Papers by Author: Jin Kyung 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: Young Chul Park, Jung Ho Kang, Jin Kyung Lee, Jang Hyun Sung, Seok Heum Baek, Young Jik Jo
Abstract: Shape memory alloy (SMA) has been used to improve the tensile strength of composite materials. Because it produces compressive residual stress in the matrix by using its shape memory effect. In order to fabricate a shape memory alloy composite, TiNi alloy and Al2024, Al6061 were used as reinforcing material and matrix, respectively. In this study, TiNi/Al2024 and TiNi/Al6061 shape memory alloy composites were made by the hot press method. The fatigue limit of a shape memory alloy composite determined the volume ratio and reduction ratio. The probabilistic stresslife curve (P-S-N curve) about the shape memory alloy composite makes up using statistical method.
309
Authors: Jin Kyung Lee, Young Chul Park, Sang Ll Lee
Abstract: A smart material is used as spectacle frames and brassiere frames, and partly in medical supplies because of its shape memory effect. The smart composite can be used on the wing of an airplane instead of the existing aluminium to control crack propagation. In this study, the smart composite was fabricated by a hot press method. TiNi alloy as reinforcement and Al6061 as matrix were used, respectively. The mechanical properties of the smart composite under thermal shock cycles were evaluated. In addition, Acoustic Emission techniques were also used to clarify the damage behavior of the smart composite under thermal shock cycles nondestructively.
1113
Authors: Sang Ll Lee, Jin Kyung Lee, Joon Hyun Lee
Abstract: The nuclear power plant has lots of pipes that the fluid of high temperature and high pressure flows. Among the pipe materials used at secondary circuit of the power plant the carbon steels are sensitive to corrosion due to their material properties. In this study, both ultrasonic test and acoustic emission test were used to study the corrosion effect for the carbon steel pipe nondestructively. The carbon steel specimens were in the pipe under 473K temperatures and 10MPa pressure conditions for corrosion processing. According to the degree of corrosion the strength of the specimen was evaluated, and the thickness of the corrosion specimens was also measured by using the ultrasonic wave. The experimental results showed that the attenuation factor was also increased as a depth of corrosion increased. The measured depth of the real corrosion by ultrasonic test shows the good agreement with that by an optical microscope. In order to understand the corrosion effect for the failure mechanism of carbon steel, a failure test on the specimen with various corrosion conditions was performed. An acoustic emission technique was also used to evaluate the degree of damage of corrosion specimen in real time. Acoustic emission technique is proved a useful method for on-line monitoring the microscopic failure mechanism and the damage location for the structures.
2411
Authors: Han Ki Yoon, Jin Kyung Lee, Yi Hyun Park, Jung Ho Lee, Jea Heon Lee
1878
Authors: Sang Ll Lee, Yun Seok Shin, Jin Kyung Lee, Joon Hyun Lee, Jun Young Park
Abstract: This paper dealt with the fabricating process of liquid phase sintered (LPS) SiC ceramics containing the oxide additives of Al2O3 and Y2O3, in conjunction with the evaluation of their mechanical properties. LPS-SiC ceramics was sintered at the temperature of 1820 oC under an applied pressure of 20 MPa and a pressure holding time of 2 hour. A commercial SiC powder with an average size of about 0.3 μm was used as a starting powder. LPS-SiC ceramics with additive composition ratios of 1.5 and 2.3 (Al2O3/Y2O3) represented an excellent density of about 3.2 Mg/m3. LPS-SiC ceramics had a flexural strength of about 800 MPa and a fracture toughness of about 8.0 MPa⋅m0.5 at an additive composition ratio (Al2O3/Y2O3) of 1.5.
1853
Authors: Sang Ll Lee, Moon Hee Lee, Jin Kyung Lee, Dong Su Bae, Joon Hyun Lee
Abstract: The long-term corrosion strength properties for the carbon steels under pressurized water atmosphere have been investigated, in the conjunction with the detailed analysis of their microstructures. The corrosion test for carbon steels was carried out at the temperature of 200°C under a water pressure of 10 MPa. The corrosion test samples were maintained up to 50 weeks in the tube shaped reactor. The mechanical strength and the microstucture of carbon steels suffered from the long term corrosion test were evaluated by SEM, XRD and tensile test. The weight loss of carbon steel by the corrosion test was also examined. The tensile strength of carbon steels decreased with the increase of corrosion time under a pressurized water atmosphere, accompanying the creation of severe corrosion damages like stress corrosion crack.
1027
Authors: Sang Ll Lee, Moon Hee Lee, Jin Kyung Lee, Joon Hyun Lee, Yu Sik Kong
Abstract: The long-term corrosion resistances for the carbon steels have been investigated under high temperature pressurized water atmosphere, in the conjunction with the analysis of nondestructive properties by the ultrasonic wave. The corrosion test for carbon steels was carried out at the temperature of 200 °C under a water pressure of 10 MPa. The corrosion test cycles for carbon steels were changed up to 65 weeks. The mechanical properties of carbon steel suffered from the corrosion cycle were investigated by a tensile test, attaching an acoustic emission sensor on the test sample. The tensile strength of carbon steels greatly decreased beyond the corrosion cycle of 35 weeks, accompanying the increase of weight loss by the creation of corrosion damages. The attenuation coefficient of carbon steels by the ultrasonic wave increased with the increase of corrosion cycles.
1063
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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