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    Finite strain endochronic plasticity with reference to metal tube under torsion

    , Article Engineering Computations (Swansea, Wales) ; Volume 20, Issue 3-4 , 2003 , Pages 248-273 ; 02644401 (ISSN) Khoei, A. R ; Bakhshiani, A ; Mofid, M ; Sharif University of Technology
    Emerald Group Publishing Ltd  2003
    Abstract
    In this paper, a new rate type endochronic constitutive model is introduced to describe deformations in the finite strain range. A new material dependent objective rate of Cauchy stress is suggested based on the general form of spin tensors, defining objective stress rates. The endochronic constitutive equations are extended using the concept of corotational stress rates and additive decomposition of deformation rate. The constitutive relations are specialized for thin-walled tubes under torsion and a procedure for solving the ordinary differential equations for cases of simple and pure torsion is developed. The axial effects for various materials, subjected to simple and pure torsion, are... 

    Intrinsic expressions for arbitrary stress tensors conjugate to general strain tensors

    , Article Scientia Iranica ; Volume 14, Issue 5 , 2007 , Pages 486-493 ; 10263098 (ISSN) Sohrabpour, S ; Naghdabadi, R ; Asghari, M ; Sharif University of Technology
    Sharif University of Technology  2007
    Abstract
    In this paper, a unified explicit tensorial relation is sought between two stress tensors conjugate to arbitrary and general Hill strains. The approach used for deriving the tensorial relation is based on the eigenprojection method. The result is, indeed, a generalization of the relations that were derived by Farahani and Naghadabadi [1] in 2003 from a component to intrinsic form. The result is unified in the sense that it is valid for all cases of distinct and coalescent principal stretches. Also, in the case of three dimensional Euclidean inner product space, using the derived unified relation, some expressions for the conjugate stress tensors are presented. © Sharif University of... 

    An inverse approach to determination of residual stresses induced by shot peening in round bars

    , Article International Journal of Mechanical Sciences ; Volume 51, Issue 9-10 , 2009 , Pages 726-731 ; 00207403 (ISSN) Farrahi, G. H ; Faghidian, S. A ; Smith, D. J ; Sharif University of Technology
    2009
    Abstract
    In this paper an analysis is presented to determine the distribution of a residual stress field from a limited incomplete set of measurements obtained from shot-peened round steel bars. Using an Airy stress function as the primary unknown the axisymmetric stress equations are solved directly. In this new method there exists the flexibility to impose physical conditions that govern the behavior of residual stress to achieve a meaningful complete stress field. This new method aims to achieve the best agreement between the model prediction and limited measured stress components in the sense of least squares approximation. The power of this new method is demonstrated by analyzing experimental... 

    Effect of initial surface treatment on shot peening residual stress field: analytical approach with experimental verification

    , Article International Journal of Mechanical Sciences ; Volume 137 , 2018 , Pages 171-181 ; 00207403 (ISSN) Sherafatnia, K ; Farrahi, G. H ; Mahmoudi, A. H ; Sharif University of Technology
    Elsevier Ltd  2018
    Abstract
    Shot peening is the most common surface treatment employed to enhance the fatigue performance of structural metallic materials and often carried out after other surface treatments. This paper mainly focuses on the effects of initial conditions of surface such as initial stress filed and hardness profile on shot peening residual stress field. The residual stress distribution induced by shot peening is obtained using Hertzian contact theory and elastic–plastic evaluation after yielding occurred during impingement and rebound of shots. Elastic plastic calculations are performed using different hardening models considering Bauschinger effect. The present model is able to predict redistribution... 

