فهرست مطالب alireza shaterzadeh

In this article, the thermal buckling and post-buckling of functionally graded plates with a matrix of isotropic polymer reinforced with graphene platelets (GPLs) have been investigated. In these multilayer plates, the thickness of all layers is the same, and by changing the weight fraction of reinforcing graphene platelets in each layer, the type of layer arrangement of nanocomposite plates changes. The plates are reinforced with three functional graded distributions: X and O and a uniform U distribution. The governing equations of the plate are obtained with the help of the first-order shear deformation theory (FSDT). The thermal buckling behavior of plates has been studied by the differential quadrature method. To find the effective Young's modulus, the Halpin-Tsai modified micromechanical model is used, and the law of mixing is used to obtain the equivalent properties of composites. The results show that the distribution of graphene platelets with an X arrangement improves the resistance of the plate against buckling. Also, the effect of parameters such as the weight fraction of graphene platelets, aspect ratio, and length-to-thickness ratio has been investigated.

Vibration problems are of great importance in design and construction of electric machines which affect both of mechanical and electrical properties of these machines. In this paper, the effects of both perfect and perturbed conditions of cyclic symmetry on the vibration behavior of spinning ring under moving electromagnetic loading have been investigated. Euler-Bernoulli beam assumptions have been implemented in the modeling of structure and electromagnetic loading has been modeled with discrete springs. Using Hamilton’s principle, the governing equations of in-plane vibrations of spinning ring have been extracted. Eigen analysis of the system has been extracted using perturbation methods. The obtained results show the condition of instability for a precise value of ring angular speed versus support speed in different vibration modes. The effects of time variation of spring’s stiffness and the variation of connection angle between springs and ring on the in-plane vibration of spinning ring, have been investigated extensively. It is shown that the deviation from cyclic symmetry could eliminate the mode splitting phenomenon in some cases. The obtained results are expected to offer better predictions of the vibrational behavior of spinning rings structures under moving loads in general, and in the design of electric machines, in particular.

An experimental study on the critical buckling load of aluminum columns reinforced with glass/epoxy composite belts containing carbon nanotubes (CNTs) are presented in this paper. The columns with solid circular cross section are subjected to axially pressure load. Aluminum column specimens reinforced with glass/epoxy and CNT/glass/epoxy are fabricated. CNTs with 0.25, 0.5 and 1 weight percent (wt.%) are dispersed into the epoxy resin. Three layers composite belts are wrapped around the column. Glass fibers are placed along the column axes in each layer. The columns are tested under fix ended boundary conditions utilizing Instron hydraulic universal testing machine. Pressure load with respect to the end shortening are plotted for each specimen. To achieve the average value of critical buckling load, four specimen is examined for each composite belt material.  Results show that when 0.5%CNT/glass/epoxy composite belt is used to reinforce the column, the critical buckling load of the column increases by 45% with respect to the column with glass/epoxy composite belt. The proper dispersion of CNTs into the matrix material along with appropriate adhesion between the nanocomposite belt and the aluminum column lead to the increase of buckling load. Furthermore, to validate the results, buckling analysis of aluminum column reinforced with glass/epoxy composite belt was done in Abaqus finite element software. Finite element simulation confirms the experimental results obtained.

Optimization in the design and maintenance of many engineering systems, economic and even social has been used to minimize the cost or maximize profits. In the buckling analysis the hybrid composite plates with cutout, the effective parameters on buckling are the cutout geometry, fiber angle, cutout size to plate size ratio, bluntness of cutout corners, and rotation angle of cutout. Therefore, in this study, using genetic algorithm method an attempt has been made to introduce the optimum parameters to achieve the Maximum amount of critical buckling temperature of hybrid composite plate with polygonal cutouts in different boundary conditions and stacking sequences, which are subject to uniform temperature rise. The cutout in this study are circular, pentagonal, and hexagonal. The solving method used to analyze this study is the finite element based on the energy method. Also, the theory used in this paper is the first-order shear deformation theory. The results presented in this case show that by choosing the appropriate shape of cutout and the Optimal selection of parameters affecting buckling, the plate's resistance to thermal buckling can be increased. It was also found that stacking sequences and boundary conditions have a significant effect on the critical buckling temperature of a hybrid composite plate with cutout.

The eccentrically stiffened cylindrical shells are one of the most important structures in aerospace industries. In this paper, semi-analytical method for eccentrically stiffened functionally graded (FG) cylindrical shells under external pressure and surrounded by an elastic medium is presented. The proposed model is based on Winkler and Pasternak elastic foundation parameters. According to the Von Karman nonlinear equations and the classical plate theory (CPT) of shells, strain displacement relations are obtained. The smeared stiffeners technique and Galerkin method, used for solving nonlinear dynamic problem. With considering three terms approximation for the deflection shape, the frequency-amplitude relation for non-linear vibrations obtained. The nonlinear dynamic response is obtained from fourth order Runge-Kutta method. The nonlinear dynamic buckling behavior of stiffened FGM shells is investigated based on the Budiansky-Roth criterion. The effect of parameters such as eccentrically stiffened, elastic foundation and excitation force on the frequency-amplitude curve of the nonlinear vibrations and parameters such as damping and loading speed on the nonlinear dynamic response of the FGM cylindrical shells have been investigated. The natural frequency, static and dynamic buckling load are analyzed, too.

Exact and numerical solution of eccentrically stiffened panels in the industry is a major step forward in the design of these structures. This paper presents an analytical approach to investigate the nonlinear stability analysis of eccentrically stiffened thin FG cylindrical panels on elastic foundations subjected to hygro-thermo-mechanical loads. The stiffeners are assumed to be spiral-type. The panel has the initial geometrical imperfection. The material properties are assumed to be temperature-dependent and graded in the thickness direction according to a simple power law distribution. The elastic foundation is considered based on Winkler and Pasternak proposed model. Governing equations are derived basing on the Lekhnitsky smeared stiffeners technique and classical shell theory incorporating Von Karman-Donnell geometrical type nonlinearity. Explicit relations of load–deflection curves for FG cylindrical panels are determined by applying stress function and Galerkin method. The effects of angel of stiffener, different dimensional parameters, volume fraction index, initial geometrical imperfection, the stiffness of elastic foundation and moisture concentration on the postbuckling of FG panel are investigated. Also effects of temperature gradient through the thickness and effects of different boundary conditions are investigated for thermo-mechanical loading. The obtained results are validated by comparing with those in the literature.

Careful and numerical analysis eccentrically stiffened shells in the industry is a major step forward in the design of these shells. In this paper, a careful analysis of post-buckling behavior of eccentrically stiffened FGM thin circular cylindrical shells is surrounded by an elastic foundation and external pressure is presented. The two parameter elastic foundation based on Winkler and Pasternak elastic model is assumed. Stringer and ring stiffeners are internal. Shell properties and eccentrically stiffened are FGM. Fundamental relations and equilibrium equations are derived based on the smeared stiffeners technique and the classical theory of shells and according to von- Karman nonlinear equations. The three-term approximation for the deflection shape, including the pre-buckling, linear buckling shape and nonlinear buckling shape was chosen that using the Galerkin method, the critical load and post-buckling pressure-deflection curves is calculated. The effects of different dimensional parameters, buckling modes, volume fraction index and number of stiffeners are investigated. Numerical results show that stiffeners and elastic foundation enhance the stability of the shells. Increasing the shell thickness, reducing the volume fraction index, raising the number of Stringer and ring stiffeners and applying foundation elastic, causes the critical buckling load is increased, too.