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김형익(Hyung-Ick Kim),석창성(Chang-Sung Seok),김상필(Sang-Pil Kim) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.8
As the huge energy transfer systems like as nuclear power plant and steam power plant are operated for a long time at a high temperature, mechanical properties are changed and ductile-brittle transition temperature is raised by degradation. So it is required to estimate degradation in order to assess the safety, remaining life and further operation parameters. BI(Ball Indentation) method was developed for evaluating the integrity of metallic components. In this study, we would like to present the evaluation technique of the ductile-brittle transition temperature by the 81 test. The four classes(virgin, 453, 933, 1820 degraded hours at 630℃) of the thermally aged 1Cr-1Mo-0.25V specimens were prepared using an artificially accelerated aging method. The tensile test and BI test were performed. The Indentation Energy to Fracture(IEF) was appropriate to estimate transition temperature for the varied test temperature. It was suggested that the IEF from the result of BI test which can be used in the estimation of the ductile-brittle transition temperature as the material degradation.
가스터빈 블레이드의 에어포일 표면균열에 미치는 불소이온세정의 영향
김형익(Hyung-Ick Kim),박홍선(Hong-Sun Park),석창성(Chang-Sung Seok),김문영(Moon-Young Kim) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
The blade of the gas turbine must withstand the most severe combination of temperature, stress and environment. After certain period operation, various types of damages are easily found and the damages are identified as due to the turbine operating mode. In order to have with initially similar mechanical properties, the blade of nickel-based superalloy components is passed by a replacement repair process. The fluoride ion cleaning (FIC) process is used to assist in the successful welding repair of nickel-based superalloy components. This work is to study the FIC influence for a gas turbine blade that was serviced 25,748 EOH after first overhaul. The conditions of blade samples were observed by optical microscope and SEM, and the chemical composition of flaws in the blade was investigated by EDS. The condition of the blade was examined from the gamma prime phase morphology and size, because the gamma prime phase coarsening rate depends largely on the exposure time and temperature.
CO₂냉매용 Scroll 압축기의 Wrap 응력 분포 해석
김형익(Hyung Ick Kim),최정훈(Jung Hun Choi),백승(Seung Baek),석창성(Chang Sung Seok),조우현(Woo Hyun Cho),김철우(Chul woo Kim),조성욱(Sung Oug Cho) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.8
Developing compressor which will be used with new cooling gas instead of Freon became a current hot issue since the fact that Freon destroys the ozone layer was discovered. CO₂ gas is getting known for the substitute cooling gas and some industrially advanced nations have succeeded to produce the CO₂ compressor. The scroll type compressor is considered for appling CO₂ gas currently. Because it is known that CO₂ gas has quite different compressive characteristics compare to existing cooling gas, the evaluation for the wrap strength of scroll is necessary. Therefore, stress distribution was analyzed with finite element method with some material experiments to the wrap of scroll type compressor which is applied CO₂ gas for the compressive cooling gas on this study.
협계용접부 강도 불균일을 고려한 소성 η계수 평가 (I)
허용,김형익,선광상,구재민,석창성,Huh, Yong,Kim, Hyung-Ick,Seon, Kwang-Sang,Koo, Jae-Mean,Seok, Chang-Sung 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.6
This study evaluated the influence of the strength mismatch of HAZ for a plastic ${\eta}$-factor, which is the principle parameter determining the plastic portion of J-integral to assess the fracture toughness of the weldment. The specimen of tensile and hardness test was manufactured from the piping applying narrow-gap welding, and the mechanical properties of weldment, HAZ and a base metal were obtained. To perform the finite element analysis according to the ratio of strength mismatch, the material properties was chosen with the change of strength using the determination method of Ramberg-Osgood constant. Also, the influence of the strength mismatch of HAZ was determined using finite element analysis by those properties.