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    Study of Melting and Rapid Solidification of TiAl alloy and Formation of its Diffusion Bonded Structure using Molecular Dynamics Simulation

    , M.Sc. Thesis Sharif University of Technology Yazdan Yar, Azade (Author) ; Aashuri, Hossin (Supervisor) ; Simchi, Abdolreza (Co-Advisor)
    The rapid pace of development of nanoscience and nanotechnology and their applications in various fields have made the study of materials in smaller scales more important than any time ever. Having an insight of materials’ microstructure and the mechanism of different phenomena in the atomic scale will be very beneficent in designing new and advanced materials or modifying the current manufacturing processes. Since molecular dynamics (MD) method has been well known as a mean of studying materials in atomic scale, it has been used in this study to investigate two different phenomena. The selection of the appropriate interatomic potential is of great importance in MD; Embedded Atom Method... 

    Multiscale Modeling of Crack Propagation under Thermal Fatigue in Nano-Structured Materials

    , Ph.D. Dissertation Sharif University of Technology Yasbolaghi, Reza (Author) ; Khoei, Amir Reza (Supervisor)
    In this research, various molecular dynamics simulations have been carried out and sensitivity of the crack propagation process to the simulation parameters including the load pattern, maximum applied strain, temperature, loading frequency, and percentage of defects is investigated. Moreover, the crack propagation in poly-crystalline structure is studied using a larger model consisting of several atomic crystals and the effect of the presence of crystals on crack growth is investigated. In the next step, a novel coupling technique is developed in the continuum–atomistic multi-scale analysis of temperature field problems. In this manner, a new thermostat is introduced based on the single-atom... 

    On the Study and Comparison of the Post-yield Strain Softening in Polymer and Cellular Solid under Compression Loading

    , Ph.D. Dissertation Sharif University of Technology Goodarzi Hosseinabadi, Hossein (Author) ; Bagheri, Reza (Supervisor)
    Strain softening after the yield point is a prevalent phenomenon in the stress-strain response of cellular solids, consisting of porosities in micro/macro-meter scale, as well as polymers, consisting of free volumes in sub-nanometer molecular scale. Although the underlying micromechanisms for softening in cellular solids are already known, the molecular origin for softening in polymers is still unknown. In this thesis, the micromechanisms of the softening in both materials are investigated. Then, a hypothesis is raised and evaluated to connect the nano-mechanics of softening in polymers to the micro-mechanics of softening in cellular solids. Experiments of compression test, positron-based... 

    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... 

    Calculation of the Thermodynamical Properties of [BMIM][PF6] via Equation of State and Molecular Dynamic Simulations Data

    , M.Sc. Thesis Sharif University of Technology Geraili, Hossein (Author) ; Parsafar, Gholamabbas (Supervisor) ; Tafazzoli, Mohsen (Supervisor) ; Shamkhali, Amir Naser (Co-Advisor)
    In this thesis, We have investigated the accuracy of general equation of state ( EoS III ) and linear isotherm regularity ( EoS I ), introduced on 2009 and 1993, respectively, and the Ghatee’s equation of state ( EoS II ) introduced on 2001, for the pvT data and thermodynamic properties of [BMIM][PF6] ionic liquid. We have carried out simulations at first in a narrow range of pressure, namely within 1-3400 atm and in temperature range from 398 K to 1000 K. The results of fitting of EoS I, EoS II and EoS III into the simulations results, leads to R2 > 0.9936, 0.9800 and 0.9949 respectively, for the pressure range of 1-3400 atm and for the temperature range of 398-1000 K. The results of... 

    Ion Separation through a Y-Shaped CNT Membrane- A Molecular Dynamics Simulation

    , M.Sc. Thesis Sharif University of Technology Karimi, Sajjad (Author) ; Mousavi, Ali (Supervisor) ; Sadrhosseini, Hani (Supervisor)
    Nowadays, water desalination is a widely-used method for producing clean and fresh water. Recent researches in this area have mostly focused on Reverse Osmosis technology which is one of the most efficient technologies in water desalination. A new idea to increase the efficiency of a recently-designed reverse osmosis membrane called “Honeycomb Carbon Nanotube Membrane” is presented through molecular dynamics simulation. Although in this study only the inlet area of the honeycomb structure which is a Y-shaped entrance, is modeled and studied, but obviously, any improvement in the membrane inlet, equals better results at outlet which means a more efficient desalination process. Present thesis... 

    Molecular Dynamic Simulation of Water Desalination Across Porous Single Layer Graphene Membrane

    , M.Sc. Thesis Sharif University of Technology Chogani, Alireza (Author) ; Moosavi, Ali (Supervisor)
    In recent years carbon nanotubes and other carbon nanostructures such as graphene sheets have attracted a lot of attention due to their unique mechanical, thermal and electrical properties. These structures can be used in desalination of sea water, removal of hazardous substances from water tanks, gases separation, and so on. The nano porous single layer graphene membranes are very efficient for desalinating water due to their very low thickness. In this study, the mechanism of passing water and salt ions through nano porous single-layer graphene membrane are simulated using classical molecular dynamics. In the simulation, in order to separate salt ions from the water, the effects of applied... 

