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    Effect of carbon nanotube geometries on mechanical properties of nanocomposite via nanoscale representative volume element

    , Article Journal of Solid Mechanics ; Volume 8, Issue 3 , 2016 , Pages 568-577 ; 20083505 (ISSN) Moghaddam, F ; Ghavanloo, E ; Fazelzadeh, S. A ; Sharif University of Technology
    Islamic Azad University  2016
    Predicting the effective elastic properties of carbon nanotube-reinforced nanocomposites is of great interest to many structural designers and engineers for improving material and configuration design in recent years. In this paper, a finite element model of a CNT composite has been developed using the Representative volume element (RVE) to evaluate the effective material properties of nanocomposites. Based on this model, the effects of geometrical characteristics such as the aspect ratio, orientation and volume fraction of the CNTs in conjunction with the interphase behavior on the mechanical properties of the nanocomposites are elucidated and the elastic properties of a complex polymeric... 

    Investigation of Mechanical Behavior of Short Carbon Nanotubes Reinforced Metal Matrix Nanocomposites Using Surface Elasticity Theory

    , M.Sc. Thesis Sharif University of Technology Saboori, Mohammad Ali (Author) ; Naghdabadi, Reza (Supervisor)
    In recent years, carbon nanotubes have been the focus of considerable researches. Numerous investigators have reported remarkable physical and mechanical properties for this new form of carbon. In particular, the exceptional mechanical properties of carbon nanotubes, combined with their low density, offer scope for the development of nanotube reinforced composite materials. The potential for nanocomposites reinforced with carbon tubes having extraordinary specific stiffness and strength represent tremendous opportunity for application in this century and recently metal matrix type of these nanocomposites, due to their advantages, have received great attention. Classical theories of... 

    Hierarchical Multiscale Modeling in Large and Plastic Deformations

    , M.Sc. Thesis Sharif University of Technology Sarkari Khorrami, Mohammad (Author) ; Khoei, Amir Reza (Supervisor)
    In this study, the hierarchical multiscale method is presented to model macro-scale materials with considering large and plastic deformations. Since the classic methods such as continuum mechanics were unable to model defects such as dislocations, voids, and etc. at nano scale. Also, the molecular dynamics methods have high computational costs; hence, recearchers try to develop multiscale methods in order to utilize them. Multiscale modeling in which two scales are considered and some information be transferred from fine scale to coarse scale. In this work, the coarse scale is modeled by finite element method (FEM) and the fine scale is analysed by molecular dynamics (MD). In fact, two... 

    Stress distribtuion on open-ended carbon nanotubes

    , Article 2008 Proceedings of the ASME - 2nd International Conference on Integration and Commercialization of Micro and Nanosystems, MicroNano 2008, 3 June 2008 through 5 June 2008, Kowloon ; 2008 , Pages 343-351 ; 0791842940 (ISBN); 9780791842942 (ISBN) Momeni, K ; Alasty, A ; Sharif University of Technology
    The stress distribution on open-ended Carbon Nanotubes (CNTs) embedded in a composite material is considered in this work and an analytical solution for the stress distribution has been obtained. The effects of CNT's thickness and CNT's length on the distribution of stress have been investigated. To find the governing relations, continuity equations of the axisymmetric problem in cylindrical coordinate (r,o,z) are used. Under some assumptions, the governing equations are solved and by using constitutive equations and applying the boundary conditions, an equation which relates the stress applied to the representative volume element with the stress distribution on the CNT, has been found. The... 

    Elastic solids with high concentration of arbitrarily oriented multiphase particles

    , Article Acta Mechanica ; Volume 189, Issue 3-4 , 2007 , Pages 125-139 ; 00015970 (ISSN) Roumi, F ; Shodja, H. M ; Sharif University of Technology
    Springer-Verlag Wien  2007
    The effective properties of elastic solids are strongly linked to their interacting micro-constituent phases. For materials containing dilute distributions of single-phase inhomogeneities, the overall behavior can be estimated in a straightforward manner. But in the non-dilute case, due to the complex inter-particle and particle-matrix interactions the treatment is rather involved. When the particles are heterogeneous, not only become the mentioned interactions more complex, but must properly account for the intra-particle interactions as well. The present work addresses an analytical approach to determine the overall moduli of elastic solids containing random distributions of arbitrarily... 

