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    A coarse-graining approach for modeling nonlinear mechanical behavior of FCC nano-crystals

    , Article Computational Materials Science ; Volume 172 , 1 February , 2020 Jahanshahi, M ; Vokhshoori, M ; Khoei, A. R ; Sharif University of Technology
    Elsevier B.V  2020
    Abstract
    The ever-increasing growth of nano-technology has elevated the necessity for development of new computational methods that are capable of evaluating large systems at nano-scale. The existing techniques, such as the molecular dynamics, lack the ability to simulate large systems of practical size and time scales. In order to provide a realistic simulation of large models, the multi-scale methods such as coarse-graining, have therefore become very popular. The coarse-grained models have mostly been used to simulate large biomolecules, such as proteins, lipids, DNA and polymers. In this paper, the Iterative Boltzmann Inversion (IBI) coarse-graining technique is applied to FCC nano-crystals; the... 

    Computer Simulation of Coiled Carbon Nanotubes Deformation By Molecular Dynamics Approach

    , M.Sc. Thesis Sharif University of Technology Shahini, Ehsan (Author) ; Karimi Taheri, Ali (Supervisor)
    Abstract
    A Coiled Carbon Nanotube (CCNT) can be geometrically viewed as a graphene sheet whose rolled and twisted to form a helically coiled nanotube. It is the strongest material ever measured with strengthexceeding more than hundred times of steel.The strength of a CCNT iscritically influenced by temperature, tube diameter, strain rate and pitch angle. In this study,a Molecular Dynamics (MD) simulationis performed to understand the effect of temperature, strain rate, tube diameter and pitch angle on the mechanical properties of CCNTs. Results indicate thatexisting the stone-wales defects is necessaryfor thermodynamic stability of CCNTs.According to the stress-strain curves it was observed thatyield... 

    Hot rolling and direct cooling

    , Article Comprehensive Materials Processing ; Vol. 3 , 2014 , pp. 377-396 ; ISBN: 9780080965338 Serajzadeh, S ; Sharif University of Technology
    Abstract
    Knowledge of process parameters during and after hot rolling is a significant requirement in order to produce a material with the desired microstructures and mechanical properties. In continuous hot rolling mills, different stages may exist, including water descaling, rolling stands, interstand sections, and run-out table. In each of these sections, various thermal and/or mechanical conditions are applied on the rolling metal that would affect material response in successive stages. In other words, an integrated model should be employed in hot rolling operations to evaluate metal behavior and microstructural events at the same time. Therefore, the thermal-mechanical response as well as... 

    Mechanical Behavior Analysis of Carbon Nanotube-Based Polymer Composites using Multiscale Modeling

    , Ph.D. Dissertation Sharif University of Technology Montazeri Hedesh , Abbas (Author) ; Naghdabadi, Reza (Supervisor) ; Rafii Tabar, Hashem (Supervisor) ; Bagheri, Reza (Supervisor)
    Abstract
    In this project, two multiscale modeling procedures have been implemented to study the mechanical behavior of SWCNT/polymer composites. First, a new three-phase molecular structural mechanics/ finite element (MSM/FE) multiscale model has been introduced which consists of three components, i.e. a carbon nanotube, an interphase layer and outer polymer matrix. The nanotube is modeled at the atomistic scale using MSM, whereas the interphase layer and polymer matrix are analyzed by the FE method. Using this model, we have investigated the macroscopic material properties of nanocomposite with and without considering the interphase and compared the results with molecular dynamics (MD) simulations.... 

    Molecular Dynamics Simulation of Mechanical Behavior of Metalic Nanostructures

    , M.Sc. Thesis Sharif University of Technology Rabiefar, Hossein (Author) ; Simchi, Abdolreza (Supervisor) ; Kazeminezhad, Mohsen (Supervisor)
    Abstract
    In this work, mechanical behavior of Ni nanowires with various dimensions under tensile loading at different temperatures and strain rates was simulated by molecular dynamics. Lennard-Jones and Sutton-Chen potential functions were utilized. The relationship between the tensile properties of Ni nanowires and temperature, strain rate, aspect ratio and crystal orientation was studied. It was shown that with increasing the aspect ratio of the nanowires the strength of the material decreases. A change in the fracture mode of the nanowire from slippage at low strain rates (<10 m/s) to amorphous deformation at high loading rates was observed. The crystal orientation was found to influence the... 

