Thermo-mechanical buckling and nonlinear free vibration analysis of functionally graded beams on nonlinear elastic foundation

In this paper, thermo-mechanical buckling and nonlinear free vibration analysis of functionally graded (FG) beams on nonlinear elastic foundation are investigated. Nonlinear governing partial differential equation (PDE) of motion is derived based on Euler–Bernoulli assumptions together with Von Karman strain–displacement relation. Based on the Galerkin’s decomposition method, the nonlinear PDE governing equation is reduced to a nonlinear ordinary differential equation (ODE). He’s variational method is employed to obtain a simple and efficient approximate closed form solution for the resulted nonlinear ODE. Comparison between results of the present work and those available in literature shows accuracy of the presented expressions. Some new results for the thermo-mechanical buckling and nonlinear free vibration analysis of the FG beams such as the effects of vibration amplitude, material inhomogeneity, nonlinear elastic foundation, boundary conditions, geometric parameter and thermal loading are presented to be used in future references.     

Static analysis fatigue and fracture of cracked beams on elastic foundation

In this paper an analysis of a long edge-cracked beam resting on elastic foundation and with rotational and translational restraints at the ends is presented. The simplified Euler-Bernoulli beam theory is employed with the cracked section represented as an elastic hinge. By using the Paris-Erdogan crack propagation law, the fatigue life of the cracked beam is represented as a function of the constraints at the ends, the initial depth of the edge-crack, its location along the beam and the stiffness of the elastic foundation. The bending moment redistribution caused by the crack growth is analyzed and graphically illustrated. The retarding effect on the crack growth rate in the case of redundant structures subjected to repeated loading is discussed.     

Nonlinear analysis of unsymmetrically laminated imperfect thick panels on elastic foundation

Based on Timoshenko—Mindlin kinematic hypotheses and Hamilton's principle, a system of equations of motion is derived for geometrically nonlinear behavior of generally laminated cylindrical thick panels of geometric initial imperfections. The variation of rotational stiffness is assumed to be identical along opposite edges. A solution for nonlinear vibration of these panels is formulated by use of a multi-mode approach. The boundary condition for the varying rotational stiffness is satisfied by replacement of the edge bending moments by an equivalent lateral pressure near the panel edges as in a previous work. The Galerkin procedure furnishes an infinite set of equations for time-dependent coefficients which is solved by the method of harmonic balance. In the post-buckling case the set of time equations reduces to algebraic equations. Numerical results in nonlinear vibration and post-buckling are presented graphically for different parameters and compared with available data.     

Analysis of large amplitude free vibrations of unsymmetrically laminated composite beams on a nonlinear elastic foundation

The large amplitude free vibration of an unsymmetrically laminated composite beam (LCB) on a nonlinear elastic foundation subjected to axial load has been studied. The equation of motion for the axial and transverse deformations of a geometrically nonlinear LCB is derived. Using the Ritz method, the governing equation is reduced to a time-dependent Duffing equation with quadratic and cubic nonlinearities. The homotopy analysis method (HAM) is used to obtain exact expressions for the dynamic response of the LCB. This study shows that the third-order approximation of the HAM leads to highly accurate solutions that are valid for a wide range of vibration amplitudes. The effects of different parameters on the ratio of nonlinear to linear natural frequency of beams and the post-buckling load-deflection relationship are studied.     

Post-buckling analysis of non-uniform elastic columns

A numerical method for the second-order analysis of elastic beam-columns is described. For nominated values of axial load and end moments the deformed states and stress distribution can be determined by an automatic iterative procedure. For centrally loaded columns of non-uniform section, the method can be used to predict the critical loads from the grossly deformed equilibrium states above the first critical load. Axial and shear strains may be accounted for as well as flexural strains. Solutions for the shape of the elastica can be obtained for non-uniform columns. The method requires a small digital computer and is demonstrated for several plane, uniform and stepped elastic members. It can be readily extended to deal with transverse and distributed axial loading as well as flexural-torsional behaviour.     

Thermomechanical nonlinear in-plane analysis of fix-ended FGM shallow arches on nonlinear elastic foundation using two-step perturbation technique

International Journal of Mechanics and Materials in Design - An attempt is made in this research to analyse the nonlinear response of functionally graded material shallow arches with both edges...     

Large deflection analysis of thermo-mechanical loaded annular FGM plates on nonlinear elastic foundation via DQM

The effects of three-parameter elastic foundations and thermo-mechanical loading on axisymmetric large deflection response of a simply supported annular FGM plate are investigated. An annular FGM plate, resting on a three-parameter elastic foundation under a transverse uniform loading and a transverse non-uniform temperature, is considered. The mechanical and thermal properties of the FGM plate are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. The mathematical modeling of the plate and the resulting nonlinear governing equations of equilibrium are derived based on the first-order shear deformation theory (FSDT) in conjunction with nonlinear von Karman assumptions. A polynomial-based differential quadrature method is used as a simple but powerful numerical technique to discretize the nonlinear governing equations and to implement the boundary conditions. Finally, the effects of certain parameters, such as nonlinear foundations stiffness, volume fraction index, and temperature, on the axisymmetric large deflection response of the FGM plate are obtained and discussed in detail.     

