Elastic constant reconstruction using resonances of coupled modes in thin anisotropic plates

Abstract

At oblique incidence of ultrasonic waves on a thin anisotropic composite plate immersed in fluid, the quasilongitudinal, flexural, and quasi‐SH vibrations are excited. At some angles of incidence, coherent interactions of these waves lead to 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 composite plate, two such minima may be observed. Their positions are only slightly dependent on frequency and are determined by plate properties and orientation. This effect was studied both theoretically and experimentally. The elastic constants have been reconstructed for a unidirectional graphite‐epoxy composite plate from experimental data that have been taken at different plate orientations and frequencies.