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The effect of carbon on the restoration phenomena during hot deformation of carbon steels
, Article International Journal of Materials Research ; Volume 94, Issue 8 , 2022 , Pages 916-921 ; 18625282 (ISSN) ; Karimi Taheri, A ; Zebarjad, S. M ; Sharif University of Technology
Walter de Gruyter GmbH
2022
Abstract
A study has been made to determine the influence of the carbon content on the kinetics of dynamic and static recrystallization during and after hot deformation of carbon steels. For this purpose, single- and double-hit hot compression experiments at various strain rates and temperatures together with the Avrami-type kinetics equation and Bergstrom approach have been utilized to investigate recrystallization behavior. The results show that the apparent activation energy of hot deformation decreases with increasing carbon content and this phenomenon results in a faster dynamic recrystallization at high temperatures and/or low strain rates. Also, increasing carbon content leads to a higher rate...
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...
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...
Experimental and Numerical Study of Pulse Shaper Geometry Effects in Split Hopkinson Pressure Bar Test
,
M.Sc. Thesis
Sharif University of Technology
;
Naghdabadi, Reza
(Supervisor)
;
Sohrabpour, Saeed
(Supervisor)
Abstract
Split Hopkinson pressure bar (SHPB) test is one of the tests used for characterizing the mechanical behavior of materials at high strain rates between and s -1. A SHPB test consists of a gas gun, a striker bar, an incident bar, a transmission bar and a specimen which is sandwiched between the incident and transmission bars. In order to achieve constant strain rate during the test which is necessary in SHPB test, the incident pulse should obey the stress-strain curve of the specimen. For shaping the incident pulse usually a thin deformable disk -called pulse shaper- is placed between the striker and incident bars. In this thesis, first we designed, implemented and calibrated the measuring...
, M.Sc. Thesis Sharif University of Technology ; Naghdabadi, Reza (Supervisor) ; Sohrabpour, Saeed (Supervisor)
Abstract
Increasing the application of elastomeric structures in industries has caused an interest in the researchers for nonlinear elasticity and viscoelasticity of solids. Such materials which show large deformation and rate dependent behavior are treated by visco-hyperelastic constitutive equations. Based on visco-hyperelastic constitutive equations, total stress is divided into two parts: quasi-static and viscous stress. The method for determining the visco-hyperelastic constitutive equation is strictly dependent on the chosen rheological model. In this project, a new visco-hyperelasic constitutive equation in the integral form was introduced based on the Zener model. Also, based on the internal...
The Effect of Strain Rate on Multi-directional Forged Aluminum
, M.Sc. Thesis Sharif University of Technology ; Kazeminezhad, Mohsen (Supervisor)
Abstract
In this study, multi directional forging as a severe plastic deformation method is applied on pure aluminum at the different strain of 0.5, 1.5, 2.5, and 3.5. Annealing has been applied to samples at 150 C, 250 C, 350 C, and 450 C for one hour. In the next step, compressive test is carried out on MDFed and annealed MFDed pure aluminum through strain rate of 0.01 1/s, 0.001 1/s, and 0.0001 1/s. Based on experimental data, when the number of MDF is passes increased, because of increasing the dislocation density and grain boundary area, yield stress is increased. As an example, the yield stress of 7 passed MDFed aluminum is 2.25 times of that of 1 passes MDFed aluminum. Annealing would...
Analytical and Numerical Investigation of Stress Wave Propagation in Split Hopkinson Pressure Bar for Studying Viscoelastic Behavior of Polymers at High Strain Rates
, M.Sc. Thesis Sharif University of Technology ; Naghdabadi, Reza (Supervisor) ; Sohrabpour, Saeed (Supervisor)
Abstract
Studying the behavior of materials at high strain rate is necessary for design and analysis of structures subjected to impact loading. Therefore, design and construction of apparatuses that enable us for testing various materials under impact loading is very important. The split Hopkinson pressure bar test -one of the most important impact tests- is utilized for dynamic loading at constant strain rates ranging from 100 to 10000 1/s.
In this thesis, first we explain about the behavior of materials at high strain rates and then focus on the behavior of polymers -that are widely used in different industries- under impact loading. Also, basic concepts of polymeric Hopkinson pressure bar and...
In this thesis, first we explain about the behavior of materials at high strain rates and then focus on the behavior of polymers -that are widely used in different industries- under impact loading. Also, basic concepts of polymeric Hopkinson pressure bar and...
