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Sintering characterizations of Ag-nano film on silicon substrate
, Article Advanced Materials Research ; Volume 829 , 2014 , Pages 342-346 ; ISSN: 10226680 ; ISBN: 9783037859070 ; Akbari, J ; Movahhedi, M. R ; Alemohammad, H ; Sharif University of Technology
Abstract
Nowadays, thin films have many applications in every field. So, in order to improve the performance of thin film devices, it is necessary to characterize their mechanical as well as electrical properties. In this research work we focus on the development of a model for the analysis of the mechanical and electrical properties of silver nanoparticles deposited on silicon substrates. The model consists of inter-particle diffusion modeling and finite element analysis. In this study, through the simulation of the sintering process, it is shown that how the geometry, density, and electrical resistance of the thin film layer are changed with sintering conditions. The model is also used to...
Electrophoretic deposition of Ni/SiO2 nanocomposite coating: Fabrication process and tribological and corrosion properties
, Article Journal of Nano Research ; Volume 26 , 6 January , 2014 , Pages 45-51 ; ISSN: 16625250 ; Ghorbani, M ; Sharif University of Technology
Abstract
To the best of our knowledge, this work presents the first successful effort to fabricate and study nanostructured Ni-based composite coatings using the electrophoretic deposition method with nanostructured SiO2 particles. In this work, Ni/SiO2 nanoparticle composite coatings were prepared by electrophoretic deposition (EPD) [1] and their hardness, wear and corrosion resistances [2] were examined. After studying the morphology of the coatings and finding the optimum conditions for uniform coating, in order to improve the mechanical properties as well as resistance to corrosion, sintering was performed. The Ni/SiO2 nanocomposite coatings show excellent hardness (∼376 HV), reduced Young's...
Investigation of mechanical properties, antibacterial features, and water vapor permeability of polyvinyl alcohol thin films reinforced by glutaraldehyde and multiwalled carbon nanotube
, Article Polymer Composites ; Vol. 35,Issue. 9 , 2014 , pp. 1736-1743 ; ISSN: 1548-0569 ; Kavoosi, G ; Mohammad Ali Dadfar, S ; Sharif University of Technology
Abstract
Polyvinyl alcohol (PVA) thin films were reinforced by glutaraldehyde and multiwalled carbon nanotubes (MWCNTs) and then mechanical, water solubility, water swelling, water uptake, water vapor permeability, and antibacterial properties of the films were examined. Cross-linking by glutaraldehyde or incorporation of MWCNT caused a significant increase in tensile strength, decrease in elongation at break, and increase in Young's modulus of the PVA films, while MWCNTs were more effective rather than that of glutaraldehyde. Cross-linking by glutaraldehyde or incorporation of MWCNT caused a significant decrease in water solubility, water swelling and water uptake, with a similar manner....
Comparison of wellbore stability of UBD in the case of laser drilling and conventional operation
, Article 76th European Association of Geoscientists and Engineers Conference and Exhibition 2014: Experience the Energy - Incorporating SPE EUROPEC 2014 ; 2014 , Pages 1736-1740 ; ISBN: 9781632666949 ; Nakhaee, A ; Koohian, A ; Irawan, S ; Habibpour, M ; Shahvar, M ; Sharif University of Technology
Abstract
In recent years, growing interest in underbalanced drilling has resulted in the rapid development of its associated equipment technology, practices, and procedures. Underbalanced drilling is used to avoid lost circulation, formation damage, and decreasing weight on bit. However, the risk of wellbore collapse due to lake of hydrostatic mud pressure is high; therefore, using good geo-mechanical model may avoid wellbore instability problems. In order to evaluate the potential for wellbore instability, it is necessary to use an elastoplastic model to compute the stresses and strains around the bore hole. Furthermore, it should be mentioned that the laser drilling process depends extremely on the...