    Material growth and remodeling formulation based on the finite couple stress theory

    , Article International Journal of Non-Linear Mechanics ; Volume 121 , 2020 Javadi, M ; Asghari, M ; Sohrabpour, S ; Sharif University of Technology
    Elsevier Ltd  2020
    Abstract
    The mathematical formulation for material growth and remodeling processes in finite deformation is developed based on the couple stress theory. The generalized continuum mechanics of couple stress theory is capable of capturing small-scale cellular effects and of modeling mass flux in these processes. The frame-indifferent balance equations of mass, linear and angular momentums, as well as internal energy together with the entropy inequality are first introduced in the presence of the mass flux based on the finite couple-stress theory. Then, within the framework of material uniformity the Eshelby and Mandel stress tensors as driving or configurational forces for local rearrangement of the... 

    Effects of vertical and pinch rolling on residual stress distributions in wire and arc additively manufactured components

    , Article Journal of Materials Engineering and Performance ; Volume 29, Issue 4 , 2020 , Pages 2073-2084 Tangestani, R ; Farrahi, G. H ; Shishegar, M ; Pourbagher Aghchehkandi, B ; Ganguly, S ; Mehmanparast, A ; Sharif University of Technology
    Springer  2020
    Abstract
    Residual stresses are inherent in parts manufactured using the wire + arc additive manufacturing (WAAM) technique, resulting in unpredictable mechanical response and structural integrity (Colegrove et al.: J Mater Process Technol 213:1782-1791, 2013). An effective post-processing technique, which enhances the mechanical properties of WAAM parts, is rolling. This study investigates the vertical and pinch rolling effects on residual stress distribution in WAAM components. Initially, a WAAM model was created using a thermo-mechanical finite element modelling approach and validated against the experimental results. Subsequent to the validation of the model, the effect of the main parameters... 

    Effect of source strength on dislocation pileups in the presence of stress gradients

    , Article Philosophical Magazine ; Volume 95, Issue 20 , 2015 , Pages 2175-2197 ; 14786435 (ISSN) Zamani, Z ; Shishvan, S. S ; Assempour, A ; Sharif University of Technology
    Abstract
    The behaviour of a dislocation pileup with a finite-strength source is investigated in the presence of various stress gradients within a continuum model where a free-dislocation region exists around the source. Expressions for dislocation density and stress field within the pileup are derived for the situation where there are first and second spatial gradients in applied stress. For a pileup configuration under an applied stress, yielding occurs when the force acting on the leading dislocations at the pileup tips reaches the obstacle strength, and at the same time, it is required that the source be at the threshold stress for dislocation production. A numerical methodology is presented to... 

    An embedded couple stress micro-/nano-obstacle with micro-inertia incident upon by SH-waves

    , Article Acta Mechanica ; Volume 229, Issue 8 , 2018 , Pages 3333-3354 ; 00015970 (ISSN) Shodja, H. M ; Ghafarollahi, A ; Sharif University of Technology
    Springer-Verlag Wien  2018
    Abstract
    An elliptic micro-/nano-obstacle bonded to an infinite body incident upon by SH-waves, where both domains are couple stress media with micro-inertia, is of major concern. The formulation of this problem in the mathematical framework of couple stress elasticity with micro-inertia leads to angular and radial Mathieu differential equations which are solved analytically. These equations carry two characteristic lengths which are peculiar to the discrete nature of each domain enabling the capture of size effect, dispersion phenomenon, as well as the enhancement of the accuracy of the results. For verification, the ratio of the semi-axis of the elliptic obstacle is set equal to 1, and the result... 

    Stress analysis in symmetric composite laminates subjected to shearing loads

    , Article International Journal of Mechanical Sciences ; Volume 75 , 2013 , Pages 16-25 ; 00207403 (ISSN) Mousanezhad viyand, D ; Yazdani Sarvestani, H ; Nosier, A ; Sharif University of Technology
    2013
    Abstract
    In the present study, an analytical solution is proposed to determine the interlaminar stresses in long symmetric laminated composite plates subjected to shearing loads. An improved first-order shear deformation theory (IFSDT) and a simplified IFSDT (SIFSDT) are utilized to calculate the unknown constants appearing in the reduced elasticity displacement field which actually demonstrate the global deformations of the plate. Then the numerical values of the interlaminar normal and shear stresses are established through the laminates by using Reddy's layerwise theory. Finally, several numerical examples are presented to study the interlaminar stresses in the interfaces of the layers and through... 

