Sharif Digital Repository

In the present work, the effect of different methods of melting, remelting and solidification conditions on the microstructural evolution of IN100 superalloy was investigated. For this purpose, the superalloy was solidified within steel and ceramic molds to provide different cooling rates. Furthermore, the re-melting processes using ESR in the water circulated copper mold and ceramic molds, VAR and combined ESR and VAR were considered. The microstructure of alloy under different casting and remelting conditions were studied by means of optical and SEM microscopy and ESD analysis. According to our results, the ingot which was cast in the ceramic molds, due to lower cooling rate during... 

In the current study, nonlinear vibration and stability of conical shells with both separate and concurrent internal and external flows are studied. External and internal flows are in the supersonic and subsonic regimes, respectively. The Krumhar’s aerodynamic piston theory is utilized to model the external loading on the structure as well as the compressible potential flow model to capture the internal fluid dynamics. The so-called compressible fluid model is obtained via simplification of the Navier-Stockes equations after applying the inviscid and irrotational assumptions. The nonlinear structural equations of motion are derived using the Hamiltonian dynamics approach and utilizing the... 

In this study, the modeling of shrink-fit connection was performed by considering the effect of friction on the connection. The behavior of a beam with shrink-fit connection was compared with the results of Adams software and the modeling accuracy was shown. Using both energy and Newton methods, the equations of motion of a rigid rotor consisting of two shafts connected by shrink-fit connection were obtained and the dynamic behavior of the rotor was investigated. Finally, the coupling parameters affecting the vibrations and stability of this rotor were introduced and the effect of each on the system behavior was shown.
 

The goal of this research is investigation and analysis of a surface consists of vertically aligned carbon nanotubes (VACNTs) using continuum mechanics modeling. Today these kinds of surfaces also known as the darkest material have a particular importance in industries. Knowing the properties of a material is one of the most important things in analysis and designing using that kind of material, so extraxting the stiffness matrix of a material could be a big step for starting analyzing it. In this thesis a lattice of VACNTs with two different layouts and several unique geometrics is simulated using molecular dynamics approach using the Lammps software. The general stiffness matrix of the... 

In the process of Additive manufacturing for metals, the ability to predict and control the microstructure can reduce the need for subsequent heat treatment and accelerate the component quality assessment process. The ability to predict and control the microstructure of materials in the laser deposition method needs to understand the thermal conditions during the solidification process. For this purpose, the present study investigated the relationship between cooling rate and temperature gradient during local solidification, and control parameters of the laser deposition process such as power, beam radius, scanning speed and strategy of laser, ambient temperature and preheating temperature.... 

With the emergence and expansion of social media in the societies, these media has become an integral part of modern society and the lives of citizens. These networks have improved communication facilities in the community and created an opportunity for politicians to use these media as a communication and marketing channel to communicate with citizens and use them to achieve their goals. Social media's ability to communicate has put politicians' relationship with citizens in a very strategic position. This has made it important to have a communication plan and, more generally, principled political marketing.Therefore, the main issue that this dissertation has investigated is the review of... 

Recently nanostructure materials have used in various technologies and hence an extensive part of research focused on preparing and optimization of growth of nanostructure materials. Usually common procedure is based on a two-step process. First, construction a pre-layer by means of different deposition methods and then formation a nanostructure with a thermal treatment which increases the cost of research. Hence with one step method such as glancing angle deposition (GLAD ( it is possible to form a desirable structure with low cost. In this research Nano columns of tungsten was deposited on Si(133) by means of GLAD-RF sputtering without any heat treatment at substrate rotational speed ( )... 

In the present investigation, the mechanical alloying (MA) technique was employed to produce nanocrystalline Al-Ti Powder mixtures. Elemental Al and Ti powders were mixed with different compositions (0, 5, 10, and 20 wt.% Ti) and then, milled in a vibratory mill up to 7 hr. The variations of powder morphology and particle size, apparent and tap densities, microstructure, grain size, lattice strain, and microhardness were studied with increasing the milling time. While dissolution of Ti in the Al matrix resulted to the formation of supersaturated Al-Ti solid solution in the samples containing 5 and 10 wt.% Ti, the specimen with 20 wt.% Ti, eventually, led to nanocomposite powder with... 

With the epidemic of viral diseases in humans and animals, and their potential to cause irreparable economic damages, due to their recent noticeable changes in their structures followed by becoming antibiotic resistance, many researchers nowadays are focusing on the new antiviral Agents with least side effects. Influenza A virus is a common seasonal virus which can lead to sever infections. This type of influenza has the ability to transmit between humans and animals, and also by antigenic shifts can transform to new type of influenza which can cause a global disaster. While classical antiviral drugs are still in use for influenza patients, new influenza A subtypes become resistant to these... 

The digital age and its interlace with the pandemic has led to rapid changes in various institutions, including higher education. One of the factors that changes higher education is the expansion of E-learning and Massive Online Open Courses (MOOCs). Although about 15 years have passed since its creation, the pandemic has expanded the E-learning infrastructure and given it more attention, so that now everyone Confesses the possibility of distance education. On the other hand, although the development of MOOCs platforms and their considerable acceptance has attracted the attention of higher education professors and future researchers in this field, it is not properly considered by the... 

Multi-part rotating parts are used in various industries with very high revolutions. Therefore, the method of assembling each part and keeping the axis of rotation of each part close to the axis passing through two supports (bearings) is important. In this research, three main steps are followed, the development of the differential equations governing the multi-part rotating system and the calculation of the range of oscillations created at the critical points, and then the calculation of the optimal assembly angles with the aim of reducing the introduced oscillations, and finally the discussion of crossing the speeds A crisis is being investigated. The method of obtaining the system of...