• Title/Summary/Keyword: Crack arrest

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Crack Growth Analysis and Crack Arrest Design of Stiffened Panels(I) - Numerical Approaches to Crack Arrest Design Chart (보강판의 균열거동해석과 Crack Arrest 설계(I) - Crack Arrest 설계기준의 수치해석)

  • Rhee, Eui-Jong;Rhee, Hwan-Woo
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.4 no.2
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    • pp.43-49
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    • 2005
  • The purpose of a fatigue crack arrest design is to prevent a fatigue fracture of machine and structure resulted from unstable crack growth. In all cases of load transfer to second elements such as stringers, doublers or flanges, crack arrest is possible; arrest occurring when the fatigue crack reaches the second element. In the present work, a numerical analysis was carried out to estimate the effect of shape parameters on fatigue crack growth and arrest behavior of integrally stiffened panels. Based on these results, a set of fatigue crack arrest design chart is presented as "non-dimensional arrest load - thickness ratio" relationship.

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Crack Growth Analysis and Crack Arrest Design of Stiffened Panels(III) - Experimental Evaluation of Crack Arrest Design Chart (보강판의 균열거동해석과 Crack Arrest 설계(III) - Crack Arrest Design 차트의 실험평가)

  • Rhee, Eui-Jong;Rhee, Hwan-Woo
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.5 no.2
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    • pp.42-48
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    • 2006
  • In order to assess the validity of fatigue crack arrest design charts obtained from our previous numerical approach to fatigue crack arrest condition, an extensive fatigue crack growth/arrest test was performed using CT-type integrally stiffened panels. The results are presented as fatigue crack growth rate and non-dimensional crack length relationship, and these are compared with numerically simulated crack growth rates. The measured values of da/dN at the moment of fatigue crack arrest occurred in stiffened panels are good agreement with those numerically simulated crack growth rates.

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Crack Growth Analysis and Crack Arrest Design of Stiffened Panels(II) - Numerical Simulation of Crack Arrest Behavior (보강판의 균열거동해석과 Crack Arrest 설계(II) - Crack Arrest 거동의 시뮬레이션)

  • Rhee, Eui-Jong;Rhee, Hwan-Woo
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.4 no.2
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    • pp.50-56
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    • 2005
  • To demonstrate the feasibility of utilizing FCAD chart proposed in our previous work, series of crack growth/arrest behavior in the integrally stiffened panels were simulated by numerical method using upper mentioned FCAD charts and a new crack growth rate equation. It is concluded that proposed family of FCAD curves, in the form of non-dimensional arrest load ranges, are reliable indicators of fatigue crack growth/arrest behavior of integrally stiffened panels considered here.

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Effect of Width and Thickness Ratio on the Fatigue Crack Arrest Behavior of SA-508 Pressure Vessel Steel Variable Thickness Plates (SA-508 압력용기용강 변후재의 피로균열 Arrest 거동에 대한 변후 형상비의 영향)

  • 이환우;이갑래;최용식
    • Journal of the Korean Society of Safety
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    • v.6 no.4
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    • pp.45-52
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    • 1991
  • The purpose of a fatigue crack arrest desing is to prvent a fatigue fracture of machine and structure resulted from unstable crack growth. In all cases of load transfer to second elements such as stringers, doublers or flangers, crack arrest is possible; arrest occuring when the fatigue crack reaches the second element. In the present work, the possibility of crack arrest and the design criterion of fatigue crack arrest in the variable thickness plates are examined numericaiiy by using fatigue crack arrest thresthod $\Delta$K$_{th}$of SA-508 reactor vessel steel and stress intensity factor which was obtained in the previous work as a result of 3-dimensional finite element analysis for CT type variable thickness plates having discontinuous interface.e.

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Design for avoid unstable fracture in shipbuilding and offshore plant structure (조선 및 해양플랜트 구조물의 불안전 파괴방지 설계기술)

  • An, Gyubaek;Bae, Hong-Yeol;Noh, Byung-Doo;An, Young-Ho;Choi, Jong-Kyo;Woo, Wanchuck;Park, Jeong-Ung
    • Journal of Welding and Joining
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    • v.33 no.1
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    • pp.35-40
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    • 2015
  • Recently, there have been the increase of ship size and the development of oil and gas in arctic region. These trends have led to the requirements such as high strength, good toughness at low temperature and good weldability for prevent of brittle fracture at service temperature. There has been the key issue of crack arrestability in large size structure such as container ship. In this report for the first time, crack arrest toughness of thick steel plate welds was evaluated by large scale ESSO test for estimate of brittle crack arrestability in thick steel plate. For large structures using thick steel plates, fracture toughness of welded joint is an important factor to obtain structural integrity. In general, there are two kinds of design concepts based on fracture toughness: crack initiation and crack arrest. So far, when steel structures such as buildings, bridges and ships were manufactured using thick steel plates (max. 80~100mm in thickness), they had to be designed in order to avoid crack initiation, especially in welded joint. However, crack arrest design has been considered as a second line of defense and applied to limited industries like pipelines and nuclear power plants. Although welded joint is the weakest part to brittle fracture, there are few results to investigate crack arrest toughness of welded joint. In this study, brittle crack arrest designs were developed for hatch side coaming of large container ships using arrest weld, hole, and insert technology.

