• Title, Summary, Keyword: 응력확대계수

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Establishment of Fracture Mechanics Fatigue Life Analysis Procedures for Offshore Tubular Joints -part II : Fatigue Life Analysis for a Multi-Plan Tubular Joint (해양구조물의 원통형 조인트에 대한 파괴역학적 피로수명 산출방법의 설정)

  • Rhee, H. C.
    • Journal of Ocean Engineering and Technology
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    • v.3 no.2
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    • pp.87-100
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    • 1989
  • 해양구조물의 원통형 조인트에 대한 파괴역학적 피로수명 산출방법이 개발되었다. 개발된 방법을 이용해서 2평면 K형 조인트에 대한 피로수명을 구체적인 파괴역학적 방법으로 산출 하였다. 이 분석을 위해 용접부위 표면균열의 응력확대 계수를 3차원 유한요소법에 의해 계산하였다. 계산된 결과에 의하면 용접부위 표면균열 첨단은 단순한 Mode I형태를 보이지 않고 Mode I, II, III이 복합된 형태임이 입증되었다. 계산된 응력확대 계수를 사용해서 16개의 용접부위균열 성장형태를 일반적인 피로균열 성장법칙을 적용해서 계산하였고, 균열성장의 안정분석을 통해 각 균열의 최종 파괴상태를 파괴해석도면(failure assessment diagram)법을 이용해서 계산하였다.

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Effective Way of Measuring $K_I$ by Means of ACPD Technique (교류전위차법을 이용한 효과적인 응력확대계수의 측정 방법)

  • Lee, Jeong-Hee
    • Journal of the Korean Society for Nondestructive Testing
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    • v.19 no.1
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    • pp.8-15
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    • 1999
  • In order to develop an effective way of measuring the mode I stress intensity factor, $K_I$, by the technique based on the alternating current potential drop (ACPD), the effect of the magnetic flux in the air on the change in potential drop due to load for both ferromagnetic and paramagnetic materials containing a two-dimensional surface crack was investigated. Additionally the effects of the demagnetization and the crack length on the change in potential drop were examined. In the case that the measuring system was designed to induce a large amount of electromotive force, the amount of the change in potential drop due to load was shown to increase largely Also the relationship between the change in potential drop and that in $K_I$ was indicated to be linear without any treatment and it was shown that the demagnetization had almost no effect on the change in potential drop. The change in potential drop did not depend on the crack length but on the measuring system. For the application of the ACPD technique to determine $K_I$.

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Damage Tolerance Analysis Using Surrogate Model (근사모델을 사용한 손상허용해석)

  • Jang, Byung-Wook;Im, Jae-Hyuk;Park, Jung-Sun
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.39 no.4
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    • pp.306-313
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    • 2011
  • The damage tolerance analysis is required to guarantee the structural safety and the reliability for aircraft components. The damage tolerance method, which evaluate the life considering the initial crack, considers a fatigue design model of the aircraft main structure. The fatigue crack growth life should be calculated in damage tolerance analysis and the inspection time to define the replacement cycle. In this paper, the damage tolerance analysis is performed for a turbine wheel which has complex geometry. The equation of the stress intensity factor for complex geometry is hard to know, so that they are usually processed by finite element analysis which takes long time. To solve this problem, the stress intensity factors at specified crack are obtained by the FEA and the crack growth life is evaluated using the surrogate model which is generated by the regression analysis of the FEA data. From the results, the efficiency of the crack growth life calculation and the damage tolerance analysis could be increased by taking the surrogate model.

Element and Crack Geometry Sensitivities of Finite Element Analysis Results of Linear Elastic Stress Intensity Factor for Surface Cracked Straight Pipes (표면균열이 있는 직관에 대한 선형탄성 응력확대계수 유한요소해석 결과의 요소 및 균열형상 민감도)

  • Ryu, Dongil;Bae, Kyung-Dong;Je, Jin-Ho;An, Joong-Hyok;Kim, Yun-Jae;Song, Tae-Kwang;Kim, Yong-Beum
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.37 no.4
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    • pp.521-527
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    • 2013
  • This study provides the elastic stress intensity factors, K, for circumferential and longitudinal surface cracked straight pipes under single or combined loads of internal pressure, bending, and torsion based on three-dimensional (3D) finite element (FE) analyses. FE results are compared with two different types of defect assessment codes (API-579-1 and RCC-MR A16) to prove the accuracy of the FE results and the differences between the codes. Through the 3D FE analysis, it is found that the stress intensity factors are sensitive to the number of elements, which they were believed to not be sensitive to because of path independence. Differences were also found between the FE analysis results for crack defining methods and the results obtained by two different types of defect assessment codes.

