Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Subject: search.filters.subject.Honeycomb structure

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  • Master Thesis
    The Investigation of Static and Dynamic Compressive Deformation Behavior of a Paper Based Sandwich Material
    (01. Izmir Institute of Technology, 2022) Taşdemirci, Alper; Taşdemirci, Alper; Taşdemirci, Alper; 03.10. Department of Mechanical Engineering; 03. Faculty of Engineering; 01. Izmir Institute of Technology
    In this study, dynamic and quasi-static compression behavior of paper-based honeycomb sandwich structures were investigated. It is known that the mechanical properties of paper-based honeycomb structures change with changing strain rate values. For this reason, dynamic and quasi-static loading conditions should be considered separately when investigating the compressive behavior of the structure. In the material characterization studies, a series of tests were conducted to examine mechanical properties of the paper layer material and sandwich structure. Using data from mechanical tests, numerical models were established in the finite element tool LS-DYNA. Outputs of numerical models were validated with mechanical test outputs. After the validation study, the effects that influence the dynamic compressive behavior of the paper-based honeycomb sandwich structure and their contribution percentages were investigated using the opportunities provided by the FE tool. The results showed a 150.48 % difference between the dynamic and quasi-static compressive behavior of the structure. The numerical results obtained from explicit and implicit solvers also showed good correlation with the experimental results. In addition, the micro-mechanical modeling approach in numerical models made it possible to investigate the effects such as strain rate sensitivity of the paper layer material, entrapped air inside the core cells, and micro-inertia individually. The contribution percentages of the effects were calculated by comparing the numerical and experimental results.
  • Master Thesis
    Electronic Properties of Artificial Graphene Nanostructure
    (01. Izmir Institute of Technology, 2021) Güçlü, Alev Devrim; Güçlü, Alev Devrim; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of Technology
    Artificial graphene is an artificial honeycomb structure which mimics the interesting properties of graphene. Such as Dirac cone in energy dispersion, zero band gap etc. Wide range of production type makes artificial graphene valuable material. It can be engineered by lasers, molecules and semiconductors. Semiconductor based artificial graphene can be produced by dot lattice with honeycomb patterned attractive potential or by antidot lattice with triangular patterned repulsive potential. In the following calculations, semiconductor (GaAs) based artificial graphene was used to compute electronic properties. Like in graphene, artificial graphene has Dirac cones in energy dispersion. However, graphene has 1.42 angstrom carbon to carbon atom distance. This distance can not be changed but artificial graphene offers us tunability. Different parameters yield tons of band structure. It offers not only Dirac cone but also gaped bands in energy dispersion. This graphene-like feature and tunability make artificial graphene an important and researchable subject. Besides, we added another tunable parameter stiffness to control the shape of potential. Stiffness became another important parameter in our calculations. We observed that stiffness dramatically changes the band structure of the material. As a first step, artificial graphene band structures are calculated from the single-electron approximation. Some parameters are compared with other works and the same results are found. Dirac cones are achieved in band structures. Hopping and Hubbard U values are computed. Those parameters are essential for computing finite structures. Mean-field Hubbard can be solved, and wave functions can be used as input for input required methods such as quantum Monte Carlo. As a second step, we used the density functional theory method to investigate electron-electron interactions. Local density approximation was chosen to solve the Kohn-Sham equation. Hopping parameters obtained from DFT are much realistic than the single-electron approximation. Stiffness plays a big role in DFT energy dispersio