Yazar "Karamanli, Armagan" seçeneğine göre listele

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    Bifurcation buckling conditions of FGM plates with different boundaries
    (Elsevier Sci Ltd, 2020) Karamanli, Armagan; Aydogdu, Metin
    [Abstract Not Available]
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    Buckling of laminated composite and sandwich beams due to axially varying in-plane loads
    (Elsevier Sci Ltd, 2019) Karamanli, Armagan; Aydogdu, Metin
    This paper is dedicated to study the elastic buckling behavior of isotropic, laminated composite and sandwich beams subjected to various axially varying in-plane loads and boundary conditions (BCs). The formulation of the problem is derived by using the Ritz method with the displacement field based on a shear and normal deformable beam theory (SNDBT). Polynomial functions are employed to present the displacement field. The convergence studies are performed and then obtained results are compared with those of reported works. Results from extensive analysis are presented for different BCs, aspect ratios, orthotropy ratios, fiber angles and loading conditions. It is observed that the type of the axially variable in-plane load significantly affects the critical buckling loads and mode shapes of the beams depending on the BCs. The normal deformation effect depends on not only the aspect ratio but also BCs and the fiber orientation angles.
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    A comprehensive study on the size-dependent analysis of strain gradient multi-directional functionally graded microplates via finite element model
    (Elsevier France-Editions Scientifiques Medicales Elsevier, 2021) Karamanli, Armagan; Aydogdu, Metin; Vo, Thuc P.
    This paper presents a comprehensive study on bending, vibration and buckling behaviours of the multi-directional FG microplates. The material properties vary continuously both in-plane and through-thickness directions. Based on a quasi-3D shear and normal deformation plate theory and the modified strain gradient theory, a finite element model is proposed and employed to solve the problems of the multi-directional FG microplates with various boundary conditions. The verification is performed by comparing the numerical results with those from the previous studies. A number of numerical examples on the multi-directional FG microplates with nine boundary conditions and power-law index have been carried out. The effects of three material length scale parameters, aspect ratio, gradient indexes in spatial directions and boundary conditions on the displacements, natural frequencies and buckling loads of 1D, 2D and 3D-FG microplates are investigated in details. Some new results, which are not available in open literature, are provided as references for the future studies. (C) 2021 Elsevier Masson SAS. All rights reserved.
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    Free vibration and buckling analysis of laminated composites and sandwich microbeams using a transverse shear-normal deformable beam theory
    (Sage Publications Ltd, 2020) Karamanli, Armagan; Aydogdu, Metin
    In this paper, the free vibration and buckling responses of laminated composite and sandwich microbeams with arbitrary boundary conditions are investigated. The governing equations based on the modified couple stress theory are derived by using the total potential energy of a microbeam and employing a transverse shear-normal deformable beam theory. Extensive analysis results in terms of dimensionless fundamental frequencies and dimensionless critical buckling loads are introduced for various boundary conditions, aspect ratios, orthotropy ratios, fiber orientation angles, thickness to material length scale parameter ratios, and core thickness to face layer thickness ratios.
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    On the vibration of size dependent rotating laminated composite and sandwich microbeams via a transverse shear-normal deformation theory
    (Elsevier Sci Ltd, 2019) Karamanli, Armagan; Aydogdu, Metin
    In this paper, the eigenfrequencies of rotating laminated composite (LC) and sandwich microbeams with different boundary conditions (BCs) are studied. The size-dependent variational formulation of the problem is obtained based on the Modified Couple Stress Theory (MCST) by employing a transverse shear-normal deformable beam theory and finite element method (FEM) formulation. The convergence and verification studies of the developed code are carried out and computed results in terms of dimensionless fundamental frequencies (DFFs) are compared with the available ones in the open literature. Various BCs, aspect ratios, fiber orientation angles, thickness to material length scale parameter (MLSP) ratios, core thickness to face layer thickness ratios, dimensionless rotation speeds (DRSs) and hub ratios are employed for the extensive analyses. It is found that the DFFs of the LC microbeams are highly affected by the small size effect accompanying with the orthotropy ratios, DRSs, hub ratios and fiber orientation angles. The effect of the small size on the DFFs of the rotating clamped-clamped LC microbeams is more pronounced than on those of the rotating clamped-free LC microbeams. The hub ratio has a significant effect on the DFFs of the rotating LC microbeams than the rotation speed.