Dynamic Stress Intensity Factors and Dynamic Crack Propagation Velocities in Polycarbonate WL-RDCB Specimen (WL-RDCB 시편의 동적 균열전파속도와 동적 응력확대계수)

  • 정석주;한민구
    • Journal of the Korean Society of Safety
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    • v.11 no.3
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    • pp.3-9
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    • 1996
  • Dynamic fracture characteristics of Polycarbonate WL-RDCB specimen were investigated. The dynamic crack propagation velocities in these specimens were measured by using both high speed camera system and silver paint grid method developed and justified in the INHA Fracture Mechanics Laboratory. The measured crack propagation velocities were fed into the INSAMCR code(a dynamic finite element code which has been developed in the INBA Fracture Mechanics Laboratory) to extract the dynamic stress intensity factors. It has been confirmed that both dynamic crack arrest toughness and the static crack arrest toughness depend on both the geometry and the dynamic crack propagation velocity of specimens. The maximum dynamic crack propagation velocity of Polycarbonate WL-RDCB specimen was found to be dependent on the material property, geometry and the type of loading. The dynamic cracks in these Polycarbonate WL-RDCB specimens seemed to propagate in a successive manner, involving distinguished 'propagation-arrest-propagation-arrest' steps on the microsecond time scale. It was also found that the relat-ionship between dynamic stress intensity factor and dynamic crack propagation velocities might be represented by the typical '$\Gamma$'shape.

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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.

The Effect of Stress Ratio on Fatigue Crack Propagation Rate and Arrest Behavior in 7075-T735 Al Alloy (7075-T735 Al 합금의 피로균열 진전속도와 정류거동에 미치는 응력비의 영향)

  • 오세욱;강상훈;허정원;김태형
    • Journal of Ocean Engineering and Technology
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    • v.6 no.1
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    • pp.131-139
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    • 1992
  • The understanding and appllication of fatigue crack propagation mechanism in variable amplitude loading is very important for life prediction of the air travel structures. Particularly, the retardation and arrest behavior of fatigue crack propagation by single tension overloading is essential to the understanding and appllication of fatigue crack propagation mechanism in variable amplitude loading. Numerous studies of the retardation behavior have been performed, however investigations of the arrest behavior have not been enough yet. As for the arrest behavior, Willenborg had reported that the overload shut-off ratio $[R_{so}=(K_{OL})/K_{max})_{crack arrest}]$ had been the material constant, but recently several investigators have reported that the overload shut-off ratio depends upon the stress ratio. In this study, authors have investigated the effect of stress ratio on the threshold overload shut-off ratio to generate arrest of fatigue crack growth in high tensile aluminum alloy 7075-T735 which have used in material for air travel structures, It has been $-0.4\leqqR\leqq0.4$ till now, the region of stress ratio investigated. The threshold overload shut-off ratio has decreased as stress ratio has increased in overall region of -$-0.4\leqqR\leqq0.4$ and the linearity has been seen in this material. Moreover, the experimental equation between $R_{so}$ and R has been made; The relation has been $R_{so}=-R+2.6$.

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Change in Fracture Toughness within Heat-Affected Zone of SA-Welded 9% Ni Steel (LNG 저장탱크 내조용 9% Ni강의 SAW 용접열영향부내 파괴인성 변화 평가)

  • Jang, Jae-Il;Lee, Jeong-Seok;Lee, Baek-U;Ju, Jang-Bok;Gwon, Dong-Il;Kim, U-Sik
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.3
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    • pp.528-536
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    • 2002
  • As one step for the safety performance of LNG storage tank, the change in fracture toughness within the X-grooved weld heat-affected zone (HAZ) of newly developed 9% Ni steel, which was submerged arc (SA)-welded, was investigated. Both crack initiation fracture toughness and crack arrest fracture toughness were evaluated by the crack tip opening displacement (CTOD) tests and compact crack arrest (CCA) tests. As the evaluated region approached the fusion line, each test result shorted different tendency, that is, crack initiation toughness decreased while crack arrest toughness increased. The results were discussed through the observation of the microstructural change.

Fracture Toughness Prediction of RPV Steels Using Crack Arrest Load of Load-Displacement Curve in Charpy V - Notch Impact Test (샤피 V - 노치 충격 하중-변위 곡선의 균열정지하중을 이용한 원자로압력용기강의 파괴인성 예측)

  • Park, Jeong-Yong;Kim, Ju-Hak;Lee, Yun-Gyu;Hong, Jun-Hwa
    • Korean Journal of Materials Research
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    • v.10 no.4
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    • pp.305-311
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    • 2000
  • Applicability of crack arrest load measured from the Charpy V-notch impact test has been investigated to predict the fracture toughness of nuclear reactor pressure vessel (RPV) steels (ASME SA508 Cl.3). The temperature dependence of the crack arrest load was well described by the type of exponential function characterized by an index temperature at which the crack arrest load is 2kN. The specific index temperature, which also well correlated with $T_{NDT}\;and\;T_{41J}$ is expected to be representative index temperature characterizing the crack arrest fracture toughness of RPV steels. Also, the crack arrest load correlated well with the stable crack length measured from the fracture surface. From the measurements of the crack arrest load and the stable crack length, the lower bound fracture toughness, $K_{Ia}$ of RPV steels could be predicted with sufficient accuracy.

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