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    On the theoretical and molecular dynamic methods for natural frequencies of multilayer graphene nanosheets incorporating nonlocality and interlayer shear effects

    , Article Mechanics of Advanced Materials and Structures ; 2021 ; 15376494 (ISSN) Nikfar, M ; Taati, E ; Asghari, M ; Sharif University of Technology
    Bellwether Publishing, Ltd  2021
    In this paper, a multiplate nonlocal shear model and molecular dynamic simulations are presented to investigate the effects of interlayer shear and nonlocality on the natural frequencies of multilayer graphene sheets (MLGSs). From one aspect in the optimal design of such structures, the interaction between graphene layers, which can significantly vary the static and dynamic behavior due to lack of solidity of layers stack, should be considered. On the other hand, it is requied that the nonlocality phenomenon which has an effective role in the mechanical analysis of nanostructures is taken into account. To this aim, the equation of motion along with corresponding boundary conditions is... 

    Mechanical properties of ester- and ether-DPhPC bilayers: A molecular dynamics study

    , Article Journal of the Mechanical Behavior of Biomedical Materials ; Volume 117 , 2021 ; 17516161 (ISSN) Rasouli, A ; Jamali, Y ; Tajkhorshid, E ; Bavi, O ; Pishkenari, H. N ; Sharif University of Technology
    Elsevier Ltd  2021
    In addition to its biological importance, DPhPC lipid bilayers are widely used in droplet bilayers, study of integral membrane proteins, drug delivery systems as well as patch-clamp electrophysiology of ion channels, yet their mechanical properties are not fully measured. Herein, we examined the effect of the ether linkage on the mechanical properties of ester- and ether-DPhPC lipid bilayers using all-atom molecular dynamics simulation. The values of area per lipid, thickness, intrinsic lateral pressure profile, order parameter, and elasticity moduli were estimated using various computational frameworks and were compared with available experimental values. Overall, a good agreement was... 

    Fabrication and characterization of an injectable reinforced composite scaffold for cartilage tissue engineering: An in vitro study

    , Article Biomedical Materials (Bristol) ; Volume 16, Issue 4 , 2021 ; 17486041 (ISSN) Khozaei Ravari, M ; Mashayekhan, S ; Zarei, F ; Sayyahpour, F. A ; Taghiyar, L ; Eslaminejad, M. B ; Sharif University of Technology
    IOP Publishing Ltd  2021
    There are limitations in current medications of articular cartilage injuries. Although injectable bioactive hydrogels are promising options, they have decreased biomechanical performance. Researchers should consider many factors when providing solutions to overcome these challenges. In this study, we created an injectable composite hydrogel from chitosan and human acellular cartilage extracellular matrix (ECM) particles. In order to enhance its mechanical properties, we reinforced this hydrogel with microporous microspheres composed of the same materials as the structural building blocks of the scaffold. Articular cartilage from human donors was decellularized by a combination of physical,... 

    Nonlocal hcp kernel functions based on ab initio calculations: Pertinent dislocation problems revisited

    , Article Mechanics of Materials ; Volume 160 , 2021 ; 01676636 (ISSN) Shahvaghar Asl, S ; Shodja, H. M ; Sharif University of Technology
    Elsevier B.V  2021
    Eringen's nonlocal theory and an accurate determination of the nonlocal kernel functions for hexagonal close-packed (hcp) crystals are of interest. The kernel functions are closely related to the anisotropy as well as any crystalline symmetries. To this end, five new distinct nonlocal kernel functions which have the characteristics of discrete atomistic Green's functions in the stress space are obtained through consideration of the nonlocal dispersion relations associated with certain directions combined with ab initio Density Functional Perturbation Theory (DFPT) calculations of the pertinent phonon frequencies. This is the first work which provides the nonlocal hcp kernel functions... 

    Discrete kernel functions for fcc crystals within eringen’s nonlocal theory of elasticity

    , Article Journal of Elasticity ; Volume 143, Issue 1 , 2021 ; 03743535 (ISSN) Shodja, H. M ; Shahvaghar Asl, S ; Sharif University of Technology
    Springer Science and Business Media B.V  2021
    The dilemma with the deficiencies of the nonlocal kernel functions as the building blocks of the Eringen’s nonlocal theory has been of concern. The aim of the current work is to provide a remedy for the calculation of the components of the nonlocal moduli tensor pertinent to face center cubic (fcc) crystals accounting for their true symmetry group. To this end, three new distinct nonlocal kernel functions which are the discrete atomistic Green’s functions in the stress space are obtained through the nonlocal dispersion relations associated with the longitudinal and shear waves in fcc crystals combined with the corresponding ones calculated via ab initio based on density functional... 

