Sharif Digital Repository

After the rise of the automotive industry, aluminum wheels have superseded steel counterparts due to their numerous advantages. Foremost among these benefits is their reduced weight, leading to fuel savings and diminished environmental impact. Moreover, aluminum wheels offer enhanced aesthetics and greater strength in comparison to steel alternatives. This thesis focuses on the geometrical optimization of an aluminum wheel model conforming to the standards set by Iran's Department of Standards, aiming to achieve a higher strength-to-weight ratio. While prior research works have mainly focused on weight reduction while maintaining strength within approved standards, this thesis aims at the... 

In the present work, nanocrystalline Al-4wt%Cu alloy reinforced with nanometric Al2O3 particles was synthesized by in-situ reactive milling of Al and CuO powder mixture and hot extrusion. The effect of nanometric Al2O3 particles on the aging behavior and mechanical properties of this alloy was investigated. During mechanical milling, copper oxide were reduced and dissolved in the aluminum lattice. consequently, Al(Cu) solid solution matrix was produced. Also, nanometric Al2O3 particles were also distributed in the matrix uniformly. The powder blend was then pressed in an Al can at 100 MPa pressure and subsequently extruded at 450 0C at the extrusion ratio of 16:1. The density of the... 

Formation of nanoparticles by the gas phase condensation process is one of the most promising methods for the nanoparticles synthesis. Finding the correlations between adjustable parameters of the process and nanoparticles properties depends on how parameters affect the mechanism of nucleation and growth. The use of classical nucleation theory at nanoscale leads to unacceptable results; hence, approaches such as molecular dynamic simulation (MD) have been proposed to investigate the mechanism of nucleation and growth at atomic scale. In the present work, the formation of iron clusters from a supersaturated gas phase was investigated via molecular dynamics simulation. For thermalization of... 

In this research, Al-20Si-5Fe-2X (X=Cu,Ni,Cr) alloys were produced by gas atomizing and melt spinning processes. Microstructure and growth morphology of powder and ribbons were investigated using optical microscopy, scanning electron microscopy and transmission electron microscopy, then, analyzed by solidification models. Powder and chopped ribbons were hot pressed at 400°C/250 MPa and microstructural variations, mechanical properties and thermal coefficient expansion were evaluated after consolidation. Results show that relatively high cooling rate in gas-atomized powders lead to refinement of the microstructure and formation of semi-equilibrium δ intermetallic phase. As the powder particle... 

In this work, multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) were synthesized in an aqueous solution of iron chloride and solfate via arc discharge. Thermogravimetric (TG) analysis showed that the multi layer structures including carbon nanotubes (CNTs) and multi-shell graphite particles were formed when DI-water was used. SWCNTs were synthezied in the presence of the iron ions. The effect of [Fe3+]/[Fe2+] ratio on the CNTs yield were investigated. Raman spectroscopy investigations showed that the highest yield was obtained when the ferric to ferro ratio was one. When the concentration of Fe3+ ion was higher than that of Fe2+, many short tubes were... 

In this work, carbon nanotubes (CNTs) were synthesized via arc discharge in an aqueous solution. The role of iron catalyst in CNTs formation was investigated utilizing arc discharge in iron salts solution (Fe2(SO4)3 and FeCl3). Thermogarvimetric (TG) analysis showed the presence of multi-layered structures including multi-walled carbon nanotubes (MWCNTs) and multi-shelled graphite particles when processing was performed in DI-water. In the presence of iron ions, single-walled carbon nanotubes (SWCNTs) and double-walled carbon nanotubes (DWCNTs) were formed. The effect of iron ions (Fe3+) concentration on CNTs yield was investigated by Raman spectroscopy. The highest yield was obtained when... 

Superparamagnetic iron oxide nanoparticles (SPION) with proper surface coatings are increasingly being evaluated for clinical applications such as hyperthermia, drug delivery, magnetic resonance imaging, transfection, and cell/protein separation. Since the particles with various sizes exhibit different flow rates in the same environment (same capillary size), it is essential to use particles of a desirable size for targeted drug delivery and imaging. Particles of different sizes may be exposed to different viscosities and behave differently, particularly with regard to their velocities as they move through capillaries. In the present work, SPION with different size, purity, shape and... 

Nano/Micro-structure of rapidly solidified (products of Atomizing and Melt Spinning processes) Al-20Si-(5Fe) alloys has been investigated at the present work. Moreover, the effect of cooling rate on microstructure and growth morphology of these alloys has been studied. Microstructure of the products was examined by using optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction.At the present work some models have been proposed for driving a relationship between microstructure and rapid solidification parameters during Atomizing and Melt Spinning processes. These models are based on macroscopic heat transfer during the processes. Model for... 

In this thesis, the classical methods of structural optimization were studied and compared. After a comprehensive study on different methods of structural optimization, a reduced number of methods were selected in order to be used in this research. Exterior penalty function method, linear and quadratic extended penalty function methods were the selected constrained optimization methods. For unconstrained optimization, univariate method, Powell method, steepest descent method, Fletcher-Reeves method, and quasi-Newton methods of DFP and BFGS were used. And from different one-dimensional search methods studied, we used the golden section method. The structures which were optimally designed by... 

In this study, the joint of co-sintered zirconia/stainless steel is investigated. To this end ZrO2-3mol%Y2O3 (TZP) and 430L stainless steel powders were utilized. The joining parameters of co-sintering in zirconia/metal were studied. In order to study the microstructure, diffusion and probable reactions at the joint boundary, HRSEM, HRTEM, EPMA and micro-focused XRD methods were employed. Shear strength of the joint was also measured. Finite element simulation of residual stresses and thermodynamic studies are utilized in the next step to analyze the experimental results. It is found that the direct joining of zirconia to 430L stainless steel is feasible by co-sintering at 1350 °C under low... 

