Ultrasonic scattering and velocity methods for characterization of fibre-matrix interphases

Abstract

Abstract This paper discusses two potential ultrasonic techniques for characterization of fibre-matrix interphases in composites: measurements of wave scattering (attenuation) and its phase velocity. The implementation procedures of these two methods are described using analytical or numerical models with an emphasis on their applicability. Examples of ultrasonic characterization of interphases are given for ceramic and intermetallic matrix composites reinforced with large diameter SiC fibres. Carbon-rich interphase coatings are added on these fibres to improve composite performance and chemical and thermal compatibility. The experimentally measured interphase moduli from ultrasonic data are compared with those determined from interphase microstructures showing good agreement. Finally, several applications of these techniques for interphasial damage assessment are demonstrated, including characterization of oxidation damage in ceramic matrix composites and of fatigue damage in metal matrix composites. These experimental results show that ultrasonic wave attenuation and velocity are significantly affected by degradation of the elastic properties of the interphasial layer; thus, both methods are very useful for non-destructive assessment of interphasial damage.