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    Experimental and thermomechanical analysis of friction stir welding of poly(methyl methacrylate) sheets

    , Article Science and Technology of Welding and Joining ; Volume 23, Issue 3 , 2018 , Pages 209-218 ; 13621718 (ISSN) Aghajani Derazkola, H ; Simchi, A ; Sharif University of Technology
    Taylor and Francis Ltd  2018
    Abstract
    In the present work, the feasibility of friction stir welding (FSW) of poly(methyl methacrylate) sheets was studied experimentally and theoretically by employing thermomechanical simulations. The effect of processing parameters including tool plunge depth, tilt angle, tool rotational speed (w), and transverse velocity (v) was investigated to determine suitable conditions to attain sound and defect-free joints. It is shown that a low tool plunge depth of 0.2 mm and a tilt angle of 2° provide suitable material flow to gain sound joints. By controlling the heat input into stir zone by increasing the tool rotational speed and decreasing linear velocity, the formation of defects can be minimised.... 

    An investigation on the dissimilar friction stir welding of T-joints between AA5754 aluminum alloy and poly(methyl methacrylate)

    , Article Thin-Walled Structures ; Volume 135 , 2019 , Pages 376-384 ; 02638231 (ISSN) Aghajani Derazkola, H ; Simchi, A ; Sharif University of Technology
    Elsevier Ltd  2019
    Abstract
    Process optimization to prepare T-joints of poly methyl methacrylate (PMMA) and AA5754 alloy by friction stir welding (FSW) was performed. Effects of processing parameters including tool rotational velocity, traverse speed, tilt angle and plunge depth (TP) were studied. The material flow and formation of interaction layer upon FSW were evaluated and the tensile strength and hardness of the joints were examined. It is shown that by controlling the heat input into stir zone through increasing the rotational velocity or decreasing travelling speed, less defects are formed while the thickness of the interaction layer increases. The optimum condition is attained at 1600 rpm/30 mm min−1 with a... 

    A new procedure for the fabrication of dissimilar joints through injection of colloidal nanoparticles during friction stir processing: Proof concept for AA6062/PMMA joints

    , Article Journal of Manufacturing Processes ; Volume 49 , 2020 , Pages 335-343 Aghajani Derazkola, H ; Simchi, A ; Sharif University of Technology
    Elsevier Ltd  2020
    Abstract
    We present a new semi-solid state procedure for efficient joining of dissimilar materials. The process called fed friction stir processing (FFSP) and works based on in-situ injection of colloidal nanoparticles in the welding line during processing. To present the efficiency of the process, friction stir welding of AA6062 aluminum alloy and poly(methyl methacrylate) (PMMA) through injection of alumina nanoparticles is presented. Microstructural features and mechanical characteristics of the weldments are elaborated. It is shown that in-situ feeding of the alumina nanoparticles during FFSP changes the thermo-mechanical regimes of the bonding zone and decreases the thickness of interaction... 

    Experimental and thermomechanical analysis of the effect of tool pin profile on the friction stir welding of poly(methyl methacrylate) sheets

    , Article Journal of Manufacturing Processes ; Volume 34 , 2018 , Pages 412-423 ; 15266125 (ISSN) Aghajani Derazkola, H ; Simchi, A ; Sharif University of Technology
    Elsevier Ltd  2018
    Abstract
    Effects of frustum, cubic and triangle tool pin profiles on the friction stir welding (FSW) of poly(methyl methacrylate) (PMMA) were studied by experimental analysis and thermomechanical simulations. It is shown that employing pins with a low contact surface area form macrocracks and voids along the joint line. Edged-type pins locally stir the polymer and cause tunnel defects which are formed at the root of the joint. In contrast, pins with relatively smooth and large surface area would yield a defect-free weldment if an appropriate processing condition is employed. Mechanical examinations in longitudinal (LS) and transverse (TS) directions indicate that the highest tensile strength (LS = 59... 

    Effects of alumina nanoparticles on the microstructure, strength and wear resistance of poly (methyl methacrylate)-based nanocomposites prepared by friction stir processing

    , Article Journal of the Mechanical Behavior of Biomedical Materials ; Volume 79 , March , 2018 , Pages 246-253 ; 17516161 (ISSN) Aghajani Derazkola, H ; Simchi, A ; Sharif University of Technology
    Elsevier Ltd  2018
    Abstract
    In this study, alumina-reinforced poly(methyl methacrylate) nanocomposites (PMMA/Al2O3) containing up to 20 vol% nanoparticles with an average diameter of 50 nm were prepared by friction stir processing. The effects of nanoparticle volume fraction on the microstructural features and mechanical properties of PMMA were studied. It is shown that by using a frustum pin tool and employing an appropriate processing condition, i.e. a rotational speed of 1600 rpm/min and transverse velocity of 120 mm/min, defect free nanocomposites at microscale with fine distribution of the nanoparticles can successfully been prepared. Mechanical evaluations including tensile, flexural, hardness and impact tests... 

