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Volume 7, Number 2, March 2019

This paper infer the transient vibration of piezoelectric sandwich nanobeams, In present work, the flexoelectric effect on the mechanical properties of vibration piezoelectric sandwich nanobeam with different boundary conditions is investigated. According to the Nonlocal elasticity theory in nanostructures, the flexoelectricity is believed to be authentic for such size-dependent properties. The governing equations are derived by Hamilton*$39;s principle and boundary condition solved by Galerkin-based solution. This research develops a nonlocal flexoelectric sandwich nanobeam supported by Winkler-Pasternak foundation. The results of this work indicate that natural frequencies of a sandwich nanobeam increase by increasing the Winkler and Pasternak elastic constant. Also, increasing the nonlocal parameter at a constant length decreases the natural frequencies. By increasing the length to thickness ratio (L/h) of nanobeam, the nonlocal frequencies reduce.

Key Words
vibration; piezoelectric sandwich nanobeam; flexoelectricity; surface effect; nonlocal elasticity theory; thermal effect

(1) Farzad Ebrahimi, Mahsa Karimiasl:
Department of Mechanical Engineering, Faculty of Engineering, Imam Khomeini International University, Qazvin, Iran
(2) Ömer Civalek:
Akdeniz University, Engineering Faculty, Civil Engineering Dept., Division of Mechanics, 07058 Antalya, Turkey;
(3) Mahesh Vinyas:
Department of Mechanical Engineering, Nitte Meenakshi Institute of Technology, Yelahanka, Bangalore, India.

In this work, the thermal buckling characteristics of zigzag single-walled boron nitride (SWBNNT) embedded in a one-parameter elastic medium modeled as Winkler-type foundation are investigated using a nonlocal first-order shear deformation theory (NFSDT). This model can take into account the small scale effect as well as the transverse shear deformation effects of nanotubes. A closed-form solution for nondimensional critical buckling temperature is obtained in this investigation. Further the effect of nonlocal parameter, Winkler elastic foundation modulus, the ratio of the length to the diameter, the transverse shear deformation and rotary inertia on the critical buckling temperature are being investigated and discussed. The results presented in this paper can provide useful guidance for the study and design of the next generation of nanodevices that make use of the thermal buckling properties of boron nitride nanotubes.

Key Words
boron nitride nanotube; critical buckling temperature; small scale effect; Winkler foundation

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

Higher-order theories are very important to investigate the mechanical properties and behaviors of nanoscale structures. In this study, a free vibration behavior of SiNW resting on elastic foundation is investigated via Eringen\'s nonlocal elasticity theory. Silicon Nanowire (SiNW) is modeled as simply supported both ends and clamped-free Euler-Bernoulli beam. Pasternak two-parameter elastic foundation model is used as foundation. Finite element formulation is obtained nonlocal Euler-Bernoulli beam theory. First, shape function of the Euler-Bernoulli beam is gained and then Galerkin weighted residual method is applied to the governing equations to obtain the stiffness and mass matrices including the foundation parameters and small scale parameter. Frequency values of SiNW is examined according to foundation and small scale parameters and the results are given by tables and graphs. The effects of small scale parameter, boundary conditions, foundation parameters on frequencies are investigated.

Key Words
nonlocal elasticity; nano beam; Euler Bernoulli beam theory; finite element formulation

(1) Büşra Uzun:
Uludağ University, Civil Engineering Department, Bursa-Turkiye;
(2) Ömer Civalek:
Akdeniz University, Civil Engineering Department, Antalya-Turkiye.

In this article, the free vibration analysis of annular sandwich plates with various functionally graded (FG) porous cores and carbon nanotubes reinforced composite (CNTRC) facesheets is investigated based on modified couple stress theory (MCST) and first order shear deformation theories (FSDT). The annular sandwich plate is composed of two face layers and a functionally graded porous core layer which contains different porosity distributions. Various approaches such as extended mixture rule (EMR), Eshelby-Mori-Tanaka (E-M-T), and Halpin-Tsai (H-T) are used to determine the effective material properties of microcomposite circular sandwich plate. The governing equations of motion are extracted by using Hamilton's principle and FSDT. A Ritz method has been utilized to calculate the natural frequency of an annular sandwich plate. The effects of material length scale parameters, boundary conditions, aspect and inner-outer radius ratios, FG porous distributions, pore compressibility and volume fractions of CNTs are considered. The results are obtained by Ritz solutions that can be served as benchmark data to validate their numerical and analytical methods in the future work and also in solid-state physics, materials science, and micro-electro-mechanical devices.

