• Title/Summary/Keyword: 응력 확대계수

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Computation of Crack Tip Mode I Stress Intensity Factor of a Specimen for Measuring Slow Crack Growth Resistance of Plastic Pipes Using Finite-Element Method (유한요소법에 의한 플라스틱 파이프의 저속균열성장 저항성 시험편 균열선단 모드 I 응력확대계수 계산)

  • Choi, Sun-Woong;Park, Yeong-Joo;Suh, Yeong-Sung
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.29 no.9 s.240
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    • pp.1225-1234
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    • 2005
  • Mode I stress intensity factor $(K_I)$ of Notched Ring Test(NRT) specimen for measuring slow crack growth resistance was found using finite-element method. The theoretical $K_I$ value of NRT was not available in any references and could not be solved analytically. At first, in order to verify the accuracy of the finite-element approach, published $K_I$ values of several cracks were calculated and compared with finite-element results. The results were in good agreement within inherent errors of theoretical $K_I$. Finally the mode I stress intensity factor of NRT was found using 2- and 3-dimensional finite-element methods and expressed as a function of the applied load. This enabled direct comparison of resistance to slow crack growth between NRT and Notched Pipe Test(NPT), which employ different loading regime.

Estimation of Elastic Fracture Mechanics Parameters for Slanted Axial Through-Wall Cracks for Leak-Before-Break and Crack Growth Analysis (파단전누설 해석 및 균열거동 평가를 위한 축방향 경사관통균열의 탄성 응력확대계수 및 균열열림변위)

  • Huh, Nam-Su;Shim, Do-Jun;Choi, Suhn;Park, Keun-Bae
    • Proceedings of the KSME Conference
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    • 2008.11a
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    • pp.725-726
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    • 2008
  • This paper proposes elastic stress intensity factors and crack opening displacements (CODs) for a slanted axial through-wall cracked cylinder under an internal pressure based on detailed 3-dimensional (3-D) elastic finite element (FE) analyses. Based on the elastic FE results, the stress intensity factors along the crack front and CODs through the thickness at the center of the crack were provided. These values were also tabulated for three selected points, i.e., the inner and outer surfaces and at the mid-thickness. The present results can be used to evaluate the crack growth rate and leak rate of a slanted axial through-wall crack due to stress corrosion cracking and fatigue. Moreover, the present results can be used to perform a detailed Leak-Before-Break analysis considering more realistic crack shape development.

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Comparison of Stress Intensity Factors for Longitudinal Semi-elliptical Surface Cracks in Cyclindrical Pressure Vessels (내압이 작용하는 원통형용기에 대한 축방향 표면결함의 응력확대계수 계산방법 비교)

  • Moonn, H.R.;Jang, C.H.
    • Proceedings of the KSME Conference
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    • 2001.06a
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    • pp.622-627
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    • 2001
  • The object of this paper is to compare stress intensity factor that be calculated by Raju-Newman's equation, finite element method, and Vessel INTegrity analysis inner flaws(VINTIN) program for longitudinal semi-elliptical cracks in cylindrical vessel under inner pressure. For this, three-dimensional finite-element analyses were performed to obtain the stress intensity factors for various surface cracks with t/R = 0.1. The finite element meshes were designed for various crack shapes with t/R of 0.1. The crack depth to thickness ratio, a/t, was set to 0.2 and 0.5 matching Raju-Newman's equation. The crack depth to length ratio, a/c, was set to 0.2 and 0.4 in the same way and 0.33 was added to extend the range of crack configuration. Finite Element Analyses(FEA) were performed using the commercial FEA program ABAQUS. The results showed that the Raiu-Newman solutions were about 4-10% lower than FEA's using symmetric model of one-eighth of a vessel and close to those of FEA using symmetric model or one-forth or a vessel. Ana VINTIN solutions were nearly equal to those or Raju-Newman.

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Finite Element Simulation of Fatigue Crack Growth: Determination of Exponent m in Paris Law (피로균열성장의 유한요소 시뮬레이션: Paris 법칙의 지수 m의 결정)

  • Chu, Seok-Jae;Liu, Cong-Hao
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.36 no.7
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    • pp.713-721
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    • 2012
  • The finite element simulations of fatigue crack growth are carried out. Using only the mechanical properties usually obtained from the tensile test as input data, we attempted to predict the fatigue crack growth behavior. The critical crack opening displacement is determined by monitoring the change in displacements at the node close to the crack tip. Crack growth is simulated by debonding the crack tip node. The exponent in the Paris law was determined and compared to the published exponent. Plotting with respect to the effective stress intensity factor range yielded more consistent results.

Stress Intensity Factors for Axial Cracks in CANDU Reactor Pressure Tubes (CANDU형 원전 압력관에 존재하는 축방향 균열의 응력확대계수)

  • Lee, Kuk-Hee;Oh, Young-Jin;Park, Heung-Bae;Chung, Han-Sub;Chung, Ha-Joo;Kim, Yun-Jae
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.7 no.1
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    • pp.17-26
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    • 2011
  • CANDU reactor core is composed a few hundreds pressure tubes, which support and locate the nuclear fuels in the reactor. Each pressure tube provides pressure boundary and flow path of primary heat transport system in the core region. In order to guarantee the structural integrity of pressure tube flaws which can be found by in-service inspection, crack growth and fracture initiation assessment have to be performed. Stress intensity factors are important and basic information for structural integrity assessment of planar and laminar flaws (e. g. crack). This paper reviews and confirms the stress intensity factor of axial crack, proposed in CSA N285.8-05, which is an fitness-for-service evaluation code for pressure tubes in CANDU nuclear reactors. The stress intensity factors in CSA N285.8-05 were compared with stress intensity factors calculated by three methods (finite element results, API 579-1/ASME FFS-1 2007 Fitness-For-Service and ASME Boiler and Pressure Vessel Code Section XI). The effects of Poisson's ratio and anisotropic elastic modulus on stress intensity factors were also discussed.

