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Öğe An equivalent single layer shear deformation plate theory with superposed shape functions for laminated composite plates(Polish Acad Sciences Inst Fundamental Technological Research, 2019) Aydogdu, M.A SINGLE LAYER SHEAR DEFORMATION PLATE THEORY WITH SUPERPOSED SHAPE FUNCTIONS for laminated composite plates has been proposed. Some of the previously developed, five degrees of freedom shear deformation theories, including parabolic [1], hyperbolic [2], exponential [3] and trigonometric [4] plate theories have been superposed by applying different theories in the different in- plane directions of the composite plate. Statics and dynamics of composite plate problems have been investigated. It was obtained that using different shape functions in the different in-plane directions may decrease the percentage error of stress and deflection. Present hyperbolic-exponential and parabolic-exponential theories predict stiffer properties (give lower bending and stress values, and higher frequency, and buckling loads when compared to the 3-D elasticity). Some improvements were determined for y-z component of the transverse shear stress using hyperbolic-exponential and parabolic-exponential theories for symmetric cross-ply composite plates when compared to available single shape function plate models. Global behaviours (vibration frequency and critical buckling loads) are predicted within %5 accuracy similar to plate theories with single shape functions.Öğe Nonlocal elasticity effect on vibration of in-plane loaded double-walled carbon nano-tubes(Springer Wien, 2007) Ece, M. C.; Aydogdu, M.Vibration and buckling of in-plane loaded simply supported double-walled carbon nanotubes were investigated using the nonlocal Timoshenko-beam theory. The influence of in-plane loads on the natural frequencies was determined. The results show that while the natural frequencies decrease with increasing compressive in-plane loads, an increase in frequencies is observed for tension type of in-plane loads. Effects of in-plane loads are more pronounced for lower modes, and some mode changes are observed at critical in-plane loads. A comparison of nonlocal elasticity solutions with local elasticity solutions indicates that the nonlocal effects should be considered for higher modes of vibration of double-walled carbon nanotubes.Öğe On the forced vibration of carbon nanotubes via a non-local Euler-Bernoulli beam model(Sage Publications Ltd, 2010) Karaoglu, P.; Aydogdu, M.This article studies the forced vibration of the carbon nanotubes (CNTs) using the local and the non-local Euler-Bernoulli beam theory. Amplitude ratios for the local and the non-local Euler-Bernoulli beam models are given for single-and double-walled CNTs. It is found that the non-local models give higher amplitudes when compared with the local Euler-Bernoulli beam models. The non-local Euler-Bernoulli beam model predicts lower resonance frequencies.Öğe Three dimensional mechanical buckling of FG plates with general boundary conditions(Elsevier Sci Ltd, 2013) Uymaz, B.; Aydogdu, M.The mechanical buckling analysis of rectangular functionally graded plates under different axial loadings is considered. The analysis is based on the small strain elasticity theory with different boundary conditions. The material properties of the plate vary through the thickness direction according to a simple power law. Three dimensional buckling solutions are obtained using the Ritz method with Chebyshev polynomials as assumed displacement functions. The convergence and comparison studies are presented and effects of the different material composition and the plate geometry (side-side ratio, side-thickness ratio) on the critical buckling loads and mode shapes are investigated. (c) 2012 Elsevier Ltd. All rights reserved.Öğe Three dimensional shear buckling of FG plates with various boundary conditions(Elsevier Sci Ltd, 2013) Uymaz, B.; Aydogdu, M.In this paper, the buckling of functionally graded plates under shear are considered for various boundary conditions. The buckling results obtained by using Ritz method based on the three-dimensional linear elasticity theory and the higher order shear deformation theories. The material properties of the plate vary through the thickness direction according to a simple power law. The comparison results are presented and the variation of the critical shear buckling load and the critical shear buckling modes with the shear buckling characteristics like the material composition, the plate geometry parameters (side-side ratio, side-thickness ratio) are investigated. (C) 2012 Published by Elsevier Ltd.Öğe Vibration and buckling analysis of nanotubes (nanofibers) embedded in an elastic medium using Doublet Mechanics(Springer, 2018) Gul, U.; Aydogdu, M.; Gaygusuzoglu, G.In the present study, vibration and buckling of nanotubes (nanofibers) embedded in an elastic medium are studied. A length scale-dependent theory called Doublet Mechanics (DM) is used in the formulation. In this theory, discrete microstructure of solids is considered in the formulation and using a bottom-up approach macro level strains and stresses are obtained from microlevel strains and stresses. Taylor series expansion of the microlevel displacement is used in the definition of the micro strains. The number of terms in the Taylor series describes the microstructure of the considered solids. In this study, nanotube fibers are assumed as an Euler-Bernoulli beam embedded in an elastic medium. Simply supported and clamped boundary conditions are considered at the edges of the beams. Free vibration frequencies and critical buckling loads are obtained and compared with the classical elasticity results. It is shown that scale-dependent DM can be used at the nanolength scale.Öğe WAVE PROPAGATION ANALYSIS IN BEAMS USING SHEAR DEFORMABLE BEAM THEORIES CONSIDERING SECOND SPECTRUM(Cambridge Univ Press, 2018) Gul, U.; Aydogdu, M.In this study, wave propagation in beams is studied using different beam theories like Euler-Bernoulli, Timoshenko and Reddy beam theories. Dispersion curves obtained for these beam theories are compared with the exact plane elasticity solutions. It is obtained that, there are two branches for Reddy beam theory similar to the Timoshenko beam theory. However, one branch is obtained for Euler-Bernoulli beam theory. The effects of in-plane load on Timoshenko and Reddy beam theories are examined and dispersion curves of the Timoshenko and Reddy beams are compared with exact plane elasticity solution. In Timoshenko beam theory, qualitative difference between the two spectrums has been lost with in-plane loads for some wave numbers.
