Hot deformation behavior of P/M Al6061-20% SiC composite

, Article 2006 Powder Metallurgy World Congress and Exhibition, PM 2006, Busan, 24 September 2006 through 28 September 2006 ; Volume 534-536, Issue PART 2 , 2007 , Pages 897-900 ; 02555476 (ISSN); 0878494197 (ISBN); 9780878494194 (ISBN) Asgharzadeh, H ; Simchi, A

Trans Tech Publications Ltd 2007

Abstract

In the present work, hot workability of particulate-reinforced Al6061-20%SiC composite produced by direct hot extrusion technique was studied. Uniaxial hot compression test at various temperatures and strain rates was used and the workability behavior was evaluated from the flow curves and the attendant microstructures. It was shown that the presence of SiC particles in the soft Al6061 matrix deteriorates the hot workability. Bulging of the specimens and flow lines were observed, which indicates the plastic instability during hot working. Microstructure of the composites after hot deformation was found to be heterogeneous, i.e. the reinforcement clusters were observed at the flow lines. The...

Hierarchical Multi-scale Analysis using Nonlinear Finite Element & its Application to Porous Media

, M.Sc. Thesis Sharif University of Technology Asgharzadeh, Mohammad Ali (Author) ; Naghdabadi, Reza (Supervisor) ; Sohrabpour, Saeed (Supervisor)

Abstract

Porous materials, with diverse applications in engineering branches, are categorized as multi-scale. A multi-scale material is one which shows different structure and/or behavior in two or more different length scales. There are physical models which can calculate the macroscopic properties of such materials by using both the properties and volume fractions of the ingredients. However, the number of such theories which can handle problems in the fields of elasticity and hydrodynamics is much less; the fields in which the tensor orders of the properties are more than one. Fortunately, in recent years, a new method named "Computational Multi-scale Homogenization" has been offered to homogenize...

Modification of carbohydrate polymers via grafting in air. 1. Ceric-Induced synthesis of starch-g-polyacrylonitrile in presence and absence of oxygen [electronic resource]

, Article Starch - Starke ; Volume 54, Issue 3-4, pages 140–147, April 2002 Pourjavadi, A. (Ali) ; Zohurian Mehr, Mohammad J

Abstract

Monomer grafting, a unique technique for polysaccharide modification, is always performed under inert (e.g., N2) atmosphere. This work is the first report related to evaluating the possibility and efficiency of the grafting of acrylonitrile (AN) onto starch in presence of oxygen. Thus, corn starch (in both granular and gelatinized states) as well as soluble starch were grafted by AN using a ceric-carbohydrate redox initiating system. Graft copolymerizations were performed under nitrogen, air, and oxygen atmospheres at similar conditions. Grafting occurrence was verified using chemical and spectral proofs. The polymerization mechanism and kinetics were investigated by recording the...

Modification of carbohydrate polymers via grafting in Air. 2. Ceric-Initiated graft copolymerization of acrylonitrile onto natural and modified polysaccharides [electronic resource]

, Article Starch - Stärke ; Volume 54, Issue 10, pages 482–488, October 2002 Pourjavad, A. (Ali) ; Zohuriaan-Mehr, Mohammad J

Abstract

Acrylonitrile (AN) was grafted onto various natural and modified polysaccharides (i.e., gum arabic, gum tragacanth, xanthan gum, sodium alginate, chitosan, sodium carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose) by using ceric-carbohydrate redox initiating system. After overcoming practical problems, mainly from the high viscosity of the aqueous solutions of the different substrates, the graft copolymerization reactions were run either in air or in N2 atmosphere under similar conditions. Grafting was confirmed using chemical and spectral (FTIR) proofs. The reactions were kinetically investigated using semi-empirical expressions and time-temperature profiles. An anomalous...

Modeling of in Plane Behavior of Retrofitted Adobe Walls with Finite Element Method under Cyclic Loading

, M.Sc. Thesis Sharif University of Technology Mohammad Panah, Hossein (Author) ; Bakhshi, Ali (Supervisor) ; Ghannad, Mohammad Ali (Co-Advisor)

Abstract

Statistical studies indicate the fact that in Iran, like many other developing countries, a significant percentage of buildings are made of traditional materials and most of them are adobe buildings especially in rural areas. Furthermore, geological data indicates that Iran is located in alps-Himalayas seismic zone and exposed by destructive earthquakes and adobe buildings suffer the most damages comparing with other type of the structures. According to these explanations, this research deals with adobe buildings behavior and provides solutions for reinforcing them and improving the seismic response of these buildings. These studies include numerical modeling with finite elements methods by...

