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원자력 배관의 파단전누설 해석을 위한 개선된 참조응력법의 수치해석적 검증
허남수,김윤재,김영진,Heo, Nam-Su,Kim, Yun-Jae,Kim, Yeong-Jin 대한기계학회 2001 大韓機械學會論文集A Vol.25 No.4
Three-dimensional, elastic-plastic finite element analyses for circumferential through-wall cracked pipes are performed using actual tensile data of stainless steels, for two purposes. The first one is to validate the recently-proposed enhanced reference stress (ERS) method to estimate the J-integral and COD for circumferential through-wall cracked pipes. The second one is to compare those results with the GE/EPRI estimations. It is found that the J-integral and COD estimations according to the GE/EPRI method can be very sensitive to how the stress-strain data are fitted using the Ramberg-Osgood relation. Moreover, no tendency can be found regarding the most appropriate fitting range for the Ramberg-Osgood fit. On the contrary, the J-integral and COD estimations based on the ERS method give more accurate results than the GE/EPRI estimation. The present results provide confidence in applying the proposed method to the Leak-Before-Break(LBB) analysis.
내압이 작용하는 원주방향 관통균열 배관의 비선형 파괴역학 해석법
허남수,김윤재,김영진,Huh, Nam-Su,Kim, Yun-Jae,Kim, Young-Jin 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.6
This paper provides engineering J-integral and crack opening displacement (COD) estimation equations for circumferential through-wall cracked pipes under internal pressure and under combined internal pressure and bending. Based on selected 3-D finite element calculations for the circumferential through-wall cracked pipes under internal pressure using the idealized power law materials, the elastic and plastic influence functions for fully plastic J-integral and COD solutions are found as a function of the normalized crack length and the mean radius-to-thickness ratio. These developed GE/EPRI-type solutions are then re-formulated based on the enhanced reference stress method. Such re-formulation not only provides simpler equations for J-integral and COD estimations, but also can be easily extended to combined internal pressure and bending. The proposed equations are compared with elastic-plastic finite element results using actual stress-strain data, which shows overall excellent agreement.
김윤재(Yun-Jae Kim),허남수(Nam-Su Huh),김영진(Young-Jin Kim) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
In order to apply the Leak-Before-Break (LBB) concept to nuclear piping, accurate fracture mechanics assessment on pipes with postulated circumferential through-wall crack subject to complex loading, such as combined tension and bending is crucial. In this case, one important element is determination of relevant J-resistance curve for pipes under combined loading. In this respect, this paper provides experimental J estimation method for the circumferential through-wall cracked pipe under combined tension and four-point bending, based on the load-crack opening displacement (COD) record to estimate J-resistance curve. To give confidence in the proposed method, the J results from detailed elastic-plastic finite element (FE) analysis are also compared with estimated J based not only on proposed method but also on conventional method using load-load line displacement, which shows that estimated J based on the proposed method provides reliable J estimates regardless of analysis condition, on the other hand, the conventional method using the load-load line displacement record gives erroneous results for shallow cracks.
정확한 비선형 파괴역학 해석을 위한 새로운 Ramberg-Osgood 상수 결정법
김윤재(Yun-Jae Kim),허남수(Nam-Su Huh),김영진(Young-Jin Kim),최영환(Young-Hwan Choi),양준석(Jun-Seok Yang) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
This paper proposes a robust method for the Ramberg-Osgood (R-O) fit to accurately estimate elasticplastic<br/> J from engineering fracture mechanics analysis based on deformation plasticity. The proposal is based<br/> on engineering stress-strain data to determine the R-O parameters, instead of true stress-strain data. Moreover,<br/> for practical applications, the method is given not only for the case when full stress-strain data are available<br/> but also for the case when only yield and tensile strengths are available. Reliability of the proposed method<br/> for the R-O fit is validated against detailed 3-D Finite Element (FE) analyses for circumferential through-wall<br/> cracked pipes under global bending using five different materials, three stainless steels and two ferritic steels.<br/> Taking the FE J results based on incremental plasticity using actual stress-strain data as reference, the FE J<br/> results based on deformation plasticity using various R-O fits are compared with reference J values.<br/> Comparisons show that the proposed R-O fit provides more accurate J values for all cases, compared to<br/> existing methods for the R-O fit. Advantages of the proposed R-O fit in practical applications are discussed,<br/> together with its accuracy.
