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Investigating The Mechanical Properties Of Two-Dimensional Silicon Dioxide With Inherent Negative Poisson's Ratio by Molecular Dynamics Method

Ghorbani, Mohsen | 2022

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56199 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Tavakoli, Ruholah
  7. Abstract:
  8. Silicon dioxide or silica with the chemical formula SiO2 is the basic component of many minerals. SiO2 films and sheets are widely used in mechanics, optics and electronics due to their outstanding mechanical and electronic performance. The main reason for research in the field of materials with negative Poisson's ratio is their unusual properties, which arise due to the inherent property of negative Poisson's ratio. In this research, the mechanical properties of four two-dimensional silica structures at a temperature of one Kelvin were investigated with the help of molecular dynamics simulation. Also, the sensitivity of the results to the system size and strain rate was studied, and the effect of temperature and the presence of cracks in the structure on the mechanical properties was investigated. The results of the tensile loading of α, β, γ and δ structures with a strain rate of 5x107 along the X and Y directions showed that there was no difference in the mechanical behavior of the γ and δ structures during tensile loading along the X and Y directions and this structures are isotropic. In contrast, the β structure is highly anisotropic and the α structure showed a significant difference in the failure strains. The β structure showed Poisson's ratio of -0.116 in the X direction and Poisson's ratio of -0.269 in the Y direction, which the Poisson's ratio and Young's modulus in the Y direction were about 2.3 and 2.6 times higher than their values in is the X direction. β and δ structures showed much larger negative Poisson's ratio values than other materials with inherent negative Poisson's ratio. By changing the size of the simulation system, no specific change was observed in the stress-strain diagram of the structures in the X and Y directions, so the simulation results are not sensitive to the system size. With increasing temperature, Young's modulus decreased and Poisson's ratio increased slightly. The increase in Poisson's ratio can be attributed to the thermal fluctuations of the steady state structure. Poisson's ratio of the δ structure with increasing temperature from 1 to 300 K went from negative Poisson's ratio first to zero Poisson's ratio and then to positive Poisson's ratio at room temperature
  9. Keywords:
  10. Silicon Dioxide ; Negative Poisson's Ratio ; Molecular Dynamic Simulation ; Mechanical Properties ; Auxetic Materials

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