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    Effective strain based on shear and principal strains in equal channel angular extrusion with outer curved corner

    , Article Computational Materials Science ; Volume 41, Issue 3 , 2008 , Pages 409-419 ; 09270256 (ISSN) Eivani, A. R ; Karimi Taheri, A ; Sharif University of Technology
    2008
    Abstract
    In this paper, with introducing and based on a new configuration of equal channel angular extrusion (ECAE) process, nominated as multi-stage equal channel angular extrusion, two relationships are derived to calculate the effective strain based on shear and principal strains. First, a solution is presented for evaluating the effective strain in multi-stage ECAE dies consisting of two or more ECAE sub-dies. Then, the solution is extended to calculate the effective strains in ECAE dies with outer curved corner. The effective strain based on shear strains shows an exact agreement with previously published results. The derived relationships were compared with each other, with the relationships... 

    Strain effect on quantum conductance of graphene nanoribbons from maximally localized wannier functions

    , Article Physical Review B: Condensed Matter ; Volume 81, Issue 12, Article number 125409 , 5 March , 2010 Rasuli, R. (Reza) ; Rafii-Tabar, H ; Iraji Zad, A. (Azam) ; Sharif University of Technology
    Abstract
    Density-functional study of strain effects on the electronic band structure and transport properties of the graphene nanoribbons (GNR) is presented. We apply a uniaxial strain (ε) in the x (nearest-neighbor) and y (second-nearest-neighbor) directions, related to the deformation of zigzag- and armchair-edge GNRs (AGNR and ZGNR), respectively. We calculate the quantum conductance and band structures of the GNR using the Wannier function in a strain range from −8% to +8% (minus and plus signs show compression and tensile strain). As strain increases, depending on the AGNR family type, the electrical conductivity changes from an insulator to a conductor. This is accompanied by a variation in the... 

    Comment on "A micro scale Timoshenko beam model based on strain gradient elasticity theory

    , Article European Journal of Mechanics, A/Solids ; 2014 ; ISSN: 09977538 Nojoumian, M. A ; Salarieh, H ; Sharif University of Technology
    Abstract
    A micro scale Timoshenko beam was modeled with strain gradient theory in "A micro scale Timoshenko beam model based on strain gradient elasticity theory" by Wang et al., European Journal of Mechanics - A/Solids, vol. 29, pp. 591-599, 7//2010. Looking at the modeling of the beam, a mistake in deriving the effect of classical moment has occurred. The classical boundary conditions of a Timoshenko beam could not be derived going backward from the strain gradient Timoshenko beam theory which has been presented in aforementioned paper. In this comment, the contradiction has been shown and the correct form of the boundary conditions and final equations has been derived  

    Non-linear behaviors of carbon nanotubes under electrostatic actuation based on strain gradient theory

    , Article International Journal of Non-Linear Mechanics ; Vol. 67, issue , 2014 , p. 236-244 Fakhrabadi, M. M. S ; Rastgoo, A ; Ahmadian, M. T ; Sharif University of Technology
    Abstract
    The paper deals with studying the deflection and pull-in voltages of the carbon nanotubes under electrostatic actuation with various dimensions and boundary conditions. The size-dependent behaviors of the carbon nanotubes (CNTs) are considered via application of the strain gradient theory. The results obtained from the strain gradient theory are compared to those estimated using the classical elasticity. The outcomes reveal that the classical elasticity theory underestimates the pull-in voltages of the carbon nanotubes and strain gradient theorem results in stiffer nano-structures with higher pull-in voltages. Increasing of the deflection due to the higher voltages increases the differences... 

    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... 

