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Evaluation of Microstructure and Fatigue Properties of HSLA-100 Steel Welded by SMAW and FCAW Methods
, M.Sc. Thesis Sharif University of Technology ; Ekrami, Ali Akbar (Supervisor)
Abstract
After World War II, steel bearings containing copper element have been developed by the Navy of the United States of America with the HSLA-100 brand. Since 1890 and in order to manufacture tanks and tools for the body of navy equipment, the steel HY 80 was used instead of HSLA-100. Because of the high carbon content, the welding properties of the HY 80 are low. Furthermore, increasing of hardness and decreasing of toughness in the heat-affected zone generated during the welding process lead to susceptibility of this alloy to hydrogen cracking and brittle fracture. Therefore, in order to minimize the cost of welding, low-alloy high strength steel (HSLA) is used which contain copper. Reducing...
Microstructural and Mechanical Properties of TLP Bonded SS 304 with Fe-base Interlayer
, M.Sc. Thesis Sharif University of Technology ; Ekrami, Ali Akbar (Supervisor)
Abstract
Cooling sandwich panels are one of the components of the heat exchangers used to cool the components of the sandwich panels . One of the applications of TLP Bonding for steel can be called cooling sandwich panels. In this research , TLP of 304 Stainless Steel , using Fe-base interlayer at 1200 C has been investigated . Cross section of bonded samples were examined by optical and scanning electron microscopes. Microscopy results revealed that 2h is sufficient for completion of isothermal solidification and there is no eutectic compound at bonding zone . Bonding in this condition resulted in the free precipitates in the diffusion affected area. By analyzing eutectic phase in bonding areas at...
Corrosion Resistance of TLP Bonded Stainless Steel 304
, M.Sc. Thesis Sharif University of Technology ; Ekrami, Ali Akbar (Supervisor)
Abstract
Transient liquid phase bonding of AISI 304 was carried out in a vaccum furnace using a Ni-based interlayer. The effect of bonding time on microstructure and mechanical properties of joints at temperature of 1150 ⁰C was investigated. The results showed that isothermal solidification was completed within 20 min and eutectic phase disappeared across the joint region. The joints with complete isothermal solidification were homogenised for 180 min at temperature of 950 ⁰C. The results of shear test showed that the average shear strength of homogenised samples was about 83% thet of the base metal at the same heat treatment cycle. Corrosion behavior of the TLP bonded and base metal was studied at...
Inflation with Light Species, A Possible Realization of Warm Inflation
, M.Sc. Thesis Sharif University of Technology ; Abolhasani, Ali Akbar (Supervisor)
Abstract
In this project we investigate the effect of coupling of the inflaton with light particles which have oscillating mass that depends on inflaton. As the inflaton slowly rolls towards the minimum of its potential, the mass of other particles changes periodically(monodromy). The monodromy structure with tuning the parameters of model allows us to produce ultrarelativistic particles during inflation. These particles dilute with the expansion of the universe but continuous particle production leads to burst of particles at the end of inflation. It should be noted that other Warm Inflation models are phenomenological models which is assumed that during the inflation, the inflaton energy is...
Mechanical characterization of the ligaments in subject-specific models of the patellofemoral joint using in vivo laxity tests
, Article Knee ; Volume 26, Issue 6 , 2019 , Pages 1220-1233 ; 09680160 (ISSN) ; Farahmand, F ; Arjmand, N ; Sharif University of Technology
Elsevier B.V
2019
Abstract
Background: The purpose of this study was to propose a methodology for mechanical characterization of the ligaments in subject-specific models of the patellofemoral joint (PFJ) of living individuals. Method: PFJ laxity tests were performed on a healthy volunteer using a specially designed loading apparatus under biplane fluoroscopy. A three-dimensional (3D) parametric model of the PFJ was developed in the framework of the rigid body spring model using the geometrical data acquired from the subject's computed tomography and magnetic resonance images. The stiffness and pre-strains of the medial and lateral PFJ ligaments were characterized using a two-step optimization procedure which minimized...
Plasmon Modes in Borophene and Graphene: Ladder Corrections
, Ph.D. Dissertation Sharif University of Technology ; Jafari, Akbar (Supervisor)
Abstract
In this thesis, we have investigated the plasmon dispersion on the Dirac matter. The Dirac matters which we consider to this end are graphene and borophene allotrope.The borophene allotrope has smaller anisotropic Fermi velocity and tilted Dirac cone in comparison with graphene. We briefly give a short introduction to these materials and then we study the propagation of electromagnetic modes in them. We begin with graphene as a well known two dimensional Dirac material. It has been found that two kinds of plasmon modes named as plasmon mode and transverse electric filed mode are allowed to propagate in graphene but just the plasmon mode can be affected by interaction. As the correlated...
A Survey in Inflation and Roots of Axionic Inflationary Models
,
M.Sc. Thesis
Sharif University of Technology
;
Abolhasani, Ali Akbar
(Supervisor)
Abstract
Inflation first introduced for solving the puzzles of the standard model of cosmology. Soon it became clear that this paradigm can provide a natural way for production of Initial conditions for the birth of large-scale structures: cosmological perturbations. But inflationary models are usually phenomenological models. They are constructed to solve the problems of the standard model of cosmology and explain the properties of cosmological fluctuations. Where do they come from? A property of a big family of inflationary models is the flatness of their potential. What would may be the cause of this flatness? . . .. In this thesis our purpose is searching about one probable field theoretic root...
