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Microstructural evolution and intermetallic formation in Al-8wt% Si-0.8wt% Fe alloy due to grain refiner and modifier additions

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International Journal of Minerals,Metallurgy and Materials 2012年第8期19卷 739-746页

作者： amir Hassani Khalil Ranjbar Sattar Sami Faculty of Materials Science and Engineering University of Semnan Semnan Iran Materials Department Faculty of Engineering Shahid Chamran University Ahwaz Iran

An alloy of A1-8wt% Si-0.8wt% Fe was cast in a metallic die, and its microstrucmral changes due to Ti-B refiner and Sr modifier additions were studied. Apart from usual refinement and modification of the microstructure, some mutual influences of the additives took place, and no mutual poisoning effects by these additives, in combined form, were observed. It was noticed that the dimensions of the iron-rich intermetallics were influenced by the additives causing them to become larger. The needle-shaped intermetallics that were obtained from refiner addition became thicker and longer when adding the modifier. It was also found that a-Al and eutectic silicon phases preferentially nucleate on different types of intermetallic compounds. The more iron content of the intermetallic compounds and the more changes in their dimensions occurred. Formation of the shrinkage porosities was also observed.

关键词： aluminum alloys metal casting grain refinement modification metallographic microstructure intermetallics

Improvement of microstructure and corrosion properties of friction stir welded AA5754 by adding Zn interlayer

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International Journal of Minerals,Metallurgy and Materials 2018年第8期25卷 967-973页

作者： Ali Shamsipur amir Anvari Ahmad Keyvani Department of Mining and Metallurgical Engineering Amirkabir University of Technology School of Metallurgy and Materials Engineering Faculty of Technology and EngineeringShahrekord University

This study investigated the effect of Zn foil layers on the microstructure and corrosion characteristics of friction stir welded aluminum alloy *** of various joints were prepared by applying different rotational and welding speeds,and their microstructures were evaluated via a metallographic technique and scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy elemental *** anticorrosion behavior of joints in the absence and presence of a Zn interlayer was studied by cyclic potentiodynamic polarization test in 3.5 wt% Na Cl aqueous solution,and sound welds were obtained in the presence of the Zn interlayer *** results revealed that the joint made at a rotational speed of 800 r/min and traveling speed of 15 mm/min achieved a chemical composition identical to that of aluminum alloy 7 xxx series,and as such,it showed the best resistance to corrosion.

关键词： friction stir welding AA5754 aluminum alloy zinc interlayer microstructure corrosion resistance

Effect of foundation flexibility on ductility reduction factors for R/C stack-like structures

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Earthquake Engineering and Engineering Vibration 2011年第2期10卷 277-290页

作者： amir M.Halabian Shabnam Kabiri Faculty of Civil Engineering Isfahan University of Technology

The most important parameter used to determine force reduction factors in force-based design procedures adopted in the current seismic codes is the structural ductility. For a structure supported on a flexible foundation, the ductility factor could be affected by foundation compliances. The ductility factors given in the current codes are mostly assigned ignoring the effect of SSI and therefore the objective of this research is to assess the significance of SSI phenomenon on ductility factors of stack-like structures. The deformed configuration of stack-fike structures is idealized as an assemblage of beam elements considering nonlinear moment-curvature relations, while a linear sway-rocking model was implemented to model the supporting soil. Using a set of artificial records, repeated linear and nonlinear analyses were performed by gradually increasing the intensity of acceleration to a level where the first yielding of steel in linear and nonlinear analyses is observed and a level corresponding to the stack collapse in the nonlinear analysis. The difference between inelastic and elastic resistance in terms of displacement ductility factors has been quantified. The results indicate that foundation flexibility can decrease the ductility of the system and neglecting this phenomenon may lead to erroneous conclusions in the prediction of the seismic performance of flexibly-supported R/C stack-like structures.

