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    Upper bound analysis of deformation and dynamic ageing behavior in elevated temperature equal channel angular pressing of Al-Mg-Si alloys

    , Article Metals and Materials International ; Volume 16, Issue 3 , June , 2010 , Pages 363-369 ; 15989623 (ISSN) Vaseghi, M ; Karimi Taheri, A ; Seop Kim, H ; Sharif University of Technology
    2010
    Abstract
    In the present study, the plastic deformation and dynamic strain ageing behavior of Al-6082 (Al-Mg-Si) alloy treated with elevated temperature equal channel angular pressing (ECAP) were investigated using upper bound analyses. Tensile tests were carried out over wide ranges of temperature and strain rate in order to evaluate the dynamic ageing conditions. ECAP processing was then experimentally performed at temperatures from room temperature up to 200 °C under various strain rates ranging between 10-4 s-1 and 10-1 s-1 . The upper bound analysis solutions and the experimental results are comparable. A theoretical dynamic ageing region was found to be in the temperature range of 90 °C to 260... 

    Constitutive modeling of hot deformation behavior of the AA6063 alloy with different precipitates

    , Article Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science ; Volume 44, Issue 13 , December , 2013 , Pages 5853-5860 ; 10735623 (ISSN) Anjabin, N ; Taheri, A. K ; Kim, H. S ; Sharif University of Technology
    2013
    Abstract
    The current study proposes a simple constitutive model that integrates the kinetics of precipitation during static aging and the kinetics of precipitate dissolution during preheating to deformation temperature to predict the hot flow behavior of AA6063 alloy. The model relates the flow behavior of the age-hardenable alloy to the alloy chemistry, thermal history as well as deformation temperature, strain, and strain rate by means of a physically based model. Different aging conditions, including supersaturated solid solution and overaging conditions with different deformation parameters, were assessed. Each part of the model was in good agreement with those of experimental and other model... 

    Deformation of outer representations of galois group II

    , Article Iranian Journal of Mathematical Sciences and Informatics ; Volume 6, Issue 2 , 2011 , Pages 33-41 ; 17354463 (ISSN) Rastegar, A ; Sharif University of Technology
    2011
    Abstract
    This paper is devoted to deformation theory of "anabelian" representations of the absolute Galois group landing in outer automorphism group of the algebraic fundamental group of a hyperbolic smooth curve defined over a number-field. In the first part of this paper, we obtained several universal deformations for Lie-algebra versions of the above representation using the Schlessinger criteria for functors on Artin local rings. In the second part, we use a version of Schlessinger criteria for functors on the Artinian category of nilpotent Lie algebras which is formulated by Pridham, and explore arithmetic applications  

    Deformation of outer representations of Galois group

    , Article Iranian Journal of Mathematical Sciences and Informatics ; Volume 6, Issue 1 , 2011 , Pages 35-52 ; 17354463 (ISSN) Rastegar, A ; Sharif University of Technology
    2011
    Abstract
    To a hyperbolic smooth curve defined over a number-field one naturally associates "ananabelian" representation of the absolute Galois group of the base field landing in outer automorphism group of the algebraic fundamental group. In this paper, we introduce several deformation problems for Lie-algebra versions of the above representation and show that, this way we get a richer structure than those coming from deformations of "abelian" Galois representations induced by the Tate module of associated Jacobian variety. We develop an arithmetic deformation theory of graded Lie algebras with finite dimensional graded components to serve our purpose  

    A new model for deformed carbon nanotubes using Green's function

    , Article Applied Physics A: Materials Science and Processing ; Volume 105, Issue 4 , 2011 , Pages 875-880 ; 09478396 (ISSN) Fathi, D ; Sarvari, R ; Sharif University of Technology
    Abstract
    A new method for modeling and analysis of deformed carbon nanotubes (CNTs) using Green's function, is presented in this paper, for the first time. Using the proposed method, a new circuit model is obtained for the deformation region of a deformed single-walled CNT (SWCNT), which the values of its elements depend on the type of deformation and also the deformation parameters such as the coupling matrices and the energy variations of deformation region. The comparison between the obtained results from the analysis of proposed model and the literature gives a good match which approves the accuracy and correctness of the proposed model  