    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) Asghari, M ; 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  

    Vibration effect on electrical resistance fluctuations in electrical connectors

    , Article Engineering Solid Mechanics ; Volume 6, Issue 4 , 2018 , Pages 299-306 ; 22918744 (ISSN) Behzad, M ; Darvish Gohari, H ; Mohammadi Dehabadi, A. A ; Sharif University of Technology
    Growing Science  2018
    Abstract
    Proper functioning of electrical connectors used in high oscillation is of great importance. Vibrations in connector pins cause stress and electrical resistance variations in the contact surface. In the present paper, the impacts of vibrational loads on electrical connectors is being modeled using the finite element method, and the electrical resistance oscillations of the connectors will be examined. Ultimately, the parameters affecting the electrical resistance oscillations of contacts will be determined and their relations with oscillations in electrical resistance are specified as well. © 2018 by the authors; licensee Growing Science, Canada, 2018 Growing Science Ltd. All rights reserved... 

    The study of the weibel electromagnetic instability growth rate in the presence of the body stress

    , Article Contributions to Plasma Physics ; Volume 59, Issue 7 , 2019 ; 08631042 (ISSN) Amininasab, S ; Sadighi Bonabi, R ; Khodadadi Azadboni, F ; Sharif University of Technology
    Wiley-VCH Verlag  2019
    Abstract
    Body stress flow can be expected in the fast ignition imploding of the inertial fusion process that strongly damps small-scale velocity structures. The Weibel instability is one of the plasma instabilities that require anisotropy in the distribution function. The body stress effect was neglected in the calculation of the Weibel instability growth rate. In this article, the propagation condition of impinging waves and the growing modes of the Weibel instability on the plasma density gradient of the fuel fusion with the body stress flow are investigated. Calculations show that the minimum value of the body stress rate threshold in the linear polarization is about 2.96 times greater than that... 

    The study of the weibel electromagnetic instability growth rate in the presence of the body stress

    , Article Contributions to Plasma Physics ; Volume 59, Issue 7 , 2019 ; 08631042 (ISSN) Amininasab, S ; Sadighi Bonabi, R ; Khodadadi Azadboni, F ; Sharif University of Technology
    Wiley-VCH Verlag  2019
    Abstract
    Body stress flow can be expected in the fast ignition imploding of the inertial fusion process that strongly damps small-scale velocity structures. The Weibel instability is one of the plasma instabilities that require anisotropy in the distribution function. The body stress effect was neglected in the calculation of the Weibel instability growth rate. In this article, the propagation condition of impinging waves and the growing modes of the Weibel instability on the plasma density gradient of the fuel fusion with the body stress flow are investigated. Calculations show that the minimum value of the body stress rate threshold in the linear polarization is about 2.96 times greater than that... 

    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) Sharghi Moshtaghin, R ; 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... 

    Trace anomaly and backreaction of the dynamical Casimir effect

    , Article General Relativity and Gravitation ; Volume 35, Issue 12 , 2003 , Pages 2279-2286 ; 00017701 (ISSN) Setare, M. R ; Sharif University of Technology
    2003
    Abstract
    The Casimir energy for massless scalar field which satisfies periodic boundary conditions in two-dimensional domain wall background is calculated by making use of general properties of renormalized stress-tensor. The line element of domain wall is time dependent, the trace anomaly which is the nonvanishing Tμμ for a conformally invariant field after renormalization, represent the back reaction of the dynamical Casimir effect  

    Prediction of microstructural changes during hot rod rolling

    , Article International Journal of Machine Tools and Manufacture ; Volume 43, Issue 14 , 2003 , Pages 1487-1495 ; 08906955 (ISSN) Serajzadeh, S ; Sharif University of Technology
    2003
    Abstract
    In this study, a mathematical model is presented for predicting temperature and velocity fields together with dynamic and static microstructural changes during hot rod rolling utilizing a finite element model. For doing so, heat transfer and plasticity equations are coupled with the additivity rule and Avrami rate-equation to consider the dynamic and static microstructural changes as well as to evaluate the effects of temperature and strain rate variations on flow stress of rolling metal. To verify the results of the employed model, a comparison is made between the measured surface temperature during rod rolling and the predicted data that confirms the validity of the model. © 2003 Elsevier... 

