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The characteristics of serrated flow in superalloy IN738LC
, Article Materials Science and Engineering A ; Volume 486, Issue 1-2 , 2008 , Pages 376-380 ; 09215093 (ISSN) ; Asgari, S ; Sharif University of Technology
2008
Abstract
Serrated flow was investigated in superalloy IN738LC, a nickel-base γ′ age-hardened alloy. In this material serrated flow appeared between 350 and 450 °C and strain rate of (8.77 × 10-5 to 8.77 × 10-3) s-1. Activation energy for this process was calculated to be 0.69-0.86 eV which is in good agreement with the values reported for similar alloys. Results show that the diffusion rate of substitutional solute atoms at this temperature range is too low to cause this effect. This suggests that the interaction of solute atoms and moving dislocation is responsible for the observed serrated flow in this alloy. © 2007 Elsevier B.V. All rights reserved
The influence of thermal exposure on the γ′ precipitates characteristics and tensile behavior of superalloy IN-738LC
, Article Journal of Materials Processing Technology ; Volume 147, Issue 3 , 2004 , Pages 343-350 ; 09240136 (ISSN) ; Asgari, S ; Sharif University of Technology
2004
Abstract
The effects of long term aging on γ′ size and distribution and its influence on tensile behavior of superalloy IN-738LC at room and in elevated temperatures were investigated. Samples were aged isothermally at 850 °C for different times up to 3000 h and tensile tests were performed on samples in both standard heat treatment (SHT) and aged conditions. For samples in SHT condition yield stress (σy) was independent of tensile temperature up to 550 °C, after which it decreased slightly and then reached a maximum at 650 °C. Also minimum ductility was observed in this temperature. For aged samples, results showed an initial decrease of σy up to 550 °C, followed by a subsequent increase in σy...
Growth kinetics of γ′ precipitates in superalloy IN-738LC during long term aging
, Article Materials and Design ; Volume 24, Issue 5 , 2003 , Pages 325-330 ; 02641275 (ISSN) ; Asgari, S ; Sharif University of Technology
Elsevier Ltd
2003
Abstract
In this research, results obtained on the growth kinetics of γ′ precipitates in superalloy IN-738LC are presented. It was found that when the coarsening of primary and secondary γ′ are considered together, the overall kinetic of coarsening followed a linear trend, as predicted by Lifshitz, Slyozov and Wagner (LSW) theory. However, when only the population of secondary γ′ was taken into account, growth rate for the secondary γ′ departed from the linear trend predicted by the theory. It is therefore suggested that the observed deviation of coarsening kinetics from linear behavior may be related to the short inter-particle distances in this system which caused elastic interaction energy to...
Effects of surface residual stress and surface elasticity on the overall yield surfaces of nanoporous materials with cylindrical nanovoids
, Article Mechanics of Materials ; Volume 51 , 2012 , Pages 74-87 ; 01676636 (ISSN) ; Naghdabadi, R ; Asghari, M ; Sharif University of Technology
Elsevier
2012
Abstract
Mechanical properties of a material near the surfaces and interfaces are different from those of the same material far from the surfaces/interfaces. The effect of this difference on the effective mechanical properties of heterogeneous materials becomes significant when the size of inhomogeneities is at the scale of nanometers. In this article, within a micromechanical framework, the effects of surface residual stress and surface elasticity are taken into account to obtain a macroscopic size-dependent yield function for nanoporous materials containing aligned cylindrical nanovoids. Based on the modified Hill's condition, the strains are decomposed into two parts, a part due to the external...
A study on the plastic properties of unidirectional nanocomposites with interface energy effects
, Article Acta Mechanica ; Volume 224, Issue 4 , 2013 , Pages 789-809 ; 00015970 (ISSN) ; Naghdabadi, R ; Asghari, M ; Sharif University of Technology
2013
Abstract
In this paper, for obtaining an overall size-dependent yield function for nanocomposites containing aligned cylindrical nanofibers, the effects of interface residual stress and interface elasticity are taken into account within a micromechanical framework. Toward this goal, the modified Hill's condition is used, and then, in order to consider effects of the interface residual stress, strains are decomposed into two parts, a part due to the external loadings and the other due to the interface residual stress. Next, utilizing the field fluctuation method, an overall yield function containing effective elastic constants of the material is derived and then simplified for practical loading...