Effect of Carbon Fiber on Frictional and Wear Properties of Automotive Brake Pads
, M.Sc. Thesis Sharif University of Technology ; Shojaei, Akbar (Supervisor)
Abstract
In the recent decade, composites have been used in safety system of automobiles due to important characteristics such as high wear resistant and durability, low weight and also low noise pollution, stable friction coefficient, availability and low cost. In recent years, composites have attracted the attention of brake pads manufacturers because of their appropriate thermal and mechanical properties. Fibers play an important role in these material. Carbon fiber due to its features such as high strength, acceptable module, proper heat transfer coefficient and excellent resistant against thermal degradation has been considered by the experts but there is not any comprehensive research on...
Mobile Robot Navigation and Localization in the Presence of Hurdles in Cluttered Environment Using Fuzzy Control and Kalman Filter
, M.Sc. Thesis Sharif University of Technology ; Khayyat, Ali Akbar (Supervisor)
Abstract
In this thesis, in order to improve the performance of the mobile robot navigation, a Fuzzy approach is used for making a safe path in the cluttered environment with hurdles in the work space of the robot. To this end, based on data collected from instantaneous location of the robot and location of the robot, heuristic rules are extracted. Also, in order to obtain optimal data fusion of the sensors, Kalman filter is used to localize the robot. In this regards, by using the kinematics of the robot and supposing the white noise in the process and measurements, the position and orientation of the mobile robot are estimated in a real-time and adaptive manner
The Role of Surface Functionalization of Nanodiamond on the Vulcanization Kinetics and Network Structure of SBR
, M.Sc. Thesis Sharif University of Technology ; Shojaie, Akbar (Supervisor)
Abstract
Elastomers are flexible polymers with various uses in different industries. But this materials dont havevalid usages without correct fillers. Today Nano technology has a main role in the industry. one of the important reasons is rubber quality improvement with adding just a little amount of this clays, opposite to Carbon Black. To achieve a high quality polymer composite, it is necessary to learn about physical and mechanical properties of nano clays and the interaction between Nano clays and matrix. Because of the effect of nano clays on vulcanization, this issue is noticeable . Nano diamond is a nanoclay used to improve rubber quality. But this method is new because of the complicated...
Preparation and Characterization of Shape Memory Biocompatible Nanocomposites of Polyurethane/Carbon-magnetic Hybrid Nanoparticles
, Ph.D. Dissertation Sharif University of Technology ; Shojaei, Akbar (Supervisor)
Abstract
Smart bio-based shape memory polymers with high performance and fast response have the exciting potential to meet the growing need in biomedical applications. A fascinating approach in SMP categories in biomedical field is the development of noncontact activation without increasing the environmental temperature through remote triggering methods, such as magnetic triggering. Magnetically responsive SMPs have received lots of attention in the biomedical applications, especially the non-contact triggering of medical equipment and implants inside the body. In this study, the biocompatible nanocomposite based on shape memory polyurethane acrylates (SMPUAs)/ hybrid carbon-magnetic nanoparticles,...
The Effect of Bainite Volume Fraction and Morphology on the Wear Resistance of a Ferrite-Bainite Dual phase Steel
, M.Sc. Thesis Sharif University of Technology ; Ekrami, Ali Akbar (Supervisor)
Abstract
The studied steel was AISI 4340 steel. In order to obtain dual-phase steel with a volume fraction of 60, 66 and 75% bainite, samples were heated in the α+γ region at temperatures of 730, 735 and 740 oC for 120 minutes and then to create lower and upper morphology of bainite, samples were transferred directly to salt bath at different target temperatures (300 oC and 400 oC) and kept 60 minutes. Also, to produce a Martemper microstructure, the full martensitic sample was tempered at 260 oC for 90 minutes. Tensile and hardness tests revealed that with the increasing volume fraction of lower bainite, yield strength, tensile strength, and hardness increased from 986 to 1211 MP, 1185 to 1519, and...
The Effect of Martensite Volume Fraction on the Wear Resistance of Triple phase (Ferritic-Bainitic-Martensitic) Steels
, M.Sc. Thesis Sharif University of Technology ; Ekrami, Ali Akbar (Supervisor)
Abstract
In this study, the effect of martensite volume fraction on the wear behaviour of 4340 steel with triple-phase steel microstructure with a constant volume fraction of 34% ferrite was investigated. Using the Holman equation, it was found that triple-phase steel with different martensite volume fraction has two stages of work hardening. By increasing martensite volume fraction, yield strength and ultimate tensile strength and work hardening exponent of first and second stages increase and the elongation decreased. To perform the wear test, the pin on disc apparatus was used according to the ASTM G99 standard, and the test was done at two forces of 10 and 50 N at a fixed distance of 400 m. The...
