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24개월 대기 노출된 Al1050 및 Al7075 알루미늄 합금 산화막에 대한 투과전자현미경 분석
김대건,김가림,최원준,반치범,Kim, Dae-Geon,Kim, Ga-Rim,Choi, Wonjun,Bahn, Chi Bum 한국표면공학회 2019 한국표면공학회지 Vol.52 No.2
Al1050 and Al7075 alloy specimens were exposed to atmospheric conditions for 24 months and analyzed by Transmission Electron Microscopy to characterize their corrosion behavior and oxide film characteristics, especially focusing on intergranular corrosion or oxidation. In general, the intergranular oxygen penetration depth of Al1050 was deeper than Al7075. Since O and Si signals were overlapped at the oxidized grain boundaries of Al1050 and Mg is not included in Al1050, it is concluded that Si segregated along the grain boundaries directly impacts on the intergranular corrosion of Al1050. Cr-Si or Mg-Si intermetallic particles were not observed along the grain boundaries of Al7050, but Mg-Si particle was barely observed in the matrix. 10-nm size Mg-Zn particles were also found all over the matrix. Mg was mainly observed along the oxidized grain boundary of Al7075, but Si was not detected due to the Mg-Si particle formation in the matrix and relatively low concentration of Si in Al7075. Therefore, it is thought that Mg plays an important role in the intergranular corrosion of Al7075 under atmospheric corrosion conditions.
열원 입력과 비드 생성 방법이 원통형 다층 금속 용접 과정의 유한요소해석에 미치는 영향
박원동(Won Dong Park),반치범(Chi Bum Bahn),김지훈(Ji Hoon Kim) 대한기계학회 2017 大韓機械學會論文集A Vol.41 No.6
본 논문에서는 원통형 다층 이종 금속 용접부를 대상으로 유한요소 해석을 수행하여, 열원 입력 방법과 용접 비드 생성 방법이 용접 잔류 응력 분포에 미치는 영향을 고려하였다. 열원 입력 방법은 열속 입력 방법과 온도 경계조건 입력 방법으로 나누어 비교하였고, 용접 비드 생성 방법은 요소망 생성 방법과 평온 요소망 방법으로 나누어 비교하였다. 두 열원 입력 방법에 따른 열 해석 결과는 차이가 있었으나, 응력 해석 결과는 유사하였다. 이것은 고온(약 1000 ℃ 이상)에 노출되었던 영역이 비슷하고, 고온에서 재료의 강도가 매우 낮아 용접 비드의 온도가 용접잔류응력에 미치는 영향이 미미하기 때문이다. 두 용접 비드 생성 방법의 용접 잔류응력 분포는 유사하였지만 요소망 생성 방법 적용 시 용접 비드 경계에서 겹침과 들뜸이 발생하였다. 대변형이 발생하는 모델의 용접부 형상을 정확하게 모사하기 위해서는 평온요소망이 더 적합하다고 판단된다. In this study, a finite element analysis of a cylindrical multi-pass weldment for dissimilar metals was performed. The effects of the heat input method and weld bead generation method were considered. We compared two heat input methods: the heat flux method and the temperature method. We also compared two weld bead generation methods: the element birth method and the quiet element method. Although the results of the thermal analysis show deviations between the two heat input methods, the welding residual stresses were similar. Because the areas exposed to high temperature were similar and the strength of the material was very low in high temperature (above the 1000 ℃), the effects of the weld bead temperature were insignificant. The distributions of the welding residual stress were similar to each other. However, gaps and overlaps occurred on the welding boundary surfaces when the element birth method was applied. The quiet element method is more suitable for a large deformation model in order to simulate a more accurate weld shape.
가압 중수로 설비신뢰도 향상 위한 Freeze Plug 설비 건전성 연구
이동준(Dong-Jun Lee),반치범(Chi Bum BAHN) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.11
A freeze plug facility of pressurized heavy water reactor (PHWR) power plants is installed to inject liquid nitrogen into the pipe to isolate the primary heat transportation system throughout the maintenance of PHWR power plants. In 2017, at a PHWR power plant, coolant leakage occurred in the freeze plug installed in front of the emergency core cooling system isolation valve. In this work, the comparative study of mock-up testing and numerical analysis was performed to analyze the cause of the leakage and further improve the reliability of PHWR power plants. A freeze plug mock-up facility was constructed and several testing was conducted from various perspectives, which was then compared with numerical analysis results from finite element analysis. Based on the comparative study, potential improvement on the maintenance procedure for the freeze plug facility is suggested, which can be useful information for the safe operation of PHWR power plants.