Papers by Author: Hyung Ick Kim

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Authors: Hong Sun Park, Hyung Ick Kim, Yong Huh, Moon Young Kim, Sang Yeol Park, Jae Mean Koo, Chang Sung Seok
Abstract: The Ni-based superalloy Inconel 718 (IN-718) was developed in the 1950s and is currently used for several critical gas turbine components due to its good balance of mechanical properties. Because of its stable mechanical properties at high temperature, the alloy is used for turbine bolts. The mechanical properties of in-service facilities are required to maintain safety operation in power plants. Ultrasonic tests, tensile tests and hardness tests were performed to evaluate the degree of the material degradation of Inconel 718. The mechanical properties decreased as degraded, but the longitudinal velocity of the ultrasonic signal increased. Also, the microstructure of the degraded Inconel 718 was to study the relationship between the result from ultrasonic test and the results from destructive methods.
Authors: Hyung Ick Kim, Yong Huh, Jeong Pyo Kim, Chang Sung Seok
Abstract: The mechanical properties of in-service facilities under harsh environment a decrease as materials of the facilities degrade. This decrease of mechanical properties can affect the safety operation of the facilities. Therefore, the extent of degradation due to prolonged service exposure must be estimated. Nondestructive evaluation method is a good technique for monitoring the change of mechanical properties of in-service facilities. The most widely used nondestructive methods are the ultrasonic method and the indentation test, which is advantageous with respect of applicability to in-service facilities. The modified theoretical Vary's equation, considering nonlinear response due to material degradation, was proposed for obtaining the correlations between ultrasonic parameters and fracture toughness. Experimental results showed that ultrasonic attenuation, velocity, and nonlinear parameters have significant correlation with fracture toughness and yield strength. The nondestructive evaluation system can be used to obtain the yield strength and ultrasonic parameters simultaneously, and this information can be used to predict the fracture toughness. The predicted results produced good correlations with the experimental results, indicating that the nondestructive evaluation system can be effective in evaluating material properties and degradation, and the life time of facilities.
Authors: Bong Kook Bae, Chang Sung Seok, Jae Mean Koo, Hyung Ick Kim, K.Linga Murty
Abstract: A burst rupture test has been mainly used for evaluating the burst properties of internal pressurized tubes. Although the burst creep test provides accurate results, its complicated and material-wasting process makes it difficult to perform this test. In the burst test, it is known that the hoop stress is a main reason of burst, so it can be expected that the burst rupture properties are strongly related with the hoop creep rupture properties. A ring test is occasionally used for obtaining the hoop directional properties of tube-shaped structures. In this study, the creep rupture properties of Zirlo tubing are investigated at temperature ranging from 365 to 570  using the ring specimens. An analysis of the fractography was performed and the estimation of service life with Larson-Miller parameter was conducted. Finally, In view of the Dorn equation of power-law, the creep mechanism was determined and discussed.
Authors: Yong Huh, Hyung Ick Kim, Chang Sung Seok
Abstract: In this study, we performed the static test of nuclear piping materials by the unloading compliance method and the normalization data reduction technique and obtained two fracture resistance curves (J-R curves). The two curves were similar, which proves that the normalization data reduction technique can be adopted in the static test. Then we performed the dynamic fracture toughness test for welding part of nuclear piping. The J-R curves were obtained from the dynamic test by the normalization data reduction technique and were compared to those of the static test results.
Authors: Chang Sung Seok, Hyung Ick Kim, Dae Jin Kim, Bong Kook Bae, Sang Pil Kim
Abstract: When huge energy transfer systems like nuclear power plants and steam power plants are operated for long times at high temperatures, mechanical properties change and ductile-brittle transition temperature increases by degradation. So we must estimate the degradation in order to assess safety, life expectancy, and other operation parameters. The sub-sized specimen test method using the surveillance specimen, and BI (Ball Indentation) method were developed for evaluating the integrity of metallic components. In this study, we will present the evaluation of the ductile-brittle transition temperature using the BI test and the sub-sized specimen test. The four classes of the thermally aged 1Cr-1Mo-0.25V specimens were prepared using an artificially accelerated aging method. The tensile test, the fracture toughness test, and the BI test were performed. The results of the fracture toughness tests using the sub-sized specimens were compared with those of the BI test. The evaluation technique of the ductile-brittle transition temperature using the BI test was also discussed. Our results show that the ductile-brittle transition temperatures rose as the aging time increased. We suggested that the fracture toughness results of the sub-sized specimen test and the IEF results of the BI test could be used in the estimation of the ductile-brittle transition temperature as material degrades.