Key Words
free vibration analysis; circular annular sandwich plate; FG-porous core; CNTRC facesheets; EMR; EMT; HT approaches

Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, Kashan, P.O. Box 87317-53153, Iran.

The Origanum vulgare L.-mediated synthesis of Ag nanoparticles was successfully realized within the present study. Various concentrations of the AgNO3 used as a silver precursor (1, 2.5, 5, 10 and 100 mM) were used. Very rapid formation of Ag nanoparticles was observed, as only minutes were necessary for the completion of the reaction. With the increasing concentration, red shift of the surface plasmon resonance peak was observed in the Vis spectra. According to photon cross-correlation spectroscopy results, the finest grain size distribution was obtained for the 2.5 mM sample. The transmission electron microscopy analysis of this sample has shown bimodal size distribution with larger crystallites with 100 nm size and smaller around 10 nm. The antibacterial activity was also the best for this sample so the positive correlation between good grain size distribution and antibacterial activity was found. The in-depth discussion of antibacterial activity with related works from the materials science point of view is provided, namely emphasizing the role of effective nanoparticles distribution within the plant extract or matrix. The antibacterial activity seems to be governed by both content of Ag nanoparticles and their effective distribution. This work contributes to still expanding environmentally acceptable field of green synthesis of silver nanoparticles.

Key Words
silver nanoparticles; green synthesis; antibacterial activity; Origanum

(1) Matej Baláž, Mária Kováčová:
Department of Mechanochemistry, Institute of Geotechnics, Slovak Academy of Sciences, Watsonova 45, 04001 Košice, Slovakia;
(2) Ĺudmila Balážová, Mária Kováčová:
Department of Pharmacognosy and Botany, University of Veterinary Medicine and Pharmacy, Komenského 73, 04181 Košice, Slovakia;
(3) Nina Daneu:
Advanced Materials Department, Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia;
(4) Aneta Salayová, Zdenka Bedlovičová:
Department of Chemistry, Biochemistry and Biophysics, Institute of Pharmaceutical Chemistry, University of Veterinary Medicine and Pharmacy, Komenského 73, 04181 Košice, Slovakia;
(5) Ĺudmila Tkáčiková:
Department of Microbiology and Immunology, University of Veterinary Medicine and Pharmacy, Komenského 73, 04181 Košice, Slovakia.

The important effect of porosity on the mechanical behaviors of a continua makes it necessary to account for such an effect while analyzing a structure. motivated by this fact, a new two-step porosity dependent homogenization scheme is presented in this article to investigate the wave propagation responses of functionally graded (FG) porous nanobeams. In the introduced homogenization method, which is a modified form of the power-law model, the effects of porosity distributions are considered. Based on Hamilton's principle, the Navier equations are developed using the Euler-Bernoulli beam model. Thereafter, the constitutive equations are obtained employing the nonlocal elasticity theory of Eringen. Next, the governing equations are solved in order to reach the wave frequency. Once the validity of presented methodology is proved, a set of parametric studies are adapted to put emphasis on the role of each variant on the wave dispersion behaviors of porous FG nanobeams.

Key Words
wave propagation; porous materials; functionally graded materials (FGMs); nonlocal elasticity theory

(1) Farzad Ebrahimi, Ali Dabbagh:
Department of Mechanical Engineering, Faculty of Engineering, Imam Khomeini International University, Qazvin, Iran;
(2) Timon Rabczuk:
Institute of Structural Mechanics (ISM), Bauhaus-University Weimar, Weimar 1599423, Germany;
(3) Francesco Tornabene:
Department of Civil, Chemical, Environmental, and Materials Engineering, University of Bologna, Bologna, Italy.

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