• Transactions of Materials Processing
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• v.18 no.5
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• pp.410-415
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• 2009

Experimental and numerical studies were performed to examine the effect of material temperature and reduction ratio on friction coefficient during hot flat rolling. We carried out a single pass pilot hot flat rolling test at the temperatures range of $900{\sim}1200^{\circ}C$ and measured the spread of deformed material while reduction ratio varied from 20% to 40%. Materials used in this study were a high carbon steel and two alloy steels. The dimension of specimen used in hot rolling experiment was $50mm{\times}50mm{\times}300mm$. We performed a series of finite element simulation of the hot rolling process to compute the friction coefficient change in terms of steel grade and reduction ratio. Results showed that temperature dependency of friction coefficient is not noteworthy but the effect of reduction ratio on friction coefficient is quite large. For high carbon steel, friction coefficient at reduction ratio of 30% is lower than that at that of 20%. Meanwhile friction coefficient at reduction ratio of 40% was one and half times large compared with that at that of 20%. The effect of steel grade on friction coefficient was significant when reduction ration was large, e.g., 40%.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.850-854
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• 2009

Approximate analysis for a building installed with a friction damper is revisited to get insight of its dynamic behavior. Energy balance equation is used to have a closed analytical form solution of dynamic magnification factor (DMF) for the building with combined viscous and friction damping. It is found out that DMF is dependent on friction force ratio and resonance frequency. Linear transfer function from input external force to output building displacement is obtained by simplifying DMF equation. Root mean square of building displacement is derived under earthquake-like random excitation. Finally, design of friction damper is proposed by processing target control ratio, damping ratio factor, and friction force in sequence.

• Tribology and Lubricants
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• v.20 no.5
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• pp.266-271
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• 2004

The aim of this paper is to investigate the effect of surface texturing on reduction friction and to understand the potential of friction reduction through micro-scale dimple to fabricate by photolithography on pin-on-disk test using flat-on-flat contact geometry. It was verify that the friction property with respect to the same pitch has been influence on the size of dimple under lubricated sliding contact. Also, we can recognize from Stribeck curve that the friction property has a connection with the size of dimple. It can explain a relationship between the friction coefficient and a dimensionless parameter for lubrication condition. The friction property has been an effect on the size of surface texture on reduction friction, not only because the density of dimple, but also because the ratio of diameter/pitch. This ratio of approximately 0.5 recommend under the tested friction condition. It suggested that the ratio of d/p is an important parameter for surface texture design.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.217-222
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• 2004

The aim of this paper is to investigate the effect of micro-dimple size on reduction friction and to understand the potential of friction reduction through micro-scale dimple to fabricate by photolithography on pin-on-disk test using flat-on-flat contact geometry. It was verify that the friction property with respect to the same pitch has been influence on the size of dimple under lubricated sliding contact. Also, we can recognize from Stribeck curve that the friction property has a connection with the size of dimple. It can explain a relationship between the friction coefficient and a dimensionless parameter for lubrication condition. The friction property has been an effect on the size of surface texture on reduction friction, not only because the density of dimple, but also because the ratio of diameter/pitch. This ratio of approximately 0.5 is recommend under the tested friction condition. It suggested that the ratio of d/p is an important parameter for surface texture design.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.1
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• pp.22-28
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• 2010

Approximate analysis for a building installed with a friction damper is performed to get insight of its dynamic behavior. Energy balance equation is used to have a closed analytical form solution of dynamic magnification factor(DMF). It is found out that DMF is dependent on friction force ratio and resonance frequency. Approximation of DMF and equivalent damping ratio of a friction damper is proposed with such assumption that the building with a friction damper shows harmonic steady-state response and narrow banded response behavior near resonance frequency. Linear transfer function from input external force to output building displacement is suggested from the simplified DMF equation. Root mean square of a building displacement is derived under earthquake-like random excitation. Finally, design procedure of a friction damper is proposed by finding friction force corresponding to target control ratio. Numerical analysis is carried out to verify the proposed design procedure.

• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.1
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• pp.78-85
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• 2013

This paper presents the sliding mode control methods for anti-lock brake system (ABS) with the friction force observer. Using a simplified quarter car model, the sliding mode controller for ABS is designed to track the desired wheel slip ratio. Here, new method to find the desired wheel slip ratio which produces the maximum friction force between road and tire is suggested. The desired wheel slip ratio is varying according road and tire conditions to produce maximum friction force. In order to find optimum desired wheel slip ratio, the sliding mode observer for friction force is used. The proposed sliding mode controller with observer is evaluated in simulation, and the control design is shown to have high performance on roads with constant and varying adhesion coefficients.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1145-1150
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• 2005

The aim of this paper is to investigate the effect of surface texturing on metal surface and to understand the potential of friction reduction through micro-scale dimple to fabricate by photolithography on pin-on-disk test using flat-on-flat contact geometry. It was verify that the friction property with respect to the same pitch has been influence on the size of dimple under lubricated sliding contact. Also, we can recognize from Stribeck curve that the friction property has a connection with the size of dimple. It can explain a relationship between the friction coefficient and a dimensionless parameter for lubrication condition. The friction property has been an effect on the size of surface texture on reduction friction, not only because the density of dimple, but also because the ratio of diameter/pitch. This ratio of approximately 0.5 is recommend under the tested friction condition. It suggested that the ratio of d/p is an important parameter for surface texture design.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.5
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• pp.587-592
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• 1999

The combined effects of radius ratio and roughness pitch ratio on the turbulent fluid flow characteristics of the fully developed flow in the annullar tubes with rib-roughened core walls were determined for Reynolds number ranging from 12,000 to 66,000. To understand the underlying physical phenomena responsible for friction factor enhancement, measurements of velocity profiles and zero shear stress and maximum velocity positions were combined to propose the friction factor correlation. Friction factors were found to be a function of the roughness pitch ratio and radius ratio.

• Journal of Power System Engineering
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• v.17 no.1
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• pp.64-70
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• 2013

The heat transfer and friction factor characteristics of turbulent flows in three stationary channels have been investigated experimentally to check out the effect of divergence ratio. These are a constant cross-sectional channel and two diverging channels with ratio of divergence(Dho/Dhi) of 1.16 and 1.49. The measurement was conducted within the range of Reynolds numbers from 15,000 to 89,000 and the dimension of uniform cross-sectional test section is $100mm{\times}100mm$ at the cross section and 1,000 mm in length. The measurements of heat transfer coefficients and friction factors in the uniform channels were conducted as a reference. Because of the streamwise flow deceleration, the heat transfer and friction factor characteristics in the diverging channel were quite different from those of the constant cross-sectional channel. The effective friction factors and convective heat transfer coefficients increased with increasing the ratio of divergence of the channel.

• Tribology and Lubricants
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• v.14 no.2
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• pp.10-20
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• 1998

In this paper, the effects of material properties on the friction and wear behavior of pure metals are investigated. The sliding material pairs are selected based on their relative compatibility and relative hardness ratio of the specimen. The initial and steady-state friction coefficients are obtained in the experiments and the wear rates are quantitatively investigated. It is shown that the initial friction coefficient is affected by the hardness ratio of sliding materials. Furthermore, in steady state condition, neither hardness ratio nor compatibility has significant influence on the frictional behavior. As for wear, the ductility of the metal affects the wear particle generation process which in turn affects the frictional behavior. The findings of this research suggest that frictional interaction cannot be simply characterized by either compatibility or hardness ratio of the materials undergoing sliding contact.