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    Molecular dynamics study of two dimensional silicon dioxides with in-plane negative poisson's ratio

    , Article Computational Materials Science ; Volume 153 , 2018 , Pages 258-267 ; 09270256 (ISSN) Safaei, S ; Tavakoli, R ; Jafary Zadeh, M ; Sharif University of Technology
    In the present work, the mechanical properties, in particular, the Poisson's ratio of four two-dimensional silica structures, called here α,β,γ and δ are studied by means of molecular dynamics simulations. The α structure has been synthesized experimentally and the others have been reported as the most stable low-energy structures that reveal in-plane negative Poisson's ratio based on the first principles calculations. Among these structures, β-silica exhibits the largest in-plane negative Poisson's ratio which is 2–4 times higher than penta-graphene. Our results illustrate that the classical molecular dynamics simulation reproduces results in agreement with those of the first principles... 

    Exploring Auxetic Metamaterials by Changing the Geometrical Parameters

    , M.Sc. Thesis Sharif University of Technology Ashouri, Amir (Author) ; Naghdabadi, Reza (Supervisor)
    The properties of metamaterials can be tailored through modification of their microstructures geometry. In this regard, a vast range of metamaterials have been designed. Auxetic metamaterials are a novel class of materials exhibiting the interesting characteristic of negative Poisson’s ratio. Theoretically, auxetic metamaterials have improved mechanical properties such as shear modulus and fracture toughness. The design and modeling of auxetic metamaterials is not completed yet. In order to exploit the interesting properties of auxetic metamaterials, their potential applications have been investigated in medical, sports, automobile and defense industries, so far. In the present work, the... 

    A Constitutive Model to Predict the Strain Rate Dependent Behavior of Auxetic Materials

    , M.Sc. Thesis Sharif University of Technology Heidari, Mohammad Hossein (Author) ; Arghavani, Jamal (Supervisor) ; Naghdabadi, Reza (Supervisor)
    A new types of architected cellular materials are those with negative poisoon’s ratio named auxetic. This materials indicate unormal behavior under different loads as if they were stretched in one direction, they also expanded in other directions and if pressure is exerted in one direction, they are compressed in all directions. Auxetic materials can improve mechanical properties such as shear strength, strength to weight ratio, thoghness, energy and vibration dissipation and crack expansion due to fatigue.The useful features of this material have been taken into account in a variety of industries, including the automotive industry, in the manufacture of parts such as body and bumper,... 

    Investigating The Mechanical Properties Of Two-Dimensional Silicon Dioxide With Inherent Negative Poisson's Ratio by Molecular Dynamics Method

    , M.Sc. Thesis Sharif University of Technology Ghorbani, Mohsen (Author) ; Tavakoli, Ruholah (Supervisor)
    Silicon dioxide or silica with the chemical formula SiO2 is the basic component of many minerals. SiO2 films and sheets are widely used in mechanics, optics and electronics due to their outstanding mechanical and electronic performance. The main reason for research in the field of materials with negative Poisson's ratio is their unusual properties, which arise due to the inherent property of negative Poisson's ratio. In this research, the mechanical properties of four two-dimensional silica structures at a temperature of one Kelvin were investigated with the help of molecular dynamics simulation. Also, the sensitivity of the results to the system size and strain rate was studied, and the... 

    Axisymmetric response of a bi-material full-space reinforced by an interfacial thin film

    , Article International Journal of Solids and Structures ; Volume 90 , July , 2016 , Pages 251–260 ; 00207683 (ISSN) Ahmadi, S. F ; Samea, P ; Eskandari, M ; Sharif University of Technology
    Elsevier Ltd  2016
    Analytical treatment of a linear elastic isotropic bi-material full-space reinforced by an interfacial thin film under axisymmetric normal loading is addressed. The thin film is modeled as an extensible membrane perfectly bonded to the half-spaces. By virtue of Love's potential function and Hankel integral transform, elastic fields of the system are explicitly written in the form of semi-infinite line integrals. The analytical results are verified by the special cases corresponding to the surface stiffened half-space and classical bi-material problem. The limiting cases of reinforced homogeneous full-space and inextensible membrane are presented and discussed. The proposed formulation is... 

    Evaluation of the equivalent mechanical properties in a novel composite cruciform honeycomb using analytical and numerical methods

    , Article Composite Structures ; Volume 275 , 2021 ; 02638223 (ISSN) Farrokhabadi, A ; Ashrafian, M. M ; Gharehbaghi, H ; Nazari, R ; Sharif University of Technology
    Elsevier Ltd  2021
    In the present study, a novel theoretical model is developed, based on the energy method, to predict the equivalent mechanical properties of a new morphing structure with zero Poisson's ratio, which is composed of continuous fiber reinforced composite struts. Due to the employing glass fiber in fabricating the proposed cruciform honeycomb, higher strength than the structures made of pure isotropic materials is obtained. The use of cells with a zero Poisson's ratio also increases the flexural strength of the structure. In the continuation of the paper, by examining the geometric effects on the equivalent properties, a parametric study is performed. Then, using the appropriate failure... 

