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    Effect of Cryogenic SPD with Various Strain Conditions on Development of Nano and Bimodal Structures in Al Alloys

    , Ph.D. Dissertation Sharif University of Technology Mohebbi, Mohammad Sadegh (Author) ; Akbarzadeh, Abbas (Supervisor)
    Abstract
    Amount of strain has been always considered as the primary parameter affecting the microstructural and strength evolutions during Severe Plastic Deformation (SPD). However, these evolutions unavoidably saturate in large strains under deformation with constant conditions, i.e. constant deformation temperature, strain rate and strain path. In this study, effects of these factors on the microstructural and flow behavior of Ultra-Fine Grain (UFG) aluminum (AA 1050 and AA 5052) processed by Accumulative Roll-Bonding (ARB) are investigated. The flow behavior and its time-dependent aspect are evaluated up to large strains by Plane Strain Compression (PSC) and Stress Relaxation (SR) tests. ... 

    Modeling the Mechanical Properties of Aluminum Series 1xxx after Severe Plastic Deformation in Corrugation Die

    , M.Sc. Thesis Sharif University of Technology Hosseini, Ehsan (Author) ; Kazeminezhad, Mohsen (Supervisor)
    Abstract
    Nowadays, modeling the behavior of materials during forming processes is so important. The role of most of them is to investigate and predict the evolutions of microstructure and mechanical properties of materials during plastic deformation. Previous researches have demonstrated that the best parameter to investigate these evolutions is the dislocation density of materials. In this study, first, the dislocation-based models, which investigate the material parameters evolutions during plastic deformation, were investigated and it was revealed that among all presented models, only the two internal variables models can investigate the behavior of materials during severe plastic deformation. ... 

    Experimental and Theoretical Analysis of Plastic Deformation of Metals under Impact Loading Using Taylor Impact Test

    , M.Sc. Thesis Sharif University of Technology Khayyer Dastjerdi Toroghi, Ahmad (Author) ; Naghdabadi, Reza (Supervisor)
    Abstract
    In most of the engineering applications, the mechanical behavior of materials in high strain rate deformations differs from their behavior in quasi-static deformations. In some engineering problems like impact loading on structures, metal forming and explosive forming, the range of strain rate is about . Taylor impact test is one of the experiments used for characterizing the dynamic behavior of materials in high strain rate deformations. In the Taylor impact test a rigid cylindrical projectile is impacted normally onto a hard and massive surface (anvil), the projectile deforms by mushrooming at the impact end. With plastic wave propagation analysis, the plastic deformation of projectile is... 

    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.... 

    Development of constitutive equations for a high carbon steel using additivity rule

    , Article ISIJ International ; Volume 43, Issue 7 , 2003 , Pages 1050-1055 ; 09151559 (ISSN) Serajzadeh, S ; Sharif University of Technology
    Iron and Steel Institute of Japan  2003
    Abstract
    Flow behavior of a high carbon steel under hot deformation condition has been studied and a mathematical model for describing the flow stress under isothermal and constant strain rate as well as under non-isothermal and varied strain rates has been developed. For doing so, Bergstrom dislocation model together with the additivity rule for strain have been employed also, hot compression experiments at various temperatures and strain rates have been utilized to achieve the kinetics of dynamic recovery and recrystallization of the high carbon steel. The comparison between the predicted and experimental results under both isothermal and non-isothermal conditions verifies the validity of the... 

    Cell-structure and flow stress investigation of largely strained non-heat-treatable Al-alloys using dislocation based model

    , Article Materials Science and Engineering A ; Volume 739 , 2019 , Pages 167-172 ; 09215093 (ISSN) Firouzabadi, S. S ; Kazeminezhad, M ; Sharif University of Technology
    Elsevier Ltd  2019
    Abstract
    A severe plastic deformation is widely used to improve the mechanical properties of non-heat-treatable alloys. Thus, the investigation and modeling of microstructural evolutions of materials during large straining are of great importance. In this research, substructural evolutions of four different kinds of Al alloys namely Al-1Mn, Al-1Mg, Al-2.77Mg and Al-5Mg, have been studied using a dislocation based model and the mechanical properties of these alloys have been compared considering all microstructural parameters such as dislocation density, subgrain size, cell wall misorientation and the effect of alloying element. As a result, a simplified general equation has been expressed in order to... 

