Search for: elasticity
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    Mechanical properties of graphene oxide: A molecular dynamics study

    , Article Fullerenes Nanotubes and Carbon Nanostructures ; Volume 24, Issue 9 , 2016 , Pages 594-603 ; 1536383X (ISSN) Khoei, A. R ; Sarkari Khorrami, M ; Sharif University of Technology
    Taylor and Francis Inc 
    In this paper, the mechanical properties of graphene oxide are obtained using the molecular dynamics analysis, including the ultimate stress, Young modulus, shear modulus and elastic constants, and the results are compared with those of pristine graphene. It is observed that the increase of oxide agents (–O) and (–OH) leads to the increase of C–C bond length at each hexagonal lattice and as a result, alter the mechanical properties of the graphene sheet. It is shown that the elasticity modulus and ultimate tensile strength of graphene oxides (–O) and (–OH) decrease significantly causing the failure behavior of graphene sheet changes from the brittle to ductile. The results of shear loading... 

    Discussion of "Rocking vibration of a rigid disk embedded in any depth of a coupled seawater-visco-poro-elastic seabed half-space" by R. He [Soil Dyn. Earthq. Eng. 85(2016), 130-133]

    , Article Soil Dynamics and Earthquake Engineering ; 2016 ; 02677261 (ISSN) Ahmadi, S. F ; Samea, P ; Eskandari, M ; Sharif University of Technology
    Elsevier Ltd  2016

    Free vibrations analysis of carbon nanotubes resting on winkler foundations based on nonlocal models

    , Article Physica B: Condensed Matter ; Volume 484 , 2016 , Pages 83-94 ; 09214526 (ISSN) Rahmanian, M ; Torkaman Asadi, M. A ; Firouz Abadi, R. D ; Kouchakzadeh, M. A ; Sharif University of Technology
    In the present study, free vibrations of single walled carbon nanotubes (SWCNT) on an elastic foundation is investigated by nonlocal theory of elasticity with both beam and shell models. The nonlocal boundary conditions are derived explicitly and effectiveness of nonlocal parameter appearing in nonlocal boundary conditions is studied. Also it is demonstrated that the beam model is comparatively incapable of capturing size effects while shell model captures size effects more precisely. Moreover, the effects of some parameters such as mechanical properties, foundation stiffness, length and radius ratios on the natural frequencies are studied and some conclusions are drawn  

    Discussion of “rocking vibration of a rigid disk embedded in any depth of a coupled seawater-visco-poro-elastic seabed half-space”

    , Article Soil Dynamics and Earthquake Engineering ; Volume 104 , 2018 , Pages 449-450 ; 02677261 (ISSN) Ahmadi, F ; Samea, P ; Eskandari, M ; Sharif University of Technology
    Elsevier Ltd  2018

    Molecular dynamics study on axial elastic modulus of carbon nanoropes

    , Article Archives of Civil and Mechanical Engineering ; Volume 19, Issue 4 , 2019 , Pages 1127-1134 ; 16449665 (ISSN) Mehralian, F ; Firouz Abadi, R. D ; Norouzi, M ; Sharif University of Technology
    Elsevier B.V  2019
    Carbon nanoropes (CNRs) are of interest for a wide variety of nanotechnological applications. Since little attention has been paid to mechanical properties of CNRs, their axial elastic modulus is explored herein. Molecular dynamics (MDs) simulations are adopted for analysis of Young's modulus of CNRs. It is also shown that increase in the initial helical angle decreases Young's modulus; however, by increase in the number of CNTs and strands, different influence on Young's modulus emerges. Therefore, the highest value of Young's modulus obtained at the lower value of initial helical angle and consequently, Young's modulus of bundle of straight CNTs is higher than CNRs with hierarchical... 

