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Theoretical Development of Resonance Acoustic Spectroscopy Technique and Its Applications for Non-destructive Evaluation of Thick-walled Cylindrical Shells

Rajabi, Majid | 2014

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 46545 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Behzad, Mehdi
  7. Abstract:
  8. Resonance acoustic spectroscopy (RAS) is one of the techniques used for monitoring the production quality and evaluation of mechanical properties of cylindrical components, due to their non-destructivity, high precision and quickness.
    In this technique, the resonance effects are caused by the excitation of eigenvibrations of structure by an incident acoustic wave located in far-field. The resonance spectroscopy (isolation and identification of the resonance features) is performed on the far-field scattered pressure field which contains valuable information about the characteristics of the target. Appropriate exploitation of these resonance informations from the theoretical model and comparison with the experimental data, and finally, solving the inverse scattering problem lead to evaluation of unknown characteristics of the target.
    It is more than one decade that the resonance acoustic spectroscopy technique has been suggested. However, its engineering applications are rare due to the limitations of this technique. The author of this thesis believes that these application limitations may be compensated in two distinct ways. First, by introducing novel configurations for implementation of the technique and second, by creation of a complete library of mathematical models of acoustic scattering from complex engineering structures where the concentration in this thesis is on the cylindrical components.
    In the first phase of this thesis, three new configurations are proposed as substitutions for the classic configuration, and the resonance response and resonance characteristics of the cylindrical structure are explored through the analyzed quantity.
    In the first configuration, the stimulation source is considered as a converging acoustic field which is modeled with a harmonic point force. The radiated pressure in far-field is proposed as the analyzed quantity for resonance spectroscopy purposes. The advantage of this configuration is its high spatial (local) sensitivity.
    In the second configuration, the excitation source is considered as a progressive harmonic acoustic field, the same as in the classic case, but the far-field scattered acoustic pressure is substituted with the static radiation force exerted on the cylindrical target. The benefit of this suggestion may be its lower sensitivity to external noise.
    One of the limitations of classic RAS is that the excitation frequency range of the ultrasonic transducers (as the source of excitation) are commonly in the order of few to several MHz while the primary resonance frequencies of the industrial cylindrical components (e.g., rods, tubes, pipes, pressure vessels, wires, and shells) are smaller than 100 kHz. Even if the transducers are set up at lower excitation frequencies, other concerns such as the insufficient spatial resolution will arise. In the third configuration, a non-contact vibro-acoustography (VA) method based on the ultrasound-stimulated vibro-acoustic spectroscopy) is proposed. In this method, the target is stimulated by an amplitude modulated acoustic field (i.e., generated by interfering ultrasound beams), and the frequency spectrum of low frequency radiated acoustic energy field from the body with the frequency of modulation is analyzed in response to a dynamic (oscillatory) radiation force, as a picture of the low frequency dynamics of the target. Due to the dependency of dynamic radiation force as the stimulation tool to high frequency resonance characteristics of the body and possible singular behavior of the exciter, it is important to analyze the contribution of the high frequency resonance response of the body in frequency spectrum of the dynamic radiation force function. This behavior is investigated via the resonance scattering theory (RST) which examines the potential application of VA for nondestructive evaluation purposes
  9. Keywords:
  10. Sloshing ; Acoustics ; Nondestructive Test ; Cylindrical Shells ; Ultrasonic Waves ; Resonance Acoustic Spectroscopy ; Nondestructive Evaluation ; Anisotropic Structures ; Acoustic Radiation

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