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#### Mechanical Behavior Analysis of Carbon Nanotube-Based Polymer Composites using Multiscale Modeling

, Ph.D. Dissertation Sharif University of Technology ; Naghdabadi, Reza (Supervisor) ; Rafii Tabar, Hashem (Supervisor) ; Bagheri, Reza (Supervisor)
Abstract

In this project, two multiscale modeling procedures have been implemented to study the mechanical behavior of SWCNT/polymer composites. First, a new three-phase molecular structural mechanics/ finite element (MSM/FE) multiscale model has been introduced which consists of three components, i.e. a carbon nanotube, an interphase layer and outer polymer matrix. The nanotube is modeled at the atomistic scale using MSM, whereas the interphase layer and polymer matrix are analyzed by the FE method. Using this model, we have investigated the macroscopic material properties of nanocomposite with and without considering the interphase and compared the results with molecular dynamics (MD) simulations....

#### Modeling and Analysis of Interaction between Tairlored CNT-Graphene Scaffolds and Stem Cell Growth and Differentitation

, Ph.D. Dissertation Sharif University of Technology ; Ahmadian, Mohammad Taghi (Supervisor) ; Firoozbakhsh, Kheikhosrow (Co-Supervisor)
Abstract

Since its successful synthesis as single layer during the past decades, Graphene and its derivatives have been extensively employed by many researchers in various science and engineering fields. The studies to characterize and define graphene behaviour are still in demand to answer the questions around these structures. The unique feathures of graphene such as high strength, good conductivity, large available surface, intoxicity and biocompatibility, has made it a suitable candidate to used in novel structures and materials. In this work, hybrid structures made from graphene and carbon nanotubes are investigated which can be utilized as scaffolds in tissue engineering.After an introduction...

#### Natural frequencies of C60, C70, and C80 fullerenes

, Article Applied Physics Letters ; Volume 96, Issue 2 , 2010 ; 00036951 (ISSN) ; Vafai, A ; Sharif University of Technology
Abstract

This letter adopts an atomistic modeling approach to study free vibrational characteristics of C60, C70, and C80 fullerenes. In this regard, we use the molecular structural mechanics consisting of equivalent structural beams to calculate the nonzero natural frequencies. The simulation results indicate that the first natural frequency of the fullerene is in the order terahertz and decreases nonlinearly with respect to the number of the carbon atoms

#### Vibrational analysis of single-walled carbon nanotubes using beam element

, Article Thin-Walled Structures ; Volume 47, Issue 6-7 , 2009 , Pages 646-652 ; 02638231 (ISSN) ; Ahmadian, M. T ; Vafai, A ; Sharif University of Technology
2009

Abstract

Vibrational analysis of single-walled carbon nanotubes (SWCNTs) is performed using a finite element method (FEM). To this end, the vibrational behavior of bridge and cantilever SWCNTs with different side lengths and diameters is modeled by three-dimensional elastic beams and point masses. The beam element elastic properties are calculated by considering mechanical characteristics of the covalent bonds between the carbon atoms in the hexagonal lattice. The mass of each beam element is assumed as point masses at nodes coinciding with the carbon atoms. Implementing the atomistic simulation approach, the natural frequencies of zigzag and armchair SWCNTs are computed. It is observed that the...

#### Potential application of single-layered graphene sheet as strain sensor

, Article Solid State Communications ; Volume 147, Issue 7-8 , August , 2008 , Pages 336-340 ; 00381098 (ISSN) ; Ahmadian, M. T ; Vafai, A ; Sharif University of Technology
2008

Abstract

Molecular structural mechanics is implemented to investigate the vibrational characteristics of defect-free single-layered graphene sheets (SLGSs), which have potential applications as strain sensors. The effect of strain on the fundamental frequencies of the defect-free zigzag and armchair models with clamped-clamped boundary condition is studied. The atomistic modeling results reveal while sensitivities of the strain sensors are not influenced significantly by chirality, they can be slightly increased by decreasing aspect ratios of the sheets. It is further shown that the SLGSs-based strain sensors are more sensitive to the applied stretch than the SWCNTs versions. © 2008 Elsevier Ltd. All...