Free vibrations of single walled carbon peapods
, Article Physica E: Low-Dimensional Systems and Nanostructures ; Vol. 56 , February , 2014 , pp. 410-413 ; Hojjati, M ; Rahmanian, M ; Sharif University of Technology
Abstract
In this paper the free vibration of single walled carbon nanopeapods encapsulating C60 molecules is considered. The nanopeapod is embedded in an elastic medium and clamped at both ends. The Euler-Bernoulli beam model is used for the carbon nanotube and the C60 molecules are considered as lumped masses attached to the beam. Based on the nonlocal elasticity theory the governing equation of motion is derived and the resonance frequencies of the nanopeapod are obtained. The effects of small scale, foundation stiffness and ratio of the fullerenes' mass to the nanotube's mass on the frequencies are studied and some conclusions are drawn
Dynamic instability of cantilevered composite pipe conveying flow with an end nozzle
, Article 21st International Congress on Sound and Vibration 2014, ICSV 2014 ; Vol. 4, issue , 13- 17 July , 2014 , pp. 3564-3571 ; ISBN: 9781634392389 ; Abtahi, H ; Haddadpour, H ; Sharif University of Technology
Abstract
In this paper, the instability of cantilevered horizontal composite pipes is investigated. To this aim, the lateral flow forces are modelled as a distributed lateral force and the nozzle effect is modelled as a compressive axial follower force and a concentrated end mass. The coupled bending-torsional equations of motion are derived using Hamilton's principal and Galerkin method. In order to obtain the stability margin of the pipe, the standard Eigen value problem is solved. Finally, effects of elastic coupling parameter and nozzle aspect ratio are considered on the stability margin of the pipe and some conclusions are drawn
Investigation on the effect of mold constraints and cooling rate on residual stress during the sand-casting process of 1086 steel by employing a thermomechanical model
, Article Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science ; Vol. 45, issue. 3 , 2014 , pp. 1157-1169 ; ISSN: 1073-5615 ; Davami, P ; Varahram, N ; Shabani, M. O ; Sharif University of Technology
Abstract
In this study, the effects of mold constraints and cooling rate on residual stress were analyzed during the shaped casting process. For this purpose, an H-shaped sample was designed in which the contraction of its middle portion is highly restricted by the mold during the cooling process. The effects of an increasing cooling rate combined with mold constraints were analyzed by reducing the thickness of the middle portion in the second sample. A three-dimensional coupled temperature-displacement analysis was performed in finite-element code ABAQUS to simulate residual stress distribution, and then numerical results were verified by the hole-drilling strain-gauge method. It was concluded that...
Wedge disclinations in the shell of a core-shell nanowire within the surface/interface elasticity
, Article Mechanics of Materials ; Vol. 68, Issue , 2014 , pp. 45-63 ; ISSN: 01676636 ; Gutkin, M. Y ; Shodja, H. M ; Sharif University of Technology
Abstract
The elastic behaviors of a two-axes dipole of wedge disclinations and an individual wedge disclination located inside the shell of a free standing core-shell nanowire is studied within the surface/interface elasticity theory. The corresponding boundary value problem is solved using complex potential functions, defined through modeling the disclination dipole by two finite walls of infinitesimal edge dislocations. The stress field, disclination strain energies and image forces acting on the disclinations, are calculated and studied in detail. It is shown that the stresses are rather inhomogeneous across the nanowire cross section, change their signs and reach local maxima and minima far from...
Polysilicon nano-beam model based on modified couple stress and Eringen's nonlocal elasticity theories
, Article Physica E: Low-Dimensional Systems and Nanostructures ; Vol. 63, issue , 2014 , p. 223-228 ; Pishkenari, H. N ; Yousefi-Koma, A ; Hoorzad, H ; Sharif University of Technology
Abstract
In recent years, extensive experiments have shown that classical continuum theory cannot predict the behavior of mechanical microstructures with small size. To accurately design and analyze micro- and nano-electro-mechanical systems, size-dependent continuum theories should be used. These theories model micro- and nano-electro-mechanical systems with higher accuracy because they include size-dependent parameters. In this paper, polysilicon nano-beam is modeled using modified couple stress and Eringen's nonlocal elasticity theories. First, partial differential equations governing the vibration of nano-beams are converted to a one D.O.F. differential equations using Galerkin method, resulting...
Rheology of interfacial layers
, Article Current Opinion in Colloid and Interface Science ; Vol. 19, issue. 6 , 2014 , pp. 514-519 ; ISSN: 13590294 ; Lotfi, M ; Kragel, J ; Javadi, A ; Bastani, D ; Miller, R ; Sharif University of Technology
Abstract
Dilational and shear viscoelasticities are important properties of interfacial layers. These quantities are particularly relevant in all systems which contain a huge internal interfacial area such as foams and emulsions. Therefore, also the 3D rheological behavior of foams or emulsions studied by respective methods is superimposed by the 2D interfacial rheology.We report on recent developments in dilational and shear rheology from an experimental point of view as well as discuss the state of the art of the underlying theories. Examples of most relevant experiments are also presented and discussed. Although not yet extensively investigated, the links between bulk rheology of foams and...