    Flow stress of 2024 aluminum alloy during multi-directional forging process and natural aging after plastic deformation

    , Article Materials Chemistry and Physics ; Volume 254 , 2020 Nouri, S ; Kazeminezhad, M ; Shadkam, A ; Sharif University of Technology
    Elsevier Ltd  2020
    Abstract
    The hardening behavior of heat treatable alloys during deformation is attributed to three mechanisms of forest dislocations, solid solution and precipitation hardening which hinder the motion of dislocations and increase the density of statistically stored dislocation. In this paper, a model for the flow stress of a 2024 heat treatable aluminum alloy during plastic deformation is developed combining the superposition of these three hardening mechanisms. This model was then implemented into the finite element model in order to evaluate the evolution of the flow stress of 2024 aluminum alloy during multi-directional forging (MDF). Subsequently, an equation is developed for evaluating the... 

    A finite element simulation and an experimental study of autofrettage for strain hardened thick-walled cylinders

    , Article Materials Science and Engineering A ; Volume 359, Issue 1-2 , 2003 , Pages 326-331 ; 09215093 (ISSN) Majzoobi, G. H ; Farrahi, G. H ; Mahmoudi, A. H ; Sharif University of Technology
    Elsevier BV  2003
    Abstract
    The effect of the autofrettage process on high pressure cylinders has been investigated. Both numerical and experimental techniques have been used for the investigation. It was observed that the best autofrettage pressure for raising the pressure capacity of the cylinder was the pressure Py2 which is just sufficient to bring the outer surface of the cylinder to yielding. Pressures higher than Py2 will have the inverse effect. It was found that the number of autofrettage stages has no effect on pressure capacity. It was also shown that to reduce the flow stress within the wall of the cylinder, the autofrettage pressure must be greater than the working pressure. For pressures lower than... 

    Study on the dynamic and static softening phenomena in Al-6Mg alloy during two-stage deformation through interrupted hot compression test

    , Article Measurement: Journal of the International Measurement Confederation ; Volume 77 , 2016 , Pages 50-53 ; 02632241 (ISSN) Pouraliakbar, H ; Pakbaz, M ; Firooz, S ; Jandaghi, M. R ; Khalaj, G ; Sharif University of Technology
    Elsevier, B. V  2016
    Abstract
    The dynamic and static softening phenomena in Al-6Mg alloy were studied through interrupted two-stage hot compression test performed isothermally at 480°C and strain rate range of 0.001-0.1 s-1. The interruptions of 29 and 90 s were considered when the true strain reached 0.5. It was concluded that the effect of static softening on the flow stress was not highlighted by extending the interruption at a constant strain rate. Also, it was exhibited that softening rate highly enhanced with the strain rate decrement at a constant time. Moreover, the static and dynamic recrystallization was revealed as the dominant softening mechanisms at low and high strain rates, respectively  

    Numerical simulation of density current using two-phase flow

    , Article 2006 ASME Joint U.S.- European Fluids Engineering Division Summer Meeting, FEDSM2006, Miami, FL, 17 July 2006 through 20 July 2006 ; Volume 2 FORUMS , 2006 , Pages 49-54 ; 0791847500 (ISBN); 9780791847503 (ISBN) Afshin, H ; Firoozabadi, B ; Sharif University of Technology
    American Society of Mechanical Engineers  2006
    Abstract
    Due to shear layer at the interface of density current and ambient fluid, density current disturbs and entrains the surrounding fluid. Most existing analytical and numerical models for density current flows are based on the equations for single-phase flows. In this research, the density current has been modeled with two-phase flow model. The governing equations are continuity, x- momentum, and y- momentum equations for every fluid. The volume-of-fluid (VOF) interface tracking technique which uses a piecewise-linear interface calculation (PLIC) in each cell is used to determine the deformation of free surface in density current, numerically. Surface tension is implemented by the continuous... 

