• Title/Summary/Keyword: Crack Branching

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Effect of specimen thickness on fatigue crack growth and retardation behavior of 7075-T73 aluminum alloy (7075-T73 알루미늄 합금의 피로균열진전거동 및 지연현상에 미치는 두께의 영향)

  • 김정규;박병훈;류석현
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.13 no.4
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    • pp.670-679
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    • 1989
  • The constant amplitude loading and 100% single overloading fatigue studies of domestic high tensile 7075-T73 aluminum alloy were performed to exmine the effect of specimen thickness and its mechanisms on fatigue crack growth behavior. The stage II fatigue crack growth rates tend to increase with decreasing specimen thickness under constant amplitude loading condition and this has relation with stress intensity factors and plastic zone size. The amount of retardation by an overload increased with decreasing specimen thickness when the crack depth and baseline stress intensity factors were constant. The crack depth is one of major factors which affect retardation phenomena by an overload and the amount of retardation increase with decreasing the crack depth. Its main mechanisms are crack closure and decreasing of K at the crack tip by branching and deflection of crack. And they are affected by near surface more severely than central portion of specimen.

The Effects of the Microstructures on the Fatigue Crack Propagation Behaviors of Cast Irons (주철의 피로전파거동에 미치는 미세조직의 영향)

  • Kim, Sug-Won;Park, Jin-Sung;Lee, Hyung-Chul;Kim, Dong-Keun;Woo, Kee-Do
    • Journal of Korea Foundry Society
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    • v.25 no.1
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    • pp.16-22
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    • 2005
  • This study aims to investigate the effects of the microstructures and nodule type on the fatigue characteristics of cast iron. Fatigue tests were carried out in tension-tension mode using a servo-hydraulic testing machine with load control mode operating at a frequency of 15 Hz. The tests were conducted at stress ratio R=Kmin/Kmax, of 0.1. Initial crack ${\Dalta}K$ values were highly performed with increase in tensile strength of DCI fatigue specimens. ${\Dalta}K_{th}$ region, fatigue crack propagation was primarily advanced through cell boundary and in periphery of near nodule. Fatigue crack propagation rate of D2 consisted with 2Phase(Ferrite+Pearlite) was slow due to crack closure enhanced by crack deflection and occurred crack branching. The generation of crack branch was occurred due to interaction of crack-nodule. At Threshold and Paris zone, the fractographs of the fatigue fracture surface for DCI show typical striations of a ductile fracture and isolated cleavage planes near graphite. The effect of microstructure on fatigue crack propagation of GC strongly depends on the type of flake. The generation of crack branch occurred due to interaction of crack-nodule. The fractographs of the fatigue fracture surface for GC show cleavage plane along the flake graphite.

Effects by the Magnitude of Shear Load on the Formation and Propagation of Mode II Branch Cracks (전단하중의 크기가 모드 II 분기균열의 형성과 전파에 미치는 영향)

  • 이정무;송삼홍
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2004.10a
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    • pp.487-490
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    • 2004
  • In this paper, we investigated the characteristics of initiation and propagation behavior for fatigue crack observed by changing various shapes of initial crack and magnitudes of loading in modified compact tension shear(CTS) specimen subjected to shear loading. In the low-loading condition, the secondary fatigue crack was created in the notch root due to friction on the pre-crack face grew to a main crack. In the high-loading condition, fatigue crack under shear loading propagated branching from the pre-crack tip. Influenced by the shear loading condition, fatigue crack propagation retardation appeared in the initial propagation region due to the reduction of crack driving force and friction on crack face. In both cases, however, fatigue cracks grew in tensile mode type. The propagation path of fatigue crack under the Mode II loading was 70 degree angle from the initial crack regardless of its shape and load magnitude.

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The Characteristics of Fatigue Crack Propagation Behavior in Shear Load (전단하중 하의 피로균열 전파거동의 특징)

  • Lee, Jeong-Moo;Song, Sam-Hong
    • Proceedings of the KSME Conference
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    • 2004.04a
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    • pp.302-307
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    • 2004
  • This paper reviewed characteristics of fatigue crack behavior observed by changing various shapes of initial crack and magnitudes of loading in compact tension shear(CTS) specimen subjected to shear loading. In the high-loading condition, fatigue crack under shear loading propagated branching from the pre-crack tip. Meanwhile, the secondary fatigue crack in the low-loading condition which was created in the notch root due to friction on the pre-crack face grew to a main crack. Influenced by the mode II loading condition, fatigue crack propagation retardation appeared in the initial propagation region due to the reduction of crack driving force and friction on crack face. In both cases, however, fatigue cracks grew in tensile mode type. Propagation path of fatigue crack under the shear loading was 70 degree angle from the initial crack regardless of its shape and load magnitude.

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Peridynamic Modeling for Crack Propagation Analysis of Materials (페리다이나믹 이론 모델을 이용한 재료의 균열 진전 해석)

  • Chung, Won-Jun;Oterkus, Erkan;Lee, Jae-Myung
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.31 no.2
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    • pp.105-114
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    • 2018
  • In this paper, the computer simulations are carried out by using the peridynamic theory model with various conditions including quasi-static loads, dynamic loads and crack propagation, branching crack pattern and isotropic materials, orthotropic materials. Three examples, a plate with a hole under quasi-static loading, a plate with a pre-existing crack under dynamic loading and a lamina with a pre-existing crack under quasi-static loading are analyzed by computational simulations. In order to simulate the quasi-static load, an adaptive dynamic relaxation technique is used. In the orthotropic material analysis, a homogenization method is used considering the strain energy density ratio between the classical continuum mechanics and the peridynamic. As a result, crack propagation and branching cracks are observed successfully and the direction and initiation of the crack are also captured within the peridynamic modeling. In case of applying peridynamic used homogenization method to a relatively complicated orthotropic material, it is also verified by comparing with experimental results.

