• The Journal of Engineering Geology
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• v.23 no.3
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• pp.217-225
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• 2013

We carried out geometrical, kinematic, and geomechanical analyses on a lineament (the Imgok fault) near Gangneung, observed in ASTER images and aerial photographs, and field surveys. Earthquake focal mechanism solutions, used to estimate the present-day stress state, revealed that the direction of maximum compression is approximately N$70^{\circ}$E and that the stress condition is in favor of either strike-slip or reverse movement on the fault. The strike of the fault is not ideal for slip under the present-day stress field and thus the fault has a low slip tendency. However, the fault may be able to slip if the frictional coefficient (${\mu}$), representing the resistance of the fault to slip, is sufficiently low (e.g., ${\mu}$ < 0.25).

• Journal of Korea Water Resources Association
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• v.31 no.3
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• pp.223-234
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• 1998

Recently, the interests of the construction of the permeable submerged breakwaters have been increased to preserve and to improve the coastal environment, and to control the incident waves and littoral transport. It is very important to predict the wave transformation precisely over the permeable submerged breakwaters. This study discusses nonlinear wave transformation and characteristics by using BEM based on the frequency domain method of the 3rd-order Stokes waves. The Dupuit-Forchheimer formula is applied to the analysis of the fluid resistance of rubble stones, and the equation about equivalent linear frictional coefficient is newly modified based on the Lorentz's condition for the equivalent work. The numerical results are compared with the experimental ones for verification. These two results give a close agreement each other. It is confirmed that the present method of the 3rd-order Stokes waves estimates more precisely than that of the 2nd-order Stokes waves.

• Journal of Drive and Control
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• v.11 no.2
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• pp.30-35
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• 2014

The pumps of electro-hydrostatic actuators operate most frequently in boundary lubrication speed range, as they compensate for the position control errors as a control element. When conventional swash plate type piston pumps are applied to electro-hydrostatic actuators, the frictional power losses as well as the wear rate of sliding components, such as piston shoes can increase drastically under the boundary friction condition. In this paper, the power losses of the piston shoes were investigated which were engendered by a frictional solid-to-solid contact and leakage flow rate of their hydrostatic bearing. In order to reduce them, DLC-coating was applied to the swash plate and the ball joint of pistons along with its effects were demonstrated. In addition, it was also shown that the wear rate of the piston shoes could be markedly reduced using the DLC-coated swash plate.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.7
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• pp.779-784
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• 2014

This study provided the analytical model describing the friction-induced noise in the ball joint system under the edge loading condition. The frictional and conformal contact kinematics between the spherical bearing and the hemispherical socket was derived and the dynamic equations of the perturbed motion were established. The numerical results revealed that the bending modes of the ball joint system can become unstable due to friction, and the axial load and contact stiffness strongly influenced the dynamic instability. In contrast, the tilting angle of the socket was not found to significantly contribute to the dynamic instability of the ball joint.

• Elastomers and Composites
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• v.36 no.2
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• pp.121-129
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• 2001

The friction characteristics of natural rubber plates under various conditions including sliding speed, normal force, hardness, lubrication conditions and thickness of plate are analyzed experimentally. The frictional force and normal force are measured by a tester pin and a load ceil with strain gages. Experimental results suggest that the coefficient of friction decreases with increasing the hardness of rubber and decreasing the thickness of plate. The effect of sliding speed is not significant over the speed range employed. The coefficient of friction is found to be about 0.1 under oil lubrication condition and varies from 0.9 to 3.9 under no lubrication condition.

• Smart Structures and Systems
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• v.23 no.1
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• pp.31-44
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• 2019

The present study investigate the compressive stress, shear stress, tensile stress, vertical electrical displacement and horizontal electrical displacement induced due to a load moving with uniform velocity on the free rough surface of an irregular transversely isotropic functionally graded piezoelectric material (FGPM) substrate. The closed form expressions ofsaid induced stresses and electrical displacements for both electrically open condition and electrically short condition have been deduced. The influence of various affecting parameters viz. maximum depth of irregularity, irregularity factor, parameter of functionally gradedness, frictional coefficient of the rough upper surface, piezoelectricity/dielectricity on said induced stresses and electrical displacements have been examined through numerical computation and graphical illustration for both electrically open and short conditions. The comparative analysis on the influence of electrically open and short conditions as well as presence and absence of piezoelectricity on the induced stresses and induced electrical displacements due to a moving load serve as the salient features of the present study. Moreover, some important peculiarities have also been traced out by means of graphs.

