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    Effect of surface stresses on elastic behavior of a screw dislocation inside the wall of a nanotube

    , Article Physica Status Solidi (B) Basic Research ; Volume 248, Issue 6 , 2011 , Pages 1437-1441 ; 03701972 (ISSN) Shodja, H. M ; Gutkin, M. Y ; Moeini Ardakani, S. S ; Sharif University of Technology
    Behavior of a screw dislocation inside a nanotube (NT) is considered in the context of surface elasticity. The elastic fields as well as the image force acting over the dislocation are derived and analyzed in detail. In contrast with the result of classical elasticity, the screw dislocation is shown to be repelled by free surfaces and occupy two stable equilibrium positions near them. The image force strongly depends on the NT's inner and outer radii as well as surface elastic characteristics  

    Elastic behavior of an edge dislocation inside the wall of a nanotube

    , Article Scripta Materialia ; Volume 64, Issue 8 , 2011 , Pages 709-712 ; 13596462 (ISSN) Moeini Ardakani, S. S ; Gutkin, M. Y ; Shodja, H. M ; Sharif University of Technology
    The problem of edge dislocation inside the wall of a multi-walled nanotube accounting for the surface effects is addressed. Within the framework of surface elasticity the stress field is obtained, using complex potentials. Furthermore, the stress field and image forces acting on the dislocation, with and without an account of the surface stress, are compared together and discussed  

    Small scale effects on the stability of carbon nano-peapods under radial pressure

    , Article Physica E: Low-Dimensional Systems and Nanostructures ; Volume 43, Issue 5 , March , 2011 , Pages 1050-1055 ; 13869477 (ISSN) Asghari, M ; Naghdabadi, R ; Rafati Heravi, J ; Sharif University of Technology
    In this paper, a nonlocal elasticity formulation is presented for analyzing the instability of nano-peapods by modeling the nanotube as a shell. Using the nonlocal elasticity theory, the small scale characteristics of Carbon Nano-Peapods (CNPs) are taken into account. While the classical elastic shell model overestimates the critical pressure for the onset of structural instability of carbon nanotubes, the obtained results show that the nonlocal elastic shell model for nano-peapods can potentially provide better predictions. According to the results, it is concluded that the presence of C 60 inside (10,10) Carbon Nanotubes (CNTs) significantly increases the stability resistance of the single... 

    Effects of couple stresses on anti-plane problems of piezoelectric media with inhomogeneities

    , Article European Journal of Mechanics, A/Solids ; Volume 26, Issue 4 , 2007 , Pages 647-658 ; 09977538 (ISSN) Shodja, H. M ; Ghazisaeidi, M ; Sharif University of Technology
    The examination of the effect of couple stresses on anti-plane electro-mechanical behaviour of piezoelectric media is of interest. The constitutive equations of piezoelectricity for a transversely isotropic piezoelectric medium of crystal class C6 v = 6   mm are derived in the context of couple stress elasticity. In this framework, a characteristic length appears in the formulation of anti-plane problems, by which examination of the size effect is possible. Also stemming from this approach is a new elasticity constant defined as the ratio of couple stress to the curvature, which based on the assumption of positive definiteness of the internal energy density, must be positive. For... 

    Size-dependent instability of carbon nanotubes under electrostatic actuation using nonlocal elasticity

    , Article International Journal of Mechanical Sciences ; Vol. 80 , 2014 , pp. 144-152 ; ISSN: 00207403 Seyyed Fakhrabadi, M. M ; Rastgoo, A ; Taghi Ahmadian, M ; Sharif University of Technology
    In this paper, the classical and nonlocal elasticity are applied to investigate the deflection and instability of electrostatically actuated carbon nanotubes. The results are presented for different geometries and boundary conditions. They reveal that increasing radius and gap and decreasing length confine to increasing pull-in voltages of the carbon nanotubes. The results prove that application of the nonlocal elasticity theorem leads to stiffer structures with higher pull-in voltages. Thus, in order to obtain more accurate results about the mechanical and electromechanical behaviors of the carbon nanotubes, one should apply the nonclassical elasticity theories such as that applied in this... 

