Micromechanical analysis and ultrasonic characterization of interphases and interphasial damage in high temperature composites

This paper describes a methodology for fiber/matrix interphase characterization in high-temperature composites reinforced with multiphase SiC (SCS-6) fibers. The effect of the interface stiffness on the overall composite moduli is analyzed using a generalized self-consistent model for multiphase composites. This model is later used as the basis for inverse determination of the effective interphase stiffnesses from the static composite moduli calculated using measured ultrasonic wave velocities. The frequency dependence of the ultrasonic wave velocity is studied both experimentally and theoretically using wave propagation models for multiphase composites. It shows that the wave velocity measured using low frequency ultrasound can be used to calculate the static composite moduli. To demonstrate the applicability of the proposed interphase characterization procedure, a summary of the experimentally measured interphase moduli in various SiC fiber composite systems are given and compared with those determined from the actual interphase microstructures. Examples of interphasial damage characterization due to oxidation of ceramic matrix composites and fracture and fatigue of metal matrix composites are also given including the use of ultrasonic wave attenuation data. (C) 1998 Elsevier Science Limited. All rights reserved.