M.S. Thesis Presentation by John Doane
Wednesday, August 1, 2001

(Dr. Jacek Jarzynski, advisor)

"Measurements on the Condition of Compliant Coatings for Prediction Acoustic Performance"

Abstract

A method for determining the complex wave speeds of a viscoelastic polymer slab bonded to a steel plate was proposed. The heart of the method is the optimization of a performance metric which relates to the difference between experimentally determined values for the complex wave propagation speeds in the polymer and the predicted results of a theoretical model whose inputs included the complex wave speeds. The experimental component of the method involved measuring the propagation of a wave introduced into the polymer layer by exciting a point on the free surface of the polymer layer. The measurements were made by using a Laser Doppler Velocimeter to record the in-plane and out-of-plane surface particle velocity at five locations along al line extending radially from the epicenter of the input excitation. The theoretical model predicted the in-plane and out-of-plane surface particle velocities at the same locations for a given frequency. A Fast Fourier Transform of the measured data provided continuous wave values which could be compared directly to the model output. A simplex optimization program then intelligently varied the complex wave speed inputs to the theoretical model until acceptable convergence was achieved.