Influence of elastic T-stress on the growth direction of two parallel cracks

  • Li, X.F.;Tang, B.Q.;Peng, X.L.;Huang, Y.
    • Structural Engineering and Mechanics
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    • v.34 no.3
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    • pp.377-390
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    • 2010
  • This paper studies fracture initiation direction of two parallel non-coplanar cracks of equal length. Using the dislocation pile-up modelling, singular integral equations for two parallel cracks subjected to mixed-mode loading are derived and the crack-tip field including singular and non-singular terms is obtained. The kinking angle is determined by using the maximum hoop stress criterion, or the ${\sigma}_{\theta}$-criterion. Results are presented for simple uniaxial tension and biaxial loading. The biaxiality ratio has a noticeable influence on crack growth direction. For the case of biaxial tension, when neglecting the T-stress the crack branching angle is overestimated for small crack inclination angles relative to the largest applied principal stress direction, and underestimated for large crack inclination angles.

A Study on the Fatigue Crack Growth Behavior of A Ti-24Al-11Nb Alloy (Ti-24Al-11Nb 합금의 피로균열성장거동에 관한 연구)

  • Bae, Gyu-Sik;Lee, Mun-Hui
    • Korean Journal of Materials Research
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    • v.2 no.5
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    • pp.313-319
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    • 1992
  • The mechanisms of fatigue crack growth (FCG) in a Ti$_3$Al-based (${\alpha}_2$) alloy, Ti-24Al-11Nb (a/o) with acicular microstructure were studied with particular attention focused on the fatigue crack path through the microstructure and on the effects of specimen orientation and crack closure. The results showed that the fatigue cracks of Ti-24Al-11Nb alloy grew much faster than conventional titanium alloys, with little difference in FCG rates for TL and TS orientations. The fatigue crack paths revealed crystallographic transgranular fracture with frequent serrations and branching. This is in agreement with the known effects of slip planarity and microstructure on the FCG behavior. The load-displacement hysteresis loops showed that the crack closure influenced the FCG behavior.

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Discrete crack analysis for concrete structures using the hybrid-type penalty method

  • Fujiwara, Yoshihiro;Takeuchi, Norio;Shiomi, Tadahiko;Kambayashi, Atsushi
    • Computers and Concrete
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    • v.16 no.4
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    • pp.587-604
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    • 2015
  • The hybrid-type penalty method (HPM) is suitable for representing failure phenomena occurring during the transition from continua to discontinua in materials such as concrete. Initiation and propagation of dominant cracks and branching of cracks can easily be modeled as a discrete crack. The HPM represents a discrete crack by eliminating the penalty that represents the separation of the elements at the intersection boundary. This treatment is easy because no change in the degrees of freedom for the discrete crack is necessary. In addition, it is important to evaluate the correct deformation of the continua before the crack formation is initiated. To achieve this, we implemented a constitutive model of concrete for the HPM. In this paper, we explain the implemented constitutive model and describe the simulation of an anchor bolt pullout test using the HPM demonstrating its capability for evaluating progressive failure.

Fracture Toughness and Crack Growth Resistance of the Fine Grain Isotropic Graphite

  • Kim, Dae-Jong;Oh, Seung-Jin;Jang, Chang-Heui;Kim, In-Sup;Chi, Se-Hwan
    • Carbon letters
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    • v.7 no.1
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    • pp.19-26
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    • 2006
  • Three point bending tests of single edge notched beam (SENB) specimens were carried out to evaluate the fracture behavior of the fine-grain isotropic nuclear grade graphite, IG-11. To measure the crack initiation point and the subsequent crack growth, the direct current potential drop (DCPD) method and a traveling microscope were used. The effects of test variables like initial crack length, specimen thickness, notch type and loading rate on the measured fracture toughness, $K_Q$, were investigated. Based on the test results, the ranges of the test variables to measure the reliable fracture toughness value were proposed. During the crack growth, the rising R-curve behavior was observed in IG-11 graphite when the superficial crack length measured on the specimen surface was used. The increase of crack growth resistance was discussed in terms of crack bridging, crack meandering, crack branching, microcracking and crack deflection, which increase the surface energy and friction force.

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Influence of Testing Method on the Fracture Toughness of Cordierite-SiC Whisker Ceramic Composites (코디어라이트-SiC위스커 복합재료에서 측정방법에 따른 파괴인성치의 변화)

  • ;Weisskopf
    • Journal of the Korean Ceramic Society
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    • v.24 no.4
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    • pp.313-320
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    • 1987
  • Fracture toughness of hot pressed cordierite-SiC whisker ceramic composites contained up to 40vol.% SiC whiskers were determined by using the indentation crack length(IC), indentation strengthin-bending(IS), and single-edge notched-beam(SENB) methods. The results were compared to stress intensity factor, KB, at the crack branching boundary measured by using the mirror zone radius (MZ) method. IS method seems to provide a more reasonable estimation of fracture toughness than other methods for these composites.

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