In this research, nano composite MgH2-TiCr1.2 Fe0.6 nano crystalline was synthesized by mechanical alloying and Vacuum arc re-melting (VAR). the effect of Milling conditions and adding nano crystalline TiCr1.2 Fe0.6 as a catalyst on the structure and hydrogen desorption properties of MgH2 were studied. MgH2 powder grain size after 4 hours milling gained to 15nm and strain network reached to 0.8%. Determined that the increasing of accumulated lattice strain because of mechanical milling combined with adding nano crystalline alloy TiCr1.2 Fe0.6 significantly improve the properties of MgH2 hydrogen desorption. After an hour mill working, high pressure phase of γ-MgH2 was appeared in... 

In the present work, Barium Titanate nanoparticles were synthesized by a facile hydrothermal method at 180oC for 4 hours and their sintering behavior was studied. The characterization tests illustrated that the obtained powder was BaTiO3 single phase with excess Ti content from stoichiometric composition. The average particle size of about 50 nm and a narrow particle size distribution was noticed. SEM investigations showed that the samples sintered at temperatures less than 1250oC had plate-like grains. This behavior resulted from twin plates existed in the grains and facetted grain boundaries. At the temperatures more than 1250oC, the grains became polygonal due to the formation of trace... 

In recent years considerable effort has been made to advance the hardware Artificial Neural Networks where in most cases, many neurons are placed on a VLSI chip. This research attempts to build individual neurons and connect them to build a hybrid of analog and digital neural network. In fact, every neuron is an AVR microcontroller which has a number of inputs and outputs. The data transfer between neurons are done by both analog (PWM- ADC) and digital (UART). In the first part, the necessary voltage source and programmer and how to build are discussed. Next A\D convertor, PWM technique, UART and their usage in this project are demonstrated. After that, the neurons are calibrated to improve... 

Taking into consideration of optimization methods has been increased recently. Optimization methods in engineering that consumes a lot of time and cost have been developed. Optimal design of structures is a matter that grabbed the attention of civil engineers and due to the deficiency of classical methods the modern approaches are being developed. One of the most important structures that are constructed for industrial and transportation purposes are truss structures.Structural control under support excitation is constraining the structure to some structural limitations. The final target in this paper is to apply the modern methods to get the optimal weight of structure under seismic loads.... 

In this project, the melting, solidification and remelting processes and also, the epitaxial growth of thin molten layer on the solidified crystalline substrate is studied using molecular dynamics simulation for the aluminum as an instance for the fcc metals. Sutton-Chen potential is used for energy calculations; the modified version of verlet algorithm is used for determination of position and velocity of atoms; and the berendsen algorithms are used as thermostat and barostat. The effects of pressure and temperature changing rate on the melting and crystallization temperatures and the crystal structure are investigated. The crystal structure of the system is examined using radial... 

Carbon-based thin films possess low friction coefficient, low surface roughness, chemical inertness and outstanding biocompatibility. In the present work, TiO2 nanoparticles were covered by a thin film of pyrolytic carbon (PyC) to provide a core-shell morphology. The PyC film was deposited by dehydrogenation of methane in a fluidized bed chemical vapour deposition (FBCVD) reactor at 1100 °C. The prepared specimens were characterized by various analytical methods including XRD, SEM, TEM, AFM, TGA and contact angle measurement techniques. Biocompatibility profiles of the resulting materials were evaluated using MTT and cell cycle assay. The results showed that the thin carbon film strongly... 

In this study, Al6063-Al203 nanocomposite powders were synthesized by reaction mechanical milling method. Nanometric reinforcement particles were formed via high- energy ball milling under a controlled oxygen containing atmosphere. Morphological and microstructural evolutions of nanocomposite powders were investigated by using X-ray diffraction (XRD), thermal analysis (DTA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) methods at different milling times. The results showed that mechanical milling stages were accelerated and the time for reaching steady- state condition was decreased by an increase in the oxygen content in the milling atmosphere. The in-situ... 

Artificial neural networks are inspired by biological neural system. These networks show great learning abilities of nonlinear systems. And due to these abilities they are extensively used in scientific modeling. Learning and generalization of ANN can be used in modeling and prediction of nonlinear system behavior. This is done through adjustment of neurons weights in an optimization procedure using training pairs, a well-trained ANN can predict a correct output for untrained input.In this research two adaptive mechanical systems inspired by ANN were introduced. The first system is a nonlinear plate with elements with varying stiffness. The plate is trained to produce desired reactions for... 

Recent investigations on construction engineering have determined that repairing of Reinforced Concrete (RC) by means of fiber reinforced polymer (FRP) composites is an effective method of retrofitting existing columns. The main research in this thesis focuses on the repair of concrete specimens which are damaged and their initial strength has been reduced. To achieve this purpose, through experimental procedures, the effect of confining damaged concrete cylinders by FRP, has been investigated. The experimental program included three parameters: type of fibers (glass or carbon), type of confining (full or partial), and the number of layers. First concrete cylinders were made and loaded to... 

Polycaprolactone (PCL) scaffolds and its composites containing bioactive glass particles (45S5) and TiO2 nanostructures with pre-defined and controlled external and internal architecture were prepared via an indirect three-dimensional (3D) printing process. The scaffolds had an interconnected structure with macro- (400-500 μm) and micro- (~25 μm) pores. Bioactivity, mechanical behavior and kinetics of tissue growth in 3D scaffolds were studied. The size effect of biogactive glass particles (6 μm, 250 nm, <100 nm) and morphology of titania nanostructures (spherical, tube, leaf-like, and flower-like particles) were elaborated. The biogactive glass particles with different sizes were prepared...