Buckling and postbuckling of CNT-reinforced composite sandwich cylindrical panels subjected to axial compression in thermal environments

An analytical investigation on the buckling and postbuckling behavior of carbon nanotube reinforced composite (CNTRC) sandwich cylindrical panels exposed to thermal environments and subjected to uniform axial compression is presented in this paper. Beside sandwich model with CNTRC face sheets in the literature, the present work suggests a sandwich model with CNTRC core layer and homogeneous face sheets. Carbon nanotubes (CNTs) are reinforced into matrix phase through uniform or functionally graded distributions. Effective properties of nanocomposite layers are determined according to extended rule of mixture. Formulations are based on the first order shear deformation theory taking into account Von Karman-Donnell nonlinearity. Approximate solutions are assumed to satisfy simply supported boundary conditions and Galerkin method is used to derive the closed-form expression of nonlinear load-deflection relation from which buckling loads and postbuckling paths are determined. Numerical examples are carried out and interesting remarks are given

EFFECT OF STATIC AND HARMONIC LOADING ON THE HONEYCOMB SANDWICH BEAM BY USING FINITE ELEMENT METHOD

The aim of this paper is to present a proposed honeycomb core shape and compare it with a normal hexagonal shape core in a sandwich beam. The sandwich cores are simulated in finite element with different materials; aluminum and epoxy-carbon with six layers are used as face sheet and the results are compared to those obtained theoretically. Simulation of 3-point bending test is performed in commercial software ANSYS to verify the analytical results with the numerical ones. Hence, for simplicity one layer of the skin is used on the equivalent model of sandwich for lesser computational time and more accurate evaluation. Simulation of harmonic analysis of hexagonal core and proposed core shape is carried out in frequency domain to identify the core with less deformation under high frequency and it can withstand harmful effects. The proposed core shape model having the same cell numbers and material as the normal hexagonal model is compared with experimental results; it is observed that the proposed core shape model has good flexural stiffness, resonance, fatigue, and stress resistance at a higher frequency

GEOMETRICALLY NONLINEAR ANALYSIS OF PIEZOELECTRIC ACTIVE LAMINATED SHELLS BY MEANS OF ISOGEOMETRIC FE FORMULATION

The topic of piezoelectric active thin-walled structures has attracted a great deal of attention over the previous couple of decades. Lightweight structures with piezoelectric material based active elements, sensors and actuators, offer numerous advantages over their passive counterparts. This explains the motivation of authors to dedicate their work to this enticing research field. Accurate and reliable numerical tools for modeling and simulation of this type of structures is still a hot topic in the research community. This paper offers an isogeometric finite element formulation for shell type of structures made of composite laminates including piezoelectric layers characterized by the electro-mechanical coupling. The shell kinematics is based on the Mindlin-Reissner assumptions, thus including the transverse shear effects. A few examples selected from the available literature are considered to demonstrate the applicability of the developed numerical tool and assess its performance

A COMBINED STRAIN ELEMENT TO FUNCTIONALLY GRADED STRUCTURES IN THERMAL ENVIRONMENT

Functionally graded materials are commonly used in a thermal environment to change the properties of constituent materials. They inherently withstand high temperature gradients due to a low thermal conductivity, core ductility, low thermal expansion coefficient, and many others. It is essential to thoroughly study mechanical responses of them and to develop new effective approaches for an accurate prediction of solutions. In this paper, a new four-node quadrilateral element based on a combined strain strategy and first-order shear deformation theory is presented to achieve the behaviour of functionally graded plate/shell structures in a thermal environment. The main notion of the combined strain strategy is based on the combination of the membrane strain and the shear strain related to tying points as well as bending strain with respect to a cell-based smoothed finite element method. Due to the finite element analysis, the first-order shear deformation theory (FSDT) is simple to implement and apply for structures, but the shear correction factors are used to achieve the accuracy of solutions. The author assumes that the temperature distribution is uniform throughout the structure. The rule of mixtures is also considered to describe the variation of material compositions across the thickness. Many desirable characteristics and the enforcement of this element are verified and proved through various numerical examples. Numerical solutions and a comparison with other available solutions suggest that the procedure based on this new combined strain element is accurate and efficient

Multimode Nonlinear Vibration Analysis of Stiffened Functionally Graded Double Curved Shells in a Thermal Environment

