• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2002.05a
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• pp.54-57
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• 2002

In order to find the effect of lubricant viscosity, sheet surface roughness, tool geometry, and forming speed on the frictional characteristics in sheet metal forming, a sheet metal friction tester was designed and manufactured and friction tests of various sheets were performed. Friction test results showed that as the lubricant viscosity becomes lower, the friction coefficient is higher. When surface roughness is extreme1y low or high, the friction coefficient is high. As punch comer radius and punch speed are bigger, the value of friction coefficient is smaller. The sensitivity of friction coefficient is mainly governed by lubricant viscosity and sheet surface roughness.

• Journal of Power System Engineering
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• v.8 no.1
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• pp.36-40
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• 2004

Two-phase loop systems using the latent heat capacity of their working fluids can meet the increasing power requirements and are well suited to thermal management systems of future large applications, due to its abilities to handle large heat loads and to provide them at uniform temperatures regardless of the changes in the heat loads. Therefore some experiments on the effect of the gas and liquid superficial velocities, $j_G,\;j_L$ on flow pattern transition, void fraction and frictional pressure loss were performed on a co-current air-water flow in an adiabatic horizontal tube. The flow patterns were depended on the superficial velocity of each phase. It snowed that the increasing $j_L$, resulted in a significant increase in the frictional pressure loss for all flow patterns, at a constant $j_G$. The experimental results were also evaluated with some of existing models and correlations.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.10a
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• pp.18-23
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• 2002

In this paper, The torque of CNC spindle motor during machining is estimated without speed measuring sensor. The CNC spindle system is divided into two parts, the induction spindle motor part and mechanical part. In mechanical part the variation of the frictional force due to the increment of the cutting torque and the effect of damping coefficient is investigated. Damping coefficient is found to be a function of spindle speed and not influenced by the weight of the load, while frictional force is a function of both the cutting torque and spindle speed. Experimental formulars are drawn for damping coefficient as a function of spindle speed and frictional force as a function of both cutting torque and spindle speed respectively, to estimate the cutting torque accurately. Graphical programming is used to implement the suggested algorithm, to monitor the torque of an induction motor in real time. Torque of the spindle induction motor is well monitored with 3% error range under various cutting conditions.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.11a
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• pp.50-58
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• 2000

A linear elastic fracture mechanics analysis of multiful subsurface cracks propagation in a half-space subjected to moving thermomechanical surface traction was peformed using the finite element method. The effect of frictional heat at the sliding surface on the crack growth behavior is analyzed in terms of the thermal load and peclet number. The crack propagation direction is predicted in light of the magnitudes of the maximum shear and tensile stress intensity factor ranges. When moving thermomechanical surface traction exists, subsurface horizontal cracks are propagation in-plane crack growth rate at the beginning but they are propagation out-of-plane crack growth rate by the frictional heat which is occurrence by the repeated sliding contact.

• Tribology and Lubricants
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• v.25 no.1
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• pp.49-55
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• 2009

The frictional properties of automotive brake pads with four different ceramic materials such as magnesia, hematite, alumina, and zircon were investigated. A Krauss type friction tester using gray iron disks was used to examine the friction coefficient, intensity of friction force oscillation, and the tribe-surfaces. Results showed that the friction coefficient increased as the hardness of abrasives increases. Friction oscillation was also increased with hardness of the abrasives. However, the friction materials containing less abrasive particles produced stable friction films on the sliding surface. The transition between two-body and three body abrasion during sliding also played a crucial role in destructing the friction film on the pad surface and in determining various frictional properties.

• The korean journal of orthodontics
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• v.34 no.3 s.104
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• pp.253-260
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• 2004