    Hot rolling and direct cooling

    , Article Comprehensive Materials Processing ; Vol. 3 , 2014 , pp. 377-396 ; ISBN: 9780080965338 Serajzadeh, S ; Sharif University of Technology
    Abstract
    Knowledge of process parameters during and after hot rolling is a significant requirement in order to produce a material with the desired microstructures and mechanical properties. In continuous hot rolling mills, different stages may exist, including water descaling, rolling stands, interstand sections, and run-out table. In each of these sections, various thermal and/or mechanical conditions are applied on the rolling metal that would affect material response in successive stages. In other words, an integrated model should be employed in hot rolling operations to evaluate metal behavior and microstructural events at the same time. Therefore, the thermal-mechanical response as well as... 

    Flow stress analysis of ultrafine grained AA 1050 by plane strain compression test

    , Article Materials Science and Engineering A ; Vol. 593 , 2014 , pp. 136-144 ; ISSN: 09215093 Mohebbi, M. S ; Akbarzadeh, A ; Yoon, Y. O ; Kim, S. K ; Sharif University of Technology
    Abstract
    Plane strain compression (PSC) test was used to study the flow stress of ultrafine grained commercially pure aluminum at large strains. AA 1050 sheets were processed by various Accumulative Roll-Bonding (ARB) cycles up to 10 cycles as the initial specimens for the test. An approach was developed to measure the coefficient of friction and to suppress its effect on the results. It is shown that as a result of having an anisotropy parameter (R-value) of less than one, Von-Mises tensile strengths are significantly higher than PSC strengths. Comparing these strengths, the R-value as an average anisotropy parameter of rolling and transverse directions is estimated for the ARBed sheets, where it is... 

    Crystal plasticity modeling of the effect of precipitate states on the work hardening and plastic anisotropy in an Al-Mg-Si alloy

    , Article Computational Materials Science ; Vol. 83 , 2014 , pp. 78-85 ; ISSN: 09270256 Anjabin, N ; Karimi Taheri, A ; Kim, H. S ; Sharif University of Technology
    Abstract
    In this study the influence of precipitates on the mechanical properties and plastic anisotropy of an age hardenable aluminum alloy during uniaxial loading was investigated using crystal plasticity modeling. The kinetics model of Myhr et al. was used to obtain the solute and precipitate features after different cycles of aging treatment. The amounts of solute, precipitate size and volume fraction, and dislocation density varying during deformation, were used to calculate the slip system strength. An explicit term was obtained based on the elastic inclusion model for the directional dependency of internal stress developed by non-shearable rod shape precipitates. Also, a dislocation evolution... 

    Dislocation density and flow stress modeling of nanostructured Al-SiC p composite during accumulative roll bonding

    , Article Computational Materials Science ; Volume 67 , February , 2013 , Pages 359-363 ; 09270256 (ISSN) Kavosi, J ; Saei, M ; Kazeminezhad, M ; Sharif University of Technology
    2013
    Abstract
    In order to investigate the dislocation structure and flow stress evolution of Al-SiCp composite during ARB process, a comprehensive model which describes the evolution of dislocation density is needed. Dislocation density, microstructure and flow stress evolution of Al-SiCp composite are predicted considering the ETMB model, strain and strain rate achieved from the mechanical model of ARB process and shear modulus calculated from the composite model. In addition, models' parameters such as dislocation generation parameters are modified due to the effect of SiC particles. The predicted results are in good agreement with experimental data  

    The use of ANN to predict the hot deformation behavior of AA7075 at low strain rates

    , Article Journal of Materials Engineering and Performance ; Volume 22, Issue 3 , 2013 , Pages 903-910 ; 10599495 (ISSN) Jenab, A ; Karimi Taheri, A ; Jenab, K ; Sharif University of Technology
    2013
    Abstract
    In this study, artificial neural network (ANN) was used to model the hot deformation behavior of 7075 aluminum alloy during compression test, in the strain rate range of 0.0003-1 s-1 and temperature range of 200-450 C. The inputs of the model were temperature, strain rate, and strain, while the output of the model was the flow stress. The feed-forward back-propagation network with two hidden layers was built and successfully trained at different deformation domains by Levenberg-Marquardt training algorithm. Comparative analysis of the results obtained from the hyperbolic sine, the power law constitutive equations, and the ANN shows that the newly developed ANN model has a better performance... 

