Loading...

**Search for:**isotropic-materials

0.008 seconds

#### Mathematical and finite element modelling of spine to investigate the effects of intra-abdominal pressure and activation of muscles around abdomin on the spinal stability

, Article 8th Biennial ASME Conference on Engineering Systems Design and Analysis, ESDA2006, Torino, 4 July 2006 through 7 July 2006 ; Volume 2006 , 2006 ; 0791837793 (ISBN); 9780791837795 (ISBN) ; Farahmand, F ; Parninapour, M ; Malekipour, F ; Shirazi Adl, A ; Arjmand, N ; Sharif University of Technology
2006

Abstract

In spite of the several experimental and modeling studies on the biomechanical characteristics of the human spine, the role and significance of the intra-abdominal pressure (IAP) in spine mechanics has remained controversial. This study represents a simple analytical and a 3-D finite element model of spine and its surrounding structures to investigate the contribution of IAP to spinal stability. The mathematical model included the lumbar spine column, the abdominal cavity and a muscular layer around it, the rib cage and the pelvic ring. The lumbar spine column was modeled as a beam and the rib cage and pelvis as rigid bodies. The intra-abdominal cavity and the surrounding muscular layer were...

#### 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...

#### An embedded elliptic nano-fiber in anti-plane strain couple stress elasticity

, Article 2008 ASME International Mechanical Engineering Congress and Exposition, IMECE 2008, Boston, MA, 31 October 2008 through 6 November 2008 ; Volume 13, Issue PART A , 2009 , Pages 145-152 ; 9780791848746 (ISBN) ; Haftbaradaran, H ; Sharif University of Technology
2009

Abstract

The application of higher order continuum theories, with size effect considerations, have recently been spread in the micro and nano-scale studies. One famous version of these theories is the couple stress theory. This paper utilizes this theory to study the anti-plane problem of an elliptic nano-fiber, embedded in an infinite medium, both made of centrosymmetric isotropic material. In this framework, a characteristic length appears in the formulation, by which examination of the size effect is possible. This work presents an analytical solution for the proposed problem. Copyright © 2008 by ASME

#### Optimal Design of Functionally Graded Materials Under Thermomechanical Loadings

, M.Sc. Thesis Sharif University of Technology ; Tavakoli, Rohollah (Supervisor)
Abstract

A numerical algorithm for the optimal design of two components functionally graded materials under thermomechanical loadings is introduced in the present study. It is based on the topology optimization method. The objective function, to be minimized, is defined as the weighted combination of the thermal and mechanical compliance of structure. The design variables are defined as the local volume fractions of contributing phases. The set of constraints includes bound constraints on local volume fractions and a global constraint on the total volume fraction of the matrix phase. The corresponding heat and elasticity equations are solved by the finite element method. The local material properties...

#### Expressions for Objective Co-Rotational Rates of Eulerian Stress Tensors

, M.Sc. Thesis Sharif University of Technology ; Asghari, Mohsen (Supervisor)
Abstract

Stress tensors and their rates are fundamental quantities in modeling the behavior of materials in the field of nonlinear continuum mechanics. One of the most remarkable applications of stress rates is their presence in the rate type constitutive equations of materials.

Co-rotational rates are corresponding to the rates which are measured by an observer who is in a reference rotating coordinate system. In general, under some specific conditions for the spin of a co-rotational rate, the rate of an Eulerian tensor would be objective. In this thesis, the objective co-rotational rates of Eulerian stress tensors for isotropic elastic materials under large deformations are obtained for the...

Co-rotational rates are corresponding to the rates which are measured by an observer who is in a reference rotating coordinate system. In general, under some specific conditions for the spin of a co-rotational rate, the rate of an Eulerian tensor would be objective. In this thesis, the objective co-rotational rates of Eulerian stress tensors for isotropic elastic materials under large deformations are obtained for the...

#### Pull-in behavior of functionally graded micro/nano-beams for MEMS and NEMS switches

, Article Microsystem Technologies ; 2018 ; 09467076 (ISSN) ; Mahdavi Adeli, M ; Hosseini, M ; Sharif University of Technology
Springer Verlag
2018

Abstract

In this paper, pull-in behavior of cantilever micro/nano-beams made of functionally graded materials (FGM) with small-scale effects under electrostatic force is investigated. Consistent couple stress theory is employed to study the influence of small-scale on pull-in behavior. According to this theory, the couple tensor is skew-symmetric by adopting the skew-symmetric part of the rotation gradients. The material properties except Poisson’s ratio obey the power law distribution in the thickness direction. The approximate analytical solutions for the pull-in voltage and pull-in displacement of the microbeams are derived using the Rayleigh–Ritz method. Comparison between the results of the...

