Search for: elastic-moduli
Total 136 records
Ab initio DFPT Based Constitutive Modelling of Crystalline Solids within Micromorphic Theory with Application to Nano/Micro-structures, Ph.D. Dissertation Sharif University of Technology ; Mohammad Shodja, Hossein
To account for certain essential features of material such as micro-structure effects and dispersive behaviour and optical branches in dispersion curves, a fundamental departure from classical elasticity to generalized continuum theories is required. Among the generalized continuum mechanics, micromorphic elasticity is capable of capturing these physical phenomena completely. In the mathematical framework of micromorphic elasticity, in addition to the traditional elastic moduli tensors, some additional tensors are introduced in the pertinent governing equations of motion. A precise evaluation of the numerical values of the aforementioned elastic moduli tensors in the realm of the...
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
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...
Ductility of saffil™ short fibre reinforced metals, Article Scripta Materialia ; Volume 53, Issue 1 , 2005 , Pages 17-21 ; 13596462 (ISSN) ; Tavangar, R ; Mortensen, A ; Sharif University of Technology
A critical combination of matrix strain hardening exponent and fiber volume exceeded to confer tensile ductility to short-fiber reinforced metal. The bimodal distribution of tensile ductilities observed in such materials can be attributed to a transition in damage mode, from fiber fragmentation to matrix voiding. Building on results for model composites of this class and making a few specification, a simple criterion can be proposed to predict whether such composites display a low or a high tensile elongation. The results show that, composites of this class are ductile if their matrix strain hardening exponent exceeds by more than around three per cent of unity the fiber volume fraction
LDPE/EVA/graphene nanocomposites with enhanced mechanical and gas permeability properties, Article Polymers for Advanced Technologies ; Volume 26, Issue 9 , 2015 , Pages 1083-1090 ; 10427147 (ISSN) ; Ramazani S. A ; Hamed Mosavian, M. T ; Tayyebi, A ; Sharif University of Technology
John Wiley and Sons Ltd 2015
In the present work, graphene oxide (GO) and reduced graphene oxide (RGO) were incorporated at low-density polyethylene (LDPE)/ethylene vinyl acetate (EVA) copolymer blend using solution casting method. Monolayer GO with 1-nm thickness and good transparency was synthesized using the well-known Hummers's method. Fourier transform infrared and X-ray photoelectron spectroscopy data exhibited efficient reduction of GO with almost high C/O ratio of RGO. Scanning electron microscopy showed the well distribution of GO and RGO within LDPE/EVA polymer matrix. The integrating effects of GO and RGO on mechanical and gas permeability of prepared films were examined. Young's modulus of nanocomposites are...
Damage evolution in Saffil alumina short-fibre reinforced aluminium during tensile testing, Article Materials Science and Engineering A ; Volume 395, Issue 1-2 , 2005 , Pages 27-34 ; 09215093 (ISSN) ; Weber, L ; Mortensen, A ; Sharif University of Technology
The evolution of microstructural damage during tensile deformation of pure aluminium reinforced with 10 vol.% alumina short fibres is studied by monitoring the evolution of density and Young's modulus as a function of tensile strain. It is found that Young's modulus drops rapidly until a strain εc ≈ 3%. The composite density remains virtually unchanged in this strain range. At strains above εc, Young's modulus decreases more slowly while the density begins to decrease linearly, indicating void growth in the composite. It is shown that the drop in Young's modulus is linked to fragmentation of fibres aligned along the stress axis, while the decrease in density is related to void opening across...
Utilization of gene expression programming for modeling of mechanical performance of titanium/carbonated hydroxyapatite nanobiocomposites: The combination of artificial intelligence and material science, Article International Journal of Engineering, Transactions A: Basics ; Volume 34, Issue 4 , 2021 , Pages 948-955 ; 17281431 (ISSN) ; Khayati, G. R ; Hasani, A ; Sharif University of Technology
Materials and Energy Research Center 2021
Titanium carbonated hydroxyapatite (Ti/CHA) nanobiocomposites have extensive biological applications due to the excellent biocompatibility and similar characteristics to the human bone. Ti/CHA nanobiocomposite has good biological properties but it suffer from diverse characteristics especially in hardness, Young's modulus, apparent porosity and relative density. This investigation is an attempt to propose the predictive models using gene expression programming (GEP) to estimate these characteristics. In this regards, GEP is used to model and compare the effect of practical variables including pressure, Ti/CHA contents and sintering temperature on their monitored properties. To achieve this...
