Papers by Author: Young Chul Park

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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: Hyun Su Kim, Young Chul Park, Seung Hwan Oh, Se Hun Kim, Young Jik Jo, Jung Ho Kang
Abstract: This is a widespread requirement for low cost lightweight thermal imaging sensors for both military and civilian applications. The feasibility of micromechanical optical and infrared (IR) detection using microcantilevers is demonstrated. Microcantilevers provide a simple Structurefor developing single- and multi-element sensors for visible and infrared radiation that are smaller, more sensitive and lower in cost than quantum or thermal detectors. Microcantilevers coated with a heat absorbing layer undergo bending due to the differential stress originating from the bimetallic effect. This paper reports a micromachined silicon uncooled thermal imager intended for applications in automated process control.
785
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: Min Rae Lee, Joon Hyun Lee, Young Chul Park
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Authors: Jin Kyung Lee, Young Chul Park, Joon Hyun Lee, Sang Ll Lee, Kwan Do Hur
Abstract: Tensile residual stress occurring due to the difference of coefficients of thermal expansion between fiber and matrix is one of the serious problems in metal matrix composites (MMC). In this study, TiNi alloy fiber was used to solve the problem of the tensile residual stress of TiNi/Al6061 shape memory alloy(SMA) composite as the reinforced material. TiNi alloy fiber improves the tensile strength of a composite by inducing compressive residual stress in the matrix using its shape memory effect. The fixture was made to hold TiNi shape memory fiber uniformly. Some tensile test specimens with several volume fractions are made by the hot pressing method under the optimum processing condition. In order to generate the compressive residual stress in TiNi/Al6061 SMA composite, 1%, 3% and 5% pre-strain was added in advance. It was evaluated the effect of compressive residual stress corresponding to pre-strains variation using the acoustic emission(AE) technique. AE technique was also used to clarify the damage behavior and the microscopic failure mechanism of TiNi/Al6061 SMA composite. In addition, a two-dimensional AE source location technique was applied to measure the position of the crack initiation and propagation in composites.
1379
Authors: Seung Hwan Oh, Jung Ho Kang, Won Sik Joo, Xue Guan Song, Hyeung Geol Kong, Young Chul Park
Abstract: The optimization of gate valve was performed using Kriging based approximation model. The DACE modeling, known as the one of Kriging interpolation, is introduced to obtain the surrogate approximation model of the function. In addition, we describe the definition, the prediction function and the algorithm of Kriging method and examine the accuracy of Kriging by using validation method.
901
Authors: Seung Hwan Oh, Joon Hong Park, Kwon Hee Lee, Dong Hun Kang, Xue Guan Song, Jung Ho Kang, Young Chul Park
Abstract: The welding process, a conventional production method of gate valves, has advantages such as light weight, but it also has disadvantages such high production price. However, the forging process, has economic merits and mass production capability. The main focus of this paper is the optimization of the preform in the forging process. This paper proposes an optimal design of the preform to improve the mechanical efficiency of the gate valve made by the forging method. The design of the preform is optimized by the use of the real response model to the Kriging model by computer simulation. Also, the optimized results were used to verify the response model. The verified response model confirmed the usefulness and reliability of the Kriging method in optimum structural design of preform achieved by finite element analysis and Kriging equations.
977
Authors: Hea Joeng Lee, Jung Hyun Kong, Dae Kyoung Yoo, Young Chul Park, Jang Hyun Sung
Abstract: This study examined the phase changes, nitride precipitation and variations in hardness of Fe-18Cr-1Mo-0.2Ti (436L) ferritic stainless steels after a nitrogen permeation heat treatment at temperatures ranging from 1050°C to 1150°C. The strong affinity between nitrogen and Ti/Cr enabled the permeation of nitrogen into the 436L ferritic stainless steels. The nitrogen content of the surface layers ranged from 0.40% to 0.87%, depending on the nitrogen permeation temperatures. The nitrogen-permeated surface layers changed into martensite plus retained austenite(RA) with rod type M2N and square type TiN precipitates. Ups and downs of hardness with increasing depth below the surface was observed, depending on the volume fraction of the RA, nitrogen content and quantity of precipitates. The maximum hardness of the nitrogen permeated surface layer was 700Hv.
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