    Constitutive Modeling and Numerical Simulation of Coronary Arteries Mechanical Behavior in Stenting and Succeeding Growth

    , Ph.D. Dissertation Sharif University of Technology Fereidoonnezhad, Behrooz (Author) ; Naghdabadi, Reza (Supervisor) ; Sohrabpour, Saeed (Supervisor)
    Abstract
    Cardiovascular diseases are the major cause of death worldwide. Atherosclerosis is one of the major types of cardiovascular diseases in which fibrous and fatty materials, called plaque, build up inside the artery and cause partial or total occlusion of the artery. Intravascular balloon angioplasty with or without stenting is the most common treatment of this disease. In 2010, approximately 954000 stent implantations were performed in the United States. The major issue associated with stenting is reclosure or renarrowing of the transverse section of the artery termed in-stent restenosis (ISR). Unfortunately, nearly one–third of the patients
    who receive stent implantation require further... 

    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)
    Abstract
    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... 

    Mechanical and Microstructural Behavior of 2024-O Aluminum Alloy in Non-Isothermal Hot Compression Test

    , M.Sc. Thesis Sharif University of Technology Taheri, Javad (Author) ; KazemiNezhad, Mohsen (Supervisor)
    Abstract
    So far, a lot of research has been done on the hot behavior of different alloys; These studies have generally been performed using tensile, compression and torsion tests and isothermal conditions, which have greatly contributed to the understanding of the mechanisms of deformation at high temperatures. Due to the fact that in real deformation processes, it is less common for the material to experience isothermal conditions during deformation, so in this project, the aim is to investigate the behavior of 2024 aluminum-alloy in non-isothermal hot compression test. In this regard, non-isothermal hot pressure test was performed from 300℃ to 600℃ و temperature range and at different deformation... 

    Dynamic analysis of carbon nanotubes under electrostatic actuation using modified couple stress theory

    , Article Acta Mechanica ; Vol. 225, Issue 6 , June , 2014 , pp. 1523-1535 ; Online ISSN: 1619-6937 Fakhrabadi, M. M. S ; Rastgoo, A ; Ahmadian, M. T ; Mashhadi, M. M ; Sharif University of Technology
    Abstract
    Modified couple stress theory is a size-dependent theorem capturing the micro/nanoscale effects influencing the mechanical behaviors of the micro- and nanostructures. In this paper, it is applied to investigate the nonlinear vibration of carbon nanotubes under step DC voltage. The vibration, natural frequencies and dynamic pull-in characteristics of the carbon nanotubes are studied in detail. Moreover, the effects of various boundary conditions and geometries are scrutinized on the dynamic characteristics. The results reveal that application of this theory leads to the higher values of the natural frequencies and dynamic pull-in voltages  

    Characterization of the effect of disturbance on the hydro-mechanical behavior of a highly collapsible loessial soil

    , Article Unsaturated Soils: Research and Applications - Proceedings of the 6th International Conference on Unsaturated Soils, UNSAT 2014 ; Vol. 1, issue , 2014 , p. 261-266 Haeri, S. M ; Khosravi, A ; Ghaizadeh, S ; Garakani, A. A ; Meehan, C. L ; Sharif University of Technology
    Abstract
    Highly collapsible loessial soils are characterized by an open void structure that can experience significant settlement upon loading. In the field, these partially saturated Aeolian deposits are particularly susceptible to wetting-induced collapse. Due to difficulties in preparing undisturbed specimens from highly collapsible soils, previous studies have generally performed laboratory tests on reconstituted specimens with different water contents and densities, and the effect of disturbance on the initial state of the soil was ignored. Disturbance in highly collapsible soil specimens may significantly affect the natural composition of the soil matrix, the non-homogeneous distribution of... 