    Nonlinear dynamic analysis of electrostatically actuated single-walled carbon nanotubes using nonlocal elasticity

    , Article Latin American Journal of Solids and Structures ; Volume 12, Issue 7 , 2015 , Pages 1224-1240 ; 16797817 (ISSN) Seyyed Fakhrabadi, M ; Rastgoo, A ; Ahmadian, M. T ; Sharif University of Technology
    Brazilian Association of Computational Mechanics  2015
    The paper investigates the effects of application of nonlocal elasticity theory on electromechanical behaviors of single-walled carbon nanotubes under electrostatic actuation. The influences of different dimensions and boundary conditions on the vibration and dynamic instability of the carbon nanotubes are studied, in detail, using this theory. The results reveal that application of the non-local elasticity theory leads to the higher pull-in voltages for the nonlocal model applied for carbon nanotubes. Thus, in order to have more accurate results, one should apply nonclassical theorems such as the nonlocal elasticity theory to scrutinize the mechanical and electromechanical behaviors of the... 

    Implementing an accurate generalized gaussian quadrature solution to find the elastic field in a homogeneous anisotropic media

    , Article Journal of the Serbian Society for Computational Mechanics ; Volume 11, Issue 1 , 2017 , Pages 11-19 ; 18206530 (ISSN) Kabir, H ; Matikolaei, S. A. H. H ; Sharif University of Technology
    In the current study, the elastic field in an anisotropic elastic media is determined by implementing a general semi-analytical method. In this specific methodology, the displacement field is computed as a sum of finite functions with unknown coefficients. These aforementioned functions exactly satisfy both the homogeneous and inhomogeneous boundary conditions in the proposed media. It is worth mentioning that the unknown coefficients are determined by implementing the principle of minimum potential energy. The numerical integration is done by employing the Generalized Gaussian Quadrature rule. Furthermore, and with the aid of the calculated unknown coefficients, the displacement fields as... 

    Surface elasticity revisited in the context of second strain gradient theory

    , Article Mechanics of Materials ; Volume 93 , 2016 , Pages 220-237 ; 01676636 (ISSN) Ojaghnezhad, F ; Shodja, H. M ; Sharif University of Technology
    Surface/interface stresses, when notable, are closely associated with a surface/interface layer in which the interatomic bond lengths and charge density distribution differ remarkably from those of the bulk. The presence of such topographical defects as edges and corners amplifies the noted phenomena by large amounts. If the principal features of interest are such studies as the physics and mechanics of evolving microscopic-/nanoscopic-interfaces and the behavior of nano-sized structures which have a very large surface-to-volume ratio, traditional continuum theories cease to hold. It is for the treatment of such problems that augmented continuum approaches like second strain gradient and... 

    Estimating Demand Function for Antihypertensives in Iran

    , M.Sc. Thesis Sharif University of Technology Roodi, Farshad (Author) ; Fatemi Ardestati, Farshad (Supervisor)
    The essential need for allocation of appropriate resources to the wellbeing and medication plans in a society can be understood from the fundamental impact of health on the performance of the labor force of the society, which can lead to significant increase in the economic growth rate. The high costs associated with research and development make pharmaceutical industry owners to be very vigilant about their investment on new drugs and expected sales. The purpose of this study is to evaluate current Iranian market for a part of Antihypertensive drugs and to estimate the demand for this group of drugs. The method used to obtain the estimation involved multi-stage budgeting, which benefits... 

    A study on a grade-one type of hypo-elastic models

    , Article ASME 2014 12th Biennial Conference on Engineering Systems Design and Analysis, ESDA 2014 ; Vol. 1 , 2014 Momeni, S. A ; Asghari, M ; Sharif University of Technology
    In Hypo-elastic constitutive models an objective rate of the Cauchy stress tensor is expressed in terms of the current state of the stress and the deformation rate tensor D in a way that the dependency on the latter is a homogeneously linear one. In this work, a type of grade-one hypo-elastic models (i.e. models with linear dependency of the hypo-elasticity tensor on the stress) is considered for isotropic materials based on the objective corotational rates of stress. A positive real parameter denoted by n is involved in the considered type. Different values can be selected for this parameter, each selection leads to a specific model within the class of grade-one hypo-elasticity. The spin of... 

