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Strengthening and ductilization mechanisms of friction stir processed cast Mg–Al–Zn alloy
, Article Materials Science and Engineering A ; Volume 781 , 2020 ; Pouranvari, M ; Movahedi, M ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
AZ91 alloy, the most widely used Mg casting alloy, exhibits low strength/ductility and weak energy absorption, which is a function of its large grain size and the presence of a coarse and continuous network of β-Mg17Al12 intermetallic compounds. This work demonstrated that friction stir processing (FSP) enables enhancement of strength and energy absorption capability of AZ91 alloy. The influence of FSP treatment on various potential strengthening mechanisms, including grain boundary, solid solution, and sub-micron particle strengthening mechanisms, was studied. It is identified that the grain boundary strengthening plays a significant contribution to the strength of the FSP treated AZ91. FSP...
Investigation on the Effect of Friction Stir Processing on the Fusion Weldability of Magnesium Alloys
, M.Sc. Thesis Sharif University of Technology ; Pouranvari, Majid (Supervisor) ; Movahedi, Mojtaba (Supervisor)
Abstract
Magnesium alloys, as the lightest structural alloys having a density of about one-fourth that of steels, offer significant potential for improving the energy efficiency of various transportation systems. Welding is a critical enabling manufacturing technology; therefore, the widespread application of a material is highly influenced by their weldability. Liquation and Liquation cracking are crucial weldability issues for fusion welding of cast AZ91 Mg alloy. The constitutional liquation of the coarse eutectic Mg17Al12 intermetallic phase is responsible for the occurrence of liquation cracking during fusion welding of this alloy. Here, friction stir processing (FSP) treatment, a successful...
Effect of collision on self-assembly of nanoparticles in zirconia microparticle suspension
, Article Journal of Dispersion Science and Technology ; 2020 ; Saidi, M. H ; Sharif University of Technology
Bellwether Publishing, Ltd
2020
Abstract
Nanoparticle halo mechanism is a stabilization method for microparticle suspensions. This study investigates suspension pH and nanoparticles–microparticles collision effects on the stabilization of an aqueous binary suspension. The long-term turbidity measurements show that for the nanosilica suspension stability is directly correlated with pH values; however, in the cases of zirconia and binary suspensions, it is not a monotonic function of pH. It is shown that for binary suspension, the halo mechanism is the primary method affecting the stability of the suspension. The suspension is best-stabilized at pH = 5 that is associated with high halo mechanism efficiency, while increased repulsive...
Effect of collision on self-assembly of nanoparticles in zirconia microparticle suspension
, Article Journal of Dispersion Science and Technology ; Volume 43, Issue 6 , 2022 , Pages 787-795 ; 01932691 (ISSN) ; Saidi, M. H ; Sharif University of Technology
Taylor and Francis Ltd
2022
Abstract
Nanoparticle halo mechanism is a stabilization method for microparticle suspensions. This study investigates suspension pH and nanoparticles–microparticles collision effects on the stabilization of an aqueous binary suspension. The long-term turbidity measurements show that for the nanosilica suspension stability is directly correlated with pH values; however, in the cases of zirconia and binary suspensions, it is not a monotonic function of pH. It is shown that for binary suspension, the halo mechanism is the primary method affecting the stability of the suspension. The suspension is best-stabilized at pH = 5 that is associated with high halo mechanism efficiency, while increased repulsive...
Enhanced resistance to liquation cracking during fusion welding of cast magnesium alloys: Microstructure tailoring via friction stir processing pre-weld treatment
, Article Materials Science and Engineering A ; Volume 798 , 2020 ; Pouranvari, M ; Movahedi, M ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Magnesium alloys provide critical opportunities for energy and lightweight-materials challenges. The alloy design approach based on utilizing the second phase strengthening mechanism plays an essential role in producing low-density high strength Mg-based alloys. However, the second phase in the microstructure (e.g., Mg17Al12 phase in Mg–Al–Zn alloys) can deleteriously affect the weldability of the metallic materials by promoting the liquation and liquation cracking during fusion welding. The lack of sufficient weldability of Mg-based alloys is a crucial barrier to their potential use in safety-critical applications. In this paper, it is shown that the severe plastic deformation induced by...
Effect of liquation on the tensile properties of cast Mg–9Al–1Zn Alloy fusion welds
, Article Science and Technology of Welding and Joining ; Volume 25, Issue 8 , 2020 , Pages 698-705 ; Jiryaei Sharahi, H ; Movahedi, M ; Sharif University of Technology
Taylor and Francis Ltd
2020
Abstract
This paper aims at understanding the role of liquation and solidification phenomena on the tensile properties of arc welded cast AZ91 magnesium alloy. Owing to its refined microstructure, the fusion zone exhibited improved ductility/strength compared to the base metal. It is demonstrated that the partially melted zone (PMZ) which is characterised by constitutional liquation of eutectic β-Mg17Al12 phase is the weakest link in the weldment. The reduced strength and ductility associated with the liquation phenomena are due to the increased volume fraction and thickness of the eutectic β-Mg17Al12 in the PMZ as well as the formation of liquation micro-cracks in a network of brittle intermetallic...