#### Applications of single-layered graphene sheets as mass sensors and atomistic dust detectors

, Article ASME 2007 International Mechanical Engineering Congress and Exposition, IMECE 2007, 11 November 2007 through 15 November 2007 ; Volume 11 , 2007 , Pages 99-104 ; 079184305X (ISBN) ; Ahmadian, M. T ; Vafai, A ; ASME ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2007

Abstract

Molecular structural mechanics is implemented to model vibrational behavior of defect free single-layered graphene sheets (SLGSs) at constant temperature. To mimic these two-dimensional layers, zigzag and armchair models with cantilever and bridge boundary conditions are adopted. Fundamental frequencies of these nano structures are calculated, and it is perceived that they are independent of the chirality and aspect ratio. Effects of point mass and atomistic dust on the fundamental frequencies are also considered in order to investigate the possibility of using SLGSs as sensors. Results of exhibit the principle frequencies are highly sensitive to the added mass in the order of 10-6 fg....

#### Nanoscale vibrational behavior of single-layered graphene sheets

, Article ASME 2007 International Mechanical Engineering Congress and Exposition, IMECE 2007, 11 November 2007 through 15 November 2007 ; Volume 11 , 2007 , Pages 229-235 ; 079184305X (ISBN) ; Ahmadian, M. T ; Vafai, A ; ASME ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2007

Abstract

Molecular structural mechanics approach is implemented to investigate vibrational behavior of single-layered graphene sheets. By using the atomistic modeling, mode shapes and natural frequencies are obtained. Vibration analysis is performed under different chirality and boundary conditions. Numerical results from the finite element technique are applied to develop empirical equations via a statistical multiple nonlinear regression model. With the proposed empirical equations, fundamental frequencies of single-layered graphene sheets under considered boundary conditions can be predicted within 3 percent accuracy. Copyright © 2007 by ASME

#### Effect of vacancy defects on the fundamental frequency of carbon nanotubes

, Article 3rd IEEE International Conference on Nano/Micro Engineered and Molecular Systems, NEMS 2008, Sanya, 6 January 2008 through 9 January 2008 ; 2008 , Pages 1000-1004 ; 9781424419081 (ISBN) ; Ahmadian, M. T ; Asempour, A ; Tajalli, S. A
2008

Abstract

Carbon nanotubes are widely used in the design of nanosensors and actuators. Any defect in the manufactured nanotube plays an important role in the natural frequencies of these structures. In this paper, the effect of vacancy defects on the vibration of carbon nanotubes is investigated by using an atomistic modeling technique, called the molecular structural mechanics method. Vibration analysis is performed for armchair and zigzag nanotubes with cantilever boundary condition. The shift of the principal frequency of the nanotube with vacancy defect at different locations on the length is plotted. The results indicate that the frequency of the defective nanotube can be larger or smaller or...

#### Investigation of the interphase effects on the mechanical behavior of carbon nanotube polymer composites by multiscale modeling

, Article Journal of Applied Polymer Science ; Volume 117, Issue 1 , March , 2010 , Pages 361-367 ; 00218995 (ISSN) ; Naghdabadi, R ; Sharif University of Technology
2010

Abstract

In this article, a multiscale modeling procedure is implemented to study the effect of interphase on the Young's modulus of CNT/polymer composites. For this purpose, a three-phase RVE is introduced which consists of three components, i.e., a carbon nanotube, an interphase layer, and an outer polymer matrix. The nanotube is modeled at the atomistic scale using molecular structural mechanics. Moreover, three-dimensional elements are employed to model the interphase layer and polymer matrix. The nanotube and polymer matrix are assumed to be bonded by van der Waals interactions based on the Lennard-Jones potential at the interface. Using this Molecular Structural Mechanics/Finite Element...

#### Investigation the stability of SWCNT-polymer composites in the presence of CNT geometrical defects using multiscale modeling

, Article 4th International Conference on Multiscale Materials Modeling, MMM 2008, 27 October 2008 through 31 October 2008 ; 2008 , Pages 163-166 ; 9780615247816 (ISBN) ; Naghdabadi, R ; Sharif University of Technology
Department of Scientific Computing, Florida State University
2008

Abstract

CNT-reinforced polymer composites have attracted attention due to their exceptional high strength. The high strength can be affected by the presence of defects in the nanotubes used as reinforcements in the practical nanocomposites. In this paper, a Molecular Structural Mechanics / Finite Element (MSM/FE) multiscale modeling is used to study the effect of carbon nanotube geometrical defects on the stability of SWCNT-polymer composites. Here, two types of representative volume elements (RVEs) for these nanocomposites are considered with perfect and defected CNT. These RVEs have the same dimensions. The nanotube is modeled at the atomistic scale using molecular structural mechanics whereas the...

