Characterization of adhesive bond properties using Lamb waves

This research combines laser ultrasonic techniques with the two-dimensional Fourier transform (2D-FFT) to characterize adhesive bond properties. The experimental procedure consists of measuring a series of equally spaced, transient Lamb waves in specimens consisting of aluminum plates joined with an adhesive bond. The frequency spectrum (dispersion curves) for each specimen are obtained by operating on these transient waveforms with the 2D-FFT. This study quantifies the effect of bond stiffness on the dispersion curves of two different bonded specimens (a single aluminum plate with an adhesive transfer tape attached to one side, and two aluminum plates joined with the same adhesive tape) and four adhesive bond conditions (un-aged, and three different aging temperatures and times). The proposed procedure consists of first determining the frequency spectrum of the Lamb waves that propagate in each of the two bonded specimens (plus a single plate); these measurements provide the dispersion curves for each specimen in their un-aged state. Degradation causes changes in the stiffness of an adhesive bond, which causes changes in the dispersion curves of the aged specimens. Experimentally measured dispersion curves are used to quantitatively track changes in the bonded specimens, as a function of age. Finally, these experimental results are interpreted in terms of an analytical model that replaces the adhesive bond layer with a linear spring boundary condition. (C) 2000 Published by Elsevier Science Ltd.