Translation Surfaces With Constant Mean Curvature or Gauss Curvature in 3-Dimensional Spaces
, M.Sc. Thesis Sharif University of Technology ; Fanaii, Hamid Reza (Supervisor)
Abstract
In Euclidean space R3 , a surface is called a translation surface if it is given by an immersion X : U 2 Rn ! Rn+1 : (x1; :::; xn) ! (x1; :::; xn; f1(x1) + ::: + fn(xn)) where fi; i = 1; ::; n are smooth functions.In this work, we give the classification of translation surfaces with constant mean curvature or Gauss curvature in 3-dimentional Euclidean space R3 and 3-dimentional Minkowski space L3 and We also characterize the minimal surfaces in the upper half-space model of 3-dimentional hyperbolic space H3 and we express this contents for spaces with arbitrary dimentional too
Structural Design of a Launch Vehicle with Reusable First Stage
, M.Sc. Thesis Sharif University of Technology ; Haddadpour, Hassan (Supervisor)
Abstract
Aerodynamics loads and aeroheating during reentry, are one of the challenging issues in designing One of the main challenges in the design and application of reusable spacecrafts is the aerodynamic and thermal loads acting on their structures during reentry into the atmosphere. For this reason, all the concepts/prototypes presented in the 20th century were either not fully reusable, or were partially canceled, or did not have economic justification. In this report, the aerodynamic loads on the first stage of a launch vehicle during the launch and return phases have been investigated. Due to the fact that the main part of the first stage of the vehicle includes fuel and oxidizer tanks, the...
Optimal Trajectory Correction for Hazardous Near-Earth Asteroids
,
M.Sc. Thesis
Sharif University of Technology
;
Zohoor, Hassan
(Supervisor)
;
Sayyadi, Hassan
(Supervisor)
Abstract
The collision of moderately large asteroids and comets also referred to as Near-Earth Objects (NEO's) with earth would have catastrophic consequences. Such events have occurred in the past and may occur again in the future. However, for the first time in known history, humanity may have the technology required to counter this threat. Methods studied for mitigation of this hazard are based on deflecting asteroid's trajectory and are normally divided into two basic categories: high energy impulsive methods, and long-duration low-thrust methods. Two parts of mission to be optimized are the trajectory of spacecraft to reach the target and the deflection strategy which could be analyzed by the...
Control of Car-Like Multi Robots for Following and Hunting of Moving Target
, M.Sc. Thesis Sharif University of Technology ; Sayyaadi, Hassan (Supervisor) ; Salarieh, Hassan (Co-Advisor)
Abstract
The main purpose of the present thesis is to establish a decentralized controller for some car–like multi robots to follow and hunt moving targets. Robots are very similar to actual cars considering geometric dimensions, mass and moment of inertia and so on; and outputs of the controller are steering-wheel and driving-wheel torques appropriately. Dynamics of the moving target is so that it escapes from the robots. Robots are equipped with antenna for getting wireless sensory signals, including range and bearing sensors. Kalman filter is used for estimation the target relative position and speed and robots state variables. The controller is designed for doing the above mentioned group...
A revised version of ACO for cutting stock problem [electronic resource]
, Article International Journal of Industrial Engineering ; Vol 15, No 4 (2008), Pages 341-348 ; Javanshir, Hassan ; Sharif University of Technology
Abstract
The one-dimensional cutting stock problem has many applications in industries and during the past few years has been one of the centers of attention among the researchers in the field of applied operations research. In this paper, a revised version of Ant Colony Optimization (ACO) technique is presented to solve this problem. This paper is a sequel to the previous ACO algorithm presented by the authors. In this algorithm, according to some probabilistic rules, artificial ants will select cutting patterns and generate a feasible solution. Computational results show the high efficiency and accuracy of the proposed algorithm for solving one- dimensional cutting stock problem
Knowledge Management Application in Developing Marketing Management
, M.Sc. Thesis Sharif University of Technology ; Shavandi, Hassan (Supervisor)
Abstract
In recent years the advent of internet and web has transformed the process of data collection and make organizational and environmental data more accessible. On the one hand, many organizations have realized that the knowledge in these huge databases is key to supporting the various organizational decisions. Particularly, the knowledge about customers from these databases is critical for the marketing function. But, much of this useful knowledge is hidden and untapped. On the other hand, the intense competition and increased choices available for customers have created new pressures on marketing decision-makers and there has emerged a need to manage customers in a long-term relationship....
Hydrodynamic Modeling of an AUV
, M.Sc. Thesis Sharif University of Technology ; Sayyadi, Hassan (Supervisor)
Abstract
Autonomous underwater vehicles (AUVs) are a type of marine vehicles which are currently being used for exploration, maintenance, repairing of marine structures and military appliances. Unmanned underwater vehicles categorize in two types: ROVs and AUVs, ROVs (remotely operated vehicles) usually are connected to the mother vessel with a cable, conduction signals transfer through this cable and there is an operator in the control loop. The vehicle may be fed up with this cable, AUVs are modern underwater vehicles which the operator on controlling and conducting is removed, there is no connection between the vehicle and mother vessel, energy sources and controlling orders are set up in the...
