원자로압력용기 노즐부 구속효과를 고려한 파괴인성 평가

권형도,이연주,김동학,이도환 한국압력기기공학회 2019 한국압력기기공학회 논문집 Vol.15 No.1

The actual stress distribution in the nozzle of a pressure vessel is not a plane strain condition. This means that the constraint effect is relaxed in the nozzle, resulting in a lower constraint. In this paper, a methodology for evaluating the fracture toughness of ASME Code is presented considering the relaxation of constraint effect in the nozzle of the reactor pressure vessel. The constraint effect at the crack tip region in the nozzle is quantified by T-stress, which is a fracture mechanics parameter. The equation, which represent the relation between the fracture toughness in the lower constraint condition and the plane strain fracture toughness, is derived using the T-stress. This equation is similar to the method for evaluating the fracture toughness of Master Curve for low constraint conditions in Europe. As a result of evaluating the fracture toughness considering the constraint effect in the reactor inlet, outlet and direct injection nozzle using the proposed equation, it was confirmed that the fracture toughness in the nozzles is higher than the plane strain fracture toughness. Applying the evaluation methodology proposed in this paper, it is possible to reflect the relaxation of the constraint effect in the nozzles of the reactor pressure vessel, therefore, the safe operation area on the pressure-temperature limit curve can be prevented from being excessively conservatively limited.

STS 316L의 균열선단 변위측정위치에 따른 구속효과 A₂ 거동

한민수(Min-Su Han),김성종(Seong-Jong Kim),장석기(Seok-Ki Jang) 한국마린엔지니어링학회 2009 한국마린엔지니어링학회 학술대회 논문집 Vol.2009 No.-

The magnitude of constraint effect Az values was experimentally estimated by using displacement at various measuring positions on the non-linear elastic plastic fracture toughness for 25.4㎜ thickness in STS 3l6L CT specimen. Constraint effect A₂ value was dependent on specimen configuration and on the measured displacement near crack front. The magnitude of constrain effects |A₂| is below 8.0 at the measurement point of upper and lower side at crack tip. A appropriate location to measure the effective constraint effects Az at Jc is r = 2㎜ and 8 = 90° from crack tip, and the constraint effects |A₂| is 5.3.

원주방향 부분 관통 균열이 존재하는 직관에 인장하중과 열하중의 복합하중이 가해지는 경우의 균열 선단 응력장

제진호(Jin Ho Je),김동준(Dong Jun Kim),김윤재(Yun Jae Kim) 대한기계학회 2014 大韓機械學會論文集A Vol.38 No.11

균열이 존재하는 구조물의 균열 선단에서 과도한 소성 상태에 도달하게 되면 파괴역학 매개변수에 의하여 예측되는 균열 선단의 응력장이 실제와는 매우 다르게 나타난다. 구조물의 크기와 형상 그리고 하중의 형태에 따라 균열 선단의 응력장이 유일하지 않다. 이는 균열 선단의 구속 효과가 단일 매개변수 파괴역학으로 표현 될 수 없기 때문이다. 따라서 전통적으로 사용되었던 K, J를 이용한 단일 매개변수 파괴역학을 보완하기 위하여 다양한 시도가 있었고, 대표적으로 Q-응력이 있다. 본 논문에서는 Q-응력을 이용하여 원주방향으로 완전히 발달한 표면 균열이 있을 경우의 균열 선단의 구속 효과를 확인하였다. 고려된 하중은 일차하중으로 축 방향 인장하중과 반경방향 열구배에 의한 이차하중의 복합하중이다. 이차하중이 일차하중보다 구속효과가 더 심하며 기계하중보다 열하중이 뒤에 가해지는 열충격조건에서 구속효과가 더 심하게 나타남을 확인하였다. Under excessive plasticity, the fracture toughness of a material depends on its size and geometry. Under fully yielded conditions, the stresses in a material near its crack tip are not unique but rather depend on the geometry. Therefore, the single-parameter J-approach is limited to a high-constraint crack geometry. The JQ theory has been proposed for establishing the crack geometry constraints . This approach assumes that the crack-tip fields have two degrees of freedom. In this study, the crack-tip stress field of a fully circumferential surface-cracked pipe under combined loads is investigated on the basis of the JQ theory by using finite element analysis. The combined loads are a tensile axial force and the thermal gradient in the radial direction. Q-stresses of the crack geometry and its loading state are used to determine the constraint effects. The constraint effects of secondary loading are found to be greater than those of primary loading. Therefore, thermal shock is believed to be the most severe loading condition of constraint effects.