Fatigue Crack Propagation Characteristics in HAZ of A106 Gr B Steel Pipe Weldments (A106 Gr B강 배관용접부의 잔류응력해석 및 피로균열성장특성)

  • 김철한;배동호;김복기;조선영;홍정균;이범노
    • Proceedings of the KWS Conference
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    • pp.237-240
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    • 1999
  • In this study, residual stresses of the weldment were calculated by finite element analysis(FEA) and experiment. And, the crack closure behaviour and fatigue crack growth characteristics in field of residual stress of A106 Gr B steel pipe weldment were investigated under various stress ratio. Obtained results are as follows. I) $K_{op}$ was independent of $K_{max}$, and load ratio in fatigue crack growth. 2) In variation of load ratio, the scatter band of crack growth curve was reduced by half considering crack closure. and 3) Neglecting crack closure behaviour, actual fatigue crack growth rate can be underestimated' and Actual fatigue crack growth rate can be overestimated by $K_{res}$, in tensile residual stress field.

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An Analysis of Stress Intensity Factors of Composite Materials by Boundary Element Method (BEM) (경계요소법(BEM)에 의한 복합재료의 응력확대계수 해석)

  • 이갑래;조상봉;최용식
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.1
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    • pp.179-189
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    • 1991
  • Composite materials are generally treated as anisotropic or an orthotropic materials. Unlike isotropic materials, the orthotropic materials can divided three groups depending upon the relationship of the four material constants or depending upon the characteristic roots of orthotropic materials. In particular, the fundamental solutions of two dimensional BEM for composite materials (orthotropic or anisotropic material) generally have a singularity in the conventional method when the characteristic roots are equal. In consideration of this singularity in the conventional method when the characteristic roots are equal. In consideration of this singular problems, in this paper, the fundamental solutions of BEM are systematically analysed for orthotropic materials. And the stress and displacement fields for a crack in an orthotropic materials are singular when the characteristic roots of orthotropic materials are equal. Therefore, these fields for a crack in an orthotropic materials are analysed by the analogous method to isotropic materials when the characteristic roots are equal.

Application of the Method of Caustics into Anisotropic Materials (이방성재료에 대한 코스틱스법의 적용)

  • 백명철;최선호;황재석;김원현
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.12
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    • pp.2226-2240
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    • 1992
  • This paper studies the applicability of the method of caustics into anisotropic materials under mode I and mixed static loading conditions and introduces the procedure to obtain stress intensity factors(S.I.F.) in anisotropic materials by the method of caustics. The mapping equations for initial and caustic curves in anisotropic materials were introduced and their computer graphical images were compared to the experimental ones to check the validity of the mapping equations proposed in this paper. The agreement between them was found to satisfactory. Two kinds of method to determine S.I.F. in anisotropic materials by the method of caustics were proposed in this paper and applied into the orthotropic materials under various loading conditions. In the case of mode I loading condition, the S.I.F.'s obtained by this paper's methods were found to be quite similar to the results by other method, boundary element method(B.E.M) and in the case of mixed loading condtion, the S.I.F's by this paper and B.E.M. showed a little differences(2.2-24.4%) with respect to the slanted angle of crack.

A Basic Study on the Crack Arrest Phenomena (균열정지현상에 관한 기초적 연구)

  • 이억섭;김상철;송정일
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.14 no.1
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    • pp.112-118
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    • 1990
  • Catastrophic fracture cannot be avoided after cracks(initiated from pre-existing defects) propagate rapidly with speeds comparable to a sound wave velocity of the materials. Preventing catastropic failure, crack arrest fracture toughness defined from dynamic(or kinetic) fracture mechanics point of view has been introduced in determining accurate and/or proper crack arrest fracture toughness of a material. For the past decades, many studies have been carried out to render proper theoretical and experimental backgrounds on the use of the static plain strain crack arrest fracture toughness, $K_{1a}$ (which seems to be a material property). $K_{1a}$ has been used to predict the performance of thick walled structures and has been considered as a measure of the ability of a material to stop a fast running crack. Determination of such a material property is of prime importance to the nuclear reactor pressure vessel and bridge materials industries. However, standards procedures for measuring toughness associated with fast running cracks are yet to exist. This study intends to give insight on the determination of the crack arrest fracture toughness of materials such as polymethylmethacrylate(PMMA), SM45C-steel, and A1 7075-T6. The effects of crack jump lengths and fast crack initiation stress intensity factor on the determination of $K_{1a}$ have been experimentally observed.erved.

Calculation of Stress Intensity Factor in Arbitrarily Shaped Plane Crack under Uniform Pressure Loading (일정 압력에 의한 3차원 평면균열에서의 응력확대계수 계산)

  • An, Deuk-Man
    • Proceedings of the KSME Conference
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    • pp.117-122
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    • 2000
  • In this paper the stress intensity factor under uniform pressure in the arbitrarily-shaped plane crack configuration transformed elliptic crack by Mobius mapping are determined. Using Dyson's formula Boussinesq-Papkovich potentials for mode I deformation are constructed. In the example the stress intensity factors are approximately calculated by least square method.

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A Fructure Mechanics Analysis on the Crack in the Variable Thickness Plate Having Fillet (필렛을 갖는 변후부재의 균열에 대한 파괴역학적 연구)

  • 양원호;최용식;조명래
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.5
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    • pp.1433-1438
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    • 1991
  • 본 연구에서는 팔렛을 갖는 유한폭 변후판재 내의 모드 Ⅰ균열에 대하여 3차 원 유한요소법으로 응력확대계수를 수치해석하였다.