LEE- Katı Cisimlerin Mekaniği-Yüksek Lisans

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http://hdl.handle.net/11527/19330

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  • Öge
    Mechanical properties of boron nanotubes
    ( 2021-11-05) Çalışkan, Emre ; Kırca, Mesut ; 503191531 ; Solid Mechanics ; Katı Cisimlerin Mekaniği
    Boron nanotubes (BNTs) which can be considered as structural analogs of carbon nanotubes (CNTs) and boron nitride nanotubes (BNNTs) offer remarkable mechanical, electrical, and chemical properties. As the building unit of BNTs, boron, the fifth element in the periodic table, is the lightest elemental substance that can form interatomic covalent bonds possessing multiple bonding states, which in turn provides a variety of allotropes with diverse physical and chemical properties. BNTs exhibit metallic behavior regardless of their chirality and diameters, which renders them extremely attractive in the design of novel electronic nanodevices, such as field-effect transistors, light-emitting diodes, field emission displays. In these applications, mechanical properties play a significant role since the mechanical strain is usually employed to adjust the electronic properties of the BNTs. Therefore, mechanical properties, such as tensile strength and elastic Young's modulus, of the boron nanotube structures hold significant importance. In literature, most of the theoretical studies regarding the boron nanotubes are based on the first-principles density functional theory calculations. As an alternative approach, reactive molecular dynamics can provide accurate and quick results depending on the accuracy of the force field. Furthermore, unlike density functional theory calculations, molecular dynamics can be used to investigate large systems. In the present study, boron nanotubes are simulated using reactive molecular dynamics simulations. Although this method has been extensively practiced for borophene, to the best of our knowledge, it has not been used to simulate BNTs yet. We created 10 different BNTs with different vacancy ratios ranging between 0 and 0.33 in two different chiral directions, zigzag and armchair. Simulations are conducted for different diameters, lengths, and aspect ratios using four different strain rates and three different temperatures, 1, 300, and 600 K. We conducted tensile tests to inspect the mechanical properties. Mechanical properties and thermal stabilities of BNTs are highly dependent on their vacancy ratio, atomic configuration, and chirality. Our results indicate that BNTs with exhibit highly anisotropic behavior. Young moduli and ultimate tensile stress of nanotubes are generally two times higher in the zigzag direction, yet the ultimate tensile strain is two times higher in the armchair direction, except for some configurations. Stiffness and strength in general decrease while the vacancy ratio and temperature increase. The potential energy difference per atom due to the bond order is the main root of the defect formation. Some structures exhibit plastic behavior owing to stable bond formations during tensile. We believe that our study will drive further research for BNTs using classical molecular dynamics since it will allow large-scale simulation and modeling. Their vacancies can be exploited for several applications such as hydrogen storage. Thermal properties, nanocomposites with BNTs can be subject to future studies.