    Determination of flow stress under hot deformation conditions

    , Article Materials Science and Engineering A ; Volume 552 , 2012 , Pages 566-568 ; 09215093 (ISSN) Solhjoo, S ; Sharif University of Technology
    2012
    Abstract
    In order to predict the flow stress curves up to peak under the hot working conditions two crucially modified models are presented. The modification is done by considering the effects of both temperature and strain rate. Besides, the ability of prediction at very low strains is added to them. Furthermore a new mathematical model has been developed to estimate the stress-strain curves beyond the peak via a secant hyperbolic function. The predicted results are found to be in accord with empirical values  

    Performance evaluation of source heterojunction strained channel gate all around nanowire transistor

    , Article Modern Physics Letters B ; Volume 26, Issue 12 , May , 2012 ; 02179849 (ISSN) Hosseini, R ; Fathipour, M ; Faez, R ; Sharif University of Technology
    2012
    Abstract
    A Gate All Around Nanowire Transistor (GAA NWT) which employs source heterojunction and strained channel is proposed which improves device characteristics. A quantum mechanical transport approach based on nonequilibrium Green's function (NEGF) method in the frame work of effective mass theory is employed in this analysis. We evaluate the variation of the threshold voltage, the subthreshold slope, ON and OFF state currents when channel length decreases. It is shown that the source heterojunction strained channel GAA NWT gives high performance transistors values of the scaled transconductance and ON current that are greater than conventional silicon GAA NWT. Furthermore, comparison of... 

    Work hardening of Duratherm 600 cobalt superalloy using repetitive corrugation and straightening process

    , Article Russian Journal of Non-Ferrous Metals ; Volume 51, Issue 1 , February , 2010 , Pages 59-61 ; 10678212 (ISSN) Sheikh, H ; Paimozd, E ; Hashemi, S. M ; Sharif University of Technology
    2010
    Abstract
    In this paper, the effect of repetitive corrugation and straightening (RCS) process on hardness of Duratherm 600 superalloy has been investigated. To do so, the RCS was carried out until 25 cycles using multiple teeth corrugative setup that the rotation of sample with 90° between cycles was utilized. The results show that the increasing of cycle number enhances the value of hardness. Also, the microstructures of samples are an evidence of slipbands formation during RCS showing the applied strain on the material. As a result, the increasing of hardness can be attributed to formation of subgrains, LAGBs and hcp martensitic plates at large strains  

    Comment on “A micro scale Timoshenko beam model based on strain gradient elasticity theory”

    , Article European Journal of Mechanics, A/Solids ; Volume 60 , 2016 , Pages 361-362 ; 09977538 (ISSN) Nojoumian, M. A ; Salarieh, H ; Sharif University of Technology
    Elsevier Ltd 
    Abstract
    A micro scale Timoshenko beam was modeled with strain gradient theory in “A micro scale Timoshenko beam model based on strain gradient elasticity theory” by Wang et al., European Journal of Mechanics – A/Solids, vol. 29, pp. 591–599, 7//2010. Looking at the modeling of the beam, a mistake in deriving the effect of classical moment has occurred. The classical boundary conditions of a Timoshenko beam could not be derived going backward from the strain gradient Timoshenko beam theory which has been presented in aforementioned paper. In this comment, the contradiction has been shown and the correct form of the boundary conditions and final equations has been derived  

    Modeling of the mutual effect of dynamic precipitation and dislocation density in age hardenable aluminum alloys

    , Article Journal of Alloys and Compounds ; Volume 683 , 2016 , Pages 527-532 ; 09258388 (ISSN) Khani Moghanaki, S ; Kazeminezhad, M ; Sharif University of Technology
    Elsevier Ltd  2016
    Abstract
    A model has been proposed to capture the complex strain rate effect on dynamic precipitation of GP zones in an age-hardenable aluminum alloy. The contributions of vacancies and dislocations to dynamically formed GP zones have been specified in the model. It has been demonstrated that the proposed model is capable for predicting the contribution of each dynamic precipitation mechanisms, accurately, which are acting during deformation. Furthermore, the vacancy and dislocation evolutions during deformation have been considered in this modeling. The effect of strain rate by considering different mechanisms of dynamic precipitation of GP zones has been studied and confirmed by experimental data... 

