Papers by Author: Chang Seog Kang

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Authors: Chang Seog Kang, Sung Kil Hong
Abstract: An attempt has been made to measure the temperature dependence of dynamic Young's modulus together with the related variation of internal friction in polycrystalline copper. A mechanical spectroscopy study was used a standard servo hydraulic fatigue testing machine equipped with a scanning laser extensometer. Dynamic Young’s modulus and internal friction are measured over a temperature range of 298 to 873K at very low frequencies of 0.1, 0.05 and 0.01Hz. One internal friction peak was observed over the ranges 450K to 700K, together with marked decreases in the dynamic Young.s modulus in the same temperature ranges. From a quantitative analysis of the experimental data with the relaxation strength, relaxation time and activation energy, it is concluded that the peak phenomenon is due to grain-boundary sliding relaxation.
Authors: Se Weon Choi, Young Chan Kim, Se Hun Chang, Ik Hyun Oh, Chang Seog Kang
Abstract: (Ti, Al) N coating had been deposited by Arc Ion Plating, in an atmosphere of nitrogen. The structure of the coatings was examined as a function of deposition conditions by X-ray diffraction, and the crystallographic orientation was determined by use of a texture coefficient. The coatings on ground titanium substrates developed a strong (111) orientation from the earliest stages of growth, although the degree of orientation was dependent on deposition conditions. TiAlN coatings, however, showed relatively multiple orientations mainly of (111) and (200). Furthermore, TiAlN films demonstrated superior corrosion resistance in a molten aluminum alloy at 680°C. This paper described in detail the corrosion and mass loss phenomena related to this steel-cast metal interaction.
Authors: Chang Yeol Jeong, Chang Seog Kang, Jae Ik Cho
Abstract: A quantitative study of the interactions between microstructural features such as secondary dendrite arm spacing (DAS), eutectic structure and fatigue behavior of two Al-Si-Mg casting alloys with silicon contents of 7% and 10% respectively, has been conducted. In the condition of minimizing casting defects, the influence of microstructural features on the mechanical performance becomes more pronounced. Depending on the magnesium content affecting the strength of the matrix, the tensile properties were changed upon experimental conditions; the tensile strength was increased with magnesium content, whereas the elongation was increased in the reverse case. The increase of both of high cycle fatigue and low cycle fatigue lives with decreasing the secondary dendritic arm spacing is observed, mainly due to homogeneous deformation owing to the fine size of eutectic silicon and Fe intermetallic particles. The fatigue dynamometer of a diesel cylinder head shows the same tendency with the results of specimen fatigue tests with microstructures.
Authors: Sung Kil Hong, S.B. Jung, Young Chan Kim, W.K. Kee, Chang Seog Kang
Authors: Se Weon Choi, Hyeon Taek Son, Chang Seog Kang, Junji Nishii
Abstract: Si and Er co-doped SiO2 films were fabricated by radio-frequency (RF) magnetron sputtering technique with a Si-Er-SiO2 target. The optical gain of 0.7 dB/cm was confirmed by the direct pumping of Er3+ using the laser diode (LD) of 980 nm in wavelength and 60 mW in output power. On the contrary, the pumping Si-nanocrystals by the Hg lamp 365 nm (1.5 W/cm2) induced the absorption loss above 1.48 μm region in wavelength, which was attributed to the free carrier absorption of Si-nanocrystals.
Authors: Chang Seog Kang, Sung Kil Hong
Abstract: A mechanical spectroscopy study has been made on fine-grained Ni-10vol%TZP(ZrO2-3mol.%Y2O3) composite in an attempt to assess the following micromechanical prediction. A dual-phase material with fine-grained constituents deforming by Coble-type boundary-diffusion creep exhibits viscoelastic behavior. Dynamic Young's modulus and internal friction are measured over a temperature range of 25 to 800oC at frequencies of 0.01, 0.05 and 0.1Hz using a specially designed tension-compression apparatus. Two relaxation peaks are observed in the composite. An exponential involved in the peak and background components are determined and, by making a further analysis based on the micromechanical formulation and also taking the well-known relaxation due to viscous grain-boundary sliding into account, the implications of these quantities are discussed in terms of constituent material parameters(boundary diffusivity, grain size, etc.).
