• Title/Summary/Keyword: multiple cracks

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Free Vibration Characteristics of a Composite Beam with Multiple Transverse Open Cracks (다중 크랙이 있는 복합재료 보의 자유진동 특성)

  • 하태완;송오섭
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 1999.11a
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    • pp.5-14
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    • 1999
  • Free vibration characteristics of a cantilevered laminated composite beam with multiple non-propagating transverse open cracks are investigated. In the present analysis a special ply-angle distribution referred to as asymmetric stiffness configuration inducing the elastic coupling between chord-wise bending and extension is considered. The multiple open cracks are modelled as equivalent rotational springs whose spring constants are calculated based on the fracture mechanics of composite material structures. Governing equations of a composite beam with open cracks are derived via Hamilton's Principle and Timoshenko beam theory encompassing transverse shear and rotary inertia effect is adopted. The effects of various parameters such as the ply angle, fiber volume fraction, crack numbers, crack positions and crack depthes on the free vibration characteristics of the beam with multiple cracks are highlighted. The numerical results show that the existence of the multiple cracks in an anisotropic composite beam affects the free vibration characteristics in a more complex fashion compared with the beam with a single crack.

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Analysis of an Isotropic Infinite Plate with Many Collinear Multiple Cracks by the Alternating Method (다수의 직선 다중균열이 존재하는 등방성 무한판의 교호법을 이용한 해석)

  • Park, Jai-Hak
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.12
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    • pp.3838-3846
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    • 1996
  • A method is proposed to obtain the stress intensity factors of multiple cracks lying on many straight llnes in an infinite isotropic plate. In this mehtod, analytical solutions for collinear multiple cracks subject to surface point forces are obrained and used as Green functions. For the multiple cracks lying onmany straight lines, the equivalent crack surface tractions are obtained by using the alternating method and the stress intensity factors are calculated. By using the proposed method several useful problems are solved and discussed.

Multiple unequal cracks between an FGM orthotropic layer and an orthotropic substrate under mixed mode concentrated loads

  • M. Hassani;M.M. Monfared;A. Salarvand
    • Structural Engineering and Mechanics
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    • v.86 no.4
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    • pp.535-546
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    • 2023
  • In the present paper, multiple interface cracks between a functionally graded orthotropic coating and an orthotropic half-plane substrate under concentrated loading are considered by means of the distribution dislocation technique (DDT). With the use of integration of Fourier transform the problem is reduced to a system of Cauchy-type singular integral equations which are solved numerically to compute the dislocation density on the surfaces of the cracks. The distribution dislocation is a powerful method to calculate accurate solutions to plane crack problems, especially this method is very good to find SIFs for multiple unequal cracks located at the interface. Hence this technique allows considering any number of interface cracks. The primary objective of this paper is to investigate the effects of the interaction of multiple interface cracks, load location, material orthotropy, nonhomogeneity parameters and geometry parameters on the modes I and II SIFs. Numerical results show that modes I/II SIFs decrease with increasing the nonhomogeneity parameter and the highest magnitude of SIF occurs where distances between the load location and crack tips are minimal.

Fatigue Life Estimation of Welded Joints by using Mk-factor under a Propagation Mechanism of Multiple Collinear Surface Cracks (Mk-계수를 고려한 용접부 복수 표면균열 진전수명 평가)

  • 한승호;한정우;신병천;김재훈
    • Journal of Welding and Joining
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    • v.22 no.4
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    • pp.73-81
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    • 2004
  • Failure mechanisms of welded joints under fatigue loads are interpreted that multiple collinear surface cracks initiating randomly along the weld toes propagate under the mutual interaction and coalescence of adjacent two cracks. To estimate fatigue crack propagation life for three types of the representative welded joints, i.e. non-load carrying cruciform, cover plate and longitudinal stiffener joint, the stress intensity factors at the front of the surface cracks have to be calculated, which are influenced strongly by the geometry of attachments, weld toes and the crack shapes. For the effective calculation of the stress intensity factors the Mk-factor was introduced which can be derived by a parametric study performed by FEM considering influence of the geometrical effects. The fatigue life of the cruciform joint was estimated by using the Mk-factors and the method considering the propagation mechanisms of the multiple surface cracks. Analysis results for the fatigue life had a good agreement with that of experiment.

Coalescence Pressure of Steam Generator Tubes with Two Different-Sized Collinear Axial Through-Wall Clacks (길이가 다른 두 개의 축방향 관통균열이 동일선상에 존재하는 증기발생기 세관의 균열 합체 압력)

  • Huh Nam-Su;Chang Yoon-Suk;Kim Young-Jin
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.30 no.10 s.253
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    • pp.1255-1260
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    • 2006
  • To maintain the structural integrity of steam generator tubes, 40% of wall thickness plugging criterion has been developed. The approach is for the steam generator tube with single crack, so that the interaction effect of multiple cracks can not be considered. Although, recently, several approaches have been proposed to assess the integrity of steam generator tube with two identical cracks whilst actual multiple cracks reveal more complex shape. In this paper, the coalescence pressure of steam generator tube containing multiple cracks of different length is evaluated based on the detailed 3-dimensional (3-D) elastic-plastic finite element (FE) analyses. In terms of the crack shape, two collinear axial through-wall cracks with different length were considered. Furthermore, the resulting FE coalescence pressures are compared with FE coalescence pressures and experimental results for two identical collinear axial through-wall cracks to quantify the effect of crack length ratio on failure behavior of steam generator tube with multiple cracks. Finally, based on 3-D FE results, the coalescence evaluation diagrams were proposed.

