Sharif Digital Repository

In this investigation, effect of processing parameters on the soft magnetic properties of nanocrystalline Fe85Si10Ni5 (at. %)-phenolic resin composites were studied. The nanostructured powders were obtained by mechanical milling in a high-energy vibratory disc mill. Annealing was performed to decrease internal strains and density of dislocations. The microstructure, morphology and DC magnetic properties of the milled powders were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and a vibrating sample magnetometer (VSM). Bulk samples were obtained by compaction in different pressures and temperatures. The effects of different compaction treatments and annealing... 

Magnetic shape memory alloys (MSMAs) are a new kind of smart materials which are great alternatives for energy harvesting systems due to some unmatched characteristics such as reversible large strain, high cycle fatigue and fast time response. In this work, an energy harvesting system using MSMA is studied. For this goal, a 3-D thermodynamic-based MSMA model is applied for predicting magnetomechanical behavior of the MSMA sample which is used in the energy harvester system. Since demagnetization effect, which has a great influence on the model’s outputs, has been neglected in the selected MSMA model, a new approach is presented for inserting demagnetization coefficients, regarding to the... 

In this paper, the response of a concrete one-story frame with smart rebars under static lateral loading has been numerically studied, using Finite Element Method. The material used in this study is Shape Memory Alloy (SMA) which contains nickel and titanium elements. During lateral loading, rebars yield or concrete crushes in compression zone in some parts of the RC frames and also residual deflections are created in the structure. The SMA exhibits little residual strains under cycles of loading and unloading even after passing the yielding zone. In addition, SMAs have a good energy dissipation capacity that helps reduce damage while increasing structural capacity. In this study, SMA rebars... 

Hot deformation behavior of Al-SiC nanocomposites was investigated in this study. Aluminum powders with mean size of 60 micron and SiC nanopowders (mean size of 45nm) in amounts of 1 and 2 volume percents, as reinforced part, were mixed and milled for 40 hours by planetary ball mill. After degassing at 450 oC for 1 hour, milled powders were pressed into Aluminum cans (in Argon atmosphere) and then hot extruded. Extrusion ratio was 1:14. High density billets (with 98% of theoretical density) were produced because of that high extrusion ratio. TEM microstructure studies showed that fine distribution of reinforcements and Aluminum Oxides obtained via this procedure. Hardness and Uniaxial... 

Metallic glasses (MG) are a group of materials that have unique properties such as high yielding strength and high elastic deformation. Because of limitation in the production of these materials, a few industrial materials of MG have been made so far. A few of binary alloys, like binary alloys made of Cu-Zr, have high Glass Forming Ability (GFA) in medium cooling rates. Between two binary systems of Cu-Zr and Ni-Zr, although constituent elements in aspect of atomic radius, electronic structure, physical properties, phase diagrams and intermetallic compounds are so similar to each other, but GFA between them are very different. For example, in Cu-Zr system there are compounds, such as... 

Recently, mechanical properties of advanced materials such as nanostructured and ultra-fine materials and especially nanocomposites were studied by lots of researcher. In this study, fatigue behavior of Al-SiC nanocomposites is observed. Ultra-fine grains Al matrix nanocomposites reinforced with 50 nm diameter SiC nanoparticles were produced by milling and hot extrusion. For this purpose, pure aluminum powder was mixed with 2, 4 and 6 Vol. % of SiC nanoparticles and then milled by planetary mill. The milled powder then were degased in an Argon atmosphere furnace, cold pressed and then hot extruded. Closed die-hot forging was used with about 18.8% reduction in cross section in order to... 

Porous NiTi specimens were produced by elemental nickel and titanium powders and two different temporary space-holder consisting of NaCl and urea and conventional sintering method. Pore characteristic and morphology of porous NiTi specimens was investigated by optical and electron microscopy. Microstructure of specimens was probed using XRD and SEM. Suitable pore distribution and size for biomedical application was obtained using temporary space-holder method. Porosity content increases with increasing space holder powder. At 70 volume percent space-holder, best pore size and distribution with fully open pores, in size 200-500 µm, was obtained and pores are interconnected that suitable for... 

The purpose of this study is to increase the strength of metal and polymer compound combinations in the direction of this increase, the electrolytic plasma oxidation coating is applied and its effect will be checked to increase bond strength. Also, due to the failure in the polymeric side of the bonding, the effect of adding short fibers of carbon to polypropylene will be checked on the strength of the polymer and bond strength. The effect of current density at coating application, the presence or absence of short carbon fiber in the polymeric field and the formation of initial hole on aluminum alloy on bond strength was studied. For further analysis, the optical and electron microscopic... 

In this research the effect of Si, Cu and Ni alloying elements on the structure and mechanical properties of the A336 alloy is investigated. Expriments were done in two situations, casting and heat treated and the results for all samples with different amount of alloying elements are compared and the effect of heat treating is also investigated. Results show that with increasing the amount of Si and Cu and decreasing the amount of Ni strength and hardness of the cast alloy are 134 MPa and 65 HB and they increase to 187 MPa and 89 HB in heat treated alloy. The elongation and coefficient of linear expansion are decreased from 2.3% and 21.94 μm/m.K to 1.1% and 21.62 μm/m.K. Also the T6 heat... 

Al-Mg alloys are used in many industrial fields, thus improvement of their mechanical properties is so important. Expressing mathematical models on the basis of physical and microstructural properties can be useful for this purpose. In this research, in order to study the microstructural evolutions and mechanical properties of the material, a dislocation based model and microstructural parameters such as grains and subgrains during plastic deformation and subsequent annealing are considered. In addition, a modification is used to make the model capable of justify the solute atom and temperature effect simultaneously. This makes the results to be more precise and accurate considering... 

