Sharif Digital Repository

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... 

Accumulative spin bonding as a severe plastic deformation process results in a finer microstructure through multi-pass processing. This method consists of successive and repeated preparation of internal and external surfaces of two similar tubes, simultaneous flow forming of two tubes and production of a tube with the same thickness as the primary one. This word was conducted to study the effect of different rotational speeds and different cooling environments on the mechanical properties and microstructure of AA1050 tubes. The samples were prepared with 0.8 mm thickness and 92.8 mm internal diameter through four passes of ASB with 250, 500, 710 rpm under air, water and acetone cooling... 

Hybrid mobile applications combine the features of Web technologies and native mobile apps. Like Web applications, they are implemented in portable, platform independent languages such as HTML and JavaScript. Like native apps, they have direct access to local device resources. In these programs, web contents are loaded into a web component, called WebView, which can render HTML5 pages and execute JavaScript code. In order for the web content to access the system resources, which are isolated from the content inside Web-View due to its sandbox, bridges need to be built between JavaScript and the native code. developers usually use third party plug-ins for native side of application. hybrid... 

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... 

Fine-grained image classification is image classification where the considered classes are all sub-classes of a certain, more general class. In this setting of the problem, the classes are visually very similar to each other, such that an unskilled human cannot discriminate between them. In this case, proposed methods for the ordinary image classification problem do not obtain good classification accuracy. So proposing new methods for solving this problem is necessary. In this thesis two new methods, based on recent advances in deep learning are proposed for solving the fine-grained image classification problem. First by improving several parts of one of the recent proposed methods for this... 

Metallic multilayer composites provide remarkable mechanical, electrical and magnetic properties. These kinds of composites are recently processed by severe plastic deformation methods. Accumulative roll bonding (ARB) is one of the SPD processes in which accumulation of strain by repeating cycles, leads to the ultra fine grains structures. The goal of this research is manufacturing of Al/AZ31 composite and investigating the relation between the rolling process parameters and the mechanical and physical properties of the final sheet. The initial composite was carried out by cladding of 1mm thick AZ31 sheet in between two commercially pure aluminum sheets with the same thickness (57%... 

Metallic multilayer composites provide remarkable mechanical, electrical and magnetic properties. These kinds of composites have been recently processed by severe plastic deformation (SPD) methods. Accumulative roll bonding (ARB) is one of the SPD processes in which accumulation of strain by repeating cycles, leads to the ultra fine grained materials. The goal of this research is manufacturing of Al/Ni composite sheets by ARB process considering the effects of thickness and number of initial sheets on their mechanical properties and microstructures. The initial composites were produced by commercially pure Al and Ni as the matrix and the reinforcement, respectively. Thickness of the Al... 

At this study, nano structure sheet composite produced by1100 and 3004 strips using Accumulative role banding then mechanical and physical properties of the composites were investigated. After surface preparation, primary composite samples produced by putting different layers on each other and then rolling. The rolling was occurred in two steps; thickness reduction at first and second step were about 50% and 34%, respectively. ARB process were done till ninth cycle for Primary composite samples. To investigate mechanical properties of the samples, hardness, micro hardness and tensile strength tests have been done. Furthermore, micro structure of selective samples were studied by light... 

In present work, nanostructured multilayer composites produced from AA1100 and St37 alloys and mechanical properties of resulted samples characterized using tension and micro hardness tests. Also dispersion pattern of second phase in matrix studied via optical microscopy. Thickness of second phase layers showed a little reduction after 2 ARB cycles; but their length decrease gradually. With increasing number of ARB cycles up to 6 cycles, sample's tensile strength first decrease rapidly and after that increased, but never reached initial value. In order to evaluation of heat treatment effects on samples grain structure, samples heat treated and tensile test carried on them. Annealing at 300... 

In recent years, severe plastic deformation processes have been widely used to correct the grain size of metals. One of these methods is equal channel angular pressing. In this research, the improvement of mechanical property and structural changes of pure magnesium and AZ91 alloy after the ECAP process are investigated. The mold is made of H13 steel with a 90-degree channel crossing angle and a zero-degree external curve angle. The purpose of this study is to find the smallest average grain size at the optimum temperature on these materials. First, pure magnesium and AZ91 are subjected to the ECAP process at temperatures of 250, 300, 350, and 400 °C to calculate the best operating... 

Magnesium and its alloys have gained much attention in medical applications, especially bio-degradable stents. However, they have not been used extensively due to their natural limitations, such as weak mechanical properties. WE43 magnesium alloy has gained attention as a bio-alloy due to its high temperature and good corrosion resistance. The present study aims to use a combination of ECAP and direct tube extrusion to fabricate thin wall tubes with good mechanical properties using WE43 magnesium alloy. In the first phase, the ECAP process at 370°C were conducted up to 4 passes on the homogenized samples to reach ultrafine grain structure. Subsequent to ECAP, direct tube extrusion at 230 °C,... 

Magnesium and its alloys have gained significant attention in medical applications due to their good biocompatibility. However, their widespread use has been limited by some inherent drawbacks, such as poor mechanical properties. The ZX00 magnesium alloy has been used in medical applications, including implants, due to its slow degradation rate and good ossification. However, this alloy lacks sufficient strength and ductility. The severe plastic deformation method can create an ultrafine grain structure and improve mechanical properties. In this study, to improve the mechanical properties and create an ultrafine grain structure, the multi-directional forging process was performed on...