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flow-stress
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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. ...
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. ...
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...
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 ; 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 ; 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) ; 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) ; 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) ; 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) ; 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) ; 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) ; 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) ; 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...
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...
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...
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...
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...
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...
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