Papers by Author: Lee Ku Kwac

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Authors: Hee Jae Shin, Lee Ku Kwac, Sun Ho Ko, Tae Hoon Kim, Hong Gun Kim
Abstract: Of the advanced composite materials for aerospace structures such as aircrafts and space devices, the carbon fiber reinforced plastics (CFRP) is applied to many sectors that require lightweight materials for its high strength and stiffness. One of the disadvantages of the CFRP, however, is that it is weak against impact. In this study, impact test specimens were manufactured with five fiber stacking angles (0°/0°, 0°/15°, 0°/30°, 0°/45°, 0°/90°) according to ASTM D7136[15], and a falling weight test was performed to analyze the correlation between their mechanical and thermal characteristics. As a result, the impact energy applied to the five test specimens with different fiber stacking angles was almost constant at 30.63 J - 30.78 J. The absorbed energy increased with the increase in the fiber stacking angle, and decreased after 0°/45°. The average temperature on the fractured surface increased with the increase in the fiber stacking angle in all specimens other than the 0°/0° specimen.
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Authors: Jae Yeol Kim, Lee Ku Kwac, Jae Ho Han
Abstract: Recently, the world is preparing for new revolution, called, ‘IT(Information Technology), NT(Nano-Technology), and BT(Bio-Technology).’ NT can be applied to various fields such as semiconductor-micro technology. Ultra precision processing is required for NT in the field of mechanical engineering. Because of radical advancement of electronic and photonics industry, necessity of ultra precision processing is on the increase for the manufacture of various kernel parts. In this paper, stability of ultra precision cutting unit is investigated and this unit is the kernel unit in ultra precision processing machine. According to alteration of shape and material of hinge, stability investigation is performed. Hinge shapes of micro stage in UPCU (Ultra Precision Cutting Unit) are designed in two types, where, hinge shapes are composed of round and rectangularity. Elasticity and strength are analyzed on micro stage with respect to hinge shapes by FE analysis. The micro stage in ultra precision processing machine has to keep hinge shape under cutting condition with 3-component force (cutting component, axial component, and radial component) and to reduce modification against cutting force. Then we investigated its elasticity and strength under these conditions. The material of the micro stage is generally used for duralumin with small thermal deformation. Since the elasticity and the strength quiet become important, the stability of the micro stage is investigated. Used materials are composed of aluminum of low strength and cooper with medium strength and spring steel with high strength. Through this stability investigation, trials and errors are reduced in design and manufacture at the same time, and we are accumulated foundation data for a unit control.
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Authors: Sun Ho Ko, Hong Gun Kim, Hee Jae Shin, Hyun Woo Kim, Yun Ju Cha, In Pyo Cha, Gwang Cheol Kim, Lee Ku Kwac
Abstract: As society became more complex, the logistics also increased, demanding for logistics transport vehicles and feeder has increased. Because the self-weight of skate for cargo transport used in this study is heavy, it needs to be weight lightening. However there is a lack of capital and technology not to improve lasting. We conducted FEM studies about weight lightening applying composites on cargo transport skate and the stiffness can be obtained at the same time. However, due to the presence of discontinuities such as holes in the parts. If you are applying composite, Because this causes the degradation of the strength of the material under static and fatigue load induced stress concentration in parts. In order to examine the safety of the cargo transport skate, you must consider the impact of the static strength damage on the stress concentration because of the discontinuous parts. In this study, therefore, the cargo skate was performed to evaluate the structural analysis through the FEM analysis. As a result, it was found that CFRP compared to existing SM45C is superior 25% when considering the characteristics. It indicated the best results in about 30% of the weight lightening.