    Influence of aluminide diffusion coating on low cycle fatigue properties of René 80

    , Article Materials Science and Engineering A ; Volume 486, Issue 1-2 , 2008 , Pages 686-695 ; 09215093 (ISSN) Rahmani, Kh ; Nategh, S ; Sharif University of Technology
    2008
    Abstract
    Low cycle fatigue is one of the most important phenomena affecting the lifetime of jet engine blades. In this paper, the effect of aluminide diffusion coating (CODEP-B) on low cycle fatigue properties of René 80 has been studied at temperature of 871 °C, R = 0 and strain rate of about 2 × 10-3 s-1. Experimental results show that the applied cyclic strain is lower than 0.8%, the presence of aforesaid coating increases the fatigue lifetime. In coated specimens, while the total cyclic strain is lower than 0.8%, the nucleation of the cracks occurs merely in substrate, but in cyclic strain more than 1%, as a result of simultaneous nucleation of cracks in the coating surface, diffusion layer and... 

    The effect of 3D and 2D deformations on flattened wires

    , Article Journal of Materials Processing Technology ; Volume 202, Issue 1-3 , 2008 , Pages 553-558 ; 09240136 (ISSN) Kazeminezhad, M ; Karimi Taheri, A ; Sharif University of Technology
    2008
    Abstract
    To investigate the effect of 3D and 2D deformations on flattened wires, the effective strain fields of flat rolled and sidepressed wires are predicted using the combined finite and slab element method (FSEM) and two-dimensional finite element method (TDFEM), respectively. The validity of the calculated strain fields are verified using the Vickers microhardness test. Utilizing the calculated strain fields, the strain inhomogeneity of the flat rolled and sidepressed wires are investigated. To assess the effects of height to width ratio and frictional condition on the strain inhomogeneity, an inhomogeneity factor (IF) is defined. The results show that for both the flat rolled and sidepressed... 

    Some basis-free expressions for stresses conjugate to Hill's strains through solving the tensor equation AX + XA = C

    , Article International Journal of Solids and Structures ; Volume 45, Issue 11-12 , 2008 , Pages 3584-3595 ; 00207683 (ISSN) Asghari, M ; Naghdabadi, R ; Sohrabpour, S ; Sharif University of Technology
    2008
    Abstract
    In the present paper, some new and compact basis-free expressions are derived for representing stresses conjugate to the Lagrangean Hill's strain measures. Solving a tensor equation in the form of AX + XA = C, a rather simple general expression is obtained for the conjugate stresses in the case of distinct principal stretches. The result decomposes the conjugate stresses additively into two parts, such that one part is coaxial with the right stretch tensor while another part is orthogonal to it. An expression for the case of double-coalescent principal stretches is also obtained. As an example of the general results, simple expressions are obtained for the stress conjugate to the logarithmic... 

    A study on strain ageing during and after warm rolling of a carbon steel

    , Article Materials Letters ; Volume 62, Issue 6-7 , 2008 , Pages 946-948 ; 0167577X (ISSN) Serajzadeh, S ; Akhgar, J. M ; Sharif University of Technology
    2008
    Abstract
    In this study, strain ageing during and after warm rolling of a carbon steel has been investigated. At the first step, the occurrence of serrated flow was studied by means of tensile tests at different temperatures and strain rates. In the next stage, warm rolling experiments were performed under different rolling conditions and then the samples were aged at the room temperature for a period of 3 months. For both aged and non-aged samples, tensile tests were employed to evaluate their mechanical properties. The results show that static strain ageing is possible to happen in the utilized ageing period and increases the yield stress of the aged steel. However, the samples that experience both... 

    On the objective corotational rates of eulerian strain measures

    , Article Journal of Elasticity ; Volume 90, Issue 2 , 2008 , Pages 175-207 ; 03743535 (ISSN) Asghari, M ; Naghdabadi, R ; Sharif University of Technology
    2008
    Abstract
    In the present paper, some new basis-free expressions for an arbitrary objective corotational rate of the general Eulerian strain measures are provided which are in compact form. Moreover, a complete discussion on the requirements for the continuity of the objective corotational rates are presented. © 2008 Springer Science+Business Media B.V  

    Stresses conjugate to the Jaumann rate of Eulerian strain measures

    , Article Acta Mechanica ; Volume 190, Issue 1-4 , 2007 , Pages 45-56 ; 00015970 (ISSN) Asghari, M ; Naghdabadi, R ; Sohrabpour, S ; Sharif University of Technology
    2007
    Abstract
    In this paper basis-free expressions are derived for the stresses conjugate to the Jaumann rate of the general Eulerian strain measures. The component-form of the expressions is also presented. The basis-free results are compact and also valid for all different cases of distinct and coalescent principal stretches. As an example, the compact basis-free expressions for the stress conjugate to the Jaumann rate of logarithmic strain lnV are determined. © Springer-Verlag Wien 2007  

