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Formulation for static behavior of the viscoelastic Euler-Bernoulli micro-beam based on the modified couple stress theory
, Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) ; Volume 9, Issue PARTS A AND B , 2012 , Pages 129-135 ; 9780791845257 (ISBN) ; Nikfar, M ; Ahmadian, M. T ; Sharif University of Technology
2012
Abstract
In this work an analytical solution is presented for a viscoelastic micro-beam based on the modified couple stress theory which is a non-classical theory in continuum mechanics. The modified couple stress theory has the ability to consider small size effects in micro-structures. It is strongly emphasized that without considering these effects in such structures the solution will be wrong and not suitable for designing systems in micro-scales. In this study correspondence principle is used for deriving constitutive equations for viscoelastic material based on the modified couple stress theory. Governing equilibrium equations are obtained by considering an element of micro-beam. Closedform...
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
Magnetic field effect on free vibration of smart rotary functionally graded nano/microplates: a comparative study on modified couple stress theory and nonlocal elasticity theory
, Article Journal of Intelligent Material Systems and Structures ; Volume 29, Issue 11 , 2018 , Pages 2492-2507 ; 1045389X (ISSN) ; Saeidi Googarchin, H ; Mahinzare, M ; Eftekhari, S. A ; Sharif University of Technology
SAGE Publications Ltd
2018
Abstract
In this article, free vibration behavior of a rotating nano/microcircular plate constructed from functionally graded magneto-elastic material is simulated with the first-order shear deformation theory. For the sake of comparison, the nonlocal elasticity theory and the modified couple stress theory are employed to implement the small size effect in the natural frequencies behavior of the nano/microcircular plate. The governing equations of motion for functionally graded magneto-elastic material nano/microcircular plates are derived based on Hamilton’s principle; comparing the obtained results with those in the literature, they are in a good agreement. Finally, the governing equations are...
Non-linear finite element implementation of micropolar hypo-elastic materials
, Article Computer Methods in Applied Mechanics and Engineering ; Volume 197, Issue 49-50 , 15 September , 2008 , Pages 4149-4159 ; 00457825 (ISSN) ; Naghdabadi, R ; Sohrabpour, S ; Sharif University of Technology
2008
Abstract
In this paper, updated Lagrangian finite element formulations for large elastic deformation of micropolar hypo-elastic materials are presented. Using representation theorems of tensor functions, the general form of the constitutive equations for the micropolar hypo-elastic materials model are presented. The finite element formulations are based on the general form of the micropolar hypo-elastic constitutive equations in conjunction with Jaumann rate and a new rate called gyration rate. Gyration rate describes the deformation of the material in view of an observer attached to the micro-structure. An incrementally objective stress and couple stress update procedure is developed and its...
Effective behavior of porous elastomers containing aligned spheroidal voids
, Article Acta Mechanica ; Volume 224, Issue 9 , September , 2013 , Pages 1901-1915 ; 00015970 (ISSN) ; Naghdabadi, R ; Sharif University of Technology
2013
Abstract
The theoretical need to recognize the link between the basic microstructure of nonlinear porous materials and their macroscopic mechanical behavior is continuously rising owing to the existing engineering applications. In this regard, a semi-analytical homogenization model is proposed to establish an overall, continuum-level constitutive law for nonlinear elastic materials containing prolate/oblate spheroidal voids undergoing finite axisymmetric deformations. The microgeometry of the porous materials is taken to be voided spheroid assemblage consisting of confocally voided spheroids of all sizes having the same orientation. Following a kinematically admissible deformation field for a...
A viscoelastic constitutive model for compressible polymers based on logarithmic strain and its finite element implementation
, Article Finite Elements in Analysis and Design ; Volume 62 , 2012 , Pages 18-27 ; 0168874X (ISSN) ; Baghani, M ; Arghavani, J ; Sharif University of Technology
2012
Abstract
In this paper, employing the logarithmic (or Hencky) strain as a more physical measure of strain, the time-dependent response of compressible viscoelastic materials is investigated. In this regard, we present a phenomenological finite strain viscoelastic constitutive model, developed within the framework of irreversible thermodynamics with internal variables. The formulation is based on the multiplicative decomposition of the deformation gradient into elastic and viscoelastic parts, together with the use of the isotropic property of the Helmholtz strain energy function. Making use of a logarithmic mapping, we present an appropriate form of the proposed constitutive equations in the...
