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    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 Moosavian, Hashem (Author) ; Mohammad Shodja, Hossein (Supervisor)
    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... 

    Weakly nonlocal micromorphic elasticity for diamond structures vis-à-vis lattice dynamics

    , Article Mechanics of Materials ; Volume 147 , 2020 Shodja, H. M ; 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... 

    Vibration characteristics of laminated composite beams with magnetorheological layer using layerwise theory

    , Article Mechanics of Advanced Materials and Structures ; Volume 25, Issue 3 , 2018 , Pages 202-211 ; 15376494 (ISSN) Naji, J ; Zabihollah, A ; Behzad, M ; Sharif University of Technology
    Taylor and Francis Inc  2018
    Vibration characteristics of laminated composite beams with magnetorheological (MR) layer are investigated using layerwise theory. In most studies, shear strain across the thickness of MR layer has been considered as a constant value, which does not precisely describe the shear strain. In this study, layerwise theory is employed to develop a finite element formulation to investigate MR-laminated beams. Experimental tests under different magnetic fields are carried out to verify the numerical results. Layerwise numerical results are compared with the experimental results and other theories. An empirical expression for complex shear modulus is presented. The effects of MR layer thickness on... 

    Variational bounds and overall shear modulus of nano-composites with interfacial damage in anti-plane couple stress elasticity

    , Article International Journal of Damage Mechanics ; Volume 29, Issue 2 , 2020 , Pages 246-271 Mohammadi Shodja, H ; Hashemian, B ; Sharif University of Technology
    SAGE Publications Ltd  2020
    It is well known that classical continuum theory has certain deficiencies in capturing the size effects and predicting the nanoscopic behavior of materials in the vicinity of nano-inhomogeneities and nano-defects with reasonable accuracy. Couple stress theory which is associated with an internal length scale for the medium is one of the higher order continuum theories capable of overcoming such difficulties. In this work, the problem of a nano-size fiber embedded in an unbounded isotropic elastic body for three different types of interface conditions: perfect, imperfect (partially damaged), and pure sliding (completely damaged) subjected to remote anti-plane loading is examined in this... 

    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) Shojaei, M. R ; 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... 

    Two-dimensional porous graphitic carbon nitride C6N7 monolayer: first-principles calculations

    , Article Applied Physics Letters ; Volume 119, Issue 14 , 2021 ; 00036951 (ISSN) Bafekry, A ; Faraji, M ; Fadlallah, M. M ; Abdolhosseini Sarsari, I ; Jappor, H. R ; Fazeli, S ; Ghergherehchi, M ; Sharif University of Technology
    American Institute of Physics Inc  2021
    The fabrication of the C6N7 monolayer [Zhao et al., Sci. Bull. 66, 1764 (2021)] motivated us to discover the optical, structural, mechanical, and electronic properties of the C6N7 monolayer by employing the density functional theory (DFT) method. We find that the shear modulus and Young's modulus of the C6N7 monolayer are smaller than the relevant values of graphene. However, Poisson's ratio is more significant than that of graphene. Applying the PBE (HSE06) functional bandgap of the C6N7 monolayer is 1.2 (1.97) eV, and the electronic dispersion is almost isotropic around the Γ point. C6N7 is more active in the ultraviolet region as compared to the visible light region. This study provides... 

    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) Shamsai, A ; 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... 

    Thermoelastic fields of a functionally graded coated lnhomogeneity with sliding/perfect interlaces

    , Article Journal of Applied Mechanics, Transactions ASME ; Volume 74, Issue 3 , 2007 , Pages 389-398 ; 00218936 (ISSN) Hatami Marbini, H ; Shodja, H. M ; Sharif University of Technology
    The determination of the thermo-mechanical stress field in and around a spherical/ cylindrical inhomogeneity surrounded by a functionally graded (FG) coating, which in turn is embedded in an infinite medium, is of interest. The present work, in the frame work of Boussinesq/Papkovich-Neuber displacement potentials method, discovers the potential functions by which not only the relevant boundary value problems (BVPs) in the literature, but also the more complex problem of the coated inhomogeneities with FG coating and sliding interfaces can be treated in a unified manner. The thermo-elastic fields pertinent to the inhomogeneities with multiple homogeneous coatings and various combinations of... 

