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Dynamic Simulation of Heart Mitral Valve
, M.Sc. Thesis Sharif University of Technology ; Zohoor, Hassan (Supervisor) ; Sohrabpoor, Saeeid (Supervisor)
Abstract
Two methods for simulating material behavior of heart mitral valve leaflet tissue are developed in this thesis, in the finite element setting. First, a mixed pressure-displacement formulation is used to implement the constitutive material behavior with general 3D elements. Second, a shell is formulated that incorporates the 3D material behavior by use of a local plane stress iteration method. Both of these works are based on an existing invariant-based strain energy function that has been experimentally determined for the mitral valve leaflet tissue. Since this material is considered to be nearly incompressible, a mixed pressure-displacement (u/p) formulation is needed to apply the material...
A strain gradient based yield criterion
, Article International Journal of Engineering Science ; Vol. 77 , 2014 , pp. 45-54 ; ISSN: 00207225 ; Ahmadian, M. T ; Firoozbakhsh, K ; Sharif University of Technology
Abstract
The classical yield criteria do not describe the yield size-dependency that has been observed in micro-scale structures (Fleck, Muller, Ashby, & Hutchinson, 1994; Stolken and Evans 1998; Moreau et al. 2005), and may also significantly underestimate the yield loads of structures at micron and sub-micron scales (Son, Jeong, & Kwon, 2003; Liu et al., 2013). The present paper suggests a specific size-dependent yield criterion based on the strain gradient theory that is aimed at addressing this inadequacy. In order to develop the strain gradient based yield criterion, the deviatoric part of the strain energy is calculated based on this theory and equated to the deviatoric strain energy of a...
A hyperelastic constitutive model for fiber-reinforced rubber-like materials
, Article International Journal of Engineering Science ; Volume 71 , 2013 , Pages 36-44 ; 00207225 (ISSN) ; Naghdabadi, R ; Arghavani, J ; Sharif University of Technology
2013
Abstract
In this paper, a Strain Energy Function (SEF) is proposed to characterize the hyperelastic behavior of transversely isotropic incompressible fiber-reinforced rubbers. The kinematics of the deformation is based on a strain measure consistent with the physics of the deformation. The SEF consists of an isotropic part and an anisotropic one where a simple form of SEF is used for both parts. In order to investigate the capabilities of the proposed model, two fiber-reinforced rubbers under homogeneous deformations are examined. The predictions of the model show a good agreement with the experimental data for both tensile and shear deformations. Also, torsion of a fiber-reinforced rubbery circular...
Effects of elastic contributions on the evolution of nano-structure Al3Sc phase: A phase-field study
, Article Scientia Iranica ; Volume 23, Issue 3 , 2016 , Pages 1539-1547 ; 10263098 (ISSN) ; Ebrahimi, H ; Sharif University of Technology
Sharif University of Technology
2016
Abstract
A micromechanical phase-field model is utilized to study the evolution of nanostructure Al3Sc phase in Al-Sc alloy. We study the formation of Al3Sc precipitates in an Al-Sc alloy by using an elastic phase-field model. Since the precipitates of Al3Sc phase are fully coherent with the Al matrix, the elastic energy will have an inuence on the resulting morphology. We have studied the effects of elastic strain energies on shape evolution of Al3Sc phase, numerically. The simulated nano-structures evolve from spherical to cubic shapes. The equilibrium shape of the coherent Al3Sc phase is found to be determined by minimizing the sum of the elastic and interfacial energies through the phase-field...
Kinematic and Constitutive Modeling of Elastic and Thermoelastic Continua with Finite Deformation using Multiplicative Decomposition of Deformation Gradient
, Ph.D. Dissertation Sharif University of Technology ; Naghdabadi, Reza (Supervisor) ; Kargarnovin, Mohammad Hassan (Supervisor)
Abstract
In this thesis, a deformation measure is introduced which leads to a class of strain measures in the Lagrangian and Eulerian descriptions. In order to develop a constitutive equation, a second-order constitutive relation based on these strain measures is considered for modeling the mechanical behavior of solids at finite deformation. For this purpose and performance evaluation of the proposed strains, a Hookean-type constitutive equation is considered and the uniaxial loading as well as simple shear and pure shear tests are examined and the results are compared with the test data. Also, in order to characterize the mechanical behavior of elastic continua, constitutive equations through a...
Interface effects on elastic behavior of an edge dislocation in a core-shell nanowire embedded to an infinite matrix
, Article International Journal of Solids and Structures ; Volume 50, Issue 7-8 , 2013 , Pages 1177-1186 ; 00207683 (ISSN) ; Enzevaee, C ; Shodja, H. M ; Sharif University of Technology
2013
Abstract
The elastic behavior of an edge dislocation located inside the core of a core-shell nanowire which is embedded in an infinite matrix is studied within the surface/interface elasticity theory. The corresponding boundary value problem is solved exactly by using complex potential functions. An important parameter so-called interface characteristic parameter which has the dimension of length and is a combination of the interface moduli enters the formulations. The stress field of the dislocation, image force acting on the dislocation, and the dislocation strain energy is calculated by considering the interface effect. The introduced characteristic parameter allows the examination of the...
