Sharif Digital Repository

Particulate ceramic reinforced aluminum matrix composites have high specific strength and stiffness; however, low fracture toughness and deformability have restricted their industrial applications. Among the methods introduced to overcome this shortcoming is fabricating the layered composites which contain alternative layers of aluminum (Al) and discontinuously reinforced aluminum (DRA). In this study, two different routes; i.e., "Powder extrusion - Casting - Rolling" and "Powder extrusion - Roll bonding" were employed to produce layered Al-DRA composites. After production of Al6061/SiCp composites via hot powder extrusion, mentioned processes were utilized to make DRA-Al-DRA laminate. In... 

In this research, friction and wear behaviors of 2024 Al and 2024 Al-20 vol.% SiC composite -prepared by powder metallurgy method- were investigated in the temperature range 20- 250°C. Dry sliding wear tests were conducted at a constant sliding velocity of 0.5 m/s, an applied load of 20 N, and a sliding distance of 2500m using a pin-on-disc apparatus. Some of the wear tests were carried out with artificially aged specimens in order to determine the aging effects. Worn surfaces and wear debris were also examined by using SEM, EDS and XRD techniques. All specimens showed a transition from mild to severe wear above a critical temperature. In the mild wear regime, the wear rate and the friction... 

TLP diffusion bonding method refers to a method in which two metal pieces can be bonded by putting an interlayer between two pieces and heating to a temperature lower than base metal melting point. Theoretically, this process shows that the bonding line disappears completely at the end of the process and it is not possible to recognize it. However, these assumptions were not accomplished in practice. Therefore, various parameters such as material of interlayer, thickness of interlayer, temperature and time of bonding, temperature and time of homogenizing and applied pressure on metal pieces should be controlled to achieve the best shearing strength results. Aluminum based composites have... 

In the present research, transient liquid phase bonding of dissimilar st52 low carbon manganese steel to 304 stainless steel by pure Cu foil, in induction furnace and SIC furnace, was investigated. Samples were bonded in induction and SIC furnace at 1150 0C for different bonding times. Samples were then cut transversely and cross section of samples was examined by optical and scanning electron microscope. Complete isothermal solidification time was more than 9 hours and 90 minutes for SIC and induction furnace, respectively. Micro hardness and shear strength tests were done on samples bonded in optimum condition. Shear strength of none homogenized samples which had been bonded in SIC... 

Many efforts have been put into increasing the efficiency of dye-sensitized solar cells that part of it has been devoted to structure and chemical composition of photoanode electrode. In this thesis, the effect of changes in the composition and its influence on light scattering ability in photoanode of dye sensitized solar cells was studied.First, the nanoparticles of titanium dioxide powder through solvothermal method as well as spherical particle and barium titanate powder by sol-gel method were synthesized. XRD and FE-SEM analyses indicated that synthesized powders are in good size and morphology regarding the intended chemical composition. Optical properties of TiO2 particles were... 

In the present investigation, the mechanical alloying (MA) technique was employed to produce nanocrystalline Al-Ti Powder mixtures. Elemental Al and Ti powders were mixed with different compositions (0, 5, 10, and 20 wt.% Ti) and then, milled in a vibratory mill up to 7 hr. The variations of powder morphology and particle size, apparent and tap densities, microstructure, grain size, lattice strain, and microhardness were studied with increasing the milling time. While dissolution of Ti in the Al matrix resulted to the formation of supersaturated Al-Ti solid solution in the samples containing 5 and 10 wt.% Ti, the specimen with 20 wt.% Ti, eventually, led to nanocomposite powder with... 

The aim of this research was to fabricate an in-situ Al-Al3Ti nanocomposite from pure microsized aluminum and titanium powders by mechanical alloying and hot extrusion without any usage of nanometric particles or applying secondary heat treatments. The focus of the present research was fabricating a nanocomposite material with high strength, modulus and hardness accompanied with high fracture toughness that could be comparable with aluminum alloys in terms of fracture toughness. Mechanical alloying and hot extrusion techniques were employed to produce in-situ fully dense Al-Ti composites. Platenary and high energy vibratiory mill was used to produce composites with different percent of... 

Blood is one of the most important biological organs. Red blood cell (RBC), as the most abundant cell of blood, plays an important role at life of the living bodies. Unique mechanical properties of RBCs enable them to pass through very narrow vessels. Any abnormality in these mechanical properties will disorder the function of the cell and many diseases affect these properties too. Studying the mechanical properties of RBCs is very importantin that it could result in a disease diagnostic method in a single-cell level. In this thesis we have tried to measure the viscoelastic properties of a single RBC by an optical trap through a passive method. This measurement is made through studying the... 

The base of dielectrophoresis(DEP) technique has been demonstrated through electro-dynamic interactions between an applied non-uniform AC electric field and induced distributed dipoles within a polarized. In particle manipulation and/or separation using the DEP method, knowledge of precise DEP force of a particle is essential in designing a DEP device and improving its separation efficiency and accuracy. In most DEP studies related to particle manipulation and/or separation, however their absolute DEP forces remain unknown[2]. Insufficient information regarding the DEP behavior of particles can result in preventing a strategic maneuver for efficient particle manipulation and/or separation... 

Surface tension is the most important interfacial parameter of a liquid. This quantity plays a key role in many processes such as extraction, distillation, absorption and chemical reactions. Various methods are proposed for measuring this quantity among which, the laser based methods are the most accurate ones. Unlike most of the mechanical methods, laser based methods remotely measure the surface tension. The aim of the current thesis is to measure the surface tension using laser beam, more specifically using homodyne detection system. This method implemented in both reflected and transmitted modes. In each of the mentioned methods, first the laser beam was incident to the liquid-air... 