    A hierarchical thermo-mechanical multi-scale technique for modeling of edge dislocations in nano-crystalline structures

    , Article Computational Materials Science ; Volume 141 , 2018 , Pages 360-374 ; 09270256 (ISSN) Jahanshahi, M ; Khoei, A. R ; Heidarzadeh, N ; Jafarian, N ; Sharif University of Technology
    Elsevier B.V  2018
    In this paper, a hierarchical multi-scale technique is developed to investigate the thermo-mechanical behavior of nano-crystalline structures in the presence of edge dislocations. The primary edge dislocations are generated by proper adjustment of atomic positions to resemble discrete dislocations. The interatomic potential used to perform atomistic simulation is based on the Finnis-Sinclair embedded-atom method as many-body potential and, the Nose-Hoover thermostat is employed to control the effect of temperature. The strain energy density function is obtained for various representative volume elements under biaxial and shear loadings by fitting a fourth order polynomial in the atomistic... 

    A hierarchical hyperelastic-based approach for multi-scale analysis of defective nano-materials

    , Article Mechanics of Materials ; Volume 140 , January , 2020 Jahanshahi, M ; Ahmadi, H ; Khoei, A. R ; Sharif University of Technology
    Elsevier B.V  2020
    In this paper, a continuum–atomistic multi-scale method is presented in modeling the nonlinear behavior of nano-materials under large deformation. In order to identify an appropriate strain energy function for crystalline nano-structures with different percentages of spherical voids, the hyperelastic method is employed for specimen whose behavior is determined based on the molecular dynamics analyses. In the atomistic level, the EAM many-body potential is employed to model the interactions between the atoms of Al RVEs. The atomistic strain energy density curves and surfaces are generated by applying the uniaxial, biaxial and simple shear deformations to the boundaries of RVEs. The material... 

    Continuum Analysis of Defects Based on Atomistic Simulat

    , M.Sc. Thesis Sharif University of Technology Heidarzadeh, Narges (Author) ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Co-Advisor)
    In this study, a new multi-scale hierarchical technique has been employed to investigate the role of temperature on nano-plates with hex atomic structure. Different number of primary edge dislocations is considered and the temperature varies from 0 up to 800 K. Primary edge dislocations are created by proper adjustment of atomic positions to resemble discrete dislocations (DD’s) and then the application of equations of motion to the relaxed configuration of this adjustment. The interatomic potential used for atomistic simulation is Finnis-Sinclair Embedded-Atom-Method (FS-EAM) as many-body interatomic potential and the Nose-Hoover thermostat has been implemented to adjust the modulation of... 

    Multi-scale Analysis of Dislocation Emission for Nano-crystalline Structures

    , M.Sc. Thesis Sharif University of Technology Fattahi Faradonbeh, Mehran (Author) ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Supervisor)
    In this study, a new multi-scale hierarchical technique has been employed to investigate the role of edge dislocation on nano-plates with hex atomic structure in large deformation. Two multiscale hierarchical atomistic/molecular dynamics (MD)–finite element (FE) coupling methods are proposed to illustrate the influence of temperature on mechanical properties of Magnesium in large deformation. The atomic nonlinear elastic parameters are obtained via computing second-order derivative of Representative atom’s energy and RVE’s strain energy density with respect to deformation criterions (deformation gradient and Green strain tensor) to bridge between atomistic and continuum level, the... 

    Utilization of CT Scan Technique to Manipulate the Heterogeneity Effect
    in Reservoir Rock Properties Determination

    , M.Sc. Thesis Sharif University of Technology Salehi, Maryam (Author) ; Ayatollahi, Shahabodin (Supervisor) ; Fazel Abdol Abadi, Babak (Supervisor) ; Nematzadeh, Mostafa (Co-Advisor)
    Petrophysical properties of reservoir rocks are of the most important parameters in fluid flow simulation and reservoir characterization. Although in core laboratories some well-known procedures for determination of these parameters are applied, in almost all of them the rocks are assumed to be homogeneous and their properties are taken up as identical in all directions. To eliminate these unrealistic assumptions, an accurate, non-destructive technique with appropriate degree of resolution is required for recognition of internal heterogeneity of cores. Medical “CT Scanner” is one of these techniques whose information in conjunction of conventional experiments could reduce their limitations... 