#### An eulerian multiplicative constitutive model of finite elastoplasticity

, Article European Journal of Mechanics, A/Solids ; Volume 28, Issue 6 , 2009 , Pages 1088-1097 ; 09977538 (ISSN) ; Vafai, A ; Desai, C ; Sharif University of Technology
2009

Abstract

An Eulerian rate-independent constitutive model for isotropic materials undergoing finite elastoplastic deformation is formulated. Entirely fulfilling the multiplicative decomposition of the deformation gradient, a constitutive equation and the coupled elastoplastic spin of the objective corotational rate therein are explicitly derived. For the purely elastic deformation, the model degenerates into a hypoelastic-type equation with the Green-Naghdi rate. For the small elastic- and rigid-plastic deformations, the model converges to the widely-used additive model where the Jaumann rate is used. Finally, as an illustration, using a combined exponential isotropic-nonlinear kinematic hardening...

#### Pull-in behavior of functionally graded micro/nano-beams for MEMS and NEMS switches

, Article Microsystem Technologies ; Volume 25, Issue 8 , 2019 , Pages 3165-3173 ; 09467076 (ISSN) ; Mahdavi Adeli, M ; Hosseini, M ; Sharif University of Technology
Springer Verlag
2019

Abstract

In this paper, pull-in behavior of cantilever micro/nano-beams made of functionally graded materials (FGM) with small-scale effects under electrostatic force is investigated. Consistent couple stress theory is employed to study the influence of small-scale on pull-in behavior. According to this theory, the couple tensor is skew-symmetric by adopting the skew-symmetric part of the rotation gradients. The material properties except Poisson’s ratio obey the power law distribution in the thickness direction. The approximate analytical solutions for the pull-in voltage and pull-in displacement of the microbeams are derived using the Rayleigh–Ritz method. Comparison between the results of the...

#### Torsional surface wave propagation in a transversely isotropic FG substrate with piezoelectric over-layer within surface/interface theory

, Article Acta Mechanica ; Volume 231, Issue 6 , 2020 , Pages 2203-2216 ; Mohamadi Shodja, H ; Sharif University of Technology
Springer
2020

Abstract

Propagation of the torsional surface waves in a medium consisting of a functionally graded (FG) substrate bonded to a thin piezoelectric over-layer has been analytically formulated in the mathematical framework of surface/interface elasticity theory. In the cases where the wavelength and/or the thickness of the over-layer are comparable to the surface/interface characteristic length, then the surface/interface effects are not negligible. It is assumed that the over-layer is made of hexagonal 622 crystals with a single axis of rotational symmetry coinciding with the axis of polarization. The half-space is made of an FG transversely isotropic material in which the elasticity tensor and the...

#### Using the hybrid DAS-SR method for damage localization in composite plates

, Article Composite Structures ; Volume 247 , 2020 ; Navazi, H. M ; Groves, R. M ; Sharif University of Technology
Elsevier Ltd
2020

Abstract

In this paper, the hybrid Delay-And-Sum (DAS) with Sparse Reconstruction (SR) method was further developed for damage location in composite plates. In composite materials, anisotropy leads to some challenges in using conventional damage location methods, which are developed for isotropic materials. In the hybrid DAS-SR method, the DAS and SR methods were combined as a complement of each other. To investigate the DAS-SR method for composite structures, the group velocity of the travelling wave for different directions was first measured experimentally via PZTs. The DAS and SR formulations were then modified to be compatible with the direction-dependent group velocities. The results show that...

#### Computational modeling of the transverse-isotropic elastic properties of single-walled carbon nanotubes

, Article Computational Materials Science ; Volume 49, Issue 3 , 2010 , Pages 544-551 ; 09270256 (ISSN) ; Sadeghi, M ; Naghdabadi, R ; Rafii-Tabar, H ; Sharif University of Technology
2010

Abstract

Various experimental and theoretical investigations have been carried out to determine the elastic properties of nanotubes in the axial direction. Their behavior in transverse directions, however, has not been well studied. In this paper, a combination of molecular dynamics (MD) and continuum-based elasticity model is used to predict the transverse-isotropic elastic properties of single-walled carbon nanotubes (SWCNTs). From this modeling study, five independent elastic constants of an SWCNT in transverse directions are obtained by analyzing its deformations under four different loading conditions, namely, axial tension, torsion, uniform and non-uniform radial pressure. To find the elastic...

#### Buckling Analysis of Composite Cylindrical Shells Under External Pressure

, M.Sc. Thesis Sharif University of Technology ; Fallah Rajabzadeh, Famida (Supervisor)
Abstract

The aim of this project is buckling and post-buckling analysis of laminated composite circular cylindrical shells under external pressure on the basis of different shell theories. Based on Donnell, Love, and Sanders nonlinear shell theories within the first-order shear deformation model and von Karman geometric nonlinearity, the potential energy of composite circular cylindrical shells under external pressure with simply supported edges is extracted and by minimizing of the total potential energy and implementing the Ritz method, buckling pressure, the nonlinear post-buckling analysis and the curves of static equilibrium paths are presented. Furthermore, the effect of the external energy due...

