Reflection and refraction of ultrasonic waves form fundamental techniques in the non-destructive evaluation of structural components. When these techniques are applied to composite structures the interface between different layers plays a crucial role. A part of the non-destructive evaluation deals with the monitoring of the health of interfaces. Delaminations along the interface and local buckling of the layer are common defects in layered composites. In this paper the effect of a geometrically perturbed flat interface on the reflection and refraction of elastic waves is considered. Specifically, the perturbation is assumed to be in the form of a sinusoid with small amplitude compared to the wave length of the incident beam. Any periodic imperfections of the interface caused by local buckling or by machining prior to fabrication, can be represented as a Fourier series. A basic solution of the reflection problem with a single sine wave imperfection can be of use in analyzing these more complicated periodic perturbation of interfaces. The method used here is the regular perturbation expansion of the equations of dynamic elasticity with the amplitude of the interfacial curve forming the small parameter.
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