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    Kinematics and kinetics modeling of thermoelastic continua based on the multiplicative decomposition of the deformation gradient

    , Article International Journal of Engineering Science ; Volume 62 , 2013 , Pages 56-69 ; 00207225 (ISSN) Darijani, H ; Naghdabadi, R ; Sharif University of Technology
    2013
    Abstract
    Solids usually show complex material behavior. If deformation is finite, the description of the kinematics makes the mechanical model complicated. In fact, one of the basic questions in the formulation and analysis procedures of finite deformation thermoelasticity is: "How can the finite deformation thermoelasticity response be best accounted for in the kinematic formulation?" A rather attractive way to proceed is to use the approach of small strain analysis, and decompose the total strain into a mechanical part and a thermal part. In this paper, based on the multiplicative decomposition of the deformation gradient, the mechanical and thermal strains are defined in the power and exponential... 

    A strain energy function for rubber-like materials

    , Article Constitutive Models for Rubber VIII - Proceedings of the 8th European Conference on Constitutive Models for Rubbers, ECCMR 2013 ; 2013 , Pages 205-210 ; 9781138000728 (ISBN) Khajehsaeid, H ; Naghdabadi, R ; Arghavani, J ; Sharif University of Technology
    2013
    Abstract
    Hyperelastic behavior of isotropic incompressible rubbers are studied to develop a strain energy function. The proposed function includes only three material parameters which are related to physical properties of the material molecular network. Furthermore, the model benefits from well suitting in all ranges of stretch as well as possessing the property of deformation mode independency. This reduces the required number of experimental tests for parameter calibration. Results of the model are compared with results of Mooney-Rivlin, Arruda-Boyce, Gent and Gao models as well as the experimental data  

    Hyperelastic materials modelling using a strain measure consistent with the strain energy postulates

    , Article Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science ; Volume 224, Issue 3 , 2010 , Pages 591-602 ; 09544062 (ISSN) Darijani, H ; Naghdabadi, R ; Kargarnovin, M. H ; Sharif University of Technology
    Abstract
    In this article, a strain energy density function of the Saint Venant-Kirchhoff type is expressed in terms of a Lagrangian deformation measure. Applying the governing postulates to the form of the strain energy density, the mathematical expression of this measure is determined. It is observed that this measure, which is consistent with the strain energy postulates, is a strain type with the characteristic function more rational than that of the Seth-Hill strain measures for hyperelastic materials modelling. In addition, the material parameters are calculated using a novel procedure that is based on the correlation between the values of the strain energy density (rather than the stresses)... 

    Inhomogeneous swelling behavior of temperature sensitive PNIPAM hydrogels in micro-valves: Analytical and numerical study

    , Article Smart Materials and Structures ; Volume 24, Issue 4 , February , 2015 ; 09641726 (ISSN) Mazaheri, H ; Baghani, M ; Naghdabadi, R ; Sohrabpour, S ; Sharif University of Technology
    Institute of Physics Publishing  2015
    Abstract
    In this work, inhomogeneous swelling of the temperature-sensitive PNIPAM hydrogel is investigated with application to micro-valves. In this regard, a modified model is considered, and an analytical solution of the inhomogeneous swelling of a hydrogel jacket coated on a rigid pillar is performed, which is valuable for the conceptual design of the micro-valve. Then, finite element implementation of the modified model is carried out, and its validity is verified by both the analytical and experimental results. Thereafter, thermo-mechanical behavior of the micro-valve is investigated considering the coupling between the inhomogeneous swelling of the jacket and contact problems due to the... 

    Strain and stress concentrations in elastomers at finite deformations: effects of strain-induced crystallization, filler reinforcement, and deformation rate

    , Article Acta Mechanica ; Volume 227, Issue 7 , 2016 , Pages 1969-1982 ; 00015970 (ISSN) Khajehsaeid, H ; Reese, S ; Arghavani, J ; Naghdabadi, R ; Sharif University of Technology
    Springer-Verlag Wien 
    Abstract
    Strain and stress concentrations are studied for elastomers at finite deformations. Effects of strain-induced crystallization, filler reinforcement and deformation rate are also investigated, and micromechanical descriptions are provided for the observed results. A simple problem is subjected to finite element simulations to show the results evidently. Material parameters are obtained from experimental tests conducted on standard tensile samples of filled and unfilled natural rubber (NR) as well as styrene–butadiene rubber (SBR) as crystallizing and non-crystallizing rubbers, respectively. In all simulations, the strain concentration factor KE is shown to decrease monotonically where the... 

