• Tribology and Lubricants
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• 제23권1호
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• pp.9-13
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• 2007

Despite numerous researches on atomic-scale friction have been carried out for understanding the origin of friction, lots of questions about sliding friction still remain. It is known that friction at atomic-scale always shows unique phenomena called 'stick-slips' which reflect atomic lattice of a scanned surface. In this work, experimental study on the effects of system stiffnesses and load on the atomic-scale stick-slip friction of graphite was performed by using an Atomic Force Microscope and various cantilevers/tips. The objective of this research is to figure out the dependency of atomic-scale friction on the nanomechanical properties in sliding contact such as load, stiffness and contact materials systematically. From this work, the experimental observation of transitions in atomic-scale friction from smooth sliding to multiple stick-slips in air was first made, according to the lateral cantilever stiffness and applied normal load. The superlubricity of graphite could be verified from friction vs. load experiments. Based on the results, the relationship between the stickslip behaviors and contact stiffness was carefully discussed in this work. The results or this work indicate that the atomic-scale stick-slip behaviors can be controlled by adjusting the system stiffnesses and contact materials.

• Journal of Mechanical Science and Technology
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• 제20권9호
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• pp.1399-1409
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• 2006

An improved friction model was proposed with consideration of the effect of the sliding speed, the contact pressure and the temperature, and it was implemented into a user subroutine of a commercial FEM code, ABAQUS/Explicit. Then, a smooth tire was simulated for free rolling, driving, braking and cornering situations using the improved friction model and the Coulomb friction model, and the effect of the friction models on the slip, the frictional energy distribution and the cornering force and moment was analyzed. For the free rolling, the driving and the braking situations, the improved friction model and the Coulomb friction model resulted in similar profiles of the slip and the frictional energy distributions although the magnitudes were different. The slips obtained from the simulations were in a good correlation with experimental data. For the cornering situation, the Coulomb friction model with the coefficient of friction of 1 or 2 resulted in lower or higher cornering forces and moments than experimental data. In addition, in contrast to experimental data it did not result in a maximum cornering force and a decrease of the cornering moment for the increase of the speed. However, the improved friction model resulted in similar cornering forces and moments to experimental data, and it resulted in a maximum cornering force and a decrease of the cornering moment for the increase of the speed, showing a good correlation with experimental data.

• 대한인간공학회지
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• 제20권2호
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• pp.47-57
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• 2001

To simulate an actual slip to measure floor slipperiness, slip resistance testers simulate slip in only forward direction because forward slip in the landing phase was found to be the most important factor for loss of balance. Backward slip in the take off phase was possible but was excluded in the friction test protocol because it was not dangerous. However, backward slip was tested in the friction test protocol without any theoretical background of the significance in generating dangerous slips and falls and was proven to be as good as forward slip in measuring floor slipperiness. Therefore, this study was designed to investigate the significance of backward slip in generating dangerous slips and falls with different combinations of floor and shoe sole. The results showed different tendency of backward slip in take off phase being significant in generating dangerous slips and falls because backward slip in the takeoff phase affected gait pattern disturbances seriously. resulted in dangerous falls. Fast toe velocity increased the severity of backward slip and confirmed the significance of backward slip in generating dangerous slips and falls. As a result, this study recommends the utilization of backward slip in the measurement of floor slipperiness.

• Smart Structures and Systems
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• 제4권4호
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• pp.493-515
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• 2008

Semi-active control systems have attracted a great deal of attention in recent years because these systems can operate on battery power alone, proving advantageous during seismic events when the main power source of the structure may likely fail. The behavior of semi-active devices is often highly non-linear and requires suitable and efficient control algorithm. This paper presents the comparative study and performance of variable semi-active friction dampers by using recently proposed predictive control law with direct output feedback. In this control law, the variable slip force of semi-active variable friction damper is kept slightly lower than the critical friction force, which allows the damper to remain in the slip state during an earthquake, resulting in improved energy dissipation capability. This control algorithm is able to produce a continuous and smooth slip forces for a variable friction damper. The numerical examples include a structure controlled with multiple variable semi-active friction dampers and with multiple passive friction dampers. A parameter, gain multiplier defined as the ratio of damper force to critical damper control force, is investigated under four different real earthquake ground motions, which plays an important role in the present control algorithm of the damper. The numerically evaluated optimum parametric value is considered for the analysis of the structure with dampers. The numerical results of the variable friction dampers show better performance over the passive dampers in reducing the seismic response of structures.