    On a new approach for finding the kern of a beam section

    , Article Engineering Structures ; Volume 23, Issue 9 , 2001 , Pages 1080-1084 ; 01410296 (ISSN) Mofid, M ; Shadnam, M. R ; McCabe, S. L ; Sharif University of Technology
    2001
    Abstract
    A new approach is presented that can be used to determine the kern of a general arbitrary section with any shape and conditions. The method is simple, practical and powerful, and is based on elementary calculus. Geometries containing curved boundaries and arbitrary shapes can be handled easily with the analytical equations presented, while the numerically specified shape of any other cross-section can also be analyzed by using a numerical form of the exact governing equations developed. The correctness of the results has been ascertained by comparison with analytical solutions, as well as with examples presented in the literature, and very good agreement has been achieved. © 2001 Elsevier... 

    Conjugate stresses of the Seth-Hill strain tensors

    , Article International Journal of Solids and Structures ; Volume 37, Issue 38 , 2000 , Pages 5247-5255 ; 00207683 (ISSN) Farahani, K ; Naghdabadi, R ; Sharif University of Technology
    Elsevier Ltd  2000
    Abstract
    In this paper, conjugate stresses of the Seth-Hill strain measures are treated by means of the definition of energy conjugacy and Hill's principal axis method. This approach results in relations between components of two different conjugate stress tensors. The results are valid for distinct as well as coalescent principal stretches. Illustrative examples are solved to demonstrate the simplicity and usefulness of the derived relations between conjugate stress tensors. © 2000 Elsevier Science Ltd  

    Interaction of two nearby CNTs/nanovoids embedded in a metal matrix using modified nonlocal elasticity

    , Article Composites Part B: Engineering ; Volume 43, Issue 8 , December , 2012 , Pages 3167-3181 ; 13598368 (ISSN) Niaki, S. A ; Naghdabadi, R ; Sharif University of Technology
    2012
    Abstract
    Interaction of Carbon Nanotubes (CNTs) and nanovoids embedded in a metal matrix is studied comparatively. For this purpose, two nearby CNTs/nanovoids are modeled as two similar cylindrical inclusions/holes in an infinite matrix. The nonlocal stresses around the CNTs/nanovoids are obtained by applying the integral constitutive equation of the nonlocal elasticity to the stresses from the complex stress potential method. Also, in order to bring different nonlocality effects of dissimilar media into account, the influence function of the nonlocal elasticity is modified. Effects of the CNTs/nanovoids size and distance as well as far-field loading ratio on the stress state in the matrix are... 

    Numerical simulation of induction hardening of torsion bar

    , Article Proceedings of the World Congress on Engineering 2011, WCE 2011, 6 July 2011 through 8 July 2011 ; Volume 3 , July , 2011 , Pages 2080-2083 ; 9789881925152 (ISBN) Norouznejad, H ; Farrahi, G. H ; Sharif University of Technology
    2011
    Abstract
    In order to improve the fatigue performance of torsion bar, induction surface hardening is performed. The aim of the present study is to compare the experimental residual stress fields measured by X-ray diffraction with those predicted from finite element modeling of the whole induction surface hardening process. Temperature and residual stress distributions are affected by the component geometry, the material behavior and the induction treatment parameters. Based on the residual stress distribution and the fatigue loading, cracks can nucleate from the surface or below the hardened layer. Therefore, it is very important to determine the residual stress distribution and optimize the process,...