关键词： soil-structure interaction R/C stack-like structures ductility

Drag Optimization of A Planing Vessel Based on the Stability Criteria Limits

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China Ocean Engineering 2019年第3期33卷 365-372页

作者： Yasin MASUMI amir H.NIKSERESHT Department of Mechanical and Aerospace Engineering Shiraz University of Technology

One of the important phases of designing a craft is stability analysis and optimization of the drag force in cruise speed. In this research the longitudinal and lateral stability of a planing hull craft (DTMB 62 model 4667-1) is investigated with some semi-empirical formulae and the effects of some important design parameters are investigated on the limit of stability region. Also on the basis of these empirical formulations and by using a genetic algorithm the drag force is optimized in each constant cruise speed with the stability criteria limits at a constant beam or projected area. Aspect ratio, the longitudinal position of the gravity center and deadrise angle are the optimization parameters. The results show that the aspect ratio and the longitudinal position of the gravity center are two important parameters in optimizing the drag force and for this planing vessel the drag force can be reduced by 22%.

关键词： longitudinal stability transverse stability drag-optimization Savitsky formula

Resilient Fixed-Order Distributed Dynamic Output Feedback Load Frequency Control Design for Interconnected Multi-Area Power Systems

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IEEE/CAA Journal of Automatica Sinica 2019年第5期6卷 1139-1151页

作者： Ali Azarbahram amir Amini Mahdi Sojoodi the Department of Electrical and Computer Engineering Ferdowsi University of MashhadMashhadIran the Department of Electrical and Computer Engineering Concordia UniversityMontrealQCCanada the Faculty of Electrical and Computer Engineering Tarbiat Modares UniversityTehran14115-143Iran

The paper proposes a novel H∞ load frequency control(LFC) design method for multi-area power systems based on an integral-based non-fragile distributed fixed-order dynamic output feedback(DOF) tracking-regulator control scheme. To this end, we consider a nonlinear interconnected model for multiarea power systems which also include uncertainties and timevarying communication delays. The design procedure is formulated using semi-definite programming and linear matrix inequality(LMI) method. The solution of the proposed LMIs returns necessary parameters for the tracking controllers such that the impact of model uncertainty and load disturbances are minimized. The proposed controllers are capable of receiving all or part of subsystems information, whereas the outputs of each controller are local. These controllers are designed such that the resilient stability of the overall closed-loop system is guaranteed. Simulation results are provided to verify the effectiveness of the proposed scheme. Simulation results quantify that the distributed(and decentralized) controlled system behaves well in presence of large parameter perturbations and random disturbances on the power system.

关键词： Dynamic output feedback control interconnected multi-area power systems load frequency control linear matrix inequalities power system control

Hot deformation behavior of microstructural constituents in a duplex stainless steel during high-temperature straining

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International Journal of Minerals,Metallurgy and Materials 2013年第10期20卷 953-960页

作者： amir Momeni Shahab Kazemi Ali Bahrani Materials Science and Engineering Department Hamedan University of Technology Department of Materials Engineering Faculty of EngineeringBu Ali Sina University

The hot deformation characteristics of 1.4462 duplex stainless steel （DSS） were analyzed by considering strain partitioning between austenite and ferrite constituents. The individual behavior of ferrite and austenite in microstructure was studied in an iso-stress condition. Hot compression tests were performed at temperatures of 800-1100~C and strain rates of 0.001-1 s-1. The flow stress was modeled by a hyperbolic sine constitutive equation, the corresponding constants and apparent activation energies were determined for the studied alloys. The constitutive equation and law of mixture were used to measure the contribution factor of each phase at any given strain. It is found that the contribution factor of ferrite exponentially declines as the Zener-HoUomon parameter （Z） increases. On the contrary, the austenite contribution polynomially increases with the increase of Z. At low Z values below 2.6. x 1015 （lnZ---35.5）, a negative contribution factor is determined for austenite that is attributed to dynamic recrystallization. At high Z values, the contribution factor of austenite is about two orders of magnitude greater than that of ferrite, and therefore, austenite can accommodate more strain. Microstructural characterization via electron back-scattered diffraction （EBSD） confirms the mechanical results and shows that austenite recrystallization is possible only at high temperature and low strain rate.