    Multiscale Modeling of Cohesive Crack and Bulk for Softening Materials

    , M.Sc. Thesis Sharif University of Technology Saadat, Mohammad Ali (Author) ; Khoei, Amir Reza (Supervisor)
    Multiscale modeling is performed within the framework of homogenization methods for problems in which the scales are separated. The existence of representative volume element (RVE) is one of the main ingredients of homogenization methods. Due to non-existence of RVE and macroscale mesh sensitivity, the continuous homogenization method is not applicable for softening materials. Despite the non-existence of RVE for softening materials, it has been demonstrated that by performing the average over the active damage zone rather than the entire domain, objective responses with respect to RVE size could be obtained. That is why discontinuous homogenization is used instead of continuous... 

    Temperature-dependent Multi Scale Large Deformation Simulation of Heterogeneous Crystals

    , M.Sc. Thesis Sharif University of Technology Gordan, Ali (Author) ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Co-Advisor)
    In this study, a novel and unprecedented multi-scale hierarchical molecular dynamics (MD) – finite element (FE) coupling method is proposed to demonstrate the influence of temperature on mechanical properties of heterogeneous Nano-crystalline structures. The embedded-atom method (EAM) many-body interatomic potential is implemented to consider pairwise interactions between atoms in the metallic alloys with face-centered-cubic (FCC) lattice structure at different temperatures. In addition, the Nose-Hoover thermostat is employed to adjust the fluctuation of temperature. In order to calculate the equivalent lattice parameter, a weight average between the lattice parameters of atomic structures... 

    Application of Dynamics Multi-scale Modeling of Dislocation in Nano-Crystalline Materials

    , M.Sc. Thesis Sharif University of Technology Karimi, Hossein (Author) ; Khoei, Amir Reza (Supervisor)
    Dislocations are one of the most important classes of defects in crystals. They have significant effects on the physical properties of crystals. They could be primarily created during the formation of a crystal or during the loading on specimen. Dislocation’s movement due to stress is the main cause of crystal plasticity. Since dislocation is a change in perfect crystal structure it is possible to identify it in the molecular level. However, the high computational cost of the MD level, has led researchers to using the multi-scale methods. Researchers have used many various multi-scale methods to study dislocations. The method used in this paper is based on energy. Total energy of system for... 

    Modeling the Nonlinear Behavior of Nano-Materials Via Hierarchical RVE-based Multi-Scale Method

    , M.Sc. Thesis Sharif University of Technology Nikravesh Kazerooni, Yousef (Author) ; Khoei, Amir Reza (Supervisor)
    In this paper, a hierarchical RVE-based continuum-atomistic multiscale framework is established on the basis of the nonlinear finite element method and molecular dynamics simulation in order to model the geometric and material nonlinearities of deformable solids. In this framework, the coarse scale material properties required for nonlinear finite element method are directly exploited via fine scale atomistic simulation of atomic RVEs designated for each coarse scale integration point and required boundary conditions for atomic RVE simulation are achieved from the coarse scale kinematical response. In order to ensure the kinematical and energetic consistency between the two scales, the... 

    Hierarchical Multi-Scale Modeling of Large Plastic Deformation with Application in Powder Compaction

    , Ph.D. Dissertation Sharif University of Technology Rezaei Sameti, Amir (Author) ; Khoei, Amir Reza (Supervisor)
    The hierarchical multi-scale approach is one of the most powerful techniques that takes the advantage of different scales and succeeds the limitations of each method in a way that the large systems in coarse-scale can be simulated with atomic precision. In this thesis, the hierarchical atomistic-continuum multi-scale method is developed for modeling the phenomena with non-homogenous deformation, large deformation and plastic behavior. In this regard at first, an atomistic-based higher-order continuum model is formulated in the framework of nonlinear finite element method to present the geometrically nonlinear behavior of nano-structures. The efficiency of higher-order Cauchy-Born hypothesis... 