    Stress gradient interpretation of boundary layers in passivated thin films

    , Article International Journal of Non-Linear Mechanics ; Volume 81 , 2016 , Pages 139-146 ; 00207462 (ISSN) Zamani, Z ; Soleymani Shishvan, S ; Assempour, A ; Sharif University of Technology
    Elsevier Ltd  2016
    Abstract
    A continuum implementation of stress gradient plasticity is established to analyze passivated thin films under tension. It is verified and evaluated by investigation of the tensile response of passivated Cu films with different thicknesses and grain sizes. The material parameters are fitted to the stress-strain experimental data, while the length scale parameter is directly characterized from the corresponding available discrete dislocation predictions. The numerical solutions give rise to boundary layers near the interface between film and passivation. This prediction is consistent with the formation of dislocation pileups at the film-passivation interface and also is responsible for the... 

    Anisotropy in the quasi-static and cyclic behavior of ZK60 extrusion: Characterization and fatigue modeling

    , Article Materials and Design ; Volume 160 , 2018 , Pages 936-948 ; 02641275 (ISSN) Pahlevanpour, A. H ; Karparvarfard, S. M. H ; Shaha, S. K ; Behravesh, S. B ; Adibnazari, S ; Jahed, H ; Sharif University of Technology
    Elsevier Ltd  2018
    Abstract
    The quasi-static and strain-controlled fatigue characteristics of ZK60 extrusion have been investigated along three different directions: the extrusion direction (ED), the radial direction (RD), and 45° to the extrusion direction (45°). The quasi-static response showed symmetric behavior for the samples tested along RD and 45° whereas the ED samples manifested completely asymmetric behavior. Although the ED samples exhibited longer fatigue lives than the RD and 45° in the high cycle fatigue, the fatigue lives in the low cycle fatigue regime were similar. The texture measurement indicated a sharp basal texture along ED, explaining its asymmetric behavior. Higher tensile mean stress and less... 

    Limiting grain size through high-pressure torsion of different materials

    , Article Materials Science and Technology (United Kingdom) ; Volume 36, Issue 2 , 2020 , Pages 245-250 Parvin, H ; Kazeminezhad, M ; Sharif University of Technology
    Taylor and Francis Ltd  2020
    Abstract
    The main goal of high-pressure torsion (HPT) process is to reduce the grain size. Experiments have shown that this aim is achievable, but there is a limit in reducing the grain size. The present paper investigates this limit through a thermodynamics-based model. However, this was investigated by other researches through dislocation density-based model. At first, the validity of the model in description of the limiting grain size obtainable by HPT of different materials is examined. Then, the influence of inherent material parameters is investigated. Finally, the present results are compared with those obtained by equal channel angular pressing. © 2019, © 2019 Institute of Materials, Minerals... 

    Simulation of thermal radiation in a micropolar fluid flow through a porous medium between channel walls

    , Article Journal of Thermal Analysis and Calorimetry ; Volume 144, Issue 3 , 2021 , Pages 941-953 ; 13886150 (ISSN) Ahmad, S ; Ashraf, M ; Ali, K ; Sharif University of Technology
    Springer Science and Business Media B.V  2021
    Abstract
    Among numerous methods which have been employed to reinforce the thermal efficiency in many systems, one is the thermal radiation which is a mode of heat transfer. Another way to improve the thermal efficiency is the utilization of the porous media. The present work includes the study of micropolar flow with allowance for thermal radiation through a resistive porous medium between channel walls. The governing coupled partial differential equations representing the flow model are transmuted into ordinary ones by using the suitable dimensionless coordinates, and then, quasi-linearization is employed to solve the set of relevant coupled ODEs. Effects of physical parameters on the flow under... 