Numerical simulation of three-dimensional flow and analysis of filling process in compression resin transfer moulding, Article Composites Part A: Applied Science and Manufacturing ; Volume 37, Issue 9 , 2006 , Pages 1434-1450 ; 1359835X (ISSN) ; Sharif University of Technology
In compression resin transfer moulding (CRTM), resin flows inside a mould filled with fibrous reinforcement as a result of resin injection and mould compression. This process facilitates the resin flow through the fibrous reinforcement particularly for high fiber content parts. This paper presents the numerical simulation of filling process of CRTM in full three-dimensional domain. A mathematical model of three-dimensional resin flow inside the CRTM mould is presented. An effective elastic modulus is introduced for multi-layer preforms connecting the mould closing speed to deformation rate of individual layers. Control volume/finite element method (CV/FEM) is used and the numerical algorithm...
On the mechanical characteristics of graphene nanosheets: A fully nonlinear modified Morse model, Article Nanotechnology ; Volume 31, Issue 11 , 2020 ; Ahmadian, M ; Firoozbakhsh, K ; Sharif University of Technology
Institute of Physics Publishing 2020
In this paper, the mechanical properties of graphene nanosheets are evaluated based on the nonlinear modified Morse model. The interatomic interactions including stretching and bending of the covalent bonds between carbon atoms, are replaced by nonlinear extensional and torsional spring-like elements. The finite element method is implemented to analyze the model under different loading conditions and linear characteristics of the graphene structure including the Young's modulus, surface modulus, shear modulus and Poisson's ratio are evaluated for various geometries and chirality where these properties are shown to be size and aspect ratio dependent. It is also found that when the dimensions...
Size-dependent interaction of an edge dislocation with an elliptical nano-inhomogeneity incorporating interface effects, Article International Journal of Solids and Structures ; Volume 49, Issue 5 , March , 2012 , Pages 759-770 ; 00207683 (ISSN) ; Ahmadzadeh Bakhshayesh, H ; Gutkin, M. Y
The elastic behavior of an edge dislocation, which is positioned outside of a nanoscale elliptical inhomogeneity, is studied within the interface elasticity approach incorporating the elastic moduli and surface tension of the interface. The complex potential function method is used. The dislocation stress field and the image force acting on the dislocation are found and analyzed in detail. The difference between the solutions obtained within the classical-elasticity and interface-elasticity approaches is discussed. It is shown that for the stress field, this difference can be significant in those points of the inhomogeneity-matrix interface, where the radius of curvature is smaller and which...
Surface/interface effect on the scattered fields of an anti-plane shear wave in an infinite medium by a concentric multi-coated nanofiber/nanotube, Article European Journal of Mechanics, A/Solids ; Volume 32 , 2012 , Pages 21-31 ; 09977538 (ISSN) ; Pahlevani, L ; Sharif University of Technology
In this paper, the scattering of anti-plane shear waves in an infinite matrix containing a multi-coated nanofiber/nanotube is studied. Based on the fact that the surface to volume ratio for nano-size objects increases, the usual classical theories which generally neglect the surface/interface effects fail to provide reasonable results. Therefore, to analyze the problem the wave-function expansion method is coupled with the surface/interface elasticity theory. In order to provide some quantitative results through consideration of several examples, the knowledge of the relevant surface and/or interface properties of the corresponding constituent materials are required. For this reason, part of...
A novel nonlinear constitutive relation for graphene and its consequence for developing closed-form expressions for Young's modulus and critical buckling strain of single-walled carbon nanotubes, Article Acta Mechanica ; Volume 222, Issue 1-2 , 2011 , Pages 91-101 ; 00015970 (ISSN) ; Delfani, M. R ; Sharif University of Technology
Carbon nanotubes (CNTs) are viewed as rolled graphene. Thus, an appropriate formulation describing the behavior of CNTs must contain the key information about both their initial configuration as graphene and final configuration as CNT.On this note, to date, somemodels, in particular based on the Cauchy- Born rule, for the description of CNTs behavior exist. A simplifying assumption in some of these models is that the length and perimeter of the CNT equal the corresponding dimensions of the unrolled initial configuration, thus neglecting the induced hoop and longitudinal strains. On the other hand, the present work offers a purely nonlinear continuum model suitable for the description of the...