Investigation of Creep Properties of Transient Liquid Phase Bonding of FSX-414 Co-based Superalloy
, M.Sc. Thesis Sharif University of Technology ; Ekrami, Ali Akbar (Supervisor)
Abstract
The repair and production of Ni-based and Co-based superalloy parts have high importance in Oil and Gas, and Aerospace industries. Due to this issue, Transient Liquid Phase bonding is one of the most reliable welding methods for repair parts and fabricating new parts.In the present study, creep properties of similar transient liquid phase bonding of FSX-414 Co-based superalloy has been investigated and compared with creep properties of the un-bonded base metal. Firstly, the optimum condition of the bonding process was resulted from microstructural observations from different bonding conditions. Then, cylindrical samples for the aim of creep test specimens were fabricated in two different...
Reheating the Universe after Inflation Via Resonant Interactions
, M.Sc. Thesis Sharif University of Technology ; Abolhasani, Ali Akbar (Supervisor)
Abstract
The inflation paradigm solves the so-called flatness problem of the standard cosmo- logical model and explains the homogeneity of the Universe by adding a period of exponential expansion at early times to the standard scenario. Moreover, it provides a mechanism for generating density perturbations, serving as the seed of large-scale structures. One of the successes of inflation is predicting primordial scale-invariant perturbations that agree with the observations of cosmic background radiation. Nev- ertheless, there will be a cold, matter-free universe after exponential expansion, so one needs a process that leads to a hot cosmos containing standard particles after the end of inflation, the...
The Origin of Angular Momentum in Cosmological Structures
, Ph.D. Dissertation Sharif University of Technology ; Abolhassani, Ali Akbar (Supervisor)
Abstract
Explaining the angular momentum of the cosmological structures is an essential part of the structure formation theory, and it is not fully understood yet. The Tidal Torque Theory (TTT) is the standard explanation of the initial angular momentum of the halos based on the gravitational instability picture. It predicts the angular momentum growth with linear approximation and has been confirmed for linear stages of proto-halos, but the final halo is a highly non-linear object. Nonlinear effects are hard to model, however, we propose a new mechanism for the nonlinear evolution of the halos. We suggest that when two halos pass by each other, their angular momentum changes with a similar mechanism...
Optical Conductivity of Fermi Arc States
, M.Sc. Thesis Sharif University of Technology ; Jafari, Akbar (Supervisor)
Abstract
Recently, some materials, such as Weyl and Dirac semimetals, have been found in condensed matter physics whose band structure behaves like Weyl fermions of elementary particles near some points of the first Birillouin zone. The Weyl equation that governs these materials, have boundary because they are finite. By applying proper boundary conditions, two-dimensional surface states have been emerged. these states are called fermi arc sates because the surface corresponding to the fermi energy is not a closed surface. Surface states are mixed with bulk states because by getting close to the end of fermi arcs, surface states tend to bulk states con-tinuously. Being able to distinguish between...
Design of Low-Power Zero Temperature Coefficient (ZTC) CMOS Oscillators
, M.Sc. Thesis Sharif University of Technology ; Akbar, Fatemeh (Supervisor)
Abstract
The increasing demand for autonomous vehicles and reliable communication protocols and hardware interfaces, such as CAN bus and USB, underscores the necessity for stable clock sources that maintain a low temperature coefficient (TC) over wide temperature ranges. This demand is particularly emphasized in applications such as wearables, network sensors, downhole devices, WSNs, and IoT, where long-lasting battery life and frequency-stable clock sources over a broad temperature range (e.g. -20 °C to 100 °C) are crucial. Traditionally, variations in frequency caused by temperature have been mitigated by employing off-chip components like crystals or ceramic based oscillators, but this approach...
Evaluation of the Friction Dampers Effect on Seismic Retrofit of Non-ductile Concrete Structures
, M.Sc. Thesis Sharif University of Technology ; Golafshani, Ali Akbar (Supervisor)
Abstract
Iran plateau is situated over the Alpide-Himalaya earthquake belt. Tectonic studies indicate that this plateau has a very high density of active and recent faults; as a result, Iran is at risk of damaging earthquakes. Experience of past severe earthquakes shows previous designed structures do not have enough strength instead of real earthquake forces, therefore vulnerability study of existing structures and give a technical and economical retrofitting plan of them is required. Conventional methods of seismic rehabilitation for example using concrete shear walls or steel braces are not suitable for some buildings. Nowadays, passive control systems have been successfully used for reducing the...
Reliability and Probabilistic Seismic Assessment of Fixed Jacket Type Offshore Platforms
,
M.Sc. Thesis
Sharif University of Technology
;
Golafshani, Ali Akbar
(Supervisor)
Abstract
This thesis encompasses a number of issues in earthquake engineering which may appear quite diverse in nature. Several methodological aspects of both conventional and novel approaches to probabilistic seismic hazard assessment are discussed here along with subjects more strictly pertinent to structural and geotechnical engineering. This work, however, has a unique, ultimate goal: to provide procedures for an effective and practical probabilistic estimation of structural demand of offshore platforms due to seismic ground shaking. In modern multi-level design and rehabilitation procedures, structural performance is in fact quantified by deformation demand levels exceeded with a specified...