Silica chloride/wet SiO2 as a novel heterogeneous system for the deprotection of acetals under mild conditions [electronic resource]

, Article Phosphorus, Sulfur, and Silicon and the Related Elements ; Volume 178:2667-2670, Issue 12, 2003 Mirjalili, B. F. (BiBi Fatemeh) ; Pourjavadi, Ali ; Zolfigol, Mohammad Ali ; Bamoniri, Abdolhamid

Abstract

A combination of silica chloride and wet SiO2 was used as an effective deacetalizating agent for the conversion of acetals to their corresponding carbonyl derivatives under mild and heterogeneous condition

Constitutive analysis and microstructural evolution in hot working of nanostructured Al6063

, Article Proceedings of the International Euro Powder Metallurgy Congress and Exhibition, Euro PM 2012, 16 September 2012 through 19 September 2012, Basel ; Volume 1 , September , 2012 ; 9781899072361 (ISBN) Asgharzadeh, H ; Simchi, A ; Sharif University of Technology

European Powder Metallurgy Association (EPMA) 2012

Abstract

Flow curves and microstructural changes of nanostructured Al6063 alloy produced by mechanical alloying followed by hot extrusion were investigated by means of uniaxial compression test in the temperature range between 300 and 450 °C and strain rate range between 10-2 and 1 s-1. The analysis of flow curves were performed by a hyperbolic sine law equation and the stress exponent and activation energy were determined to be 2.9 and 228 kJ mol-1, respectively. The microstructural constituents for elaboration of deformation mechanisms were observed by TEM and EBSD under FEG-SEM. The microstructural observations determine that dynamic recovery through the formation of subgrains within the grains...

Development of a stream function-upper bound analysis applicable to the process of plate rolling

, Article Multidiscipline Modeling in Materials and Structures ; Volume 12, Issue 2 , 2016 , Pages 254-274 ; 15736105 (ISSN) Asgharzadeh, A ; Serajzadeh, S ; Sharif University of Technology

Emerald Group Publishing Ltd 2016

Abstract

The purpose of this paper is to develop a mathematical solution to estimate the deformation pattern and required power in cold plate rolling using coupled stream function method and upper bound theorem. Design/methodology/approach-In the first place, an admissible velocity field and the geometry of deformation zone are derived from a new stream function. Then, the optimum velocity field is obtained by minimizing the corresponding power function. Also, to calculate the adiabatic heating during high speed rolling operations, a two-dimensional conduction-convection problem is sequentially coupled with the mechanical model. To verify the predictions, rolling experiments on aluminum plates are...

Supersolidus liquid phase sintering of Al6061/SiC metal matrix composites

, Article Powder Metallurgy ; Volume 52, Issue 1 , 2009 , Pages 28-35 ; 00325899 (ISSN) Asgharzadeh, H ; Simchi, A ; Sharif University of Technology

2009

Abstract

The aim of the present work is to study the effect of reinforcement content and sintering temperature on the densification and microstructural development during sintering of Al6061/SiC composite compacts. Prealloyed Al6061 powder was mixed with various amounts of SiC particles up to 27 vol.-% and compacted at 350 MPa. Sintering was carried out in a dry nitrogen atmosphere at 580-620°C. It was shown that the presence of SiC particles retards the densification of the prealloyed powder during solid phase sintering and liquid phase sintering. This effect is particularly noticeable at SiC fractions higher than ∼9 vol.-%, at which continuous networks of the hard particles are formed. Increasing...

Hot deformation of PM Al6061 alloy produced by sintering and powder extrusion

, Article Powder Metallurgy ; Volume 51, Issue 4 , July , 2008 , Pages 354-360 ; 00325899 (ISSN) Asgharzadeh, H ; Simchi, A ; Sharif University of Technology

2008

Abstract

Compression test was used to study the deformation behaviour of sintered (12% porosity) and powder extruded (1% porosity) Al6061 alloy at high temperatures ranging from 350 to 500°C. The flow curves of the materials were determined at strain rates of 0.001, 0.01 and 0.1 s-1. The extruded alloy exhibited plastic instability in the form of bulging and formation of shear bands. The deformation activation energy of the extruded material was determined to be QI=77±16 kJ mol-1 (T<450°C) and OII=136±12 kJ mol-1 (T≥450°C). The values of activation energy and appearance of strain softening in the stress-strain curves revealed that thermally activated restoration processes, i.e. dynamic recovery and...

