• 제목/요약/키워드: Elliptical Surface Crack

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복합하중이 작용하는 원주방향 표면균열배관에 대한 소성한계하중식 (Plastic Limit Load Solutions for Circumferential Surface Cracked Cylinders Under Combined Loading)

  • 심도준;김윤재;김영진;황성식;김정수
    • 대한기계학회논문집A
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    • 제27권9호
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    • pp.1469-1476
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    • 2003
  • This paper provides plastic limit load solutions of cylinders with circumferential part-through surface cracks under combined axial tension, internal pressure and global bending. Such solutions are developed based on detailed three-dimensional (3-D) finite element (FE) limit analyses using elastic-perfectly-plastic material behaviour, together with analytical solutions based on equilibrium stress fields. For the crack location, both external and internal cracks are considered. Furthermore, in terms of the crack shape, both semi-elliptical and constant-depth surface cracks are considered. The resulting limit load solutions are given in a closed form, and thus can be easily used in practical situations. Being based on detailed 3-D FE limit analysis, the present solutions are believed to most reliable, and thus to be valuable information for integrity assessment of piping.

3차원 균열의 응력확대계수에 대한 해석의 자동화 (Automation of Analysis for Stress Intensity Factor of 3-D Cracks)

  • 이준성
    • 한국정밀공학회:학술대회논문집
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    • 한국정밀공학회 1997년도 춘계학술대회 논문집
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    • pp.496-500
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    • 1997
  • This paper describes an automated system for analyzing the stress intensity factors(SIFs) of three-dimensional (3D) cracks. A geometry model, i.e.a solid containing one or several 3D cracks is defined. Several distributions of local node density are chosen, and then automatically superposed on one another over the geometry model by using the fuzzy knowledge processing. Nodes are generated by the bucketing method, and ten-noded quadratic tetrahedral solid elements are generated by the Delauuay triangulation techniques. The singular elements such that the mid-point nodes near crack fornt are shifted at the quarter-points are automatically placed along the 3D crack front. THe complete finite element (FE) model generated, i.e the mesh with material properties and boundary conditions is given to one of the commercial FE codes, and a stress analysis is performed. The SIFs are calculated using the displacement extrapolation method. To demonstrate practical performance of the present system, a semi- elliptical surface crack in a plate subjected to tension is solved.

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결함발생 시점을 고려한 CANDU 압력관 결함의 확률론적 건전성평가 (Probabilistic Integrity Assessment of CANDU Pressure Tube for the Consideration of Flaw Generation Time)

  • 곽상록;이준성;김영진;박윤원
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2001년도 추계학술대회논문집A
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    • pp.155-160
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    • 2001
  • This paper describes a probabilistic fracture mechanics (PFM) analysis based on Monte Carlo (MC) simulation. In the analysis of CANDU pressure tube, it is necessary to perform the PFM analyses based on statistical consideration of flaw generation time. A depth and an aspect ratio of initial semi-elliptical surface crack, a fracture toughness value, delayed hydride cracking (DHC) velocity, and flaw generation time are assumed to be probabilistic variables. In all the analyses, degradation of fracture toughness due to neutron irradiation is considered. Also, the failure criteria considered are plastic collapse, unstable fracture and crack penetration. For the crack growth by DHC, the failure probability was evaluated in due consideration of flaw generation time.

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가압열충격에 대한 일체형원자로 SMART의 구조건전성 평가 (Structural Integrity Evaluation of the Integral Reactor SMART under Pressurized Thermal Shock)

  • 김종욱;이규만;최순;박근배
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2001년도 춘계학술대회논문집A
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    • pp.441-446
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    • 2001
  • In the integral type reactor, SMART, all the major components such as steam generators, pressurizer and pumps are located inside the single reactor pressure vessel. The objective of this study is to evaluate the structural integrity for RPV of SMART under the postulated pressurized thermal shock by applying the finite element analysis. Input data for the finite element analysis were generated using the commercial code I-DEAS, and the fracture mechanics analysis was performed using the ABAQUS. The crack configurations, the crack aspect ratio and the clad thickness were considered in the parametric study. The effects of these parameters on the reference nil-ductility transition temperature were also investigated.

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인장하중이 작용하는 평판에 존재하는 반타원 표면균열의 J-적분 계산식 (Engineering J-Integral Estimation for Semi-Elliptical Surface Cracked Plates in Tension)

  • 심도준;김윤재;최재붕;김영진
    • 대한기계학회논문집A
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    • 제25권11호
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    • pp.1777-1784
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    • 2001
  • This paper provides d simplified engineering J estimation method fur semi-e1liptical surface cracked plates in tension, based on the reference stress approach. Note that the essential element of the reference stress approach is the plastic limit lead in the definition of the reference stress. However, for surface cracks, the definition of the limit load is ambiguous ("local" or "global"limit lead), and thus the most relevant limit load (and thus reference stress) for the J estimation should be determined. In the present work, such limit load solution is found by comparing reference stress bated J results with those from extensive 3-D finite element analyses. Validation of the proposed equation against FF J results based on tactual experimental tensile data of a 304 stainless steel shows excellent agreements not only far the J values at the deepest point but also for those at an arbitrary paint along the crack front, including at the surface point. Thus the present results provide a good engineering tool for elastic-plastic fracture analyses of surface cracked plates in tension.