Authors: Chang Sung Seok, Jae Sil Park, Hyung Ick Kim, Young Min Lee, Won Hak Cho, Weon Keun Song
Abstract: The fatigue characteristic of a material or a structure is derived from fatigue tests of standard specimens. However, many researches have reported that test results of standard specimens are very different from those of real structures or components. One reason for this difference is the constraint effects according to the geometrical difference. Therefore, to calculate more accurate fatigue life, the constraint effect must be considered by comparing test results of standard specimens with those of real structures or components. Another reason for this difference is the surface condition. All surfaces of a standard specimen are polished to obtain similar conditions in a fatigue test. However, in a piping system, surface conditions of components are different from each other and very different from that of a standard specimen. Because fatigue life is effected by a surface condition, to evaluate the fatigue life of a piping system, fatigue tests must be conducted with a specimen extracted from a pipe with the same surface condition. The objective of this paper is to evaluate the fatigue characteristic of a real waterworks pipe by conducting fatigue tests with standard specimens and non-standard specimens of base metal and weld metal. Standard fatigue specimens and non-standard specimens were extracted from a steel pipe used in waterworks. Also, fatigue tests of pipes used in water service were carried out and then compared with those of standard specimens and non-standard specimens. From these results the relation between the S-N diagram of a specimen and that of a pipe specimen was evaluated.
Authors: Hyung Ick Kim, Hong Sun Park, Bong Kook Bae, Young Min Lee, Chang Sung Seok, Moon Young Kim
Abstract: The Ni-based superalloy GTD-111DS has been widely used as the material of the first stage blade of gas turbine. But there are little data available on the microstructure and mechanical property. The strength and ductility of GTD-111DS decrease more rapidly due to the acceleration of its microstructure degradation under high temperature. The results of study showed that the shape of γ' did not change with increased aging time but the amount and volume fraction of the deposition of secondary γ' increased and secondary γ' grew among primary γ'. Also there was difference of yield strength and tensile strength in room temperature according to heat treatment and collecting region.
Authors: Sang Young Kim, Hyung Ick Kim, Chang Sung Seok, Jae Kwan Lee, Jin Yong Mo, Deug Yong Park
Abstract: Used pipes in various mechanisms and structures are produced from raw material by extruding and drawing. The properties such as yield strength, tensile strength, and elongation of a pipe produced by these methods are different from the properties of their raw material. But designers use the properties of the raw material because the actual properties of the pipes are difficult to obtain from testing. Also, the pipe is used after it has been bent in a complex manner and cut to fit it to mechanisms and structures. The bending process, especially, induces deformation of the pipe’s section and residual stress, which are involved in the plastic deformation of the bended pipes. This residual stress affects the pipe’s properties, including its fatigue life. Therefore, it is very important to understand the residual stress of a material. But, the distribution of residual stress of a U-shaped pipe, which is examined in this study, is very complicated and cannot be measured exactly.
Authors: Hyung Ick Kim, Yong Huh, Jae Sil Park, Chang Sung Seok
Abstract: The safety and reliability of industrial machineries and structures used in various, and severe conditions has become an increasing concern. This study proposes ductile-brittle transition temperature (DBTT) evaluation technique by the sub-sized specimen test to prevent cleavage fracture. Four classes of the thermally aged 1Cr-1Mo-0.25V specimens were prepared. The fracture toughness tests were performed on sub-sized specimens both at room and low temperatures. The results of the fracture toughness tests were analyzed to obtain the DBT behaviours of the specimen materials
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