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Modeling the Mechanical Properties of Aluminum Series 1xxx after Severe Plastic Deformation in Corrugation Die
, M.Sc. Thesis Sharif University of Technology ; 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 ; 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...
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 ; 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. ...
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) ; 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...
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) ; Karimi Taheri, A ; Sharif University of Technology
2009
Abstract
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
The influence of heat treatment and hot deformation conditions on γ′ precipitate dissolution of Nimonic 115 superalloy
, Article International Journal of Advanced Manufacturing Technology ; Volume 45, Issue 9-10 , 2009 , Pages 841-850 ; 02683768 (ISSN) ; Sadeghi, M. H ; Akbarzadeh, A ; Cheraghzadeh, M ; Sharif University of Technology
Abstract
In precipitation hardenable materials, it is desirable to determine the precipitate dissolution temperature for homogenizing the microstructure by controlling the size and distribution of the precipitates. In this research, the influence of various heat treatment and hot deformation conditions on the kinetics of γ ′ dissolution and its morphological evolution in Nimonic 115 was studied. In addition, hot deformation behavior of the material was investigated using hot compression experiments at varying temperature (between 1,050°C and 1,175°C) and strain rates (between 0.01 and 1 s-1) up to a true strain of 0.8. The values obtained for the solvus temperature of γ ′ precipitates by two methods...
The effects of annealing phenomena on the energy absorption of roll-bonded Al-steel sheets during wedge tearing
, Article Materials Science and Engineering A ; Volume 527, Issue 27-28 , 2010 , Pages 7329-7333 ; 09215093 (ISSN) ; Kazeminezhad, M ; Sharif University of Technology
Abstract
The purpose of this paper is to investigate the effects of annealing phenomena on the energy absorption of Al-steel bilayer sheets, bonded by cold rolling, through wedge tearing. Tearing by wedge is a dissipating energy system that includes three components: cutting, friction and plastic deformation due to bending. In order to find the bonding and annealing effects on energy absorption, the non-bonded bilayer sheets are prepared in the same condition of bonded ones. The results show that energy absorption of bonded sheets is larger than that of non-bonded ones. This is due to different plastic bending moment of bonded and non-bonded bilayer sheets. Whenever the bond is improved by heat...
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) ; 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
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) ; Sharif University of Technology
2006
Abstract
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...
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) ; Sharif University of Technology
2003
Abstract
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...
Prediction of flow stress at hot working condition
, Article Mechanics Research Communications ; Volume 30, Issue 1 , 2003 , Pages 87-93 ; 00936413 (ISSN) ; Taheri, A. K ; Sharif University of Technology
2003
Abstract
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
Physically based material model for evolution of stress-strain behavior of heat treatable aluminum alloys during solution heat treatment
, Article Materials and Design ; Volume 31, Issue 1 , 2010 , Pages 433-437 ; 02641275 (ISSN) ; Karimi Taheri, A ; Sharif University of Technology
2010
Abstract
A mathematical model based on Kocks-Mecking-Bergstrom model, has been proposed to predict the flow behavior of age hardenable aluminum alloys, under different conditions of solution heat treatment and hot deformation. Considering the published literature, most researchers have taken into account the precipitation and solution strengthening contribution to the flow stress by a constant and some others have ignored these effects. So these available descriptions cannot be applicable directly to different conditions of solution heat treatment. In order to enable these constitutive descriptions to take into account the effects of soaking time and temperature, we introduce in this research a...
Optimum groove pressing die design to achieve desirable severely plastic deformed sheets
, Article Materials and Design ; Volume 31, Issue 1 , 2010 , Pages 94-103 ; 02641275 (ISSN) ; Hosseini, E ; Sharif University of Technology
2010
Abstract
In this paper, considering the problems of common finite element (FE) codes that consider simple constitutive equations, a developed FE code that considers a new constitutive model is used to simulate the behavior of copper sheets under severe plastic deformation (SPD). The new proposed constitutive model, that considers dislocation densities in cell interiors and cell walls of material as true internal state variables, can investigate all stages of flow stress evolution of material during large plastic deformations and also can explain the effects of strain rate magnitude on the mechanical response of material, during room temperature SPD. The proposed FE analysis is used to investigate the...
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) ; Kazeminezhad, M ; Mani, A ; Rafizadeh, E ; Sharif University of Technology
2009
Abstract
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) ; 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...
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) ; Behjati, P ; Sharif University of Technology
2010
Abstract
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...
Investigation into characteristics of Portevin-Le Chatelier effect of an Al-Mg Alloy
, Article Journal of Materials Engineering and Performance ; Volume 19, Issue 9 , 2010 , Pages 1264-1267 ; 10599495 (ISSN) ; Sharif University of Technology
Abstract
In this study, the plastic instabilities associated with the Portevin-Le Chatelier (PLC) and their effects on the mechanical properties and the fracture surfaces have been investigated for AA 5083. Tensile tests were performed at various temperatures and strain rates in order to do so. Then, serrated and smooth yielding domains were determined in Ln ε̇-1/T diagram. The stress-strain curves related to the serrated domain show the values of flow stress decreases by increasing the strain rate at a constant temperature. In addition, the plot of critical strain versus imposed strain rate indicates an inverse manner at very low strain rates. It is confirmed that the type of PLC bands alters the...
Implementation of a constitutive model in finite element method for intense deformation
, Article Materials and Design ; Volume 32, Issue 2 , February , 2011 , Pages 487-494 ; 02641275 (ISSN) ; Kazeminezhad, M ; Sharif University of Technology
2011
Abstract
Since the constitutive information is one of the most important aspects of material deformation analysis, here a new constitutive model is proposed that can investigate the behavior of material during intense deformation better than existent models. The model that is completely based on physical mechanisms can predict all stages of flow stress evolution and also can elucidate the effects of strain and strain rate on flow stress evolution of material during intense plastic deformation. Here as an application, implementation of the constitutive model in finite element method (FEM) is used to compare two methods of sever plastic deformation (SPD) processes of copper sheet; repetitive...
Hot rolling and direct cooling
, Article Comprehensive Materials Processing ; Vol. 3 , 2014 , pp. 377-396 ; ISBN: 9780080965338 ; 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...
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) ; 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...