강판항(鋼板桁) 덮개판 형상에 따른 피로균열성장특성 (Fatigue Crack Growth Characteristics by the Cover Plate Shapes in the Steel Plate Girder)

  • 정영화;김익겸;정진석;이형근
    • 산업기술연구
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    • 제19권
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    • pp.269-278
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    • 1999
  • When a variety of repeated loads are given, most steel structures failed in much lower level of loads than static failure loads. In addition, bridge always includes the internal defects or discontinuities. from these, fatigue cracks initiates and can lead to sudden failure. Thus, in this study, tensile specimens by the cover plate shapes were used as the test specimens. The fatigue test was performed by constant amplitude fatigue loading and beach mark. From the results of this study, each specimen's fatigue section was observed. in addition, stress intensity factor at crack tip was calculated by using the Green's function which applied to discontinuous section where causing stress concentration. Therefore, the fatigue life of structural detail was investigated by adopting the theories of fracture mechanics. each specimen's crack shape is a semi-elliptical surface crack or center crack sheet, stress gradient correction factor, Fg is the most subjective of all stress intensity correction factors and fatigue life should be predicted by previous proposed function and finite element analysis.

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가압열충격을 받는 원자로용기의 확률론적 건전성 평가 (Probabilistic Evaluation of RV Integrity Under Pressurized Thermal Shock)

  • 김종민;배재현;손갑헌;윤기석;최택상
    • 대한기계학회:학술대회논문집
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    • 대한기계학회 2004년도 추계학술대회
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    • pp.90-95
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    • 2004
  • The probabilistic fracture analysis is used to determine the effects of uncertainties involved in material properties, location and size of flaws, etc, which can not be addressed using a deterministic approach. In this paper the probabilistic fracture analysis is applied for evaluating the RV(Reactor Vessel) under PTS(Pressurised Thermal Shock). A semi-elliptical axial crack is assumed in the inside surface of RV. The selected random parameters are initial crack depth, neutron fluence, chemical composition of material (copper, nickel and phosphorous) and $RT_{NDT}$. The deterministically calculated $K_I$ and crack tip temperature are used for the probabilistic calculation. Using Monte Carlo simulation, the crack initiation probability for fixed flaw and PNNL(Pacific Northwest National Laboratory) flaw distribution is calculated. As the results show initiation probability of fixed flaw is much higher than that of PNNL distribution, the postulated crack sizes of 1/10t in this paper and 1/4t of ASME are evaluated to be very conservative.

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배관에 존재하는 원주방향 표면균열에 대한 파괴거동 해석 (I) -J-적분 예측식 - (Fracture Behavior Estimation for Circumferential Surface Cracked Pipes (I) - J-Integral Estimation Solution -)

  • 김진수;김윤재;김영진
    • 대한기계학회논문집A
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    • 제26권1호
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    • pp.131-138
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    • 2002
  • This paper provides the fully plastic J solutions for circumferential cracked pipes with inner, semi- elliptical surface cracks, subject to internal pressure and global bending. Solutions are given in the form of two different approaches, the GEF/EPRl approach and the reference stress approach. For the GE/EPRl approach, the plastic influence functions for fully plastic J are tabulated based on extensive 3-D FE calculations using the Ramberg-Osgood (R-O) materials, covering a wide range of pipe and crack geometries. The developed GEf/EPRl-type fully plastic J estimation equations are then re-formulated using the concept of the reference stress approach for wider applications. Based on the FE results, optimized reference load solutions for the definition of the reference stress are found for internal pressure and for global bending. Advantages of the reference stress based approach over the GE/EPRl-type approach are fully discussed. Validation of the proposed reference stress based J estimation equations will be given in Part II, based on 3-D elastic-plastic or elastic creep FE results using typical tensile properties of stainless steels and generalized creep- deformation behaviours.

Engineering criticality analysis on an offshore structure using the first- and second-order reliability method

  • Kang, Beom-Jun;Kim, Jeong-Hwan;Kim, Yooil
    • International Journal of Naval Architecture and Ocean Engineering
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    • 제8권6호
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    • pp.577-588
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    • 2016
  • Due to the uncertainties related to the flaw assessment parameters, such as flaw size, fracture toughness, loading spectrum and so on, the probability concept is preferred over deterministic one in flaw assessment. In this study, efforts have been made to develop the reliability based flaw assessment procedure which combines the flaw assessment procedure of BS7910 and first-and second-order reliability methods (FORM/SORM). Both crack length and depth of semi-elliptical surface crack at weld toe were handled as random variable whose probability distribution was defined as Gaussian with certain means and standard deviations. Then the limit state functions from static rupture and fatigue perspective were estimated using FORM and SORM in joint probability space of crack depth and length. The validity of predicted limit state functions were checked by comparing it with those obtained by Monte Carlo simulation. It was confirmed that the developed methodology worked perfectly in predicting the limit state functions without time-consuming Monte Carlo simulation.

원자력 배관 이종금속 용접부 웅력부식균열의 역학적 평가 (Mechanics Evaluations of Stress Corrosion Cracking for Dissimilar Welds in Nuclear Piping System)

  • 박준수;나복균;김인용
    • 대한용접접합학회:학술대회논문집
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    • 대한용접접합학회 2005년도 추계학술발표대회 개요집
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    • pp.38-40
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    • 2005
  • Fracture mechanics evaluation of stress corrosion cracking (SCC) in the dissimilar metal weld (DMW) for the nuclear piping system is performed; simulating the transition joint of the ferritic nozzle to austenitic safe-end fabricated with the Inconel Alloy A82/182 buttering and welds. Residual stresses in the DMW are computed by the finite element (FE) analyses Then, to investigate the SCC in the weld root under the combined residual and system operation stresses, the fracture mechanics parameters for a semi-elliptical surface crack are evaluated using the finite element alternating method (FEAM). As a result, it is found that the effect of weld residual stresses on the crack-driving forces is dominant, as high as three times or more than the operation stresses.

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