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asghari--reza
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Statistical Analysis of Parameter Fluctuation on Performance of Giga Scale Integration
, M.Sc. Thesis Sharif University of Technology ; Sarvari, Reza (Supervisor)
Abstract
Developing to the sub-micron dimentions reduces the size of integrated circuits, so interconnects and a variations in their characteristics has more effects on circuit performance. Worst case study is the most common method in these systems, but in many cases interconnect lines are independent from eachother. Analysis state that worst case is out of the distribution in many cases (with zero possibility) and result in a pessimistic design. Statistical analysis should replace worst case analysis in multi varient systems. In this titile, statistical analysis will be used to investigate performance of interconnects in new technology. Maximum variation in interconnect parameters are considered...
Experimental and Analytical Investigation of Elastic-Plastic Behavior of Glass Fiber Reinforced Polymer Composites
, M.Sc. Thesis Sharif University of Technology ; Naghdabadi, Reza (Supervisor) ; Asghari, Mohsen (Supervisor)
Abstract
In this thesis, we aim to study the elastic-plastic behavior of short fiber reinforced composites experimentally and analytically. The experimental investigation is applied to glass fiber-polypropylene composites (PP/GF). The samples are produced by injection process with maximum temperature of 190C. Fibers are randomly oriented in this procedure of fabrication. The samples are tested in tension, and the mechanical strength is measured by changes in fiber content. The Young's modulus is also investigated in these experiments.Also in this thesis, an analytical model for calculation of Young’s modulus of fiber reinforced composite materials is proposed. In this analysis a displacement field is...
Elastic-Plastic Analysis of Fiber Reinforced Metal Matrix Composite Structures
, M.Sc. Thesis Sharif University of Technology ; Naghdabadi, Reza (Supervisor) ; Asghari, Mohsen (Supervisor)
Abstract
In this study, an elastic-plastic analysis of fiber reinforced metal matrix composite structures loaded by uniaxial uniform tension in the direction perpendicular to the fiber is carried out by assuming elastic-plastic matrix with kinematic hardening. Representative volume element (RVE) is used for this analysis. The element consists of a combined square field composed of a solid circular cylinder fiber and matrix in plane strain condition. Elastic analysis is carried out using Airy stress function and Michell solution. Unknown coefficients of the Airy stress function are determined by satisfying boundary conditions as well as continuity conditions. The governing equation of plastic zone is...
Investigation of Mechanical Properties of Particulate Metal Matrix Nanocomposites Using Surface Elasticity Theory
, M.Sc. Thesis Sharif University of Technology ; Naghdabadi, Reza (Supervisor) ; Asghari, Mohsen (Supervisor)
Abstract
Excellent mechanical properties and high aspect ratio of carbon nanotubes have been the reason for extensive research on nanocomposites reinforced by this nanostructure, and recently metal matrix type of these nanocomposites, due to their advantages, have received great attention. Moreover, nanoporous materials are another type of nanostructured materials which due to their very high porosity have special applications in hydrogen storage, separating molecules, purification and energy absorption. Because of completely neglecting the details of nanoscale structure and not paying attention to the length scale, classical continuum mechanics methods are not precise enough for evaluating different...
Spectral Element Simulations of Wave Propagation in Porous Fluid-Saturated Media
, M.Sc. Thesis Sharif University of Technology ; Naghd Abadi, Reza (Supervisor) ; Asghari, Mohsen (Supervisor) ; Mazaheri, Hashem (Co-Advisor)
Abstract
The aim of this work is numerical analysis of wave propagation in earth by using spectral element method for single and multi phase with application in oil industry. In this method, numerical solution has high accuracy due to using high order polynomials and appropriate integration points. Also, the mass matrix is diagonal by using this method which results in considerable decrease in computational cost with respect to finite element method.
The wave propagation in the mentioned models is studied by many researchers. The main problem in petroleum industry is large dimension of the model which results in high computational costs. Thus, using the proper numerical approach for these...
The wave propagation in the mentioned models is studied by many researchers. The main problem in petroleum industry is large dimension of the model which results in high computational costs. Thus, using the proper numerical approach for these...