On phase transformations in a Ni-based superalloy
, Article Philosophical Magazine ; Volume 93, Issue 10-12 , Mar , 2013 , Pages 1351-1370 ; 14786435 (ISSN) ; Sharghi Moshtaghin, R ; Sadeghahmadi, M ; Pirouz, P ; Sharif University of Technology
2013
Abstract
In this study, a particular nickel-based superalloy has been studied by transmission electron microscopy and the results are discussed in terms of phase transformations that may have taken place. The alloy has been found to consist of three major phases; a FCC γ phase containing a random distribution of nearly spherical γ′ - Ni3Al(Ti) - precipitates and elongated thin Ni3Ti(Ta) platelets with a hexagonal structure. The orientation relationships between the different phases have been determined; loss of coherency and possible occurrence of misfit-relieving interfacial dislocations are discussed and compared with experimental observations, and possible mechanisms of phase transformations are...
The effect of thermal exposure on the γ′ characteristics in a Ni-base superalloy
, Article Journal of Alloys and Compounds ; Volume 368, Issue 1-2 , 2004 , Pages 144-151 ; 09258388 (ISSN) ; Asgari, S ; Sharif University of Technology
2004
Abstract
In this investigation, changes in γ′ characteristics in superalloy IN-738LC during aging are presented. The SEM studies revealed that coarsening kinetics of γ′ follows a linear law at different aging time for different temperatures. Whereas when coarsening of secondary γ′ is studied, it was found that at the early stage of aging, volume fraction of secondary γ′ is high, leading to short inter-particle distances. In this condition interfacial energy is dominant and variation of [r3-r03] as a function of aging time is linear. As the coarsening proceeds, volume fraction of secondary γ′ decreases and elastic interaction energy becomes dominant. In such case a deviation in variation of [r3-r03]...
An analytical approach for buckling analysis of generally laminated conical shells under axial compression
, Article Acta Mechanica ; Volume 227, Issue 4 , 2016 , Pages 1181-1198 ; 00015970 (ISSN) ; Shakouri, M ; Kouchakzadeh, M. A ; Sharif University of Technology
Springer-Verlag Wien
2016
Abstract
In the present investigation, the buckling of generally laminated conical shells with various boundary conditions subjected to axial pressure is studied using an analytical approach. The governing equations are obtained using classical shell theory with Donnell assumptions in strain–deformation relations and the principle of minimum potential energy. The differential equations are solved using trigonometric functions in circumferential and power series in longitudinal directions. All types of boundary conditions can be applied in this method. The results are compared and validated with the results available in the literature, and good agreement is observed. Finally, the effects of the...
Analytical Approach for Buckling Analysis of Generally Laminated Conical Shells under Axial Compression
, M.Sc. Thesis Sharif University of Technology ; Kouchakzadeh, Mohammad Ali (Supervisor)
Abstract
In this thesis, buckling of truncated conical shells made of composite laminates with general lamination sequence is investigated. The conical shell is considered under axial compression with simply supported or clamped boundary condition. First, Donnel type nonlinear equations and boundary conditions for doubly curved shells are obtained using Hamilton principle. Second, using adjacent equilibrium criterion, the nonlinear equations was linearized then with defining lame parameters and curvature radius, the linear equations of conical shell was extracted. The power series and Galerkin method was used to solve differential equations. The obtained results are in good agreement with available...
Revitalizing CO2 photoreduction: fine-tuning electronic synergy in ultrathin g-C3N4 with amorphous (CoFeNiMnCu)S2 high-entropy sulfide nanoparticles for enhanced sustainability
, Article Chemical Engineering Journal ; Volume 496 , 2024 ; 13858947 (ISSN) ; Fayazi, D ; Kakavandi, B ; Giannakis, S ; Sharghi, M. R ; Han, N ; Bahadoran, A ; Sharif University of Technology
2024
Abstract
Sustainability is a key issue in developing stable and efficient catalysts for solar-catalyzed CO2 conversion. The concept of structural stabilization by quenching the Gibbs free energy, which is achieved by increasing the configurational entropy level of the system, introduced high-entropy materials. However, because alloying immiscible multimetallic atoms into a unit system is still an arduous process, the potential of high-entropy materials has not yet been fully exploited. Surprisingly, although metal sulfide photocatalysts have an enviable reputation for CO2 photoreduction (CO2-PR) owing to their optical/electronic merits and more negative redox potential than other materials, the...