탄성-소성-크리프 상태에서 하중 크기에 따른 SE(B) 시편의 구속효과

이한상(Han-Sang Lee),제진호(Jin-Ho Je),김윤재(Yun-Jae Kim) 대한기계학회 2014 대한기계학회 춘추학술대회 Vol.2014 No.11

This paper investigates a constraint effect according to load level under elastic-plastic-creep conditions for single edge cracked bar in bending (SE(B)) specimen, via two-dimensional (2-D) finite element (FE) analyses. Q-stresses of a crack geometry are used to determine constraint effect, and give a characteristic order for constraint. Q-stresses according to load level can’t be calculated by certain standard when using existing proposed method. In this paper, a new method to calculate Q-stress is proposed. It is confirmed that Q-stress according to load level are calculated by certain standard when using the method. Moreover, it is found that constraint effect of SE(B) specimen under elasticplastic-creep conditions slightly decrease with increasing load magnitude.

비표준 시편의 J-적분 시험에서의 3차원 구속효과 영향 연구

김윤재(Yun-Jae Kim),김진수(Jin-Su Kim),조수만(Soo-Man Cho),김영진(Young-Jin Kim) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.8

This paper compiles solutions of plastic ? factors and crack tip stress triaxialites for standard and non-standard fracture toughness testing specimens, via detailed three-dimensional (3-D) finite element (FE) analyses. Fracture toughness testing specimens include a middle cracked tension (M(T)) specimen, SE(B), single-edge cracked bar in tension (SE(T)) and C(T) specimen. The ligament to thickness ratio of the specimen is systematically varied. It is found that the use of the CMOD overall provides more robust experimental J estimation than that of the LLD, for all cases considered in the present work. Moreover, the J estimation based on the load-CMOD record is shown to be insensitive to the specimen thickness, and thus can be used for testing specimen with any thickness. The effects of in-plane and out-of-plane constraint on the crack tip stress triaxiality are also quantified, so that when experimental J value is estimated according to the procedure recommended in this paper, the corresponding crack tip stress triaxiality can be estimated. Moreover, it is found that the out-of-plane constraint effect is related to the in-plane constraint effect.

SA508 PCVN 시편의 균열깊이에 따른 구속력 손실 평가

박상윤(Sang-Yun Park),이호진(Ho-Jin Lee),이봉상(Bong-Sang Lee) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11

In general structures, cleavage fracture may develop under the low constraint condition of large scale yielding with a shallow surface crack. However, standard procedures for fracture toughness testing require very severe restrictions of specimen geometry So the standard fracture toughness data makes the integrity assessment irrationally conservative. In this paper, cleavage fracture toughness tests have been made on side-grooved PCVN (precracked charpy V-notch) type specimens (10 by 10 by 55 ㎜) with varying crack depth. The constraint effects on the crack depth ratios are quantitatively evaluated by scaling model and Weibull stress method using 3-D finite element method. After correction of constraint loss due to shallow crack depths, the statistical size effect are also corrected according to the standard ASTM E 1921 procedure. The results showed a good agreement in the geometry correction regardless of the crack size, while some over-corrections were observed in the corrected values of T?.

균열선단 개구변위와 유한요소해석을 이용한 구속효과 평가

한민수(Min-Su Han),장석기(Seok-Ki Jang),김성종(Seong-Jong Kim),고재용(Jae-Yong Ko),오영철(Yeong-Cheol Oh) 한국마린엔지니어링학회 2007 한국마린엔지니어링학회 학술대회 논문집 Vol.2007 No.-

The fracture toughness by R-method and the magnitude of constraint effect, A₂ using crack tip opening displacement on the behaviors of non-linear elastoplastic fracture were experimentally estimated. The CT specimen of 25.4㎜ thickness for SS400 carbon steel were tested according to guide line of ASTM standard E 1737-96. The stresses and plastic region near crack tip also were calculated by finite element analysis By this paper, constraint effect, A₂ was experimentally depend on measuring position near crack tip, and the measuring point(θ= π/2, r=2.5㎜) was not applicable for but the measuring point (θ= 68°, r=1.0㎜) near crack tip was suitable for estimating constraint effect. For estimating appropriate constraint effect, displacement measurement position near crack front should be existed within plastic region. But it was found that the displacement measurement position recommended by the δ? method was not reasonable because of its elasticity at crack growth initiation.

