MICROMECHANICAL ANALYSIS AND ULTRASONIC CHARACTERIZATION OF INTERPHASES AND INTERPHASIAL DAMAGE IN HIGH-TEMPERATURE COMPOSITES

This paper describes a methodology for fiber/matrix interphase charact erization in high-temperature composites reinforced with multiphase Si C (SCS-6) fibers. The effect of the interface stiffness on the overall composite moduli is analyzed using a generalized self-consistent mode l for multiphase composites. This model is later used as the basis for inverse determination of the effective interphase stiffnesses from th e static composite moduli calculated using measured ultrasonic wave ve locities. The frequency dependence of the ultrasonic wave velocity is studied both experimentally and theoretically using wave propagation m odels for multiphase composites. It shows that the wave velocity measu red using low frequency ultrasound can be used to calculate the static composite moduli. To demonstrate the applicability of the proposed in terphase characterization procedure, a summary of the experimentally m easured interphase moduli in various SiC fiber composite systems are g iven and compared with those determined from the actual interphase mic rostructures. Examples of interphasial damage characterization due to oxidation of ceramic matrix composites and fracture and fatigue of met al matrix composites are also given including the use of ultrasonic wa ve attenuation data. (C) 1998 Elsevier Science Limited. All rights res erved.