Electrical bending instability in electrospinning visco-elastic solutions
, Article Journal of Polymer Science, Part B: Polymer Physics ; Volume 54, Issue 11 , 2016 , Pages 1036-1042 ; 08876266 (ISSN) ; Bonn, D ; Ejtehadi, M. R ; Iraji Zad, A ; Sharif University of Technology
John Wiley and Sons Inc
Abstract
The electrical bending instability in charged liquid jets is the phenomenon determining the process of electrospinning. A model of this phenomenon is lacking however, mostly due to the complicated interplay between the viscosity and elasticity of the solution. To investigate the bending instability, we performed electrospinning experiments with a solution of polyethylene oxide in water/ethanol. Using a fast camera and sensitive multimeter, we deduced an experimental dispersion relation describing the helix pitch length as a function of surface charge. To understand this relation, we developed a theoretical model for the instability for a wide range of visco-elastic materials, from conducting...
Two-dimensional modeling of functionally graded viscoelastic materials using a boundary element approach
, Article Advanced Materials Research, 7 January 2012 through 8 January 2012 ; Volume 463-464 , January , 2012 , Pages 570-574 ; 10226680 (ISSN) ; 9783037853634 (ISBN) ; Bahadori, M. R ; Shariyat, M ; Sharif University of Technology
Abstract
In this paper, a 2D boundary element approach able to model viscoelastic functionally graded materials (FGM) is presented. A numerical implementation of the Somigliana identity for displacements is developed to solve 2D problems of exponentially graded elasticity. An FGM is an advanced material in which its composition changes gradually resulting in a corresponding change in properties of the material. The FGM concept can be applied to various materials for structural and functional uses. Our model needs only the Green's function of nonhomogeneous elastostatic problems with material properties that vary continuously along a given dimension. We consider the material properties to be an...
Micropolar hypo-elasticity
, Article Archive of Applied Mechanics ; Volume 80, Issue 12 , December , 2010 , Pages 1449-1461 ; 09391533 (ISSN) ; Naghdabadi, R ; Sharif University of Technology
2010
Abstract
In this paper, the concept of hypo-elasticity is generalized to the micropolar continuum theory, and the general forms of the constitutive equations of the micropolar hypo-elastic materials are presented. A new co-rotational objective rate whose spin is the micropolar gyration tensor is introduced which describes the deformation of the material in view of an observer attached to the micro-structure. As special case, simplified versions of the proposed constitutive equations are given in which the same fourth-order elasticity tensors are used as in the micropolar linear elasticity. A 2-D finite element formulation for large elastic deformation of micropolar hypo-elastic media based on the...
Bending-torsional instability of a viscoelastic cantilevered pipe conveying pulsating fluid with an inclined terminal nozzle
, Article Journal of Mechanical Science and Technology ; Volume 32, Issue 7 , July , 2018 , Pages 2999-3008 ; 1738494X (ISSN) ; Abtahi, H ; Firouz Abadi, R. D ; Haddadpour, H ; Dowell, E. H ; Sharif University of Technology
Korean Society of Mechanical Engineers
2018
Abstract
In the present study, dynamic stability of a viscoelastic cantilevered pipe conveying fluid which fluctuates harmonically about a mean flow velocity is considered; while the fluid flow is exhausted through an inclined end nozzle. The Euler-Bernoulli beam theory is used to model the pipe and fluid flow effects are modelled as a distributed load along the pipe which contains the inertia, Coriolis, centrifugal and induced pulsating fluid flow forces. Moreover, the end nozzle is modelled as a follower force which couples bending vibrations with torsional ones. The extended Hamilton's principle and the Galerkin method are used to derive the bending-torsional equations of motion. The coupled...
