• 소성∙가공
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• 제27권5호
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• pp.289-295
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• 2018

The profile ring rolling process can realize various ring shapes unlike conventional rectangular cross-sectional ring products. In this paper, the defective groove in the bottom surface of L-shaped ring products was analyzed. Grooves are generated by non-uniform external forces due to profile main roll and initial blank shape. Process parameters such as the motion of dies and working temperature were determined. Mechanism of groove formation was analyzed by FE simulation on the basis of local external forces acting on the blank. Analysis results were similar to the groove actually occurring in the production line. Based on results of the analysis, two solutions were proposed for the groove. The position of the base plate supporting the blank was adjusted and edge length of the main roll was extended to suppress growth of grooves. It has been verified that groove was improved by applying two proposed methods in the shop-floor.

• 한국기계가공학회지
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• 제15권4호
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• pp.101-108
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• 2016

Endmill fillet cutting at the corner was conducted with the online measurement of cutting forces and tool deflection by a tool dynamometer and an eddy current sensor system. The profile of the machined surface was also compared with the CAD profile with a Coordinate Measuring Machine (CMM) and CALYPSO software. It was found that the end mill cutter with four blades has a better surface profile than that with two blades, and the cutting forces and tool deformation were increased as the cutting speed was increased. When the tool located at the degree $45^{\circ}$ corner was found to conduct the maximum cutting force than started to the point of the workpiece. As it was compared with the CMM and ANOVA analysis result in the case that the cutting force and tool deformation was the maximum, it was found that the result was affected by the spindle speed and the number of blades.

• 대한물리치료과학회지
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• 제19권1호
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• pp.63-69
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• 2012

Background : The purpose of this study was to investigate the frequency domain characteristics of ground reaction forces during quiet standing on inclined surfaces twenty healthy individuals(10 elderly women $68.78{\pm}3.29$ years and 10 young women $20.90{\pm}0.74$ years) participated. Methods : Subjects stood in quiet stance over a force platform positioned in one of three different fixed positions: flat, down and up. Healthy participants completed with eyes open for 120 s trials. Evaluation of postural control were generally based on the interpretation of center of pressure(COP) time series. The COP have been determined using an experimental setup with 3D kinematic and the ground reaction force system. All the data were expressed means and standard deviation by using SAS package program. Results : SEF 50% were not significant in AP and ML direction according to surface slope of both groups. SEF 95% were showed highest frequency in AP direction on down slope of both groups. MEF were not significant all direction according to surface slopes of elderly women. There was no difference between young and elderly women. Conclusion : Elderly women used to ankle strategy during a quiet stance according to COP perturbation of AP direction showed more expanded than ML direction. SEF 95% were showed highest frequency on down slope in elderly women who showed more used ankle strategy for postural control on down slope.

• Tribology and Lubricants
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• 제18권1호
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• pp.1-8
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• 2002

Nano adhesion and friction between a $Si_{3}N_{4}$ AFM(atomic force microscope) tip and thin silver films were experimentally studied. Tests were performed to measure the nano adhesion and friction in both AFM and LFM(lateral force microscope) modes in various range of normal loads. Thin silver films deposited by IBAD (ion beam assisted deposition) on Si-wafer (100) and other Si-wafers of different surface roughness were used. Results showed that nano adhesion and friction decreased with the surface roughness. When the Si surfaces were coated by pure silver, the adhesion and friction decreased. But the adhesion and friction were not affected by the thickness of IBAD silver coating. As the normal force increased, the adhesion forces of bare Si-wafer and IBAD silver coating film remained constant, but the friction forces increased linearly. Test results suggested that the friction was mainly governed by the adhesion as long as the load was low.

• 대한기계학회논문집A
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• 제39권8호
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• pp.787-791
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• 2015

장갑차의 창정비나 성능개량시 인서트를 교체할 수 없는 특수한 경우에는 크로메이트처리를 재수행함에 따라 체결력이 저하될 수 있는 리스크가 있다. 본 논문에서는 장갑차의 소재로 사용되는 알루미늄 판재에 인서트를 삽입한 채로 크로메이트를 할 경우, 인서트 체결력의 변화에 대하여 연구하였다. 판재의 표면처리와 인서트의 종류에 따른 영향성을 파악하기 위해 실제조건과 동일한 시편으로 파단강도를 측정하였다. 이러한 시험을 통해 차량 동체 제작 공정 기반을 마련하였다.