A Photoelastic Study on the Stress Intensity Factor of Circular Disk with an Are-crack (광탄성법에 의한 원고형상크랙을 갖는 원판의 응력확대계수에 관한 연구)

  • Lee, Chi-Woo;Kim, Tae-Gyu;Yang, Jang-Hong;O, Se-Uk
    • Journal of Ocean Engineering and Technology
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    • v.2 no.2
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    • pp.96-103
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    • 1988
  • The stress distribution in the vicinity of the crack tip in the fracture mechanics is ordenarily indicated by the stress intensity factor. In the analysis of stress intensity factors, there are many theoretical and experimental methods. The stress analysis in photoelastic technique is usually made by using the difference of the principal stress of isochromatic fringe patterns. In this paper, the teflon molding technique is adopted to make a test specimen with a circular arc-crack, and that upgraded the accuracy of experiment. As the result, the experimental values of the stress intensity factors for the circular disk with a straight crack are coincided with the theoretical values. But, there is quite a difference between this expermental results on the finite plate for circular arc-crack and its theoretical values on the infinite one. Therefore, a boundary condition with regard to the loading condition on finite disk must be considered.

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Characteristics of Parameters for the Distribution of Fatigue Crack Growth Lives under Constant Stress Intensity Factor Control (일정 응력확대계수 제어하의 피로균열전파수명 분포의 파라메터 특성에 관하여)

  • Kim, Seon-Jin;Kim, Young-Sik;Jeong, Hyeon-Cheol
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2002.10a
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    • pp.301-306
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    • 2002
  • The characteristics of parameters for the probability distribution of fatigue crack growth lives by the non-Gaussian random process simulation method is investigated. In this paper, the material resistance to fatigue crack growth is treated as a spatial random process, which varies randomly on the crack surface. Using the previous experimental data, the crack length - the number of cycles curves are simulated. The results are obtained for constant stress intensity factor range conditions with stress ratio of R=0.2, three specimen thickness of 6, 12 and 18mm, and the four stress intensity level. The probability distribution function of fatigue crack growth lives seems to follow the 3-parameter Wiubull and shows a slight dependence on specimen thickness and stress intensity level. The shape parameter, ${\alpha}$, does not show the dependency of thickness and stress intensity level, but the scale parameter, ${\beta}$, and location parameter, ${\upsilon}$, are decreased by increasing the specimen thickness and stress intensity level. The slope for the stress intensity level is larger than the specimen thickness.

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Integrity Evaluation for 3D Cracked Structures(I) (3차원 균열을 갖는 구조물에 대한 건전성 평가(I))

  • Lee, Joon-Seong
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.13 no.8
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    • pp.3295-3300
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    • 2012
  • Three Dimensional finite element method (FEM) was used to obtain the stress intensity factor for subsurface cracks and surface cracks existing in inhomogeneous materials. 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. Nodes are generated by the bubble packing, and ten-noded quadratic tetrahedral solid elements are generated by the Delaunay triangulation techniques. To examine accuracy and efficiency of the present system, the stress intensity factor for a semi-elliptical surface crack in a plate subjected to uniform tension is calculated, and compared with Raju-Newman's solutions. Then the system is applied to analyze interaction effects of two dissimilar semi-elliptical cracks in a plate subjected to uniform tension.

Comparison of Stress Intensity Factors for Cylindrical Structure with Circumferential Through-Wall Cracks subjected to Tensile Load (원주방향 관통균열이 존재하는 원통형 구조물의 인장하중에 의한 응력확대계수 비교)

  • Dal Woo Jung;Chang Kyun Oh;Hyun Su Kim;Hyeong Do Kweon;Jun Seok Yang
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.17 no.2
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    • pp.101-108
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    • 2021
  • To date, a number of stress intensity factor (SIF) solutions have been proposed for the cylindrical structure with circumferential through-wall cracks. However, each solution has a different format as well as applicable range. It is also known that there is a significant difference in predicted SIF values depending on the shape of the structure and the size of the crack. In this study, the applicability of various SIF solutions was analyzed by comparing the finite element analysis results for the case where a tensile load is applied to the cylindrical structure with circumferential through-wall crack. It is found that the calculated SIF gradually decreases and converges to a certain value with increasing length-to-radius ratio. Therefore, an appropriate length-to-radius ratio should be set in consideration of the dimensions of the actual cylindrical structure. For piping with sufficiently long cylinder, the ASME solution is found to be the most appropriate, and for a short cylinder, the API solution should be applied. On the other hand, the WEC solution requires careful attention to its application.

Stress Intensity Factor Analysis of Elliptical Arc Through Cracks at Mechanical Fastener Holes by Weight Function Method (II) - Mixed-Mode Stress Intensity Factor Analysis - (가중함수법에 의한 기계적 체결홀에 존재하는 타원호형: 관통균열의 음력확대계수 해석 (II) - 혼합모드 음력확대계수 해석 -)

  • Heo, Seong-Pil;Yang, Won-Ho;Ryu, Myeong-Hae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.10
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    • pp.1671-1677
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    • 2001
  • Cracks at mechanical fastener holes usually nucleate as elliptical comer cracks at the faying surface of the mechanical joints and grow as elliptical arc through cracks. The weight function method for elliptical arc through cracks at mechanical fastener holes has been developed and verified in the part I of this study. In part H, applying the weight function method, the effects of the amount of clearance on the mixed-mode stress intensity (actors are investigated and the change of crack shape is predicted from the analysis for various crack shapes. The stress intensity factors leer inclined crack are analyzed and critical angle at which mode I stress intensity factor becomes maximum is determined.