    Analysis of micro-rotating disks based on the strain gradient elasticity

    , Article Acta Mechanica ; Vol. 225, issue. 7 , 2014 , pp. 1955-1965 ; ISSN: 00015970 Danesh, V ; Asghari, M ; Sharif University of Technology
    Abstract
    In this paper, the mechanical behavior of micro-rotating disks is investigated utilizing the strain gradient theory. The governing equation and boundary conditions are derived utilizing the variational method. The analytical solution for the derived equation is also presented. As a case study, some numerical results are presented to emphasize the importance of utilization of non-classical theories such as the strain gradient elasticity instead of the classical continuum theory in dealing with micro-rotating disks  

    Investigation of the mechanical behaviors of carbon nanotubes under electrostatic actuation using the modified couple stress theory

    , Article Fullerenes Nanotubes and Carbon Nanostructures ; Volume 21, Issue 10 , Oct , 2013 , Pages 930-945 ; 1536383X (ISSN) Fakhrabadi, M. M. S ; Rastgoo, A ; Ahmadian, M. T ; Sharif University of Technology
    2013
    Abstract
    The paper presents size-dependant mechanical behaviors of carbon nanotubes under electrostatic actuation using modified couple stress theory. The behaviors of the carbon nanotubes with different geometries and boundary conditions are studied in detail. The results reveal that application of this theory results in higher pull-in voltages for both cantilever and doubly clamped boundary conditions  

    On the influence of deformation rate and cooling media on the static strain aging of a warm-rolled low carbon steel

    , Article International Journal of Material Forming ; Volume 6, Issue 3 , February , 2013 , Pages 417-422 ; 19606206 (ISSN) Koohbor, B ; Ohadi, D ; Sharif University of Technology
    2013
    Abstract
    An investigation was performed on the static strain aging behavior of warm-rolled low carbon steel during a nearly 1-year aging period, from the view point concerning with influence of changing the deformation speed and cooling media. Mechanical response of the examined material during aging period was evaluated through variations occurred in strength and hardness of the warm-deformed steel. It was shown that changing the rolling speed as well as cooling rate, may result in the occurrence of different metallurgical phenomena, consequently altering the aging kinetics of the material. It was also found that by increasing rolling speed, an increase in the value of hardness and UTS takes place,... 

    Thermo-mechanical behavior of functionally graded circular sector plates

    , Article Acta Mechanica ; Volume 226, Issue 1 , January , 2015 , Pages 37-54 ; 00015970 (ISSN) Fallah, F ; Nosier, A ; Sharif University of Technology
    Springer-Verlag Wien  2015
    Abstract
    By reformulating the governing equations of the first-order theory into those describing the interior and edge-zone problems of the plate, closed-form solutions are presented for analysis of functionally graded circular sector plates with vertex angle (Formula presented.) whose radial edges are simply supported and subjected to transverse loading and heat conduction through the plate thickness. Various types of clamped, simply supported, and free-edge boundary supports are considered on the circular edge of the plate. The material properties are graded through the plate thickness according to a power-law distribution of the volume fraction of the constituents. The effects of material... 

    Hydro-mechanical behavior of collapsible soils in unsaturated soil mechanics context

    , Article 15th Asian Regional Conference on Soil Mechanics and Geotechnical Engineering, ARC 2015, 9 November 2015 through 13 November 2015 ; November , 2015 , Pages 25-40 Haeri, S. M ; Association for Disaster Prevention Research; et al.; Fukuoka Convention and Visitors Bureau; Japan Society for the Promotion of Science - Grant-in-Aid for Publication of Scientific Research Results; Kyushu Regional Planning Association; The Maeda Engineering Foundation ; Sharif University of Technology
    Asian Regional Conference on Soil Mechanics and Geotechnical Engineering  2015
    Abstract
    This paper is related to the studies taken place during last decade to understand the intact behavior of a Collapsible Loess subjected to loading and wetting at Advanced Soil Mechanics Laboratory of Sharif University of Technology, Tehran, Iran. In this regard intact block samples are carefully taken from Hezar Pich Hill in the city of Gorgan, Iran, and various tests are performed on undisturbed specimens recovered from the intact block samples. In this way three automated unsaturated oedometer are built and a conventional triaxial apparatus is upgraded to a fully automated unsaturated triaxial device to accommodate rigorous and different stress and wetting path with continuous data... 

