• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.471-474
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• 2005

This study investigates the nano/microstructure, the aging response, and the mechanical/tribological properties of the eutectic regions in rheoformed A356 alloy-T5 parts using nano/micro-indentation and mechanical scratching, combined with optical microscopy and atomic force microscope (AFM). Most eutectic Si crystals in the A356 alloy showed a modified morphology as fine-fibers. The loading curve for the eutectic region was more irregular than that of the primary Al region due to the presence of various particles of varying strength. The aging responses of the eutectic regions in the rheoformed A356 alloys aged at $150^{\circ}C$ for different times (0, 2, 4, 8, 10, 16, 24, 36, and 72 h) were investigated. Both Victors hardness $(H_v)$ and indentation $(H_{IT})$ test results showed a similar trend of aging curves, and the peak was obtained at the same aging time of 10 h. A remarkable size-dependence of the tests was found.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.7
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• pp.723-729
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• 2012

Spring-like leg models have been employed to explain various dynamic characteristics in human walking. However, this leg stiffness model has limitations to represent complex motion of actual human gait, especially the behaviors of each lower limb joint. The purpose of this research was to determine changes of total leg stiffness and lower limb joint stiffness with gait speed in knee osteoarthritis. Joint stiffness defined as the ratio of the joint torque change to the angular displacement change. Eight subjects with knee osteoarthritis participated to this study. The subject walked on a 12 m long and 1 m wide walkway with three sets of four different randomly ordered gait speeds, ranging from their self-selected speed to maximum speed. Kinetic and kinematic data were measured using three force plates and an optical marker system, respectively. Joint torques of lower limb joints calculated by a multi-segment inverse dynamics model. Total leg and each lower limb joint had constant stiffness during single support phase. The leg and hip joint stiffness increased with gait speed. The correlation between knee joint angles and torques had significant changed by the degree of severity of knee osteoarthritis.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.748-753
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• 2000

Nowadays, many studies and researches in data storage have been carried out and storage capacity is increased. But the limitation of storage capacity is happened for several problems. One of them is spot & pit size in optical and magnetic data storage and another is the resolution of actuators. The problems in spot & pit size is covered by new data storage methods- for example, NFR{Near-Field Recoding) system. But the resolution limit of an actuator doesn't follow up the development of spot & pit size. Because of them, we should improve a resolution of an actuator. Especially, in this paper an actuator is studied and designed for NFR(in using SIL(Solid Immersion Lens) system. It is a dual stage actuator, which consists of a Fine actuator and a Coarse actuator, and should desire 100nm accuracy. But, our actuator system only includes tracking mechanism execpt focusing mechanism which is controlled by slider mechanism used in HDD. Its actuating force generation method is VCM(Voice Coil Motor). The Fine actuator is composed of 4-leaf springs and a bobbin wrapped by coil. The Coarse actuator has Coils and 3-Roller bearings.

• Journal of the Semiconductor & Display Technology
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• v.9 no.3
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• pp.41-45
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• 2010

The ZnO thin films doped with Ga(GZO) and both Ga and Ge(GZO:Ge) were deposited on glass substrate by using RF sputtering system respectively. Structural, morphological and optical properties of the films deposited in the same condition were investigated. Structural properties of the films were investigated by Field Emission Scanning Electron Microscopy, FE-SEM images and X-ray diffraction, XRD analysis. These studies showed shape of films' surface and direction of film growth respectively. It's showed that all films were deposited by vertical orientation strongly. It can be confirmed that all dopants of targets were included in deposited films by results of EDX analysis. UV-Vis spectrometer results showed that all samples had highly transparent characteristics in visible region and have similar 3.28~3.31 eV band gap. It was found that existence of all dopants by EDX analysis. Morphology and roughness of surface of each film were clearly shown by Atomic Force Microscopy, AFM images. It was found in this research that film doped with Ge more dense and stable with hardly any difference in gap energy compared to ZnO films.

• Tribology and Lubricants
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• v.34 no.6
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• pp.209-216
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• 2018

Sapphire is a substrate material that is widely used in optical and electronic devices. However, the processing of sapphire into a substrate takes a long time owing to its high hardness and chemical inertness. In order to process the sapphire ingot into a substrate, ingot growth, multiwire sawing, lapping, and polishing are required. The lap grinding process using pellets is known as one of the ways to improve the efficiency of sapphire substrate processing. The lap grinding process ensures high processing efficiency while utilizing two-body abrasion, unlike the lapping process which utilizes three-body abrasion by particles. However, the lap grinding process has a high material removal rate (MRR), while its weakness is in obtaining the required surface roughness for the final polishing process. In this study, we examine the effects of free abrasives in lap grinding on the material removal characteristics of sapphire substrate. Before conducting the lap grinding experiments, it was confirmed that the addition of free abrasives changed the friction force through the pin-on-disk wear test. The MRR and roughness reduction rate are experimentally studied to verify the effects of free abrasive concentration on deionized water. The addition of free abrasives (colloidal silica) in the lap grinding process can improve surface roughness by three-body abrasion along with two-body abrasion by diamond grits.