• 한국정밀공학회지
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• 제18권4호
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• pp.64-71
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• 2001

In general, precise linear actuators using piezoelectric element are driven by friction force. Exact understanding of friction plays an important role in analysis and control of a motor. In this research, we designed a precise linear actuator using piezoelectric elements and observed its dynamic characteristics. By varying phase angle difference and amplitudes of the sinusoidal waves that are driving inputs, we can know that it is possible to control moving direction and distance of the slider. As preload is increased, its moving distance is decreased. And also, we have modeled a precise linear actuator using stick slip friction models such as classical, Karnopp. and reset integrator. Finally, by comparing the results of simulation and experiment, it was verified that the model is well designed.

• 한국항공운항학회지
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• 제23권1호
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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.

• 한국음향학회지
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• 제43권3호
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• pp.270-276
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• 2024

본 연구에서는 기계전자 제품에 사용되는 소재의 마찰실험을 통해 스틱슬립 특성을 분석하고 냉장고 내부에서 발생하는 이상소음을 저감하는 개선안을 제안하였다. 소재의 스틱슬립 현상을 분석하기 위해 마찰실험장치를 제작하고 마찰실험을 수행하였다. 또한 냉장고 내부에서 발생하는 이상소음의 현상과 위치를 분석하기 위해 내부부품의 진동과 소음 레벨을 측정하였다. 그리고 냉장고 현상분석 결과와 마찰실험 결과를 비교하여 냉장고 내부에서 발생하는 이상소음은 내부부품의 스틱슬립 현상에 의한 것임을 확인하였다. 마지막으로 이상소음을 저감하는 개선안을 제안하기 위해 다구찌 기법을 이용한 마찰실험을 수행하였다. 그리고 개선안을 냉장고에 적용하여 성능을 검증하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2009년도 춘계학술대회 논문집
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• pp.214-215
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• 2009

The friction is inevitable and unpredictable phenomena, so most mechanical systems are designed to low friction effect by using bearings and lubricants. However, the slip-stick actuator applies the friction force to its movement. The slip-stick mechanism is applied the piezoelectric actuator to overcome short displacement. Fast response of piezoelectric actuator is also good characteristic for the slip-stick mechanism. However, the piezoelectric actuator with slip-stick mechanism isn't common, because its cost and driving voltage are too high. In this paper, a voice-coil actuator with slip-stick mechanism is introduced. The cost and the driving voltage of a voice-coil actuator are much less than the piezoelectric actuator. And a dynamic vibration amplifier is proposed to adjust the dynamic performance of the actuator. By the results of numerical analysis, the feasibility of a dynamic vibration amplifier is verified.

• Earthquakes and Structures
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• 제18권2호
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• pp.185-199
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• 2020

A computationally-efficient method for multi-criteria optimisation is developed for performance-based seismic design of friction energy dissipation dampers in RC structures. The proposed method is based on the concept of Uniform Distribution of Deformation (UDD), where the slip-load distribution along the height of the structure is gradually modified to satisfy multiple performance targets while minimising the additional loads imposed on existing structural elements and foundation. The efficiency of the method is demonstrated through optimisation of 3, 5, 10, 15 and 20-storey RC frames with friction wall dampers subjected to design representative earthquakes using single and multi-criteria optimisation scenarios. The optimum design solutions are obtained in only a few steps, while they are shown to be independent of the selected initial slip loads and convergence factor. Optimum frames satisfy all predefined design targets and exhibit up to 48% lower imposed loads compared to designs using a previously proposed slip-load distribution. It is also shown that dampers designed with optimum slip load patterns based on a set of spectrum-compatible synthetic earthquakes, on average, provide acceptable design solutions under multiple natural seismic excitations representing the design spectrum.

• Safety and Health at Work
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• 제9권2호
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• pp.180-183
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• 2018

Background: This research investigates the degrees of slipperiness felt by the participants who walk on contaminants applied to a floor surface to decide degrees of slipperiness for various contaminants. Methods: For the experiment, 30 participants walked on a floor to which six contaminants were applied. All participants took the analytic hierarchy process (AHP)-based slipperiness questionnaire survey for the six kinds of contaminants, and the results were compared with the coefficient of friction. Results: The results of slip risk from the AHP indicate that grease is the most slippery of the six contaminants, followed by diesel engine oil, hydraulic oil, cooking oil, water-soluble cutting oil, and water in a decreasing order of slipperiness. When the results of slip risk from the AHP are compared with the static coefficient of friction for each contaminant, the order of slip risk follows the same trend. Although the results of slip risk from the AHP coincide with the static coefficient of friction, further study would be needed to investigate this relationship. Conclusion: This study will contribute as reference material for future research on preventing industrial accidents that result in falls from high places due to slipping.