    Utilization of gene expression programming for modeling of mechanical performance of titanium/carbonated hydroxyapatite nanobiocomposites: The combination of artificial intelligence and material science

    , Article International Journal of Engineering, Transactions A: Basics ; Volume 34, Issue 4 , 2021 , Pages 948-955 ; 17281431 (ISSN) Shojaei, M. R ; Khayati, G. R ; Hasani, A ; Sharif University of Technology
    Materials and Energy Research Center  2021
    Titanium carbonated hydroxyapatite (Ti/CHA) nanobiocomposites have extensive biological applications due to the excellent biocompatibility and similar characteristics to the human bone. Ti/CHA nanobiocomposite has good biological properties but it suffer from diverse characteristics especially in hardness, Young's modulus, apparent porosity and relative density. This investigation is an attempt to propose the predictive models using gene expression programming (GEP) to estimate these characteristics. In this regards, GEP is used to model and compare the effect of practical variables including pressure, Ti/CHA contents and sintering temperature on their monitored properties. To achieve this... 

    Hybrid finite volume-finite element methods for hydro-mechanical analysis in highly heterogeneous porous media

    , Article Computers and Geotechnics ; Volume 132 , 2021 ; 0266352X (ISSN) Asadi, R ; Ataie Ashtiani, B ; Sharif University of Technology
    Elsevier Ltd  2021
    In this study, two classes of advanced finite volume schemes, including Multi-Point Flux Approximation (MPFA) and Dual Discrete Finite Volume (DDFV) method, have been employed in conjunction with the finite element (FE) geomechanics simulator to model the coupled fluid-solid system. Fully saturated porous media with poroelastic behavior, random field permeability and elastic modulus are considered as parameters. The performance of the proposed hydro-mechanical models, including MPFA O-FEM and DDFV-FEM, is examined through different test cases. First, the models are validated and compared with the closed-form solutions in the homogeneous domain. Second, the methods' stability and convergence... 

    Mechanical behaviors of titanium nitride and carbide MXenes: A molecular dynamics study

    , Article Applied Surface Science ; Volume 566 , 2021 ; 01694332 (ISSN) Hatam Lee, S. M ; Esfandiar, A ; Rajabpour, A ; Sharif University of Technology
    Elsevier B.V  2021
    MXenes have recently witnessed significant evolution and advances in terms of their applications in different areas such as flexible electronics, energy storage devices, and coatings. Here, the mechanical properties of both pristine and functionalized Tin+1CnO2 and Tin+1NnO2 (n = 1, 2) are investigated utilizing classical molecular dynamics simulations. For eight different MXene structures, the stress-strain curves are calculated including Young's modulus, strength, and fracture strain. It is found that Ti2N holds the highest Young's modulus with the value of 517 GPa while Ti3C2 has the lowest one with the amount of 133 GPa. In addition, the strongest MXene structure is Ti2N while the... 

    On a theorem of Ihara

    , Article Scientia Iranica ; Volume 12, Issue 1 , 2005 , Pages 1-9 ; 10263098 (ISSN) Rastegar, A ; Sharif University of Technology
    Sharif University of Technology  2005
    Let p be a prime number and let n be a positive integer prime to p. By an Ihara-result, one means the existence of an injection with torsion-free cokernel, from a full lattice, in the space of p-old modular forms, into a full lattice, in the space of all modular forms of level np. In this paper, Ihara-results are proven for genus two Siegel modular forms, Siegel-Jacobi forms and Hilbert modular forms. Ihara did the genus one case of elliptic modular forms [1]. A geometric formulation is proposed for the notion of p-old Siegel modular forms of genus two, using clarifying comments by R. Schmidt [2] and, then, following suggestions in an earlier paper [3] on how to prove Ihara results. The main... 

    A single cone-cap plasticity with an isotropic hardening rule for powder materials

    , Article International Journal of Mechanical Sciences ; Volume 47, Issue 1 , 2005 , Pages 94-109 ; 00207403 (ISSN) Khoei, A. R ; Azami, A. R ; Sharif University of Technology
    In this paper, a new single cone-cap plasticity with an isotropic hardening rule is presented for powder materials. A general form is developed for the cap plasticity, which can be compared with some common double-surface plasticity models proposed for powders in literature. The constitutive elasto-plastic matrix and its components are derived based on the definition of yield surface, hardening parameter and nonlinear elastic behavior, as a function of relative density of powder. Different aspects of the model are illustrated and the procedure for determination of powder parameters is described. Finally, the applicability of the proposed model is demonstrated in numerical simulation of... 

