The propagation of Lamb waves in elastic plates is analyzed both numerically and experimentally. A Scanning Laser Doppler Vibrometer (SLDV) is here used to detect and visualize transient waveforms propagating in an elastic plate at low ultrasonic frequencies. The waves are excited by a piezoelectric crystal glued to the plate surface and actuated by sinusoidal pulses of varying frequency. The pulse sequence is triggered by the SLDV internal controller so that phase and delay information are preserved. Such information allows visualization of the waveform pattern as it propagates over the plate surface. The experiment produces animated displacement maps where the interaction with discontinuities in the plate such as defects becomes apparent. This capability suggests application of the SLDV technique as part of an overall damage detection methodology which combines the recognized sensitivity of ultrasonic waves with the localization of damage via wavefield visualization. The interpretation of the experimental results is aided by numerical simulations of ultrasonic waves in plate structures. The simulations are performed using a Local Interaction Simulation Approach (LISA), which represents a simple and effective tool for simulating and visualizing waveforms in isotropic or orthotropic plate-like structures.

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A diagnostic method of inspecting structural integrity using vibration, which is generated and monitored by piezoelectric transducers, is presented. When damage occurs in structures, the flexural-wave propagation characteristics change because of discontinuities in structural properties. To monitor this change, frequency-dependent variation of the wavenumber is measured from the piezoelectrically actuated harmonic vibration of a structure. The theoretical model was proposed to analyze the wave propagation and standing-wave pattern in the structure. Its prediction was compared to the measured vibration response on the basis of which the theoretical model was verified. Using the predicted response, the sensitivity of the potential energy to damage is obtained. With damages of different sizes and locations induced on the beam, the change in the wavenumber and equivalent dynamic stiffness was obtained from the measured transfer functions. The location and size of damage was identified from the damage index accurately. The correlation coefficient between the sensitivity of the potential energy and the variation of the dynamic stiffness was used in estimating the damage index. Analysis of the flexural-wave propagation from piezoelectric actuation allowed continued and precise structural health monitoring.

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An experimental method is proposed to measure the rheological properties of fluids. The effects of fluids on the vibration actuated by piezoelectric patches were analyzed and used in measuring viscoelastic properties. Fluid-structure interactions induced changes in the beam vibration properties and frequency-dependent variations of the complex wavenumber of the beam structure were used in monitoring these changes. To account for the effects of fluid-structure interaction, fluids were modelled as a simple viscoelastic support at one end of the beam. The measured properties were the fluid's dynamic shear modulus and loss tangent. Using the proposed method, the rheological properties of various non-Newtonian fluids were measured. The frequency range for which reliable viscoelasticity results could be obtained was 10-400 Hz. Viscosity standard fluids were tested to verify the accuracy of the proposed method, and the results agreed well with the manufacturer's reported values. The simple proposed laboratory setup for measurements was flexible so that the frequency ranges of data acquisition were adjustable by changing the beam's mechanical properties.