Fabrication of Micro-Strain Gauge Using Electrohydrodynamic 3D Printing Technique
, M.Sc. Thesis Sharif University of Technology ; Movahhedy, Mohammad Reza (Supervisor)
Abstract
A significant number of small-scale sensor sales have been reported in recent years. Strain gauges are one of the most common tools for measuring the length change of a part. Nowadays, 3D printing technology can be used in the fabrication of small-scale sensitive sensors, and metal nanoparticles printing are especially suitable for the production of flexible electronic sensors. Electro-hydrodynamic printer, with micro-scale printing capabilities, can be used as a new invention in fabrication of sensors. This type of printer uses the inkjet printing method and the basis of this type of printer is to apply an electric field to shrink the fluid jet. In the present study, pure ethanol was first...
Effect of Environmental Conditions on Fracture Behavior of Solder Joints
, M.Sc. Thesis Sharif University of Technology ; Nourani, Amir (Supervisor)
Abstract
Double cantilever beam (DCB) specimens were prepared according to standard surface mount technology (SMT). The samples were stored inside an environmental chamber at two different relative humidity values (i.e. 40 or 100%) for either 2 or 4 hours. Then they were aged at 25ºC, 75ºC or 125℃ for the same time. Finally, after being cooled to room temperature, fracture tests were performed under mode-I loading conditions at a strain rate of 0.03 s-1 at room temperature. Storage time did not have a significant effect on the fracture behavior. The fracture load and energy of the solder joints decreased significantly when the temperature was increased from 25 to 75℃. By further increase in the...
Investigating the Fracture Behavior of Adhesive Joints at Different Strain Rates and Under Drop
, M.Sc. Thesis Sharif University of Technology ; Nourani, Amir (Supervisor)
Abstract
Nowadays adhesives with the development of technology and the numerous benefits they have, are becoming a replacement for traditional joining methods in industries like electronics, automotive, aerospace, and naval. That’s why the need for studying the fracture behavior of adhesive joints becomes vital. So far, many engineers and designers are trying to investigate the behavior of adhesive joints in different conditions that these joints actually deal with. Also, finding solutions to predict the behavior of adhesive joints is the researchers’ other concern. The purpose of this research is to find the effect of factors that are less focused in the literature, on the fracture of adhesive...
Mechanical and Microstructural Behavior of 2024-O Aluminum Alloy in Non-Isothermal Hot Compression Test
, M.Sc. Thesis Sharif University of Technology ; KazemiNezhad, Mohsen (Supervisor)
Abstract
So far, a lot of research has been done on the hot behavior of different alloys; These studies have generally been performed using tensile, compression and torsion tests and isothermal conditions, which have greatly contributed to the understanding of the mechanisms of deformation at high temperatures. Due to the fact that in real deformation processes, it is less common for the material to experience isothermal conditions during deformation, so in this project, the aim is to investigate the behavior of 2024 aluminum-alloy in non-isothermal hot compression test. In this regard, non-isothermal hot pressure test was performed from 300℃ to 600℃ و temperature range and at different deformation...
Investigating the Effect Strain Rate on the Poisson’s Ratio of Auxetic Polyurethane Foams
, M.Sc. Thesis Sharif University of Technology ; Nourani, Amir (Supervisor)
Abstract
Auxetic materials have a negative Poisson ratio (NPR), which is their most distinguishable characteristic as compared to regular materials. Test specimens were made of conventional polyurethane (PU) foams according to ASTM ; then, with a thermo-mechanical process, the foam was converted to auxetic PU foam. The reproducibility of specimens' fabrication was checked with CoV= for the final foam thickness. With regard to the fact that changing loading conditions can vary Poisson's ratio, in this study, the variations occurred in Poisson's ratio due to changing loading conditions are investigated. The applied strain and strain rate were altered in experiments and statistical analysis was...
Investigating the Fracture Behavior of Adhesive Joints at Different Strain Rates and under Drop
, M.Sc. Thesis Sharif University of Technology ; Nourani, Amir (Supervisor)
Abstract
Nowadays adhesives with the development of technology and the numerous benefits they have, are becoming a replacement for traditional joining methods in industries like electronics, automotive, aerospace, and naval. That’s why the need for studying the fracture behavior of adhesive joints becomes vital. So far, many engineers and designers are trying to investigate the behavior of adhesive joints in different conditions that these joints actually deal with. Also, finding solutions to predict the behavior of adhesive joints is the researchers’ other concern. The purpose of this research is to find the effect of factors that are less focused in the literature, on the fracture of adhesive...
