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In the present study, the frequency analysis of a smart sandwich plate is investigated using the finite element method. The sandwich plate is consisted of a magnetorheological elastomer (MRE) layer between two cross ply composite elastic faces. MRE is a smart material with controllable properties and a short time response when subjected to a magnetic field. This property can be used for improvement of the dynamic behavior of the structure. To model the sandwich plate with MRE layer, a complex shear modules is used to show the pre-‌yield behavior of MRE layer. In this study, effect of imperative parameters are discussed. In the present paper, the effect of different parameters such as applied magnetic field, the stacking sequences of the cross ply laminated faces in the sandwich plate and applying different boundary conditions on the natural frequencies and modal loss factors of the smart sandwich plate with MRE is investigated. The results show that considering special value for magnetic field, the stacking sequences of the composite layers of the sandwich plate and the boundary condition of the sandwich structure can lead to the satisfactory design of the sandwich plate.

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This paper presents prediction of static behavior of composite beams with arbitrary anisotropic materials. The procedure is based on decomposing a 3-D nonlinear elasticity problem into a 2-D analysis of cross section and a 1-D analysis across the beam length. This is accomplished by assuming that magnitude of strain is small compared to unity and cross section size is small relative to wave length of deformation, inherent to beam-like structures. In 2-D cross sectional analysis warping functions are calculated in terms of 1-D strain parameters and finally, fully coupled classical stiffness constants are derived which include extension, torsion and bending in two directions. 1-D analysis is modeled by Finite Element Method through calculating beam strain energy. In this article warpings are derived using Rayleigh-Ritz method. The great advantage of using Rayleigh-Ritz is simplifying cross sectional analysis in contrast with the mesh generation in FEM of similar procedures. Different cross section stiffnesses are investigated for ply orientation angle. Calculated results for symmetric and anti-symmetric composite box beams correlate well with 3-D FEM using Abaqus software as well as experimental results. The present solution has more accurate results for anti-symmetric composite box beam. According to costly use of 3-D FEM analysis, the present procedure with high speed and acceptable accuracy, is truly sufficient for preliminary and optimization problems.

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This paper deals with the nonlinear transient vibration of composite sandwich plates with an electrorheological (ER) fluid core. The initial excitation is a distributed transverse load or the flutter instability due to supersonic airflow. The Bingham plastic model is adopted to accurately model the post-yield behavior of the ER material. . The first order piston theory is used for evaluating the aerodynamic forces. The von Karman strain-displacement relations are employed to account for moderately large deflection. The Hamilton’s principle is applied in conjunction with the finite element method to derive the equations of motion. The solution is then obtained through use the Newmark time integration scheme. Numerical investigations are conducted to study the effect of ER core layer on the vibration characteristics of the sandwich plate. The influence of the electric filed strength, ER core thickness, initial excitation and the boundary conditions on the settling time of transient vibration are also examined. The results show that the damping of transient vibration is significantly improved as the electric field applied to the ER layer, but the amplitude of post-flutter oscillations remains unchanged.

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This paper, presents the static analysis of composite beams with transverse shear effects using polynomials based dimensional reduction method. In dimensional reduction method, a three dimensional elasticity problem is split into a two dimensional cross section analysis and a one dimensional beam analysis. FEM is commonly used to analyze beam cross section in the literature. In this study, polynomial functions and Rayleigh-Ritz method are used to present an analytical procedure for two dimensional cross section analysis. Variational Asymptotic Method (VAM) is employed considering shear stiffnesses of composite beam cross section. VAM, asymptotically generates fully coupled cross section stiffness matrix. VAM benefits small parameters, related to characteristic length of cross section, to find stationary values of beam energy functional. By minimizing the energy functional with respect to warpings, in and out of plane warping functions are acquired. In this article, isotropic beams with different cross section geometries and symmetric as well as anti-symmetric composite box beams are investigated. Presented results show appropriate correlation of the present study with theoretical and experimental results, as well as 3D Finite Element analysis. Using dimensional reduction method reduces the computing time and empowers researchers to design and optimize composite beam-like structures.

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In this paper, dynamic stability of a laminated composite beam subjected to a tip follower force is investigated. Using elementary theory of bending, Euler-Bernoulli beam theory and Classical Lamination Theory (CLT), bending moment of laminated composite beam is calculated with respect to it’s extensional, bending and bending-extensional coupling stiffness matrices, A, B and D, and dynamic stability equation of laminated beam is established. Due to similarity between this equation and isotropic stability equation, as an assumption, isotropic beam boundary conditions are used for composite beam. Cantilever- free boundary conditions are used and a closed form solution is established. Flutter instability problems for symmetric and un– symmetric laminated beams are solved by this method and results are compared with finite element results in literatures. Considering the simplicity of the present method, results show good agreement with the finite element method. Finally dynamic stability behavior of laminates with different stacking sequences are investigated by present method and effect of different parameters such as fiber orientation, number of layers, and stacking sequence, on the flutter load and corresponding frequency of symmetric and un -symmetric laminates are investigated.

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Numerical investigation of failure modes of composite plates subjected to the hail ice impact presented in this paper. Compare to rain and snow, hail is known as a serious threat to the aircraft exterior structure and engine due to its high density. First, numerical simulation of composite plate subjected to a rigid projectile impact is conducted using commercial finite element software, LS-DYNA and validated with previous investigations. After validation, a numerical study is performed for a composite plate subjected to the hail impact and the effect of stacking sequences of composite plate, velocity and shape of projectile are investigated. Results show, for identical mass and velocity, only the matrix extensional mode occurs in hail impact while for the rigid impact all failure modes are observed. Also, increased fiber angle produced higher damage threshold velocity in ice impact. Highest and lowest damage showed for ±15° and ±45° orientations. Moreover, it has been observed that more layers damaged with larger velocity ice impact. Result illustrate that the cylindrical shape hail caused more damage compared with hemispherical shape.

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In this research, aero-thermo-elastic stability of fibrous laminated plates subjected to supersonic airflow has been investigated. The experimental method was used to determine the effect of carbon nanotubes on the thermo-elastic properties of the composite matrix material. Young’s modulus and linear coefficient of thermal expansion of neat epoxy and carbon nanotube reinforced epoxy was determined using the tensile test and dilatometry method. The modified Halpin-Tsi micromechanical model was used to characterize the mechanical properties of the carbon nanotubes-fiber-epoxy laminated composites. A rectangular simply supported plate subjected to supersonic airflow was assumed. The governing equation of motion was extracted using the energy method and Hamilton’s principle. Linear piston theory was used to evaluate the aerodynamic pressure. Galerkin's method was employed to solve the governing equation. The influence of adding carbon nanotubes in epoxy resin was illustrated when glass or carbon fibers were used as microscale reinforcements. Moreover, the effect of plate aspect ratio and temperature on the aeroelastic stability boundary was investigated. Results show that for the plates with high aspect ratio, adding carbon nanotubes into the epoxy resin has more effect on the aeroelastic stability boundary especially when the glass fibers are used. According to the results, in high temperatures, carbon nanotubes have less effect on the expanding of the stability region.