Simulation and Measurement of Ultrasonic Waves in Elastic Plates Using Laser Vibrometry

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.