• Journal of the Korean Society for Precision Engineering
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• v.25 no.11
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• pp.119-125
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• 2008

The objective of this study was to compare micro-scale friction coefficients with and without synovial fluid, and micro-scale measurements were performed using atomic force microscopy (AFM) with a $5{\mu}m$ spherical probe. Four cylindrical cartilage specimens were harvested from two fresh bovine humeral heads (4-6 months old). $Average{\pm}standard$ deviation values of the micro-scale AFM frictional coefficients calculated from the liner fit of friction versus normal force was $0.177{\pm}0.012$ and $0.130{\pm}0.010$ with and without synovial fluid coating on AFM probe respectively, showing its reduction by ${\sim}27%$ with synovial fluid. To the best of our knowledge, this experimental study investigates the first such comparisons of frictional response of articular cartilage with and without synovial fluid coating on AFM probe, and provides significant insights into the role of synovial fluid in the articular cartilage friction and lubrication independently of the confounding effect of fluid pressurization in the articular cartilage.

• Journal of the Korean Institute of Rural Architecture
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• v.23 no.3
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• pp.1-8
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• 2021

Rural multi-purpose buildings needs to ensure their safety against various disasters. Therefore, a pile foundation, which is a foundation type that can transmit the load of the structure to the bedrock layer, has been designed. The pile foundation method is largely divided into driving piles method and pre-bored pile method. Recently, in order to respond to the Noise and Vibration Control Act and related environmental complaints, construction of pile foundation adopts pre-bored pile method. The bearing capacity of the pre-bored pile method is calculated through a load test in situ. However, a disadvantage stems in that it is difficult to measure the ultimate bearing capacity due to field conditions. Therefore, in this study, the skin frictional force of pre-bored pile was measured through a model test in laboratory for each pile filling material. In result, the pile filling material with using circulating resources shows superior skin frictional force than ordinary portland cement. This study also judged that the result can be applied in place of ordinary Portland cement in the field.

• Design & Manufacturing
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• v.17 no.4
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• pp.8-13
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• 2023

In this study, it was studied whether a new measurement factor "frictional vibration" that occurs due to the material flow of the die and sheet metal in the flange area during deep drawing process, could be measured using an vibration sensor. The blank holder force acting on the flange area during drawing processing acts as a friction force in the opposite direction into which the sheet material flows and causes friction vibration. As the blank holder force increases, the friction force increases, and as the blank holder force decreases, the friction force also decreases. Because of this, friction vibration also increases and decreases in proportion to the size of the blank holder force. According to this theory, whether frictional vibration occurs was measured using a flange simulator and a vibration sensor. The initial pressure was created using a torque wrench, and it was confirmed that the amplitude increased by about 4 times when torque 6 Nm was increased. When the forming velocity was rapidly changed to 300 mm/min, the amplitude increased approximately 4 times. It was confirmed that the amplitude of frictional vibration according to the measurement location was greater the further away from the specimen. It was verified that a new measurement factor "friction vibration" in the flange area can be measured and used for online monitoring.

• Fashion & Textile Research Journal
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• v.4 no.3
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• pp.273-283
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• 2002

In this study, the correlations of the two frictional testers have been investigated; one is the KES-FB4 system, the other is the Fabric-on-Fabric Frictional tester which was devised by authors. According to the results, the correlation between the frictional coefficients measured by the two testers has been shown highly as the load increased. But the effect of roughness of fabric surface was not dearly revealed in this study. The frictional characteristics of fabric woven from filament yarns were different with those of fabric woven from spun yarns. And, like the other materials, the effect of load on fabrics used in this experiment was related with the frictional force between two fabrics. The frictional behaviors, however, were obviously different with harder material because the frictional coefficients were not constant as the load increased.

• Journal of the Korean Geotechnical Society
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• v.36 no.11
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• pp.107-117
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• 2020

Open-ended steel pipe piles have outside frictional force and inside frictional resistance in which blocked soil acts on the inside of the steel pipe during installation. It is expected that the ultimate load will change depending on the inside and outside resistance. And, if the ground on which the piles were constructed is clay soil, it is predicted that it will have effect on the negative skin friction caused by the ground settlement. Therefore, in this study, the behavior according to the inside and outside resistance characteristics of steel pipe piles was analyzed numerically, and the frictional force distribution, axial load and settlements before and after the occurrence of ground settlement were calculated. As a result of the analysis, the inside frictional resistance had less influence than the outside frictional resistance. However, inside frictional resistance is considered to be one of the important factors considering the effect on the overall pile behavior, and both resistance factors need to be considered in the design process.

