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Volume 3, Number 1, February 2021

In this research, the behavior of free vibrations of sandwich structure with viscoelastic piezoelectric composite face sheets reinforced by Functionally Graded Carbon Nanotubes (FG-CNTs) and simply supported boundary conditions using a new improved higher-order sandwich panel theory were investigated. The viscoelastic sandwich structure is rested on viscoelastic foundation. There are 33 freedom degree based on higher order plate theories for top, center and bottom of the sandwich plate. To calculate exact solution, all of the stress components were engaged. The governing equations and boundary conditions were derived via the Hamilton's principle and finally, these equations solved by Navier's method. The accuracy of the present solutions is verified by comparing the obtained results with the existing solutions. The effect of different distributions of carbon nanotubes on non-dimensional natural frequency were inquired. Also, the effect of some important parameters such as those of length-to-thickness ratio and volume percentages of fibers, core thickness, elastic foundation, temperature and humidity changes, magnetic field, viscosity and voltage on free vibration response of sandwich structure were investigated.

Key Words
free vibration; sandwich structures; carbon nanotubes; viscoelastic foundation; piezoelectric

Alireza Pourmoayed:
Department of Mechanical Engineering, University of Khatamul-Anbiya Air Defense, Tehran, Iran
Keramat Malekzadeh Fard:
Department of Aerospace Engineering, MalekAshtar University of Technology, Tehran, Iran
Borhan Rousta:
Institute of Aviation Industry, Tehran, Iran

In this paper, the porosities effect on the dynamic analysis of the simply supported FGM sandwich plates is studied using a new refined shear deformation theory taking into account transverse shear deformation effects. This porosity may possibly occur inside the Functionally Graded Materials (FGMs) during their fabrication. Two common types of FGM sandwich plates are considered, namely, the sandwich with the FGM face sheet and the homogeneous core and the sandwich with the homogeneous face sheet and the FGM core. The results are presented for two constituent metal-ceramic functionally graded plates that have a power law through-the-thickness variation of the volume fractions of the constituents. The results obtained reveal that the dynamic response is significantly influenced by the volume fraction of the porosity, power law index, the thickness-side ratios and the thickness of the functionally graded layer.

Key Words
FGM sandwich plates; dynamic response; refined plate theory; porosity

Rabia Benferhat, Tahar Hassaine Daouadji and Rabahi Abderezak:
Laboratory of Geomatics and Sustainable Development, University of Tiaret, Algeria

This article presents a theoretical study taking into account the effect of air bubbles in concrete (as a material manufacturing defect) on interfacial stresses, in reinforced concrete beams, strengthening with an externally bonded FRP composite plate. Both even distribution and uneven distribution of the air bubbles are taken into account and the effective properties of RC beams with air bubbles are defined by theoretical formula with an additional term of porosity. In particular, reliable evaluation of the adhesive shear stress and of the stress in the composite plates is mandatory in order to predict the beam's failure load. The model is based on equilibrium and deformations compatibility requirements in and all parts of the strengthened beam, i.e. the concrete beam, the FRP plate and the adhesive layer. Numerical results from the present analysis are presented both to demonstrate the advantages of the present solution over existing ones and to illustrate the main characteristics of interfacial stress distributions. This research is helpful for the understanding on mechanical behaviour of the interface and design of the hybrid structures.

Key Words
imperfect RC beam; air bubbles, interfacial stresses; strengthening; composite plates

Benferhat Rabia, Tahar Hassaine Daouadji and Rabahi Abderezak:
Laboratory of Geomatics and sustainable development, University of Tiaret, Algeria;
Department of Civil Engineering, Ibn Khaldoun University of Tiaret, Algeria

The present paper deals with the study of Stoneley wave propagation at the interface of two dissimilar homogeneous orthotropic thermoelastic solids with three phase lags in the context of fractional order theory of thermoelasticity. By using appropriate boundary conditions the secular equations of Stoneley waves are derived in the form of the determinant. The wave characteristics like phase velocity, attenuation coefficient are computed numerically. The numerical simulated results have shown with the help of graphs to show the effect of fractional parameter on the phase velocity, attenuation coefficient, displacement components, stress components and temperature change.

Key Words
orthotropic medium; fractional order; Stoneley wave propagation; phase velocity; attenuation coefficient; phase lags

Parveen Lata and Himanshi:
Department of Basic and Applied Sciences, Punjabi University, Patiala, Punjab, India

This paper is concerned to investigate the static bending and buckling response of Functionally Graded (FG) nanobeams by employing a new refined first order shear deformation beam theory. The elegancy of this novel theory is that, not only has one variable in terms of equations of motion as in classical beam theory (EBT) but also accounts for the effect of transverse shear deformation without any requirement of Shear Correction Factors (SCFs). The material properties of FG nanobeam are supposed to change gradually across the thickness direction and are evaluated via the power-law model. Nonlocal elasticity theory of Eringen is incorporated in order to capture the small scale effect into current investigation. The nonlocal governing equations of motion and boundary conditions are obtained through Hamilton

Key Words
FG nanobeam; nonlocal elasticity theory; bending; buckling; novel refined beam model; one variable shear deformation

Ismail Bensaid and Ahmed Bekhadda:
IS2M Laboratory, Faculty of Technology, Mechanical Engineering Department, University Abou Beckr Belkaid (UABT), Tlemcen, Algeria
Bachir Kerboua:
Faculty of Technology, Mechanical Engineering Department, University Abou Beckr Belkaid (UABT), Tlemcen, Algeria

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