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

Montazeri Hedesh , Abbas | 2010

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 40836 (48)
  4. University: Sharif University of Technology
  5. Department: Institute for Nanoscience and Nanotechnology
  6. Advisor(s): Naghdabadi, Reza; Rafii Tabar, Hashem; Bagheri, Reza
  7. Abstract:
  8. 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. It is shown that there is a noticeable deviation from MD results with two-phase model. Meanwhile the three-phase modeling, shows that by considering the effect of the interphase, the elastic constants of these nanocomposites could be calculated the same as the MD results with maximum deviation of 1.8% and negligible computational costs in comparison with the MD simulation. The verified model has been used to study the effect of the interphase layer on the stability of defected SWCNT/polymer composites. The buckling onset strain has been calculated for defected CNTs in the polymer nanocomposites with and without considering the interphase layer. It is concluded that the existence of a more compact layer than the polymer chains coated on the nanotube can enhance drastically the buckling behavior of these nanocomposites (about 35%). Using this approach, we have also examined the effect of the diameter and length of defected SWCNTs on the stability of these nanocomposites. In the second method, a combination of MD, continuum elasticity and FEM has been used to predict the effect of carbon nanotube orientation on the shear modulus of the polymer nanocomposites embedded with single-walled carbon nanotubes (SWCNTs). To this end, first, a transverse-isotropic elastic model of SWCNTs has been developed based on the continuum elasticity theory and molecular dynamics simulation to compute the transverse-isotropic elastic constants of SWCNTs. These elastic constants have then been used in an FEM-based simulation to explore the effect of SWCNT orientation on the shear modulus of nanocomposites. Furthermore, the shear stress distributions along the nanotube axis and over its cross sectional area have been investigated to study the effect of CNT orientation on the shear load transfer. The results show that the total shear load sustained by the CNTs is greatest in the case of 45 ۫ orientation.
  9. Keywords:
  10. Multiscale Modeling ; Nanocomposite ; Carbon Nanotubes ; Mechanical Behavior ; Molecular Dynamics ; Molecular Structural Mechanics

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