    Thermal buckling analysis of bridged single walled carbon nanotubes using molecular structural mechanics

    , Article Journal of Applied Physics ; Volume 117, Issue 11 , 2015 ; 00218979 (ISSN) Firouz Abadi, R. D ; Badri Kouhi, E ; Sharif University of Technology
    American Institute of Physics Inc  2015
    This paper is concerned with the stability analysis of bridged single walled carbon nanotubes (SWCNT) under temperature changes. A molecular structural mechanics model is utilized to investigate the free vibration frequencies and thermal buckling of SWCNT. In comparison with most of the previous studies, a temperature-variable thermal-expansion-coefficient is used that is negative under a certain temperature. Also thermal variation of Young's modulus of the CNTs is considered. Several studies are performed to investigate the critical temperature change due to heating and cooling of SWCNTs with different chiralities and slenderness ratios and the stability boundaries are determined  

    The effect of nano-TiO2 additions on the densification and mechanical properties of SiC-matrix composite

    , Article Ceramics International ; Volume 46, Issue 5 , April , 2020 , Pages 6477-6483 Khodaei, M ; Yaghobizadeh, O ; Baharvandi, H. R ; Alipour Shahraki, A ; Mohammadi, H ; Sharif University of Technology
    Elsevier Ltd  2020
    This research studied the effect of adding TiO2 nanoparticles along with Al2O3 and Y2O3 additives on the physical and mechanical properties of a SiC-matrix composite. The samples were fabricated through a pressureless process at 1900 °C. The results showed that the addition of TiO2 nanoparticles up to 4.5 wt% inhibited the excessive growth of SiC grains. According to the investigations, the microstructure and final properties of composites were affected by density, synthesized phases as well as their distribution in the matrix, and grain size. The highest density, Young's modulus, hardness, indentation fracture resistance, and flexural strength, alongside with the lowest brittleness index... 

    Surface energy effects on the yield strength of nanoporous materials containing nanoscale cylindrical voids

    , Article Mechanics of Materials ; Volume 42, Issue 9 , September , 2010 , Pages 852-862 ; 01676636 (ISSN) Goudarzi, T ; Avazmohammadi, R ; Naghdabadi, R ; Sharif University of Technology
    Surfaces and interfaces behave differently from their bulk counterparts especially when the dimensions approach small scales. The recent studies have shown that the surface/interface free energy (surface stress) plays an important role in the effective mechanical properties of solids with nanosized inhomogeneities. In this work, within a micromechanical framework, the effect of surface stress is taken into account to obtain a macroscopic yield function for nanoporous materials containing cylindrical nanovoids. Gurtin-Murdoch model of surface elasticity is incorporated in the generalized self-consistent method to obtain a closed-form expression for the transverse shear modulus of transversely... 

    Surface/interface effects on elastic behavior of a screw dislocation in an eccentric core-shell nanowire

    , Article International Journal of Solids and Structures ; Volume 49, Issue 13 , 2012 , Pages 1665-1675 ; 00207683 (ISSN) Ahmadzadeh Bakhshayesh, H ; Gutkin, M.Y ; Shodja, H. M ; Sharif University of Technology
    The elastic behavior of a screw dislocation which is positioned inside the shell domain of an eccentric core-shell nanowire is addressed with taking into account the surface/interface stress effect. The complex potential function method in combination with the conformal mapping function is applied to solve the governing non-classical equations. The dislocation stress field and the image force acting on the dislocation are studied in detail and compared with those obtained within the classical theory of elasticity. It is shown that near the free outer surface and the inner core-shell interface, the non-classical solution for the stress field considerably differs from the classical one, while... 

    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) Gutkin, M. Yu ; Rezazadeh Kalehbasti, S ; Shodja, H. M ; Sharif University of Technology
    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... 

    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) Shodja, H. M ; 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... 

