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Extracting ductile fracture toughness from small punch test data using numerical modeling
Jeon, J.Y.,Kim, Y.J.,Lee, S.Y.,Kim, J.W. Applied Science Publishers ; Elsevier Science Ltd 2016 The International journal of pressure vessels and Vol.139 No.-
<P>This paper presents a numerical method to extract ductile fracture toughness from notched small punch test data using FE ductile damage analysis based on the stress-modified fracture strain model. To validate the proposed method, analysis results are compared with series of mechanical (notched tensile, fracture toughness and small punch) test data for three different materials; low alloy steel SA508 Gr.3, TP316L austenitic stainless steel and CF8M cast austenitic stainless steel. Comparison with experimental fracture toughness data shows that the proposed method can predict fracture initiation values relatively well and tearing resistance conservatively. (C) 2016 Elsevier Ltd. All rights reserved.</P>
Parametric Study on Fracture Behaviors of Non-aligned Twin Cracked Pipe Under Bending
Thanh-Long Nguyen,Myeong-Woo Lee(이명우),Yun-Jae Kim(김윤재) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12
To analyze the fracture behavior of multiple cracks and their effect, researchers did some bending tests. However, tests could not be stopped to observe details of crack propagation path and interaction due to the limitation of numbers of the test. Therefore, from test geometries in the previous studies, non-aligned twin cracked pipe simulation was performed by applying the FE damage model which based on stress modified fracture strain. In this paper, crack behaviors and the interaction effects between non-aligned twin cracks on the maximum bending stress were investigated.
C(T) 시편 측면 홈 유무에 따른 파괴저항곡선 변화가 유한요소 손상모델 변수 결정에 미치는 영향 평가
김훈태(Hune-Tae Kim),류호완(Ho-Wan Ryu),김윤재(Yun-Jae Kim),김종성(Jong-Sung Kim),최명락(Myung-Rak Choi),김진원(Jin-Weon Kim) 대한기계학회 2016 大韓機械學會論文集A Vol.40 No.6
본 연구에서는 C(T) 시편 측면 홈의 유무에 따른 J-R 곡선의 변화가 유한요소 손상해석의 모델변수 결정에 미치는 영향을 알아보았다. 손상해석은 수정 응력 파괴변형률 모델을 이용하였다. C(T) 시편은 SA508 Gr. 1a 배관재에서 채취하였고 일부에 측면 홈이 가공되었다. 시험은 상온과 원전 운전 온도인 316℃에서 각각 수행되었으며, 시험 결과 얻은 J-R 곡선을 모사하여 손상모델 변수를 얻었다. 그 결과, 측면 홈의 유무에 따른 J-R 곡선의 변화는 손상모델 변수 결정에 영향을 주지 않음을 확인하였다. In this paper, the effect of J-R curve changes on the determination of parameters in a failure model owing to the presence or absence of a side groove in a C(T) specimen is investigated. A stress-modified fracture strain model is implemented for FE damage simulations. C(T) specimens were taken from SA508 grade 1a low-alloy steel piping material, and some of them were processed with a side groove. Fracture toughness tests were performed at room temperature and at 316℃. The parameters of the failure model were determined by damage simulations using the J-R curves obtained from the tests. Finally, the results show that the determination of failure model parameters is not affected by variations in J-R curves owing to the presence or absence of a side groove.
Blunt defect assessment in the framework of the failure assessment diagram
Han, J.J.,Larrosa, N.,Kima, Y.J.,Ainsworth, R.A. Applied Science Publishers ; Elsevier Science Ltd 2016 The International journal of pressure vessels and Vol.146 No.-
<P>In order to reduce over-conservatism in fitness-for-service assessment procedures, experimental evidence and recent analytical developments recognise the importance of considering the actual shape of non-sharp flaws and/or the real geometric constraint conditions at the crack tip. This paper addresses the effect of blunt defects on the structural integrity assessment of reactor pressure vessel (RPV) and pipeline steels. Parametric studies for compact tension specimens with various notch root radii are performed using finite element analysis. The notch fracture toughness, the resistance to the onset of ductile cracking and the J-integral, quantifying the notch driving force, are evaluated. A stress-modified fracture strain model is used as a virtual testing method. The results are analyzed in the framework of the failure assessment diagram (FAD), showing that the existing shape of the FAD is also suitable for assessments of blunt defects and how the concepts introduced can be used to reduce the conservatism in defect assessment, define margins on failure and indicate when plastic collapse is the dominant failure mechanism. (C) 2016 Elsevier Ltd. All rights reserved.</P>
수정 응력 파괴변형률 모델의 파손 기준 변경을 통한 노치 C(T) 시편의 균열 개시 파괴 인성 예측
이동근(Dong Geun Lee),윤교근(Gyo Geun Yoon),남현석(Hyun Suk Nam),김윤재(Yun Jae Kim),Masayuki Kamaya 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.11
In this study, the fracture criterion of the conventional modified stress fracture strain model for the notch defect was changed from the mean value of the triaxial stress of the tensile specimen to the maximum value and evaluated by the fracture mechanics method. Finite element analysis was performed using ductile fracture simulation technique with varying notch radius based on SM490A experimental data. The fracture toughness of the notched specimen was lower than that of the experimental specimen when the fracture criterion using the average value of the triaxial stress of the conventional tensile specimen deepest point was used. The crack initiation fracture toughness was predicted when the maximum torsional stress was used as the fracture criterion. These results show that it is reasonable to use modified fracture criteria to determine fracture toughness for notch defects.