Geometrically nonlinear micro-plate formulation based on the modified couple stress theory
, Article International Journal of Engineering Science ; Volume 51 , 2012 , Pages 292-309 ; 00207225 (ISSN) ; Sharif University of Technology
2012
Abstract
The couple stress theory is a non-classical continuum theory which is capable to capture size effects in small-scale structures. This property makes it appropriate for modeling the structures in micron and sub-micron scales. The purpose of this paper is the derivation of the governing motion equations and boundary conditions for the geometrically nonlinear micro-plates with arbitrary shapes based on the modified version of the couple stress theory. The consistent boundary conditions are provided at smooth parts of the plate periphery and also at the sharp corners of the periphery using variational approach
Basis free expressions for the stress rate of isotropic elastic materials in the cases of coalescent principal stretches
, Article International Journal of Solids and Structures ; Volume 47, Issue 5 , 2010 , Pages 611-613 ; 00207683 (ISSN) ; Sharif University of Technology
2010
Abstract
In this paper, some basis-free expressions for the material time derivative of Lagrangian stress tensors are presented which are generally valid in all cases of coalescent principal stretches. The material is assumed to be elastic and isotropic
Study of Nanocrystallization Kinetics, Microstructure and Magnetic Properties of Finemet-type Soft Magnetic Materials
, Ph.D. Dissertation Sharif University of Technology ; Madaah Hosseini, Hamid Reza (Supervisor) ; nozad, Ahmad (Supervisor) ; Beitollahi, Ali (Co-Advisor)
Abstract
Nanocrystallization kinetics of amorphous Finemet-type alloys was studied using Isokinetic and Isoconversional methods (Kissinger model-fitting method, Vyazovkin advance method, Kissinger–Akahira–Sunose(KSA),Flynn–Wall–Ozawa(FWO),Tang and Starink) under isothermal and non-isothermal conditions. Effects of chemical composition on the nanocrystallization kinetics, microstructure and magnetic properties of Fe73.5Si13.5B9Nb3Cu1 and Fe77Si11B9Nb2.4Cu0.6 alloys were also investigated. Kinetic triplet (activation energy, frequency factor and reaction model) were determined by these methods and compared for the alloys. According to isoconversional methods, the activation energy is variable as a...
Study on Adsorption of Uranium from Saghand Ore Leach Liquor by Continuous Ion Exchange Systems
, M.Sc. Thesis Sharif University of Technology ; Outokesh, Mohammad (Supervisor) ; Godocynejhad, Davood (Supervisor) ; Saberyan, Kamal (Co-Supervisor) ; Asghari, Reza (Co-Supervisor)
Abstract
The current study was attributed to uranium uptake by Varion-AP resin from Saghand, Iran Uranium Mine, ore leach liquor. A suitable high-efficiency system was designed for continuous ion exchange at the bench scale and the uranium uptake parameters were optimized. In this system, 1 reactors was used with a volume of 3 liters in stage with the same height difference. A leach liquor containing uranium with a concentration of between 200 and 300 mg/l was flowed from the feed storage by gravity between reactor 1 to 10 at a flow rate of 30 lit/h and Varion-AP resin was transferred in counter-current flow from stage 10 to 1 by a pneumatic pump. The output of each reactor had a screener that...
A size-dependent model for functionally graded micro-plates for mechanical analyses
, Article JVC/Journal of Vibration and Control ; Volume 19, Issue 11 , 2013 , Pages 1614-1632 ; 10775463 (ISSN) ; Taati, E ; Sharif University of Technology
2013
Abstract
In this paper, a size-dependent formulation is presented for mechanical analyses of inhomogeneous micro-plates based on the modified couple stress theory. The plate properties can arbitrarily vary through the thickness. The governing differential equations of motion are derived for functionally graded (FG) plates with arbitrary shapes utilizing a variational approach. Moreover, the boundary conditions are provided at smooth parts of the plate periphery and also at the sharp corners of the periphery. Utilizing the derived formulation, the free-vibration behavior as well as the static response of a rectangular FG micro-plate is investigated
Variational principles for stability analysis of multi-walled carbon nanotubes based on a nonlocal elastic shell model
, Article ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, ESDA2010, Istanbul, 12 July 2010 through 14 July 2010 ; Volume 5 , 2010 , Pages 591-598 ; 9780791849194 (ISBN) ; Rafati, J ; Sharif University of Technology
2010
Abstract
The nonlocal continuum theories are capable to reflect the small length characteristic of nanostructures. In this work, variational principles are presented for the stability analysis of multi-walled carbon nanotubes under various mechanical loadings based on the nonlocal elastic Donnell's shell by the semi-inverse method. In this manner, a set of proper essential and natural boundary conditions for each layer of the multi-walled nanotube is derived
Flexural vibration characteristics of micro-rotors based on the strain gradient theory
, Article International Journal of Applied Mechanics ; Volume 7, Issue 5 , October , 2015 ; 17588251 (ISSN) ; Hashemi, M ; Sharif University of Technology
World Scientific Publishing Co. Pte Ltd
2015
Abstract
In this paper, the coupled three-dimensional flexural vibration of micro-rotors is investigated by taking into account the small-scale effects utilizing the strain gradient theory, which is a powerful nonclassical continuum theory in capturing small-scale effects. A micro-rotor consists mainly of a flexible micro-rotating shaft and a disk. With the aid of Hamilton's principle, governing equations of motion are derived and then transformed to the complex form. By implementing the Galerkin's method, a coupled ordinary differential equation is attained for the system. Expressions for the first two natural frequencies of the spinning micro-rotors are obtained with truncated two-term equation....
A three-dimensional elasticity solution for functionally graded rotating disks
, Article Composite Structures ; Volume 92, Issue 5 , 2010 , Pages 1092-1099 ; 02638223 (ISSN) ; Ghafoori, E ; Sharif University of Technology
2010
Abstract
A semi-analytical three-dimensional elasticity solution for rotating functionally graded disks for both of hollow and solid disks is presented. The aim is to generalize an available two-dimensional plane-stress solution to a three-dimensional one. Although for the thin disks problems the two-dimensional solution provides appropriate results, for the thick disks, a three-dimensional elasticity solution should be considered to avoid poor results. It is shown that although the plane-stress solution satisfies all the governing three-dimensional equations of motion and boundary conditions, it fails to give a compatible three-dimensional strain field. A valid three-dimensional solution has been...
