Generalized Boundary Conditions for Ultrasonic Scattering from a Cylindrical Layer Between Two Solids

By asymptotically expanding the transfer matrix that relates stresses and displacements on both sides of a thin cylindrical interface between two solids, a new spring model is proposed to describe the scattering of an obliquely incident ultrasonic wave from an interface layer in composite structures. Generalized three-dimensional boundary conditions at the cylindrical interface are obtained. Two stiffness constants, besides three mass terms, for the interface layer are introduced. It is found that the accuracy of the new model satisfies the precision demand in ultrasonic nondestructive evaluation.