원자로 상부헤드 제어봉구동장치 관통노즐 형상이 J-Groove 용접잔류응력에 미치는 영향
김주희(Ju Hee Kim),김윤재(Yun Jae Kim),이성호(Sung Ho Lee),허남용(Nam Young Hur),배홍열(Hong Yeol Bae),오창영(Chang Young Oh),김지수(Ji Soo Kim),박흥배(Heung Bae Park),이승건(Seung Geon Lee),김종성(Jong Sung Kim),허남수(Nam Su Huh) 대한기계학회 2011 大韓機械學會論文集A Vol.35 No.10
가압경수로형 원자로의 원자로압력용기 상부헤드에는 많은 제어봉구동장치(CRDM) 노즐이 분포한다. 최근 10 여 년 동안 제어봉구동장치 alloy 600 CRDM 노즐에서 균열 발생 사례가 증가하고 있으며, 이는 용접과 연관성이 매우 깊은 것으로 알려져 있다. CRDM 노즐에서 발생하는 축 및 원주방향 균열은 유럽과 미국의 원자력 발전소에서 발견되었으며, 사고의 원인은 용접 잔류응력 및 작용하중에 기인하는 일차수응력부식균열(PWSCC)임이 확인되었다. 이러한 이유로 본 연구에서는 유한요소해석을 통해 한국형 원자로의 CRDM 관통 노즐 용접부를 대상으로 용접 잔류응력을 예측하였으며, 특히, 관통노즐의 위치와 형상, 용접부 필렛 형상 및 인접노즐 용접에 의한 영향을 분석하였다. In pressurized water reactors (PWRs), the reactor pressure vessel (RPV) upper head contains numerous control rod drive mechanism (CRDM) nozzles. In the last 10 years, the incidences of cracking in alloy 600 CRDM nozzles and their associated welds has increased significantly. Several axial and circumferential cracks have been found in CRDM nozzles in European PWRs and U.S. nuclear power plants. These cracks are caused by primary water stress corrosion cracking (PWSCC) and have been shown to be driven by welding residual stresses and operational stresses in the weld region. Therefore, detailed finite-element (FE) simulations for the Korea Nuclear Reactor Pressure Vessel have been conducted in order to predict the magnitudes of the weld residual stresses in the tube materials. In particular, the weld residual stress results are compared in terms for nozzle location, geometry factor r<sub>o</sub>/t, geometry of fillet, and adjacent nozzle.
다양한 평가방법을 이용한 원형 노치 CT 시편의 피로수명평가
장동주(Dong-Joo Chang),강주연(Ju-Yeon Kang),허남수(Nam-Su Huh),김진원(Jin-Weon Kim),김종성(Jong-Sung Kim),김윤재(Yun-Jae Kim),김대수(Dae-Soo Kim),김형욱(Hyeong-Wook Kim) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12
In the present work, the fatigue life of a round-notched compact tension (CT) specimen has been evaluated using two different fatigue life evaluation methods. One is Design-By-Analysis (DBA) procedure given in ASME B&PV Code, Sec. III and the other is structural stress based approach provided in ASME B&PV Code, Sec. VIII. The fatigue crack initiation tests were conducted using a round-notched CT specimen, which is made of SA312 TP316 stainless steel, under displacement-controlled cyclic condition, and then experimental fatigue initiation life of that specimen was measured. To predict fatigue life of this CT specimen using DBA based approach, 3-D elastic FE analyses were carried out using experimental condition, and fatigue life was predicted based on both design and best-fit fatigue curve of same material suggested in ASME B&PV Code, Sec. II. Moreover, the fatigue life of CT specimen was also investigated using the structural stress based approach. Finally, the fatigue lives predicted either based on DBA procedure or structural stress based approach were compared with experimental results, and the accuracy of such engineering fatigue life evaluation methods was discussed.