Integration of adaptive neuro-fuzzy inference system, neural networks and geostatistical methods for fracture density modeling
, Article Oil and Gas Science and Technology ; Vol. 69, issue. 7 , 2014 , pp. 1143-1154 ; ISSN: 12944475 ; Kadkhodaie-Ilkhchi, A ; Sharghi, Y ; Ghaedi, M ; Sharif University of Technology
2014
Abstract
Image logs provide useful information for fracture study in naturally fractured reservoir. Fracture dip, azimuth, aperture and fracture density can be obtained from image logs and have great importance in naturally fractured reservoir characterization. Imaging all fractured parts of hydrocarbon reservoirs and interpreting the results is expensive and time consuming. In this study, an improved method to make a quantitative correlation between fracture densities obtained from image logs and conventional well log data by integration of different artificial intelligence systems was proposed. The proposed method combines the results of Adaptive Neuro-Fuzzy Inference System (ANFIS) and Neural...
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...
Engineering stable construction of MnCo2O4 yolk-in-double-shell amalgamated with bio-synthesized ZnMn2O4 nanoparticles for superior artificial CO2 reduction
, Article Journal of Materials Chemistry A ; Volume 11, Issue 36 , 2023 , Pages 19465-19482 ; 20507488 (ISSN) ; Roshan De Lile, J ; Hasanvandian, F ; Sharghi, M ; Kakavandi, B ; Mishra, Y. K ; Giannakis, S ; Rama Krishna, S ; Sharif University of Technology
Royal Society of Chemistry
2023
Abstract
Multi-shelled configurations of mixed bimetallic oxides, which are well-known candidates for CO2 photoreduction, were prepared via the calcination of rigid spheres of the self-template glycerate-assisted metal-organic structure. However, the fabrication of highly efficient, stable constructions is still a significant challenge. The effectiveness of this strategy is restricted by the questionable stability of the structure, which collapses under harsh calcination conditions. Herein, we focused our attention on manipulating the initial solvothermal reaction, through which MnCo2O4 yolk-in-double-shell hollow spheres (YDSHS-MCO) were engineered via the formation of two sequential yolk-shells,...
Unlocking the potential of V2O5 decorated on crossed g-C3N4 monolayers derived from synergistic bio-transformation of ZnMn2O4 for antibiotic photodegradation
, Article Journal of Materials Chemistry A ; Volume 12, Issue 24 , 2024 , Pages 14619-14635 ; 20507488 (ISSN) ; Ajinkya, N ; Sharghi, M ; Hasanvandian, F ; Wang, Y ; Chen, H ; Namvari, M ; Kakavandi, B ; Marsili, E ; Galluzzi, M ; Ramakrishna, S ; Sharif University of Technology
2024
Abstract
Although the physiochemical merits of g-C3N4-based photocatalysts have garnered increasing interest in the fields of energy and environmental science, insufficient layer detachment has created a gap between fundamental research and practical applications. To unlock the intrinsic potential of g-C3N4, a bio-transformation of the ZnMn2O4 ((6)ZM) gel was employed to introduce highly-ordered modulation caused by steric hindrance during melamine pyrolysis. Phytomediated (6)ZM reorganized traditional carbon nitride into crossed C3N4 (CCN) monolayers, simultaneously engineering an auspicious Z-schematic system ((6)ZM/CCN). Phytoconverted (6)ZM retained the crystalline-amorphous configuration for...