    Investigation of Wear Properties of Nanocrystalline through Multiscale Modeling of Nanoindentation and Nanoscratch Test

    , Ph.D. Dissertation Sharif University of Technology Chamani, Mohammad (Author) ; Farrahi, Gholamhossein (Supervisor) ; Movahhedy, Mohammad Reza (Supervisor)
    Nanocrystalline materials have received increasing attention during the last decades. Polycrystalline structures with grain sizes less than 100 nm are referred as nanocrystalline (NC). Their mechanical properties differ significantly from polycrystalline structures. As an example, hardness and wear resistance of nanocrystalline structures are higher than those of polycrystalline structures. With the reduction of grain size, hardness increases based on the Hall–Petch relation. However, at the very small grain sizes the Hall–Petch relation breaks down and a fundamental shift takes place in hardening mechanism. Molecular dynamics (MD) simulation offers a powerful method for the investigation of... 

    Size-Dependent Elastic Properties of Ultra-Thin Objects Containing a Nano-Inclusion or a Nano-Inhomogeneity

    , Ph.D. Dissertation Sharif University of Technology Pahlevani, Ladan (Author) ; Mohammadi Shoja, Hossein (Supervisor)
    The broad range of applicability of nano devices particularly in electronics, optoelectronics, and micro/ nano-electro- mechanical systems has drawn the attentions of the industrial and scientific communities of various disciplines. This work is devoted to study the effect of surface and interface elasticity in the analysis of the mechanical behavior of ultra-thin objects in the presence of some statical or dynamical loadings. Based on the fact that the surface-volume ratio increases in nano-scale, description of the behavior of such a small structure via usual classical theories, which generally neglect the surface/interface effect, ceases to hold. In the present study, first, a... 

    Pore-Scale Investigation of Polymer Enhanced Low Salinity Water flooding EOR

    , M.Sc. Thesis Sharif University of Technology Posht Panah, Mohammad Reza (Author) ; Mahani, Hassan (Supervisor) ; Rostami, Behzad (Supervisor)
    Low salinity water flooding (LSWF) is a relatively new EOR method in which low salinity or modified ionic composition water is injected into the reservoir to alter its wettability toward a more water-wettable state to accelerate oil recovery. Ease of field deployment and relatively low cost, as well as laboratory results confirming the positive effect of this method in improving the oil recovery factor, have made this technique attractive in the oil industry.Despite the many advantages of this method, overcoming the mixing between low and high salinity water which occurs due to a high mobility ratio between these two fluids is essential because it negatively affects the efficiency of LSWF.... 

    Investigation of Surfactin Behavior at the Presence of Wate, Oil, and Asphaltene

    , M.Sc. Thesis Sharif University of Technology Pezeshgi Modarres, Hassan (Author) ; Roosta Azad, Reza (Supervisor) ; Yaghmaee, Soheyla (Supervisor)
    In this research, the behavior of surfactin at the presence of water, decane, and asphaltene is investigated. Decane is chosen instead of crude oil to simplify the model. In the first chapter, basic molecular structures are introduced. Furthermore, in the second chapter molecular dynamics simulation, as the main tool in these simulations, is introduced. In the third chapter, one of the most important quantities in chemical engineering, diffusion coefficient, is chosen to investigate the efficiency and accuracy of molecular dynamics simulation method to calculate such a quantity and results show that molecular dynamics simulation can present accurate quantities, more accurate than common... 

    Mechanical Behavior of Metalic Nano-structures Using a Nonlinear Multi-scale Model Based on Coarse Graining Approach

    , M.Sc. Thesis Sharif University of Technology Pezeshkzadeh, Alireza (Author) ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Co-Supervisor)
    In this thesis ،molecular dynamics simulation of structural and mechanical properties of pure aluminium and copper crystals as well as of the alloyed crystals including 10%,30%,50%,70% and 90% aluminium alloyed have been investigated using two various all-atom and coarse-grained models. Molecular dynamics simulations calculate the realistic behavior of the system and then use them in order to calculate the time average properties of the system. Embedded atom method (eam) and the numerical iterative Boltzmann Inversion method are employed to describe the interaction between atoms. The results are then compared with coarse-grained model. The demonstrated peaks in the radial distribution... 

    Mechanical Properties of Lubricants in Nano Powders Compaction Process Using Molecular Dynamics and Continuum Mechanics Methods

    , M.Sc. Thesis Sharif University of Technology Palahang, Pezhman (Author) ; Khoei, Amir Reza (Supervisor)
    The primary objective of this study entails the examination of the impact of lubricants intended for implementation in the compaction process of nano-powders, intending to mitigate friction at the nano scale during compaction. Molecular dynamics modeling is employed to scrutinize this phenomenon and derive the friction parameters within the framework of equations derived from continuum mechanics, based on data acquired from the nanoscale investigations. The manufacturing procedure of metallic components from metal powder compaction necessitates the application of immense pressures, thereby engendering notable friction between the powder particles and the confines of the mold. Consequently,... 

