Sharif Digital Repository

Considering that automobile weigth reduction in industry is important, improvement the strength of low carbon steel sheets is important. These sheets can be supported the service condition in lower thicknesses. Bulk nano-structured materials have been mostly attracted in materials science due to their unique physical and mechanical properties. Severe plastic deformation (SPD) is one of the most efficient methods to produce ultra fine grained or nano-structured materials. Materials produced by SPD are of great importance because of (1) non-porous structure, (2) great mechanical properties such as high strength and toughness and (3) proper dimension for mechanical and physical testing. ... 

The study on new rheoforming technologies of semi-solid alloys has recently been one main subject interesting many researchers and industrials, and so many new methods about preparing semi-solid alloy slurry and rheoforming process have been suggested. Among more than 20 proposed methods, only MHD (Magneto Hydro Dynamics) and EMS (electromagnetic stirring) methods has been industrialized. In this research, the semi-solid slurry of A356 aluminum alloy was fabricated by electromagnetic stirrer under different conditions of stirring current, stirring time and pouring temperatures. Then the semi-solid slurry prepared in optimum conditions was injected into a step-die cavity by a drop device and... 

The extrusion process of flat dies in non-symmetrical sections is among processes which in spite of enormous applications, has not been thoroughly understood due to complexities of analyzing the section deformation process. In these dies, a zone is formed during egression of billet from die in which the material is stationary and accordingly the material on profile of this zone shears. This zone is called the dead metal zone. Dead metal zone is a natural non-linear die and it is pragmatic to obtain the value of the deviation. In the present work, determine the curvature of the exit profile by using prediction of the dead metal zone profile is target. The dead metal zone profile is assumed... 

In this thesis, equations related to large deformation of a polymer were derived by considering viscoelastic effects. To express type of material behavior which includes elastoplastic and viscoelastic property at the same time, two-layer viscoplastic model was used. An axisymmetric model was used for modeling problem in finite element software. By derivation of parameters related to two layer model and entering them in finite element software and also entering other properties required to model the forming process, modeling was performed by special profile connecting input and output sections. Due to favorable properties of spline functions, profiles used in die geometry, were selected from... 

One of the most common processes in shaping profiles with various cross-sections (with parallel surfaces), is a direct extrusion process. Always in the process, minimize the extrusion pressure and reduce the output profile curvature form of the main goals of researchers. Minimize the extrusion pressure in the mold design using nonlinear, many relationships are presented. Also, to reduce the output profile curvature of the mold, extrusion molding is used mostly at the outlet of the bearing. The purpose of this research is suitable for bearing design eliminates the curvature of the final product is extrusion. In this study interior design templates and profiles bearing acts simultaneously on... 

In the last decade, magnesium alloy has been developed owing to it’s low density, high specific strength, good castability and damping property. AZ91 alloy is proved to be the most common and most important magnesium casting alloy. It is shown that, rheocasting process is a proper way which increases the mechanical properties of the products. Since 28 years, so many new methods for preparing Semi-Solid alloy slurry and rheoforming process have been suggested. Electromagnetic Stirring ( EMS ) method was used for making globular structures. In this research, the semi-solid slurry of AZ91 magnesium alloy was prepared by electromagnetic stirrer under different conditions of stirring current and... 

More than 70% of the components used in aerospace, aircraft and defence industries Are made of aluminum alloys. The 7xxx series of Al alloys such as AA7075 and AA7175 are typical alloys utilized in the mentioned industries. For these alloys, the optimization of the extrusion process in term of reaching a maximum extrusion quality without jeoparding the extrudate, the surface and microstructural properties is far more complex than other aluminum alloys. It is generally accepted that product properties are closely correlated to microstructure. So it is of paramount importance to understand the way in which the structure is modified and how the forming parameters i.e. temperature, ram speed,... 

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... 

One of the most practical deformation processes has been used to produce profiles with a diversity of shapes is forward extrusion. Minimizing the extrusion pressure along with reducing the curvature of the final product have always been the main concerns of the researchers in this area. To achieve the former, researchers have designed nonlinear dies and proposed various equations to determine proper die profile. To accomplish the latter, they have used bearing at the exit section of the extrusion die. The primary object of the current study is to design a proper bearing in order to eliminate the curvature of the final product in extrusion process. The effects of both bearing and die profile... 

Big-data server workloads have vast datasets, and hence, frequently access off-chip memory for data. Consequently, server workloads lose significant performance potential due to off-chip latency and bandwidth walls. Recent research advocates using 3D stacked DRAM to break the walls. As 3D stacked DRAM cannot accommodate the whole datasets of server workloads, most proposals use 3D DRAM as a large cache. Unfortunately, a large DRAM cache imposes latency overhead due to (1) the need for tag lookup and (2) inefficient utilization of on-chip and off-chip bandwidth, and as a result, lowers the benefits of 3D stacked DRAM. Moreover, storing the tags of a multi-gigabyte DRAM cache requires changes... 

