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Analysis of Thermoelastic Damping in Microbeams and Microplates Based on the Non-Classical Continuum Mechanics and Heat Conduction Theories

Borjalilou, Vahid | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 51924 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Asghari, Mohsen
  7. Abstract:
  8. Due to the features like small dimensions, low manufacturing cost and low power consumption, micro-electromechanical systems (MEMS) are widely utilized in engineering applications. Many experimental investigations have indicated that the mechanical behavior of constructive microelements of these systems isn’t predictable by classical continuum theory. Therefore, to analyze the behavior of microelements, the non-classical continuum theories which can capture size effects should be utilized. On the other hand, various experimental observations have confirmed that thermoelastic damping (TED) is a dominant source of energy dissipation in microelements, in contrast to the non-small parts and structures. During the bending behavior of oscillating structures like beams and plates, one side of them is subjected to tension and the other side is subjected to compression. Due to the coupled nature of the mechanical and thermal domains, a transverse temperature gradient is generated across the structure. This phenomenon is an irreversible process which leads to energy dissipation. In this thesis, thermoelastic damping in microbeams and microplates is analyzed on the basis of the non-classical continuum theories of modified couple stress (MCS) and strain gradient (SG) together with the non-classical heat conduction theory of dual-phase-lag (DPL). In the framework of DPL model, the type of heat conduction equations are hyperbolic, which is in contrast to the classical thermoelasticity (CTE) theory. After derivation of coupled equations of motion and heat conduction based on the mentioned non-classical theories, explicit relations are obtained in the framework of complex frequency and energy dissipation approaches to calculate the amount of TED in microstructures. Moreover, the effect of different parameters such as geometrical dimensions, boundary conditions and type of material on the TED is numerically investigated in case studies. In the next section of this thesis, TED in the electrically actuated microbeams and microplates is studied and the influence of different parameters on the amount of TED is explored. Finally, the small-scale effect on the dynamic response of a microbeam under laser pulse is investigated
  9. Keywords:
  10. Microbeam ; Microplate ; Thermoelastic Damping ; Strain Gradient Theory ; Modified Couple Stress Theory ; Continuum Mechanics ; Conduction Heat Transfer

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