作者: Usik Lee, Yong Ju Jun, Il Wook Park

摘要: A computer-aided time reversal process (CTRP) is proposed for the structural damage diagnosis. In the standard time reversal process (STRP), both forward and backward processes are conducted by the measurement. However, in the proposed CTRP, the forward process is conducted by the measurement while the backward process is conducted by the computation. As a benefit of the computer-based backward process, the unwanted Lamb wave modes which do not carry damage information can be readily removed from the signals reconstructed at the input excitation point. The reconstructed signals refined in such a way can make the signal processing for the damage diagnosis more efficient and easier.

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作者: António F. Mateus, Joel A. Witz

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作者: Ali Mahieddine, Mohammed Ouali

摘要: A mathematical model for plates with partially delaminated layers is presented to investigate their behavior. In this formulation account is taken of lateral strains. The principal advantage of the element is that it allows the modeling of delamination anywhere in the structure. The region without delamination is modeled to carry constant peel and shear stresses; while the region with delamination is modeled by assuming that there is no peel and shear stress transfer between the top and bottom layers. Numerical results of the present model are presented and its performance is evaluated for static problems. Laminated beams and plates are often used as primary load-carrying structures. However, the mechanical properties of composite materials may degrade severely in the presence of damage. One of the common types of damage modes in laminated composites is delamination. The presence of delamination is one of the most prevalent life-limiting failure modes in laminated composite structures. Many researchers had been studying the effect of delamination. Wee and Boay [1] developed an analytical model to predict the critical load of a delaminated composite laminated beam. Lee et al. [2] investigated the buckling behavior of the beam plate with multiple delaminations under compression. Kapania and Wolfe [3] examined the buckling behavior of a beam plate with two delaminations of equal length. Wang et al. [4] improved the analytical solution by including the coupling between the flexural and axial vibrations of the delaminated sub-laminates. Lee et al. [5] studied a composite beam with arbitrary lateral and longitudinal multiple delamination. Finite-element methods have been developed using the layerwise theory by Kim et al. [6]. Tan and Tong [7] developed a dynamic analytical model for the identification of delamination embedded in a laminated composite beam. To investigate the effects of delamination of a plate layers, a finite-element model is developed. Both displacement continuity and force equilibrium conditions are imposed between the regions with and without delamination. The accuracy of the approach is verified by comparing results with previously published data.

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作者: Aurora Cătălina Ianăşi

摘要: Wood is a material of construction relatively inexpensive and easy to put into practice because of its lightness, reusability, simplicity in fabrication and environmental compatibility. However, its ability to lift load small compared to other building materials, it greatly limits the range of its use. Increasing the mechanical strength of wood elements used in construction is a goal that, once achieved, would expand the use of this material, with notable economic repercussions. The use of composite materials such as CFRP (carbon fiber reinforced plastic) as reinforcement for wood elements under bending loads like beams requires attention to the techniques of reinforcing for different layouts of CFRP elements. Each choice of reinforcing could potentially lead to different results. When the choice has been made, the next step is the selection of the most adequate CFRP elements. For this reason, selection of the reinforcement layout and material should be guided by an accurate analysis of the characteristics of the element to be reinforced in order to avoid ineffective interventions. The present paper is concerned with determination the performances of wood beams reinforced with CFRP composites by investigating their bending resistance and showing crushing damage in the bending region. All tested wood beamspresented in this paper were made from beech. The results for the un-reinforced beams are reported solely for the purpose of quantitatively evaluating the effectiveness of the interventions through a comparison with the results for CFRP strengthened beams. The technology of composite material reinforcement is based on using CFRP plates bonded with an epoxy resin on the wood beams. After bonding, the beams were tested to bending on a universal testing machine with a punctuated force placed at the middle of the beams. The results indicate that the behavior of reinforced beams with CFRP is totally different from that of un-reinforced one. During the performed tests, observations of the experimental loaddisplacement relationships showed that bending strength increased for wood beams reinforced with CFRP compared to those without CFRP reinforcement. Mechanical tests on the reinforced wood beams proved that CFRP materials produced flexural displacement and lifting increases of the beams that entitles us to say this kind of materials have improved the mechanical performances of tested wooden beams.