Authors: Hyun Rok Cha, Hyeon Taek Son, Cheol Ho Yun, Jae Ik Cho, Ik Hyun Oh, Jae Seol Lee, Chang Seog Kang, Hyoung Mo Kim
Abstract: Magnetic core components are often made from laminated sheet steel, but they are difficult to manufacture in near net shape, resulting in large core losses at higher frequencies. In this study, the pure iron powder was treated with aqueous phosphoric acid to produce phosphate insulating layer on the surface. After drying the powder, it was mixed with 0.5wt% Zn stearate and compacted in a mold with a diameter of 20mm at 800MPa. The powder compacts were then heat treated at 500°C for 1 hour. The results showed that insulated iron powder was obtained with uniform phosphate layer by chemical reaction. With increased amount of phosphate layer, the core loss and density of compacts were decreased. It was also found that the addition of ethyl alcohol during insulating reaction resulted in improved core loss value.
Authors: Chang Seog Kang, Ik Hyun Oh, Jae Ik Cho, Jae Seol Lee, Cheol Ho Yun, Hyeon Taek Son, H.L. Cha, Jung Chan Bae
Abstract: Anelastic behavior of a 9Al2O3·2B2O3 (AlBw) whisker reinforced aluminum composite has been examined through the measurements of the dynamic Young’s modulus and internal friction over a temperature range of 25 to 500°C at frequencies of 0.01, 0.05 and 0.1 Hz. A standard servo-hydraulic mechanical testing machine equipped with an infrared lamp heater was employed, but the dynamic measurement system therein was especially designed by assembling a scanning laser extensometer and a frequency response analyzer for detecting the amplitude and phase lag of strain in response to a sinusoidal time-varying stress. Two peaks of internal friction were observed over the ranges 100 to 250°C (LT peak) and 250 to 400°C (HT peak), together with marked decreases in the dynamic Young's modulus in the same temperature ranges. From a quantitative analysis of the experimental data, it is concluded that the HT peak phenomenon is due to grain-boundary relaxation, whereas the LT peak phenomenon is ascribable to the relaxation caused by stress-directed interfacial diffusion of Al atoms along the whisker-matrix interface.
Authors: Young H. Ko, Hyeon Taek Son, Jae Ik Cho, Chang Seog Kang, Ik Hyun Oh, Jae Seol Lee, Hyoung Mo Kim, J.C. Kim
Abstract: Although glass wool and polyurethane foam are the most widely used sound-absorber and insulating materials, there are some critical problems related to the environmental issues. In this reason, there is a lot of attention on the aluminum foam as a sound absorption material, therefore, in this research, sound absorption and transmission loss properties were studied. The results showed that low density aluminum foam performed better in both sound absorption and transmission loss and the properties were improved as increased air cavity and space.
Authors: Young H. Ko, Se Hun Chang, Ik Hyun Oh, Jae Ik Cho, Chang Seog Kang
Abstract: Aluminum foam is lightweight structures, energy absorption and thermal management. In this reason, there is a lot of attention on the aluminum foam as a structural material. The present papers showed various conventional joining techniques can be applied for foam-sheet structures, i.e., riveting, screwing, welding, gluing and soldering. This research presents new joining technique of Aluminum foam/Aluminum metal using spark plasma sintering (SPS) process. The Aluminum foam/Aluminum metals were fabricated by changing of various SPS holding temperature and holding time conditions. With increasing holding temperature and holding time, the tensile stress increased. The specimen sintered at 550°C for 20 min shows σts = 1.47 MPa. Also, it was found that the SPS holding time is dominant factor than the holding temperature for sound joining of two joint materials.
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