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Evaluation of Material Properties of Short Carbon Nanotube-Based Composites Using Nonlocal ElasticityTheory

Amelirad, Omid | 2011

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 41418 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Naghdabadi, Reza
  7. Abstract:
  8. Classical theory of elasticity, which is founded upon results of mechanical experiments on the large scale materials, has reasonable results in predicting mechanical properties. The basic idea in this theory is that stress at a point of the material is only a function of the local strain and it is independent of the nonlocal strains. Therefore, the size of the material does not play any role in analyzing mechanical behavior of materials using this theory. However, results from experiments and atomic simulations have shown that in nano scale materials, such as carbon nanotubes (CNTs) and their composites, mechanical properties are strongly dependent on the size parameters of these materials. In nonlocal theory of elasticity, considering a scale parameter in the constitutive equation of the material, dependency of mechanical properties on the size of the material can be investigated. In this thesis, the nonlocal theory of elasticity is employed to examine mechanical properties of carbon nanotubes composites. In this way, length dependent Young modulus of carbon nanotubes is studied. Afterwards, the Young moduli of two representative volume elements (RVE) containing long and short carbon nanotubes are determined. Using the nonlocal elasticity theory, stress distribution around a carbon nanotube in an infinite plate under uniaxial tension is calculated. The results of these studies show that Young moduli of RVEs containing short and long CNTs are dependent on the length of the CNT such that by increasing the length of the CNT from 1nm to 5nm the value of the Young modulus increases by 15%. In the matrix around the CNT, it is seen that the stress distribution is strongly dependent on the diameter of the CNT, and the stress concentration factor also decreased by decreasing in diameter of embedded CNT. Comparing the results of the nonlocal elasticity with atomic simulations and the classical elasticity, it is concluded that the results of the nonlocal theory of elasticity are in good agreement with molecular dynamics simulations, and the classical elasticity theory gives conservative results for mechanical properties of the nano scale materials
  9. Keywords:
  10. Carbon Nanotubes ; Nanocomposite ; Youngs Modulus ; Nonlocal Elasticity Theory ; Stress Concentration

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