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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.
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.
장석기 한국마린엔지니어링학회 2000 한국마린엔지니어링학회지 Vol.24 No.6
This paper investigates the relationship between J-integral and crack tip opening displacement, ${\delta}_t$ using Gordens results of numerical analysis. Estimation were carried out for several strength levels such as ultimate, flow, yield, ultimate-flow, flow-yield stress to determine the influence of strain hardening and the ratio of crack length to width on the $J-{\delta}_t$ relationship. It was found that for SE(B) specimens, the $J-{\delta}_t$ relationship can be applied to relate J to ${\delta}_t$ as follows $J=m_j{\times}{\sigma}_i{\times}{\delta}_t$ where $m_j=1.27773+0.8307({\alpha}/W)$, ${\sigma}_i:{\sigma}_U$, ${\sigma}_{U-F}={\frac{1}{2}} ({\sigma}_U+{\sigma}_F$), ${\sigma}_F$, ${\sigma}_F}$ $Y=({\sigma}_F+{\sigma}_Y)$, ${\sigma}_Y$
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.
시편두께 및 균열깊이 영향을 고려한 비표준시편의 J 시험법 및 구속효과의 정량화
김진수,조수만,김윤재,김영진,Kim, Jin-Su,Cho, Soo-Man,Kim, Yun-Jae,Kim, Young-Jin 대한기계학회 2003 大韓機械學會論文集A Vol.27 No.9
This paper compiles solutions of plastic $\eta$ factors and crack tip stress triaxialites for standard and nonstandard 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.
주석재 대한기계학회 1995 대한기계학회논문집 Vol.19 No.7
The energy release rates for a dynamically growing crack in orthotropic materials are expressed explicitly in terms of dynamic stress intensity factors. The stress functions suitable for the problem are found and the evaluation of the J-integral for the theoretical singular crack tip fields yields energy release rates. The present results are simpler than the existing ones and can be reduced to the well known solutions in special cases. Examples of extracting stress intensity factors from the finite element solution using the present results are given for the dynamically growing crack problem of orthotropic materials.