Sharif Digital Repository

Due to ignoring the effect of length scale and neglecting the details at nanosize, classical methods are not sufficiently accurate to determine the properties of nanostructured materials. More reliable results can be obtained, using surface elasticity theory. Lots of analytical, experimental and numerical investigations have been done on the effect of interphase on the mechanical properties of polymer nanocomposites whereas metal matrix nanocomposites are in the first stages of analytical and numerical researches and have attracted so much attention.
The main objective of this research is to investigate the effects of interphase as well as coating, on the mechanical behavior of metal... 

The main goal of the current study is to incorporate the effect of microstructural deformation mechanisms, such as detwinning-induced plasticity, into constitutive and computational modeling of NiTi shape memory alloys. Therefore, based on thermodynamic considerations a new inelastic mechanism, detwinning-induced plasticity (DIP), is proposed for modelling the response of NiTi SMAs to cyclic loading. DIP is incorporated into a constitutive framework that also includes other well-established inelastic mechanisms of phase transformation, transformation-induced plasticity, residual martensite and detwinning. The model is constructed at the single crystal scale using the framework of... 

Nowadays, World is witnessing an epidemic increase in Robotic Concepts and its usage in diverse fields such as Explore and Rescue Missions, Conservation and Guarding of Environments and various Millenarian Applications. While, different Goals like increasing the precision and speed of missions performance, and decreasing the costs have been always the major priorities in design and building robots. One of the best methodologies to achieve aforementioned goals is to replace a highly capable robot with a group of simple and restricted robots. This suggestion is inspired by the nature and lots of its animals, like birds, fishes and insects. These creatures use socializing in order to forage and... 

This research aimed at production of Cu-rGO via the combination of Molecular-Level-Mixing (MLM) method and powder metallurgy route (PM). First, Cu-GO composite powder was produced via MLM method. Subsequently, the resultant powder was mixed with electrolytic copper powder.Synthesis process included adjustment of the solution containing copper sulfate and 2Na.EDTA using NaOH solution. In the next step, GO suspension was added to the aforementioned solution. Finally, reduction of copper powder and formation of nanocomposite powder completed via the addition of Sodium Borohydrate. Nanocomposite powder was washed and dried in vacuum oven in 70˚C. GO reduction process took place using a tube... 

Capital market is one of the important ways to invest. Investors use different ways to analyze this market. One of the most important ways is to use stock filters that people need to learn both programming and capital market concepts. Automatic programming tools emerged to solve the need to learn a lot of programming languages in different fields but in stock filters have not been used until now in ower knowledge. In this research, the goal is to create automatic programming techniques to recognize stock filters from input-output examples. For this task, in the first step, the history of stock market have been used and a lot of stock filters with different length have been created. After... 

Nowadays, modeling the deformation behavior of materials is an indispensable tool to describe the evolutions of microstructure and mechanical properties of materials during deformation. As previous investigations have shown, the dislocation density is the most appropriate parameter for investigating the deformation behaviour of materials. In present research, considering the effect of stacking fault energy (SFE), the deformation behavior is investigated. In this regard, at first a thermodynamics based modeling of deformation is presented. Previous studies have shown that due to heterogeneous distribution of dislocations during severe plastic deformation, it is needed to use multi-variable... 

In recent years, severe plastic deformation has received significant attention as a technique for improving the mechanical properties of materials. In this regard, modeling the deformation behavior of materials during severe plastic deformation is of importance. As previous investigations have shown, dislocation density is one of the most applicable parameters for the mentioned purpose. On the other hand, strengthening mechanisms and the presence of strengthening agents in the material are important metallurgical phenomena that can play a significant role during severe plastic deformation. In this regard, the present research investigates the development of a dislocation density-based model... 

According to the Government policy in order to make targeted subsidies and apply it on various sectors in the industrial, commercial, agricultural, household and etc. changes in the energy supply needed resources in this section are required to appear. The agriculture sector is one of the most important parts of the food production is the production of security and health product. In this regard, the production of greenhouse products in terms of the use of high yielding varieties, production of the off-season, better control factors in production and reduce water consumption has increased drastically. The main source of supply in the internal energy of the greenhouse heating is mainly fossil... 

WC-Co hardmetals that are produced through powder metallurgy rout are vastely used as wear resistant parts. In these materials hard particles of wolfram carbide are embodied in a cobalt binder. Because of their high hardness and adequate toughness, hardmetals have found wide range of applications in cutting tool industry. During the last decades a number of researches have been carried out to improve their mechanical and wear properties by different binders and carbide particle sizes. Because of high hardness, Tungsten carbide has a good wear resistant. It has very low thermal expansion coefficient and high wetting ability with molten metals. Unlike high hardness, it has limited toughness.... 

In this study, Cu-TiC nanocomposites were produced by high energy ball milling of elemental powders and in situ formation of TiC in the copper base. Cu and 5,10,20 and 40 wt% Ti powder blend were milled for 60 h, then graphite powders were added and milling was continued for 10 h again and Finally Cu-TiC composite powders with 10.68, 20.16, 36.24 and 60.25 vol% of reinforcements (6.18, 12.2, 23.82 and 45.47 wt%) were produced. The effect of time on the solution of titanium in the copper was studied by X-Ray diffraction analysis (XRD). crystallite size and lattice strain of copper were determined 12nm and 1.04% subsequently for Cu-40wt%TiC after 60 h milling. to ensure the formation of... 

Nickel aluminides are intermetalics with complex structures that have high metlting points. However, brittlement at room temperature and low high_temperature strength (above 700 ̊C) can be mentioned as their short comings. Nowadays, many efforts have been proceeded to produce theirs composites, so that one can benefit from ceramics and intermettalics properties simultaneously. In this project, the main was aim to produce NiAl matrix nanocomposite reinforced with Alumina Al2O3. The composite is processed using milling and mechanical alloying. This is a good way to produce intermetallics and their composites with high melting points without any need to supply high temperature during... 

Due to the shrinkage defects, casting parts is sometimes unusable; as a result, researchers is tackling porosity removal problem, so that they would be able to cast parts in a way that have the least porosity. Nowadays, simulation is used to predict the location of the porosity. The design and the elimination of defects, which leads to additional costs, can reduce the overall costs in the projects.
In this thesis, we focus on shrinkage defects. The main cause of porosity is the drop of pressure. As a matter of fact, the thermal agitation of the molecules is weaker than the strong intermolecular forces that would pull the molecules; therefore, the molten metals’ density will be increased... 

In applications such as high duty sliding contacts and other electrical components requiring good electrical- and thermal-conductivity, proper mechanical wear resistance in combination with arc erosion resistance are required.The Cu/TiB2 nano-composite seems to be a good candidate for such cases. At present work TiB2 nano-particles has been selected as reinforcement, due to its valuable properties, i.e., high melting point (2850 - 2900 °C), low linear CTE (8.10 µmm-1 °C-1), thermal conductivity (60.0 - 120 W/m-K) as well as low specific electrical resistivity (10 - 30 μΩ.cm) and high hardness (25-35 GPa HV). Additionally, there are limited articles which have focused on evaluation of...