REFLECTION OF LONGITUDINAL WAVES UNDER INITIAL STRESSES AT AN INTERFACE IN PIEZOELECTRIC MEDIA

摘要

The propagation of plane longitudinal waves at an interface of a semi-infinite piezoelectric elastic medium under the influence of the initial stresses is discussed. The free surface of the piezoelectric elastic medium is considered to be adjacent to vacuum. We assumed that the piezoelectric material is anisotropic and of a type of transversely isotropic crystals (hexagonal crystal structure, class 6 mm). For an incident of longitudinal plane wave, four types (two for the displacement and two the electric potential) of reflected plane waves, called quasi-longitudinal (qP) and quasi-shear vertical (qSV) waves are shown to exist. The relations governing the reflection coefficients of these reflected waves for various boundary conditions (mixed-free-fixed) are derived. It has shown analytically that reflected coefficients of (qP) and (qSV) waves depend upon the angle of incidence, the parameters of electric potential, the material constants of the medium as will as the initial stresses presented in the medium. The numerical of reflection coefficients for different values of initial stresses have been carried out by computer for PZT-5H Ceramic as an example and the results are given in the form of graphs. These graphs show the prominent effect of the prestressing, the parameters of electric potential and the angle of incidence as well on the reflection coefficients. Finally, a particular case is considered in the absence of the initial stresses and the electric potential. Some earlier studies have been compared to the special case and are in good agreement with it.