    Post deformation at room and cryogenic temperature cooling media on severely deformed 1050-aluminum

    , Article Metals and Materials International ; Volume 24, Issue 2 , 2018 , Pages 401-414 ; 15989623 (ISSN) Sarkari Khorrami, M ; Kazeminezhad, M ; Sharif University of Technology
    Korean Institute of Metals and Materials  2018
    Abstract
    The annealed 1050-aluminum sheets were initially subjected to the severe plastic deformation through two passes of constrained groove pressing (CGP) process. The obtained specimens were post-deformed by friction stir processing at room and cryogenic temperature cooling media. The microstructure evolutions during mentioned processes in terms of grain structure, misorientation distribution, and grain orientation spread (GOS) were characterized using electron backscattered diffraction. The annealed sample contained a large number of “recrystallized” grains and relatively large fraction (78%) of high-angle grain boundaries (HAGBs). When CGP process was applied on the annealed specimen, the... 

    Dependency modeling of steady state grain size on the stacking fault energy through severe plastic deformation

    , Article Materials Letters ; Volume 159 , November , 2015 , Pages 410-412 ; 0167577X (ISSN) Parvin, H ; Kazeminezhad, M ; Sharif University of Technology
    Elsevier  2015
    Abstract
    Recent investigations have shown that the steady state grain size of severely deformed materials is dependent on the stacking fault energy. In this paper, a model is presented to investigate such a dependency which uses thermodynamics based calculations. The present model shows that the relationship between the steady state grain size and the stacking fault energy of material is in power law form, directly. Furthermore, the model shows that the steady state grain size has an exponential relationship with the self-diffusion activation energy and a decrease in the self-diffusion activation energy increases the steady state grain size. The model predictions are in good agreement with the... 

    Kinematics and kinetics description of thermoelastic finite deformation from multiplicative decomposition of deformation gradient viewpoint

    , Article Mechanics Research Communications ; Volume 37, Issue 6 , 2010 , Pages 515-519 ; 00936413 (ISSN) Darijani, H ; Kargarnovin, M. H ; Sharif University of Technology
    Abstract
    In this paper, using the multiplicative decomposition of the deformation gradient into mechanical and thermal parts, both kinematic and kinetic aspects of finite deformation thermoelasticity are considered. At first, the kinematics of the thermoelastic continua in the purely thermal process of nonisothermal deformation is investigated for finite deformation thermoelasticity. Also, a linear relation between the thermal expansion tensor and the rate of the thermal deformation tensor is presented. In order to model the mechanical behavior of thermoelastic continua in the stress-producing process of nonisothermal deformation, an isothermal effective stress-strain equation based on the... 

    Deformation characteristics evaluation of modified equal channel angular pressing processes

    , Article Materials Transactions ; Volume 51, Issue 1 , 2010 , Pages 46-50 ; 13459678 (ISSN) Yoon, S. C ; Nagasekhar, A. V ; Yoo, J. H ; El Aal, M. I. A ; Vaseghi, M ; Kim, H. S ; Sharif University of Technology
    2010
    Abstract
    In current studies, equal channel angular pressing process (ECAP) and modified ECAP processes are simulated under ideal conditions to compare the deformation characteristics. The deformation behaviour is more complicated and the strain induced during the processes is highly non-uniform in the modified ECAP processes except in the equal channel multi-angular pressing (ECMAP) process with Route C. The strain homogeneity is more of a possibility with ECAP and ECMAP with Route C processes. The deformation stress state is widely distributed in nature in modified ECAP processes than in conventional ECAP. In addition, the load requirements are also higher in modified ECAP processes with that of the... 

