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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.
상변화물질을 이용한 PMMA 복합필름의 방열 성능 향상에 관한 연구
권준혁,윤범용,조승현,김형익,김동현,박경의,서종환,Kwon, Junhyuk,Yoon, Bumyong,Cho, Seung-hyun,Lee, Stephanie K.,Kim, Hyung-ick,Kim, Donghyun,Park, Kyungui,Suhr, Jonghwan 한국복합재료학회 2017 Composites research Vol.30 No.5
본 연구에서는 전자기기 사용에 이슈가 되고 있는 발열 문제를 해결하고자 상변화물질(PCM)의 잠열 특성을 이용하여 폴리메틸메타크릴레이트(PMMA) 복합필름을 제조하고 방열 성능을 평가하였다. 이를 위해 용융온도가 서로 다른 두 가지의 상변화물질을 사용하여 제작한 PCM/PMMA 복합필름의 열적 특성을 비교 분석하여 다양한 사용조건에 따른 유효성을 검증하였고, Compression Molding 방법과 PCM Paste Sealing 방법에 따른 PCM/PMMA 복합필름의 방열 특성을 비교 분석하여 최대의 방열 효과를 달성할 수 있는 최적의 방법을 도출하였다. 또한 PCM/PMMA 복합필름의 방열 성능을 최대화하기 위해 열전도율이 높은 흑연과 그래핀을 추가로 적층하여 제조한 Hybrid 복합필름의 열적 특성을 분석하였고, 이들을 통해 향상된 방열 성능을 실험적으로 검증하였다. 본 연구를 통해 개발된 방열 성능이 우수한 복합필름은 다양한 전자기기에 활용되어 발열 문제를 효과적으로 해결할 수 있을 것으로 기대된다. The focus of this study is to experimentally investigate the heat dissipation characteristics of poly (methyl methacrylate) (PMMA) composite films with phase change materials (PCM) to resolve heat build-up problems encountered in various electronic devices. In this study, two different types of phase change materials were used to fabricate the composite films by compression molding method and PCM paste sealing method then compared. It was observed in this study that the heat dissipation capability of PCM/PMMA composite films was remarkably enhanced by applying graphite sheet or graphene film into the composite due to their high thermal conductivity. These PCM/ PMMA composite films were attached on the hot spot inside smart phone and tested its surface temperature change according to time. The heat dissipation capability of PCM/PMMA composite film incorporated smart phone was increased 154% and hybrid PCM/PMMA composite film incorporated smart phone was increased 286% over the reference, respectively.