ULTRASONIC SCATTERING AND VELOCITY METHODS FOR CHARACTERIZATION OF FIBER-MATRIX INTERPHASES

This paper discusses two potential ultrasonic techniques for character ization of fibre-matrix interphases in composites: measurements of wav e scattering (attenuation) and its phase velocity. The implementation procedures of these two methods are described using analytical or nume rical models with an emphasis on their applicability. Examples of ultr asonic characterization of interphases are given for ceramic and inter metallic matrix composites reinforced with large diameter SIC fibres. Carbon-rich interphase coatings are added on these fibres to improve c omposite performance and chemical and thermal compatibility. The exper imentally measured interphase moduli from ultrasonic data are compared with those determined from interphase microstructures showing good ag reement. Finally, several applications of these techniques for interph asial damage assessment are demonstrated, including characterization o f oxidation damage in ceramic matrix composites and of fatigue damage in metal matrix composites. These experimental results show that ultra sonic wave attenuation and velocity are significantly affected by degr adation of the elastic properties of the interphasial layer; thus, bot h methods are very useful for non-destructive assessment of interphasi al damage.