Showing papers by "Amin Hadi published in 2017"

Torsional vibration of nano-cone based on nonlocal strain gradient elasticity theory

Abstract: This paper investigates free torsional vibration behavior of a nonlinear nano-cone, based on the nonlocal strain gradient elasticity theory. The nano-cone is made of homogeneous and isotropic materials. Moreover, the cross-sectional area of the nano-cone varies in the longitudinal direction by a nonlinear function. Governing equation and boundary conditions are derived using Hamilton’s principle. These equations are solved by employing the generalized differential quadrature method (GDQM). The effects of some parameters, such as cross-sectional area change and small-scale parameter, are investigated. Results show that the cross-sectional area change has a significant effect on the torsional vibration behavior of the nano-cone. These results are also compared with the results reported in the literature, which shows consistency.

Analysis of functionally graded nanodisks under thermoelastic loading based on the strain gradient theory

Abstract: In this paper, the thermoelastic behavior of a functionally graded nanodisk is studied based on the strain gradient theory. It is assumed that the nanodisk thickness is constant, and a power-law model is adopted to describe the variation of functionally graded material properties. Furthermore, the nanodisk angular acceleration is taken to be zero while it is subjected to an axisymmetric loading. Also, it is assumed that any variation in temperature occurs only in the radial direction. The equilibrium equation and the boundary conditions are deduced from Hamilton’s principle. The obtained results are compared with those of classical theory. These results show that both theories predict the same trend for the variation in radial displacements. The differences between the stresses obtained from classical and strain gradient theories are clearly highlighted. Increasing the value of the material inhomogeneity parameter, n, considerably affects the magnitudes and the corresponding peak values of the high-order stress $$\bar{\tau }_{rrr}$$ . Any rise in temperature at the outside radius has a direct effect on the total stresses and radial displacements in the nanodisk. Also, the effects of external load at the inner and outer radii on radial displacement as well as stress components are fully investigated.

Size-Dependent Stress Analysis of Single-Wall Carbon Nanotube Based on Strain Gradient Theory

Abstract: This paper studies stress distribution in a single-walled carbon nanotube (SWCNT) under internal pressure with various chirality. Strain gradient theory is used to capture the size-dependent behavior of the SWCNT. Minimum total potential energy principle is successfully applied to derive the governing differential equation and its associated boundary conditions. Due to complexity of the governing differential equation and boundary conditions, numerical scheme is used to solve the problem. Comparing the results based on strain gradient theory and that of classical elasticity shows a major difference between these two methods. However, a close examination of the results indicates that both theories predict the same trend for variations in the radial displacement along the SWCNT radius. Numerical results also indicate that the proposed model can lead into the classical elasticity model, provided the material length scale parameters are taken to be zero. Additionally, for plane strain condition, the radial di...

A review of functionally graded thick cylindrical and conical shells

Abstract: Thick shells have attracted much attention in recent years as intelligent and functional graded materials because of their unique properties. In this review paper, some critical issues and problems in the development of thick shells made from Functionally graded piezoelectric material (FGPM) are discussed. This review has been conducted on various types of methods which are available for thick shell analysis and mainly focuses on elasticity theories, shear deformation theory, simplified theories and mixed theories since they were widely used in the modeling of FG thick shells. It is expected that this comprehensive study will be very beneficial to everyone involved or interested in the shell models.

Elastic analysis of functionally graded rotating thick cylindrical pressure vessels with exponentially-varying properties using power series method of Frobenius

Abstract: Based on the Frobenius series method, stresses analysis of the functionally graded rotating thick cylindrical pressure vessels (FGRTCPV) are examined. The vessel is considered in both plane stress and plane strain conditions. All of the cylindrical shell properties except the Poisson ratio are considered exponential function along the radial direction. The governing Navier equation for this problem is determined, by employing the principle of the two-dimensional elastic theories. This paper presents a closed-form analytical solution for the Navier equation of FGRTCPV as the novelty of the present paper. Moreover, a finite element (FE) model is developed for comparison with the results of the Frobenius series method. This comparison demonstrates that the results of the Frobenius series method are accurate. Finally, the effect of some parameters on stresses analysis of the FGRTCPV is examined. In order to investigate the inhomogeneity effect on the elastic analysis of functionally graded rotating thick cylindrical pressure vessels with exponentially-varying properties, values of the parameters have been set arbitrary in the present study. The presented outcomes illustrate that the inhomogeneity constant provides a major effect on the mechanical behaviors of the exponential FG thick cylindrical under pressure.

Consistent couple-stress theory for free vibration analysis of Euler-Bernoulli nano-beams made of arbitrary bi-directional functionally graded materials

Abstract: In this paper, using consistent couple stress theory and Hamilton\'s principle, the free vibration analysis of Euler- Bernoulli nano-beams made of bi-directional functionally graded materials (BDFGMs) with small scale effects are investigated. To the best of the researchers\' knowledge, in the literature, there is no study carried out into consistent couple-stress theory for free vibration analysis of BDFGM nanostructures with arbitrary functions. In addition, in order to obtain small scale effects, the consistent couple-stress theory is also applied. These models can degenerate into the classical models if the material length scale parameter is taken to be zero. In this theory, the couple-tensor is skew-symmetric by adopting the skew-symmetric part of the rotation gradients as the curvature tensor. The material properties except Poisson\'s ratio are assumed to be graded in both axial and thickness directions, which it can vary according to an arbitrary function. The governing equations are obtained using the concept of Hamilton principle. Generalized differential quadrature method (GDQM) is used to solve the governing equations for various boundary conditions to obtain the natural frequencies of BDFG nano-beam. At the end, some numerical results are presented to study the effects of material length scale parameter, and inhomogeneity constant on natural frequency.

Dielectrophoretic effect of nonuniform electric fields on the protoplast cell

Abstract: In recent years, dielectrophoresis based microfluidics systems have been used to manipulate colloids, inert particles, and biological microparticles, such as red blood cells, white blood cells, platelets, cancer cells, bacteria, yeast, micro‌organisms, proteins, DNA, etc. In the current study the governing electric potential equations have been solved in the presence of cell for the purpose of studying particle-electric field dielectrophoretic interaction. Immersed Interface Method (IIM) which is a modified finite difference method is used to solve the governing 2D elliptic electrostatic equations with irregular boundaries. A neutral particle polarizes under the application of an electric field and causes local nonuniformity in electrostatic potential distribution. So cells experience electric stresses on its surface. The electric stress on cell surface is calculated by Maxwell Stress Tensor (MST) on both sides of cell. DEP force is calculated by integrating electric stress on particle surface. In the present study calculated electric stresses is validated by DEP force calculated using EDM method and exact solution. we neglect other electrokinetic effects such as electrophoresis and electro-osmosis. Electrophoresis can be neglected if the particles are not charged. The effect of applied voltage, dielectric constants of cells and cells orientation on particle-particle interaction force has been studied.