    Mechanical properties of double-layered graphene sheets

    , Article Computational Materials Science ; Volume 69 , 2013 , Pages 335-343 ; 09270256 (ISSN) Hosseini Kordkheili, S. A ; Moshrefzadeh Sani, H ; Sharif University of Technology
    In this paper, the molecular structural mechanics method is employed to calculate the mechanical properties of a double-layered carbon graphene sheet more accurately. For this purpose, covalent bonds are modeled using nonlinear beam elements and van der Waals interactions are replaced by nonlinear truss elements. Morse potential and Lennard-Jones potential equations are used to simulate the covalent bonds and van der Waals interactions, respectively. For each atom, van der Waals forces are considered with respect to all the other atoms located in its cut-off radius. In addition to in-plane mechanical properties of single and double-layered graphene sheets some out-of-plane properties like... 

    Molecular dynamics investigation of β-SiC behavior under three-axial tensile loading

    , Article Journal of Computational and Theoretical Nanoscience ; Volume 8, Issue 11 , 2011 , Pages 2187-2192 ; 15461955 (ISSN) Mortazavi, B ; Simchi, A ; Besharati Givi, M. K ; Rajabpour, A ; Sharif University of Technology
    Molecular dynamics (MD) simulations were used to study the mechanical behaviour of β-SiC at nano-scale under tensile loading. Effects of loading rate and tensile temperature on the mechanical properties and failure were studied. Modified embedded-atom method (MEAM) potential and Berendsen thermostat were utilized for modelling. Periodic boundary conditions were employed and the behaviour of material was analyzed under three-axial loading condition at which the stress- strain relation was acceptably size independent. It is shown that with increasing the loading rate from 5 m/s to 70 m/s, the failure strain increases without a remarkable change in the stress-strain relationship. The MD... 

    Temperature and thickness effects on thermal and mechanical stresses of rotating FG-disks

    , Article Journal of Mechanical Science and Technology ; Volume 25, Issue 3 , 2011 , Pages 827-836 ; 1738494X (ISSN) Damircheli, M ; Azadi, M ; Sharif University of Technology
    In the present paper, radial and hoop thermal and mechanical stress analysis of a rotating disk made of functionally graded material (FGM) with variable thickness is carried out by using finite element method (FEM). To model the disk by FEM, one-dimensional two-degree elements with three nodes are used. It is assumed that the material properties, such as elastic modulus, Poisson's ratio and thermal expansion coefficient, are considered to vary using a power law function in the radial direction. The geometrical and boundary conditions are in the shape of two models including thermal stress (model-A) and mechanical stress (model-B). In model-A there exists no pressure in both external and... 

    Nonlinear thermoelastic stress analysis of the rotating FGM disk with variable thickness and temperature-dependent material properties using finite element method

    , Article ASME International Mechanical Engineering Congress and Exposition, Proceedings, 13 November 2009 through 19 November 2009 ; Volume 14 , 2010 , Pages 359-364 ; 9780791843871 (ISBN) Azadi, M ; Damircheli, M ; Sharif University of Technology
    In this paper, nonlinear radial and hoop thermoelastic stress analysis of rotating disk made of functionally graded material (FGM) with variable thickness is carried out by using the finite element method. In this method, one-dimensional second order elements with three nodes have been used. The geometrical and boundary conditions are in the shape of nonexistence of the pressure (zero radial stress) in both external and internal layers and zero displacement at the internal layer of rotating disk. Furthermore, it's assumed that heat distribution is as second order curve while material properties such as elasticity modulus, Poisson's ratio and thermal expansion coefficient vary by using a... 

    Nonlinear hierarchical multiscale modeling of cortical bone considering its nanoscale microstructure

    , Article Journal of Biomechanics ; Volume 42, Issue 10 , 2009 , Pages 1560-1565 ; 00219290 (ISSN) Ghanbari, J ; Naghdabadi, R ; Sharif University of Technology
    We have used a hierarchical multiscale modeling scheme for the analysis of cortical bone considering it as a nanocomposite. This scheme consists of definition of two boundary value problems, one for macroscale, and another for microscale. The coupling between these scales is done by using the homogenization technique. At every material point in which the constitutive model is needed, a microscale boundary value problem is defined using a macroscopic kinematical quantity and solved. Using the described scheme, we have studied elastic properties of cortical bone considering its nanoscale microstructural constituents with various mineral volume fractions. Since the microstructure of bone...