    Elastic-plastic modeling of kinematic hardening materials based on F = FeFp decomposition and the logarithmic strain tensor

    , Article Proceedings of the 7th Biennial Conference on Engineering Systems Design and Analysis - 2004, Manchester, 19 July 2004 through 22 July 2004 ; Volume 1 , 2004 , Pages 337-342 ; 0791841731 (ISBN); 9780791841730 (ISBN) Ghavam, K ; Naghdabadi, R ; Sharif University of Technology
    American Society of Mechanical Engineers  2004
    In this paper, based on the multiplicative decomposition of the deformation gradient tensor an elastic-plastic modeling of kinematic hardening materials is introduced. In this model, the elastic constitutive equation as well as the flow rule and hardening equation are expressed in terms of the corotational rate of the elastic and plastic logarithmic strains. As an application, the simple shear problem is solved and the stress components are plotted versus shear displacement for a kinematic hardening material  

    Loading and unloading behaviour of a thermoplastic disc

    , Article International Journal of Pressure Vessels and Piping ; Volume 78, Issue 9 , 2001 , Pages 637-645 ; 03080161 (ISSN) Jahed, H ; Shirazi, R ; Sharif University of Technology
    The calculation of loading and residual stresses, and associated strains and displacements, are reported for shrink fitted rotating discs at elevated temperatures. A range of material behaviour is considered including unloading described by an actual material curve, or modelled by isotropic of kinematic hardening with a variable Bauschinger effect. Various collapse loads are obtained and discussed for design boundaries. The influence of reloading on the residual stresses is also studied. It is shown that after the first few loadings of a disc, the residual stress field becomes constant. © 2001 Elsevier Science Ltd. All rights reserved  

    First order decoupling of equations of motion formultibody systems consisting of rigid and elastic bodies

    , Article Iranian Journal of Science and Technology, Transaction B: Technology ; Volume 24, Issue 3 , 2000 , Pages 342-343 ; 03601307 (ISSN) Meghdari, A ; Fahimi, F ; Sharif University of Technology
    An improved method for deriving elastic generalized coordinates is considered and Kane's equations of motion for multibody systems consisting of an arbitrary number of rigid and elastic bodies are presented. The equations are in general form and are applicable for any desired holonomic system. Flexibility in choosing generalized speeds in terms of generalized coordinate derivatives in Kane's method is used. It is shown that proper choice of a congruency transformation between generalized coordinate derivatives and generalized speeds leads to first order decoupled equations of motion for holonomic multibody systems consisting of an arbitrary number of rigid and elastic bodies. In order to... 

    Definition of the persistence length in the coarse-grained models of DNA elasticity

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 86, Issue 5 , November , 2012 ; 15393755 (ISSN) Fathizadeh, A ; Eslami Mossallam, B ; Ejtehadi, M. R ; Sharif University of Technology
    By considering the detailed structure of DNA in the base pair level, two possible definitions of the persistence length are compared. One definition is related to the orientation of the terminal base pairs, and the other is based on the vectors which connect two adjacent base pairs at each end of the molecule. It is shown that although these definitions approach each other for long DNA molecules, they are dramatically different on short length scales. We show analytically that the difference mostly comes from the shear flexibility of the molecule and can be used to measure the shear modulus of DNA  

    Axisymmetric thermo-electro-elastic analysis of a piezoelectric half space

    , Article Mathematics and Mechanics of Solids ; Volume 17, Issue 5 , September , 2012 , Pages 500-515 ; 10812865 (ISSN) Kargarnovin, M. H ; Hashemi, R ; Hashemi, M ; Sadeghi, H ; Sharif University of Technology
    In this study, an analytical solution is presented for thermo-electro- elastic analysis of piezoelectric semi-infinite bodies. For this purpose, governing equations are derived for a transversely isotropic piezoelectric material under an axisymmetric thermo-electro-mechanical loading condition. A general closed-form analytical solution is presented for the complementary and particular parts of the components of the displacement vector and also for the electric potential function. Then, boundary conditions are imposed and in that case an explicit solution is obtained for piezoelectric semi-infinite bodies. Results show that when a piezoelectric half space is subjected to constant/ramp surface... 