Laparoscopy is a minimally invasive surgical (MIS) procedure specific to the surgical sites within the abdomen. For this surgical method a laparoscope, a camera (endoscope), and a grasping instrument is needed. They all inserted in to the abdomen through openings (5 - 10 mm diameter side port). Currently used grasper heads are small and often with steel material. With respect to these two properties applying large forces that cause damage in the organs is inevitable. The aim of this project is to design a new large laparoscopic grasper head that applies pressure along the length of the lever arms and can take up tissues of large sizes. Based on surveys and estimations SMA, artificial muscles... 

Aluminum alloy (A356.0) is used in the production of cylinder head. Automobile engines are often subjected to thermo-mechanical loadings. In order to investigate the material performance, it is crucial to obtain fatigue properties of the material under thermo-mechanical and isothermal fatigue tests. The specimen is subjected to tensile and compressive stresses in a constant temperature. But in thermo-mechanical tests, the temperature and the strain vary in a specific span (between maximum and minimum values). By using the strain- stress hysteresis loop (obtained by fatigue tests), we can determine fatigue properties. Then, these properties are used in the simulation. In this thesis,... 

Corrosion is a main problem for oil and gas industries at refineries and petrochemical process. Presence of sulfur compounds in crude oil and creation a corrosive environment for steel structure, caused failure and unfortunate damages. H2S which present at cracking and sweetening process in sour feed obtain hydrogen atoms that can diffuse into steel structure which involve with its instruments and consequent to hydrogen damage .distribution and storage of these sour environments can be done by high strength low alloy steel (HSLA).Electrochemical hydrogen permeation test were performed to measure the hydrogen permeation current through A106/GR B pipeline steel in the electrolytes simulating... 

In this thesis, an analytical solution is presented for pure bending of SMA curved beams with rectangular cross section and both loading and unloading stages are considered. Moreover, by appropriate simplification, its application in elastoplastic pure bending of curved beams made of regular materials is investigated. Elastic-linear kinematic hardening behavior of the material is assumed and both loading and unloading stages are considered. Exact plane plasticity solution of the elastoplastic pure bending of curved beams made of regular materials which exists in loading and is available for rectangular cross section has many unknowns and longsome equations. Therefore, it is difficult to use... 

Friction stir spot welding (FSSW), as a solid state welding process, can be used instead of resistance spot welding (RSW) for dissimilar joining of aluminum and steel sheets due to its advantages over the RSW process including the non-preferential melting of aluminum as well as the formation of thinner intermetallic phases at the joint interface. In the present study, it has been tried out to investigate the effect of rotational speed, dwell time and pin length on the tensile-shear strength of the Al-5083/St-12 friction stir spot welded joints. The pin diameter was 5 mm while the pin lengths of 2.8 and 3.2 were used to weld the samples. Rotational speeds of 800, 900 and 1100 rpm were applied... 

In this study, the solution treatment of severely deformed AA 2024-O and its post-severe plastic deformation is investigated. The investigation was performed in two cases of pre-multi directional forging (pre-MDF) and post-multi directional forging (post-MDF) on the solution treatment. After applying pre-MDF, finding kinetics of temperature and solution time caused that natural aging to be studied as a treatment after solid solution. By measuring the difference in hardness before and after natural aging in pre-MDFed and un-MDFed samples, 500℃ and 5 minutes were found to be the most desirable temperature and time in terms of mechanical properties and microstructure. Continuous... 

Various types of passive energy dissipating systems have been introduced for controlling the seismic response of structures during the last few decades. A number of these control devices have been practically implemented in different structures all over the world. Shape Memory Alloy (SMA) is among those passive control systems that have attracted a large attention due to its innate features, i.e., recovering the induced residual strains upon unloading (superelastic effect) or by heating (shape memory effect).This study investigates the seismic behavior of a set of steel structural models with different number of stories and eccentricities equipped with a type of fixed SMA connections. In the... 

High-strength low alloy (HSLA) E275 developed specifically for automotive application. Also St12 Steel is used in autobodies. On the other hand the resistance spot weld of dissimilar materials is generally more challenging than that of similar materials due to differences in the physical, chemical and mechanical properties of the base metals. The influence of the primary welding parameters affecting the heat input such as; current and time on the morphology, fracture mode, microhardness, and tensile shear load bearing capacity of dissimilar welds between HSLA E275 steel and St12 steel in two different thicknesses (1,2 mm) has been investigated in this study which consisted six group. The... 

Nowadays, Thermomechanical processes are used to change the microstructure and create desirable mechanical properties in metals. In this research, with the aim of improving the mechanical properties and formability of 7000 series aluminum alloys, the Cyclic Quench-Rolling (CQR) process was designed and investigated as a new thermomechanical process with solid solution strengthening mechanism. First, for solution heat treatment, the 7075-T6 aluminum sheet was placed in the oven at 460 °C for 5 hours and quenched in water. After making the solid solution, in each cycle of CQR, a rolling step was performed, then intermediate solutioning heat treatment and then quenching was performed. To study... 

In this research, the effects of natural and artificial aging heat treatments on the mechanical and wear behavior of an aluminum alloy from the 7xxx series have been investigated. The study commenced with annealing of the received samples, which were subsequently divided into four categories. One of these categories was placed in a freezer as annealed samples, while the other two underwent artificial aging heat treatments at temperatures of 180 and 210 degrees Celsius. The final category naturally aged over time. As a result, different structures with varied distributions and morphologies of precipitates were formed, and the mechanical properties, mechanisms, and wear resistance of the...