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 ; 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...
Experimental investigation of the hot deformation behavior of AA7075: Development and comparison of flow localization parameter and dynamic material model processing maps
, Article International Journal of Mechanical Sciences ; Vol. 78, issue , 2014 , pp. 97-105 ; ISSN: 00207403 ; Karimi Taheri, A ; Sharif University of Technology
Abstract
The hot deformation characteristics of 7075 aluminum alloy (AA7075) are investigated by means of hot compression tests carried out in the temperature range of 200-450 C and strain rate range of 0.0003-1 s-1. Two novel processing maps based on flow localization parameter and enhanced DMM are developed and compared with conventional DMM results. It is observed that processing maps based on flow localization parameter can be used successfully to predict AA7075 thermomechanical behavior. Also, the comparison of the DMM results indicates that the new approach to calculate DMM power dissipation efficiency and instability criteria corresponds better with experimental observations. The occurrence of...
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) ; 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...
The effect of the imposed boundary rate on the formability of strain rate sensitive sheets using the M-K Method
, Article Journal of Materials Engineering and Performance ; Volume 22, Issue 9 , April , 2013 , Pages 2522-2527 ; 10599495 (ISSN) ; Ghazanfari, A ; Abrinia, K ; Assempour, A ; Sharif University of Technology
2013
Abstract
In spite of the fact that the experimental results indicate the significant effect of strain rate on forming limits of sheets, this effect is neglected in all theoretical methods of prediction of Forming Limit Diagrams (FLDs). The purpose of this paper is to modify the most renowned theoretical method of determination of FLDs (e.g., M-K model) so as to enable it to take into account the effect of strain rate. To achieve this aim, the traditional assumption of preexistence of an initial geometrical inhomogeneity in the sheet has been replaced with the assumption of a preexisting "material" inhomogeneity. It has been shown that using this assumption, the strain rate would not be omitted from...
A 3D finite strain phenomenological constitutive model for shape memory alloys considering martensite reorientation
, Article Continuum Mechanics and Thermodynamics ; Volume 22, Issue 5 , June , 2010 , Pages 345-362 ; 09351175 (ISSN) ; Auricchio, F ; Naghdabadi, R ; Reali, A ; Sohrabpour, S ; Sharif University of Technology
2010
Abstract
Most devices based on shape memory alloys experience both finite deformations and non-proportional loading conditions in engineering applications. This motivates the development of constitutive models considering finite strain as well as martensite variant reorientation. To this end, in the present article, based on the principles of continuum thermodynamics with internal variables, a three-dimensional finite strain phenomenological constitutive model is proposed taking its basis from the recent model in the small strain regime proposed by Panico and Brinson (J Mech Phys Solids 55:2491-2511, 2007). In the finite strain constitutive model derivation, a multiplicative decomposition of the...
Investigation into occurring dynamic strain aging in hot rolling of AA5083 using finite elements and stream function method
, Article Materials Science and Engineering A ; Volume 486, Issue 1-2 , 2008 , Pages 138-145 ; 09215093 (ISSN) ; Sheikh, H ; Sharif University of Technology
2008
Abstract
Two-dimensional finite element analysis together with stream function and neural network models are employed to determine thermo-mechanical behavior during hot strip rolling of AA5083. An appropriate velocity field and stream function is first determined using the rule of volume constancy and upper bound theorem and then temperature field within the metal is predicted by means of a two-dimensional conduction-convection model. In order to consider the effect of flow stress and its dependence on temperature, strain and strain rate, a neural network model is also employed in the analysis. Based on the performed tensile tests, two different neural network models are constructed one for smooth...
Hardening materials modeling in finite elastic-plastic deformations based on the stretch tensor decomposition
, Article Materials and Design ; Volume 29, Issue 1 , 2008 , Pages 161-172 ; 02613069 (ISSN) ; Naghdabadi, R ; Sharif University of Technology
Elsevier Ltd
2008
Abstract
In this paper, finite elastic-plastic deformations of hardening materials are analyzed based on the modified multiplicative decomposition of the left stretch tensor. This decomposition is the modified form of the Metzger and Dubey's decomposition used in the frame work of the principal axes of the left stretch tensor. For this purpose, basis-free corotational constitutive equations are derived for elastic-plastic hardening materials with the Armstrong-Frederick kinematic hardening and isotropic hardening models. The proposed governing equations are solved with different corotational rates for the simple shear problem with the material properties of the stainless steel SUS 304. The results...