• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.89-90
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• 2002

Ball reducer (HERB Drive: High Efficient Wave Rolling Ball Drive) with waved grooves has many advantages over other types of reducers for high-reduction ratio, low noise and low energy loss, etc. The mechanism of force transmission is very similar to that of cam and follower in automobile valve train system especially in contact behaviors. In this study, we have investigated the traces of contact between ball and outer ring, and the dynamic contact behaviors of elastohydodynamic lubrication(EHL) with a certain reduction ratio. In order to verify the contact behaviors between ball and outer ring for the critical endurance lift, the contact velocity and load are computed for a cycle. During some intervals of a cycle, the contact velocity reverses its direction very suddenly. It is expected that changing the contact direction causes undesirable endurance performance because EHL film frequently col lapse at the moment of velocity reversal. From the computational investigation in this work, we hope to predict similar contact damages in other machinery due to this kind of contact behaviors, which is very typical in many contact phenomena.

• Tribology and Lubricants
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• v.36 no.3
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• pp.147-152
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• 2020

This paper is within the framework of an adhered complete contact problem wherein the contact between a half plane and sharp edged indenter, both of which are elastic in character, is constituted. The eigensolutions of the contact shear and normal stresses, σ_rq and σ_q, respectively, are evaluated via asymptotic analysis. The ratio of σ_rq/σ_qq is investigated and compared with the coefficient of friction, μ, of the contact surface to observe the propensity to slip on the contact surface. Interestingly, there exists a region of |σ_rθ/σ_θθ| ≥ |μ|. Thus, slipping can occur, although the problem is solved under the condition of an adhered contact without slipping. Given that a tribological failure potentially occurs at the slipping region, it is important to determine the size of the slipping region. This aspect is also factored in the paper. A simple example of the adhered contact between two elastically dissimilar squares is considered. Finite element analysis is used to evaluate generalized stress intensity factors. Furthermore, it is repeatedly observed that slipping occurs on the contact surface although the size of it is extremely small compared with that of the contacting squares. Therefore, as a contribution to the field of contact mechanics, this problem must be further explained logically.

• Tribology and Lubricants
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• v.35 no.1
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• pp.37-43
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• 2019

This paper presents an optimization method to determine the shoulder height of an angular contact ball bearing by 3D contact analysis using nondimensional-shaped variables. The load analysis of the ball bearing is performed to calculate the internal load distributions and contact angles of each rolling element. From the results of bearing load analysis and the contact geometry between the ball and inner/outer raceway, 3D contact analyses using influence function are conducted. The nondimensional shoulder height and nondimensional load are defined to give the generalized results. The relationship between the shoulder height and radius of curvature of the shoulder under various loading conditions is investigated in order to propose a design method for the two design parameters. Using nondimensional parameters, the critical shoulder heights are optimized with loads, contact angles, and conformity ratios. We also develop contour maps of the critical shoulder height as functions of internal loads and contact angles for the different contact angles using nondimensional parameters. The results show that the dimensionless shoulder height increased as the contact angle and dimensionless load increased. Conversely, when the conformity ratio increased, the critical shoulder height decreased. Therefore, if the contact angle is reduced and the conformity ratio is increased within the allowable range, it will be an efficient design to reduce the shoulder height of ball bearings.

• Journal of Korean Foot and Ankle Society
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• v.14 no.1
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• pp.5-10
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• 2010

Purpose: This study was performed to compare the contact area between three different correcting angles after the proximal crescentic and Ludloff osteotomies of the first metatarsal. Materials and Methods: We used the two sawbone models. Proximal crescentic (PCO) and Ludloff osteotomies (LO) were performed and secured using K-wires under the correcting intermetatarsal angle (IMA) $5^{\circ}$, $10^{\circ}$, and $15^{\circ}$. Then each 6 osteotomized model was scanned five times and measured the contact area using the calculating program. We excluded the highest and lowest values. Results: The mean area of cutting surface was 189 $mm^2$ in PCO, 863 $mm^2$ in LO. The mean contact area (contact ratio; contact area $\times$100/area of cutting surface) of PCO was 149 $mm^2$ (79%) in $5^{\circ}$, 139.5 $mm^2$ (74%) in $10^{\circ}$, 107 $mm^2$ (57%) in $15^{\circ}$ IMA. The mean contact area (contact ratio) of LO was 711 $mm^2$ (82%) in $5^{\circ}$, 535.5 $mm^2$ (62%) in $10^{\circ}$, 330 $mm^2$ (38%) in $15^{\circ}$ IMA. Conclusion: A significant decrease in the contact area and contact ratio according to increase in correcting IMA was noticed in LO. We recommend the PCO rather than LO, when the IMA is needed to correct over $15^{\circ}$.