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Authors: Hee Jae Shin, In Pyo Cha, Min Sang Lee, Tae Ho Kim, Hyun Kyung Yun, Lee Ku Kwac, Hong Gun Kim
Abstract: The fiber is considered the most important element in fiber reinforced composite materials, as it generally occupies the largest volume in a composite material; further, delivers the heaviest loads. therefore, it is important to select types, quantity and proper stacking angles of the fiber. In this study, the fiber directions were arranged in different orientation angles, i.e. in symmetric (0°/0°,15°/15°,30°/30°,45°/45°,90°/90°) and asymmetric (0°/15°,0°/30°,0°/45°,0°/90°), to analyze the tensile strengths depending on the fiber orientation angles through the tensile test. In addition, a thermal imaging camera was used to investigate the thermal characteristics of the test specimens generated during the tensile test. the tensile strength showed a tendency of decreasing while the orientation angle increased. the maximum temperature generated when the fracture occurred increased at the fiber orientation angle of 30°, and showed a tendency of decreasing as the orientation angle increased.
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Authors: Seung Hyun Choi, Lee Ku Kwac, Jae Yeol Kim
Abstract: The infrared thermography technique is being applied in many areas. Particularly these days, non-destructive inspection and evaluation using the ultrasound-infrared thermography technique are hogging the spotlight in a wide range of study areas. The ultrasound-infrared thermography technique uses the principle that ultrasound waves projected to objects with cracks or defects at connections generate local heat from the defective surface. In this research, introduce nondestructive evaluation method for total inspection of special shoes applying Ultrasound Infrared thermography Technique. Performance of the proposed method are shown by through thermo-Image. The total inspection system using infrared thermal camera for special shoes, its applicability, and system configuration are introduced.
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Authors: Choul Jun Choi, Jung Ki Lee, Lee Ku Kwac, Jae Yeol Kim
Abstract: Combustion gas of gas turbine is about 1100 ~ 1300 °C. Is doing TBC(Thermal Barrier Coating) on the base metal surface to protect rotor or blade from high temperature flame. TBC system reduced heat transfer as metal base metal. TBC system is divided by bond coating of prevent oxidation and corrosion and Top coating reduced of heat transfer by high Temperature flame. The objective of this study was to development of an advance TBC system for high Temperature (>1350°C) gas turbine components. Used coating powder developed newly in coating process, and more than 1350°C by parameter control in usable coating method develop. Internal studies looked at the effect of TBC coating thickness, material chemistry, substrate composition, surface temperature and bond coat as-sprayed surface profile/particle size on technical performance.
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Authors: Hong Gun Kim, Lee Ku Kwac, Yoo Shin Kim, Young Woo Kang
Abstract: An experimental and numerical study of polymer electrolyte membrane fuel cell (PEMFC) is presented and compared with the experimental data to investigate the effects of pressure gradient, flow rate, humidification and supplied oxidant type for the practical application. The membrane and electrolyte assembly (MEA) materials are implemented by double-tied catalyst layers. A single-phase two-dimensional steady-state model is is implemented for the numerical analysis. Testing condition is fixed at 60sccm and 70°C in anode and cathode, respectively. It is found that the performance of PEMFC depend highly on the conditions as gas pressure, temperature, thickness, supplied oxidant type (Oxygen/Air) as well as humidification. The results show that the humidification effect enhances the performance more than 20% and the pure oxygen gas as fuel improves current density more than 25% compared to ambient air suppliance as oxidant.
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Authors: Hong Gun Kim, Lee Ku Kwac, Sung Soo Kang, Young Woo Kang
Abstract: An experimental study is carried out to investigate the performance and the practical application of polymer electrolyte membrane fuel cell(PEMFC) with the double-tied catalyst layers in a Membrane Electrolyte Assembly (MEA). Characteristics of PEMFC depend highly on the conditions such as gas pressure, temperature, thickness, supplied oxidant type (Oxygen/Air) as well as humidification. They are controlled under the same condition for the comparison of the simulation. Testing condition is fixed at 60sccm and 70°C in anode and cathode, respectively. The humidification about 15% the performance is improved no humidification rather. The current density is increased around 20% significantly when pure oxygen gas is provided as an oxidant. It is found that measured values of unit cell voltage and current are influenced strongly by the type and amount of oxidant, which give more enhanced values in case of oxygen compared to the ambient air as oxidant.
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Authors: Lee Ku Kwac, Jae Yeol Kim, Young Tae Cho
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