• Journal of the Korean Society for Precision Engineering
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• v.25 no.4
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• pp.140-147
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• 2008

This paper represents an ultra precision rotational device where the smooth impact drive mechanism (SIDM) is utilized as driving mechanism. Linear motions of piezoelectric elements are converted to the rotational motion of disk by frictional forces generated between the rotational disk and the friction part that is attached to the piezoelectric element. This device was designed to drive the rotational disk using slip-slip motion mechanism instead of stick-slip motion mechanism occurred in conventional impact drive mechanism. Experimental results show that the angular velocity is increased in proportion to the magnitude and frequency of supplied voltage to piezoelectric element and decreased as the preload is increased. In our device, the smooth rotational motion was obtained when the driving frequency has been reached to 500Hz under the driving voltage of 100V.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.296-299
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• 2002

The precision blanking of thin sheet metal is important process on production of precision electronic machine parts such as IC leadframe. In the blanking process, the factors that friction coefficient, tool clearance, material properties are the most important factors in the precision blanking process, because these factors affect the sheared face of product, side forces to punch during blanking process and surface condition after blanking process. So, many investigations have been performed. But, the former studies did not take up the characteristic of material. In this paper, in order to investigate the characteristic of blank, such as K(strength coefficient) and n(strain hardening coefficient), on the sheared face of blank and the side force to punch, FE-simulation has been analyzed by means of DEFORM-2D. To obtain input Parameters on FE-simulation, tensile and friction test has been done.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.888-891
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• 2002

This paper presents the lubrication characteristics of a disk type wavy thrust bearing. The hydrodynamic pressure distributions in the fluid film are numerically solved the Reynolds equation and then the bearing load capacity and friction forces acting on the disk are calculated. Especially the effects of number and amplitude of the circumferential waves are investigated for tilted operating conditions. The results showed that the load capacity increases with wave amplitude and optimum wave number exists for given design conditions. Therefore the results can be applied to enhance the lubrication performance of thrust bearing adopted in the scroll compressor.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.9 s.90
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• pp.779-784
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• 2004

This paper numerically analyzes the dynamic characteristics of a spindle system supported by two identical journal bearingsconsidering bearing span that has dynamic load due to its mass unbalance. The Reynolds equation is transformed to solve a herringbone grooved journal bearing. The Reynolds equations are solved using FEM in order to calculate the pressure distribution in a fluid film. Reaction forces and friction torque are obtained by integrating the pressure and shear stress along the fluid film, respectively. Dynamic behaviors, such as whirl radius or angular displacement of a rotor, are determined by solving its nonlinear equations of motion with the Runge-Kutta method. This research shows that the same bearing spans of upper and lower journal bearings produce the minimum runout and friction torque of a spindle system.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.7_spc
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• pp.503-508
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• 2016

In this study, effectiveness of seismic retrofitting methods using passive damping devices was investigated through numerical analyses of short-period structures under earthquakes which have short-duration and high-frequency impulse characteristics similar to Geyongju earthquakes. Displacement spectra of elastic systems and ductility demand of inelastic systems were evaluated by increasing viscous or friction damping. The damping devices could reduce responses of the structures with shorter structural period than 0.2s. The earthquakes similar to impulse load did not induce the responses of the structures with longer period than 0.4s, and the effects of the damping devices which generates damping forces proportional to structural responses became insignificant.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.6
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• pp.683-691
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• 2018

Numerical simulations of turbulent flows around KCS have been performed to study the sensitivity of ship resistance to wall-adjacent grids and disclose the influence of near-wall treatment on the sensitivity of ship resistance. The resistance coefficients of viscous and pressure forces were compared when using realizable $k-{\varepsilon}$ and SST $k-{\omega}$ turbulence models in structured and unstructured grids, respectively. The calculation of friction velocity was found to be mainly responsible for the reduction of viscous and total resistances when the height of wall-adjacent cells increased. Since the assumption of equilibrium state between turbulent production and dissipation was not met in a bulbous bow, it was more reasonable to iteratively calculate the friction velocity from empirical laws of the wall for near-wall treatment rather than explicitly estimate it from the turbulent kinetic energy.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.06a
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• pp.49-54
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• 2001

Monolayers such as self-assembled monolayer (SAM) have received considerable attention to reduce stiction and friction in micro-devices and microelectromechanical systems (MEMS). Various organic molecular films were investigated to obtain better understanding of their tribological behaviors and adhesion property. The organic molecular films studied in this work are: epoxysilane SAMs, octadecyltricholosilane (OST), multi-layers composed of epoxysilane SAMs, poly〔styrene-b-(ethylene-co-butylene)-b-styrene〕(SEBS) and compound of epoxy resin and poly (paraphenylene) (EP/PPP). The pull-off forces of these films were also obtained from force-distance curves measured in static mode of operation of atomic force microscope (AFM). Tribological tests were conducted with a ball-on-flat reciprocating friction tester. The OST showed the lowest pull-off force, indicating its low adhesion property. It was revealed that, the OST, EP/PPP and the multi-layer of epoxysilane SAMs, SEBS and EP/PPP exhibited good tribological properties at the lower load (0.3 N) whereas the OST showed best performance at the higher load (1.8 N).

• Journal of the Korean Society for Precision Engineering
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• v.10 no.4
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• pp.206-215
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• 1993

The finite element method is applied to analyze the mechanism of metal cutting, especially micro metal cutting. This paper introduces some effects, such as constitutive deformation laws of workpiece material, friction of tool-chip contact interfaces, tool rake angle and also simulate the cutting process, chip formation and geometry, tool-chip contact, reaction force of tool. Under the usual plane strain assumption, quasi-static analysis were performed with variation of tool-chip interface friction coefficients and tool rake angles. In this analysis, cutting speed, cutting depth set to 8m/sec, 0.02mm, respectively. Some cutting parameters are affected to cutting force, plastic deformation of chip, shear plane angle, chip thickness and tool-chip contact length and reaction forces on tool. Several aspects of the metal cutting process predicted by the finite element analysis provide information about tool shape design and optimal cutting conditions.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.51-52
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• 2002

We report results on microtribological studies of chemically grafted nanoscale polymer layers of different architecture with thickness below 30 nm. We have fabricated the molecular lubrication coatings from elastomeric tri-block copolymers and tested two different designs of corresponding nanocomposite coatings. We observed a significant reduction of friction forces and an increase of the wear stability when a minute amount of oil was trapped within the grafted polymer layer. These polymer gel layers exhibited a very steady friction response and a small value of the coefficient of friction as compared to the initial polymer coating. A polymer 'triplex' coating has been formed by a multiple grafting technique. The unique design of this layer Includes a hard-soft-hard architecture with a compliant rubber interlayer mediating localized stresses transferred through the topmost hard layer. This architecture provides a non-linear mechanical response under a normal compression stress and allows additional dissipation of mechanical energy via the elastic rubber interlayer.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.2
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• pp.183-190
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• 2016

Engine torque is transferred to the transmission where drag torque is minimized improving fuel efficiency. This is particularly true in a wet clutch pack. This study measures slip friction when the wet clutch pack in a DCT (Dual-Clutch Transmission) is disengaged, and the friction pads are slipping. Shudder engagement velocity, and applied forces can be measured under various working conditions through these torque transfer experiments. Test results demonstrate that the design parameters, and engagement conditions of wet clutch packs can be optimized to reduce shudder and frictional vibration during engagement in a dual clutch transmission.