    Friction stir welding of polycarbonate lap joints: Relationship between processing parameters and mechanical properties

    , Article Polymer Testing ; Volume 79 , 2019 ; 01429418 (ISSN) Aghajani Derazkola, H ; Simchi, A ; Lambiase, F ; Sharif University of Technology
    Elsevier Ltd  2019
    Abstract
    The relation between process parameters and properties of polycarbonate (PC) sheet after friction stir welding (FSW) was investigated. Effects of FSW tool rotation speed (ω), travelling speed (V), tilt angle (α) and plunge depth on material flow, joint tensile strength, flexural strength, impact energy and hardness were investigated. It is shown that at low and high levels of heat input sound joints cannot be attained. At low heat inputs, the local temperature is not high enough to decrease the viscosity of the polymer to fill the interface, and thus voids and large planar cracks are formed in the joint root and stir zone. At high heat inputs, expelling of materials due to high peak... 

    Friction-stir lap-joining of aluminium-magnesium/poly-methyl-methacrylate hybrid structures: thermo-mechanical modelling and experimental feasibility study

    , Article Science and Technology of Welding and Joining ; Volume 23, Issue 1 , 2018 , Pages 35-49 ; 13621718 (ISSN) Aghajani Derazkola, H ; Khodabakhshi, F ; Simchi, A ; Sharif University of Technology
    Taylor and Francis Ltd  2018
    Abstract
    In this research, the feasibility of friction-stir welding (FSW) for dissimilar lap-joining of an aluminium-magnesium alloy (AA5058) and poly-methyl-methacrylate sheets to attain sound and defect-free joints was examined. The inter-mixing flow patterns between the metal and polymer counterparts during FSW were predicted by employing three-dimensional finite element models. It is shown that the bonding mechanism between the dissimilar materials is mechanical interlocking at the interface which controls the joint strength depending on the processing parameters. The most suitable dissimilar lap-joining regarding microstructural soundness is attained at w= 1600 rev min−1 and v = 25 mm min−1.... 

    Evaluation of a polymer-steel laminated sheet composite structure produced by friction stir additive manufacturing (FSAM) technology

    , Article Polymer Testing ; Volume 90 , 2020 Derazkola, H. A ; Khodabakhshi, F ; Simchi, A ; Sharif University of Technology
    Elsevier Ltd  2020
    Abstract
    Laminated polymer-steel composites are promising layered materials for practical applications in the automotive industry considering their superior crush resistance capacity in terms of enhanced damping potential. In this research, the sheet lamination (SL) route of friction stir additive manufacturing (FTAM) technology was implemented for the production of a poly-methyl-methacrylate (PMMA) polymer matrix composite structure as reinforced by textile stainless steel layers, and feeding of PMMA granulates inside the stirred region. Layers bonding and the soundness of composite formation during fabrication of the laminated structure were studied. Possible chemical interactions between the steel... 

    Modeling and experimental validation of material flow during FSW of polycarbonate

    , Article Materials Today Communications ; Volume 22 , 2020 Derazkola, H. A ; Eyvazian, A ; Simchi, A ; Sharif University of Technology
    Elsevier Ltd  2020
    Abstract
    Friction stir welding (FSW) of thermoplastic materials is an attractive but a challenging process due to inherent chemical and mechanical characteristics of polymeric materials. In the present work, thermo-mechanical models were employed to investigate the effect of processing parameters on of FSW of polycarbonate (PC). The heat flux during the joining process was localized around the PC join line and led to the formation of circular rings on the upper surface. According to the simulation results, increasing the tool rotational velocity reduced the temperature gradient and decfeased the suseptibelity of crack formation around the joint line. Cracks were formed at low frictional heats and... 

    Friction stirwelding and friction spot stir welding processes of polymers-state of the art

    , Article Materials ; Volume 13, Issue 10 , May , 2020 Lambiase, F ; Aghajani Derazkola, H ; Simchi, A ; Sharif University of Technology
    MDPI AG  2020
    Abstract
    In the last decade, the friction stir welding of polymers has been increasingly investigated by the means of more and more sophisticated approaches. Since the early studies, which were aimed at proving the feasibility of the process for polymers and identifying suitable processing windows, great improvements have been achieved. This owes to the increasing care of academic researchers and industrial demands. These improvements have their roots in the promising results from pioneer studies; however, they are also the fruits of the adoption of more comprehensive approaches and the multidisciplinary analyses of results. The introduction of instrumented machines has enabled the online measurement... 

