• Title/Summary/Keyword: 균열전파

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Fatigue crack propagation life evaluation of an autofrettaged thick-walled cylinder (자긴가공된 두꺼운 실린더의 피로균열 전파수명평가)

  • Lee, Song-In;Kim, Jin-Yong;Jeong, Se-Hui;Go, Seung-Gi
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.22 no.2
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    • pp.321-329
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    • 1998
  • To ensure the structural integrity of the autofrettaged thick-walled cylinder subjected to cyclic internal pressure loading, the fatigue crack propagation life of the cylinder was evaluated. Stress intensity factors of the external cracked cylinder due to internal pressure and autofrettage loadings were calculated using the finite element method. The fatigue crack propagation lives of the cylinder based on the fracture mechanics concepts were predicted and compared to the experimental fatigue lives evaluated from the C-shaped simulation specimens. There were good correlations between the predicted and experimental fatigue lives within a factor of 3 for the single and double grooved C-shaped simulation specimens. Predicted fatigue crack propagation lives of the double grooved cylinders were about 1.5-5 times longer than those of the single grooved cylinders depending on the levels of autofrettage.

A Study on Estimation of the Probability Distribution of Fatigue Crack Growth Life for Steels (강의 피로균열전파수명의 확률분포 추정에 관한 연구)

  • 김선진;윤성환;전창환;정규연;안석환
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • 2000.04a
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    • pp.40-45
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    • 2000
  • Presented are the estimation of the probability distribution of fatigue crack growth life and reliability assessment of structures by simulating material resistance to fatigue crack growth along a crack path. The material resistance is treated as a Weibull stochastic process. A non-Gaussian stochastic fields simulation method proposed by Shimozuka, et al is applied with the statistical data obtained experimentally. Test results are obtained for $\Delta$K constant amplitude load in tension with stress ratio of R=0.2 and three specimen thicknesses of 6, 12 and 18mm. This simulation method is useful to estimate the probability distribution of fatigue crack growth life and the smallest life.

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A Stochastic Study on Fatigue Crack Propagation and Retardation Behavior of Pressure Vessel Steel (압력용기용강의 피로균열전파 및 지연거동에 관한 확률통계적 연구)

  • 김선진;남기우;김부안
    • Journal of Ocean Engineering and Technology
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    • v.9 no.1
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    • pp.132-141
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    • 1995
  • The purpose of the present study is to investigate the statistical characteristics of m and C in the fatigue crack propagation law, da/dN=C(.DELTA.K)/sup m/ and to studies on the randomness of fatigue crack propagation and retardation behavior. Fatigue tests were perfomed on 32 CT specimens of SPV50 steel under the same one condition. First, the value of m and C were determined for each specimen, and all the data were analyzed statistically. second, the material's resistance to fatigue crack propagation is modeled as a stchastic process, which varies randomly along the crack path. The statistical analysis of the material resistance is performed with the data obtained by constant load controlled tests. Finally, retardation behavior was examined experimentally by using a CT specimen, and a retardation parameters were analyzed statistically.

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Crack Propagation in a Piezoelectric Layer Bonded between Two Orthotropic Layers (직교 이방성 탄성체에 접합된 압전 재료의 균열 전파 거동)

  • Kim, Chuel-Gon;Kwon, Soon-Man;Lee, Kang-Yang
    • Proceedings of the KSME Conference
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    • 2001.11a
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    • pp.22-26
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    • 2001
  • In this paper, we examine the steady state dynamic electromechanical behavior of an eccentric Yoffe crack in a piezoelectric ceramic layer bonded between two orthotropic elastic layers under the combined anti-plane mechanical shear and in-plane electrical loadings. We adopted permeable crack face condition. Numerical values on the dynamic energy release rate are obtained. The initial crack propagation orientation for PZT-5H piezoceramic is also predicted by maximum energy release rate criterion.

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Dynamic Stress Intensity Factor $K_{IIID}$ for a Propagating Crack in Liner Functionally Gradient Materials Along X Direction (X방향의 선형함수구배인 재료에서 전파하는 균열의 동적응력확대계수 $K_{IIID}$)

  • Lee, Kwang-Ho
    • Proceedings of the KSME Conference
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    • 2001.11a
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    • pp.3-8
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    • 2001
  • Dynamic stress intensity factors (DSIFs) are obtained when a crack propagates with constant velocity in rectangular functionally gradient materials (FGMs) under dynamic mode III load. To obtain the dynamic stress intensity factors, it is used the general stress and displacement fields of FGMs for propagating crack and the boundary collocation method (BCM). The stress intensity factors and energy release rates are the greatest in the increasing properties $(\xi>0)$, next constant properties $(\x=0)$ and decreasing properties $(\xi<0)$ under constant crack tip properties and crack tip speed.