    Deformation behavior of severely deformed al and related mechanisms through warm tensile test

    , Article Journal of Materials Engineering and Performance ; Volume 26, Issue 3 , 2017 , Pages 1311-1324 ; 10599495 (ISSN) Charkhesht, V ; Kazeminezhad, M ; Sharif University of Technology
    Springer New York LLC  2017
    Abstract
    Flow stress and ductility behaviors of the annealed and severely deformed Al were investigated at warm deformation temperatures. Constrained groove pressing (CGP) method as a severe plastic deformation process was used. The tensile test was carried out at the temperature range of the 298-573 K and strain rate range of 0.001-0.1 s−1 to present the elevated temperature deformation behavior utilizing hyperbolic sine constitutive equation. The flow stress of the CGPed sample is increased with the number of CGP passes and decreased with temperature. Dynamic recovery and strain softening are found as main restoration mechanisms. Flow stress amounts are not remarkably affected by the strain rate.... 

    Calculating post-uniform deformation energy using tensile parameters

    , Article Materials Science and Technology (United Kingdom) ; Vol. 30, issue. 6 , 2014 , pp. 715-718 ; ISSN: 02670836 Khani Moghanaki, S ; Pouraliakbar, H ; Jandaghi, M. R ; Bagheri, R ; Khalaj, G ; Sharif University of Technology
    Abstract
    Post-uniform deformation energy of materials is defined as absorbed energy per unit area after necking. The energy is constant for a material type and its experienced specific processing history and also depends on its mechanical parameters as workhardening exponent, strain rate sensitivity, post-necking extension and inhomogeneity factor. Different methods such as single and multiple tensile testing had been proposed in the literature to calculate tearing energy, but the effect of post-necking extension had not been expressed explicitly. A new model by implementing uniform and failure elongations with the combination of Unwin theory is introduced. Based on the model, it was shown that... 

    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... 

    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,... 

    Dual-pipe damper

    , Article Journal of Constructional Steel Research ; Volume 85 , 2013 , Pages 81-91 ; 0143974X (ISSN) Maleki, S ; Mahjoubi, S ; Sharif University of Technology
    2013
    Abstract
    In this paper, a new passive earthquake energy dissipative device, called the dual-pipe damper (DPD), is introduced, tested and analytically studied. The device consists of two pipes welded at selected locations and loaded in shear. The inelastic cyclic deformation dissipates energy mainly through flexure of the pipe body. However, at large displacements a tension diagonal forms in the middle of the device which further adds to stiffness and strength. The strength, stiffness and energy dissipation of the DPD is more than two single pipe dampers that were previously studied. Cyclic quasi-static tests were performed on four samples of DPD. Excellent ductility, energy absorption and stable... 

    A large deformation framework for shape memory polymers: Constitutive modeling and finite element implementation

    , Article Journal of Intelligent Material Systems and Structures ; Volume 24, Issue 1 , 2013 , Pages 21-32 ; 1045389X (ISSN) Baghani, M ; Naghdabadi, R ; Arghavani, J ; Sharif University of Technology
    2013
    Abstract
    Shape memory polymers commonly experience both finite deformations and arbitrary thermomechanical loading conditions in engineering applications. This motivates the development of three-dimensional constitutive models within the finite deformation regime. In the present study, based on the principles of continuum thermodynamics with internal variables, a three-dimensional finite deformation phenomenological constitutive model is proposed taking its basis from the recent model in the small strain regime proposed by Baghani et al. (2012). In the constitutive model derivation, a multiplicative decomposition of the deformation gradient into elastic and inelastic stored parts (in each phase) is... 

