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In this paper, free axial vibration of nanorods is investigated by focusing on the inertia of the lateral motions effects. To this end, Rayleigh and nonlocal theories considering the inertia of the lateral motions and the small scale effects, respectively, are used. Then, by implementing the Hamilton’s principle nonlocal governing equation of motion and boundary conditions are derived. Since using nonlocal elasticity causes that the 2-order local governing equation is changed to the 4-order nonlocal governing equation while number of boundary condition remains constant (one boundary condition at each end of nanorod), the governing equation is solved using Rayleigh-Ritz method. In Rayleigh-Ritz method a suitable shape function for the problem should be selected. The shape function must at least satisfy the geometrical boundary conditions. In the present study, orthogonal polynomials are selected as shape functions then they are normalized by using the Gram-Schmidt process for more rapid convergence. Then, the first five axial natural frequencies of nanorod with clamped-clamped and clamped-free end conditions are obtained. In the next step, effects of various parameters like length of nanorod, diameter of nanorod and nonlocal parameter value on natural frequencies are investigated. Results of the present study can be useful in more accurate design of nano-electro-mechanical systems in which nanotubes are used.

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In this work, axial vibration of nanorod was analyzed based on two phase integro-differential nonlocal elasticity theory using isogeometric method. Two phase integro-differential nonlocal elasticity theory not only shows the nonlocal property in an integrated manner based on kernel weight function, but also combines local and nonlocal linear curvature for a two phase nonlocal elastic material. The new isogeometric approach combines finite element method with computational geometry and can present an accurate geometric model for the problem. Also, using b-spline basis functions with arbitrary continuity order, it can be a better alternative for classical finite element methods. The obtained results indicated that isogeometric approach was superior to finite element method in term of speed and convergence quality. Moreover, in this model, the effects of phase and nonlocal parameters on the natural frequencies of the nanorod were investigated and it was shown that increase of parameters of local phase and nonlocal length scale, respectively, increased and decreased the values of natural frequencies of nanorods. Finally, for two special cases, asymptotic frequencies for a single type of nonlocal rod, two phase integro-differential was obtained and the results were compared with corresponding available differential Eringen results.

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In the present paper, free axial vibration behavior of functionally graded nanorods is studied using the surface elasticity theory. For modelling of free axial vibration of nanorods, the Simple theory of rods is implemented. Besides using the Simple theory of rods, the surface elasticity theory is used for considering the surface energy parameters in the governing equations and boundary conditions. The surface energy parameters are the surface elasticity, the surface density, and the surface residual stress. The surface and bulk material properties of nanorod are considered to vary in the length direction according to the power law distribution. Then, the governing equation of motion and boundary conditions of nanorod are derived using the Hamilton’s principle. Due to considering the surface energy parameters, the obtained governing equation of motion becomes non-homogeneous. But in none of the previous researches, for example investigation of free transverse vibration of nanobeams and free torsional vibration of nanorods in presence of the surface energy, the surface energy parameters do not cause the non-homogeneity of the governing equation or the boundary conditions. To extract the natural frequencies of the nanorod, firstly the non-homogeneous governing equation is converted to a homogeneous one using an appropriate change of variable, and then for clamped-clamped and clamped-free boundary conditions the governing equation is solved using Galerkin method. In order to have a comprehensive research, effects of various parameters like the length and radius of nanorod on axial frequencies of functionally graded nanorod is investigated.