Search for: flow-stress
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    Prediction of microstructural changes during hot rod rolling

    , Article International Journal of Machine Tools and Manufacture ; Volume 43, Issue 14 , 2003 , Pages 1487-1495 ; 08906955 (ISSN) Serajzadeh, S ; Sharif University of Technology
    In this study, a mathematical model is presented for predicting temperature and velocity fields together with dynamic and static microstructural changes during hot rod rolling utilizing a finite element model. For doing so, heat transfer and plasticity equations are coupled with the additivity rule and Avrami rate-equation to consider the dynamic and static microstructural changes as well as to evaluate the effects of temperature and strain rate variations on flow stress of rolling metal. To verify the results of the employed model, a comparison is made between the measured surface temperature during rod rolling and the predicted data that confirms the validity of the model. © 2003 Elsevier... 

    An investigation into the effect of carbon on the kinetics of dynamic restoration and flow behavior of carbon steels

    , Article Mechanics of Materials ; Volume 35, Issue 7 , 2003 , Pages 653-660 ; 01676636 (ISSN) Serajzadeh, S ; Taheri, A. K ; Sharif University of Technology
    A study has been made to determine the influence of the carbon content on the kinetics of dynamic recrystallization and recovery as well as flow stress during hot deformation of carbon steels. For this purpose, single hit hot compression experiments at various strain rates and temperatures on two grades of carbon steel together with the Avrami-type kinetics equation and Bergstrom approach have been utilized. The results show that the apparent hot deformation activation energy decreases with increasing carbon content and this phenomenon results in a faster dynamic recrystallization and recovery and a lower flow stress at high temperatures and/or low strain rates in high carbon steels, while... 

    Prediction of flow stress at hot working condition

    , Article Mechanics Research Communications ; Volume 30, Issue 1 , 2003 , Pages 87-93 ; 00936413 (ISSN) Serajzadeh, S ; Taheri, A. K ; Sharif University of Technology
    A mathematical model has been developed to determine flow stress at hot deformation condition. The proposed model is capable of including work softening due to dynamic phase transformations as well as the effect of temperature and strain rate variation on flow stress utilizing the additivity rule for strain. To verify the model, hot compression tests for two grades of steels has been carried out. The comparison between the experimental and theoretical results confirms the validity of the model  

    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
    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... 

    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
    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... 

    Analysis of flow stress up to the peak at hot deformation

    , Article Materials and Design ; Volume 30, Issue 8 , 2009 , Pages 3036-3040 ; 02641275 (ISSN) Solhjoo, S ; Sharif University of Technology
    A mathematical model has been developed to predict stress-strain curve up to the peak stress at hot deformation. This model is based on the linear estimation of work hardening rate-stress curve up to the peak stress. This equation is expressed in terms of peak stress, peak strain. In addition, in order to find the value of peak strain, Zenner-Hollomon parameter is modified. The predicted results are found to be in accord with the experimental flow stress curves which can be used to predict the required deformation forces in hot deformation processes. © 2008 Elsevier Ltd. All rights reserved  

    Hot rolling and direct cooling

    , Article Comprehensive Materials Processing ; Vol. 3 , 2014 , pp. 377-396 ; ISBN: 9780080965338 Serajzadeh, S ; Sharif University of Technology
    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... 

    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)
    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)
    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... 

    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
    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  

    The prediction of hot flow behavior of Al-6%Mg alloy

    , Article Mechanics Research Communications ; Volume 36, Issue 2 , 2009 , Pages 252-259 ; 00936413 (ISSN) Gholamzadeh, A ; Karimi Taheri, A ; Sharif University of Technology
    In this research, the plastic flow behavior of Al-6%Mg alloy was studied by analyzing the results of hot compression tests in a range of temperature and strain rate. Then, an artificial neural network (ANN) model was trained at which the temperature, strain-rate, and strain parameters were used as the input layer and the flow stress as the output. The comparison of the predicted and experimental results of stress-strain curve proved the prediction capability of the ANN model. © 2008 Elsevier Ltd. All rights reserved  

    Prediction of temperature and velocity distributions during hot rolling using finite elements and neural network

    , Article Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture ; Volume 220, Issue 7 , 2006 , Pages 1069-1075 ; 09544054 (ISSN) Serajzadeh, S ; Sharif University of Technology
    Temperature and velocity distributions during hot strip rolling of a low-alloy steel are determined using a finite element method together with a neural network model. The finite element method is utilized to solve the governing equations of heat conduction and plastic deformation; at the same time a neural network model is employed for assessing flow stress of the metal being deformed. In this way, the effects of temperature, strain, and strain rate on flow stress could be included in the finite element analysis. In order to examine validity of the mathematical model, laboratory hot rolling experiments are carried out where the surface temperature and roll force are recorded. Comparison... 

    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
    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... 

    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
    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... 

    Modelling correlation between hot working parameters and flow stress of IN625 alloy using neural network

    , Article Materials Science and Technology ; Volume 26, Issue 5 , Jul , 2010 , Pages 621-625 ; 02670836 (ISSN) Montakhab, M ; Behjati, P ; Sharif University of Technology
    In this work, an optimum multilayer perceptron neural network is developed to model the correlation between hot working parameters (temperature, strain rate and strain) and flow stress of IN625 alloy. Three variations of standard back propagation algorithm (Broyden, Fletcher, Goldfarb and Shanno quasi-Newton, Levenberg-Marquardt and Bayesian) are applied to train the model. The results show that, in this case, the best performance, minimum error and shortest converging time are achieved by the Levenberg-Marquardt training algorithm. Comparing the predicted values and the experimental values reveals that a well trained network is capable of accurately calculating the flow stress of the alloy... 

    On the evolution of flow stress during constrained groove pressing of pure copper sheet

    , Article Computational Materials Science ; Volume 45, Issue 4 , 2009 , Pages 855-859 ; 09270256 (ISSN) Hosseini, E ; Kazeminezhad, M ; Mani, A ; Rafizadeh, E ; Sharif University of Technology
    Using a mechanical model and dislocation density based model, the evolutions of dislocation density and flow stress of pure copper during constrained groove pressing (CGP) process are investigated. In this regard, the strain and strain rate are achieved from the mechanical model and then input into the dislocation model. To verify the predicted flow stress, the process of constrained groove pressing is performed on the sheets of pure copper from one to three passes. The predicted flow stresses are compared with the experimental data and a good agreement is observed. Also, it is found that during the straining of the copper sheet in CGP process, the dislocation density and strength dropping... 

    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
    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... 

    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)
    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. ... 

    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
    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
    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...