The motivation of the current work is to develop a multi-modal analysis of the nonlinear response of stiffened double curved shells made of functionally graded materials under thermal loads. The formulation is based on the first order shear deformation shell theory in conjunction with the von Kármán geometrical nonlinear strain-displacement relationships. The nonlinear equations of motion of stiffened double curved shell based on the extended Sanders’s theory were derived using Galerkin’s method. The resulting system of infinite nonlinear ordinary differential equations, that includes both cubic and quadratic nonlinear terms, was solved using a nonlinear dynamic software XPPAUT to obtain the force-amplitude relationship. The effect of both, longitudinal and transverse stiffeners, was considered using the Lekhnitsky’s technique and the material properties are temperature dependent and vary in the thickness direction according to the linear rule of mixture. In order to obtain accurate natural frequency in thermal environments, critical buckling temperature differences are carried out, resulting in closed form solutions. The effect of temperature’s variation as well as power index, functionally graded stiffeners, geometrical parameters, temperature depended materials and initial imperfection on the nonlinear response of the stiffened shell are considered and discussed. This dissertation showed that the nonlinear study of problems of thin-walled structures with even stiffeners is of paramount importance. It was also found that the difference between single-mode and multi-mode analyses could be very significant for nonlinear problems in a thermal environment. Hence, multimode vibration analysis is necessary for structures of this nature

Static and free vibration analysis of laminated composite skew plate with and without cutout

Most of the structures generally under severe static and dynamic loading and different constrained conditions during their service life. This may lead to bending, buckling and vibration of the structure. Therefore, it is necessary to predict the static and vibration responses of laminated composite plates/skew plates precisely with less computational cost and good accuracy of these complex structures and. A suitable finite element model is proposed and developed based on first order shear deformation theory using ANSYS parametric design language (APDL) code. This is well that, the theory accounts for the linear variation of shear stresses along the longitudinal and thickness direction of the laminates. The model has been discretised using an appropriate four noded isoparametric element (SHELL181) from the ANSYS element library. The free vibration and bending responses are computed using Block-Lanczos and Gauss elimination algorithm steps. The responses like, transverse deflections, normal and shear stresses and natural frequencies of composite laminates are obtained through batch method of APDL code. The convergence test has been done of the developed model for all different cases and compared with those available published literature. Parametric effects (modular ratio, support conditions, ply orientations, number of layers, thickness ratio, geometry of cutout, cutout side to plate side ratio and skew angle) on the static and free vibration responses are discussed in detail

Stability Analysis of Plates and Shells

This special publication contains the papers presented at the special sessions honoring Dr. Manuel Stein during the 38th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference held in Kissimmee, Florida, Apdl 7-10, 1997. This volume, and the SDM special sessions, are dedicated to the memory of Dr. Manuel Stein, a major pioneer in structural mechanics, plate and shell buckling, and composite structures. Many of the papers presented are the work of Manny's colleagues and co-workers and are a result, directly or indirectly, of his influence. Dr. Stein earned his Ph.D. in Engineering Mechanics from Virginia Polytechnic Institute and State University in 1958. He worked in the Structural Mechanics Branch at the NASA Langley Research Center from 1943 until 1989. Following his retirement, Dr. Stein continued his involvement with NASA as a Distinguished Research Associate

A NEW C0 THIRD-ORDER SHEAR DEFORMATION THEORY FOR THE NONLINEAR FREE VIBRATION ANALYSIS OF STIFFENED FUNCTIONALLY GRADED PLATES

Nonlinear free vibration of stiffened functionally graded plates is presented by using the finite element method based on the new C0 third-order shear deformation theory. The material properties are assumed to be graded in the thickness direction by a power-law distribution. Based on the Von Karman theory and the third-order shear deformation theory, the nonlinear governing equations of motion are derived from the Hamilton’s principle. An iterative procedure based on the Newton-Raphson method is employed in computing the natural frequencies and mode shape. The comparison between these solutions and the other available ones suggests that this procedure is characterized by accuracy and efficiency

Large-Amplitude Vibration of Imperfect Rectangular, Circular and Laminated Plate with Viscous Damping

Large-amplitude vibration of thin plates and shells has been critical design issues for many engineering structures. The increasingly more stringent safety requirements and the discovery of new materials with amazingly superior properties have further focused the attention of research on this area. This thesis deals with the vibration problem of rectangular, circular and angle-ply composite plates. This vibration can be triggered by an initial vibration amplitude, or an initial velocity, or both. Four types of boundary conditions including simply supported and clamped combined with in-plane movable/immovable are considered. To solve the differential equation generated from the vibration problem, Lindstedt\u27s perturbation technique and Runge-Kutta method are applied. In previous works, this problem was solved by Lindstedt\u27s Perturbation Technique. This technique can lead to a quick approximate solution. Yet based on mathematical assumptions, the solution will no longer be accurate for large amplitude vibration, especially when a significant amount of imperfection is considered. Thus Runge-Kutta method is introduced to solve this problem numerically. The comparison between both methods has shown the validity of the Lindstedt\u27s Perturbation Technique is generally within half plate thickness. For a structure with a sufficiently large geometric imperfection, the vibration can be represented as a well-known backbone curve transforming from soften-spring to harden-spring. By parameter variation, the effects of imperfection, damping ratio, boundary conditions, wave numbers, young\u27s modulus and a dozen more related properties are studied. Other interesting research results such as the dynamic failure caused by out-of-bound vibration and the change of vibration mode due to damping are also revealed