Constitutive equations for micropolar hyper-elastic materials
, Article International Journal of Solids and Structures ; Volume 46, Issue 14-15 , 2009 , Pages 2765-2773 ; 00207683 (ISSN) ; Naghdabadi, R ; Sohrabpour, S ; Sharif University of Technology
2009
Abstract
In this paper, the concept of hyper-elasticity in the micropolar continuum theory is investigated. The restrictions on the fourth-order elasticity tensors are investigated. Using the representation theorems, a general form of constitutive equations for micropolar hyper-elastic isotropic materials is presented. As some special cases, generalizations of the neo-Hookean and Mooney-Rivlin type materials to the micropolar continuum theory are presented. The generalized constitutive equations reduce to those of the microplar linear elasticity theory when the deformations are infinitesimal. Also, Updated Lagrangian finite element formulations for the micropolar hyper-elastic materials are...
On the geometrically nonlinear analysis of sandwich shells with viscoelastic core: a layerwise dynamic finite element formulation
, Article Composite Structures ; Volume 230 , 2019 ; 02638223 (ISSN) ; Khorasani, R ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
The objective of this work is to present a finite element formulation for dynamic analysis of sandwich shells with viscoelastic core under large deformation. The present study is based on an incremental updated Lagrangian approach together with the Newmark integration scheme. The viscoelastic constitutive model which is used to define the behavior of the core, comes from the Riesz theorem and the corresponding creep functions are estimated using Dirichlet-Prony series. Also, the viscoelastic deferred strain is derived in an appropriate incremental form using the state variables. The employed layerwise shell element which is based on zig-zag theory has eight nodes on its mid layer. What's...
Surface characterization of face-centered cubic crystals
, Article Mechanics of Materials ; Volume 129 , 2019 , Pages 15-22 ; 01676636 (ISSN) ; Enzevaee, C ; Sharif University of Technology
Elsevier B.V
2019
Abstract
To date, the examination of surface energy and surface layer relaxation has been the subject of several experimental and simulation works, whereas evaluation of surface residual stresses and surface elastic constants has received very little attention. In addition to the fundamental importance of these properties in the understanding of such phenomena as crystal equilibrium shape, surface roughening and segregation, they are also crucial for use in the theoretical studies based on continuum theory of elastic material surfaces. This work focuses on developing a theoretical approach for the calculations of the surface residual stress and surface elastic constants for (100) planes of fcc...
Surface characterization of face-centered cubic crystals
, Article Mechanics of Materials ; Volume 129 , 2019 , Pages 15-22 ; 01676636 (ISSN) ; Enzevaee, C ; Sharif University of Technology
Elsevier B.V
2019
Abstract
To date, the examination of surface energy and surface layer relaxation has been the subject of several experimental and simulation works, whereas evaluation of surface residual stresses and surface elastic constants has received very little attention. In addition to the fundamental importance of these properties in the understanding of such phenomena as crystal equilibrium shape, surface roughening and segregation, they are also crucial for use in the theoretical studies based on continuum theory of elastic material surfaces. This work focuses on developing a theoretical approach for the calculations of the surface residual stress and surface elastic constants for (100) planes of fcc...
Rigid-bar loading on pregnant uterus and development of pregnant abdominal response corridor based on finite element biomechanical model
, Article International Journal for Numerical Methods in Biomedical Engineering ; Volume 36, Issue 1 , January , 2020 ; Ahmadian, M. T ; Mohammadi, H ; Sharif University of Technology
Wiley-Blackwell
2020
Abstract
During pregnancy, traumas can threaten maternal and fetal health. Various trauma effects on a pregnant uterus are little investigated. In the present study, a finite element model of a uterus along with a fetus, placenta, amniotic fluid, and two most effective ligament sets is developed. This model allows numerical evaluation of various loading on a pregnant uterus. The model geometry is developed based on CT-scan data and validated using anthropometric data. Applying Ogden hyper-elastic theory, material properties of uterine wall and placenta are developed. After simulating the “rigid-bar” abdominal loading, the impact force and abdominal penetration are investigated. Findings are compared...
