Ultrasonic spectral characterization of fibers embedded in a metal matrix

Results from both numerical modeling and experimental techniques that have been used to study the ultrasonic response resulting from a plane compression wave impinging on a long isolated fiber embedded in a titanium alloy matrix are presented. The numerical model is based on a normal-mode expansion of the acoustic wave components in cylindrical coordinates for three material regions: fiber inner core, fiber outer layer, and matrix. The numerical model predicts a diffraction spectrum that contains a series of sharp dips caused by a resonant condition in the fiber. The locations of the low-frequency dips are indicative of bulk elastic constants and fiber radius. The model predictions were tested experimentally using a Ti-6-4 metal matrix sample with various types of embedded fibers. A broadband (0-100 MHz) system was used to acquire the ultrasonic echo spectrum from each fiber type. The deconvolved spectrum was then calculated using standard signal processing techniques. The correlation between numerical model and experiment was excellent