Frictional force between the orthodontic bracket and arch wire during sliding tooth movement is related to many factors, such as the size, shape and material of both the bracket and wire, ligation method and the angle formed between the bracket and wire. There have been clear conclusions drawn in regard to most of these factors, but as to the effect of bracket width on frictional force there are only conflicting studies. This study was designed to investigate the effect of bracket width on the amount of frictional forces generated during clinically simulated tooth movement. Three different widths of brackets $(0.018{\times}0.025'\;standard)$ narrow (2.40mm), medium (3.00mm) and wide (4.25mm) were used in tandem with $0.016{\times}0.022'$ stainless steel wire. Three bracket-arch wire combinations were drawn on for 4 minutes on a testing apparatus with a head speed of 0.5mm/min and tested 7 times each. To reproduce biological conditions, dentoalveolar models were designed with indirect technique using a material with similar elastic properties as periodontal ligament (PDL). In addition, to minimize the effect of ligation force, elastomer was used with added resin, which was attached to the bracket to make up for the discrepancies of bracket width. The results were as follows: 1. Maximum frictional force for each bracket-arch wire combination was: Narrow (2.40mm): $68.09\pm4.69gmf$ Medium (3.00mm): $72.75\pm4.98 gmf$ Wide (4.25mm): $72.59\pm4.54gmf$ 2. Frictional force was increased with more displacement of wire through the bracket slot. 3. The ANOVA psot-hoc test showed that the bracker width had no significant effect on frictional force when tested under clinically simulated conditions(p>0.05).

• Journal of Mechanical Science and Technology
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• v.20 no.9
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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.

• Elastomers and Composites
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• v.44 no.4
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• pp.401-407
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• 2009

Commercial grades of solution styrene-butadiene rubbers extended with high aromatic oils having high polycyclic aromatic compounds (PCA) and low PCA oils were used to study the effect of the processing oil particularly on the crack propagation resistance and frictional wear resistance of the vulcanizates. The aromatic oil based vulcanizates exhibited superior fracture behavior over the low PCA oil extended vulcanizates based on tensile and trouser tear tests. Compounds with aromatic oil showed superior crack propagation resistance compared with those containing low PCA oil, especially at the lower ranges of tearing energy. In terms of frictional wear resistance, the aromatic oil extended compounds showed superior performance particularly in the lower frictional work ($W_f$) range but in the higher $W_f$ range the low PCA oil extended vulcanizates performed better.

• The korean journal of orthodontics
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• v.28 no.5 s.70
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• pp.813-823
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• 1998

The frictional force has been considered as an harmful factor in an active unit where tooth movement occurs, but as an advantageous factor in anchor unit that resist tooth movement. That is, efficient tooth movement is planned by using ligation methods that have low levels of bracket-wire frictional force and the anchorage control can be achieved by using ligation methods that have high levels of bracket-wire frictional force that result in binding of the bracket accompanied by little or no tooth movement. The purpose of this study was to evaluate the frictional force generated between bracket and wire in accordance with the methods of ligation, the material of ligation and the passage of time under artificial saliva. Tested were 0.017x0.022 inch stainless steel wires in standard edgewise twin brackets for upper central incisors in a 0.018-inch slot. The wires were ligated into the brackets with elastomeric modules and stainless steel ligatures. Whole tie, half tie, twisting tie and double overlay tie were done with elastomeric modules. With 0.009-inch stainless steel ligature whole tie and half tie were done by needle holder and whole tie by ligature tying plier. With 0.012-inch stainless steel ligature whole ties were done by needle holder. Whole tie groups of elastomeric module were kept in artificial saliva bath at $37^{\circ}C$ for 28 days. The frictional force was recorded by means of an Instron universial testing instrument (4202 INSTRON, Instron Co., U.S.A.) at initial, 7, 14, 21, and 28 days. The results for ligated samples in a simulated oral environment revealed the fellowing : ${\cdot}$In elastomeric module whole tie, 28 days group was significantly greater mean static frictional force than any other group but there were no significant differences among any other group (p>0.05). ${\cdot}$Elastomeric module twisting ties were significantly greater mean static frictional forces than any other ligation method but there were no significant differences between twisting tie and double overlay tie (p>0.05). Twisting tie, double overlay tie, whole tie, half tie showed differences in decreasing order. ${\cdot}$Stainless steel half tie produced lower mean static frictional force than whole tie, ligation by ligature tying plier produced greater mean static frictional force than by needle holder and ligation with 0.012-inch stainless steel ligature produced greater mean static frictional force than with 0.009-inch stainless steel ligature (p<0.05). ${\cdot}$There were no significant differences between the mean static frictional forces of elastomeric whole tie and stainless steel whole tie (p>0.05).

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.3
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• pp.540-547
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• 1994

Contact and frictional locking conditions and the effect of shielding due to contact at the facet, which could be represented by the difference in energy release rate, as a function of phase angle of loading are analyzed in this study for the case of interfacial cracks by assuming single crack-kink model. The analysis of contact effects on interfacial fracture resistance shows that relative shielding increases as the shear component was increased, which indicates a qualitative agreement with the previous experimental results.