Papers by Author: Hyeon Taek Son

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Authors: Hyun Rok Cha, K.S. Lee, Cheol Ho Yun, Hyeon Taek Son, Tea Uk Jung
Abstract: In this paper, we suggested the new standards of motor design in using of Soft magnetic composite (SMC) material. Previous motor design in using of SMC material executed the same procedures of silicon steel. These procedures assumed that all places of material have the same density distribution and B-H curves. But we showed that the SMC material has inequality density distribution. By using powder forming analysis with FEM analysis, we showed that difference of density distribution could not be avoided because of the shear stress on powder, surface of the mold and punch. Therefore the magnetic characteristic was not the same in all places of material. So, we suggested the new method of motor design which considered the inequality density distribution in using of SMC material. And we compared previous method results and new method results and showed the differences of the result values. The density deviation of the SMC motor core was 5.8% and efficiency deviation was 3%. Especially the output value was different above 11% when we got the results by using previous method.
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Authors: Jae Seol Lee, Hyeon Taek Son, Ki Yong Lee, Soon Sub Park, Dae Guen Kim, Jung Chan Bae
Abstract: AZ31 Mg / 5083 Al clad sheet was fabricated by the hot rolling method and its mechanical properties were investigated in this study. The tensile strength and yield strength of Mg- Al clad samples were slightly higher than that of AZ31 Mg sample, resulting in high strength 5083 Al alloy. Also, in the case of the AZ31 Mg sample, tensile strength indicated different values to the rolling directions. The thickness of interface layers between magnesium and aluminum materials increased with increasing rolling temperature. The thickness of interface layer was about 1.2 μm and 1.6 μm, respectively. The difference of thickness on the interface layer with variation of rolling temperature was attributed to promote the diffusion between magnesium and aluminum materials. The Vickers hardness of Mg-Al interface layer was around 125 Hv. The interface layer composed of hard inter-metallic phases which may act a increment of Vickers hardness depending upon its thickness.
409
Authors: Dae Guen Kim, Hyeon Taek Son, Jae Seol Lee
Abstract: The effect of Ca addition on microstructure change, precipitation behaviours and mechanical properties, in the present work, of Mg-Sn based alloys were investigated. With increasing of Ca additions, size of the Mg-Sn-Ca ternary phases (A-type) with fine needle shape was decreased and volume fraction of these phase were increased. As Ca was increase from 1 wt.%, 2 wt.%, size and volume fraction of Mg2Sn with coarse needle shape phase (B-type) was increased. However, in 3 wt.% Ca containing alloy, size of these Mg2Sn phase was smaller than that of 2 wt% Ca addition alloy and volume fraction of these phase was decreased.
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Authors: Dae Guen Kim, Jae Seol Lee, Seul Ki Park, Young Mo Kim, Hyeon Taek Son, Moo Young Huh
Abstract: In the present work, the effect of Nd addition on microstructure change, precipitation behaviours and mechanical properties, of Mg-5Sn-3Ca based alloys were investigated. With increasing of Nd addition, size of the Mg-Sn-Ca ternary phases with fine needle shape (A-type) was decreased and volume fraction of these phase were increased. As Nd was increase from 0.5, 1.0 and 3.0 wt.%, size and volume fraction of Mg2Sn with coarse needle shape phase (B-type) was decreased. However, in 3.0 wt.% Nd containing alloy, size of these Mg2Sn phase was smaller than that of 0.5 and 1.0 wt% Nd addition alloy and volume fraction of these phase was decreased.
1558
Authors: Hyeon Taek Son, Jae Seol Lee, Young Kyun Kim, Ik Hyun Oh, Kyosuke Yoshimi, Kouichi Maruyama
Abstract: As samarium addition was increased, α- Mg matrix morphology was changed from dendritic to equiaxed grains and average value of grain size was decreased from 101.6㎛ to 39.3㎛. Samarium addition to Mg-5Al-3Ca based alloys resulted in the formation of Mg-Al-Sm thernary intermetallic compounds at grain boundarys and α-Mg matrix grains. In these alloys, two kinds of eutectic structure were observed; coarse irregular-shape structure at grain boundary and fine needle-shape structure in the α-Mg matrix grain. It is found that the yield strength and ultimate strength showed the maximum value of 109.1MPa and 139.3 at Mg-5Al-3Ca-2Sm alloy, respectively.
295
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.
515
Authors: Jae Seol Lee, Hyeon Taek Son, Toyohiko Yano
Abstract: The layers of ZrO2-Al2O3 were coated on the surface of SiC fibers (Tyranno SA fiber) by dip-coating process. The citric acid-ethylene glycol solution containing Al and Zr ions was polymerized at 150oC to obtain a polymerized complex precursor. The 2D-woven SiC Tyranno SA fibers were dipped into this precursor few times. Heat treatment for coated fiber was conducted at 800-1200oC for 1 h in air. Thin film of mixed zirconium/aluminum oxides on SiC fibers were successfully elaborated using the sol-gel process. The coated zirconium/aluminum oxides layer of SiC Tyranno SA fiber was about 200-1000 nm. The coated fibers were stable in an oxidizing environment even at high temperatures.
1386
Authors: Young Mo Kim, Soon Sub Park, Seul Ki Park, Hyeon Taek Son, Jae Seol Lee
Abstract: The microstructure of as-cast Mg-xAl-2Sn alloys consists of an α-Mg matrix, a Mg17Al12 eutectic phase and a Mg2Sn phase. In as-cast alloys, the Mg17Al12 eutectic phase was located at along grain boundaries. The eutectic phase of the extruded alloys was elongated in the extrusion direction and crushed into fine particles because of deformation during hot extrusion, and the grain size was refined with an increased Al content. The maximum values of the yield strength and tensile strength were 240 MPa and 300 MPa at 9 wt.% containing Al element, respectively.
1037
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.
1329
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.
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