Elastic moduli tensors, ideal strength, and morphology of stanene based on an enhanced continuum model and first principles, Article Mechanics of Materials ; Volume 110 , 2017 , Pages 1-15 ; 01676636 (ISSN) ; Ojaghnezhad, F ; Etehadieh, A ; Tabatabaei, M ; Sharif University of Technology
Elsevier B.V 2017
The present work aims to provide an accurate description of the tensile behavior of the planar as well as low-buckled stanene and to capture their ideal strength in armchair (AC)- and zigzag (ZZ)-directions. For an accurate description of anisotropic response of such hyperelastic materials as stanene, consideration of a highly nonlinear constitutive model in which up to the fourth power of strains is incorporated is inevitable. By utilizing first principles calculations based on density functional theory (DFT), the second, third, fourth, and fifth order elastic moduli tensors corresponding to both planar and low-buckled states are obtained. Moreover, the morphology of the free-standing...
Effective shear modulus of solids reinforced by randomly oriented-/aligned-elliptic nanofibers in couple stress elasticity, Article Composites Part B: Engineering ; Volume 117 , 2017 , Pages 150-164 ; 13598368 (ISSN) ; Alemi, B ; Sharif University of Technology
Nowadays, by adding a small amount (about 0.5–5% by weight) of a desired nanomaterial to a matrix having certain properties one may design a multifunctional nanocomposites with a remarkably improved macroscopic properties of interest. The capability of conventional continuum theories in treating the problems of embedded ultra-small inhomogeneity with any of its dimensions comparable to the characteristic lengths of the involved constituent phases is questioned, mainly, on the grounds of the accuracy and the size effect. The micromechanical framework based on the Eshelby's ellipsoidal inclusion theory  which has been widely used to estimate the overall behavior of composites falls under...
Weakly nonlocal micromorphic elasticity for diamond structures vis-à-vis lattice dynamics, Article Mechanics of Materials ; Volume 147 , 2020 ; Moosavian, H ; Sharif University of Technology
Elsevier B.V 2020
In this work, after formulating the weakly nonlocal micromorphic equations of motion for non-Bravais crystals with general anisotropy, specialization to diamond structures is made. A critical dilemma is the determination of the elastic moduli tensor appearing in the equations of motion. From the equivalency of these equations with the pertinent equations obtained in the context of lattice dynamics, the expressions of the components of the elastic moduli tensors in terms of the atomic force constants are derived analytically. Subsequently, the atomic force constants are calculated via ab initio density functional perturbation theory (DFPT) with high precision. As a benchmark for the accuracy...
A general unified treatment of lamellar inhomogeneities, Article Engineering Fracture Mechanics ; Volume 74, Issue 9 , 2007 , Pages 1499-1510 ; 00137944 (ISSN) ; Ojaghnezhad, F ; Sharif University of Technology
Consider a lamellar inhomogeneity embedded in an unbounded isotropic elastic medium. When the elastic moduli of the lamellar inhomogeneity are zero it is a crack, if its elastic moduli are infinite it is an anticrack, and when its elastic moduli are finite it is called a quasicrack. Based on the Eshelby's equivalent inclusion method (EIM), the present paper develops a unified approach for determination of the exact closed-form expressions for modes I, II, and III stress intensity factors (SIFs) at the tips of lamellar inhomogeneities under a remote applied polynomial loading. © 2006 Elsevier Ltd. All rights reserved
Discrete kernel functions for fcc crystals within eringen’s nonlocal theory of elasticity, Article Journal of Elasticity ; Volume 143, Issue 1 , 2021 ; 03743535 (ISSN) ; Shahvaghar Asl, S ; Sharif University of Technology
Springer Science and Business Media B.V 2021
The dilemma with the deficiencies of the nonlocal kernel functions as the building blocks of the Eringen’s nonlocal theory has been of concern. The aim of the current work is to provide a remedy for the calculation of the components of the nonlocal moduli tensor pertinent to face center cubic (fcc) crystals accounting for their true symmetry group. To this end, three new distinct nonlocal kernel functions which are the discrete atomistic Green’s functions in the stress space are obtained through the nonlocal dispersion relations associated with the longitudinal and shear waves in fcc crystals combined with the corresponding ones calculated via ab initio based on density functional...