균열선단 개구변위를 이용한 파괴인성 평가와 구속효과와의 관계

한민수(Min-Su Han),장석기(Seok-Ki Jang),이돈출(Don-Chool Lee),김성종(Seong-Jong Kim),박종식(Jong-Seek Park) 한국마린엔지니어링학회 2006 한국마린엔지니어링학회 학술대회 논문집 Vol.2006 No.-

For the CT specimen of 25.4㎜ thickness SS400 steel, the fracture toughness and the magnitude of constraint effect, A₂ on the non-linear elastoplastic fracture behaviors were experimentally estimated by crack tip opening displacement. In order to estimate constraint effect, displacement measurement position near crack front should be the existed within plastic region. But it is found that the displacement measurement positions by the δ? method are in elastic region at crack growth initiation. Hence the estimate of constraint effect, A₂ by the δ? method was not reliable.

PTS 사고하에서 원자로 압력용기 표면균열에 대한 구속효과의 정량화 : J-Q 접근법의 적용

김진수(Jin-Su Kim),최재붕(Jae-Boong Choi),김영진(Young-Jin Kim),박윤원(Youn-Won Park) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.8

In recent years, the integrity of Reactor Pressure Vessel(RPV) under pressurized thermal shock (PTS) accident has been treated as one of the most critical issues. Under PTS condition, the combination of thermal and mechanical stress by steep temperature gradient and internal pressure causes considerably high tensile stress at the inside of RPV wall. As a result, cracks on inner surface of RPV may experience elastic-plastic behavior which can be characterized by J-integral. In such a case, however, J-integral may possibly lose its validity due to the constraint effect. The degree of constraint effect is influenced by the loading mode, crack geometry and material properties. In this paper, in order to investigate the effect of clad thickness and crack geometry on constraint effect, three dimensional finite element analyses were performed for various surface cracks. Total of 27 crack geometries were analyzed and results were presented by a two-parameter characterization based on the J-integral and the Q-stress.

SENT 시험편을 이용한 실배관 파괴저항곡선 예측

김익중(Ik-Joong Kim),김영표(Young-Pyo Kim),김철만(Chul-Man Kim),장윤영(Youn-Young Jang),허남수(Nam-Su Huh),석창성(Chang-Sung Seok) 대한기계학회 2019 대한기계학회 논문집. Transactions of the KSME. C, 산업기술과 혁신 Vol.7 No.1

본 연구에서는 실 배관의 균열저항특성을 평가하기 위하여, 기존 SENB(Single edge notched bending, 단일측면노치굽힘시험)시험편 대비 실 배관과 유사한 구속조건을 갖는 것으로 알려진 SENT(Single edge notched tension, 단일측면노치인장시험)시험편을 이용하여 라인파이프 강재인 API 5L X70 의 파괴저항곡선을 산출하였다. 구속조건은 균열부위의 응력상태에 영향을 미치는 요인으로 구조물의 기하학적 형상, 균열 깊이, 하중조건, 재료물성 등에 의해 결정되는 것으로 알려져 있다. 이에, 시험편 형상 및 하중조건에 따른 구속영향을 정량적으로 평가하기 위하여, J-적분에 기초한 J-Q 해석을 수행하였다. 그리고 SENT 시험편을 이용하여 API 5L X70 강재의 파괴저항 곡선을 산출하였다. 시험은 BS 8571 규격에 따라 수행하였으며, 탄·소성 파괴역학 매개변수인 J-적분과 CTOD(Crack tip opening displacement, 균열선단개구변위)를 모두 이용하여 각각의 파괴저항곡선을 산출하였다. In this study, fracture resistance curve for API 5L X70 line-pipe steel was estimated by using SENT specimen, which is known to have similar constraint condition to the full-scale pipe. The constraints of structure are known to be affected by geometry, initial crack depth, loading condition and material properties. To assess the constraint effect for various geometries, such as SENB, SENT and full-scale pipe structure, the J-Q analysis was performed using the HRR stress field based on J-integral using finite element analysis. Fracture resistance curve obtained from SENT specimen were performed according to BS 8571 standards and J-R curve & CTOD-R curve were presented, respectively.