    Simulation of thermal radiation in a micropolar fluid flow through a porous medium between channel walls

    , Article Journal of Thermal Analysis and Calorimetry ; Volume 144, Issue 3 , 2021 , Pages 941-953 ; 13886150 (ISSN) Ahmad, S ; Ashraf, M ; Ali, K ; Sharif University of Technology
    Springer Science and Business Media B.V  2021
    Abstract
    Among numerous methods which have been employed to reinforce the thermal efficiency in many systems, one is the thermal radiation which is a mode of heat transfer. Another way to improve the thermal efficiency is the utilization of the porous media. The present work includes the study of micropolar flow with allowance for thermal radiation through a resistive porous medium between channel walls. The governing coupled partial differential equations representing the flow model are transmuted into ordinary ones by using the suitable dimensionless coordinates, and then, quasi-linearization is employed to solve the set of relevant coupled ODEs. Effects of physical parameters on the flow under... 

    Kinematic and Constitutive Modeling of Elastic and Thermoelastic Continua with Finite Deformation using Multiplicative Decomposition of Deformation Gradient

    , Ph.D. Dissertation Sharif University of Technology Darijani, Hossein (Author) ; Naghdabadi, Reza (Supervisor) ; Kargarnovin, Mohammad Hassan (Supervisor)
    Abstract
    In this thesis, a deformation measure is introduced which leads to a class of strain measures in the Lagrangian and Eulerian descriptions. In order to develop a constitutive equation, a second-order constitutive relation based on these strain measures is considered for modeling the mechanical behavior of solids at finite deformation. For this purpose and performance evaluation of the proposed strains, a Hookean-type constitutive equation is considered and the uniaxial loading as well as simple shear and pure shear tests are examined and the results are compared with the test data. Also, in order to characterize the mechanical behavior of elastic continua, constitutive equations through a... 

    A constitutive model for shape memory polymers with application to torsion of prismatic bars

    , Article Journal of Intelligent Material Systems and Structures ; Volume 23, Issue 2 , 2012 , Pages 107-116 ; 1045389X (ISSN) Baghani, M ; Naghdabadi, R ; Arghavani, J ; Sohrabpour, S ; Sharif University of Technology
    Abstract
    In this article, satisfying the second law of thermodynamics, we present a 3D constitutive model for shape memory polymers. The model is based on an additive decomposition of the strain into four parts. Also, evolution laws for internal variables during both cooling and heating processes are proposed. Since temperature has considerable effect on the shape memory polymer behavior, for simulation of a shape memory polymer-based structure, it is required to perform a heat-transfer analysis. Commonly, an experimentally observed temperature rate-dependent behavior of shape memory polymers is justified by a rate-dependent glassy temperature, but using the heat-transfer analysis, it is shown that... 

    A novel nonlinear constitutive relation for graphene and its consequence for developing closed-form expressions for Young's modulus and critical buckling strain of single-walled carbon nanotubes

    , Article Acta Mechanica ; Volume 222, Issue 1-2 , 2011 , Pages 91-101 ; 00015970 (ISSN) Shodja, H. M ; Delfani, M. R ; Sharif University of Technology
    2011
    Abstract
    Carbon nanotubes (CNTs) are viewed as rolled graphene. Thus, an appropriate formulation describing the behavior of CNTs must contain the key information about both their initial configuration as graphene and final configuration as CNT.On this note, to date, somemodels, in particular based on the Cauchy- Born rule, for the description of CNTs behavior exist. A simplifying assumption in some of these models is that the length and perimeter of the CNT equal the corresponding dimensions of the unrolled initial configuration, thus neglecting the induced hoop and longitudinal strains. On the other hand, the present work offers a purely nonlinear continuum model suitable for the description of the... 