Evaluating the effects of different plasticizers on mechanical properties of starch/ clay nanocomposites, Article Advanced Materials Research ; Volume 829, 2014 , 2014 , Pages 279-283 ; ISSN: 10226680 ; ISBN: 9783037859070 ; Mousavi, S. M. A ; Emam Djomeh, Z ; Bagheri, R ; Sharif University of Technology
Nano-biocomposites are a new class of hybrid materials composed of nano-sized filler (nanofiller) incorporated into a bio-based matrix. Such an association between eco-friendly biopolymers and nano-objects, with the aim to obtain synergic effects, is one of the most innovating routes to enhance the properties of these bio-matrices. In recent years, there has been an increasing interest in Starch as an inexpensive and renewable source has been used as a filler for environmentally friendly plastics for about two decades. However, the poor mechanical properties of starch based biopolymers, leads to use of nanoparticles as reinforcing materials. In the present study, the influence of a...
Contribution of ordered-inordered phenomenon within the interphase region toward increasing elastic modulus in CNT/polymer nanocomposites, Article Materials Science and Technology Conference and Exhibition 2015, MS and T 2015, 4 October 2015 through 8 October 2015 ; Volume 1 , October , 2015 , Pages 595-602 ; 9781510813939 (ISBN) ; Goodarzi Hosseinabadi, H ; NACE International ; Sharif University of Technology
Association for Iron and Steel Technology, AISTECH 2015
Exceptional mechanical properties of carbon nanotubes (CNTs) such as high elastic modulus, stiffness and tensile strength have made them as promising reinforcement in polymer nanocomposite systems. The characteristics of CNTs/polymer interphase region directly affect the efficiency of nanotubes for improving the nanocomposite mechanical properties. In this work, the influence of chains alignment within the interphase region on elastic response of the nanocomposite is assessed using a novel ordered-inordered approach. The applicability of the presented approach is examined by implementing the approach on a series of reported data available in the literature. The effects of CNT content,...
Thermo-mechanical analysis of Roller Compacted Concrete (RCC) dams (Jahgin Dam), Article Proceedings of the Symposium on the Application of Geophyics to Engineering and Environmental Problems, SAGEEP, 29 March 2009 through 2 April 2009, Fort Worth, TX ; Volume 1 , 2009 , Pages 417-427 ; 15548015 (ISSN) ; 9781615670512 (ISBN) ; Ghaemian, M ; Azimfar, S. M ; Sharif University of Technology
In this paper a procedure for two-dimensional unsteady thermo-mechanical analysis of layered structures is presented, allowing the determination of the temperature and stress field at each step the construction period. The finite element method is employed in the methodology. Numerical simulation are focused on concrete structures, particularly roller compacted concrete (RCC) dams. A time varying elasticity modulus is introduced in the model. One case study is presented and analysis under different design approaches. Thermal effects must be considered in the process of designing of certain types of concrete structures in order to prevent the damage during either the construction phase (early...
Nonlocal hcp kernel functions based on ab initio calculations: Pertinent dislocation problems revisited, Article Mechanics of Materials ; Volume 160 , 2021 ; 01676636 (ISSN) ; Shodja, H. M ; Sharif University of Technology
Elsevier B.V 2021
Eringen's nonlocal theory and an accurate determination of the nonlocal kernel functions for hexagonal close-packed (hcp) crystals are of interest. The kernel functions are closely related to the anisotropy as well as any crystalline symmetries. To this end, five new distinct nonlocal kernel functions which have the characteristics of discrete atomistic Green's functions in the stress space are obtained through consideration of the nonlocal dispersion relations associated with certain directions combined with ab initio Density Functional Perturbation Theory (DFPT) calculations of the pertinent phonon frequencies. This is the first work which provides the nonlocal hcp kernel functions...