S. Amir

Electro-thermal non-local vibration analysis of embedded DWBNNTs

In this article, electro-thermal transverse vibration behaviour of double-walled boron nitride nanotubes embedded in a surrounded elastic medium is investigated using non-local piezoelasticity cylindrical shell theory. The effects of the elastic medium including Winkler spring and Pasternak shear constants and van der Waals interaction between inner and outer nanotubes are taken into account. The higher order governing equations of motion are derived based on Hamiltons principle. Effects of parameters such as Winkler spring constant, Pasternak shear constant, electric field, and temperature change on the dimensionless natural frequency are investigated. The results indicate a decrease in the dimensionless natural frequency as both temperature change and electric field are increased for various aspect ratios. However, the decreasing trend is significant for the former and may be considered constant for the latter.

Nonlocal vibration and instability analysis of embedded DWCNT conveying fluid under magnetic field with slip conditions consideration

In this study, vibration of double-walled carbon nanotubes (DWCNTs) conveying fluid placed in uniform magnetic field is carried out based on nonlocal elasticity theory. DWCNT is embedded in Pasternak foundation and is simulated as a Timoshenko beam (TB) model which includes rotary inertia and transverse shear deformation in the formulation. Considering slip boundary conditions and van der Waals (vdW) forces between inner and the outer nanotubes, the governing equations of motion are discretized and differential quadrature method (DQM) is applied to obtain the frequency of DWCNTs for clamped–clamped boundary condition. The detailed parametric study is conducted, focusing on the remarkable effects of small scale, Knudsen number, elastic medium, magnetic field, density, and velocity of conveying fluid on the stability of DWCNT. Results indicate that considering slip boundary conditions has significant effect on stability of DWCNTs. Also, it is found that trend of figures have good agreement with the previous researches. Results of this investigation could be applied for optimum design of nano/micro mechanical devices for controlling stability of DWCNTs conveying fluid under magnetic fields.

Nonlinear vibration analysis of protein microtubules in cytosol conveying fluid based on nonlocal elasticity theory using differential quadrature method

In this article, nonlinear vibration of protein microtubules in cytosol with internal flow is studied. Based on the Euler–Bernoulli beam theory with von Kármán nonlinearity type and using Hamilton’s principle, the equations of motion for fluid-conveying microtubules are derived. The size effect is taken into account using Eringen’s nonlocal elasticity theory; moreover, the effect of an elastic surrounding filament network and the surface traction of cytosol are studied. The governing differential equations for vibration response of microtubules are solved using the differential quadrature method. The nonlinear frequency response of microtubules, considering the effect of microtubule properties, size effect, the surrounding elastic media, and the fluid motion are reported in this article. It has been found that the effect of nonlocal parameter on the vibration behavior and instability of the embedded microtubule conveying fluid are significant. In this regard, we need to point out that the critical flow velocity for a range of nonlocality parameter from 0 to 2 nm varies between 41 and 47 m/s, which should be avoided due to instability of the microtubule system. Therefore, they should be taken into account in the design of nano/micro-devices for measuring density of a fluid, such as drugs flowing through such microtubules, with great applications in biomechanics.

Electro-thermo-mechanical response of thick-walled piezoelectric cylinder reinforced by boron-nitride nanotubes

Electro-thermo-elastic stress analysis of piezoelectric polymeric thick-walled cylinder reinforced by boron-nitride nanotubes subjected to electro-thermo-mechanical fields is presented. The electrothermo-elastic properties of piezoelectric fiber reinforced composite was studied by a modified XY micromechanical model capable of exhibiting full coupling relation between electric, thermal and elastic fields. Assuming piezoelectric fiber reinforced composite material and its composite constituents to be linear, homogenous, orthotropic, and perfectly bonded with uniform applied field, the basic relation for the axisymmetric deformation of a thick-wall cylinder subjected to uniform internal and external pressures, an axial electrical load, a temperature change between inner and outer radius are derived. Although the cylinder has end caps and is free to change length, displacement, strains, and stresses at location far removed from the end caps have been investigated. The stress results suggest that increasing boron-nitride nanotubes content in longitudinal direction reduces the effective stress. Displacement along radial direction indicates an optimum content of 5% boron-nitride nanotube for this. Furthermore, at normal working conditions, the influence of thermal and mechanical fields are much higher than the electric one on the effective stress; hence, this smart structure is best suited for applications as sensors than actuators.

Size-dependent vibration analysis of a three-layered porous rectangular nano plate with piezo-electromagnetic face sheets subjected to pre loads based on SSDT

ABSTRACT In the present research vibration of a porous rectangular plate which is located between two piezo-electromagnetic layers based on two variables sinusoidal shear deformation plate theory and according to nonlocal theory is investigated. The plate is resting on Winkler–Pasternak foundation and was subjected to pre loads. The motion equations have been obtained using Hamilton principle and are solved using analytical Naviers solution method. The effects of porosity coefficient, pores distribution, nonlocal parameter, pre load values, foundation constants and geometric size of the plate have been discussed in details. The results can be used to design more efficient sensors and actuators.

Buckling analysis of nanocomposite sandwich plates with piezoelectric face sheets based on flexoelectricity and first-order shear deformation theory

In piezoelectric materials and at the nano-scale, there is a coupling between electrical polarization and strain gradients fields, which is called flexoelectricity. The effects of this phenomenon seem to be negligible in micro/macro scales. The current study has attempted to have a cohesive concentration on the buckling behaviors of sandwich plates. To achieve the abovementioned aim with a higher accuracy, the flexoelectric effect assumes to be existing on the top and bottom face sheets and the core is a composite plate. Also, based on statistics, the first-order shear deformation theory seems to lead to more accurate results. Therefore, in the present research we follow this method to obtain results. The analytical method is applied to solve higher order governing equations. In addition, the critical buckling voltage is calculated considering the flexoelectricity, and it is found that the effects of flexoelectricity play significant roles in determining the critical buckling voltage. Moreover, it is revealed that the thickness of the flexoelectric face sheets and the aspect ratio of the sandwich plate play the same role in critical buckling load variations. It means that the critical buckling load decreases when the thickness of the flexoelectric face sheets or the aspect ratio of the sandwich plate increases and vice versa. The results of the present work can be used for the optimum design and control of similar systems such as micro-electro-mechanical and nano-electromechanical devices.

Nonlinear fluid-induced vibration and instability of an embedded piezoelectric polymeric microtube using nonlocal elasticity theory

Nonlinear vibration and instability of a smart piezoelectric microtube made of poly-vinylidene fluoride embedded in an elastic medium is investigated. The tube conveys an isentropic, incompressible fluid flowing in a fully developed irrotational manner. This smart microtube is modeled as a thin shell based on the nonlinear Donnells shell theory. Effects of mean flow velocity, fluid viscosity, elastic medium modulus, temperature change, imposed electric potential, small scale and aspect ratio on the vibration behavior of the microtube are analyzed. The results indicated that increasing mean flow velocity considerably changes the nonlinearity effects on instability of embedded piezoelectric polymeric microtube so that small scale and temperature change effects become negligible. It has also been found that stability of the system is strongly dependent on the imposed electric potential. The system studied in this article can be used as sensors and actuators in sensitive applications.