ABSTRACT
The velocity of wave propagation in an arbitrary direction in a composite will be a function of the direction cosines of the wave normal and the elastic moduli of the media. Hence, ultrasonic velocity measurements can in principle be used to nondestructively measure elastic constants. This fact is well appreciated in isotropic media where velocity measurements are commonly used to replace destructive mechanical tests to accomplish this purpose. For composite media, however, several difficulties have slowed this application of ultrasonic testing. One of the principal difficulties encountered is the algebraic complexity of the problem. The precise determination of material properties via ultrasonic testing hinges upon the accurate measurement of transit time. Direct visual observations of echo traces on an oscilloscope are usually insufficient for this purpose, and therefore a variety of more sensitive techniques have been devised. The digital-based signal processing techniques have supplanted analog methods for most ultrasonic transit time measurements.