    Intrinsic expressions for arbitrary stress tensors conjugate to general strain tensors

    , Article Scientia Iranica ; Volume 14, Issue 5 , 2007 , Pages 486-493 ; 10263098 (ISSN) Sohrabpour, S ; Naghdabadi, R ; Asghari, M ; Sharif University of Technology
    Sharif University of Technology  2007
    Abstract
    In this paper, a unified explicit tensorial relation is sought between two stress tensors conjugate to arbitrary and general Hill strains. The approach used for deriving the tensorial relation is based on the eigenprojection method. The result is, indeed, a generalization of the relations that were derived by Farahani and Naghadabadi [1] in 2003 from a component to intrinsic form. The result is unified in the sense that it is valid for all cases of distinct and coalescent principal stretches. Also, in the case of three dimensional Euclidean inner product space, using the derived unified relation, some expressions for the conjugate stress tensors are presented. © Sharif University of... 

    Multiaxial stress-strain modeling and effect of additional hardening due to nonproportional loading

    , Article Journal of Mechanical Science and Technology ; Volume 21, Issue 8 , 2007 , Pages 1153-1161 ; 1738494X (ISSN) Rashed, G ; Ghajar, R ; Farrahi, G ; Sharif University of Technology
    Korean Society of Mechanical Engineers  2007
    Abstract
    Most engineering components are subjected to multiaxial rather than uniaxial cyclic loading, which causes multiaxial fatigue. The pre-requisite to predict the fatigue life of such components is to determine the multiaxial stressstrain relationship. In this paper the multiaxial cyclic stress-strain model under proportional loading is derived using the modified power law stress-strain relationship. The equivalent strain amplitude consisted of the normal strain excursion and maximum shear strain amplitude is used in the proportional model to include the additional hardening effect due to nonproportional loading. Therefore a new multiaxial cyclic stress-strain relationship is devised for out of... 

    Unified basis-free relation between two stress tensors conjugate to arbitrary Hill's strain measures

    , Article ASME PVP2006/ICPVT-11 Conference, Vancouver, BC, 23 July 2006 through 27 July 2006 ; Volume 2006 , 2006 ; 0277027X (ISSN); 0791837823 (ISBN); 9780791837825 (ISBN) Asghari, M ; Naghdabadi, R ; Sharif University of Technology
    American Society of Mechanical Engineers(ASME)  2006
    Abstract
    The concept of energy conjugacy for stress and strain measures states that a stress tensor T is conjugate to a strain measure E if T: Ė provides the rate of change of the internal energy per unit reference volume of the body in an adiabatic process. The applications of the conjugate stress and strain measures are in the development of the basic relations in nonlinear analysis of solids. In this paper using eigenprojection method, unified explicit basis-free relation between two arbitrary stress tensors T(f) and T (g), respectively conjugate to two measures of Hill's strains is determined. The result is valid for arbitrary dimension of the Euclidean inner product space and for all cases of... 

    Effect of rolling speed on the occurrence of strain aging during and after warm rolling of a low-carbon steel

    , Article Journal of Materials Science ; Volume 45, Issue 13 , July , 2010 , Pages 3405-3412 ; 00222461 (ISSN) Koohbor, B ; Ohadi, D ; Serajzadeh, S ; Akhgar, J. M ; Sharif University of Technology
    2010
    Abstract
    In this study, effect of rolling speed on strain aging phenomena in warm rolling of a carbon steel has been investigated. For this purpose, by using a mathematical model and predicting temperature and strain rate fields, the possibility of occurrence of dynamic strain aging during the warm rolling was first evaluated. In the next stage, warm-rolled samples were aged up to 11 months at room temperature for studying the kinetics of static strain aging, while mechanical tests as well as microstructural evolutions have been performed to determine the effect of strain aging on material behavior. The results indicate that dynamic strain aging may not occur for the employed rolling program;...