• Tribology and Lubricants
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• v.27 no.5
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• pp.264-268
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• 2011

In this study, we examined the friction characteristics of a dimple pattern on a carbon nitride coating. The study was conducted with a hexagonal array 40 ${\mu}m$ dimple pattern on a steel bearing containing a CNx coating. The area density of the dimple patterns were varied between 5% and 25%, the speed was varied from 0.06-0.26 m/s, and the load was varied between 20-100N. In general, we found that as the velocity increased, the friction coefficient increased. Furthermore, the friction coefficient was lowest at a load of 40N. The friction coefficient of the non-coated specimen was 0.025-0.15; on the other hand, the friction coefficient of the coated specimen was 0.002-0.02. Thus, we determined that the coated materials could reduce the friction coefficient by a factor of 7.5.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.10
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• pp.74-79
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• 2006

In this study, the tempering effect on the wear characteristics of induction-hardened SPS5 steel was investigated. For this purpose, three tempering conditions were applied to control the hardness of heat-treated SPS5 steel. Ball-on-disk wear tests have been performed using zircornia balls on the tempered specimens to determine the variation of wear characteristics. The results showed that friction coefficient decreased with increasing hardness for induction hardening conditions. This seems to occur because real contact area between specimen and mating ball was affected by the specimen hardness.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.1
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• pp.53-56
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• 2008

The commercial parallel plate electrodes system with guard-ring electrode have been widely used for measurement of dielectric constants of solid materials. And the specification of the electrodes system is about 1 % of measurement uncertainty. This measurement uncertainty is only estimated the error come from mechanical measurements such as the area of the electrodes and the gap between the electrodes except the error come from the air gap between the electrodes and dielectric specimen. Because it is impossible to measure the air gap. This study analyze the total measurement uncertainties of the commercial dielectric constant test cell using 3 kinds of Standard Reference Materials. As a results, the total measurement uncertainty is much bigger than 1 % and the most of the uncertainty can be reduced by compensation of the error values evaluated in this study.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.515-518
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• 2002

In this study, the ellipsoidal cap type magnetic pole structure was proposed for the electro-magnet in B-H curve tracer. From the simulation for the electro-magnet without specimen, the area of effective uniform field(99% range for the central field value) was considerably increased in case of the newly proposed ellipsoidal cap type magnetic pole than that of the conventional simple-inclined cap type magnetic pole. Also, through the simulation for the electro-magnet with permanent magnet specimen(NaFe30), the optimal Positions of the magnetic field measurement sensor(Hall sensor) were found out in each case and the errors were decreased in case of the newly proposed ellipsoidal cap type magnetic pole.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1386-1388
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• 2003

In this study. the fatigue behavior of cracked aluminum repaired by unidirectional graphite/epoxy composites was experimentally investigated. The aluminum used was 7075-T6 and the patch used was four plied unidirectional ([0]$_4$) composites. The composite patch was adhesively bonded to the cracked aluminum using secondary bonding procedure. Two different specimens of cracked aluminum and cracked aluminum repaired with patch were used in the fatigue tests. Load ratio and the frequency applied in the fatigue tests were 0 and 10 Hz, respectively. The results showed that the fatigue behavior of cracked aluminum was improved by repairing the cracked area with composite patch. Specifically, the specimen repaired by composite patch showed 30% more improved fatigue behavior than regular specimen.

• Progress in Superconductivity and Cryogenics
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• v.15 no.2
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• pp.48-51
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• 2013

The thermal contact resistance (TCR) is one of the important components in the cryogenic systems. Especially, cryogenic measurement devices using a cryocooler can be affected by TCR because the systems have to consist of several metal components in contact with each other for heat transferring to the specimen without cryogen. Therefore, accurate measurement and understanding of TCR is necessary for the design of cryogenic measurement device using a cryocooler. The TCR occurs at the interface between metals and it can be affected by variable factors, such as roughness of metal surface, contact area and contact pressure. In this study, we designed TCR measurement system at various temperatures using a cryocooler as a heat sink and used steady state method to measure the TCR between metals. The copper is selected as a specimen in the experiment because it is widely used as a heat transfer medium in the cryogenic measurement devices. The TCR between Cu and Cu is measured for various temperatures and contact pressures. The effect of the interfacial materials on the TCR is also investigated.

• Transactions of the Korean Society of Mechanical Engineers
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• v.6 no.3
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• pp.232-238
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• 1982

The behavior of corner crack propagation by unidirectional plane bending fatigue was investigated in the butt welded joints of SS41 and SM50 steel plates including an edge through-thickness notch. The properties of fatigue crack propagation were inspected in the weld metal, heat-affected zone, and base metal of the welded joints. Main results obtained are as follows; (1) When a plate with an edge through-thickness notch is loaded by plane bending fatigue in indirection, the 2 variant corner cracks on the upper and lower edge of the plate are initiated and propagated respectively from the notch. (2) In case of a specimen containing a corner crack, it is more reasonable to estimate the crack propagation rate by area of fracture surface than by crack surface length. (3) The rate of fatigue crack propagation becomes faster in the following order; weld metal, heat-affected zone, and base metal. (4) The specimen including reinforcement shape is rapidly failed throughout bond due to effect of its shape when the repeated load exceeds a certain cycle.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.409-410
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• 2006

In this study, the tempering effect on the wear characteristics of induction-hardened SPS5 steel was investigated. For this purpose, three tempering conditions were applied to control the hardness of heat-treated SPS5 steel. Ball-on-disk wear tests have been performed using zircornia balls on the tempered specimens to determine the variation of wear characteristics. The results showed that friction coefficient decreased with increasing hardness for induction hardening conditions. This seems to occur because real contact area between specimen and mating ball was affected by the specimen hardness.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.10-12
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• 2014

In ISO 10140-5:2010, defines the reverberation time conditions of the receiving room. The sound absorption side of test specimen is installed in the source room generally. In this study, examined at the change in the sound insulation characteristics for the test specimen of asymmetric structure attached sound absorbing material by changing the installed position. A difference of sound insulation performance was maxium Rw 1 dB, it is preferable to place the larger sound absorption area in source room.

• Applied Microscopy
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• v.46 no.2
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• pp.110-115
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• 2016

Transmission electron microscopy (TEM) is a powerful tool for analyzing a broad range of materials and provides localized information about the microstructure. However, the analysis results are strongly influenced by the quality of the thin foil specimen. Sample preparation for TEM analysis requires considerable skill, especially when the area of interest is small or the material of interest is difficult to thin because of its high hardness and its mechanical instability when thinned. This article selectively reviews recent advances in TEM sample preparation techniques using a tripod polisher. In particular, it introduces two typical types (fl at type and wedge type) of TEM sample preparation and the benefits and drawbacks of each method; finally, a method of making better samples for TEM analysis is suggested.