Human eye is one of the most important organs of the human body. Performance of the eye may be decreased by some anomalies such as myopia, hyperopia, astigmatism, cataract, glaucoma, etc. There are variety of techniques to treat eye anomalies including surgery, using optical elements and training methods.The easiest way of treating refractive errors of the eye, is to use optical elements such as contact lenses, intraocular lenses and glasses. In the case of cataract, Crystalline lens loses its opacity and should be replaced by artificial lens. The best choice is Fresnel lens which has lower weight and thickness than refractive lenses.Fresnel lens is a diffractive optical element which uses... 

The aim of this study is to investigate the effect of Copper oxide on the microstructure, properties, and grain growth kinetic in Tin oxide- Based varistors. Copper oxide was mixed in Tin oxide with different concentration, including 0, 0.1, 0.25, 0.5, and 1 mol% and the samples were sintered at 1250, 1300, and 1350 oC. Then, phase and microstructural characterization was investigated and consequently, electrical properties were evaluated. According to results, Copper Oxide with forming the liquid phase through the sintering process, accelerated grain growth. It was found that, by increasing concentration of CuO, mean grain size was increased from 2.6 µm in 1250 oC and 5 hours to 17.1 µm... 

Today, base lead piezoelectrics are the center of attention due to their very good electrical properties, and low cost of production. Among these ceramics are PZT which is a combination of Pb(ZrxTi1-x)O3 and PCN which is a combination of Pb(CoxNb1-x)O3. PZT is a normal piezoelectric whose dielectric properties would be improved if relaxor is added. PCN is ferroelectric with perovskite structure and curie temperature -27℃ which is known as a relaxor with high constant dielectric properties. In this research, adding PCN to PZT was done by sol-gel seeding method. Calcination at a temperature of 900℃ was causing the creation of single-phase perovskite powder. After that, conventional sintering... 

F-BAR protein is one of the Bin/Amphiphysin/Rvs (BAR) superfamily proteins which contributes in curvature generation and stabilization of lipid membranes. These proteins usualy form lattices on the membrane and can sculpt the membrane. In this project the interaction of F-BAR protein with a lipid membrane is modeled using coarse grained molecular dynamics approach. In order to describe the curvature generation and stabilization we would need an appropriate coarse grained model for the lipid membrane. In this project the proposed model for the membrane describes a membrane in liquid phase with a lateral diffusion in the lipid bilayer. Depth and width of the lipids potential is determined in... 

In this research, the surface of multi-walled carbon nanotubes (CNTs), as template, were coated by Lead zirconate titanate (PZT) with composition of Pb(Zr0.52Ti0.48)O3 via sol-gel process. The final product is called PZT-CNT hybrid material. For functionalizing of CNTs, benzyl alcohol was used. Simultaneous thermal analysis (STA) proved that the as-derived amorphous material crystallized at 520 ˚C. Scanning Electron Microscope (SEM) images verified the deposition of a uniform coating of PZT on the surface of CNTs and proved that the functionalizing treatment was done successfully. X-ray diffraction (XRD) showed that the crystal structure of the hybrid was tetragonal perovskite.... 

In recent years, due to greater attention scientific communities to environment and environmental friendly material, use of natural fibers as reinforcing the polymers has increased significantly. High specific strength, low density, cheap, stiffness and recycled by nature, are including promotional items using natural fibers as reinforcing in the polymer composites. In This study has tried in the first place an appropriate method for producing polypropylene composites reinforced with short jute fibers should be presented and then the physical and mechanical properties of composites will be investigated. Used MAPP and Silane for compatibility took improved between natural jute fibers as a... 

The goal of this project is production of composite laminated sheetswith bimodal microstructure using ARB process. It is planned to produce a laminated sheet having bimodal grain size distribution in microstructure to increase the formability while maintaining the strength. Two different aluminum alloys including AA 1050 and AA5083 were ARB processed up to 9 cycles, Then the ARB samples were annealed under controlled temperatures and times. Due to structural differences like stacking fault energy,stored cold work energy and solute atoms concentration, annealing ofThese two alloys lead to different recrystallized grain sizes. In order to evaluate the recovery and recrystallization behavior of... 

Last generation of solar cells which are organo-metal halide perovskite solar cells (PSCs) with power conversion efficiency over 20% are increasingly comparable to the silicon types, these PSCs are poorly stable under working environment. Carbon-based PSCs with lower cost and more stability seem a better choice for commercialization in future. In these PSCs TiO2 and NiO are working as electron and hole transporting materials, respectively. In addition, ZrO2 film between two mentioned layers works as a buffer layer to prevent direct contact. In this thesis, the initial powder, necessary for fabricating the buffer layer is synthesized at the first place. Then, since the printing method is a... 

In this study, friction stir lap welding of Al-5083 alloy sheets with 3 mm thickness to St-12 steel sheets with 1 mm thickness (joint without intermediate layer) and to Al-1100 clad St-12 sheets (joint with the Al-1100 intermediate layer) was investigated. The cladding process was done by rolling. For each type of joints, the bonding mechanism, optimum process parameters to reach the joints with the highest fracture loads and also the microstructure evolutions at the joint region were studied. Furthermore, for the joints without intermediate layer, the effects of the Al-5083 annealing treatment before welding and the post-weld heat treatment of the joints on the fracture loads were explored....