    Ab initio calculations of characteristic lengths of crystalline materials in first strain gradient elasticity

    , Article Mechanics of Materials ; Volume 61 , 2013 , Pages 73-78 ; 01676636 (ISSN) Shodja, H. M ; Zaheri, A ; Tehranchi, A ; Sharif University of Technology
    Incorporation of the first gradient of strain, in addition to the strain itself, into the strain energy density of an elastic solid leads to Mindlin's first strain gradient theory, which is useful for examination of size effect as well as other mechanical phenomena at the nano-scale. For isotropic elastic solids, the first strain gradient theory, in addition to the two independent Lamé constants, gives rise to five new material constants which in turn reduce to two material parameters, ℓ1 and ℓ2 with dimension of length. The evaluation of these parameters, however, has posed serious challenges, both experimentally and theoretically. In this work ab initio method is used to compute the... 

    An FGM coated elastic solid under thermomechanical loading: A two dimensional linear elastic approach

    , Article Surface and Coatings Technology ; Volume 200, Issue 12-13 , 2006 , Pages 4050-4064 ; 02578972 (ISSN) Shodja, H. M ; Ghahremaninejad, A ; Sharif University of Technology
    A thin coating made of linear elastic functionally graded material (FGM) perfectly bonded to an elastic substrate is considered. This work which is of particular interest to tribological community is devoted to the determination of the thermal and mechanical stresses due to mixed normal and tangential Hertzian surface pressure. The thermomechanical properties of the FGM coating are assumed to vary exponentially through the thickness. Solutions for temperature rise and stresses are obtained by use of Fourier transform technique. The influences of coating thickness, Peclet number and friction coefficient on temperature rise and stresses in the FGM coating are investigated. Comparative studies... 

    Analysis of large amplitude free vibrations of clamped tapered beams on a nonlinear elastic foundation

    , Article Applied Mathematical Modelling ; Volume 38, Issue 3 , 1 February , 2014 , Pages 1176-1186 ; ISSN: 0307904X Baghani, M ; Mazaheri, H ; Salarieh, H ; Sharif University of Technology
    The purpose of this paper is to present efficient and accurate analytical expressions for large amplitude free vibration analysis of single and double tapered beams on elastic foundation. Geometric nonlinearity is considered using the condition of inextensibility of neutral axis. Moreover, the elastic foundation consists of a linear and cubic nonlinear parts together with a shearing layer. The nonlinear governing equation is solved by employing the variational iteration method (VIM). This study shows that the second-order approximation of the VIM leads to highly accurate solutions which are valid for a wide range of vibration amplitudes. The effects of different parameters on the nonlinear... 

    Free vibrations of single walled carbon peapods

    , Article Physica E: Low-Dimensional Systems and Nanostructures ; Vol. 56 , February , 2014 , pp. 410-413 Firouz-Abadi, R. D ; Hojjati, M ; Rahmanian, M ; Sharif University of Technology
    In this paper the free vibration of single walled carbon nanopeapods encapsulating C60 molecules is considered. The nanopeapod is embedded in an elastic medium and clamped at both ends. The Euler-Bernoulli beam model is used for the carbon nanotube and the C60 molecules are considered as lumped masses attached to the beam. Based on the nonlocal elasticity theory the governing equation of motion is derived and the resonance frequencies of the nanopeapod are obtained. The effects of small scale, foundation stiffness and ratio of the fullerenes' mass to the nanotube's mass on the frequencies are studied and some conclusions are drawn  

    Application of perturbation theory to elastic models of DNA

    , Article Proceedings of the 13th Regional Conference on Mathematical Physics, Antalya, Turkey ; October , 2013 , Pages 241-253 ; 9789814417525 (ISBN) Eslami-Mossallam, B ; Ejtehadi, M. R ; Sharif University of Technology
    In this paper, we demonstrate the applicability of the perturbation methods to different elastic models of DNA molecule. Two different kinds of perturbation methods are presented to find a first approximation for the force-extension characteristic of DNA in the anisotropic wormlike chain model, and the persistence length of DNA in the asymmetric elastic rod model. In both cases we show that it is meaningful to use the perturbation theory, and a first-order calculation is enough to find the result with an acceptable accuracy  

    Surface/interface effects on elastic behavior of an edge dislocation in the shell of a core-shell nanowire

