Papers by Author: Jong Baek Lee

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Authors: Jin Kyung Lee, Young Chul Park, Sang Ll Lee, Joon Hyun Lee, Jong Baek Lee
Abstract: Tensile residual stress happen by difference of coefficients of thermal expansion between fiber and matrix is one of the serious problems in metal matrix composite (MMC). TiNi alloy fiber was used to solve the problem of the tensile residual stress as the reinforced material. TiNi alloy fiber improves the tensile strength of composite by occurring compressive residual stress using shape memory effect in the matrix. A hot press method was used to create the optimal condition for the fabrication of shape memory alloy (SMA) composite. The bonding effect between the matrix and the reinforcement within the SMA composite was strengthened by the cold rolling. The fabricated composite by these processes can be applied as a part of the aircraft, and this part is operated under severe flying condition such as low temperature and high pressure. In this study, an acoustic emission technique was used to quantify the microscopic damage behavior of cold rolled TiNi/Al6061 SMA composite at low temperature condition. The results showed that the tensile strength of the TiNi/Al6061 SMA composite increased with the TiNi reinforcement at low temperature condition, but the strength for the specimen subjected to the cold rolling decreased. AE parameters of AE counts, amplitude and energy were useful to evaluate the microscopic damage behavior of the composite.
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Authors: Sang Ll Lee, Yun Seok Shin, Jin Kyung Lee, Jong Baek Lee, Jun Young Park
Abstract: The microstructure and the mechanical property of liquid phase sintered (LPS) SiC materials with oxide secondary phases have been investigated. The strength variation of LPS-SiC materials exposed at the elevated temperatures has been also examined. LPS-SiC materials were sintered at the different temperatures using two types of Al2O3/Y2O3 compositional ratio. The characterization of LPS-SiC materials was investigated by means of SEM with EDS, three point bending test and indentation test. The LPS-SiC material with a density of about 3.2 Mg/m3 represented a flexural strength of about 800 MPa and a fracture toughness of about 9.0 MPa⋅√m.
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Authors: Byung Won Kang, T. Yoshida, Jong Baek Lee, S.J. Jeon, H.D. Choi
Abstract: In order to elucidate the relationship between the structure and biological activity such as anti-HIV and blood anticoagulant activity, sulfonated polysaccharides and amino-polysaccharides having pentofuranosidic structures were synthesized. These sulfonated polysaccharides had potent anti-HIV activity in spite of low molecular weights, and which was dependent on the degree of sulfonation. For the blood anticoagulant activity, the conformation of polymer backbone and sulfamide group plays an important role on the interactions with the blood anticoagulant factor.
721
Authors: Jong Baek Lee, Byung Won Kang
Abstract: A new type of thermotropic main-chain liquid crystalline polyurethanes containing biphenyl units was synthesized by polyaddition reaction of diisocyanates such as 2,6-tolylene diisocyanate, 2,5-tolylene diisocyanate, 2,4-tolylene diisocyanate, and 1,4-phenylene diisocyanate, with 4,4′-Bis(8-hydroxyoctoxy)biphenyl (BP8). The structure of the monomer and the corresponding polymers were confirmed using FT-IR and 1H-NMR spectroscopic methods. BP8 exhibited a smectic type mesophase, however, nematic phases were found for all synthesized liquid crystalline polyurethanes except for 1,4-phenylene diisocyanate/BP8 based polyurethane. For example, polyurethane 2,5-TDI/BP8 exhibited monotropic liquid crystallinity in the temperature ranging from 172 to 160 °C on the cooling stage. Properties of these polyurethanes were studied by differential scanning calorimetry (DSC), and optical polarizing microscopy. The FT-IR study indicated that the hydrogen bonding among urethane linkages attributed to the mesomorphism.
729
Authors: Jong Baek Lee, Kwang Hyun Lee, Byung Chul Kang, Byung Won Kang, Sang Ll Lee, Jin Kyung Lee
Abstract: A new type of thermotropic main-chain liquid crystalline polyurethanes containing biphenyl units was synthesized by polyaddition reaction of diisocyanates such as 2,6-tolylene diisocyanate, 2,5-tolylene diisocyanate, 2,4-tolylene diisocyanate, and 1,4-phenylene diisocyanate, with 4,4′-Bis(11-hydroxyundeyloxy)biphenyl (BP11). The structure of the monomer and the corresponding polymers were confirmed FT-IR and 1H NMR spectroscopic methods. BP11 exhibited a smectic type mesophase, however, nematic phase was found for all synthesized liquid crystalline polyurethanes except for 1,4-phenylene diisocyanate/BP11 based polyurethane. For example, polyurethane 2,5-TDI/BP11 exhibited monotropic liquid crystallinity in the temperature ranges from 173 to 156 °C on the cooling stage.
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