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2.25Cr-1Mo 강의 열화와 기계적 성질변화에 관한 연구
정희돈,Jeong, Hee-Don 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.5
As recieved boiler tuve steel was aged artificially at $650^{\circ}C$ and$690^{\circ}C$ for various time duration to simulate the material deterioration which could be occurred during the operation of fossiol power plants. And the tensile tests, the microhardness tests and the characterization of carbides formed in the aging process were performed to asses the relationship between the mechanical properties and the effect of thermal aging. Furthernore, the amout of Mo-rich carbide were investigated by ondestructive method by noticing the fact that formation of Mo-rich carbide were investigated by ondestructive melthod by noticing the fact that formation of Mo-rich carbides($Mo_6C$) which stabilizes lastly affects the mechanical properties. It was known that the microhardness results of service exposed materials were similar to the ones which are aged at $650^{\circ}C$. The room temperature measurement showed small variation in the yield points and ultimate strength in materials aged at $650^{\circ}C$. Those properties at $540^{\circ}C$ showed the abrupt decrease compared with as received material even if short aging time. And it was found that $650^{\circ}C$ $690^{\circ}C$ aging cause different effects on mechanical properties, although the temperature time parameters(LMP;Larson-Miller parameter) are same. And it was concluded that the aigng at $650^{\circ}C$ is more appropriate to simulate the service exposed condition. Finally, the relationship between high temperature tensile properties and Ip values were established, which offers a potential way of reliability tests onthe power plant components.
화력발전설비 진단기술 및 전문가 시스템개발에 관한 연구
백영민(Young-Min Baik),정희돈(Hee-Don Jeong),신은주(Eun-Ju Shin) 대한설비공학회 2008 대한설비공학회 학술발표대회논문집 Vol.2008 No.2
In order to analyze the causes of fossil power plant facilities due to a degradation and corrosion, artificial degraded materials composed of the facilities were manufactured. Various experiment were performed based on mechanical test, microstructure observation, hardness test, electrochemical potentiokinetic reactivation test(EPR) and corrosion scale thickness measurement test. The master curves were write out using Larson-Miller parameter to evaluate the degree of degradation with the above diagnosis methods. These data were applied to materials database of fossil power plant diagnosis. Finally expert system on the fossil power plant diagnosis was developed using the master curves and diagnosis algorithms.
백영민(Young-Min Baik),정희돈(Hee-Don Jeong),신은주(Eun-Ju Shin) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
본 연구에서는 발전설비의 열화도를 측정하기 위한 각종기법들에 대한 연구를 수행하고 각 측정법별로 잔존수명평가 및 차기 점검시기를 산정하기 위한 소재별 master curve를 작성하였다. 이들 자료들을 활용하여 설비의 사용환경 하에서 열화도를 평가하기 위한 물성DB를 구축하고, 발전설비에 대한 진단 알고리즘 개발하였다. 전문가 시스템에는 다양한 형태의 진단기법들을 채용하여 진단결과의 신뢰도를 높였다. 향후 개발된 전문가 시스템은 발전설비의 효율적인 관리와 신뢰성 향상 및 유지 보수 비용의 절감에 기여할 것으로 기대된다. In order to analyze the causes of fossil power plant facilities due to a degradation and corrosion, artificial degraded materials composed of the facilities were manufactured. Various experiment were performed based on mechanical test, microstructure observation, hardness test, electrochemical potentiokinetic reactivation test(EPR) and corrosion scale thickness measurement test. The master curves were write out using Larson-Miller parameter to evaluate the degree of degradation with the above diagnosis methods. These data were applied to materials database of fossil power plant diagnosis. Finally expert system on the fossil power plant diagnosis was developed using the master curves and diagnosis algorithms.
鄭世喜,金台永,林載奎,鄭熙敦,朴昌彦 全北大學校 1984 論文集 Vol.26 No.-
The susceptibility of weld metal(AWS, F76-EH14) on hot straining embrittlement has been examined. The sharp notch was machined on the weld metal of 1st bead and on coarse-grained HAZ transformed by next pass. After machining the notch, these specimens were bended at 250℃ to receive the hot straining embrittlement and they were done COD fracture toughness test by the three point bending, and then the change of plastic zone at notch tip was evaluated by microhardness test. The obtained results are summarized as follows. 1. Fracture toughness of weld metal was greater than that of base metal. 2. Fracture toughness of the coarse-grained HAZ was similar to that of weld metal. 3. Hardness of weld metal reheated by next pass was lower than that of weld metal owing to the effect of heat treatment. 4. Plastic deformation of the coarse-grained HAZ was less than that of weld metal.