Network vulnerability analysis through vulnerability take-grant model (VTG)
, Article 7th International Conference on Information and Communications Security, ICICS 2005, Beijing, 10 December 2005 through 13 December 2005 ; Volume 3783 LNCS , 2005 , Pages 256-268 ; 03029743 (ISSN); 3540309349 (ISBN); 9783540309345 (ISBN) ; Sadoddin, R ; Jalili, R ; Zakeri, R ; Omidian, A. R ; Sharif University of Technology
2005
Abstract
Modeling and analysis of information system vulnerabilities helps us to predict possible attacks to networks using the network configuration and vulnerabilities information. As a fact, exploiting most of vulnerabilities result in access rights alteration. In this paper, we propose a new vulnerability analysis method based on the Take-Grant protection model. We extend the initial Take-Grant model to address the notion of vulnerabilities and introduce the vulnerabilities rewriting rules to specify how the protection state of the system can be changed by exploiting vulnerabilities. Our analysis is based on a bounded polynomial algorithm, which generates the closure of the Take-Grant graph...
Sequence dependence of the binding energy in chaperone-driven polymer translocation through a nanopore
, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 83, Issue 1 , January , 2011 ; 15393755 (ISSN) ; Ejtehadi, M. R ; Metzler, R ; Sharif University of Technology
2011
Abstract
We study the translocation of stiff polymers through a nanopore, driven by the chemical-potential gradient exerted by binding proteins (chaperones) on the trans side of the pore. Bound chaperones prevent backsliding through the pore and, therefore, partially rectify the polymer passage. We show that the sequence of chain monomers with different binding affinity for the chaperones significantly affects the translocation dynamics. In particular, we investigate the effect of the nearest-neighbor adjacency probability of the two monomer types. Depending on the magnitude of the involved binding energies, the translocation speed may either increase or decrease with the adjacency probability. We...
First passage time distribution of chaperone driven polymer translocation through a nanopore: Homopolymer and heteropolymer cases
, Article Journal of Chemical Physics ; Volume 135, Issue 24 , 2011 ; 00219606 (ISSN) ; Metzler, R ; Ejtehadi, M. R ; Sharif University of Technology
2011
Abstract
Combining the advection-diffusion equation approach with Monte Carlo simulations we study chaperone driven polymer translocation of a stiff polymer through a nanopore. We demonstrate that the probability density function of first passage times across the pore depends solely on the Péclet number, a dimensionless parameter comparing drift strength and diffusivity. Moreover it is shown that the characteristic exponent in the power-law dependence of the translocation time on the chain length, a function of the chaperone-polymer binding energy, the chaperone concentration, and the chain length, is also effectively determined by the Péclet number. We investigate the effect of the chaperone size on...
Reply: Abedpour, asgari, and tabar
, Article Physical Review Letters ; Volume 106, Issue 20 , 2011 ; 00319007 (ISSN) ; Asgari, R ; Tabar, M. R. R ; Sharif University of Technology
2011
Irreversibility in response to forces acting on graphene sheets
, Article Physical Review Letters ; Volume 104, Issue 19 , May , 2010 ; 00319007 (ISSN) ; Asgari, R ; Tabar, M. R. R ; Sharif University of Technology
2010
Abstract
The amount of rippling in graphene sheets is related to the interactions with the substrate or with the suspending structure. Here, we report on an irreversibility in the response to forces that act on suspended graphene sheets. This may explain why one always observes a ripple structure on suspended graphene. We show that a compression-relaxation mechanism produces static ripples on graphene sheets and determine a peculiar temperature Tc, such that for T
Analysis of design goals of cryptography algorithms based on different components
, Article Indonesian Journal of Electrical Engineering and Computer Science ; Volume 23, Issue 1 , 2021 , Pages 540-548 ; 25024752 (ISSN) ; Aref, M. R ; Khorshiddoust, R. R ; Sharif University of Technology
Institute of Advanced Engineering and Science
2021
Abstract
Cryptography algorithms are a fundamental part of a cryptographic system that is designed and implemented to increase information security. They are the center of attention of experts in the information technology domains. Although the cryptography algorithms are implemented to attain the goals such as confidentially, integrity, and authenticity of designing, but other matters that must be noticed by designers include speed, resource consumption, reliability, flexibility, usage type, and so on. For the useful allocation of hardware, software, and human resources, it is important to identify the role of each of the factors influencing the design of cryptographic algorithms to invest in the...