In Situ Estimation of Applied Biaxial Loads with Lamb Waves (Preprint)
Interim rept. 1 Jun1 Jul 2012
GEORGIA INST OF TECH ATLANTA
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Spatially distributed arrays of piezoelectric discs are being applied to monitor the integrity of critical metallic structures using guided elastic waves. These transducers are subjected to in situ operational and environmental conditions, and stress variations are of particular importance because of their cumulative effects on the fatigue life of the structures. Waves propagating between array elements are directly affected by applied loads because of both dimensional changes and the acoustoelastic effect. In particular, changes in phase velocity are a function of the direction of propagation for a particular Lamb wave mode and frequency. This paper shows from numerical solutions of the acoustoelastic wave equation that it is possible to decouple the effects of a homogeneous biaxial stress into its two principal components. As a consequence of this decoupling combined with material isotropy, the acoustoelastic response of guided waves is described by only two constants, both of which can be determined from a single uniaxial loading experiment.