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Vibration Analysis of Nanocomposite FGM Microbeam under Electric Field Effect, using the Non-classical Strain Gradient Theory

Mohammadi Hooyeh, Ali | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49985 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Ahmadian, Mohammad Taghi; Firoozbakhsh, Keikhosrow
  7. Abstract:
  8. Recently, micro-electromechanical systems have absorbed much attention due to their many applications in various industries, such as actuators, sensors, microswitches, and so on. These systems usually consist of a cantilever beam or a fixed-fixed beam in micro scale which can change shape under electrical force. In sensors and electrical actuators, Microbeams are under so much vibration that they undergo distortion and fracture in a short period of time. One way to prevent such phenomena is to use materials that have high flexibility during use and have a longer life span. In order to achieve this, the selection of nanocomposite microbeams which incorporate light materials as the matrix phase and carbon nanotubes as reinforcements is a practical solution. In this study, the effects of electric field on the static and dynamic behavior of functionally graded nanocomposite microbeam reinforced with single-walled carbon nanotubes (SWCNT) have been investigated. For this purpose, the microbeam is assumed to be a fixed-fixed Euler–Bernoulli beam, in front of which an electrode plate is placed. Electric excitation is performed by applying electrical voltage between the microbeam and the electrode which causes an electrostatic force between the electrode and the microbeam surfaces. Using the non-classical strain gradient theory and applying the Hamilton principle, the equations of motion and boundary conditions of the problem have been obtained. In deriving these equations, the effect of initial axial force, air viscous dissipation, thermal stresses and mid- plane stretching are considered. In order to solve the derived static and dynamic equations, numerical methods of finite element and Runge Kutta were used and semi-analytic homotopy analysis method was also utilized. The effects of different system parameters such as input voltages values, size-dependent ratios, volume fraction and distribution forms of nanotubes and the damping values on the static deformation, natural frequency and system damping have been investigated. Also, for the purpose of verification, the results of the present study are compared with those previous studies, and results indicates very good agreement exist with one-three percent difference.The results show that by increasing the volume fraction of nanotubes, the vibration frequency and the values of static and dynamic pull-in voltages of microbeam increases. Besides, the values of the natural frequencies obtained using the strain gradient theory are higher than the ones obtained by the coupled-stress and classical theory
  9. Keywords:
  10. Nanocomposite ; Microbeam ; Carbon Nanotubes ; Pull-in Voltages ; Homotopy Analysis Method ; Nonclassical Microbeams ; Vibrational Analysis

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