The couple stress-based nonlinear coupled three-dimensional vibration analysis of microspinning Rayleigh beams
, Article Nonlinear Dynamics ; Volume 87, Issue 2 , 2017 , Pages 1315-1334 ; 0924090X (ISSN) ; Hashemi, M ; Sharif University of Technology
Springer Netherlands
2017
Abstract
The nonlinear coupled three-dimensional vibrations of microspinning Rayleigh beams are analytically studied utilizing the modified couple stress theory to take into account the small-scale effects. The considered nonlinearity is of geometrical type due to the mid-plane stretching. The rotary inertia and gyroscopic effects are both included in the formulation. Governing equations of motion are derived with the aid of the Hamilton Principle and then transformed into complex form. Then, the Galerkin and multiple scales methods are utilized to solve the nonlinear partial differential equation. Approximate analytical expressions for nonlinear natural frequencies of the spinning beams in forward...
On the objective corotational rates of eulerian strain measures
, Article Journal of Elasticity ; Volume 90, Issue 2 , 2008 , Pages 175-207 ; 03743535 (ISSN) ; Naghdabadi, R ; Sharif University of Technology
2008
Abstract
In the present paper, some new basis-free expressions for an arbitrary objective corotational rate of the general Eulerian strain measures are provided which are in compact form. Moreover, a complete discussion on the requirements for the continuity of the objective corotational rates are presented. © 2008 Springer Science+Business Media B.V
Unified basis-free relation between two stress tensors conjugate to arbitrary Hill's strain measures
, Article ASME PVP2006/ICPVT-11 Conference, Vancouver, BC, 23 July 2006 through 27 July 2006 ; Volume 2006 , 2006 ; 0277027X (ISSN); 0791837823 (ISBN); 9780791837825 (ISBN) ; Naghdabadi, R ; Sharif University of Technology
American Society of Mechanical Engineers(ASME)
2006
Abstract
The concept of energy conjugacy for stress and strain measures states that a stress tensor T is conjugate to a strain measure E if T: Ė provides the rate of change of the internal energy per unit reference volume of the body in an adiabatic process. The applications of the conjugate stress and strain measures are in the development of the basic relations in nonlinear analysis of solids. In this paper using eigenprojection method, unified explicit basis-free relation between two arbitrary stress tensors T(f) and T (g), respectively conjugate to two measures of Hill's strains is determined. The result is valid for arbitrary dimension of the Euclidean inner product space and for all cases of...
Conjugate stresses to two-point deformation tensors
, Article International Journal of Solids and Structures ; Volume 44, Issue 22-23 , 2007 , Pages 7457-7467 ; 00207683 (ISSN) ; Naghdabadi, R ; Sharif University of Technology
2007
Abstract
In this paper some expressions for stresses conjugate to two-point deformation tensors are derived. These expressions are offered in both the component and basis-free forms. Although, the material time rate of a two-point deformation tensor is not an objective quantity, the stress tensor conjugate to it may be determined. The component-form expressions are obtained by using the notion of conjugacy together with the objectivity of the stress power. The component-form expressions are then extended to a unified basis-free form, using a theorem established for this purpose. The specific results are provided for all different cases of distinct and coalescent principal stretches in a...
Introducing a Set of Material Strain Measures in Non-Linear Kinematics of Micropolar Continuum Mechanics and Determining their Time Rates
, M.Sc. Thesis Sharif University of Technology ; Asghari, Mohsen (Supervisor)
Abstract
The concept of generalized strains is a well-established subject in the classical continuum mechanics. The characteristics and various applications of the generalized strains have been the point of interest of many researchers in the classical continuum mechanics. The aim of this thesis is the introduction of generalized strains in the micropolar theory, as a non-classical continuum theory. A set of generalized strains is suggested for the deformation of macro-elements. Moreover, a set of generalized strains is proposed for the micro-structures. Since the rate of strains possesses a significant importance in the constitutive equations of nonlinear analysis of solids, expressions for the rate...
Formulation for Analyzing of the Functionally Graded Kirchhoff Plate Based on the Modified Couple Stress Theory
, M.Sc. Thesis Sharif University of Technology ; Asghari, Mohsen (Supervisor)
Abstract
In this project, a size-dependent formulation is presented for mechanical analyses of inhomogeneous micro-plates based on the modified couple stress theory. The modified couple stress theory as a non-classical continuum theory has the ability to consider the small size effects in the mechanical behavior of the structures.The material properties are supposed arbitrarily to vary through the thickness of the plate. The governing differential equations of motion are derived for functionally graded plates utilizing variational approach. Based on the derived formulation, the static and free-vibration behaviors as well as buckling analysis of a rectangular functionally graded micro-plate are...