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Fatigue Crack Initiation and Propagation at Notches (노치 에서의 피로 균열 발생 과 전파 에 관한 연구)

  • 이강용;이택성
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.8 no.2
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    • pp.141-144
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    • 1984
  • The fatigue limits of crack initiation and propagation on the edge elliptical notched semi-infinite plate under completely reversed fatigue stress are determined theoretically. Assuming that the crack initiation and propagation occur when stress intensity factors of notched plate reach the critical values obtained from critical micro-crack length under plain fatigue limit loading and the threshold stress intensity factory, respectively, the fatigue limits of crack initiation and propagation are obtained. The induced theoretical fatigue limit of crack initiation is expressed in terms of plain fatigue limit, critical micro-crack length and notch shape. The one of crack propagation is in terms of threshold stress intensity factor, plain fatigue limit and notch shape. These theoretical results are showed to be in good agreement of Frost's experimental data.

Analysis of a Crack Propagating Along the Gradient in Functionally Gradient Materials with Exponential Property Gradation (지수형적 물성변화를 갖는 함수구배 재료에서 구배방향을 따라 전파하는 균열 해석)

  • Lee, Kwang-Ho
    • Proceedings of the KSME Conference
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    • 2003.04a
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    • pp.113-118
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    • 2003
  • Stress and displacement fields for a propagating crack in a functionally gradient material (FGM) which has exponentially varying elastic and physical properties along the direction of the crack propagation, are derived. The equations of motion in nonhomogeneous material are developed using displacement potentials. The solutions to the displacement fields and the stress fields for a crack propagating at constant speed along the gradient are obtained through an asymptotic analysis. The influences of nonhomogeneity on the higher order terms of the stress fields are explicitly brought out. Using these stress components, isochromatic fringes around the stationary crack are generated at crack for different nonhomogeneity and the effects of nohonhomgeneity on these fringes are discussed.

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Fatigue Crack Propagation Behavior under Mixed Mode Loading (혼합모드 하중에서의 피로균열 전파거동)

  • 송삼홍;이정무;최병호
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2000.11a
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    • pp.481-484
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    • 2000
  • Practical structures are subject not only to tension but also to shear and torsional loading. Even under uniaxial loading, when the load is not perpendicular to the crack plane, mixed mode crack can occur. Hence, it is necessary to evaluate the fatigue behavior under mixed mode loading. In this study, the propagation behavior of the fatigue crack of the STS304 steels under mixed mode loading condition was investigated. The mode I and II stress intensity factors of CTS specimen were calculated using elastic finite element method with experimental results. The fatigue crack propagation under mixed mode was evaluated by the effective stress intensity factor proposed by Tanaka.

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The Fatigue Behavior of Laser Weldment in Heterogeneous Materials (이종재료 레이저 용접부의 피로거동)

  • 권응관;오택열;곽대순;이종재
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1997.10a
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    • pp.759-764
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    • 1997
  • In this study, Fatigue behavior of laser weldment in heterogeneous materials was investigated. Fatigue strength test and fatigue crack propagation test were performed for specimens with laser weldment in heterogeneous materials, and hardness test was performed. From the fatigue strength test. it was observed that the difference of strength between heterogeneous materials had eflect on crack initiation position and fatigue limit. From the fatigue crack propagation test. it was observed that fatigue behavior of laser weldment in heterogeneous materials is different from that in same materials. The difference of strength between heterogeneous materials and laser weldment had effect on fatigue crack propagation rate.

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Analysis of Propagating Crack In Isotropic Material under Dynamic Mode I Constant Displacement (동적모드 I 등변위상태하에서 전파하는 등방성체의 균열해석)

  • Lee, Gwang-Ho
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.8 s.179
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    • pp.2007-2014
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    • 2000
  • It has been reported that the dynamic stress intensity factor for a propagating crack is increasing or decreasing according to the increasement of the crack propagating velocity. It is confirmed in this study that the increasement or decreasement of stress intensity factor with crack growing velocity is accused by loading condition. When the crack propagates under a constant displacement along upper and lower boundary in finite plate, the dynamic stress intensity factor decreases according to the increasement of the propagating crack velocity. When the crack propagates under a constant stress along upper and lower boundary in finite plate, the dynamic stress intensity factor increases according to the increasement of the propagating crack velocity. The increasement or decreasement of stress intensity factor with crack growing velocity is greater in a fast crack propagation velocity than in a slow one.