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This work deals with the damping and vibration characteristics evaluation of sandwich beams based on higher-order shear deformation theories (HSDT's). The studied sandwich beams are composed of composite materials at faces and homogeneous, isotropic viscoelastic material in the core layer. This latter (viscoelastic material) is described by complex Young's modulus in the frequency domain. Indeed, the real part represents the stiffness, and the imaginary one describes the damping property. Nonlinear damping parameters and frequency curves are obtained using the nonlinear equation of frequency amplitude governed by multiple complex coefficients. In conjunction with a one-mode Galerkin's procedure, the harmonic balance method is employed to obtain the nonlinear loss factor and the response frequency curves. The nonlinear frequency value and, in turn, the system loss factor ratio are obtained for various amplitudes to examine the impacts of the ply angle of fiber-reinforced composite faces, the viscoelastic shear modulus, the shear deformation model, for considering different geometric and material parameters. In the framework of this study, one attempt is to describe a better way to achieve satisfactory passive vibration control of the laminated beams. [ABSTRACT FROM AUTHOR]

This work aims to examine the stability of rectangular hollow section (RHS) beams with functionally graded (FG) thin walls that are subjected to thermo-mechanical loads and different boundary conditions. A nonlinear analytical model for predicting thermal buckling that introduces distortional deformation and takes porosity into account is presented. Using Ritz’s method, coupled nonlinear equilibrium equations are established and then the tangential matrix is formed to obtain critical values. Material properties vary continuously and progressively across the thickness according to a power law of the porous volume fraction and are assumed to be unrelated to the temperature. A finite element (FE) simulation using the FE ABAQUS software is employed to verify the applicability of the current model in predicting lateral torsional buckling (LTB) resistance. Several numerical examples are used to illustrate the impacts of temperature, porosity, power-law index, and axial loads on the instabilities of FG box beams. [ABSTRACT FROM AUTHOR]