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Investigation and Extraction of an Appropriate Yield Criterion in Auxetic Metamaterial Structures: Numerical and Experimental Approaches

Nabavi, Amir Mohammad | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57879 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Movahhedy, Mohammad Reza; Mohammadi, Kaivan
  7. Abstract:
  8. In this thesis, the behavior of an auxetic metamaterial has been studied with the aim of investigating and deriving the appropriate yield surface and criteria for it. For this purpose, first by studying the available literature, the appropriate antielastic structure was selected for the research and then its 3D model was created using design softwares. Then the optimal simulation method was selected and its results were validated using the experimental results found in other articles. After ensuring the validation of the numerical results, obtaining the appropriate yield level for the structure was considered. For this purpose, three yielding relations of Von Mises, Hill and Tsia-Wu were studied and according to the features of these relations as well as the geometric features of the structure, Von Mises relation was used. Two criteria were introduced to identify the beginning of the yield stage based on the yield of the first point of the middle cell and the 0.2% plastic strain. Due to the difficulties of using the 0.2% plastic strain criterion for anisotropic materials, an alternative criterion based on accumulated plastic work was presented, which is well applicable to anisotropic materials. Then, by carrying out uniaxial and biaxial loading simulations on the structure in the finite element software, the yield surface of the structure and the mechanical properties of structure such as Poisson's ratio and Young's modulus were obtained. At the end, the effect of changing the geometrical parameters of the unit cell on the yield surface and the mechanical properties of the structure was investigated. Metamaterial studied in this research has a simple structure to create auxetic property and in a wide range of changes in the geometrical parameters of its unit cell, it shows auxetic property and negative Poisson's ratio. Also, by changing the geometrical parameters of the unit cell, a wide range of mechanical properties values for the structure can be achieved. For example, with a 1 mm change in the thickness of the struts of unit cell, Young's modulus changes by about 90%, Poisson's ratio changes by about 50%, the strength of the structure in the y direction changes by about 73%, and the strength of the structure in the x direction changes by about 25%. Also, with a 10-degree change in the angle between the struts of unit cell, the Young's modulus changes by about 83%, the strength of the structure in the y direction changes by about 88%, and the strength of the structure in the x direction changes by about 72% (the Poisson ratio of the structure does not change significantly). By use of this issue Structure can optimised for various types of applications by changing its geometrical parameters and producing appropriate mechanical properties
  9. Keywords:
  10. Metamaterial ; Numerical Simulation ; Quasi-Static Loading ; Yield Criterion ; Auxetic Metamaterials

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