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Investigation of Mechanical Behavior of Short Carbon Nanotubes Reinforced Metal Matrix Nanocomposites Using Surface Elasticity Theory

Saboori, Mohammad Ali | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43397 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Naghdabadi, Reza
  7. Abstract:
  8. In recent years, carbon nanotubes have been the focus of considerable researches. Numerous investigators have reported remarkable physical and mechanical properties for this new form of carbon. In particular, the exceptional mechanical properties of carbon nanotubes, combined with their low density, offer scope for the development of nanotube reinforced composite materials. The potential for nanocomposites reinforced with carbon tubes having extraordinary specific stiffness and strength represent tremendous opportunity for application in this century and recently metal matrix type of these nanocomposites, due to their advantages, have received great attention. Classical theories of elasticity, which are founded upon results of mechanical experiments on the large scale materials, have reasonable results in predicting mechanical properties. However the size of the material does not play any role in analyzing mechanical behavior of materials using these theories. On the other hand, 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. Therefore non-classical theories such as surface elasticity theory have been developed which have the ability to evaluate properties of nanomaterials with enough precision and lower calculation cost with respect to atomic methods. Surfaces/interfaces behave differently in comparison to their bulk counterparts especially when the dimensions are in small scale. Due to high surface area to volume ratio, surface effect plays an important role in determining mechanical properties of nano-heterogeneous materials, so surface elasticity theory modifies the classical equations from this point of view. The main objective of this project is to understand the effects of surface/interface stress on the stress distribution of metals containing aligned short carbon nanotubes. Based on the classical models and considering surface effects, an analytical solution for short fiber nanocomposites is presented. Two sets of matrix and fiber displacement solutions, i.e. the far-field solution and the transient solution, were developed exactly based on the theory of elasticity and superposed to obtain simplified analytical expressions for the matrix and fiber three-dimensional stress field components. Surface effects are introduced via Gurtin-Murdoch linear model of surface/interface and generalized Young-Laplace equations and then stress distribution in the fiber and matrix were found. Moreover, considering some numerical examples, it is shown that the surface stress has significant influence on shear, radial and hoop stresses especially for fiber radii smaller than 10 nm.
  9. Keywords:
  10. Metal Matrix Nanocomposite ; Surface Elasticity ; Short Carbon Nanotube ; Representative Volume Element

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