The Effects of In-Plane Stress on Waves in Thin Films
The application of acoustoelasticity for the nondestructive evaluation of residual stress has, for the most part, been limited to waves which may be classified as being of short wavelength. For many thin films, whose thicknesses may be on the order of 1 μm or less, the frequency required to obtain a “short wavelength” is well into the gigahertz regime. Thus, for acoustoelasticity to be applicable to such thin films, an improved understanding of the effect of stress on the wave response in the intermediate to long wavelength regimes must be available. This paper considers the effect of stress on the response of waves propagating in plate-like structures. The frequency equation is derived in the context of three-dimensional elastodynamics in which a small disturbance is superposed on a finite deformation of the nonlinearly elastic plate. Particular attention is directed toward the lowest order antisymmetric (flexural) mode which exhibits membrane response in the long wavelength limit. Results showing the details of the transition from the long wavelength limit to the short wavelength limit (bulk wave response) are presented for this mode.
KeywordsResidual Stress Wave Speed Rayleigh Wave Velocity Change Biaxial Tension
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