• Tribology and Lubricants
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• v.39 no.3
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• pp.118-122
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• 2023

In our study, we develop a finite element model based on Archard's wear law to predict the cumulative wear and the evolution of the tool profile in friction stir welding (FSW) applications. Our model considers the rotational and translational behaviors of the tool, providing a comprehensive description of the wear process. We validate the accuracy of our model by comparing it against experimental results, examining both the predicted cumulative wear and the resulting changes to the tool profile caused by wear. We perform a detailed comparison between the predictions of the model and experimental data by manipulating non-dimensional coefficients comprising model parameters, such as element sizes and time increments. This comparison facilitates the identification of a specific non-dimensional coefficient condition that best replicates the experimentally observed cumulative wear. We also directly compare the worn tool profiles predicted by the model using this specific non-dimensional coefficient condition with the profiles obtained from wear experiments. Through this process, we identify the model settings that yield a tool wear profile closely aligning with the experimental results. Our research demonstrates that carefully selecting non-dimensional coefficients can significantly enhance the predictive accuracy of finite element models for tool wear in FSW processes. The results from our study hold potential implications for enhancing tool longevity and welding quality in industrial applications.

• Transactions of Materials Processing
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• v.32 no.6
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• pp.360-366
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• 2023

This study is concerned with the surface quality of products according to the material and coating condition of the forming tool in incremental sheet forming. Three forming tools, SKD11 with and without diamond-like-coating (DLC) and polymer tool tip, were used to form conical and pyramidal geometries to take into account the influence of friction between the forming tool and the sheet on the surface quality including geometric accuracy of deformed samples. Each test was performed using SUS304 with a thickness of 0.4 mm according to different incremental depths per lap of 0.5 mm, 1.0 mm, and 1.5 mm for the contour tool path, considering the increase in normal force which is associated with the frictional behavior during local deformation. The surface quality was then investigated through surface roughness measured with KEYENCE VR-6000 and relative strain distribution including deformed shape analyzed with ARGUS which is a non-contact optical strain measurement system. Differences between 3D CAD surfaces and captured geometry from experiments were evaluated to compare the effect of friction on geometric accuracy. From comparisons of experimental results, it was revealed that the polymer-based tool tip can improve surface quality and geometric accuracy by reducing the undesired material flow due to local friction in the increment sheet forming process.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.06a
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• pp.24-33
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• 2000

The effect of particulate contamination on friction and wear between a negative-pressure picoslider / tri-pad nanoslider and laser-textured disk was studied. Particles of different concentration were injected at the head-disk interface consisting of disks with various textures and slider types at different speed. Durability increased and coefficient of friction decreased as the disk speed increased in a contaminated environment. Frictional characteristics and durability in the data zone were better for those of the laser-textured zone. It was also found that durability of head-disk interface (HDI)decreased as the particle concentration increased. The interface durability with a picoslider was better than that with a nanoslider at any condition in a contaminated environment. Based on the test results, mechanisms were proposed to explain the reasons why durability with a picoslider was superior to that with a nanoslider.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.7
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• pp.1138-1145
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• 2003

In this paper, a study on the dynamic behavior and lubrication characteristics of a reciprocating compression mechanism used in small refrigeration compressor is performed. In the problem formulation of the compressor dynamics, the viscous frictional force between piston and cylinder wall is considered in order to determine the coupled dynamic behaviors of piston and crankshaft. The solutions of the equations of motion of the reciprocating mechanism along with the time dependent Reynolds equations for the lubricating film between piston and cylinder wall and oil films of the journal bearings are obtained simultaneously. The hydrodynamic forces of journal bearings are calculated using finite bearing model and Gumbel boundary condition. And, a Newton-Raphson procedure was employed in solving the nonlinear equations of piston and crankshaft. The results explored the effects of design parameters on the stability and lubrication characteristics of the compression mechanism.