#### Mechanical properties of double-layered graphene sheets

, Article Computational Materials Science ; Volume 69 , 2013 , Pages 335-343 ; 09270256 (ISSN) ; Moshrefzadeh Sani, H ; Sharif University of Technology
2013

Abstract

In this paper, the molecular structural mechanics method is employed to calculate the mechanical properties of a double-layered carbon graphene sheet more accurately. For this purpose, covalent bonds are modeled using nonlinear beam elements and van der Waals interactions are replaced by nonlinear truss elements. Morse potential and Lennard-Jones potential equations are used to simulate the covalent bonds and van der Waals interactions, respectively. For each atom, van der Waals forces are considered with respect to all the other atoms located in its cut-off radius. In addition to in-plane mechanical properties of single and double-layered graphene sheets some out-of-plane properties like...

#### A numerical investigation on the free vibration of carbon nanopeapods as variable frequency beam resonators

, Article Modern Physics Letters B ; Volume 27, Issue 21 , August , 2013 ; 02179849 (ISSN) ; Alavi, S. M ; Sharif University of Technology
2013

Abstract

This study aims at investigation of the resonance frequencies of carbon nanopeapods constructed by a single wall carbon nanotube and encapsulated buckyball molecules (C60). A nanopeapod can be used as a nanoscale variable frequency beam resonator according to the number and positions of the encapsulated fullerenes. Using the molecular structural mechanics method the covalence bonds are simulated by equivalent beam elements and the van der Waal interactions between the buckyballs and nanotube are modeled as linear springs. Also, an equivalent beam model is proposed for the nanopeapod with sectional properties which are obtained by the molecular structural mechanics model. The beam-like modes...

#### Free vibrations of single-walled carbon nanotubes in the vicinity of a fully constrained graphene sheet

, Article Computational Materials Science ; Volume 53, Issue 1 , 2012 , Pages 12-17 ; 09270256 (ISSN) ; Hosseinian, A. R ; Sharif University of Technology
2012

Abstract

Carbon nanotubes (CNTs) have been recently taken into consideration as mechanical resonators of distinguished capabilities. This study aims at investigating the free vibration characteristics of a single-walled CNT in the vicinity of a fully constrained graphene sheet. Using a molecular structural mechanics model and considering nonlinear van-der-Waals interactions, the static deformation of the nanotube is obtained using an iterative procedure. Then, the governing equations of motion are linearized about the static equilibrium state and the natural frequencies are obtained. The molecular structural mechanics model is verified using established results in literature and then a survey is...

#### 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) ; Badri Kouhi, E ; Sharif University of Technology
American Institute of Physics Inc
2015

Abstract

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

#### A modified molecular structural mechanics model for the buckling analysis of single layer graphene sheet

, Article Solid State Communications ; Volume 225 , 2016 , Pages 12-16 ; 00381098 (ISSN) ; Moshrefzadeh Sany, H ; Mohammadkhani, H ; Sarmadi, M ; Sharif University of Technology
Elsevier Ltd

Abstract

In this paper the classical molecular structural mechanics model of graphene is modified to improve its accuracy for the analysis of transverse deformations. To this aim, a sample graphene sheet under a uniform pressure is modeled by both molecular dynamics and molecular structural mechanics methods. The sectional properties of the beam element, by which the covalent bonds are modeled, are modified such that the difference between the results of the molecular mechanics model and molecular dynamics simulation is minimized. Using this modified model, the buckling behavior of graphene under a uniform edge pressure is investigated subjected to different boundary conditions for both zigzag and...

#### Shell-like instability of large diameter single-walled carbon nanotubes conveying fluid

, Article Journal of Mechanical Science and Technology ; Volume 26, Issue 11 , 2012 , Pages 3389-3397 ; 1738494X (ISSN) ; Firouz Abadi, R. D ; Haddadpour, H ; Noorian, M. A ; Sharif University of Technology
2012

Abstract

The instability of large diameter single-walled carbon nanotubes (SWCNTs) conveying fluid is investigated based on the molecular mechanics. Using the modal expansion for structural displacements, the governing equations of coupled fluid-structural dynamics of SWCNTs are derived. The natural frequencies and mode shape of the SWCNTs are obtained based on the molecular structural mechanics to account for the effect of chirality and discrete nature of SWCNTs. The results show that the vibrational behavior of large diameter SWCNTs conveying fluid is size dependent, but the effect of chirality is negligible. The obtained results are compared with the equivalent continuum-based model in the...