Frequency characteristics of FG-GPLRC viscoelastic thick annular plate with the aid of GDQM
, Article Thin-Walled Structures ; Volume 150 , 2020 ; Ghabussi, A ; Ebrahimi, F ; Habibi, M ; Safarpour, H ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
This is the first research on the free vibration analysis of functionally graded graphene platelets reinforced composite (FG-GPLRC) viscoelastic annular plate resting on the visco-Pasternak foundation and subjected to the nonlinear temperature gradient and mechanical loading within the framework of higher-order shear deformation theory (HSDT). Hamilton's principle is employed to establish governing equations within the framework of HSDT. In this paper, viscoelastic properties are modeled according to Kelvin-Voigt viscoelasticity. The deflection as the function of time can be solved by the fourth-order Runge-Kutta numerical method. Generalized differential quadrature method (GDQM) is applied...
Nonlinear dynamics of viscoelastic pipes conveying fluid placed within a uniform external cross flow
, Article Applied Ocean Research ; Volume 94 , 2020 ; Haddadpour, H ; Hosseini Kordkheili, S. A ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
This paper investigates the nonlinear dynamic response of a viscoelastic pipe conveying fluid subjected to a uniform external cross flow based on the Euler-Bernoulli theory. The main objective of this work is to find the proper viscoelastic coefficients to mitigate the dynamic response of a marine riser. A nonlinear oscillator is utilized to simulate the mean drag force and the vortex-induced lift force. Also, the pipe material is assumed to be viscoelastic and consisted of the Kelvin-Voigt type. The extended Hamilton's principle along with the Galerkin discretization are employed to construct the nonlinear model of the coupled fluid-structure system. Moreover, the assumed mode method along...
On the vibrations and stability of moving viscoelastic axially functionally graded nanobeams
, Article Materials ; Volume 13, Issue 7 , 2020 ; Jung, D. W ; Mohammad Sedighi, H ; Zur, K. K ; Habibi, M ; Safa, M ; Sharif University of Technology
MDPI AG
2020
Abstract
In this article, size-dependent vibrations and the stability of moving viscoelastic axially functionally graded (AFG) nanobeams were investigated numerically and analytically, aiming at the stability enhancement of translating nanosystems. Additionally, a parametric investigation is presented to elucidate the influence of various key factors such as axial gradation of the material, viscosity coecient, and nonlocal parameter on the stability boundaries of the system. Material characteristics of the system vary smoothly along the axial direction based on a power-law distribution function. Laplace transformation in conjunction with the Galerkin discretization scheme was implemented to obtain...
Implementation of visco-pseudo-elastic dampers for vibration reduction of sandwich shells using a large deformation FE technique
, Article International Journal of Mechanical Sciences ; Volume 207 , 2021 ; 00207403 (ISSN) ; Hosseini Kordkheili, S. A ; Razov, A ; Resnina, N ; Sharif University of Technology
Elsevier Ltd
2021
Abstract
This study introduces a numerical method for investigating the appropriate arrangement of visco-pseudo-elastic dampers applicable to shell and plate structures under large deformation. These passive dampers are considered as discrete shape memory alloy (SMA) wires and viscoelastic layers. The SMA constitutive model is adopted and developed based on carried out experimental tests (i.e., calorimetry and tensile tests) on Ni-rich Nitinol alloy samples. Pseudoelastic, pseudoplastic, strain recovery and de-twinning phenomena are perceived experimentally. The presented model characterizes pseudoelastic response of shape memory alloys. The current finite element formulation is based on an...
Modeling of visco-hyperelastic behavior of foams
, Article 2008 ASME International Mechanical Engineering Congress and Exposition, IMECE 2008, Boston, MA, 31 October 2008 through 6 November 2008 ; Volume 12 , 2009 , Pages 425-433 ; 9780791848739 (ISBN) ; Asghari, M ; Naghdabadi, R ; Sharif University of Technology
2009
Abstract
In this paper, a new visco-hyperelastic constitutive law for describing the rate dependent behavior of foams is proposed. The proposed model was based on a phenomenological Zener model: a hyperelastic equilibrium spring, which describes the steady-state, long-term response, parallel to a Maxwell element, which captures the rate-dependency. A nonlinear viscous damper connected in series to a hyperelastic intermediate spring, controls the rate-dependency of the Maxwell element. Therefore, the stress is the sum of equilibrium stress on the equilibrium spring and overstress on the intermediate spring. In hyperelastic theory stress is not calculated directly as in the case of small-strain, linear...