    Weighted start-time fair queuing: A new start-time fair queuing for elastic traffic

    , Article 2009 Spring Simulation Multiconference, SpringSim 2009, 22 March 2009 through 27 March 2009 ; 2009 Allahyar, E ; Movaghar, A ; Sharif University of Technology
    Association for Computing Machinery, Inc  2009
    In this paper, we present a new Start-time Fair Queuing (SFQ) algorithm called Weighted Start-time Fair Queuing (WSFQ) which is more efficient and achieves better fairness than SFQ in the presence of small and huge elastic traffic flows. WSFQ scheduler, like SFQ uses a start time eligibility criterion to select packets and when the start-time of two packets in two flows are the same, it acts like Weighted Fair Queuing (WFQ) which selects the smallest virtual finish time first. Afterward, we compared the performance of our model with that of the applied scheduling algorithms such as First-In-First-Out (FIFO), SFQ as well as WFQ on the end-to-end delay and the throughput in small and... 

    Asymmetric elastic rod model for DNA

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 80, Issue 1 , 2009 ; 15393755 (ISSN) Eslami Mossallam, B ; Ejtehadi, M. R ; Sharif University of Technology
    In this paper we consider the anharmonic corrections to the anisotropic elastic rod model for DNA. Our model accounts for the difference between the bending energies of positive and negative rolls, which comes from the asymmetric structure of the DNA molecule. We will show that the model can explain the high flexibility of DNA at small length scales, as well as kink formation at high deformation limit. © 2009 The American Physical Society  

    Dynamic model of a flying manipulator with two highly flexible links

    , Article Applied Mathematical Modelling ; Volume 32, Issue 10 , 2008 , Pages 2117-2132 ; 0307904X (ISSN) Zohoor, H ; Khorsandijou, S. M ; Sharif University of Technology
    Nonlinear dynamic model of a flying manipulator with two revolute joints and two highly flexible links is obtained using Hamilton's principle. Flying base of the manipulator is a rigid body. Stress is treated three dimensionally in the isotropic linearly-elastic links, but the in-plane and out-of-plane warpings of the links' cross-sections are neglected. Although the links' cross-sections undergo negligible elastic orientation, their models are more accurate than a nonlinear 3D Euler-Bernoulli beam. Tension, compression, twisting and spatial deflections of each link are coupled to each other by some nonlinear terms including two new ones. In the issue of flying flexible-link manipulators new... 

    Elastic field of a nano disk shape defect in an fcc thin film

    , Article 2007 2nd IEEE International Conference on Nano/Micro Engineered and Molecular Systems, IEEE NEMS 2007, Bangkok, 16 January 2007 through 19 January 2007 ; 2007 , Pages 142-146 ; 1424406102 (ISBN) ; 9781424406104 (ISBN) Mohammadi Shodja, H ; Pahlevani, L ; Hamed, E ; Sharif University of Technology
    In this paper, we develop a theory to study the nano defects of various geometries within thin films. The considered thin films have face centered cubic (fee) structure. The eigenstrain method is combined with the long-range Sutton-Chen (SC) inter-atomic potential function which is appropriate for fee crystals. The disturbance caused by a defect in a thin film is determined from the equilibrium equation using the discrete Fourier transformation. The disturbed field is also determined using three dimensional (3D) Molecular Dynamics (MD) simulation in which the constant NVT ensemble is applied to the atomic system. For illustration, the problem of nano disk shape defect in thin film is studied... 

    Computational aspects of the cosserat finite element analysis of localization phenomena

    , Article Computational Materials Science ; Volume 38, Issue 2 , 2006 , Pages 303-315 ; 09270256 (ISSN) Sharbati, E ; Naghdabadi, R ; Sharif University of Technology
    The computational aspects of the finite element solution procedure based on the Cosserat theory are studied for some elastic-plastic problems, in which the localization occurs. For this purpose, the equations of the Cosserat elasto-plasticity, which include effects of couple stress, micro-rotation and length scale, are presented. The Cosserat finite element formulation is derived and an algorithm for the solution procedure is proposed. For the elastic-plastic problems considered here, the mesh-independency of the Cosserat-based results is quantified and effects of the internal length and Cosserat material parameter a are investigated on the results. Also, the influence of the internal length... 

