• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.1
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• pp.69-75
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• 2004

This paper presents the thermal characteristics analysis of a high-speed motor-separated spindle system consisted of angular contact ball bearings and built-in motor with oil-jet lubrication. The spindle system is composed of the main spindle and sub-spindle which are mechanically connected by a flexible coupling. The spindles are supported by two front and rear bearings, and the built-in motor is located between the front and rear bearings of the sub-spindle. The thermal analysis model of spindle system is constructed by the finite element method, and the thermal characteristics in the design stage are estimated based on temperature distribution and heat flow under the various testing conditions related to material of bearing ball, spindle speed and coolant temperature.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1277-1282
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• 2008

Recently LCD panels have becom very important components for portable electronics. In the high density interconnection material, ACF's are used to connect the outer lead of the tape automated bonding to the transparent indium tin oxide electrodes of the LCD panel. ACF consists of an adhesive polymer matrix and randomly dispersed conductive balls. In this study, we analyzed Failure Mode / Mechanism of ACF which is identified Conductive ball Corrsion, Delamination, Crack and Polymer Expansion / Swelling. In ALT(Accelerated Life Test), we select primary stress factors as temperature and humidity. As time passes by, an increase of connection resistance was observed. In conclusion, we have found that high temperature / humidity affects the adhesion.

• Tribology and Lubricants
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• v.15 no.2
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• pp.171-177
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• 1999

Many lubricated systems experience boundary lubrication condition during operation. However, the friction and wear characteristics of boundary lubrication are not clearly understood. In this work the factors which affect the friction and wear between boundary lubricated metallic surfaces are investigated. Experiments were performed using a pin-on-disk type tester with pure aluminum, pure copper, and SM45C steel as the disk material and steel, stainless steel and bearing ball as the ball. The experimental conditions were determined according to the Taguchi experimental method. From the experimental results, the major factors that influence the friction and wear characteristics of boundary lubrication could be identified.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.347-351
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• 2004

The cryogenic test facility is developed for test of deep groove ball bearings, floating ring seals, materials (steel & copper) for High Pressure Turbopump of liquid rocket engine (LRE). The cryogenic bearing test is performed to evaluate the flow rate of cooling water and the load-carrying capacity of bearings. The cryogenic seal test is performed to evaluate the determination of magnitude of leakages through the seal, a time variation of this magnitude. The test of the materials Pair is performed to evaluate its fitness for operation in the liquid oxygen medium.

• Journal of the Korean Ceramic Society
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• v.32 no.7
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• pp.825-831
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• 1995

Reaction-bonded SiC-Si material was fabricated by infiltration of Si melt into a mixture of $\alpha$-SiC and carbon at 175$0^{\circ}C$ under the vacuum atmosphere. Wear properties were analyzed by ball-on-plate wear tester, changing loading weight, sliding speed, sliding time and atmosphere, Results showed that the friction coefficient was decreased with increasing load and sliding velocity. The lowest friction coefficient of 0.05 was obtained under an oil atmosphere. The analysis of the wear surface indicated that the areas wehre particles were pulled out and where free silicon particles worn out preferentially serve as liquid reservoirs to decrease the wear resistance.

• Transactions on Electrical and Electronic Materials
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• v.4 no.5
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• pp.1-5
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• 2003

ZnO nanobelts, nanorods, and nanowires were synthesized at three different substrate temperatures from the thermal evaporation of ball-milled ZnO powders at 1380$^{\circ}C$. Transmission electron microscopy (TEM) revealed that the ZnO nanobelts are single crystalline with the growth direction perpendicular to the (010) lattice planes, and that the ZnO nanorods and nanowires are single crystalline with the growth directions perpendicular to the (001) and (110) lattice planes, respectively. In cathodoluminescence (CL), the peak energy of near bandedge (NBE) emission was determined for nanobelts, nanorods, and nanowires.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.633-636
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• 2004

Acoustic response control of a corner-pinned plate using piezoelectric wafers was studied, both theoretically and experimentally. Three different sizes of aluminum alloy plates were used and available ball joints were employed to hold the plate at the four comers. The plate with the largest aspect ratio showed the largest and most clear responses to the acoustic excitation in the range of frequencies $(0\sim200Hz)$, and sound pressure levels $(80\sim100dB)$ as predicted. The reduction of the acoustic response of the plate by piezoelectric actuator was very significant, more than expected, but abatement of the sound transmission through the plate was only slightly altered by the piezoelectric actuator. This work is an original work extending earlier work with doors excited by acoustic fields. The important difference is the used of ball joints to simulate the joints.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.3 s.168
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• pp.130-136
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• 2005

The nondestructive evaluation system consisted of a ball indentation tester and a ultrasonic tester was developed to evaluate material properties. The relations between the parameters from test results using the system and the results of tensile and fracture toughness tests were investigated. The fracture toughness and tensile properties could be determined using the system. Some metallic materials were experimented to predict the fracture toughness and tensile properties and verify the relations between them. The predicted fracture toughness and tensile properties show a good agreement with the results obtained by conventional tests. It is found that the material properties and the material degradation can be evaluated using the nondestructive evaluation system.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.267-272
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• 2003

In order to investigate the effect of face material on Ti/Al alloy laminates under high velocity impact, a ballistic testing was conducted. Ballistic resistance of these materials was measured by protection ballistic limit($V_{50}$), a statistical velocity with 50% probability penetration. Fracture behaviors and ballistic tolerance, described by penetration modes, were respectfully observed, by $V_{50}$ test and Projectile Through Plates (PTP) test at velocities greater than $V_{50}$. PTP tests were conducted with $0^{\circ}$obliquity at room temperature using 5.56mm ball projectile. $V_{50}$ tests with $0^{\circ}$obliquity were also done with projectiles that were able to achieve near or complete penetration during PTP tests. Resistance to penetration, and penetration modes which face material was Titanium alloy, were compared to those which face material was anodized Al alloy after cold-rolling.

• Journal of Magnetics
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• v.20 no.1
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• pp.21-25
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• 2015

Fine Nd-Fe-B-type particles were prepared by ball milling of different types of Nd-Fe-B precursor materials, such as die-upset magnet, HDDR-treated material, and sintered magnets. Coercivity dependence on the grain and particle size of the powder was investigated. Coercivity of the milled particles was reduced as the particle size decreased, and the extent of coercivity loss was dependent upon the precursor material. Coercivity loss in the finely milled particles was attributed to the surface oxidation. The extent of coercivity loss in the fine particles was closely linked to grain size of the precursor materials. Coercivity loss was more profound for the fine particles with larger grain size. Contrary to the fine particles from the sintered magnets with larger grain size the fine particles (~10 um) from the die-upset magnet and HDDR-treated material with much finer grain size still retained high coercivity (> 10 kOe for die-upset magnet, > 4 kOe for HDDR-treated material).