    Smeared rotating crack model for reinforced concrete membrane elements

    , Article ACI Structural Journal ; Volume 107, Issue 4 , 2010 , Pages 411-418 ; 08893241 (ISSN) Broujerdian, V ; Kazemi, M. T ; Sharif University of Technology
    2010
    Abstract
    A set of stress-strain relations for normal-strength concrete and mild steel bars embedded in concrete is presented in this paper. The salient features of the proposed constitutive laws are: 1) considering the effect of reinforcement ratio on average stressstrain relationships of cracked concrete; and 2) considering the gradual reduction of average stiffness of steel bars embedded in concrete. Equilibrium, compatibility, and constitutive relationships were incorporated into an algorithm to obtain a procedure for analyzing reinforced concrete membrane elements. Corroboration with data from panel test specimens shows that the presented model provides good predictions for the entire... 

    Hyperelastic materials behavior modeling using consistent strain energy density functions

    , Article Acta Mechanica ; Volume 213, Issue 3-4 , 2010 , Pages 235-254 ; 00015970 (ISSN) Darijani, H ; Naghdabadi, R ; Sharif University of Technology
    Springer-Verlag Wien  2010
    Abstract
    Hyperelastic materials have high deformability and nonlinearity in load-deformation behavior. Based on a phenomenological approach, these materials are treated as a continuum, and a strain energy density is considered to describe their hyperelastic behavior. In this paper, the mechanical behavior characterization of these materials is studied from the continuum viewpoint. For this purpose, the strain energy density is expressed as sum of independent functions of the mutual multiple of principal stretches. These functions are determined by applying the governing postulates on the form of the strain energy density. It is observed that a consistent strain energy density is expressible in terms... 

    Dynamical strain-induced charge pumping in monolayer graphene

    , Article Physica Status Solidi - Rapid Research Letters ; Volume 12, Issue 2 , 2018 ; 18626254 (ISSN) Farajollahpour, T ; Phirouznia, A ; Sharif University of Technology
    Wiley-VCH Verlag  2018
    Abstract
    Emergence of high pseudo-magnetic field as a result of mechanical deformations is one of the intriguing characteristics of the graphene honeycomb structure. For a time-dependent nonuniform strain and in the context of Berry curvature approach, the topological charge pumping is studied theoretically. Calculations have been performed in time–momentum parametric space. Within the Berry curvature approach, it has been revealed that time-dependent deformations result in nonzero valley-dependent charge pumping in the gapped graphene when there is a population imbalance between the valleys. This indicates that the valley polarization can be measured by the amount of topological charge pumping in... 

    High-temperature deformation and structural restoration of a nanostructured Al alloy [electronic resource]

    , Article Journal of Scripta Materialia (Pergamon) ; June 2012, Volume 66, Issue 11, Pages 911–914 Asgharzadeh, H ; Simchi, A. (Abdolreza) ; Kim, H. S ; Sharif University of Technology
    Abstract
    We studied the flow stress and microstructural changes of nanostructured Al-6063 alloy produced by mechanical alloying at various temperatures and strain rates. The analysis of flow curves was performed by a constitutive equation, and the stress exponent and activation energy were determined as functions of strain. The deformation mechanisms were elaborated through microstructural observations by electron backscattering diffraction and transmission electron microscopy. Coarsening of the subgrains and grain growth upon deformation was monitored and related to the Zener–Hollomon parameter  

    Simulation and experimental analyses of dynamic strain aging of a supersaturated age hardenable aluminum alloy

    , Article Materials Science and Engineering A ; Volume 585 , 2013 , Pages 165-173 ; 09215093 (ISSN) Anjabin, N ; Karimi Taheri, A ; Kim, H. S ; Sharif University of Technology
    2013
    Abstract
    In this paper, dynamic strain aging (DSA) behavior in a temperature range of (25-235°C) and strain rate range of (10-4-5×10-2s-1) was investigated using a supersaturated age hardenable aluminum alloy. It was found that two mechanisms consisted of pinning of solute atoms to mobile dislocations and dynamic precipitation, were responsible for DSA in the testing conditions. The effects of both mechanisms on the macroscopic flow curve were studied using experimental and improved physically based material modeling approaches. It was shown that both phenomena lead to a negative strain rate hardening in the alloy. Dynamic precipitation acting at high temperature results in considerable work...