    Elastic-plastic modeling of the hardening materials based on an Eulerian strain tensor and a proper corotational rate

    , Article 2005 ASME Pressure Vessels and Piping Conference, PVP2005, Denver, CO, 17 July 2005 through 21 July 2005 ; Volume 2 , 2005 , Pages 201-206 ; 0277027X (ISSN) Naghdabadi, R ; Ghavam, K ; Sharif University of Technology
    In this paper a model for analyzing elastic-plastic kinematic hardening materials is introduced, based on the additive decomposition of the corotational rate of an Eulerian strain tensor In this model, the elastic constitutive equation as well as the flow rule and the hardening equation is expressed in terms of the elastic and plastic parts of the corotational rate of the mentioned Eulerian strain tensor and its conjugate stress tensor. In the flow rule, the plastic part of the corotational rate of the Eulerian strain tensor is related to the difference of the deviatoric part of the conjugate stress and the back stress tensors. A proportionality factor is used in this flow rule which must be... 

    Periodicity in the response of nonlinear plate, under moving mass

    , Article Thin-Walled Structures ; Volume 40, Issue 3 , 2002 , Pages 283-295 ; 02638231 (ISSN) Shadnam, M. R ; Rahimzadeh Rofooei, F ; Mofid, M ; Mehri, B ; Sharif University of Technology
    The dynamics of nonlinear thin plates under influence of relatively heavy moving masses is considered. By expansion of the solution as a series of mode functions, the governing equations of motion are reduced to an ordinary differential equation for time development of vibration amplitude, which is Duffing's oscillator with time varying coefficients. Through the application of Banach's fixed-point theorem, the periodic solutions are predicted. The method presented in this paper is general so that the response of plate to moving force systems can also be considered. © 2002 Published by Elsevier Science Ltd  

    Micropolar hypo-elasticity

    , Article Archive of Applied Mechanics ; Volume 80, Issue 12 , December , 2010 , Pages 1449-1461 ; 09391533 (ISSN) Ramezani, S ; Naghdabadi, R ; Sharif University of Technology
    In this paper, the concept of hypo-elasticity is generalized to the micropolar continuum theory, and the general forms of the constitutive equations of the micropolar hypo-elastic materials are presented. A new co-rotational objective rate whose spin is the micropolar gyration tensor is introduced which describes the deformation of the material in view of an observer attached to the micro-structure. As special case, simplified versions of the proposed constitutive equations are given in which the same fourth-order elasticity tensors are used as in the micropolar linear elasticity. A 2-D finite element formulation for large elastic deformation of micropolar hypo-elastic media based on the... 

    Effect of interface stresses on the elastic deformation of an elastic half-plane containing an elastic inclusion

    , Article International Journal of Solids and Structures ; Volume 46, Issue 14-15 , 2009 , Pages 2897-2906 ; 00207683 (ISSN) Avazmohammadi, R ; Yang, F ; Abbasion, S ; Sharif University of Technology
    The effect of the interface stresses is studied upon the size-dependent elastic deformation of an elastic half-plane having a cylindrical inclusion with distinct elastic properties. The elastic half-plane is subjected to either a uniaxial loading at infinity or a uniform non-shear eigenstrain in the inclusion. The straight edge of the half-plane is either traction-free, or rigid-slip, or motionless, which represents three practical situations of mechanical structures. Using two-dimensional Papkovich-Neuber potentials and the theory of surface/interface elasticity, the elastic field in the elastic half-plane is obtained. Comparable with classical result, the new formulation renders the... 

    Magnetic field effect on free vibration of smart rotary functionally graded nano/microplates: a comparative study on modified couple stress theory and nonlocal elasticity theory

    , Article Journal of Intelligent Material Systems and Structures ; Volume 29, Issue 11 , 2018 , Pages 2492-2507 ; 1045389X (ISSN) Shojaeefard, M. H ; Saeidi Googarchin, H ; Mahinzare, M ; Eftekhari, S. A ; Sharif University of Technology
    SAGE Publications Ltd  2018
    In this article, free vibration behavior of a rotating nano/microcircular plate constructed from functionally graded magneto-elastic material is simulated with the first-order shear deformation theory. For the sake of comparison, the nonlocal elasticity theory and the modified couple stress theory are employed to implement the small size effect in the natural frequencies behavior of the nano/microcircular plate. The governing equations of motion for functionally graded magneto-elastic material nano/microcircular plates are derived based on Hamilton’s principle; comparing the obtained results with those in the literature, they are in a good agreement. Finally, the governing equations are...