Papers by Author: Jong Sung Kim

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Authors: Yun Jae Kim, Chang Gyun Oh, Jong Sung Kim, Tae Eun Jin
Abstract: Detailed two- and three-dimensional finite element analyses are performed to develop an engineering method to estimate elastic-plastic J for cracked structures under combined primary and secondary stresses, based on the V-factor. Extensive analyses with a wide range of geometry and load combination are considered. The results suggest important factors affecting the value of the V-factor. The most important one is the load magnitude, parameterized by the proximity of plastic yielding. The second one is the relative magnitude of the secondary stress to the primary stress. Although the effect of material, in particular materials with Lüders strain seems to be present, such an effect could be neglected, compared to those of the above two parameters. Based on the present results, an engineering method to estimate J for combined primary and secondary stress can be proposed using bilinear equations in terms of the above two parameters.
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Authors: Tae Soon Kim, Jai Hak Park, June Soo Park, Jong Sung Kim, Tae Eun Jin
Abstract: In order to simulate the growth of arbitrarily shaped three-dimensional cracks, the finite element alternating method is extended. As the required solution for a crack in an infinite body, the symmetric Galerkin boundary element method formulated by Li and Mear is used. In the study, a crack is modeled as distribution of displacement discontinuities, and the governing equation is formulated as singularity-reduced integral equations. With the proposed method several example problems, such as a penny-shaped crack, an elliptical crack in an infinite solid and a semi-elliptical surface crack in an elbow are solved. And their growth under fatigue loading is also considered and the accuracy and efficiency of the method are demonstrated.
55
Authors: Tae Kwang Song, Chang Kyun Oh, Yun Jae Kim, Jong Sung Kim, Tae Eun Jin
Abstract: The present work proposes a method for elastic-plastic fracture mechanics analysis of the circumferential through-wall crack in between elbows and attached straight pipes, subject to in-plane bending. Based on small strain finite element limit analyses, closed-form limit load solutions are given first. Then applicability of the reference stress based method to approximately estimate J is proposed. One interesting finding is that a popular approach to assume that the crack locates in the straight pipe could lead to significantly different assessment results.
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Authors: Jin Won Kim, Jong Sun Park, Jong Sung Kim, Tae Eun Jin
Abstract: This study performed tensile test using small-size flat specimen and ball indentation test at room temperature to characterize the local tensile properties of bi-metallic weld joints. The weld specimens used were fabricated by joining between SA508 Gr.3 ferritic steel and Type 316 stainless steel with Alloy 82 buttering on the ferritic steel side and Alloy 82/182 weld metal. The test results showed that yield stress (YS) of weld metal was slightly higher than that of Type 316 and smaller than that of SA508 Gr.3, and ultimate tensile stress (UTS) of weld metal was similar as those of Type 316 and SA508 Gr.3 base metals. Also, the values of YS and UTS of buttering layer (Alloy 82) were nearly same as those of weld metal. Heat-affected-zones (HAZs) showed higher YS and UTS values compared to their base metals. Especially, the strengths of SA508 Gr.3 were significantly higher than those of surrounding materials. Also, it was known that the ball indentation test reasonably measured the local YS and UTS of bi-metallic weld joints.
2073
Authors: Yun Kyung Lee, Young Soo Yoon, Dal Ho Lee, Jong Sung Kim
Abstract: Amplification of the p53 gene using the polymerase chain reaction (PCR) was performed in a silicon-based micro-PCR chip. Metal deposition, photolithography, and anodic bonding were used to fabricate micro-PCR chip and a thermal cycling system with dual peltier devices and PID controller was integrated for controlling the cycling temperature of the PCR mixture. We have demonstrated the amplification of exon 6(182bp) of the p53 gene with the micro-fabricated PCR chip. Temperature control accuracy was within  0.5  . The amplified p53 genes using both conventional PCR and micro fabricated PCR were analyzed using micro-capillary electrophoresis. The PCR performance strongly depends on the cycling temperature, and the Si surface treatment with protein. The micro-PCR products show higher specificity than those of conventional PCR products, and this is attributed to the uniform temperature distribution of the PCR mixture in micro-chip.
1241
Authors: Jong Sung Kim, Tae Eun Jin
Abstract: In the paper, the validity of the modified mesh-insensitive SS (structural stress) procedure to apply to the welded joints with local thickness variation is identified via the comparison of SCFs (stress concentration factors) calculated for various FE (finite element) models. FCI (fatigue crac kinitiation) cycles are determined by using the SS/EPFM (elasto-plastic fracture mechanics) approach and the various fatigue crack growth models. Fatigue test is performed to identify the validity of the fatigue analysis results. Finally, as a result of comparison among test and various analysis results, it is found that the SS/FM (fracture mechanics) approach agrees well with the fatigue test results over all cycle regions and the SS/EPFM approach is more reliable than the SS/LEFM (linear elastic fracture mechanics) approach.
774
Authors: Jong Sung Kim, Hag Ki Youm, Tae Eun Jin
2262
Authors: Hyun Su Kim, Jong Sung Kim, Tae Eun Jin, Hong Deok Kim, Han Sub Chung
1240
Authors: Ouk Sub Lee, Hyun Su Kim, Jong Sung Kim, Tae Eun Jin, Hong Deok Kim, Han Sub Chung
Abstract: Operating experience of steam generators has shown that cracks of various morphologies frequently occur in the steam generator tubes. These cracked tubes can stay in service if it is proved that the tubes have sufficient safety margin to preclude the risk of burst and leak. Therefore, integrity assessment using exact limit load solutions is very important for safe operation of the steam generators. This paper provides global and local limit load solutions for surface cracks in the steam generator tubes. Such solutions are developed based on three-dimensional (3-D) finite element analyses assuming elastic-perfectly plastic material behavior. For the crack location, both axial and circumferential surface cracks, and for each case, both external and internal cracks are considered. The resulting global and local limit load solutions are given in polynomial forms, and thus can be simply used in practical integrity assessment of the steam generator tubes, because the comparison between experimental data and FE solutions shows good agreement.
1704
Authors: Seung Gun Lee, Jong Sung Kim, Jin Seok Park, Tae Eun Jin
Abstract: The multi-pass welding generates residual stress which may change fatigue crack growth rate and impair the lifetime of nuclear welded structures. In this paper, we performed fatigue test with notched specimens and evaluate the effect of residual stress on fatigue crack growth rate of welds. In order to identify the magnitude of residual stress, the residual stress was measured by HDM (hole drilling method) and residual stress analysis was performed by using FEM (finite element method). In order to review the effect of residual stress on fatigue crack growth rate, the fatigue crack growth analysis was also performed to determine the fatigue crack growth curves by using FEM and ASME B&PV Code, Sec.XI, App.A. Finally, as a result of comparison among the fatigue crack growth curves, it is found that the fatigue crack growth rate was quite different according to the crack location even if the residual stresses are considered.
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