An exact analysis for the hoop elasticity and pressure-induced twist of CNT-nanovessels and CNT-nanopipes
, Article Mechanics of Materials ; Volume 82 , 2015 , Pages 47-62A ; 01676636 (ISSN) ; Shodja, H. M ; Sharif University of Technology
Elsevier
2015
Abstract
Carbon nanotubes (CNTs) with and without end caps may be used for fluid storage and transport, respectively, referred to as CNT-nanovessel and CNT-nanopipe. The determination of the stiffness in the hoop (circumferential) and radial directions, ideal hoop strength, and hoop stress-strain curve of such nanostructures is of particular interest. Due to the proposed viewpoint, a chiral free-standing single-walled CNT (SWCNT) has a natural angle of twist and natural extension along the axis of the tube. For example, for the SWCNT (9,3) with diameter of 0.85 nm and chirality angle of 13.9°, the natural angle of twist per unit length is 1.45×10-3 rad/nm. Previously, only Vercosa et al. (2010) who...
Numerical investigation of crack orientation in the fretting fatigue of a flat rounded contact
, Article International Journal of Engineering, Transactions B: Applications ; Volume 23, Issue 3-4 , 2010 , Pages 223-232 ; 1728-144X (ISSN) ; Farrahi, G. H ; Sharif University of Technology
Materials and Energy Research Center
2010
Abstract
The growth of slant cracks by fretting fatigue of a half plane in contact with a flat rounded pad was studied. The mode I and mode II stress intensity factors for cracks of various lengths and directions were calculated using the semi-analytical method of the distribution of dislocations, and their cumulative effect on the crack growth was investigated using the strain energy density criterion. The results showed dominance of mode I fracture on crack growth, and based on the observation of strain energy density factor versus crack orientation, the results also suggest that depending on the crack length, the most critical orientations of cracks are at 0° to 20° outward the contact zone. Good...
Micromechanics of brain white matter tissue: a fiber-reinforced hyperelastic model using embedded element technique
, Article Journal of the Mechanical Behavior of Biomedical Materials ; Volume 80 , April , 2018 , Pages 194-202 ; 17516161 (ISSN) ; Shamloo, A ; Farahmand, F ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
A transverse-plane hyperelastic micromechanical model of brain white matter tissue was developed using the embedded element technique (EET). The model consisted of a histology-informed probabilistic distribution of axonal fibers embedded within an extracellular matrix, both described using the generalized Ogden hyperelastic material model. A correcting method, based on the strain energy density function, was formulated to resolve the stiffness redundancy problem of the EET in large deformation regime. The model was then used to predict the homogenized tissue behavior and the associated localized responses of the axonal fibers under quasi-static, transverse, large deformations. Results...
Modeling of rate dependent finite deformation viscoelastic 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 435-442 ; 9780791848739 (ISBN) ; Asghari, M ; Naghdabadi, R ; Sharif University of Technology
2009
Abstract
The behavior of foams is typically rate-dependent and viscoelastic. In this paper, multiplicative decomposition of the deformation gradient and the second law of thermodynamics are employed to develop the differential constitutive equations for isotropic viscoelastic foams experiencing finite deformations, from a phenomenological point of view, i.e. without referring to micro-structural viewpoint. A model containing an equilibrium hyperelastic spring which is parallel to a Maxwell model has been utilized for introducing constitutive formulation. The deformation gradient tensor is decomposed into two parts: elastic deformation gradient tensor and viscoelastic deformation gradient tensor. A...
Nonlinear mechanics of soft composites: hyperelastic characterization of white matter tissue components
, Article Biomechanics and Modeling in Mechanobiology ; Volume 19, Issue 3 , 2020 , Pages 1143-1153 ; Shamloo, A ; Farahmand, F ; Sharif University of Technology
Springer
2020
Abstract
This paper presents a bi-directional closed-form analytical solution, in the framework of nonlinear soft composites mechanics, for top-down hyperelastic characterization of brain white matter tissue components, based on the directional homogenized responses of the tissue in the axial and transverse directions. The white matter is considered as a transversely isotropic neo-Hookean composite made of unidirectional distribution of axonal fibers within the extracellular matrix. First, two homogenization formulations are derived for the homogenized axial and transverse shear moduli of the tissue, based on definition of the strain energy density function. Next, the rule of mixtures and...