Hub location problem considering an elastic demand
, Article CIE 2014 - 44th International Conference on Computers and Industrial Engineering and IMSS 2014 - 9th International Symposium on Intelligent Manufacturing and Service Systems, Joint International Symposium on "The Social Impacts of Developments in Information, Manufacturing and Service Systems" - Proceedings ; 2014 , pp. 581-588 ; Akbari Jokar, M. R ; Sharif University of Technology
Abstract
In most hub location problem in the literature, the demand is independent of the market share. However, especially about the services and products which are not essential, this assumption does not mirror the reality. Considering the elastic demand increases the complexity and solution of the problem. The elasticity of demand depends on the utility of available hub. For simplicity, we assume that the utility of hub nodes are additive. Utility of the nodes is based on the attraction of the facility on that node and also the decay function of distance. In this paper we propose a new model for hub location problem in an airline industry with elastic demand. In this problem, passengers use hubs...
Nonlocal and strain gradient based model for electrostatically actuated silicon nano-beams
, Article Microsystem Technologies ; Vol. 21, Issue 2 , 2014 , pp. 457-464 ; Online ISSN: 1432-1858 ; Yousefi-Koma, A ; Pishkenari, H. N ; Sharif University of Technology
Abstract
Conventional continuum theory does not account for contributions from length scale effects which are important in modeling of nano-beams. Failure to include size-dependent contributions can lead to underestimates of deflection, stresses, and pull-in voltage of electrostatic actuated micro and nano-beams. This research aims to use nonlocal and strain gradient elasticity theories to study the static behavior of electrically actuated micro- and nano-beams. To solve the boundary value nonlinear differential equations, analogue equation and Gauss–Seidel iteration methods are used. Both clamped-free and clamped–clamped micro- and nano-beams under electrostatical actuation are considered where...
Strain gradient thermoelasticity of functionally graded cylinders
, Article Scientia Iranica ; Volume 21, Issue 4 , 2014 , Pages 1415-1423 ; ISSN: 10263098 ; Baghani, M ; Naghdabadi, R ; Sharif University of Technology
Abstract
In this paper, strain gradient thermo-elasticity formulation for axisymmetric Functionally Graded (FG) thick-walled cylinders is presented. For this purpose, the elastic strain energy density function is considered to be a function of gradient of strain tensor in addition to the strain tensor. The material properties are assumed to vary according to a power law in radial direction. Using the constitutive equations and equation of equilibrium in the cylindrical coordinates, a fourth order non-homogenous governing equation for thermo-elastic analysis of thick-walled FG cylinders subjected to thermal and mechanical loadings is obtained and solved numerically. Results show that the intrinsic...
A study on a grade-one type of hypo-elastic models
, Article ASME 2014 12th Biennial Conference on Engineering Systems Design and Analysis, ESDA 2014 ; Vol. 1 , 2014 ; Asghari, M ; Sharif University of Technology
Abstract
In Hypo-elastic constitutive models an objective rate of the Cauchy stress tensor is expressed in terms of the current state of the stress and the deformation rate tensor D in a way that the dependency on the latter is a homogeneously linear one. In this work, a type of grade-one hypo-elastic models (i.e. models with linear dependency of the hypo-elasticity tensor on the stress) is considered for isotropic materials based on the objective corotational rates of stress. A positive real parameter denoted by n is involved in the considered type. Different values can be selected for this parameter, each selection leads to a specific model within the class of grade-one hypo-elasticity. The spin of...
Influence of fines content and type on the small-strain shear modulus of sand
, Article Scientia Iranica ; Vol. 21, issue. 4 , 2014 , p. 1281-1296 ; Ahmadi, M. M ; Sharif University of Technology
Abstract
The small-strain shear modulus, Go, is an important fundamental soil property. Although many studies have been conducted on this property for clean sands and pure clays, small-strain behavior for mixtures of sand and fines has been less addressed. This paper presents the results of a comprehensive laboratory study on G0 value of sand containing various amounts of different fines. To this aim, bender elements were integrated into a conventional triaxial apparatus, and shear wave velocity was measured on samples of sand with different amounts of highly-plastic, medium-plastic, low-plastic, or non-plastic fines at different void ratios. Measuring the shear wave velocity and thus...