    Evolution of the electronic structure and structural properties of BaFe2As2 at the tetragonal-collapsed tetragonal phase transition

    , Article Physica C: Superconductivity and its Applications ; Volume 516 , 2015 , Pages 36-43 ; 09214534 (ISSN) Aghajani, M ; Khosroabadi, H ; Akhavan, M ; Sharif University of Technology
    Elsevier  2015
    Abstract
    Density functional theory generalized gradient approximation has been used to calculate the electronic and structural properties of BaFe2As2 compound up to 56 GPa by using Quantum Espresso code. Structural properties like bulk modulus, Fe-As bond length, and As-Fe-As bond angles have been investigated by pressure especially near the tetragonal to collapsed tetragonal (T-cT) structural phase transition. This study shows considerable changes of these parameters in the cT phase, which happens near our calculated critical pressure, Pc = 24 ± 2 GPa. Electronic band structure and its orbital-resolved, total and partial density of states and Fermi surfaces have been... 

    Pressure dependence of effective Coulomb interaction parameters in BaFe2As2 by first-principle calculation

    , Article Physica C: Superconductivity and its Applications ; Volume 548 , 15 May , 2018 , Pages 61-64 ; 09214534 (ISSN) Aghajani, M ; Hadipour, H ; Akhavan, M ; Sharif University of Technology
    Elsevier B.V  2018
    Abstract
    Pressure dependence of the onsite Coulomb interactions of the BaFe2As2 has been studied by employing the constrained random phase approximation within first-principle calculations. Analyzing total and projected density of states, a pseudogap is found for dxy band at the energy roughly 0.25 eV higher than the Fermi level. Also, by applying pressure the spectral weight of the dxy orbital vanishes while other orbitals remain metallic. The different screening channels, as discussed in four different models, affect significantly on the Hubbard U while the Hund J remains almost unchanged. The average onsite bare and partially and fully screened Coulomb interactions increase with different rates... 

    Mechanical and chemical pressure effects on the AeFe 2 As 2 (Ae = Ba, Sr, Ca) compounds: Density functional theory

    , Article Computational Materials Science ; Volume 160 , 2019 , Pages 233-244 ; 09270256 (ISSN) Aghajani, M ; Hadipour, H ; Akhavan, M ; Sharif University of Technology
    Elsevier B.V  2019
    Abstract
    We have studied the pressure-induced structural, magnetic and electronic properties of AeFe 2 As 2 (Ae = Ba, Sr, Ca) compounds in the framework of density functional theory within the GGA-PBE method. The effects of chemical pressure generated by Sr and Ca substitutions in BaFe 2 As 2 have been investigated. We have found a magnetic transition at the same primitive unit cell volume, around 81 Å 3 for the (Ba⧹Ca)Fe 2 As 2 compounds, which predicts a magnetic transition pressure of 12 GPa for SrFe 2 As 2 . The structural parameters of FeAs 4 tetrahedra are obtained after ionic relaxation and compared with the existing experimental results. The change of these internal parameters is ascribed to... 

    Experimental investigation of the roles of blood volume and density in finger photoplethysmography

    , Article IEEE Sensors Journal ; Volume 13, Issue 5 , 2013 , Pages 1397-1398 ; 1530437X (ISSN) Keikhosravi, A ; Zahedi, E ; Attar, H. M ; Aghajani, H ; Sharif University of Technology
    2013
    Abstract
    Using simultaneous photoplethysmogram (PPG) and pulse transducer signals from the same finger, a high correlation (Mean: 98.6, STD: 1) is obtained between the AC part of the PPG and estimated volume changes (after normalization). These results point to the fact that in the resting fingertip, PPG signal variations are only due to volume changes and that blood density does not change thus has no contribution  

    Experimental study of asphaltene precipitation behavior during miscible carbon dioxide injection

    , Article Energy Sources, Part A: Recovery, Utilization and Environmental Effects ; Vol. 36, issue. 14 , July , 2014 , pp. 1523-1530 ; ISSN: 15567036 Alizadeh, A ; Nakhli, H ; Kharrat, R ; Ghazanfari, M. H ; Aghajani, M ; Sharif University of Technology
    2014
    Abstract
    Many reservoir and production engineers face asphaltene precipitation as a major problem during miscible carbon dioxide flooding projects. Experimental studies regarding asphaltene precipitation are therefore employed to assist in selecting appropriate facilities and proper operation schemes. During this study, a series of high pressure, high temperature experiments are designed and performed to analyze asphaltene precipitation behavior of an Iranian light reservoir crude at reservoir conditions due to natural production and miscible CO2 gas injection. For both sets of experiments, two different temperature levels (including reservoir temperature) are selected to investigate the role of... 