• Journal of the Korean Society for Precision Engineering
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• v.13 no.11
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• pp.92-99
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• 1996

The contact pressure in jointed plates was measured by means of an improved ultrasonic technique. In order to get calibration curve, the relationship between contact pressure and ratio of boundary and bottom echo of normal beam probes were obtained for the calibration blocks with various surface roughness. The ratio of boundary and bottom echoes were measured for the upper/under plates locally compressed with uniform pressure, and the distribution of contact pressure was obtaines. The measured pressure has a good agreement with results of FEM analysis. Thus the proposed ultrasonic method in this work is very useful to measure the contact pressure.

• Journal of Astronomy and Space Sciences
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• v.23 no.3
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• pp.189-198
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• 2006

We present newly observed BVRI CCD light curves for low mass ratio contact binaries, HN UMa and II UMa. The absolute dimensions of these objects were obtained by applying the Wilson-Devinney program to previously published spectroscopic analysis and to our observed photometric data. The evolutionary status of all 21 low mass ratio contact binary system including HN UMa and II UMa was then considered. The secondaries of all low mass ratio contact binaries are located below the zero age main sequence in HR diagram. This phenomenon could be explained by mass loss from the secondary component in the low mass contact binary system because even small mass loss affects luminosity decrease in the low mass stars.

• Journal of Korean Clinical Health Science
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• v.3 no.4
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• pp.435-443
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• 2015

Purpose. This study was to investigate comparison of the near eye position according to the spectacle and contact lens wearing. Methods. We measured the AC/A ratio and near horizontal phoria using modified Thorington method in each case spectacle and contact lens wearing of equivalent spherical power after measuring the full corrected diopter for 20 subjects (men 5, woman 15, $21.15{\pm}1.35$ years) without specific ocular diseases, ocular surgery experience and vision anomalies. Results. It was shown high correlation between spectacle and contact lens wearing as AC/A ratio is a correlation coefficient 0.99 (p=0.00), near horizontal phoria is a correlation coefficient 0.95 (p=0.00). And contact lens wearing increased as AC/A ratio by $0.32{\pm}1.35$ ${\Delta}/D$ (p=0.31) and near horizontal phoria by $-0.17{\pm}2.18$ ${\Delta}$ (p=0.73) than spectacle wearing but there was no statistically significant difference. As the higher myopic grade AC/A ratio increased and then was shown decreased tendency in -6.00 D < $SED{\leq}-4.00$ D group (p>0.05) and as the higher myopic grade near exophoria increased but there was no statistically significant difference (p>0.05). Conclusions. We should consider that the subjects who had the lower AC/A ratio or higher near exophoria in -6.00 D < $SED{\leq}-4.00$ D group were necessary to measure AC/A ratio and near horizontal phoria when they were wearing contact lens because contact lens wearing tended to increase the near exophoria than spectacle wearing.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.463-464
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• 2006

This paper present experimental results by non-contact mode Atomic Force Microscopy using high aspect ratio tips (HAR-T). We fabricated the carbon nanotube tip based on dielectrophoresis and the carbon nano probe by focused ion beam after dielectrophoretic assembling. In this paper, we measure AAO sample and trench structure to estimate HAR-T's performance and compared with conventional Si tip. We confirmed that results of HAR-T's performance in non contact mode was very superior than conventional tip.

• Journal of the Korean Society of Industry Convergence
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• v.9 no.4
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• pp.269-276
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• 2006

Strength Design method for involute spur gears is developed. The developed gear strength design system can design the optimized gear that minimize the number of pinion teeth with face tooth. Method of optimization is matrix form which is developed from this study. Design variables are transmitted power, gear volume, gear ratio, allowable contact stress and allowable bending stress, etc. Gear design method developed this study can be apply to the gears of plants, machine tools, automobiles.

• Proceedings of the Korean Institute of Industrial Safety Conference
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• 2002.11a
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• pp.263-269
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• 2002

Design method for Involute bevel gears is developed. The developed gear design system can design the optimized gear that minimize the number of pinion teeth with face tooth. Method of optimization is MS(matrix search) which is developed from this study. Design variables are pressure angle 20, transmitted power, gear volume, gear ratio, allowable contact stress and allowable bending stress, etc. Design method developed this study can bd applide to the plane, machine tools, automobiles.