Third Day Poster Session, 17 June 2010 - NanoTR-VI

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Poster Session, Thursday, June 17
Theme F686 - N1123
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Study the Effect of Carbon Nanotube Orientation on the Shear Modulus of SWCNT/polymer
Composites using Hierarchical MD/FE Multiscale Modeling
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Abbas MontazeriP P*,P P SadeghiP
PReza NaghdabadiP Hasehm Rafii-TabarP
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PInstitute for Nano Science and Technology, Sharif University of Technology, Tehran, Iran
PDepartment of Mechanical Engineering, Sharif University of Technology, Tehran, Iran
PDepartment of Medical Physics and Biomedical Engineering, and Research Centre for Medical Nanotechnology and Tissue Engineering,
Shahid Beheshti University of Medical Sciences, Evin, Tehran, Iran.
Abstract- In this paper, a combination of molecular dynamics (MD) and finite element method (FEM) is used to predict the effect of CNT
orientation on the shear modulus of nanocomposites containing SWCNTs as reinforcing elements. The results show that in the case of 45
orientation, SWCNTs have the most effect on the shear modulus of polymer composites.
Recent experimental and theoretical investigations have
demonstrated that substantial improvements in the mechanical
properties of polymers can be obtained by using small volume
fractions of carbon nanotubes as reinforcing materials.
Various properties such as elastic modulus and break strength,
yield strength, max strain, buckling behavior, hardness,
ductility and toughness, fatigue life and fatigue properties,
creep performance and glass transition temperature have been
measured in these studies. A noticeable void in current
literature is the lack of a computational model for determining
the shear modulus of these nanocomposites. Meanwhile, the
study of shear deformation is of particular interest as not only
it is a basic mode of deformation at the microscopic level, but
it also could be used to create high orientation throughout a
large cross section of polymer material. Highly oriented
polymers are well-known to exhibit enhanced mechanical
properties. Furthermore, shear failure is one of the most
famous failure mechanisms of nanotube reinforced
composites. In addition, shear deformation of nanocomposites
has a great effect on the shear-based production techniques of
these nanostructures like shear mixing methods.
The objective of the present article is to analyze the effect of
single-walled carbon nanotube alignment on the shear
modulus of SWCNT-reinforced polymer composites using a
new hierarchical MD/FE multiscale method. To achieve this
end, first, a transverse-isotropic elastic model of SWCNTs is
formulated that combines methods from continuum elasticity
theory and molecular dynamics simulation. This model is
employed to predict the transverse-isotropic elastic properties
of SWCNTs. MD simulations are used to model the
mechanical behavior of SWCNTs under axial, torsional and
radial loadings. Also, continuum-based models using the
linear elasticity theory were employed to model the
mechanical behavior of SWCNTs under these loading
conditions. The methodology developed herein combines a
unit cell continuum model with MD simulations to determine
the transverse-isotropic elastic constants of SWCNTs. These
atomically informed carbon nanotubes are used in a finite
element simulation in the next step to investigate the effect of
single-walled carbon nanotube alignment on the shear
modulus of CNT-based nanocomposites. Also, continuumbased
finite element formulation was implemented to analyze
the polymer matrix. Using this hierarchical MD/FE multiscale
model, we could obtain the shear properties of these
nanocomposites based on the interatomic interactions of
SWCNT atoms with negligible computational costs.
Figure 1. (a) A Schematic illustration of the four loading conditions
of SWCNTs: (a) axial tension, (b) torsion, (c) uniform radial pressure
(end view), and (d) non-uniform radial pressure (end view).
The results depicted the noticeable effect of adding SWCNTs
as reinforcement on the shear deformation of polymers.
Increasing the carbon nanotube orientation from 0° caused an
increase in the shear modulus of the polymer up to 45° and
then, the reinforcement role of SWCNT decreased. Note that
in 90°, there was not any change in the shear modulus of
polymer due to addition of the SWCNT. The fact that
maximum shear modulus of nanocomposite appears in the
case of 45° carbon nanotube orientation, arises from the
transverse-isotropic elastic properties of SWCNTs as depicted
by the hybrid MD/continuum model presented in this work.
The results revealed that longitudinal Young’s modulus of the
SWCNT was much greater than this elastic constant in the
transverse direction. Hence it was anticipated that in the case
of 45° where the resultant tensile force of the shear forces
imposed on the side walls corresponds to the axial direction of
the SWCNT, the maximum increase in the shear modulus of
SWCNT-reinforced composites should be obtained. Our
simulation results confirmed the idea.
*Corresponding author: a_montazeri@mehr.sharif.edu
6th Nanoscience and Nanotechnology Conference, zmir, 2010 749