    Proposing a Control Method for Malaria

    , M.Sc. Thesis Sharif University of Technology Rezanezhad Derazkola, Hadi (Author) ; Shahrokhi, Mohammad (Supervisor)
    Abstract
    In every year malaria has enormous fatality around the world, so this disease has to be controlled. In this thesis based on a model given in the literature[12], a model predictive controller has been designed and its performance has been compared with that of the optimal control. The simulation results show that in the case of model mismatch, the performance of model predictive control is superior. In model selection, it has been tried that a comprehensive model that has enough inputs for control to be selected. A linear time varying model is used to simulate the nonlinear behavior of the nonlinear system. The Least Squares method is used to update the model parameters  

    A robust voice activity detection based on wavelet transform

    , Article 2nd International Conference on Electrical Engineering, ICEE, Lahore, 25 March 2008 through 26 March 2008 ; 2008 ; 9781424422937 (ISBN) Aghajani, K ; Manzuri, M. T ; Karami, M ; Tayebi, H ; Sharif University of Technology
    2008
    Abstract
    Voice activity detection is an important step in some speech processing systems, such as speech recognition, speech enhancement, noise estimation, speech compression ... etc. In this paper a new voice activity detection algorithm based on wavelet transform is proposed. In this algorithm we use the energy in each sub band, and by two methods we extract feature vector from these values. Experimental results demonstrate advantage over different VAD methods. ©2008 IEEE  

    Assessing the explanatory power of naturalism in addressing ultimate questions

    , Article Vestnik Sankt-Peterburgskogo Universiteta, Filosofiia i Konfliktologiia ; Volume 37, Issue 2 , 2021 , Pages 217-228 ; 25422278 (ISSN) Aghajani, J. D ; Sharif University of Technology
    Saint Petersburg State University  2021
    Abstract
    A typical scientist has no responsibility other than to explain how a natural event occurred. However, when a philosopher asks about the conditions under which a scientist’s explanation is true, he is, in fact, raising an ultimate question, the concept which Karl Popper used for the first time. Answering this question requires that no elements are neglected in the explanation, and no significant factors in the explanation are overlooked. In other words, in explaining a phenomenon, at any level of its explanation, there should be no remainder. These requirements can be achieved through the full explanation. In the present article, by drawing on concepts such as theory-ladenness of... 

    Metaphysical necessity in the neo-sadraian school and assessment of necessitarian theories of the laws of nature

    , Article Teorie Vedy / Theory of Science ; Volume 43, Issue 1 , 2021 , Pages 33-57 ; 12100250 (ISSN) Aghajani, J. D ; Sharif University of Technology
    Czech Academy of Sciences  2021
    Abstract
    To differentiate between the laws of nature and accidental generalizations, we must adopt a view of necessity that is capable of being realized in relationships existing among natural objects. In neo-Sadraian Islamic philosophy, metaphysical necessity is accepted as part of the cause-effect relationship. This paper compares the neo-Sadraian interpretation of necessity and necessitarian theories about the laws of nature, particularly essentialism and universal theory. By resorting to specific forms al-shûrat al-naw’iyyah, the origin of the essential properties of natural objects, I argue that neo-Sadraians have proposed a perspective on metaphysical necessity that is epistemologically a... 

    Assessing the explanatory power of naturalism in addressing ultimate questions

    , Article Vestnik Sankt-Peterburgskogo Universiteta, Filosofiia i Konfliktologiia ; Volume 37, Issue 2 , 2021 , Pages 217-228 ; 25422278 (ISSN) Darvish Aghajani, J ; Sharif University of Technology
    Saint Petersburg State University  2021
    Abstract
    A typical scientist has no responsibility other than to explain how a natural event occurred. However, when a philosopher asks about the conditions under which a scientist’s explanation is true, he is, in fact, raising an ultimate question, the concept which Karl Popper used for the first time. Answering this question requires that no elements are neglected in the explanation, and no significant factors in the explanation are overlooked. In other words, in explaining a phenomenon, at any level of its explanation, there should be no remainder. These requirements can be achieved through the full explanation. In the present article, by drawing on concepts such as theory-ladenness of...