DETERMINATION OF MACROMECHANICAL AND MICROMECHANICAL AND INTERFACIAL ELASTIC PROPERTIES OF COMPOSITES FROM ULTRASONIC DATA

A self-reference ultrasonic bulk wave method for nondestructive measurement of elastic properties of ceramic matrix composites has been developed. The method has the advantage of minimizing the effect of geometrical imperfection of the sample. The experiment has been done on silicon carbide (SiC) fiber-reinforced reaction-bonded silicon nitride (Si3N4) matrix composites. The composite elastic constants are extracted from the experimental phase velocities using a nonlinear optimization procedure to find the best fit between experimental data and the solutions of the Christoffel equation. The effect of individual constituents on the overall composite properties has been investigated. The effects of porosity on the matrix properties and water saturation of pores on the immersion ultrasonic measurements are taken into account using a micromechanical model for two-phase particulate composites. This model is validated by experimental data. A microstructural model for analysis of elastic properties of ceramic matrix composites and their interfaces from experimental data is introduced. The fiber and the interface are modeled by effective fibers with anisotropic properties and a perfect bond between fiber and matrix. The properties of the effective fibers are extracted from the measured composite elastic moduli using a nonlinear optimization procedure. Shear and longitudinal elastic moduli of 3-mu-m-thick carbon-rich coatings are determined using measured effective and estimated actual elastic properties of the fibers.