Nonlinear oscillation of unsymmetric angle-ply plate on elastic foundation having nonuniform edge supports

This paper is analytically concerned with nonlinear flexural oscillation of an unsymmetrically laminated angle-ply rectangular plate resting on a Pasternak-type elastic foundation. The plate edges are subjected to the varying rotational constraints. Based on dynamic von Kármán-type nonlinear plate theory a single-mode analysis is carried out. In the formulation of a solution the force function and bending moments along the four edges are expanded into generalized Fourier series. These moments are also replaced by an equivalent lateral pressure near these edges. Galerkin's procedure and the perturbation technique are applied to the equation of motion and the time equation respectively. Numerical results for the amplitude-frequency response of the plate are presented graphically for various high-modulus composite materials, geometries of lamination, aspect ratios, moduli of elastic foundation and boundary conditions. Present results are compared with the existing values.     

Vibrational analysis of advanced composite plates resting on elastic foundation

This paper presents a free vibration analysis of functionally graded plates (FGPs) resting on elastic foundation. The displacement field is based on a novel non-polynomial higher order shear deformation theory (HSDT). The elastic foundation follows the Pasternak (two-parameter) mathematical model. The governing equations are obtained through the Hamilton’s principle. These equations are then solved via Navier-type, closed form solutions. The fundamental frequencies are found by solving the eigenvalue problem. The degree of precision of the current solution can be noticed by comparing it with the 3D and other closed form solutions available in the literature.     

弹性地基上间断中厚矩形板的非线性振动

研究了弹性地基上带传力杆的间断中厚矩形板结构的非线性振动特性。荷载在传力杆中的传递由竖向弹簧模拟，其弹簧刚度取决于传力杆的特性以及杆与板间的相互作用。根据能量变分原理，考虑地基耦合效应，建立了双参数地基上带传力杆的间断矩形中厚板的非线性运动控制方程。应用伽辽金法和谐波平衡法对该组非线性方程进行了求解。在算例中，讨论了传力杆参数、板的结构参数以及地基参数对中厚矩形板的非线性自由振动特性的影响。     

Linear and nonlinear free vibration of a multilayered magneto-electro-elastic doubly-curved shell on elastic foundation

Nonlinear and linear free vibration of symmetrically laminated magneto-electro-elastic doubly-curved thin shell resting on an elastic foundation is studied analytically. The shell is considered to be simply-supported on all edges and the magneto-electro-elastic body is poled along the z direction and subjected to electric and magnetic potentials between the upper and lower surfaces. To obtain the equations of motion, the Donnell shell theory in the presence of rotary inertia effect is used. Moreover, Gauss' laws for electrostatics and magnetostatics are used to model the electric and magnetic behavior. The nonlinear partial differential equations of motion are reduced to a single nonlinear ordinary differential equation by introducing a force function and using the single-term Galerkin method. The resulting equation is solved analytically by Lindstedt-Poincare perturbation method. After validation of the present study, several numerical studies are done to investigate the effects of foundation parameters, geometrical properties of the shell, and electric and magnetic potentials on the linear and nonlinear behavior of these smart shells.     

基于振型控制的变厚度梁的优化设计研究

提出了计算梁弯曲振动的新方法。从弯曲变形的角度出发,利用有限差分的方法,建立了梁弯曲振动的计算模型,模型同时适用于等厚度梁和变厚度梁。使用不同类型的梁对模型的准确性进行了验证,结果表明模型具有较好的计算精度。同时,尝试使用该模型进行梁的振型优化设计,对模型做适当的变形后,就可以以梁的频率和振型作为目标,通过数值方法来获取最佳的厚度分布值。最后用一个实例对方法进行了验证,结果表明利用该模型进行梁的振型优化设计是可行的。     

Nonlinear elastic analysis of adhesive blister test

A nonlinear elastic analysis of a blister test is conducted for rubber-like material described by the Ogden-Tschoegl strain energy function. A finite element program is applied to the analysis which is formulated based on the total Lagrangian procedure and capable of treating deformation-dependent pressure loading problems. The dependence of specific adhesive fracture energy _a on critical pressure p _cris analyzed for a blister test specimen with different geometry and different material constants. It is suggested that the unbonded radius a in the dimensionless representation p _cr ² a/E_a should be replaced by an average value in the numerical analysis. The numerical analysis of the blister test is also discussed in general.     

