Sharif Digital Repository

In this study, Al-5052 aluminium alloy sheet was lap joined to aluminium clad steel sheet using pulsed gas tungsten arc welding and Al-Si filler metal. Effect of heat-input, thickness of clad layer and frequency were investigated on the formation of intermetallic reaction layer, microstructure of the weld seam and shear strength of the joints are explored. Stress analysis in weld is also used in order to justify the fracture location in the welds the microstructure and shear-tensile strength of the welds (joining with A1-1050 clad layer with two thickness of 350 μm and 1000 μm). Before welding, aluminum clad steel sheets were produced by roll bonding and 450 °C annealing temperature and 90... 

The new generation of advanced high-strength steels use in the automotive industry cause resistance spot welding study and their failure characteristics during static and dynamic loading are important. In this study, the relationship among microstructure, failure mode and mechanical properties are investigate during similar and dissimilar DP980 and MS1400 jointing advanced high-strength steels resistance spot welding. To search for micro and macro structural changes, the optical microscope, stereographic microscope and scanning electron microscope were used. Micro-hardness test, tensile shear test and Cross tension test to evaluate the mechanical properties were conducted. As well as... 

Friction Stir Processing (FSP) was used to fabricate Al1050/Fe3O4 nanocomposite in three different weight percent (2.5%, 4% and 5.3%). The effects of rotational speed (1200-1600 rpm), traverse speed (5-15 cm/min) and the number of FSP passes (1, 2, 3 and 6 passes) on microstructure and mechanical properties were investigated. In order to study microstructure evolution, optical and field emission scanning electron microscopes were used. Micro hardness, longitudinal and transverse tensile and wear test were carried out to investigate mechanical properties of the obtained composites. Results showed that increase of the rotational speed and decrease of the traverse speed in 1 pass processed... 

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... 

Aluminum alloys are used in many industries because of its high strength to weight ratio. Due to many problems of fusion welding of aluminum alloys, In the past decade, much attention of scientists and craftsman has been directed towards friction stir welding (FSW) as a solid-state welding process. In this study, joint strength of butt friction stir welded wrought 1050 aluminum alloy with the thickness of 4mm increased by inserting pure copper foil (100 µm), pure zinc foil (250 µm), brass foil (100.250.500 µm) with chemical composition of 60wt% Cu and 40 wt% Zn. FSW was conducted at a tool traverse speed of 25 mmmin−1 and a rotational speed of 1200, 1600 and 2000 rpm. Results showed... 

Joining between aluminum alloys and steels by resistance spot welding accompanies critical technological and metallurgical difficulties. The main problem is formation of brittle intermetallic compounds (IMC) at the welding interface which results in poor mechanical properties. There are some researches based on the microstructure and mechanical properties of resistace spot welding of aluminum to steel and each of them has tried to enhance the joint properties. Using Zn interlayer is an approach to improve Al to steel resistance spot welding properties. Up to now there is few information on the influence of Zn as an interlayer between steel and aluminum on the Al/Steel dissimilar welding... 

Joining metals to polymers is an increasing demand in industry mainly due to weight savings. Polymer-metal hybrid structures are widely used in aerospace and automotive industries. However, dissimilar joining of polymer to metal is very difficult due to large mechanical and physical properties differences. Since conventional methods for joining polymers to metals have various limitations, it is necessary to employ new practical and environmental friendly joining processes. In this study, the feasibility of joining an aluminum alloy (AA5052) to polypropylene (C30S) sheets via friction stir welding was examined. Lap joint configuration was determined as the optimized configuration by analyzing... 

Selective laser sintering is an additive manufacturing technique based on fusion of powder bed, wherein after spreading a powder layer, a focused laser beam directs onto selected points of powder bed to fuse powder particles together. This process is repeated layer by layer until the final part is created. Although utilization of blade as a conventional powder spreading (CPS) mechanism has a good compression ability, the fixed contact line between blade and powder bed surface results in improper powder flowability and increasing shear forces applied on underneath layer. In this study, in order to obtain the basis for conducting practical experiments, discrete element simulation of powder... 

Energy subsidies are one of the most challenging issues for many countries in the world, specially oil and gas exporting countries. Iran is one of the countries that has lost more than ten percent of its GDP due to energy subsidies in recent years. In this thesis, we are going to analyze experiences of different countries and try to provide policy makers with generalizations about this problem so they can implement reform policies more successfully. We have used Qualitative Comparative Analysis (QCA) methodology. This method can provide modest generalizations by using systematic cross-case comparison between a small number of cases. Details of this method and reasons behind choosing it are... 

Today, the need for high-speed machine tools, in areas such as defense, medical and electronic for producing parts with millimeter dimensions, and with features smaller than the millimeter, increased. To meet this need, the machine tool can be used with smaller dimensions and with high speed. These machines are able to produce these parts with high production rates.The project aims to improve technical design and construction of a micro spindle to achieve sustained speed about one hundred thousand RPM. In this project, the first step in understanding the fundamentals of the theory and the system components, and the whole operation was performed. The design is based on studies carried out in... 

For validation of simulation, plasma actuator was modelled on a flat plate in quiescent flow, which is result in low-speed jet near the wall. The results were compared with similar model and were showed good agreement with them. After that, blade was modelled in three-dimensional manner with MRF technique and periodic method and the results were validated in clean situation (absence of plasma). In the following, turbine was analysed with a code, which was written in MATLAB software based on BEM method and the results were compared with present CFD simulation. Then, plasma actuator was used in chordwise in parts of the blade to improve wind turbine performance. Also it was used in spanwise... 

Selective Laser Sintering (SLS) is one of the powder-based Additive Manufacturing (AM) technology in which parts built by CO2 laser. In this research work, Titanium-PMMA-Stearic Acid powders are mixed together to produce parts by Indirect Metal Laser Sintering (IMLS) method. The optimum process parameters such as energy density, Percentage composition of Titanium-PMMA and Scan Sintering are obtained by adopting the Taguchi method for getting the maximum density and minimum porosity. Experiments are planned by Taguchi’s Mix-L8 orthogonal array. According to the results obtained from this study, the percentage of combination Ti-PMMA and Energy density, respectively, are a major parameters that... 

In machining processes, chip formation is one of the most important methods to obtain the final shape of a work-piece. Improving the machining processes leads to the increase in the material removal rate (MRR) and reduction of high economical costs. Vibration is an undesirable phenomenon in machining processes because it results in reduction of material removal rate (MRR), poor surface finish and increased tool wear. Among various types of vibration, self-excited vibration or chatter is the most important one. It is obvious from previous investigations that for prediction of machine tools vibration, many simplifications were assumed while the linear and non-linear effects are not considered... 

Forging process is recognized as the high speed method, economical and with ability to produce high strength parts between metal forming processes. Preform design is the most important step in forging process. In the past this work was done based on experiences. In the complex parts because of error in design there was probability of diverse dies, so that method needed to spent so many times and costs. However recently with progress in computer programming we don’t need to produce diverse dies but spend many times. In this field many investigations are done to dispose designers skills, so forging preform design based on inverse finite elements method is denoted for this gold. In this thesis...