) relation implying possible stick-slip generation at low speed. The negative ${\mu}$-ν relation was not observed when the Cu-containing friction materials were rubbed against the. Al-MMC counter surface. As applied loads increased, friction materials showed higher friction coefficients comparatively. Friction materials slid against cast iron disks exhibited higher friction coefficients than Al-MMC disks during high temperature tests. On the other hand, high temperature test results suggested that copper fibers in the friction material improved fade resistance and the steel fibers were not compatible with Al-MMC disks showing severe material transfer and erratic friction behavior during sliding at elevated temperatures.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.06a
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• pp.72-78
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• 2001

An experimental investigation was conducted to examine the tribological behavior of NAO (non-asbestos organic) type brake linings containing different volume ratios of graphite and antimony trisulfide (Sb$_2$S$_3$). In order to investigate the effect of the solid lubricants on brake performance, three different friction tests (pressure, speed, and temperature sensitive tests) were carried out using a scale dynamometer. The test results showed that the friction characteristics were strongly affected by the type and the amount of solid lubricants in the brake lining. It was found that the brake linings with both solid lubricants were better in friction stability due to the complementary role of the two disparate lubricating properties at various pressure and speed conditions. In particular, the brake lining containing higher concentrations of graphite showed better fade resistance than others during high temperature friction test.