Effect of sintering atmosphere and carbon content on the densification and microstructure of laser-sintered M2 high-speed steel powder

, Article Materials Science and Engineering A ; Volume 403, Issue 1-2 , 2005 , Pages 290-298 ; 09215093 (ISSN) Asgharzadeh, H ; Simchi, A ; Sharif University of Technology

2005

Abstract

In the present work, the role of graphite addition and sintering atmosphere on the laser sintering of M2 high-speed steel (HSS) powder was studied. The test specimens were produced using a continuous wave CO2 laser beam at power of 200 W and at varying scan rate ranges from 50 to 175 mm s-1 under nitrogen and argon atmospheres. It was found that laser scan rate and sintering atmosphere strongly influence the densification of M2 HSS powder. Opposite to the conventional sintering that the sinterability of HSS is improved by graphite addition, the result of this work demonstrated that graphite addition decreases the sintered density of M2 HSS at relatively low laser scan rates, i.e. <100 mm...

Evaluation and Modeling of Modified Binders Master Curves

, Ph.D. Dissertation Sharif University of Technology Asgharzadeh, Mohammad (Author) ; Tabatabaee, Nader (Supervisor)

Abstract

With a surge in consumption of modified binders in recent years, different methods have been used to evaluate the properties of modified binders with relative success. None of these methods are able to fulfill all the requirements for evaluation and intrerpretation of the physical, chemical and rheologocal properties of modified binders. Since rheological master curves can present a mechanical interpretation of the binders in a wide range of times and temperatures, in conjunction with other evaluation metheods, they are considered a promising means of evaluating the suitability of modified bindrers. The available master curve models do not possess the sufficient diversity for this purpose....

Conditions for Integrity of Multivariable Systems with Input Saturation

, M.Sc. Thesis Sharif University of Technology Asgharzadeh, Abbas (Author) ; Nobakhti, Amin (Supervisor)

Abstract

Multivariable control systems as used in the industry usually contain integral action in order to improve tracking of the output with respect to step reference changes. These systems are usually subject to input saturation due to actuator or sensor nonlinearities. The aim of this work is find the conditions for the integrity concept of such multivariable system, e.g. IS, IC, ICI and DIC. First we develop the conditions on the controller gains necessary stabilize the systems and then show that these conditions can changes when one examines integrity conditions

Numerical Assessment of Optimum Baffle Configuration and Hydrodynamics of Settling Tanks

, M.Sc. Thesis Sharif University of Technology Asgharzadeh, Hafez (Author) ; Firoozabadi, Bahar (Supervisor)

Abstract

Sedimentation tanks are channels designed for sedimentation of suspended solids in water. These tanks are one of the most important parts of water treatment plants and their performance directly affects the functionality of water treatment plants. Therefore, researchers have tried to find better designs of sedimentation tanks. Among several design methods have been presented, modification of the geometry of tanks by installing baffles is one of the most effective and economic methods. According to the importance of performance improvement of industrial sedimentation tanks as well as the diversity in reported results, development and completion of previous studies seem to be necessary. In...

Distributed Fault-tolerant Computation for Massive Data

, M.Sc. Thesis Sharif University of Technology Mahvari Habibabadi, Mohammad Mahdi (Author) ; Maddah-Ali, Mohammad Ali (Supervisor)

Abstract

In this thesis we consider the problem of distributed computation by many processors.We mainly concentrate on matrix multiplication problem in this thesis because of its importance. A distributed system consists of N worker processors and one master processor. The master processor should distribute the computation between workers and after computation in each of them, collect the results. In this thesis, we are going to mitigate the effect of straggler processors by using coding methods. Straggler processors can cause delays in the computation time.In this thesis, we firstly introduce a method to multiply any number of matrices in each other. The proposed method occurred in one shot without...