    Computational investigation of graphene behavior under differential water pressure and possible mass transfer influences

    , Article ASME 2016 5th International Conference on Micro/Nanoscale Heat and Mass Transfer, MNHMT 2016, 4 January 2016 through 6 January 2016 ; Volume 2 , 2016 ; 9780791849668 (ISBN) Jafari, S ; Darbandi, M ; Saidi, M.S ; Heat Transfer Division ; Sharif University of Technology
    American Society of Mechanical Engineers  2016
    Abstract
    Because of its unique properties, graphene has attracted the attentions of many academic research groups and recently, the industry. One of the promising applications of the graphene is in micro/nano-sensors, e.g. using it as a pressure sensor. To use it in mechanical-based nano-sensors, it is very important to investigate the mechanical behavior of the nano-sized graphene sheet and its sensitivity to the medium changes applied on its faces. In this work, we use the molecular dynamics MD method and simulate the behavior of graphene sheet under differential water pressure influences. In this regard, a square straight monolayer graphene sheet is placed as a separator diaphragm between two... 

    Experimental and numerical investigation of the effect of laser input energy on the mechanical behavior of stainless steel and polyamide joint in the LAMP joining method

    , Article International Journal of Advanced Manufacturing Technology ; Volume 113, Issue 11-12 , 2021 , Pages 3585-3597 ; 02683768 (ISSN) Ghanavati, R ; Ranjbarnodeh, E ; Shoja Razavi, R ; Pircheraghi, G ; Sharif University of Technology
    Springer Science and Business Media Deutschland GmbH  2021
    Abstract
    The present study investigated the effect of laser input energy on the quality and mechanical behavior of a 304 stainless steel–polyamide 6 joint in the laser-assisted metal and polymer direct joining (LAMP) method experimentally and numerically. After the proposed heat transfer model was validated, it was determined whether there was an optimal amount of laser input energy that could produce a joint with favorable quality and mechanical behavior. Among different laser input energies used in this study, 28-J/mm energy can provide more uniform and extensive wetting of the metal surface by the polymer, while excessive polymer degradation in the joint zone was prevented. As a result, an optimal... 

    Critical state concepts for a cemented gravely sand

    , Article Electronic Journal of Geotechnical Engineering ; Volume 10 E , 2005 ; 10893032 (ISSN) Hamidi, A ; Haeri, S. M ; Sharif University of Technology
    2005
    Abstract
    The shear behavior of a cemented gravely sand that can be considered as the representative of Tehran alluvium has been studied using triaxial equipment. Artificially cemented samples were prepared using gypsum plaster as the cementing agent. The plaster was mixed with the base soil at the weight percentages between 1.5 and 6. The critical state concepts were used to illustrate the mechanical behavior of tested soil. © 2005 ejge  

    Hydro-mechanical behavior of undisturbed collapsible loessial soils under different stress state conditions

    , Article Engineering Geology ; Volume 195 , September , 2015 , Pages 28-41 ; 00137952 (ISSN) Garakani, A. A ; Haeri, S. M ; Khosravi, A ; Habibagahi, G ; Sharif University of Technology
    Elsevier  2015
    Abstract
    A conventional triaxial test device was modified to characterize the hydro-mechanical behavior of a loessial soil during isotropic and shear loadings. This device is capable of precise and continuous measurements of water outflow during the application of loading. The tests were performed on "undisturbed" cylindrical specimens, which were taken from loessial deposits in Gorgan, a city in the northeast of Iran. Experimental measurements indicate that the hydro-mechanical behavior of loess is highly affected by the extent of applied mean net stress and the level of suction. During both isotropic and shearing stages of loading, the tested specimens may exhibit collapse, abrupt decrease in... 

    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
    Abstract
    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...