    Constitutive modeling of rubberlike materials based on consistent strain energy density functions

    , Article Polymer Engineering and Science ; Volume 50, Issue 5 , 2010 , Pages 1058-1066 ; 00323888 (ISSN) Darijani, H ; Naghdabadi, R ; Kargarnovin, M. H ; Sharif University of Technology
    Abstract
    Rubberlike materials are characterized by high deformability and reversibility of deformation. From the continuum viewpoint, a strain energy density function is postulated for modeling the behavior of these materials. In this paper, a general form for the strain energy density of these materials is proposed from a phenomenological point of view. Based on the Valanis-Landel hypothesis, the strain energy density of incompressible materials is expressed as the sum of independent functions of the principal stretches meeting the essential requirements on the form of the strain energy density. It is cleared that the appropriate mathematical expressions for constitutive modeling of these materials... 

    A dislocation-based model considering free surface theory through HPT process: Nano-structured Ni

    , Article Scientia Iranica ; Volume 17, Issue 1 F , 2010 , Pages 52-59 ; 10263098 (ISSN) Hosseini, E ; Kazeminezhad, M ; Sharif University of Technology
    2010
    Abstract
    In this study, a dislocation-based model is presented for investigating the evolution of micro structure and mechanical properties of thin films during a wide range of straining. The model is applied to the High Pressure Torsion (HPT) process of thin nickel disks that provides valuable information on the evolution of material parameters during deformation. The model considers a free surface theory for thin films and can explain the size effect phenomenon in agreement with previous reported trends in literature  

    Impact crushing behavior of foam-filled paraboloid shells using numerical and experimental methods

    , Article Scientia Iranica ; Volume 24, Issue 4 , 2017 , Pages 1912-1921 ; 10263098 (ISSN) Shams, S ; Haddadpour, H ; Tuzandejani, H ; Hosseini, S. A. A ; Vatanparast, M ; Zahab, S ; Sharif University of Technology
    Sharif University of Technology  2017
    Abstract
    This paper deals with the dynamic response and energy absorption of foam-filled aluminum parabolic tubes under axial impact loading. The numerical crush analysis of empty and foam-filled tubes is performed using non-linear finite element techniques. The effects of geometrical (wall thickness) and material parameters (foam density and Young's relaxation modulus) on the impact response and energy absorption capacity of foam-filled tube are investigated using numerical models. The results show that the foam properties have significant effect on the crushing behavior, force and impact acceleration magnitude, and energy absorption capacity. Furthermore, there is a critical foam density beyond... 

    Non-linear finite element implementation of micropolar hypo-elastic materials

    , Article Computer Methods in Applied Mechanics and Engineering ; Volume 197, Issue 49-50 , 15 September , 2008 , Pages 4149-4159 ; 00457825 (ISSN) Ramezani, S ; Naghdabadi, R ; Sohrabpour, S ; Sharif University of Technology
    2008
    Abstract
    In this paper, updated Lagrangian finite element formulations for large elastic deformation of micropolar hypo-elastic materials are presented. Using representation theorems of tensor functions, the general form of the constitutive equations for the micropolar hypo-elastic materials model are presented. The finite element formulations are based on the general form of the micropolar hypo-elastic constitutive equations in conjunction with Jaumann rate and a new rate called gyration rate. Gyration rate describes the deformation of the material in view of an observer attached to the micro-structure. An incrementally objective stress and couple stress update procedure is developed and its... 

    Investigation of the influence of permeability coefficient on the numerical modeling of the liquefaction phenomenon

    , Article Scientia Iranica ; Volume 19, Issue 2 , 2012 , Pages 179-187 ; 10263098 (ISSN) Rahmani, A ; Ghasemi Fare, O ; Pak, A ; Sharif University of Technology
    2012
    Abstract
    The soil permeability coefficient plays a key role in the process of numerical simulation of the liquefaction phenomenon. Liquefaction causes a considerable increase in soil permeability, due to the creation of easier paths for water flow. The work presented in this paper tries to investigate the effects of permeability coefficient on the results of numerical modeling of the liquefaction phenomenon. To do this, a fully coupled (u-P) formulation is employed to analyze soil displacements and pore water pressures. Two different versions of a well-calibrated critical state bounding surface plasticity model, which possesses the capability to utilize a single set of material parameters for a wide...