    Analyses on the flow stress of an Al-Mg alloy during dynamic recovery

    , Article Journal of Materials Engineering and Performance ; Volume 22, Issue 3 , March , 2013 , Pages 700-705 ; 10599495 (ISSN) Mostafaei, M. A ; Kazeminezhad, M ; Sharif University of Technology
    2013
    Abstract
    A comprehensive analysis on flow stress of a wrought Al-Mg alloy is performed to examine the effect of strain. For this study, hot compression tests were carried at different temperatures and strain rates. Corrections of friction and adiabatic heating effects lead to the true stress-true strain curves in the form of dynamic recovery, which reach to a steady-state condition. After correction, constitutive analysis at a constant strain is carried out using hyperbolic-sine equation. The effect of strain on each constitutive parameter is studied to derive a strain-dependent constitutive equation based on hyperbolic-sine equation. Some of constitutive parameters reach to the constant values at... 

    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  

    A study on the hot workability of wrought NiTi shape memory alloy

    , Article Materials Science and Engineering A ; Volume 528, Issue 18 , July , 2011 , Pages 5656-5663 ; 09215093 (ISSN) Morakabati, M ; Kheirandish, S ; Aboutalebi, M ; Taheri, A. K ; Abbasi, S. M ; Sharif University of Technology
    2011
    Abstract
    The hot workability of a wrought 49.8 Ni-50.2 Ti (at pct) alloy was assessed using the hot compression tests in temperature range of 700-1000°C, strain rate of 0.001-1s-1, and the total strain of 0.7. The constitutive equations of Arrhenius-type hyperbolic-sine function was used to describe the flow stress as a function of strain rate and temperature. The preferable regions for hot workability of the alloy were achieved at Z (Zener-Holloman parameter) values of about 109-1013 corresponding to the peak efficiency of 20-30% in the processing map. However, a narrow area in the processing map including the deformation temperature of 1000°C and strain rate of 1s-1 is inconsistent with the related... 

    Hot ductility of a Fe-Ni-Co alloy in cast and wrought conditions

    , Article Materials and Design ; Volume 32, Issue 5 , 2011 , Pages 2956-2962 ; 02641275 (ISSN) Yazdani, M ; Abbasi, S. M ; Momeni, A ; Karimi Taheri, A ; Sharif University of Technology
    2011
    Abstract
    The hot ductility of Fe-29Ni-17Co alloy was studied in both cast and wrought conditions by hot tensile tests over temperature range of 900-1250°C and at strain rates of 0.001-1s-1. Over the studied temperature range, the wrought alloy represented higher elongation and reduction in area as compared to the cast alloy. Dynamic recrystallization was found responsible for the higher hot ductility of the wrought alloy and the improvement of hot ductility of the cast alloy at high temperatures. At temperature range of 1000-1150°C the wrought alloy exhibited a hot ductility drop while a similar trough was not observed in case of the cast alloy. It was also found that at temperatures of 1150-1250°C... 

    An investigation into the deformation behaviour of AA6061-5% SiC p composite during and after hot extrusion process

    , Article Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications ; Volume 225, Issue 1 , 2011 , Pages 22-31 ; 14644207 (ISSN) Akhgar, J. M ; Mirjalili, A ; Serajzadeh, S ; Sharif University of Technology
    Abstract
    In this study, hot extrusion of AA6061-5% SiCp composite was studied to determine the composite thermo-mechanical behaviour during deformation and the mechanical properties of extruded composite. Hot compression tests were first carried out to obtain the flow stress behaviour of the composite at different temperatures and strain rates. Then a mathematical model was used to estimate the required energy as well as to predict temperature and strain distributions during the process. Finally, hot extrusion experiments were performed in order to verify the predictions and, also, tensile and hardness testing were conducted to evaluate mechanical properties of extruded material. Comparison between...