Influence of joint arrangement on the fracture behavior of lead-free solder joints
, Article Journal of Electronic Materials ; Volume 50, Issue 4 , 2021 , Pages 2117-2128 ; 03615235 (ISSN) ; Nourani, A ; Honarmand, M ; Assempour, A ; Sharif University of Technology
Springer
2021
Abstract
The capability to standardize the fracture strength of solder joints is an effective tool to investigate the reliability of electronic devices. To achieve this purpose, in this research, the influences of joint arrangement (loading arm and load sharing) on the level of constraint imposed on joint deformation, fracture energy, and generally, fracture behavior of solder joints were investigated. Fracture behavior of solder joints using double-cantilever-beam (DCB) specimens as a function of loading arm and load sharing (i.e., the distance between two solder joints) was studied under mode I loading conditions at a strain rate of 0.03 s−1. By increasing the loading arm, the fracture force, Fci,...
Geometrically non-linear vibration of concrete shallow funicular shells
, Article Proceedings of the Institution of Civil Engineers: Structures and Buildings ; Volume 174, Issue 3 , 2021 , Pages 169-180 ; 09650911 (ISSN) ; Mofid, M ; Daneshmand, N ; Sharif University of Technology
ICE Publishing
2021
Abstract
This study deals with the geometrically non-linear vibration analysis of concrete shallow funicular shells of rectangular plan with four clamped edges under impulse loads. The shape of a concrete funicular shell is such that the shell is subjected to pure compression under its dead weight. Following the existing method presented for the linear vibration analysis, the geometrically non-linear vibration analysis is considered through the use of non-linear shallow shells theory. Each displacement component is expanded in a double Fourier series and the kinetic energy, the elastic strain energy and the virtual work done by external forces are calculated in terms of the displacement components....
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...
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...
Surface/interface effects on elastic behavior of an edge dislocation in the shell of a core-shell nanowire
, Article European Journal of Mechanics, A/Solids ; Volume 41 , September–October , 2013 , Pages 86-100 ; 09977538 (ISSN) ; Rezazadeh Kalehbasti, S ; Shodja, H. M ; Sharif University of Technology
2013
Abstract
The elastic behavior of an edge dislocation placed in the shell of a free-standing core-shell nanowire is considered within the theory of surface/interface elasticity. Using the method of complex potential functions the expressions for the stress field of the dislocation, image forces on the dislocation, and the dislocation strain energy are derived and studied in detail. A special attention is paid to non-classical effects revealed within the surface/interface elasticity approach where a characteristic length parameter referred to as surface/interface modulus is introduced. These effects are (i) the stress oscillations along the shell surface and core-shell interface for negative values of...
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...
Free vibration analysis of cylindrical panels with spiral cross section
, Article International Journal of Mechanical Sciences ; Volume 133 , 2017 , Pages 376-386 ; 00207403 (ISSN) ; Ahmadian, M. T ; Asghari, M ; Pugno, N. M ; Sharif University of Technology
Abstract
In this paper, free vibration of open noncircular cylinders with spiral cross section are studied under arbitrary boundary conditions. For deriving the strain energy function, Kirchhoff-Love hypotheses are employed. To obtain the solutions, Rayleigh-Ritz technique is implemented by selecting Chebyshev orthogonal polynomials of first kind as admissible displacement functions in three directions. Convergence of the proposed formulation is verified for spiral cylindrical panel and the results are compared with those of ABAQUS. Parametric study is undertaken to highlight the effect of inner radius, separation distance, subtended angle, thickness, and length of the spiral cylinders on the free...
Coupling microplane-based damage and continuum plasticity models for analysis of damage-induced anisotropy in plain concrete
, Article International Journal of Plasticity ; Volume 95 , 2017 , Pages 216-250 ; 07496419 (ISSN) ; Ghaemian, M ; Sharif University of Technology
Elsevier Ltd
2017
Abstract
A novel plastic-damage constitutive model for plain concrete is developed in this paper. For this purpose, the microplane theory is proposed for overcoming the deficiency of available anisotropic continuum plastic-damage models in reproducing the true anisotropic nature of damage in multidimensional loadings. Based on the microplane theory, the degeneration process in concrete is considered along with plastic deformations. Using the principle of strain energy equivalence, a transformation between the nominal and effective states of material is achieved, that results in a decoupled formulation for damage and plasticity. A yield function with multiple internal variables and a non-associative...
Torsional buckling of generally laminated conical shell
, Article Meccanica ; Volume 52, Issue 4-5 , 2017 , Pages 1051-1061 ; 00256455 (ISSN) ; Sharghi, H ; Kouchakzadeh, M. A ; Sharif University of Technology
Springer Netherlands
2017
Abstract
Buckling of generally laminated conical shells under uniform torsion with simply-supported boundary conditions is investigated. The Donnel type strain displacement relations are used to obtain potential strain energy of the shell and membrane stability equation is applied to acquire the external work done by torsion. The Ritz method is used to solve the governing equations and critical buckling loads are obtained. The accuracy of the results is validated in comparison of with other investigations and finite element method. The effects of lamination sequence, semi-vertex angle and length to radius ratio of the cone are evaluated and mode shapes are presented for two types of lamination...