Free vibration analysis of multiple open-edge cracked beams by component mode synthesis

  • Kisa, M.;Brandon, J.A.
    • Structural Engineering and Mechanics
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    • v.10 no.1
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    • pp.81-92
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    • 2000
  • This study is an investigation of the effect of cracks on the dynamical characteristics of a cantilever beam, having multiple open-edge transverse cracks. The flexibilities due to crack have been identified for several crack depths and locations. In the study the finite element method and component mode synthesis methods are used. Coupling the components is performed by a flexibility matrix taking into account the interaction forces. Each component is modelled by cantilever beam finite elements with two nodes and three degrees of freedom at each node. The results obtained lead to conclusion that, by using the drop in the natural frequencies and the change in the mode shapes, the presence and nature of cracks in a structure can be detected. There is some counter-evidence, however, that the effects due to multiple cracks may interact to make detection more difficult than for isolated cracks.

Theory and Experiments of Free Vibration Characteristics for the Composite Beam with Transverse Open Cracks (크랙이 있는 복합재료 보 자유진동특성의 이론과 실험적 입증)

  • 하태완
    • Journal of the Korea Institute of Military Science and Technology
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    • v.5 no.2
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    • pp.217-227
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    • 2002
  • Theoretical and experimental free vibration characteristics of cantilevered laminated composite beams with single or multiple transverse non-propagating open cracks are investigated. The presence of intrinsic cracks in beams modifies the flexibility and in turn free vibration characteristics of the structures, and the existence of the multiple cracks in an anisotropic composite beam affects the free vibration characteristics in a more complex fashion compared with the beam with a single crack. Also the experimental results are well coincide with the numerical results in the decrease of natural frequencies and the transformation of mode shapes because of intrinsic cracks in the composite or aluminum beams. It is revealed that non-destructive crack detection(NDT) or vibration based inspection(VBI) is possible by analyzing the free vibration responses of cracked composite beams.

Finite Element Analysis of Subsurface Multiple Horizontal Cracks Propagation in a Half-space Due to Sliding Contact (유한요소법을 이용한 미끄럼 접촉시 내부 복수 수평균열 전파해석)

  • 이상윤;김석삼;권영두
    • Tribology and Lubricants
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    • v.16 no.5
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    • pp.373-380
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    • 2000
  • Finite element analysis is performed on the subsurface crack propagation in brittle materials due to sliding contact. The sliding contact is simulated by a rigid asperity moving across the surface of an elastic half-surface containing single and multiple cracks. The single crack, coplanar cracks and parallel cracks are modeled to investigate the interaction effects on the crack growth in contact fatigue. The crack location is fixed and the friction coefficients between asperity and half-space are varied to analyze the effect of surface friction on stress intensity factor for horizontal cracks. The crack propagation direction is predicted based on the maximum range of shear and tensile stress intensity factors. With a coplanar crack, the stress intensity factor was increased. However, with a parallel crack, the stress intensity factor was decreased. These results indicate that the interaction of a coplanar crack increases fatigue crack propagation, whereas that of a parallel crack decreases it.

Fatigue Life Estimation of Cruciform Welded Joint Considering Multiple Collinear Surface Cracks (십자형 필렛용접 이음부의 복수균열 진전수명 평가)

  • Han Seung Ho;Shin Byung Chun;Kim Jae Hoon;Han Jeong Woo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.10
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    • pp.1549-1557
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    • 2004
  • Fatigue life of welded joints is governed by the propagation of multiple collinear surface cracks distributed randomly along weld toe. These cracks propagate under the mechanisms of mutual interaction and coalescence of the adjacent two cracks. To estimate the fatigue life, its influences on the above two mechanisms should be taken into account, which appear through the stress intensity factors disturbed mutually. However, it is difficult to calculate the stress intensity factors of the multiple surface cracks located in vicinity of weld toe due to its geometrical complexity. They are calculated normally by using the Μk-factors, but such Mk-factors are very rare in literature. In this study, the Μ$textsc{k}$-factors were obtained from a parametric study on crack length and depth, for which a finite element method is used. A fatigue test for a cruciform welded Joint was conducted and the fatigue life of the tested specimen was estimated using the present method with the informations obtained from the test, such as the number, size, and locations of the cracks. The estimated and measured fatigue life showed a good agreement.

Analysis of Multiple Curved Cracks in An Orthotropic Plate (직교이방성 판 내의 다중 곡선균열 해석)

  • Kim, Maan-Won;Park, Jai-Hak
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.27 no.6
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    • pp.969-980
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    • 2003
  • The interactions between curved cracks are examined in an orthotropic plate and the effects of rectilinear anisotropy on the stress intensity factors are analyzed. The finite element alternating method (FEAM) is used in this study to get the stress intensity factors for the multiple curved cracks. To obtain analytical solutions, which is necessary in FEAM, the curved cracks are modeled as continuous distributions of dislocations, and integral equations are formulated for unknown dislocation density functions to satisfy the given resultant forces on the crack surfaces. Several basic problems are solved to verify the accuracy and efficiency of the proposed method and it can be found that present results show good agreements with the previously published results.