DQEM for free vibration analysis of Timoshenko beams on elastic foundations

 A differential quadrature element method (DQEM) based on first order shear deformation theory is developed for free vibration analysis of non-uniform beams on elastic foundations. By decomposing the system into a series of sub-domains or elements, any discontinuity in loading, geometry, material properties, and even elastic foundations can be considered conveniently. Using this method, the vibration analysis of general beam-like structures is to be studied. The governing equations of each element, natural compatibility conditions at the interface of two adjacent elements and the external boundary conditions are developed in a systematic manner, using Hamilton's principle. The present DQEM is to be implemented to Timoshenko beams resting on partially supported elastic foundations with various types of boundary conditions under the action of axial loading. The general versality, accuracy, and efficiency of the presented DQEM are demonstrated having solved different examples and compared to the exact or other numerical procedure solutions. Received: 11 October 2002/Accepted: 26 November 2002     

Free out-of-plane vibration of cracked curved beams on elastic foundation by estimating the stress intensity factor

Abstract

This paper is concerned with evaluating stress intensity factors (SIFs), for a cracked curved beam of rectangular cross section, applying an approach which allows us to estimate the strain energy release rate. The beam is located on an elastic foundation. The out-of-plane vibration of the beam is investigated. This approach requires an additional factor namely correction factor, on the basis of the energy release zone slope to approximate the SIFs. The initial curvature of the beam, however, adds some complication in using this factor. The second part of this study is investigating a numerical approach, namely differential quadrature element method (DQEM), to gain the natural frequencies of the cracked beam. This method is applied to show the application of the SIFs to calculate the compliance of the cracked section for modeling the crack. The other method which is used to obtain the natural frequencies is the finite element method (FEM). The results of these two methods are found to be in good agreement, which shows the precision of the stress intensity factors of the cracked beam.     

Nonlinear analysis of elastic space cable-supported membranes

In this paper a solution method is presented for the coupled problem of elastic flat or space membranes supported by elastic flexible cables. Both membrane and cable undergo large deflections. Starting from the minimal surface the membrane is prestressed by imposed boundary displacements under the self-weight. Then an iterative procedure is employed, which consists in solving the membrane and the cable large deflection problems separately in each iteration step and checking the continuity of displacements and forces between membrane and cable. The procedure is repeated until convergence is achieved. Both membrane and cable problems are solved using the analog equation method (AEM). The displacements as well as the stress resultants are evaluated at any point of the membrane and the cable from the integral representations of the solution of the analog equations, which are used as mathematical formulae. Example problems are presented, for both flat and space membranes, which illustrate the method and demonstrate its efficiency and accuracy.     

An approach for the Pasternak elastic foundation parameters estimation of beams using simulated frequencies

As a first attempt, a mix of differential quadrature (DQ) and simplex (S) method for the Pasternak elastic foundation parameters estimation of beams using simulated frequencies is presented. The method is applied for the parameters estimation of functionally graded (FG) beams. The first-order shear deformation theory is employed to derive governing equations of FG beam on the Pasternak elastic foundation. The equations are discretized by utilizing the DQ method and frequencies of the beam are calculated. Then, the simulated frequencies are obtained by applying random error to the calculated frequencies. The simulated frequencies are used as input data for estimating parameters of the problem. An objective function as a root-mean-square error between the calculated and simulated frequencies is defined. The DQ method and simplex technique as a classical optimization technique are coupled to minimize the function via finding the best foundation parameters, iteratively. Some examples are solved to show applicability, robustness and accuracy of the mixed method for elastic foundation parameters estimation of the beam. Also, it has been found that using only the first simulated frequency of the beam cannot give correct parameters of the foundation.     

A general finite element for beams or beam-columns with or without an elastic foundation

A general finite element is derived for beams or beam-columns with or without a continuous Winkler type elastic foundation. The need to discretize members into shorter elements for convergence towards an ‘exact’ solution is eliminated by employing in the derivation of the element exact shape functions obtained from the equation of the elastic line. Inter-nodal values of deflections, bending moments and shear forces are obtained using the exact shape functions and trigonometric series. The effect of heavy compressive or tensile axial forces on bending stiffness is treated as a linear problem by considering the axial force as a constant parameter affecting the stiffness. FORTRAN subroutines to compute the stiffness matrix, equivalent nodal forces, deflected shape, bending moments and shear forces are provided and verified by an example.     

Stochastic nonlinear free vibration of laminated composite plates resting on elastic foundation in thermal environments

This paper presents the nonlinear free vibration analysis of laminated composite plates resting on elastic foundation with random system properties in thermal environments. System parameters are modeled as basic random variables for accurate prediction of system behavior. A C ⁰ nonlinear finite element based on HSDT in von Karman sense is used to descretize the laminate. A direct iterative method in conjunction with first-order perturbation technique is outlined and applied to solve the stochastic nonlinear generalized eigenvalue problem. The developed stochastic procedure is successfully used for thermally induced nonlinear free vibration problem with a reasonable accuracy. Numerical results for various combinations of boundary conditions, geometric parameters, amplitude ratios, foundation parameters and thermal loading have been compared with those available in literature and an independent MCS. Some new results are also presented which clearly demonstrate the importance of the randomness in the system parameters on the response of the structures.