    , Article European Journal of Mechanics, A/Solids ; Volume 41 , September–October , 2013 , Pages 86-100 ; 09977538 (ISSN) Gutkin, M. Yu ; Rezazadeh Kalehbasti, S ; Shodja, H. M ; Sharif University of Technology
    The elastic behavior of an edge dislocation placed in the shell of a free-standing core-shell nanowire is considered within the theory of surface/interface elasticity. Using the method of complex potential functions the expressions for the stress field of the dislocation, image forces on the dislocation, and the dislocation strain energy are derived and studied in detail. A special attention is paid to non-classical effects revealed within the surface/interface elasticity approach where a characteristic length parameter referred to as surface/interface modulus is introduced. These effects are (i) the stress oscillations along the shell surface and core-shell interface for negative values of... 

    Far-field dynamic behavior of a half-space under an inertial strip foundation subjected to a time-harmonic force

    , Article Latin American Journal of Solids and Structures ; Volume 10, Issue 3 , 2013 , Pages 453-471 ; 16797817 (ISSN) Dehestani, M ; Malidarreh, N. R ; Choobbasti, A. J ; Vafai, A ; Sharif University of Technology
    Recent research works demonstrated that the interaction between the loads and the carrying structure's boundary which is related to the inertia of the load is an influential factor on the dynamic response of the structure. Although effects of the inertia in moving loads were considered in many works, very few papers can be found on the inertial effects of the stationary loads on structures. In this paper, an elastodynamic formulation was employed to investigate the dynamic response of a homogeneous isotropic elastic half-space under an inertial strip foundation subjected to a time-harmonic force. Fourier integral transformation was used to solve the system of Poisson-type partial... 

    Determination of stress distribution around two Carbon Nonotubes embedded in infinite metal matrix using nonlocal theory of elasticity

    , Article Applied Mechanics and Materials, 29 July 2011 through 31 July 2011 ; Volume 110-116 , July , 2012 , Pages 1696-1700 ; 16609336 (ISSN) ; 9783037852620 (ISBN) Niaki, S. A ; Naghdabadi, R ; Sharif University of Technology
    Stress distribution in Carbon Nanotube (CNT) reinforced composites is studied using nonlocal theory of elasticity. Two nearby CNTs are modeled as two circular inclusions embedded in an infinite elastic medium, and classical stresses are obtained using the complex stress potential method. Nonlocal stresses are calculated using nonlocal integral elasticity equation. Effects of the distance between CNTs as well as effects of the nonlocal parameters on the stress distribution and stress concentration are studied. For unit normal stress at infinity, stress at the interface of the CNT and matrix increases from 0.1 for classical analysis to 0.85 for nonlocal analysis. Furthermore, when two CNTs... 

    Free vibration analysis of nanocones using a nonlocal continuum model

    , Article Physics Letters, Section A: General, Atomic and Solid State Physics ; Volume 375, Issue 41 , 2011 , Pages 3593-3598 ; 03759601 (ISSN) Firouz Abadi, R. D ; Fotouhi, M. M ; Haddadpour, H ; Sharif University of Technology
    This Letter aims at the investigation of free-vibration properties of nanocones based on a nonlocal continuum shell model. A novel approach is used for derivation of the governing equations of motion and the Galerkin technique is used to obtain the natural frequencies of vibrations. The effects of small-scale and geometrical parameters of the nanocone on the natural frequencies are studied and some conclusions are drawn  

    Buckling analysis of nonlocal anisotropic thin-walled cylindrical shells subject to combined loading

    , Article Journal of Engineering Mechanics ; Volume 142, Issue 12 , 2016 ; 07339399 (ISSN) Ghavanloo, E ; Fazelzadeh, S. A ; Sohrabpour, S ; Sharif University of Technology
    American Society of Civil Engineers (ASCE)  2016
    The equilibrium governing equations of nonlocal anisotropic thin-walled circular cylindrical shell under combined axial compressive force, torsional load, and external pressure are explicitly derived. This is accomplished by appropriately combining the equilibrium equations and the strain-displacement relations according to Flügge's shell theory and the stress-stain equations of Eringen's nonlocal elasticity theory. An analytical solution for the buckling of the shells is presented by using the complex method. This model is validated by a good agreement between the results given by the present model and available data in the literature. Furthermore, the model is utilized to elucidate the...