Papers by Author: Chang Sung Seok

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Authors: Seung Baek, Jae Mean Koo, Chang Sung Seok
Abstract: In this study, we performed fracture tests on thermally aged DLC thin films by using micro-indentation and nano-indentation and investigated the deformation and fracture characteristics of these films. The aged high hydrogen films have better characteristics such as thermal and mechanical stability than low hydrogen films.
Authors: Seung Baek, Jae Mean Koo, Chang Sung Seok
Abstract: Nano-indentation test is used widely to determine the fracture toughness of brittle materials and to provide information on important material properties such as the Young’s modulus and hardness. In this study, using nano-indentation testing, atomic force microscope (AFM), and finite element method (FEM), we performed the indentation fracture toughness and fracture strength measurement for a (100) single crystalline silicon at different load states. In addition, the loads of the phase transformation events during unloading were estimated by the load-depth curves. The phase transformation load and micro-crack propagation events at pop-out during the unloading process depended on the maximum applied indentation load.
Authors: Jae Sil Park, Chang Sung Seok
Authors: Yong Won Lee, Jong Hoon Kim, Young Sik Song, Chang Sung Seok
Abstract: The formation of intermetallic compounds in brazed joints between SUS304 and nickel-based filler metal is a major concern, since they considerably degrade the mechanical properties of joints. In this study, the SUS304, which is used widespread, as a general material was vacuum brazed with BNi-2 filler metal, and discussed to determine the influence of different brazing temperature and time on the strength of brazed joints. The results showed that, the mechanical properties of brazing layer could be stabilized through increasing the brazing temperature over 100° C more than melting temperature of filler metal, and increasing the brazing time over 120min. long, and diffusing enough the intermetallic compounds formed in the brazing layer to the base metal.
Authors: Cheol Kim, Heung Bae Park, Tae Eun Jin, Ill Seok Jeong, Chang Sung Seok
Authors: Yoon Suk Chang, T.R. Lee, Jae Boong Choi, Chang Sung Seok, Young Jin Kim
Abstract: In this paper, the applicability of local approach is examined for SA515 Gr.60 nuclear steel through a series of finite element analyses incorporating modified GTN and Rousselier models as well as fracture toughness tests. To achieve the goal, fracture toughness test data of standard compact tension (CT) specimens are used for calibration of micro-mechanical parameters. Then, from finite element analyses employing the calibrated parameters, fracture resistance (J-R) curves of CT specimens with different crack length to width ratio, with different thickness and with/without 20% side-grooves are predicted. Finally, suitability of the numerically estimated J-R curves was verified by comparison with the corresponding experimental J-R curves.
Authors: Chang Sung Seok, Bong Kook Bae, Jae Mean Koo, Jae Sil Park, Yong Huh
Abstract: In the case of inner pressurized pipe, the hoop stress mainly causes the failure of pipe. For evaluating the hoop tensile properties of pipes, a ring test is used although it has an inevitable shortcoming of disturbance by the bending. Arsene suggested a central piece-inserted ring test for reducing the bending. At high temperatures, the friction between the specimen and the central piece exerts a serious influence on the results, so an effect on friction should be considered in the analysis. In this study, for the evaluation of the hoop properties using the central piece-inserted ring model of Arsene, we performed the ring tensile tests at several temperatures. From the ring tensile tests and numerical analysis the load-displacement conversion relationship of ring specimen (LCRR) was determined. We could obtain the hoop tensile properties by means of applying the LCRR to the results of the ring tensile test. From the result, it was observed that the strength decreased as the temperature increased, and the elongation dropped a little around 400°C.
Authors: Young Min Lee, Yong Huh, Jae Sil Park, Chang Sung Seok
Abstract: Generally, the shape of graphite and the contents of elements strongly affect the tensile strength of cast iron. In this study, hardness tests and tensile tests for the two types of gray cast iron were carried out. The test results showed the similarity in the hardness but considerable difference in the tensile strength between two materials. Microstructure analysis and chemical analysis were conducted to determine the cause for the difference in the tensile strength between the two types of cast iron. The experimental results showed differences in the microstructure and chemical composition between the two materials. B-type brake disk material(B-type) that had higher tensile strength includes flake, vermicular and spheroidal graphite, whereas A-type brake disk material (A-type) included only flake graphite in the structure. Nodularity of graphite in the B-type was higher than that in the A-type. Also, the B-type had the higher Si content and lower Mn content. In addition, the B-type had Cu, while the A-type did not. Therefore, we concluded that the difference in the strength between the two types of cast iron was due to the difference in the shape of the graphite and the contents of Cu in the cast irons.
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