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    Size dependent flapwise vibration analysis of rotating two-directional functionally graded sandwich porous microbeams based on a transverse shear and normal deformation theory
    (Pergamon-Elsevier Science Ltd, 2019) Karamanli, Armagan; Aydogdu, Metin
    Within this study, the free vibration behavior of rotating two-directional functionally graded porous sandwich microbeams is studied based on the modified couple stress theory by employing a transverse shear-normal deformation beam theory. The effects of the thickness to material length scale parameter accompanying with the porosity volume fraction coefficient, boundary condition, aspect ratio, hub ratio, dimensionless rotation speed and gradient index on the dimensionless fundamental frequencies of the two-directional functionally graded porous sandwich microbeams are investigated. It is found that the dimensionless fundamental frequencies are significantly affected by the variation of the thickness to material length scale parameter, hub ratio, dimensionless rotation speed and porosity volume fraction coefficient. The normal deformation effect is very important especially while the variations of the dimensionless rotation speed, hub ratio and gradient index are considered. Moreover, the mode shapes of the rotating two-directional functionally graded porous sandwich microbeams are also influenced with respect to the variation of the porosity volume fraction coefficient. As a result, the optimum design of the microstructures accompanying with the lightweight and low-cost objectives can be achieved by controlling the material and porosity distribution through the body of the microstructure.
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    Structural dynamics and stability analysis of 2D-FG microbeams with two-directional porosity distribution and variable material length scale parameter
    (Taylor & Francis Inc, 2020) Karamanli, Armagan; Aydogdu, Metin
    Since the two-directional functionally graded (2D-FG) materials can satisfy the new requirements raised based on the elimination of the stress concentration, delamination and cracking problems accompanying with the low cost and lightweight on the structures without sacrificing the stiffness and strength, the structural analyses of these structures become more important than ever. Moreover, the usage of the micro-electromechanical systems composed of 2D-FG materials has been increasing in automotive, military, space, biomedical, and nuclear energy industries. Within this study, the free vibration and buckling behaviors of 2D-FG porous microbeams are investigated based on the modified couple stress theory by employing a transverse shear-normal deformation beam theory and using finite element method. The effects of the thickness to material length scale parameter (MLSP) accompanying with the micro-porosity volume fraction ratio, boundary condition, aspect ratio, and gradient index on the dimensionless fundamental frequencies and dimensionless critical buckling loads of the 2D-FG porous microbeams are investigated. Moreover, with assumption of the variable material length scale parameters (VMLSP), the computed results are compared with ones obtained by employing constant MLSP. It is found that VMLSP increases the stiffness of the 2D-FG porous microbeams and effects the free vibration and buckling responses of these structures. Communicated by Corina Sandu.
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    Vibration behaviors of two-directional carbon nanotube reinforced functionally graded composite plates
    (Elsevier Sci Ltd, 2021) Karamanli, Armagan; Aydogdu, Metin
    The dynamical analysis of two directional functionally graded carbon nanotube reinforced composite (2DFG-CNTRC) plates are studied for various boundary conditions. The effects of the CNT distribution in the two directions on the dimensionless frequencies are investigated and compared with the unidirectional CNT distri-butions (1DFG-CNTRC) with respect to the variation of the CNT configuration, volume fraction and aspect ratio. Based on the variational formulation, the numerical results are obtained by using a finite element model. It is found that the volume fraction of the CNTs is affected with respect to the y direction and the difference between the dimensionless fundamental frequencies calculated based on the 2DFG-CNTRC and 1DFG-CNTRC configurations is significant. Moreover, for CFFF plates, the difference between the dimensionless fre-quencies obtained based on the 2DFG-CNTRC and 1DFG-CNTRC configurations is approximately 43.5% and 39% for 5th mode of the ?U? and ?V? type CNT configurations and 42% for 6th mode of the ?X? type CNT con -figuration while the aspect ratio is set to 50.
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    Vibration of functionally graded shear and normal deformable porous microplates via finite element method
    (Elsevier Sci Ltd, 2020) Karamanli, Armagan; Aydogdu, Metin
    The size dependent natural frequencies of functionally graded (FG) shear and normal deformable porous square microplates are investigated within this paper for arbitrary boundary conditions. By utilizing the modified couple stress theory, the finite element model is developed based on a shear and normal deformation plate theory and the variational formulation. The material length scale parameter (MLSP) is taken as variable. The effects of the aspect ratio, gradient index, boundary condition, thickness to MLSP ratio, porosity volume fraction and variable MLSP on the dimensionless natural frequencies are investigated for the FG shear and normal deformable porous square microplates. It is found that the difference between the numerical computations employing the constant and variable material length scale parameters is significant. In addition, it is found that with an increment in the aspect ratio, the effect of the MLSP on the natural frequencies increases, especially for the thick microplates. It can be concluded that for the thick microplates (length/thickness <= 10), the effect of the variable MLSP on the natural frequencies with respect to the changing of the thickness to MLSP is more emphasized than the effect obtained by the constant MLSP for all studied boundary conditions.