#### A plasticity model for metals with dependency on all the stress invariants

, Article Journal of Engineering Materials and Technology, Transactions of the ASME ; Volume 135, Issue 1 , 2013 ; 00944289 (ISSN) ; Hoseini, S. H ; Farrahi, G. H ; Sharif University of Technology
2013

Abstract

Recent experiments on metals have shown that all of the stress invariants should be involved in the constitutive description of the material in plasticity. In this paper, a plasticity model for metals is defined for isotropic materials, which is a function of the first stress invariant in addition to the second and the third invariants of the deviatoric stress tensor. For this purpose, the Drucker-Prager yield criterion is extended by addition of a new term containing the second and the third deviatoric stress invariants. Furthermore for estimating the cyclic behavior, new terms are incorporated into the Chaboche's hardening evolution equation. These modifications are applied by adding new...

#### Green's functions of a surface-stiffened transversely isotropic half-space

, Article International Journal of Solids and Structures ; Volume 49, Issue 23-24 , 2012 , Pages 3282-3290 ; 00207683 (ISSN) ; Ahmadi, S. F ; Sharif University of Technology
2012

Abstract

Green's functions of a transversely isotropic half-space overlaid by a thin coating layer are analytically obtained. The surface coating is modeled by a Kirchhoff thin plate perfectly bonded to the half-space. With the aid of superposition technique and employing appropriate displacement potential functions, the Green's functions are expressed in two parts; (i) a closed-form part corresponding to the transversely isotropic half-space with surface kinematic constraints, and (ii) a numerically evaluated part reflecting the interaction between the half-space and the plate in the form of semi-infinite integrals. Some limiting cases of the problem such as surface-stiffened isotropic half-space,...

#### Constitutive modeling of rubberlike materials based on consistent strain energy density functions

, Article Polymer Engineering and Science ; Volume 50, Issue 5 , 2010 , Pages 1058-1066 ; 00323888 (ISSN) ; Naghdabadi, R ; Kargarnovin, M. H ; Sharif University of Technology
Abstract

Rubberlike materials are characterized by high deformability and reversibility of deformation. From the continuum viewpoint, a strain energy density function is postulated for modeling the behavior of these materials. In this paper, a general form for the strain energy density of these materials is proposed from a phenomenological point of view. Based on the Valanis-Landel hypothesis, the strain energy density of incompressible materials is expressed as the sum of independent functions of the principal stretches meeting the essential requirements on the form of the strain energy density. It is cleared that the appropriate mathematical expressions for constitutive modeling of these materials...

#### Hyperelastic materials modelling using a strain measure consistent with the strain energy postulates

, Article Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science ; Volume 224, Issue 3 , 2010 , Pages 591-602 ; 09544062 (ISSN) ; Naghdabadi, R ; Kargarnovin, M. H ; Sharif University of Technology
Abstract

In this article, a strain energy density function of the Saint Venant-Kirchhoff type is expressed in terms of a Lagrangian deformation measure. Applying the governing postulates to the form of the strain energy density, the mathematical expression of this measure is determined. It is observed that this measure, which is consistent with the strain energy postulates, is a strain type with the characteristic function more rational than that of the Seth-Hill strain measures for hyperelastic materials modelling. In addition, the material parameters are calculated using a novel procedure that is based on the correlation between the values of the strain energy density (rather than the stresses)...

#### Dynamic analysis of an inclined Timoshenko beam traveled by successive moving masses/forces with inclusion of geometric nonlinearities

, Article Acta Mechanica ; Volume 218, Issue 1-2 , 2011 , Pages 9-29 ; 00015970 (ISSN) ; Kargarnovin, M. H ; Sharif University of Technology
2011

Abstract

In the first part of this paper, the nonlinear coupled governing partial differential equations of vibrations by including the bending rotation of cross section, longitudinal and transverse displacements of an inclined pinned-pinned Timoshenko beam made of linear, homogenous and isotropic material with a constant cross section and finite length subjected to a traveling mass/force with constant velocity are derived. To do this, the energy method (Hamilton's principle) based on the large deflection theory in conjuncture with the von-Karman strain-displacement relations is used. These equations are solved using the Galerkin's approach via numerical integration methods to obtain dynamic...

#### Nonlinear dynamic analysis of an inclined Timoshenko beam subjected to a moving mass/force with beam's weight included

, Article Shock and Vibration ; Volume 18, Issue 6 , 2011 , Pages 875-891 ; 10709622 (ISSN) ; Kargarnovin, M. H ; Sharif University of Technology
2011

Abstract

In this study, the nonlinear vibrations analysis of an inclined pinned-pinned self-weight Timoshenko beam made of linear, homogenous and isotropic material with a constant cross section and finite length subjected to a traveling mass/force with constant velocity is investigated. The nonlinear coupled partial differential equations of motion for the rotation of warped cross section, longitudinal and transverse displacements are derived using the Hamilton's principle. These nonlinear coupled PDEs are solved by applying the Galerkin's method to obtain dynamic responses of the beam. The dynamic magnification factor and normalized time histories of mid-point of the beam are obtained for various...