Analytical Solutions of Actin-Retrograde-Flow in a Circular Stationary Cell: A Mechanical Point of View
, Article Bulletin of Mathematical Biology ; Vol. 76, issue. 3 , March , 2014 , p. 744-760 ; 00928240 ; Firoozabadi, B ; Saidi, M. S ; Sharif University of Technology
Abstract
The network of actin filaments in the lamellipodium (LP) of stationary and migrating cells flows in a retrograde direction, from the membrane periphery toward the cell nucleus. We have theoretically studied this phenomenon in the circular stationary (fully spread) cells. Adopting a continuum view on the LP actin network, new closed-form solutions are provided for the actin-retrograde-flow (ARF) in a polar coordinate system. Due to discrepancy in the mechanical models of the actin network in the ARF regime, solutions are provided for both assumptions of solid and fluid behavior. Other involved phenomena, including polymerizing machine at the membrane periphery, cytosol drag, adhesion...
Comparison of the effects of different implant apical designs on the magnitude and distribution of stress and strain in bone: A finite element analysis study
, Article Journal of Long-Term Effects of Medical Implants ; Vol. 24, issue. 2-3 , 2014 , p. 109-120 ; Lafzi, A ; Raoofi, S ; Khademi, M ; Amid, R ; Movahhedy, M. R ; Torabi, H ; Sharif University of Technology
Abstract
Objectives: The aim of this study was to investigate the effects of implant design on the apex area and on stress and stress patterns within surrounding bone. Methods: Three commercially available implants with the same diameter (3.5 mm), same length (10-11 mm), and same complement abutment were selected for modeling as follows: (1) flat apical design with light tapering degree, (2) dome-shaped apical design with light tapering, and (3) flat apical design with intense tapering in one-third of the apical area. According to human cone-beam computed tomography (CBCT), the bone was modeled using a cortical thickness of 2 mm and cancellous bone. Forces of 100 N and 300 N in the vertical and 15°...
Size-dependent generalized thermoelasticity model for Timoshenko micro-beams based on strain gradient and non-Fourier heat conduction theories
, Article Composite Structures ; Vol. 116, issue. 1 , July , 2014 , p. 595-611 ; Molaei Najafabadi, M ; Reddy, J. N ; Sharif University of Technology
Abstract
The governing equations of coupled thermoelasticity of Timoshenko micro-beams are developed based on the generalized thermoelastic theory and non-Fourier heat conduction model. Such problems may arise in MEMS such as micro-pumps as well as micro-sensors. The present model is on the basis of non-classical continuum theory and non-Fourier heat conduction model which has capability of capturing the size-effect in micro-scaled structures. Governing equations and both classical and non-classical boundary conditions of motion are obtained using the variational approach. As the case study, the present model is utilized for the simply supported micro-beams subjected to a constant impulsive force per...
Effective mechanical properties of unidirectional composites in the presence of imperfect interface
, Article Archive of Applied Mechanics ; Vol. 84, issue. 6 , June , 2014 , pp. 807-819 ; Print ISSN: 0939-1533 ; Toozandehjani, H ; Sharif University of Technology
Abstract
In this paper, the equivalent inclusion method is implemented to estimate the effective mechanical properties of unidirectional composites in the presence of an imperfect interface. For this purpose, a representative volume element containing three constituents, a matrix, and interface layer, and a fiber component, is considered. A periodic eigenstrain defined in terms of Fourier series is then employed to homogenize non-dilute multi-phase composites. In order to take into account the interphase imperfection effects on mechanical properties of composites, a stiffness parameter in terms of a matrix and interphase elastic modulus is introduced. Consistency conditions are also modified...
Free-edge stresses in general cross-ply laminates
, Article Scientia Iranica ; Vol. 21, issue. 2 , April , 2014 , p. 387-402 ; Sharif University of Technology
Abstract
Within elasticity theory, the reduced form of a displacement field is obtained for general cross-ply composite laminates subjected to a bending moment. The firstorder shear deformation theory of plates and Reddy's layerwise theory are then utilized to determine the global deformation parameters and the local deformation parameters appearing in the displacement fields, respectively. For a special set of boundary conditions an elasticity solution is developed to verify the validity and accuracy of the layerwise theory. Finally, various numerical results are presented within the layerwise theory for edge-effect problems of several cross-ply laminates under the bending moment. The results...