• Journal of Ocean Engineering and Technology
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• v.24 no.4
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• pp.13-22
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• 2010

While a caisson used for breakwater is carried by a floating dock, accompanying stability problem by its existing motions in the dock is quite important and should be pre-checked against sea environmental condition. In the stability analysis, the acceleration, velocity, angle of roll and pitch motions are important to calculate frictional force and separation force. If separation force becomes bigger than frictional force, serious collision may be occurred between caisson and floating dock. In this study, stability evaluation during the transportation of a caisson on floating dock for breakwater was performed by using a commercial program, HydroD and CHARM3D/HARP.

• Tribology and Lubricants
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• v.39 no.6
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• pp.273-277
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• 2023

This paper presents a molecular dynamics simulation-based numerical investigation of the influence of surface energy on water lubrication. Models composed of a crystalline substrate, half cylindrical tip, and cluster of water molecules are prepared for a tribological-characteristic evaluation. To determine the effect of surface energy on lubrication, the surface energy between the substrate and water molecules as well as that between the tip and water molecules are controlled by changing the interatomic potential parameters. Simulations are conducted to investigate the indentation and sliding processes. Three different normal forces are applied to the system by controlling the indentation depth to examine the influence of normal force on the lubrication of the system. The simulation results reveal that the solid surface's surface energy and normal force significantly affect the behavior of the water molecules and lubrication characteristics. The lubrication characteristics of the water molecules deteriorate with the increasing magnitude of the normal force. At a low surface energy, the water molecules are readily squeezed out of the interface under a load, thus increasing the frictional force. Contrarily, a moderate surface energy prevents expulsion of the water molecules due to squeezing, resulting in a low frictional force. At a high surface energy, although squeezing of the water molecules is restricted, similar to the case of moderate surface energy, dragging occurs at the soil surface-water molecule interface, and the frictional force increases.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.06a
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• pp.36-41
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• 2001

In this work, the changes in the friction force(lateral force) with respect to nanoscale geometric variation were investigated using an Atomic Force Microscope and a Lateral Force Microscope. It could be concluded that the changes in the friction force correspond well to the slope change rather than the surface slope itself, and that the influence of slope change on the frictional behavior is dependent on the magnitude of the slope and the torsional stiffness of the cantilever. Also, the nominal friction force is found to be more significantly affected by the material and the physical-chemical state of the surface rather than by nanoscale geometric steps. However, the change in nanoscale geometric details of the surface cause instantaneous change and slight variation in the friction signal.

• Journal of Fisheries and Marine Sciences Education
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• v.9 no.1
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• pp.40-48
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• 1997

In this study, uniform pressure distribution with small hole on the surface of symmetric object were given to reduce the viscous frictional force. The results were as follows : 1. The velocity on upper stream were accelerated by uniform pressure distribution on symmetric objects for reducing the viscous frictional resistances. 2. The effects of the distributed small holes were reduced the viscous frictional resistances in down stream region more than upper stream due to the increasing pressure in reverse flow region. 3. The viscous skin friction on surface of symmetric objects with and without distributed small holes are effect in region of upper stream and much decreased in down stream region due to increasing of boundary layer thickness.

• Transactions of the Korean Society of Automotive Engineers
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• v.8 no.3
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• pp.56-64
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• 2000

A friction force measurement system using the floating liner method was developed to study the frictional behavior of piston rings. The measurement system was carefully designed to control the effect of the piston secondary motion and the temperature of cylinder wall and oil. The friction force between the barrel shaped piston ring and the cylinder liner, was measured under the condition of flooded oil supply. The measured friction forces were classified into five frictional modes with regard to the combination of predominant lubrication regimes(boundary, mixed and hydrodynamic lubrication) and stroke regions(midstroke and dead centers). The modes could be identified on the Stribeck diagram of the friction coefficients and the dimensionless number of ㎼/p, where the friction coefficients are evaluated at near the midstroke and dead centers.