• Coupled systems mechanics
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• 제1권1호
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• pp.39-57
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• 2012

This study intends to explore dynamic interaction behaviors between actively controlled maglev vehicle and guideway girders by considering the nonlinear forms of electromagnetic force and current exactly. For this, governing equations for the maglev vehicle with ten degrees of freedom are derived by considering the nonlinear equation of electromagnetic force, surface irregularity, and the deflection of the guideway girder. Next, equations of motion of the guideway girder, based on the mode superposition method, are obtained by applying the UTM-01 control algorithm for electromagnetic suspension to make the maglev vehicle system stable. Finally, the numerical studies under various conditions are carried out to investigate the dynamic characteristics of the maglev system based on consideration of the linear and nonlinear electromagnetic forces. From numerical simulation, it is observed that the dynamic responses between nonlinear and linear analysis make little difference in the stable region. But unstable responses in nonlinear analysis under poor conditions can sometimes be obtained because the nominal air-gap is too small to control the maglev vehicle stably. However, it is demonstrated that this unstable phenomenon can be removed by making the nominal air-gap related to electromagnetic force larger. Consequently it is judged that the nonlinear analysis method considering the nonlinear equations of electromagnetic force and current can provide more realistic solutions than the linear analysis.

• 대한기계학회논문집B
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• 제21권10호
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• pp.1284-1293
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• 1997

The electrostatic effect on particle deposition onto a heated, Horizontal free-standing wafer surface was investigated numerically. The deposition mechanisms considered were convection, Brownian and turbulent diffusion, sedimentation, thermophoresis and electrostatic force. The electric charge on particle needed to calculate the electrostatic migration velocity induced by the local electric field was assumed to be the Boltzmann equilibrium charge. The electrostatic forces acted upon the particle included the Coulombic, image, dielectrophoretic and dipole-dipole forces based on the assumption that the particle and wafer surface are conducting. The electric potential distribution needed to calculate the local electric field around the wafer was calculated from the Laplace equation. The averaged and local deposition velocities were obtained for a temperature difference of 0-10 K and an applied voltage of 0-1000 v.The numerical results were then compared with those of the present suggested approximate model and the available experimental data. The comparison showed relatively good agreement between them.

• 전산구조공학
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• 제10권2호
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• pp.161-169
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• 1997

차량의 동적특성, 즉 소음, 진동, 승차감 및 조종안정성능 등에 중요한 영향을 미치는 부품중에 하나로 차체의 중량을 지지하고 노면과 접촉하여 회전하면서 조타성을 지니는 타이어를 고려하지 않을 수 없다. 지금까지의 이러한 타이어 최적설계에 이용되어지고 있는 예측기법으로는 유한요소해석 방법이 널리 활용되어 지고 있으나, 이는 타이어에 공기압 주입 및 차량의 조종안정성능이 우수한 타이어 제품개발 및 개선을 위해 차량 주행시 타이어와 노면과의 접지면에 작용하는 힘과 모멘트를 예측할 수 있는 유한요소해석 적용기법을 개발하였으며,이러한 해석기법을 통한 결과와 실측치는 매우 유사한 관계를 지니고 있음을 알 수 있었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 하계학술대회 논문집 Vol.7
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• pp.561-562
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• 2006

The purpose of this study was to investigate the root cause of adhesion of silica and ceria particles during Poly-Si, TEOS, and SiN CMP process, respectively. The zeta-potentials of abrasive particles and wafers were observed negative surface charges in the alkaline solutions. SAC and STI patterned wafers have intermediate values of their composition surface's zeta potentials. The theoretical interaction force and adhesion force of silica and ceria particle were calculated in solution with acidic, neutral and alkaline pH. A stronger attractive force was calculated for silica and ceria particles on wafers in acidic solutions than in alkaline solutions. The theoretical interaction forces of the SAC and STI patterned wafers have intermediate values of their constitution wafer's values. The adhesion forces is observed lower values in alkaline solutions than in acidic solutions. And the ceria particle has lower adhesion than that of the silica particle.

• 한국도로학회논문집
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• 제18권1호
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• pp.85-90
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• 2016

PURPOSES : The objective of this paper is to understand the deterioration phenomenon and causes in the pavement of a ramp area. METHODS : Ramp areas need to be sloped because of the centrifugal force, which depends on the vehicle speed and grade of the ramp area. As a result, vertical and horizontal forces are applied on the pavement surface of the ramp area. Furthermore, the horizontal force depends on the vehicle speed and grade of the ramp area. In order to analyze the pavement structure of a ramp area, a multi-layered elastic analysis program was used to evaluate the weakest link of fatigue cracking deterioration, according to the simultaneously applied vertical and horizontal forces. RESULTS : From case studies related to the bonding conditions between the surface and base layer in a ramp area, it was found that the partially bonded cases resulted in a critical potential of fatigue cracking deterioration, in a comparison of 50%, 70%, and fully bonded cases. CONCLUSIONS : According to the results of the case studies, the pavement structure system should be reinforced by upgrading the material or increasing the thickness compared to the general pavement areas, in order to provide a performance life similar to the mainline pavements in the ramp areas.