유도초음파를 이용한 박판에서의 결함의 검출에 관한 연구
정희돈,신현재,Rose,Joseph L. 韓國非破壞檢査學會 1998 한국비파괴검사학회지 Vol.18 No.6
본 연구는 박판 용접부 결함 검출 기법의 확립을 위해서 실시된 기초 연구로서, 전기강판 소재의 모재에 인위적인 결함을 작성하고, 이론 및 시험적 결과를 이용하여 결함을 검출하기 위한 최적의 조건과 임계 검출 결함 크기를 조사한 것이다. 이를 위해서 소재의 dispersion curve를 구하고, 두께 2.4mm의 박판에 대해서 tone burst방식에 의한 초음파 탐상을 실시하였다. 실험적 검토를 행한 결과 840kHz의 가진 주파수와 30도 그리고 85도의 입사각이 최적의 탐상 조건임을 알았다. 한편, 초음파의 속도와 dispersion커브를 비교 검토하여 본 바, 30도의 입사각에서 발생하여 전파하는 초음파는 symmetric mode이고 85도의 입사각에서는 antisymmetric mode의 파가 전파하고 있었다. 결함의 위치와 형상에 따라 반사파의 특성이 다르게 나타나고 있었으며, 특히 표면 결함의 경우에는 antisymmetric 모드의 초음파가 symmetric 모드 보다 높은 반사파 에너지를 나타내고 있었다. 또한 이러한 초음파 모드의 종류와 결함 검출과의 관계에 대해서는 유도파의 구조에 의해서 설명이 가능했다. In order to establish a technical concept for the detection of defects in weldments in thin steel plate, an experimental and theoretical investigation was carried out for artificial defects in a steel plate having a thickness of 2.4mm by using the guided wave technique. In particular the goal was to find the most effective testing parameters paying attention to the relationship between the excitation frequency by a tone burst system and various incident angles. It was found that the test conditions that worked best was for a frequency of 840kHz and an incident angle of 30 or 85 degrees, most of the defects were detected with these conditions. Also, it was clear that a guided wave mode generated under an incident angle of 30 degrees was a symmetric mode, So, and that of 85 degrees corresponded to an antisymmetric mode, Ao. By using the two modes, most of all of the defects could be detected. Furthermore, it was shown that the antisymmetric mode was more sensitive to defects near the surface than the symmetric mode. Theoretical predictions confirmed this sensitivity improvement with Ao for surface defects because of wave structure variation and energy concentration near the surface.
화력발전소 보일러 튜브 및 대형 유체수송관 자동 진단을 위한 이동로봇 시스템 개발
박상덕,정희돈,임종수 한국비파괴검사학회 2002 한국비파괴검사학회지 Vol.22 No.3
화력발전소 보일러 튜브 및 대형 유체수송관의 자동 진단을 위해 비파과검사 방법을 사용하는 두 가지 형태의 이동로봇을 개발하였다. 개발된 이동로봇은 보일러 튜브 또는 유체수송관의 외면을 주행하면서 전자기 초음파 탐촉자를 이용하여 파이프 벽면에 발생하는 미세한 구멍, 균열 또는 부식 및 침식에 의한 감육 등과 같은 결함을 검출한다. 이와 같은 이동로봇을 이용한 결함 검출의 자동화는 열악한 환경에서 작업자의 위험 없이 구조물의 중대한 결함을 방지하는 유용한 수단으로 활용될 수 있다. In this study, two types fo mobile robotic systems using NDT(Non destructive testing) method are developed for automatic diagnosis of the boiler and large size pipeline. The developed mobile robots crawl the outer surface of the tubes or pipelines and detect in pipe such as pinholes, cracks and thickness reduction by corrosion and or erosion using EMAT(Electro magnetic Acoustic Transducer). Automation of fault detection by means of mobile robotic systems for these large scale structure helps to prevent significant troubles without danger of human beings under harmful environment.