    A Multi-Scale Method for Non-Linear Mechanical Behavior of Nanostructures Based on Coarse-Grained Model

    , M.Sc. Thesis Sharif University of Technology Vokhshoori Koohi, Melika (Author) ; Khoei, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Supervisor)
    The ever-increasing growth of Nanotechnology has elevated the necessity for the development of new numerical and computational methods that are better capable of evaluating systems at this scale. The existing techniques, such as Molecular Dynamics Methods, in spite of being fully capable of evaluating nanostructures, lack the ability to simulate large systems of practical size and time scales. Therefore, in order to be able to provide a realistic simulation of a large model, simulation of which is limited by the computational cost of the current molecular dynamics methods at hand, Coarse-Graining technique has recently become a very effective and beneficial method which refers to the... 

    Calculating the Stiffness Matrix of VACNTs Using Structural or Continuum Modelling

    , M.Sc. Thesis Sharif University of Technology Vahidmoshtagh, Alireza (Author) ; Dehghani Firouz Abadi, Ruhollah (Supervisor)
    The goal of this research is investigation and analysis of a surface consists of vertically aligned carbon nanotubes (VACNTs) using continuum mechanics modeling. Today these kinds of surfaces also known as the darkest material have a particular importance in industries. Knowing the properties of a material is one of the most important things in analysis and designing using that kind of material, so extraxting the stiffness matrix of a material could be a big step for starting analyzing it. In this thesis a lattice of VACNTs with two different layouts and several unique geometrics is simulated using molecular dynamics approach using the Lammps software. The general stiffness matrix of the... 

    Collective Motion and Molecular Assembly of Nanocars on the Surface

    , Ph.D. Dissertation Sharif University of Technology Vaezi, Mehran (Author) ; Nejat Pishkenari, Hossein (Supervisor) ; Ejtehadi, Mohammad Reza (Supervisor)
    In the present thesis, the movement of the clusters of fullerenes and nanocars are separately investigated on graphene surface, using molecular dynamics simulations. Investigating the fullerene clusters with different populations, it is concluded that, as the number of molecules inside the cluster increases, the displacement range of the motion decreases. In fact, some parts of the energy of the fullerene cluster are wasted through the intermolecular interactions, and as a result, the mobility of the cluster diminishes. During the investigation of the three-dimensional structures of fullerene, the wetting property of the clusters is revealed relative to the graphene surface. The decrease of... 

    A Temperature-Dependent Coarse-Graining Method for Nano Crystalline Materials

    , M.Sc. Thesis Sharif University of Technology Vahed Mohammad Ghasemloo, Zahra (Author) ; Khoie, Amir Reza (Supervisor) ; Jahanshahi, Mohsen (Co-Advisor)
    The molecular dynamic (MD) method was first reported by Alder and Wainwright in the late 1950s to study the interaction of hard spheres. Molecular dynamic (MD) simulation is a technique for computing equilibrium and forwarding properties for classical many-body systems. This is a reasonable and often excellent approximation for a wide range of systems and properties. Although molecular dynamics method provide the kind of detail necessary to resolve molecular structure and localized interaction, this fidelity comes with a price. Namely, both the size and time scales of the model are limited by numerical and computational boundaries.The multi scale approach taken by the computational materials... 

    Study of Thermal Behavior and mechanical properties of Phenolic/Clay Nanocomposits by Molecular Dynamics Simulations

    , M.Sc. Thesis Sharif University of Technology Hashemi, Niloofar (Author) ; Hosseni Kordkheili, Ali (Supervisor)
    Polymer/clay nanocomposites (PCNs) are multifunctional materials that have superior mechanical and thermal properties than polymer-based materials. These materials are obtained by adding small amounts of nanoclays to a polymer matrix. In this work, a molecular dynamics simulation was carried out to investigate the thermomechanical properties of thermosetting clay nanocomposites. The polymer matrix was composed of phenolic molecules with the crosslink density of 0.74, and different structures of PCNS were considered by varying the amount of polymer molecules. Molecular dynamics simulations of different nanocomposite structures were used to provide the atomistic insights, the molecular... 

    Theoretical Investigation of Ab-initio MD Approach to Increase the Efficiency and Accuracy of VCD Spectrum Calculation

    , M.Sc. Thesis Sharif University of Technology Hadi, Hossein (Author) ; Jamshidi, Zahra (Supervisor)
    Understanding of the Molecules is the main purpose of the chemistry. Ab-initio molecular dynamics (AIMD) as a branch of the computational chemistry, tries to give us a deep comprehension of the molecule, and its chemical, physical and optical activities. This comprehension, relies on the accuracy of quantum mechanics, in addition to the speed of the classical mechanics. The mixing of the quantum mechanics and the classical mechanics could simulate activities of the atoms in the time-domain, provided the mixing is done with precaution. This, in turn, helps us to forecast the response of a molecule in different situations, and also translating the macroscopic phenomena in a nanoscopic... 

    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...