    Suction-induced hardening effects on the shear modulus of unsaturated silt

    , Article International Journal of Geomechanics ; Volume 16, Issue 6 , 2016 ; 15323641 (ISSN) Khosravi, A ; Salam, S ; McCartney, J. S ; Dadashi, A ; Sharif University of Technology
    American Society of Civil Engineers (ASCE) 
    The small-strain shear modulus Gmax is a key material parameter in modeling the behavior of soils subjected to dynamic loading. Recent experimental results indicate that seasonal weather interaction with near-surface soils causes Gmax to change by up to an order of magnitude in some climates, with a hysteretic response upon drying and wetting. The increase in Gmax during drying and the stiffer response during subsequent wetting have been postulated to be due to plastic hardening during drying. To further understand this behavior, a series of isotropic compression tests were performed on compacted silt specimens at different values of matric suction to evaluate changes in the preconsolidation... 

    Structure, swelling and mechanical behavior of a cationic full-IPN hydrogel reinforced with modified nanoclay

    , Article Iranian Polymer Journal (English Edition) ; Volume 24, Issue 5 , May , 2015 , Pages 379-388 ; 10261265 (ISSN) Kheirabadi, M ; Bagheri, R ; Kabiri, K ; Sharif University of Technology
    Springer-Verlag London Ltd  2015
    Despite various applications of hydrogels, they have poor gel strength and low resistance against crack propagation which lead to the limitation of their applications. For overcoming this inherent weakness, the current study has focused on the simultaneous utilization of interpenetrating polymer network (IPN) structure and nanocomposite hydrogels. It is known that IPN and nanocomposite gels can improve gel strength. The combination of IPN and nanocomposite structure was developed in hydrogels for improving gel strength. For this purpose, bentonite was successfully modified with a cationic surfactant, (3-methacrylamidopropyl) trimethyl ammonium chloride (MAPTAC), as intercalate, and... 

    Small-strain shear modulus of cement-admixed kaolinite

    , Article Geotechnical and Geological Engineering ; Volume 30, Issue 1 , Oct , 2012 , Pages 163-171 ; 09603182 (ISSN) Bahador, M ; Pak, A ; Sharif University of Technology
    An experimental study is conducted to measure small-strain shear modulus of clay-cement mixture using bender element apparatus setup in a triaxial cell. Bender element tests were conducted on cement-treated soils and the results were analyzed to study the variation of shear modulus properties of soil specimens at different cement contents, confining pressures, curing times, and compaction moisture contents. Based on the obtained results increasing the cement ratio has a significant effect on the small-strain shear modulus of the treated soils, and this effect signifies with increasing the moisture content and curing time. Rates of shear modulus enhancements due to cement content, curing... 

    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) Shodja, H. M ; 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... 

    Sintering characterizations of Ag-nano film on silicon substrate

    , Article Advanced Materials Research ; Volume 829 , 2014 , Pages 342-346 ; ISSN: 10226680 ; ISBN: 9783037859070 Keikhaie, M ; Akbari, J ; Movahhedi, M. R ; Alemohammad, H ; Sharif University of Technology
    Nowadays, thin films have many applications in every field. So, in order to improve the performance of thin film devices, it is necessary to characterize their mechanical as well as electrical properties. In this research work we focus on the development of a model for the analysis of the mechanical and electrical properties of silver nanoparticles deposited on silicon substrates. The model consists of inter-particle diffusion modeling and finite element analysis. In this study, through the simulation of the sintering process, it is shown that how the geometry, density, and electrical resistance of the thin film layer are changed with sintering conditions. The model is also used to... 

    Sandwich beam model for free vibration analysis of bilayer graphene nanoribbons with interlayer shear effect

    , Article Journal of Applied Physics ; Vol. 115, issue. 17 , May , 2014 ; ISSN: 00218979 Nazemnezhad, R ; Shokrollahi, H ; Hosseini-Hashemi, S ; Sharif University of Technology
    In this study, sandwich beam model (SM) is proposed for free vibration analysis of bilayer graphene nanoribbons (BLGNRs) with interlayer shear effect. This model also takes into account the intralayer (in-plane) stretch of graphene nanoribbons. The molecular dynamics (MD) simulations using the software LAMMPS and Adaptive Intermolecular Reactive Empirical Bond Order (AIREBO) potential are done to validate the accuracy of the sandwich model results. The MD simulation results include the two first frequencies of cantilever BLGNRs with different lengths and two interlayer shear moduli, i.e., 0.25 and 4.6GPa. These two interlayer shear moduli, 0.25 and 4.6GPa, can be obtained by sliding a small...