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Daniel J Inman - One of the best experts on this subject based on the ideXlab platform.

  • free vibration analysis of cracked composite beams subjected to coupled bending torsion loads based on a first order shear deformation theory
    Applied Mathematical Modelling, 2013
    Co-Authors: Alireza Daneshmehr, Alireza Nateghi, Daniel J Inman
    Abstract:

    Abstract In this paper, free vibration analysis of cracked composite beam subjected to coupled bending–torsion loading is presented. The composite beam is assumed to have an open edge crack of length a. A first order shear deformation theory is applied to count for the effect of shear deformations on natural frequencies as well as the effect of coupling in torsion and bending modes of vibration. Governing equations and boundary conditions are derived using Hamilton principle. Local Flexibility Matrix is used to obtain the additional boundary conditions of the beam in cracked area. After obtaining the governing equations and boundary conditions, generalized differential quadrature (GDQ) method is applied to solve the obtained eigenvalue problem. Finally, some numerical results of beams with various boundary conditions and different fiber orientations are given to show the efficiency of the method. In addition, to study the effect of shear deformations, numerical results of the current model are compared with previously given results in which shear deformations were neglected.

  • free vibration analysis of cracked composite beams subjected to coupled bending torsion loads based on a first order beam theory
    Applied Mechanics and Materials, 2013
    Co-Authors: Alireza Daneshmehr, Daniel J Inman, Alireza Nateghi
    Abstract:

    In this paper free vibration analysis of cracked composite beams subjected to coupled bending-torsion loads are presented. The composite beam is assumed to have an open edge crack. A first order theory is applied to count for the effect of the shear deformations on natural frequencies as well as the effect of coupling in torsion and bending modes of vibration. Local Flexibility Matrix is used to obtain the additional boundary conditions of the beam in the crack area. After obtaining the governing equations and boundary conditions, GDQ method is applied to solve the obtained eigenvalue problem. Finally, some numerical results are given to show the efficacy of the method. In addition, to count for the effect of coupling on natural frequencies of the cracked beams, different fiber orientations are assumed and studied.

  • modeling and analysis of a cracked composite cantilever beam vibrating in coupled bending and torsion
    Journal of Sound and Vibration, 2005
    Co-Authors: Kaihong Wang, Daniel J Inman, Charles R. Farrar
    Abstract:

    The coupled bending and torsional vibration of a fiber-reinforced composite cantilever with an edge surface crack is investigated. The model is based on linear fracture mechanics, the Castigliano theorem and classical lamination theory. The crack is modeled with a local Flexibility Matrix such that the cantilever beam is replaced with two intact beams with the crack as the additional boundary condition. The coupling of bending and torsion can result from either the material properties or the surface crack. For the unidirectional fiber-reinforced composite, analysis indicates that changes in natural frequencies and the corresponding mode shapes depend on not only the crack location and ratio, but also the material properties (fiber orientation, fiber volume fraction). The frequency spectrum along with changes in mode shapes may help detect a possible surface crack (location and magnitude) of the composite structure, such as a high aspect ratio aircraft wing. The coupling of bending and torsion due to a surface crack may serve as a damage prognosis tool of a composite wing that is initially designed with bending and torsion decoupled by noting the effect of the crack on the flutter speed of the aircraft.

B F Spencer - One of the best experts on this subject based on the ideXlab platform.

  • experimental verification of the Flexibility based damage locating vector method
    Journal of Engineering Mechanics-asce, 2007
    Co-Authors: B F Spencer, Y Gao, Dionisio Bernal
    Abstract:

    In recent years, numerous approaches have been proposed for detecting damage in structures, in which the Flexibility-based damage locating vector (DLV) method is one of the promising techniques. By computing a set of load vectors from the change of the Flexibility Matrix before and after damage and then applying them as static forces to the undamaged analytical model for static computation, the DLV method is able to locate damage in structures. The main purpose of this paper is to experimentally verify this method. Following a brief introduction and discussion of the motivation for the Flexibility-based method, an overview of the DLV method and construction of the Flexibility Matrix from limited sensor information is presented. The DLV method is then experimentally verified employing a 5.6 m (18 ft)-long three-dimensional truss structure. To simulate damage in the structure, the original truss member is replaced by one with reduced stiffness. Experimental results show that the DLV method can successfully detect the damage using a limited number of sensors and modes.

  • damage detection in ambient vibration using proportional Flexibility Matrix with incomplete measured dofs
    Structural Control & Health Monitoring, 2007
    Co-Authors: Zhongdong Duan, Guirong Yan, B F Spencer
    Abstract:

    Structural damage detections based on the changes of dynamic properties are a major concern for structural health monitoring. In this paper, efforts are made to extend the Flexibility-based damage localization methods, especially the damage locating vector (DLV) method, to the case of ambient vibration with incomplete measured degree of freedom, where Flexibility matrices are not available. First, the method to assemble a proportional Flexibility Matrix (PFM) with arbitrarily scaled modal shapes of full measured degrees of freedom (DOF) is introduced. The PFM is within a scalar multiplier to the real Flexibility Matrix, and the multiplier is shown to be the first modal mass theoretically. In the case of incomplete measured degrees, it is proved that the FEM model with full measured DOFs has the same modal masses and modal stiffnesses as the condensed model with partially measured DOFs as the retained degrees. Based on this deduction, the PFM at sensor locations is achieved with arbitrarily scaled test modes at partially measured DOFs. Assuming that the modal masses do not change significantly before and after being damaged, the PFMs for pre- and post-damage structures are made comparable, and the DLV method is implemented with the proposed PFMs at sensor locations. Finally an example of multi-damage sites localization for a 14 bays planar truss is given. Five damaged members in this structure are successfully identified by the proposed approach with only outputs and measurements at partial DOFs. Copyright © 2005 John Wiley & Sons, Ltd.

