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API X65 강의 인장 및 굽힘 시편에 대한 유한요소 연성파괴 해석
오창균(Chang-Kyun Oh),진태은(Te-Eun Jin),김윤재(Yun-Jae Kim) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
This paper presents a micro-mechanical model of ductile fracture for the API X65 steel using the Gurson-Tvergaard-Needleman (GTN) model. Experimental tests and FE damage simulations using the GTN model are performed for smooth and notched tensile bars, from which the parameters in the GTN model are calibrated. As application, the developed GTN model is applied to simulate small-sized, single-edge-cracked tensile and bend bars, via three-dimensional FE damage analyses. Comparison of FE damage analysis results with experimental test data shows overall good agreements.
구조물의 형상이 용접부 균열의 크리프 C*-적분에 미치는 영향
오창균(Chang-Kyun Oh),김윤재(Yun-Jae Kim),박진무(Jin-Moo Park) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
Defect assessment of a welded component is important in fitness-for-service evaluation of plant components. Typically a J and C* estimation method for a defective homogeneous component is extended to a mismatched component, by incorporating the effect due to the strength mismatch between the weld metal and the base material. The key element is a mismatch limit load. For instance, the R6/R5 procedure employs an equivalent material concept, defined by a mismatch limit load. A premise is that if a proper mismatch limit load solution is available, the same concept can be used for any defect location (either a weld centre defect or a heat affected zone (HAZ) defect) and for any material combination (either two-material or multi-material combinations; either similar or dissimilar joints). However, validation is still limited, and thus a more systematic investigation is needed to generalise the suggestion to any geometry, any defect location and any material combination. This paper describes the effect of structural geometry on the C* integral for defective similar welds, based on systematic elastic-creep 2-D and 3-D finite element (FE) analyses, to attempt to elucidate the questions given above. It is found that the existing “equivalent material” concept is valid only for limited cases, although it provides conservative estimates of C* for most of cases. A modification to the existing equivalent material concept is suggested to improve accuracy.
원전 안전등급 1 배관의 온도구배 열응력 평가에 대한 기술적 고찰
오창균(Chang Kyun Oh),신희재(Hee Jae Shin),김현수(Hyun Su Kim),정성규(Sung Gyu Jung) 대한기계학회 2019 大韓機械學會論文集A Vol.43 No.3
본 연구에서는 안전등급 1 배관의 피로 건전성 평가에 사용되는 ASME NB-3600 설계요건 중 온도 구배 열응력을 중심으로 평가요건의 기술적 배경을 분석하였으며, 시범 배관에 대해 ASME NB-3600 요건에 따른 평가 결과를 상세 유한요소해석 결과와 정량적으로 비교하였다. 반경 방향 선형적인 온도 분포에 따른 열응력은 온도 의존적 재료물성의 영향으로 ASME NB-3600 수식을 활용한 결과가 유한요소해석 결과에 비해 비교적 낮게 도출되는 반면에, 반경 방향 비선형 온도 분포에 의한 열응력과 축 방향 불연속에 의한 열응력은 NB-3600 수식을 활용함에 따라 과다 예측함을 확인하였다. This study analyzed the technical background of an evaluation method for temperature gradient thermal stress used in fatigue integrity assessment according to ASME NB-3600 for nuclear class 1 piping. The results of applying the ASME NB-3600 evaluation formula to the representative piping were quantitatively compared with the detailed finite element analysis results. The thermal stress results, according to the ASME NB-3600 formula for the radial linear temperature distribution were lower than those of the finite element analysis because of temperaturedependent material properties. Conversely, we found that thermal stress results obtained using the ASME NB-3600 equation for the radial nonlinear temperature distribution and axial discontinuity were conservative.