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As a first attempt, optimum stacking sequences of thick laminated composite plate is obtained to maximize its buckling load via employing the finite element (FE), genetic algorithms (GAs) and particle swarm optimization (PSO) methods. The higher-order shear deformation theory (HSDT) is used to obtain governing equations of the plate. The finite element method (FEM) is employed to solve these equations and to gain buckling load of the plate. The FEM solution is linked with a developed optimization algorithm which is a mix of genetic algorithms (GAs) and particle swarm optimization (PSO) techniques. Some examples are solved to show applicability and usefulness of the proposed hybrid method for maximizing buckling load of the plate via finding optimum stacking sequences of the plate. Also, influences of different parameters on the optimum stacking sequences of the thick plate are studied. [ABSTRACT FROM AUTHOR]

Semi-analytical models for the linear buckling analysis of unstiffened laminated composite cylinders and cones with flexible boundary conditions are presented. The Classical Laminated Plate Theory and the First-order Shear Deformation Theory are used in conjunction with the Donnell’s non-linear equations to derive the buckling equations. Axial, torsion and pressure loads can be applied individually or combined in the proposed models. The stiffness matrices are integrated analytically and for the conical shells an approximation is proposed to overcome non-integrable expressions. Comparisons with the literature show that the classical base functions available for axial compression cannot capture the buckling modes for non-orthotropic laminates. For torsion loads these classical shape functions do not catch the buckling modes even when applying the assumption of pure orthotropy, and it is shown how the proposed models correlate well with experimental data from the literature and finite element results. The use of elastic constraints at the boundaries allows the simulation of different boundary conditions in a versatile way and it is shown how those constants can be adjusted in order to change from one type of boundary condition to another. [ABSTRACT FROM AUTHOR]

The vibration behaviors of functionally graded carbon nanotube (FG-CNT) reinforced composite rectangular plates subjected to in-plane loads are studied in this paper. Three types of carbon nanotube (CNT) distributions are researched in this investigation. Reddy’s third-order shear deformation theory (HSDT) is applied to evaluate the displacement fields of the plate. The equation of motion of the structural system is formulated with use of the Hamilton’s principle. The plates investigated in this study are simply-supported on two opposite edges and therefore, in order to solve the coupling set of equations of motion, the state-space Levy method is applied. Based on the Levy solution, the natural frequencies and vibration mode shapes of FG-CNT reinforced composite plates subjected to in-plane loads with different boundary conditions are presented for different thickness-length ratios and aspect ratios. Moreover, the critical in-plane loads for the buckling of different FG-CNT plates are calculated and compared. [ABSTRACT FROM AUTHOR]

Thin-walled composite beams of complex sectional contour are widely used along with the traditional elements of reinforced structures. Based on the generalized theory of elasticity of thin-walled beams, the mathematical model of flexural–torsional deformation of open-profile thin-walled composite beams of non-uniform cross section under thermo-mechanical loading has been developed. To confirm the reliability of developed approach to determination of the spatial displacements of thin-walled composite beams of non-uniform cross section, several experimental studies were conducted. Based on the analysis of the range of typical profiles, for the further analysis we selected several compound cross sections for which the analytical dependences were obtained regarding displacements of their characteristic points. Our studies can serve as a base for development of the practical recommendations for the optimal designing and manufacturing of thin-walled anisotropic profiles, as well as proposing the measures to reduce the value of deformations caused by the production process. [ABSTRACT FROM AUTHOR]

The problems of a multi-mode buckling approach which is based on Koiter’s theory of a hybrid column are presented in this paper. An interaction of global buckling modes with the local ones is discussed. There are many different local and global buckling modes. Their selected combinations are dangerous and cause a reduction in the load-carrying capacity. All walls of the hybrid column were plane and made of many layers. The outer layers were thermal barriers and made of a TiC ceramic layer or an AL-TiC-type FGM. The inner layers were composed of aluminium layers and a few carbon-epoxy laminate layers. The classical laminate theory is used to define the ABD matrix which described the relations between applied loads and the associated deformations. The layup configuration of the hybrid column is general, so the coupling submatrix B is non-trivial. This submatrix has a significant impact on the value of local buckling load, whereas its effect on the value of global buckling load can be neglected. The main topic discussed in this paper is whether and how individual elements of the B submatrix can change the load-carrying capacity of a hybrid column. A detailed discussion is conducted for simple supported columns with opened cross-sections subjected to mechanical loads only. Thermal effects are neglected. [ABSTRACT FROM AUTHOR]

The present paper deals with the linear and non-linear dynamic instability of functionally graded materials (FGMs) plate subjected to non-uniform loading. Due to this loading, the in-plane stress distributions within the FG plate in pre-buckling state are evaluated using plate membrane analysis. The FG plate is modeled using higher order shear deformation theory (HSDT) considering von-Kármán geometric nonlinearity. The Galerkin’s method is used to reduce the non-linear governing partial differential equations into a set of ordinary differential equations describing the plate non-linear dynamic instability. Bolotin’s method is used to obtain the boundaries of dynamic instability regions. These boundaries are traced by the periodic solution of linear ordinary differential equation (Mathieu-Hill equation) with period T and 2T. Effects of power index, span-to-thickness ratio, aspect ratio, static load factor, boundary conditions and various types of linearly varying loadings and parabolically distributed loadings on the linear and nonlinear dynamic instability are studied. The study of linear and non-linear response in stable and unstable regions are carried out to identify the dynamic instability behaviour such as dependence of forcing frequency, existence of beats, effect of nonlinearity on the response and influence of the initial conditions. [ABSTRACT FROM AUTHOR]