High-temperature deformation and structural restoration of a nanostructured Al alloy [electronic resource]

, Article Journal of Scripta Materialia (Pergamon) ; June 2012, Volume 66, Issue 11, Pages 911–914 Asgharzadeh, H ; Simchi, A. (Abdolreza) ; Kim, H. S ; Sharif University of Technology

Abstract

We studied the flow stress and microstructural changes of nanostructured Al-6063 alloy produced by mechanical alloying at various temperatures and strain rates. The analysis of flow curves was performed by a constitutive equation, and the stress exponent and activation energy were determined as functions of strain. The deformation mechanisms were elaborated through microstructural observations by electron backscattering diffraction and transmission electron microscopy. Coarsening of the subgrains and grain growth upon deformation was monitored and related to the Zener–Hollomon parameter

Microstructure, strengthening mechanisms and hot deformation behavior of an oxide-dispersion strengthened UFG Al6063 alloy [electronic resource]

, Article Journal of Materials Characterization ; January 2013, Volume 75, Pages 108–114 Asgharzadeh, H ; Kim, H. S ; Simchi, A. (Abdolreza) ; Sharif University of Technology

Abstract

An ultrafine-grained Al6063/Al2O3 (0.8 vol.%, 25 nm) nanocomposite was prepared via powder metallurgy route through reactive mechanical alloying and hot powder extrusion. Scanning electron microcopy, transmission electron microscopy, and back scattered electron diffraction analysis showed that the grain structure of the nanocomposite is trimodal and composed of nano-size grains (< 0.1 μm), ultrafine grains (0.1–1 μm), and micron-size grains (> 1 μm) with random orientations. Evaluation of the mechanical properties of the nanocomposite based on the strengthening-mechanism models revealed that the yield strength of the ultrafine-grained nanocomposite is mainly controlled by the high-angle...

Microstructure features, strengthening mechanisms and hot deformation behavior of oxide-dispersion Strengthened Al6063 alloy with ultrafine-grained structure [electronic resource]

, Article AIP Conference Proceedings (American Institute of Physics, Ste. 1 NO. 1 Melville NY 11747-4502 United States) ; Volume 75, January 2013, Pages 108–114 Asgharzadeh, H ; Kim, H. S ; Simchi, A. (Abdolreza) ; Sharif University of Technology

Abstract

Ultrafine-grained (UFG) Al6063/Al2O3 (0.8 vol%, 25 nm) nanocomposite was prepared via powdr metallurgy route. The grain structure of the nanocomposite composed of nano-size grains (< 0.1 μm), ultrafine grains (0.1-1 μm) and micron-size grains (>1 μm) with random orientations. It was found that the yield strength of the UFG nanocomposite is mainly controlled by the Orowan mechanism rather than the grain boundaries. The deformation activation energy at temperature ranges of T <300 ˚C and 300 ˚C ≤T < 450 ˚C was determined to be 74 and 264 kJ mol-1, respectively. At the higher temperatures, significant deformation softening was observed due to dynamic recrystallization of non-equilibrium grain...

Hot deformation of ultrafine-grained Al6063/Al2O3 nanocomposites [electronic resource]

, Article Journal of Materials Science ; July 2011, Volume 46, Issue 14, P.4994-5001 Asgharzadeh, H ; Simchi, A. (Abdolreza) ; Kim, H. S ; Sharif University of Technology

Abstract

Ultrafine-grained (UFG) Al6063 alloy reinforced with 0.8 vol% nanometric alumina particles (25 nm) was prepared by reactive mechanical alloying and direct powder extrusion. Transmission electron microscopy and electron backscatter diffraction analysis showed that the grain structure of the nanocomposite composed of nanosize grains (<0.1 μm), ultrafine grains (0.1–1 μm) and micronsize grains (>1 μm) with random orientations. Mechanical properties of the material were examined at room and high temperatures by compression test. It was found that the yield strength of the UFG composite material is mainly controlled by the Orowan mechanism rather than the grain boundaries. The deformation...

Microstructural features, texture and strengthening mechanisms of nanostructured Al6063 alloy processed by powder metallurgy [electronic resource]

, Article Journal of Materials Science and Engineering: A ; 15 May 2011, Volume 528, Issue 12, Pages 3981–3989 Asgharzadeh, H ; Simchi, A. (Abdolreza) ; Kim, H. S ; Sharif University of Technology

Abstract

Nanostructured AA6063 (NS-Al) powder with an average grain size of ∼100 nm was synthesized by high-energy attrition milling of gas-atomized AA6063 powder followed by hot extrusion. The microstructural features of the consolidated specimen were studied by transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques and compared with those of coarse-grained AA6063 (CG-Al) produced by hot powder extrusion of gas-atomized powder (without using mechanical milling). The consolidated NS-Al alloy consisted of elongated ultrafine grains (aspect ratio of ∼2.9) and equiaxed nanostructured grains. A high fraction (∼78%) of high-angle grain boundaries with average...