Aeroelasticiy of Supersonic Wing Made of Functionally Graded Materials Using Finite Element Method
, M.Sc. Thesis Sharif University of Technology ; Haddadpour, Hassan (Supervisor)
Abstract
The aeroelastic behavior of wings made of functionally graded materials in supersonic flow is studied. For this purpose the flutter speed is calculated and in the next step the post flutter behavior is investigated. The structural model is based on the classical plate theory and material properties are assumed to be graded in the thickness direction according the power law distribution in terms of the volume fraction of material constituents. The linear piston theory which is modified to include thickness effects is used for supersonic aerodynamic modeling. The nonlinear structural model based on the Von-Karman strains is considered for prediction of the post-flutter behavior of the wing....
Solving the P-Center Problem under Uncertainty
, M.Sc. Thesis Sharif University of Technology ; Shavandi, Hassan (Supervisor)
Abstract
Facility location decisions play a prominent role in strategic planning of many firms, companies and governmental organizations. Since in many real-world facility location problems, the data are subject to uncertainty, in this thesis, we consider the P-center problem under uncertainty of demand nodes. Using Bertsimas and Sim approach, we modeled the problem as a linear optimization model. Furthermore, we develop a tabu search algorithm to solve the problem. Finally we designed some experiments to adjust the parameters of tabu search algorithm. We presented the numerical result accordingly
Developing a Fuzzy Expert System Based on a Hybrid Artificial Intelligence Model for Sales Forecasting Modeling
, M.Sc. Thesis Sharif University of Technology ; Shavandi, Hassan (Supervisor)
Abstract
Success in forecasting and analyzing sales for a given good or service can mean the difference between profit and loss for an accounting period and, ultimately, the success or failure of the business itself. Therefore reliable prediction of sales becomes a very important task. This thesis presents a novel sales forecasting approach by integration of Genetic Fuzzy Systems (GFS) and Data Clustering to construct a sales forecasting expert system. At first, we use stepwise regression analysis (SRA) to determine factors which have most influence on sales. At the next stage we divide our raw data into k clusters by means of K-means algorithm. Finally, all clusters will be fed into independent...
Nonlinear Distributed-Parameters Vibration Analysis of an AFM Microcantilever Beam in Dynamic Mode
, Ph.D. Dissertation Sharif University of Technology ; Zohoor, Hassan (Supervisor)
Abstract
Dynamic and vibration behavior of AFM microcantilever beam subject to the tip-sample interaction and/or contact is systematically investigated. An Euler-Bernoli microcantilever in 2D plane is considered with longitudinal and bending displacements. Inextensibility assumption and extended Hamilton’s principle is utilized to extract the single-variable integro partial equation of motion under: 1) tip-nanoparticle interactions, 2) tip-surface interactions in non-contact mode and 3) tip-surface interactions and contacts in intermittent-contact mode. Galerkin’s first mode approximation is then used to discretize the derived equations; and multiple time scales method is adopted to analyze the...
Aeroelastic Analysis of Aircraft Composite Wings in a Compressible Flow
, M.Sc. Thesis Sharif University of Technology ; haddadpour, Hassan (Supervisor)
Abstract
In this research, an anistropic thin-walled beam composite is used to consider the effects of fiber orientation and lay-up configuration on the aeroelastic stability and response of an aircraft wing. The circum ferentially asymmetric stiffness (CAS) model consists of a group of non-classical effects; such as transverse shear, material anisotropic, warping inhibition, etc. The aerodynamic load has been modeled based on the strip theory and compressible unsteady flow in the finite- state form. In addition, to form the mass, stiffness and damping matrices of non-conservative aeroelastic systems the extended Galerkin’s method (EGM) and the method of separation of variables has been used. After...
Seismic Retrofit of Reinforced Concrete Columns With Post-Tensioned Metal Strips
, Ph.D. Dissertation Sharif University of Technology ; Moghaddam, Hassan (Supervisor)
Abstract
This thesis presents the results of an experimental and analytical study on the application of the strapping technique for seismic retrofit of reinforced concrete columns. In this technique, the columns are externally confined by post-tensioned metal strips. In the first phase of the experiments, the compressive stress-strain behavior of strapped cylindrical and prismatic specimens was studied. Effects of several parameters were studied including shape and size of specimens, strength of plain concrete, mechanical characteristics of confining strips and the level of pre-tensioning of the strips. The second phase of the tests included studying the lateral performance of strapped RC columns....
Assessment of Performance Based Behavior of Steel Moment Resisting Frames
, M.Sc. Thesis Sharif University of Technology ; Moghaddam, Hassan (Supervisor)
Abstract
In order to reduce structural and nonstructural damages and associated financial losses during intense seismic events such as Bam earthquake, seismic retrofitting of existing structures should be considered as a special issue. In this regard, for quantifying the seismic performance of structures a guideline termed “instruction for seismic rehabilitation of existing building No.360” is issued which is mainly borrowed from performance-based assessment procedures FEMA 356. In contrast to conventional seismic design methods which are based on controlling stress ratio for different load combinations, in performance-based earthquake engineering methodology, the displacement control of structural...