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CONTENTS
Volume 6, Number 2, June 2018
 

Abstract
An analytical solution of the buckling governing equations of functionally graded piezoelectric (FGP) nanobeams obtained by using a developed third-order shear deformation theory is presented. Electro-mechanical properties of FGP nanobeam are supposed to change continuously in the thickness direction based on power-law model. To capture the small size effects, Eringen's nonlocal elasticity theory is adopted. Employing Hamilton's principle, the nonlocal governing equations of a FG nanobeams made of piezoelectric materials are obtained and they are solved using Navier-type analytical solution. Results are provided to show the effect of different external electric voltage, power-law index, nonlocal parameter and slenderness ratio on the buckling loads of the size-dependent FGP nanobeams. The accuracy of the present model is verified by comparing it with nonlocal Timoshenko FG beams. So, this study makes the first attempt for analyzing buckling behavior of higher order shear deformable FGP nanobeams.

Key Words
functionally graded piezoelectric nanobeam; buckling; nonlocal elasticity theory; third-order beam theory

Address
(1) Farzad Ebrahimi:
Mechanical Engineering department, faculty of engineering, Imam Khomeini International University, Qazvin, P.O.B. 16818-34149, Iran;
(2) Mohammad Reza Barati:
Aerospace Engineering Department & Center of Excellence in Computational Aerospace, Amirkabir University of Technology, Tehran, Iran.

Abstract
In this work, free vibration characteristics of functionally graded piezoelectric (FGP) nanobeams based on third order parabolic shear deformation beam theory are studied by presenting a Navier type solution as the first attempt. Electro-mechanical properties of FGP nanobeam are supposed to change continuously throughout the thickness based on power-law model. To capture the small size effects, Eringen's nonlocal elasticity theory is adopted. Using Hamilton's principle, the nonlocal governing equations for third order shear deformable piezoelectric FG nanobeams are obtained and they are solved applying analytical solution. By presenting some numerical results, it is demonstrated that the suggested model presents accurate frequency results of the FGP nanobeams. The influences of several parameters including, external electric voltage, power-law exponent, nonlocal parameter and mode number on the natural frequencies of the size-dependent FGP nanobeams is discussed in detail.

Key Words
functionally graded piezoelectric nanobeam; free vibration; nonlocal elasticity theory; Reddy beam theory

Address
(1) Farzad Ebrahimi:
Department of Mechanical Engineering, Faculty of Engineering, Imam Khomeini International University, Qazvin, Iran;
(2) Ramin Ebrahimi Fardshad:
Faculty of Industrial and Mechanical Engineering, Qazvin Branch, Islamic Azad University, Qazvin, Iran.

Abstract
This work represents the study of the vibration response of the double walled carbon nanotubes (DWCNT) for various boundary conditions. The inner and outer carbon nanotubes are modeled as two individual Euler-Bernoulli's elastic beams interacting each other by Van der waals force. Differential transform method (DTM) is used as a numerical method to solve the governing differential equations and associated boundary conditions. The influence of Winkler elastic medium on vibration frequency is also examined and results are interpreted. MATLAB is used as a tool for solving the governing differential equations. The fundamental natural frequencies are validating with those available in literature and observed a good agreement between them.

Key Words
vibration; DWCNT; DTM; winkler; natural frequency

Address
School of Mechanical Engineering, SASTRA Deemed University, Thanjavur, Tamilnadu, 613401, India.


Abstract
A new nonlocal higher order shear deformation theory (HSDT) is developed for buckling properties of single graphene sheet. The proposed nonlocal HSDT contains a new displacement field which incorporates undetermined integral terms and contains only two variables. The length scale parameter is considered in the present formulation by employing the nonlocal differential constitutive relations of Eringen. Closed-form solutions for critical buckling forces of the graphene sheets are obtained. Nonlocal elasticity theories are used to bring out the small scale influence on the critical buckling force of graphene sheets. Influences of length scale parameter, length, thickness of the graphene sheets and shear deformation on the critical buckling force have been examined.

Key Words
buckling; graphene sheets; nonlocal elasticity; HSDT

Address
(1) Abed Bouadi, Abdelmoumen Anis Bousahla:
Centre Universitaire de Relizane, Algérie;
(2) Abed Bouadi, Abdelmoumen Anis Bousahla, Houari Heireche:
Laboratoire de Modélisation et Simulation Multi-échelle, Département de Physique, Faculté des Sciences Exactes, Département de Physique, Université de Sidi Bel Abbés, Algeria;
(3) Mohammed Sid Ahmed Houari, Abdelouahed Tounsi:
Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology, Civil Engineering Department, Algeria;
(4) Mohammed Sid Ahmed Houari:
Université Mustapha Stambouli de Mascara, Department of Civil Engineering, Mascara, Algeria;
(5) Abdelouahed Tounsi:
Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia.

Abstract
Based on the Reissner mixed variational theorem (RMVT), the authors present a nonlocal Timoshenko beam theory (TBT) for the nonlinear free vibration analysis of multi-walled carbon nanotubes (MWCNT) embedded in an elastic medium. In this formulation, four different edge conditions of the embedded MWCNT are considered, two different models with regard to the van der Waals interaction between each pair of walls constituting the MWCNT are considered, and the interaction between the MWCNT and its surrounding medium is simulated using the Pasternak-type foundation. The motion equations of an individual wall and the associated boundary conditions are derived using Hamilton's principle, in which the von Karman geometrical nonlinearity is considered. Eringen's nonlocal elasticity theory is used to account for the effects of the small length scale. Variations of the lowest frequency parameters with the maximum modal deflection of the embedded MWCNT are obtained using the differential quadrature method in conjunction with a direct iterative approach.

Key Words
foundations; multi-walled carbon nanotubes; nonlinear vibration; nonlocal Timoshenko beams; Reissner's mixed variational theorem; van der Waals interaction

Address
Department of Civil Engineering, National Cheng Kung University, Taiwan, ROC.


Abstract
In the present study silver nanoparticles (AgNPs) were successfully synthesized using aqueous extract of Sargassum muticum. The aqueous extract (10%) treated with 1 mM silver nitrate solution resulted in the formation of AgNPs and the surface plasmon resonance (SPR) of the formed AgNPs was recorded at 360 nm using UV-Visible spectrophotometer. The molecules involved in the formation of AgNPs were identified by Fourier transform infrared spectroscopy (FT-IR), surface morphology was studied by using scanning electron microscopy (SEM), SEM micrograph clearly revealed the size of the AgNPs was in the range of 40-65 nm with spherical, hexagonal in shape and poly-dispersed nature, and X-ray diffraction spectroscopy (XRD) was used to determine the crystalline structure. High positive Zeta potential (36.5 mV) of formed AgNPs indicates the stability and XRD pattern revealed the crystal structure of the AgNPs by showing the Bragg's peaks corresponding to (111), (200), (311) and (222) planes of facecentered cubic crystal phase of silver. The synthesized AgNPs exhibited effective anticancerous activity (at doses 25 and 50 μg/ml of AgNPs) against Breast cancer cell line (MCF7).

Key Words
Sargassum muticum; silver nanoparticles; antimicrobial activity; anti-cancerous efficacy

Address
(1) Nookala Supraja, J. Dhivya, Ernest David:
Department of Biotechnology, Thiruvalluvar University, Serkkadu, Vellore 632 115, TN, India;
(2) T.N.V.K.V. Prasad:
Nanotechnology Laboratory, Institute of Frontier Technology, Regional Agricultural Research Station, Acharya N G Ranga Agricultural University, Tirupathi 517 502, AP, India.


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