The effects of viscoelasticity on the reflection and transmission of ultrasonic waves by an orthotropic plate.

In this paper both theoretical and experimental investigations on the reflection and transmission of an incident plane wave by immersed viscoelastic orthotropic plates are presented. Taking the anisotropy of the layer into account the reflection and transmission coefficients are expressed in terms of nine complex elastic constants. In agreement with the Snell's laws, any waves generated in the layer are bulk heterogeneous plane waves. Using a method already described in the isotropic case, the reflection and transmission coefficients are obtained as a function of the reflection and refraction coefficients of bulk heterogeneous plane waves at the two single solid/liquid interfaces, which limit the plate. In this way, these coefficients can be easily expanded in Debye's series. In addition, for many incident and azimuthal angles, the calculations are compared with trial results on a composite made of unidirectional carbon fibers and epoxy matrix. Finally, by the measurement of the variation of attenuation versus the frequency, a linear model permits the computations in a large frequency range. Conclusions are carried out regarding the use of the LLW method in the inverse problem to recover elastic constants of composite materials.