  • damage localization in ambient vibration by constructing proportional Flexibility Matrix
    Journal of Sound and Vibration, 2005
    Co-Authors: Zhongdong Duan, Guirong Yan, B F Spencer
    Abstract:

    Damage localization approaches based on changes of flexibilities constitute an important technique for damage detection. However, the unavailability of Flexibility Matrix with output-only data makes Flexibility-based approaches not really applicable in the very important cases of ambient vibrations. An algorithm is presented to construct a proportional Flexibility Matrix (PFM) from a set of arbitrarily scaled tested modal shapes and modal frequencies. The constructed PFM is just within a scalar multiplier to the real Flexibility Matrix, and the scalar multiplier is theoretically the first modal mass, which is undetermined before the mode is properly scaled. Instead of real flexibilities, the PFMs are incorporated into the damage locating vectors (DLV) method for damage localizations in ambient vibrations. PFMs for the pre- and post-damaged structure need to be comparable before being integrated into the DLV procedure. This requirement is guaranteed when there is at least one reference degree with unchanged mass after damage. Two numerical examples show that a small number of measured modes can produce PFMs with sufficient accuracy to correctly locate the damages by the DLV method from output-only data.

M Topcu - One of the best experts on this subject based on the ideXlab platform.

  • free vibration analysis of cracked beams by a combination of finite elements and component mode synthesis methods
    Computers & Structures, 1998
    Co-Authors: Murat Kisa, J Brandon, M Topcu
    Abstract:

    Abstract Previous work on the dynamics of defective structures, by the authors’ colleagues and other studies in the literature, has revealed substantial variability in predicted vibration behaviour depending on the interface conditions. In the current project the authors have set out to develop a strategy which retains the maximum amount of common information concerning the linear regions of the structure, whilst allowing the maximum scope to vary conditions at the (nonlinear) interface. In this paper, the vibrational characteristics of a cracked Timoshenko beam are analysed. The study integrates the finite element method and component mode synthesis. The beam divided into two components related by a Flexibility Matrix which incorporates the interaction forces. These forces can be derived from fracture mechanics theory as the inverse of the compliance Matrix calculated using stress intensity factors and strain energy release rate expressions. Each substructure is modelled by Timoshenko beam finite elements with two nodes and 3 degrees-of-freedom (axial, transverse and rotation) at each node.

Alireza Daneshmehr - One of the best experts on this subject based on the ideXlab platform.

  • free vibration analysis of cracked composite beams subjected to coupled bending torsion loads based on a first order shear deformation theory
    Applied Mathematical Modelling, 2013
    Co-Authors: Alireza Daneshmehr, Alireza Nateghi, Daniel J Inman
    Abstract:

    Abstract In this paper, free vibration analysis of cracked composite beam subjected to coupled bending–torsion loading is presented. The composite beam is assumed to have an open edge crack of length a. A first order shear deformation theory is applied to count for the effect of shear deformations on natural frequencies as well as the effect of coupling in torsion and bending modes of vibration. Governing equations and boundary conditions are derived using Hamilton principle. Local Flexibility Matrix is used to obtain the additional boundary conditions of the beam in cracked area. After obtaining the governing equations and boundary conditions, generalized differential quadrature (GDQ) method is applied to solve the obtained eigenvalue problem. Finally, some numerical results of beams with various boundary conditions and different fiber orientations are given to show the efficiency of the method. In addition, to study the effect of shear deformations, numerical results of the current model are compared with previously given results in which shear deformations were neglected.

  • free vibration analysis of cracked composite beams subjected to coupled bending torsion loads based on a first order beam theory
    Applied Mechanics and Materials, 2013
    Co-Authors: Alireza Daneshmehr, Daniel J Inman, Alireza Nateghi
    Abstract:

    In this paper free vibration analysis of cracked composite beams subjected to coupled bending-torsion loads are presented. The composite beam is assumed to have an open edge crack. A first order theory is applied to count for the effect of the shear deformations on natural frequencies as well as the effect of coupling in torsion and bending modes of vibration. Local Flexibility Matrix is used to obtain the additional boundary conditions of the beam in the crack area. After obtaining the governing equations and boundary conditions, GDQ method is applied to solve the obtained eigenvalue problem. Finally, some numerical results are given to show the efficacy of the method. In addition, to count for the effect of coupling on natural frequencies of the cracked beams, different fiber orientations are assumed and studied.

Masoud Motavalli - One of the best experts on this subject based on the ideXlab platform.

  • damage identification using modal data experiences on a prestressed concrete bridge
    Journal of Structural Engineering-asce, 2005
    Co-Authors: Olaf Huth, Nedim Kilic, J Maeck, Glauco Feltrin, Masoud Motavalli
    Abstract:

    Large scale tests with progressive damage on a prestressed concrete highway bridge have been performed to investigate the sensitivity of several damage detection, localization, and quantification methods based on modal parameters. To investigate the quality of modal parameters, the data set of one damage step was analyzed by several output-only identification techniques. Although the bridge was severely cracked, natural frequencies as well as mode shapes display only minor changes. However, the relative changes of mode shapes are larger than those observed for natural frequencies. A novel damage indicator, called mode shape area index, based on changes of mode shapes, has been developed and found as the most sensitive damage detection approach. Damage detection or localization via changes of the Flexibility Matrix performed better than natural frequencies or mode shapes alone. The application of the direct stiffness calculation and a sensitivity-based model update technique showed results having a high level of ambiguity about the location and quantification of damage also at the highest damage level. Evaluating the information collected in this study the test results indicate that an early stage damage identification in prestressed concrete bridges is hardly possible because of the nearly complete recovery of stiffness after closing of cracks in prestressed concrete and the effect of environmental parameters on modal data.