• Journal of Powder Materials
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• v.26 no.1
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• pp.11-15
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• 2019

In this study, a method to remove residual powder on a multi-layered graphene and a new approach to transfer multi-layered graphene at once are studied. A graphene one-step transfer (GOST) method is conducted to minimize the residual powder comparison with a layer-by-layer transfer. Furthermore, a residual powder removing process is investigated to remove residual powder at the top of a multi-layered graphene. After residual powder is removed, the sheet resistance of graphene is decreased from 393 to 340 Ohm/sq in a four-layered graphene. In addition, transmittance slightly increases after residual powder is removed from the top of the multi-layered graphene. Optical and atomic-force microscopy images are used to analyze the graphene surface, and the Ra value is reduced from 5.2 to 3.7 nm following residual powder removal. Therefore, GOST and residual powder removal resolve the limited application of graphene electrodes due to residual powder.

• Tribology and Lubricants
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• v.35 no.2
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• pp.106-113
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• 2019

We investigated the application of tetrahedral amorphous carbon (ta-C) coatings to fabricate a glass lens manufactured using a glass molding process (GMP). In this work, ta-C coatings with different thickness (50, 100, 150 and 200 nm) were deposited on a tungsten carbide (WC-Co) mold using the X-bend filter of a filtered cathode vacuum arc. The effects of thickness on mechanical and tribological properties of the coating were studied. These ta-C coatings were characterized by atomic force microscopy, scanning electron microscopy, nano-indentation measurements, Raman spectrometry, Rockwell-C tests, scratch tests and ball on disc tribometer tests. The nano-indentation measurements showed that hardness increased with an increase in coating thickness. In addition, the G-peak position in the Raman spectra analysis was right shifted from 1520 to $1586cm^{-1}$, indicating that the $sp^3$ content increased with increasing thickness of ta-C coatings. The scratch test showed that, compared to other coatings, the 100-nm-thick ta-C coating displayed excellent adhesion strength without delamination. The friction test was carried out in a nitrogen environment using a ball-on-disk tribometer. The 100-nm-thick ta-C coating showed a low friction coefficient of 0.078. When this coating was applied to a GMP, the life time, i.e., shot counts, dramatically increased up to 2,500 counts, in comparison with Ir-Re coating.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.2
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• pp.129-133
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• 2019

TiN thin films were fabricated using an unbalanced magnetron sputtering (UBMS) system, and their structure and surface characteristics as well as their optical and tribological properties were evaluated. The hardness, elastic modulus, adhesive force, surface roughness, and transmittance of the Ti thin films fabricated using the UBMS system were 11.5 GPa, 103 GPa, 27.5 N, 2.45 nm and 20%, respectively. The TiN films prepared with various proportions of nitrogen as the reaction gas exhibited maximum values for the hardness, elastic modulus, critical load, RMS roughness and transmittance of approximately 19.2 GPa, 182 GPa, 27.3 N, 0.98 nm, and 85%, respectively. Moreover, the TiN thin film fabricated under the condition of 30 sccm nitrogen gas showed the optimal physical properties. In summary, the TiN thin films fabricated using the UBMS system exhibited excellent hardness, elastic modulus, adhesion, and smooth surface in addition to good hydrophilic properties.

• The Journal of Korea Robotics Society
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• v.16 no.1
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• pp.41-48
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• 2021

In this paper, we review papers which report to the all solid-state electroactive polymer-based tunable lens. Since electroactive polymer-based tunable lenses change their focal length by responding to electric stimuli, it can be minimized the size and weight of optical modules. Thus, it has been received attention in the robot, mobile device and display industry. The all solid-state electroactive polymer-based tunable lenses can be classified into two categories depending on the classification of materials: ionic electroactive polymer-based lenses and non-ionic electroactive polymer-based lenses. Most of the ionic electroactive polymer-based tunable lenses are fabricated with ionic polymer-metal composite. So, the ionic electroactive polymer-based tunable lenses can be operated under low electric voltage. But small force, slow recovery time and environmental limitation for operation has been pointed to the disadvantage of the lenses. The non-ionic electroactive polymer-based tunable lenses are classified again into two categories: dielectric polymer-based tunable lenses and polyvinylchloride gel-based tunable lenses. The advantage of the dielectric polymer-based tunable lenses is fast response to electric stimuli. But the essential flexible electrodes degrade performance of the lens. Polyvinylchloride gel-based tunable lens has reported impressive performance without flexible electrodes.

• Applied Chemistry for Engineering
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• v.22 no.5
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• pp.579-581
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• 2011

Spectroscopic evaluation of hair chemical damage was performed by SEM/EDS, CLSM, and FT-IR spectroscopy. In SEM/EDS, hydrogen peroxide treated hair showed the loose packing of surface scales, lower ratio of sulfur element and higher ratio of oxygen atom. In the optical single section by using CLSM, high fluorescent intensity appeared in untreated hair. However, in case of treated hair, low fluorescent intensity appeared. This results the aromatic amino acids which can be autofluorescent were more abundant than bleached hair. FT-IR spectra showed that cysteic acid band intensity was increased by performing the bleaching treatments. These results indicate that the oxidative damage cleaves the S-S bond and results in the lower working force of hair fiber.