关键词： duplex stainless steel compression testing strain partitioning high temperature operations deformation

Equating incremental dynamic analysis with static nonlinear analysis at near-field excitation

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Earthquake Engineering and Engineering Vibration 2015年第3期14卷 465-476页

作者： Asghar Bahramirad Mohsen Tehranizadeh amir Moshref Department of Civil and Environmental Engineering Amir Kabir University of Technology

In an incremental dynamic analysis(IDA) using a set of ground motion records,nonlinear time history analysis needs to be performed on *** is well recognized that IDA calls for high computational efforts and the results are highly sensitive to selected ground *** a result,alternative static methods are *** study aims to introduce a new double-stage(N1- N2) static method to estimate capacity curves of MR *** technique is regulated to resemble IDA results with specific emphasis on near-field ground *** an ensemble of 56 near-field earthquake records,required ID As have been carried out for SAC-Los Angeles 3-,9- and 20-story buildings and an additional 15-story *** results of the proposed static method are compared with those from IDA,displacement-based adaptive procedure(DAP),and multimodal procedure(MMP).The results indicate that in addition to enhanced accuracy,very little time is required in the case of N1-N2 ***,for the 3-story structure,the time required is less than 1 *** proposed N1-N2 method shows the best accuracy in terms of lateral mechanisms for the 15-story frame while for the other cases,the first mode load pattern leads to the best accuracy.

关键词： incremental dynamic analysis new adaptive static p

Concept of Intelligent Mechanical Design for Autonomous Mobile Robots

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Journal of Bionic Engineering 2007年第4期4卷 217-226页

作者： amir A. F Nassiraei Kazuo Ishii Kyushu Institute of Technology Kitakyushu Fukuoka 808-0196 Japan

The concept of Intelligent Mechanical Design （IMD） is presented to show how a mechanical structure can be designed to affect robot controllability, simplification and task performance. Exploring this concept produces landmarks in the territory of mechanical robot design in the form of seven design principles. The design principles, which we call the Mecha-Telligence Principles （MTP）, provide guidance on how to design mechanics for autonomous mobile robots. These principles guide us to ask the right questions when investigating issues concerning self-controllable, reliable, feasible, and compatible mechanics for autonomous mobile robots. To show how MTP can be applied in the design process we propose a novel methodology, named as Mecha-Telligence Methodology （MTM）. Mechanical design by the proposed methodology is based on preference classification of the robot specification described by interaction of the robot with its environment and the physical parameters of the robot mechatronics. After defining new terms, we investigate the feasibility of the proposed methodology to the mechanical design of an autonomous mobile sewer inspection robot. In this industrial project we show how a passive-active intelligent moving mechanism can be designed using the MTM and employed in the field.

关键词： mechanical design intelligent autonomous robot mobile robot

Parametric relationship between hypoid gear teeth and accurate face-milling cutter

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Advances in Manufacturing 2020年第4期8卷 537-555页

作者： Mahmoud Rababah Muhammad Wasif Syed amir Iqbal Department of Mechanical Engineering Hashemite UniversityZarqaJordan Department of Industrial and Manufacturing Engineering NED University of Engineering and TechnologyKarachiPakistan

The cutter systems of hypoid gear cutting machines contain groups of inside and outside *** these cutter systems,the side cutting edges of the blades machine the convex and concave gear teeth while rotating about the cutter rotation *** side cutting edges lay on the rake face formed through the blade,rake,and relief angles;hence,the normal cross-section of the cutter swept surface forms hyperboloid gear *** the accurate geometry of the cutter system,a relationship between the pressure and spiral angles of the gear tooth and the parameters of the cutter system is developed for the FORMAT machining of a hypoid gear.A new parameterization of the gear tooth surfaces is introduced to determine these angles for the accurate gear tooth by the accurate cutter system.A numerical example with different cutter systems and blade parameters is presented,demonstrating the effects of rake and relief angles over the pressure and spiral angles on mea n point projections and gear tooth ***,the change in pressure and spiral angles with respect to the rake and relief angles are plotted,and the results are ***,it is concluded that the pressure and spiral angles are changed up to a few seconds of a degree in the operating area of the tooth with the change in the back and side rake *** side relief angle exhibited little or no effect over the geometry of the gear tooth.

关键词： Hypoid gear Pressure angle Spiral angle Accurate blade Cutter head