    Ductility of saffil™ short fibre reinforced metals

    , Article Scripta Materialia ; Volume 53, Issue 1 , 2005 , Pages 17-21 ; 13596462 (ISSN) Weber, L ; Tavangar, R ; Mortensen, A ; Sharif University of Technology
    A critical combination of matrix strain hardening exponent and fiber volume exceeded to confer tensile ductility to short-fiber reinforced metal. The bimodal distribution of tensile ductilities observed in such materials can be attributed to a transition in damage mode, from fiber fragmentation to matrix voiding. Building on results for model composites of this class and making a few specification, a simple criterion can be proposed to predict whether such composites display a low or a high tensile elongation. The results show that, composites of this class are ductile if their matrix strain hardening exponent exceeds by more than around three per cent of unity the fiber volume fraction  

    Nanoscale vibrational analysis of a multi-layered graphene sheet embedded in an elastic medium

    , Article Composites Science and Technology ; Volume 65, Issue 7-8 , 2005 , Pages 1159-1164 ; 02663538 (ISSN) Behfar, K ; Naghdabadi, R ; Sharif University of Technology
    In this paper, nanoscale vibrational analysis of a multi-layered graphene sheet embedded in an elastic medium is investigated and the corresponding natural frequencies and the associated modes are determined. The modeling is based on the fact that the elastic moduli of a graphene sheet in two perpendicular orientations are different, so the plate is considered to be anisotropic. The graphene layers stacking at the top of each other bond with carbon-carbon van der Waals forces between two adjacent ones. Also, the whole multi-layered graphene sheet is influenced by polymer-carbon van der Waals forces from the surrounding elastic medium. © 2005 Elsevier Ltd. Al rights reserved  

    Localization of elastic waves in heterogeneous media with off-diagonal disorder and long-range correlations

    , Article Physical Review Letters ; Volume 94, Issue 16 , 2005 ; 00319007 (ISSN) Shahbazi, F ; Bahraminasab, A ; Vaez Allaei, S. M ; Sahimi, M ; Rahimi Tabar, M. R ; Sharif University of Technology
    Using the Martin-Siggia-Rose method, we study propagation of acoustic waves in strongly heterogeneous media which are characterized by a broad distribution of the elastic constants. Gaussian-white distributed elastic constants, as well as those with long-range correlations with nondecaying power-law correlation functions, are considered. The study is motivated in part by a recent discovery that the elastic moduli of rock at large length scales may be characterized by long-range power-law correlation functions. Depending on the disorder, the renormalization group (RG) flows exhibit a transition to localized regime in any dimension. We have numerically checked the RG results using the... 

    Damage evolution in Saffil alumina short-fibre reinforced aluminium during tensile testing

    , Article Materials Science and Engineering A ; Volume 395, Issue 1-2 , 2005 , Pages 27-34 ; 09215093 (ISSN) Tavangar, R ; Weber, L ; Mortensen, A ; Sharif University of Technology
    The evolution of microstructural damage during tensile deformation of pure aluminium reinforced with 10 vol.% alumina short fibres is studied by monitoring the evolution of density and Young's modulus as a function of tensile strain. It is found that Young's modulus drops rapidly until a strain εc ≈ 3%. The composite density remains virtually unchanged in this strain range. At strains above εc, Young's modulus decreases more slowly while the density begins to decrease linearly, indicating void growth in the composite. It is shown that the drop in Young's modulus is linked to fragmentation of fibres aligned along the stress axis, while the decrease in density is related to void opening across... 

    Modeling and analysis of AN ultra light slow flyer with variable shape control surfaces using shape memory alloy actuators

    , Article Proceedings of the 7th Biennial Conference on Engineering Systems Design and Analysis - 2004, Manchester, 19 July 2004 through 22 July 2004 ; Volume 2 , 2004 , Pages 153-162 ; 0791841731 (ISBN); 9780791841730 (ISBN) Alasty, A ; Alemohamad, S. H ; Khiabani, R. H ; Khalighi, Y ; Sharif University of Technology
    American Society of Mechanical Engineers  2004
    Applying flexible variable shape control surfaces (wing and elevator) structures is a way to increase efficiency and maneuverability of the planes, which is recently under research. In this paper, modeling of the flight of an unmanned ultra light plane is discussed. The modeling is done based on a real ultra light plane presented recently. To increase maneuverability of the plane, flexible variable shape structures are designed for the wing and the elevator. In design procedure, having an ultra light plane is considered. The elevator and the wing are used as control surfaces for longitudinal and lateral maneuvers respectively. Shape memory alloys (SMA) are used for reshaping the flexible... 

    Comparison of the experimental behavior of a shape memory alloy in compression and tension

    , Article 2003 ASME International Mechanical Engineering Congress, Washington, DC., 15 November 2003 through 21 November 2003 ; Volume 68 , 2003 , Pages 471-478 ; 07334230 (ISSN) Hesse, T ; Ghorashi, M ; Inman, D. J ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2003
    The concept of Shape Memory Alloy (SMA) has been a subject of extensive research in the recent few years. In many SMA applications, wire elements have been used in order to control structural specifications like shape and stiffness. Since a wire can only be subjected to tensile forces, the available theoretical models for SMA discuss only the tensile loading. The present paper is an endeavor to overcome this shortcoming. It gives experimental results for tension and compression tests on specimens (having different geometries) made of an identical shape memory alloy. The corresponding results are compared with each other. Using stress-strain diagrams, several important material properties are...