In today’s industrial world production is considered as a competitive weapon. This has caused many companies active in this field to move towards creating competitive advantage to reduce costs of design, construction and increase production. In particular molding as one of the main industries is among the most economical technological resources of each country. About 50 to 70 percent of the price of a production operation is spent of the strip of sheet by pressing; thus the proper design of a strip of sheet has a great impact on the mold design. Today, in most sectors of the industry there is a need for cutting and packaging of products and form molding and glass cutting to fitting the... 

Operating systems employ free space of main memory as a buffer cache to reduce the number of accesses to the disk subsystem with the aim of improving performance. Main memory which consists of DRAM modules, suffers from data loss in case of power failure and also high cost per gigabyte. Therefore, buffer cache layer needs to redirect critical writes to the disk subsystem which degrades the performance. Non-Volatile Memories (NVMs) are emerging memory devices that can preserve data without need for power current. NVMs, however, cannot replace DRAM due to the shortcomings such as limited endurance and low performance. Previous studies suggested employing hybrid DRAM-NVM buffer caches to... 

Aluminum is the lightest industrial element after magnesium. As a result, aluminum alloys have many industrial usages because of their high specific strength. Semisolid casting is one of the processes that is capable of producing aluminum alloys with high mechanical properties. In this process, there are a wide variety of methods to prepare semisolid slurry, one of the best ways of which to produce globular structure is electromagnetic stirrer. In this research, the semisolid slurry of A356 aluminum alloy is fabricated by electromagnetic stirrer under different conditions of stirrer intensity current, stirring time and pouring temperature. Then the fabricated semisolid slurry is injected... 

This thesis was conducted both numerically and experimentally. In the experimental investigations aqueous solutions of high molecular weight Carboxymethylcellulose (CMC) was used. The experimental set-up was composed of a glass syringe, and a piston which can easily move through the syringe. Different die with aspect ratio ranging from 5.25 to 28.8 can be attached to the syringe. The syringe then is filled with the CMC solution with different weight fractions. Then using a force exerting on the piston, the solution comes out of the die and exiting velocity was calculated from weight of CMC solution that exit from die in a definite time. High quality photographs were taken from extrudate... 

In this work, minimization of the exit profile curvature in multi-hole extrusion die was studied by specifying an appropriate location for exit holes using analytical, finite element and experimental approaches. First by considering linear dead metal zone in flat multi-hole dies, the velocity field constructed. Then based on an objective function, the deviation of the exit profile obtained for any positioning of the exit holes. Additionally, the deviation obtained from theoretical method was verified with the result of the commercially available bulk forming simulation software (Deform 3D v5). Also to verify the result the direct extrusion process was simulated physically by plasticine.... 

In this study, a two-hole die with unsymmetrical T-shape holes has been investigated. At first, a kinematically admissible velocity field in outlet of die has determined. Then, appropriate length of die has calculated by upper bound method. Finally, suitable position of holes has achieved in aspect of minimum pressure and curvature. To calculate curvature of exit profile, a realistic deviation function has been defined. To validation of results, finite element simulation and physical modeling have been used. Analytical, experimental and finite element results have decent agreement to each other  

In recent years, various research has been done on the severe deformation of low carbon steel sheets. One of the methods used is the pressing in the grooved die, only two passes of the pressing process in the grooved mold have been successful when applied to these sheets, but on the other hand, these two passes also lessen the sheet's ductility while increasing its strength. Due to the fact that the sheet surface produced by the pressing in the grooved die is not entirely smooth, the attempt in this project was to improve the ductility to some extent using warm rolling in addition to the smoothness of the surface using higher temperature while improving the strength or maintain it. To... 

The precipitation hardenable 7075 Aluminum Alloy is one of the most important heat-treated aluminum alloys. The high strength of this alloy has led to its widespread use in the manufacture of various components in the automotive, aerospace, marine, defense and military industries. Although the production costs of this alloy sheet are high, but since the 7075 aluminum alloy has the capacity to be as strong as steels, by reducing the production process and thus reducing production costs, this alloy can be used more widely in various industries. Therefore, in this study, the mechanical properties of the 7075 aluminum sheet are improved by a new quenching method in the die (HFDQ), which is a... 

Al-4.5% Cu alloy, an age-hardenable alloy, is an important alloy in industry due to such unique characteristics as high strength-to-weight ratio and considerable strength at elevated temperatures. In this study, the aim was to evaluate the combined effect of cooling rate and heat treatment on an A206 alloy having more impurities—especially iron—than the nominal specifications. To this end, the melt was poured in a five-step mold. Afterwards, each step was subjected to T4 and T6 treatments in order to study the changes compared to the as-cast samples. Ultimate tensile strength, yield strength, elongation, and grain size were determined by using tensile tests and optical microscopy,... 

Nowadays, the application of magnesium alloys as biodegradable implants in the medical industry has garnered significant attention. However, the low mechanical properties and rapid degradation rate of pure magnesium implants in the biological environment have hindered their widespread use for clinical applications. Magnesium-calcium alloys, due to their low degradation rate and promotion of faster bone healing, have become attractive choices for orthopedic applications. Nevertheless, the micro alloy X0 used in this study lacks sufficient strength and flexibility, limiting its potential applications. Utilizing severe plastic deformation methods to create ultrafine microstructures can greatly...