Measurements of elastic constants of ceramic composites using ultrasonic plate mode antiresonances

Abstract

With oblique incidence of an ultrasonic wave upon a thin anisotropic plate immersed in fluid, in general the quasilongitudinal, flexural, and quasi-SH vibrations are excited. At some angles of incidence, coherent interactions of these waves lead to antiresonance-type minima of the normal displacement on the back surface of the plate and therefore to minima of the transmission coefficient. At off-axis orientations of the thin anisotropic plate relative to the incidence plane, several minima may be found. One of them may be used for shear modulus measurement. The measurements have been performed on (1) a porous aluminum oxide membrane, which is transversely isotropic in the plane of the membrane, and (2) a unidirectional SiC/Al composite membrane, where the fibers lie in the plane of the plate. The elastic constants were extracted from the experimental data by a nonlinear least-squares optimization technique. It is demonstrated that the method gives very good results for determination of in-plane longitudinal and shear moduli.