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作者: Dmitri Gornostajev, Gennady Aryassov, Sergei Zhigailov

摘要: The problem of plates and shells under the effect of local loading was treated. In this paper, a direct solution for a round plate is proposed, which greatly raises its accuracy. The obtained results are generalized for shells of revolution. The result will be used in barge model calculations striving to increase accuracy of the calculations. It should help to decrease weight of the barge which is very important in order to increase load capacity of the barge. In order to solve equation in better tolerance, improved method of grids will be used. The proposed method will totally change current methods of calculation for the hull thickness due to its accuracy.

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作者: Hossein Hosseini-Toudeshky, Bijan Mohammadi, Pooya Saniei

摘要: In this paper multiple fatigue cracks propagation are simulated in two-dimensional plates. Since re-meshing the cracked bodies in each increment of crack extension is a time-consuming and complicated procedure, numerical simulation of mixed-mode crack propagation with FEM is a difficulty. For this purpose, a FEM software is programmed and mesh refinement in each increment of crack is performed by Delaunay Refinement Algorithm. Using different refinement methods, complex boundaries such as multiple cracks and discontinuities which are closed together are easily refined by this algorithm. Crack propagation path is predicted using domain form of J-integral. Modified tensile stress (MTS) criterion is used to predict the crack propagation path in each increment. Different numerical examples illustrate the validation and reliability of present software.

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作者: Viktor I. Kucheryuk, Olga L. Umanskaya, Natalya A. Krivchun

摘要: This article provides an overview of the analysis of the selection of the reduced (equivalent) characteristics of the material. The selection and definition of the elastic characteristics of composite materials depend on many factors: the geometry of the design element of the structure, the stress-strain state and the mathematical model of this state, the calculation methods, and the necessary accuracy of the solution. Technical methods for calculating elements such as rods, plates, and shells are analytically related to the formulation of resolving equations. One of the most common approaches to implementing practical tasks is the method of bringing an inhomogeneous material to a homogeneous isotropic or orthotropic material. In this paper, the most common options for choosing the mechanical characteristics of a composite material are considered. A restriction is introduced - work in the elastic region and the compatibility of deformations of the matrix with reinforcement. These limitations are in good agreement with the reliability of the construction. The article gives a qualitative analysis of formulas depending on the task. A choice of design for a dispersion-hardened material is proposed for a uniform reinforcement distribution for bent elements. The above analysis of formulas for determining the efficiency of physical and mathematical characteristics of composite rods, plates, and shells, allows for the calculation of more complex problems.

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作者: A. Köllner, Maria Kashtalyan, Igor Guz, C. Völlmecke

摘要: The mechanical behavior of cross-ply laminates loaded under in-plane compression containing matrix cracks and delaminations is investigated in order to study their influence on the structural stability behavior. This is done by employing a semi-analytical modelling approach which comprises an analytical framework for a structural stability analysis of damageable structures and the Equivalent Constrained Model for deriving reduced stiffness properties of the cracked layers. Cross-ply laminates with varying delamination depths as well as varying matrix crack densities are studied.

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作者: J.N. Reddy, A. Srinivasa, A. Arbind, P. Khodabakhshi

摘要: In this paper two different nonlinear elasticity theories that account for (a) geometric nonlinearityand (b) microstructure-dependent size effects are revisited to establish the connection betweenthe two theories. The first theory is based on modified couple stress theory of Yang et al. [1]and the second one is based on Srinivasa–Reddy gradient elasticity theory [2]. The modified couplestress theory includes a material length scale parameter that can capture the size effect in a material.The gradient elasticity theory was developed for finitely deforming hyperelastic cosserat continuum,and it is a generalization of small deformation couple stress theories. The Srinivasa–Reddy theorycontains, as a special case, the first one. These two theories are used to derive the governing equationsof beams and plates. In addition, a discrete peridynamics idea as an alternative to the conventionalperidynamics is also presented.

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