Translation Surfaces With Constant Mean Curvature or Gauss Curvature in 3-Dimensional Spaces

, M.Sc. Thesis Sharif University of Technology Razgordani Sharahi, Masumeh (Author) ; Fanaii, Hamid Reza (Supervisor)

Abstract

In Euclidean space R3 , a surface is called a translation surface if it is given by an immersion X : U 2 Rn ! Rn+1 : (x1; :::; xn) ! (x1; :::; xn; f1(x1) + ::: + fn(xn)) where fi; i = 1; ::; n are smooth functions.In this work, we give the classification of translation surfaces with constant mean curvature or Gauss curvature in 3-dimentional Euclidean space R3 and 3-dimentional Minkowski space L3 and We also characterize the minimal surfaces in the upper half-space model of 3-dimentional hyperbolic space H3 and we express this contents for spaces with arbitrary dimentional too

Enhanced resistance to liquation cracking during fusion welding of cast magnesium alloys: Microstructure tailoring via friction stir processing pre-weld treatment

, Article Materials Science and Engineering A ; Volume 798 , 2020 Sharahi, H. J ; Pouranvari, M ; Movahedi, M ; Sharif University of Technology

Elsevier Ltd 2020

Abstract

Magnesium alloys provide critical opportunities for energy and lightweight-materials challenges. The alloy design approach based on utilizing the second phase strengthening mechanism plays an essential role in producing low-density high strength Mg-based alloys. However, the second phase in the microstructure (e.g., Mg17Al12 phase in Mg–Al–Zn alloys) can deleteriously affect the weldability of the metallic materials by promoting the liquation and liquation cracking during fusion welding. The lack of sufficient weldability of Mg-based alloys is a crucial barrier to their potential use in safety-critical applications. In this paper, it is shown that the severe plastic deformation induced by...

Strengthening and ductilization mechanisms of friction stir processed cast Mg–Al–Zn alloy

, Article Materials Science and Engineering A ; Volume 781 , 2020 Jiryaei Sharahi, H ; Pouranvari, M ; Movahedi, M ; Sharif University of Technology

Elsevier Ltd 2020

Abstract

AZ91 alloy, the most widely used Mg casting alloy, exhibits low strength/ductility and weak energy absorption, which is a function of its large grain size and the presence of a coarse and continuous network of β-Mg17Al12 intermetallic compounds. This work demonstrated that friction stir processing (FSP) enables enhancement of strength and energy absorption capability of AZ91 alloy. The influence of FSP treatment on various potential strengthening mechanisms, including grain boundary, solid solution, and sub-micron particle strengthening mechanisms, was studied. It is identified that the grain boundary strengthening plays a significant contribution to the strength of the FSP treated AZ91. FSP...

Effect of liquation on the tensile properties of cast Mg–9Al–1Zn Alloy fusion welds

, Article Science and Technology of Welding and Joining ; Volume 25, Issue 8 , 2020 , Pages 698-705 Pouranvari, M ; Jiryaei Sharahi, H ; Movahedi, M ; Sharif University of Technology

Taylor and Francis Ltd 2020

Abstract

This paper aims at understanding the role of liquation and solidification phenomena on the tensile properties of arc welded cast AZ91 magnesium alloy. Owing to its refined microstructure, the fusion zone exhibited improved ductility/strength compared to the base metal. It is demonstrated that the partially melted zone (PMZ) which is characterised by constitutional liquation of eutectic β-Mg17Al12 phase is the weakest link in the weldment. The reduced strength and ductility associated with the liquation phenomena are due to the increased volume fraction and thickness of the eutectic β-Mg17Al12 in the PMZ as well as the formation of liquation micro-cracks in a network of brittle intermetallic...

Pre-weld friction stir processing enabling strong and ductile fusion welds on AZ91 magnesium alloy

, Article Science and Technology of Welding and Joining ; Volume 28, Issue 2 , 2023 , Pages 162-171 ; 13621718 (ISSN) Jiryaei Sharahi, H ; Pouranvari, M ; Movahedi, M ; Sharif University of Technology

Taylor and Francis Ltd 2023

Abstract

Liquation in the partially melted zone (PMZ) is the critical weldability issue of cast AZ91 magnesium alloy. Friction stir processing (FSP) is used as a local pre-weld treatment to create a local liquation-resistant microstructure in cast AZ91 alloy during arc welding. The effects of tool rotational speed during pre-weld FSP on the liquation-related microstructural features (i.e. grain structure, size and volume fraction of eutectic β-Mg17Al12) and the liquation characteristics of the fusion-welded AZ91 (i.e. PMZ size and grain boundary liquid film thickness) were investigated. The pre-weld FSP treatment of the cast AZ91 significantly improved the tensile strength and ductility of the welds...

Application of Titania Nanoparticles for Lichen Removal from Ancient Stone Surface (Case Study: Takhte Jamshid)

, M.Sc. Thesis Sharif University of Technology Hosseini, Hossein (Author) ; Khorasheh, Farhad (Supervisor) ; Sohrabi, Mohammad (Supervisor) ; Ghobadnezhd, Masumeh (Co-Advisor)

Abstract

Iran is one of the richest historic countries in the world, as extention of cultural heritage and historic building is unique. Infestation of lichens to those heritages for doing strategic actions wants the coordination of systems and organizations and universities. All the actions that do in this field, about the conservation and preservation of heritage made by stone related to architecture, be limited to lasers, electromagnetic waves, and application of jet methods such as sand storm, water jet, and prior to this mechanical and handful methods that approximately all be destructive. Application of nanoparticles of titania, as a smart photocatalytic material with antimicrobial and...

Non-orthogonal Multiple Access Techniques with Simultanious Wireless Information and Energy Transfer

, M.Sc. Thesis Sharif University of Technology Eslami Manoochehri, Farzad (Author) ; MirMohseni, Mahtab (Supervisor) ; Nasiri Kenari, Masumeh (Supervisor)

Abstract

Non-Orthogonal multiple access (NOMA) has been considered as a promising multiple access technique for the 5th generation (5G) of wireless networks. In contrast to orthogonal multiple access, NOMA supports more than one user in each subchannel and thus, improve spectral efficiency. On the other hand, energy efficiency which is another key consideration in future 5G networks, can be improved by energy harvesting (EH) methods. In the NOMA scheme, the user with the better channel condition performs successive interference cancellation (SIC) to detect the data of the user with the worse channel condition and then subtract it from the received signal to decode its own data. Since the data of the...

Investigation on the Effect of Friction Stir Processing on the Fusion Weldability of Magnesium Alloys

, M.Sc. Thesis Sharif University of Technology Jiryaei Sharahi, Hassan (Author) ; Pouranvari, Majid (Supervisor) ; Movahedi, Mojtaba (Supervisor)

Abstract

Magnesium alloys, as the lightest structural alloys having a density of about one-fourth that of steels, offer significant potential for improving the energy efficiency of various transportation systems. Welding is a critical enabling manufacturing technology; therefore, the widespread application of a material is highly influenced by their weldability. Liquation and Liquation cracking are crucial weldability issues for fusion welding of cast AZ91 Mg alloy. The constitutional liquation of the coarse eutectic Mg17Al12 intermetallic phase is responsible for the occurrence of liquation cracking during fusion welding of this alloy. Here, friction stir processing (FSP) treatment, a successful...