    A Progressive Multiscale Model to Predict the Fatigue life of Laminated Composite Reinforced with Nanoparticles

    , Ph.D. Dissertation Sharif University of Technology Toozandehjani, Hossein (Author) ; Hoseini Kordkhili, Ali (Supervisor)
    The increasing growth of composite materials in various industries and the use of these materials in the production of the main structures, recognized study and simulation of accurate behavior of these materials at different scales. On the other hand, the appearance of Nano-scale materials with amazing physical and mechanical properties and the use of these nanoparticles as reinforcement in the structure of polymer composites, further highlights the importance of simulating the behavior of polymer nanoparticles at different scales. One of the issues that is considered in various industries, especially in the airspace industry, is the phenomenon of fatigue. The complexity of the fatigue... 

    Micromechanic Failure Analysis of Carbon/Phenolic Composite Conic Structures under Thermal Loading

    , M.Sc. Thesis Sharif University of Technology Hodaei Esfahani, Mohammad Ali (Author) ; Hosseini Kordkheili, Ali (Supervisor)
    In this study, through explaining a micromechanical model of progressive damage, failure in a composite conical structure under mechanical and thermal loads with 36 layers of carbon/phenolic material have been studied. To this end, first, mechanical behaviors of composite layers in micro and macro scale and their properties via fiber and matrix characterizations are discussed. In the following, selection of a proper RVE along with different types of boundary conditions on RVE are discussed. Then stress reinforcement coefficients in order to convert the mechanical and thermal stresses from macro to micro scale for carbon / phenolic material are extracted through defining appropriate RVE for... 

    Multiscale nonlinear constitutive modeling of carbon nanostructures based on interatomic potentials

    , Article Computers, Materials and Continua ; Volume 10, Issue 1 , 2009 , Pages 41-64 ; 15462218 (ISSN) Ghanbari, J ; Naghdabadi, R ; Sharif University of Technology
    Continuum-based modeling of nanostructures is an efficient and suitable method to study the behavior of these structures when the deformation can be considered homogeneous. This paper is concerned about multiscale nonlinear tensorial constitutive modeling of carbon nanostructures based on the interatomic potentials. The proposed constitutive model is a tensorial equation relating the second Piola-Kirchhoff stress tensor to Green-Lagrange strain tensor. For carbon nanotubes, some modifications are made on the planar representative volume element (RVE) to account for the curved atomic structure resulting a non-planar RVE. Using the proposed constitutive model, the elastic behavior of the... 

    Investigation the stability of SWCNT-polymer composites in the presence of CNT geometrical defects using multiscale modeling

    , Article 4th International Conference on Multiscale Materials Modeling, MMM 2008, 27 October 2008 through 31 October 2008 ; 2008 , Pages 163-166 ; 9780615247816 (ISBN) Montazeri, A ; Naghdabadi, R ; Sharif University of Technology
    Department of Scientific Computing, Florida State University  2008
    CNT-reinforced polymer composites have attracted attention due to their exceptional high strength. The high strength can be affected by the presence of defects in the nanotubes used as reinforcements in the practical nanocomposites. In this paper, a Molecular Structural Mechanics / Finite Element (MSM/FE) multiscale modeling is used to study the effect of carbon nanotube geometrical defects on the stability of SWCNT-polymer composites. Here, two types of representative volume elements (RVEs) for these nanocomposites are considered with perfect and defected CNT. These RVEs have the same dimensions. The nanotube is modeled at the atomistic scale using molecular structural mechanics whereas the... 

    Progressive damage analysis of an adhesively bonded composite T-joint under bending, considering micro-scale effects of fiber volume fraction of adherends

    , Article Composite Structures ; Volume 258 , 2021 ; 02638223 (ISSN) Barzegar, M ; Davoodi Moallem, M ; Mokhtari, M ; Sharif University of Technology
    Elsevier Ltd  2021
    In this study, a numerical study on failure assessment and stress distribution on the adhesive region in a composite T-joint under bending load case is investigated using cohesive zone method (CZM). The Finite Element Model (FEM) has been verified with experimental results. To study the load transfer capability of the T-joint, five different adhesives are considered in the adhesive region and the effect of geometrical parameters such as stringer thickness, corner radius, and adherend thickness as well as micromechanical properties of reinforced fiber composite adherends are investigated. Effective properties of two composite adherends including Carbon-Epoxy (IM7/8552) and Glass-Epoxy...