Determination of thickness and elastic constants of aluminumplatesfrom full-field wavelength measurements of single-mode narrowband Lamb waves

摘要

A method based on fitting the theoretical dispersion curves of Lamb waves to experimental data ispresented to determine, the thickness and two independent elastic constants of aluminum plates a fewmillimeters thick. The waves are generated by means of the wedge method using a narrowbandsource, selecting the wedge angle and the acoustic frequency f so that mainly one mode is excited.A self-developed pulsed electronic speckle pattern interferometry system renders a two dimensionalmap of the out-of-plane acoustic displacement field at the plate surface, which allows an accuratemeasurement of the acoustic wavelength λ_1. For any mode, the relation between λ_1 and f dependson the three unknown parameters, so at least three experimental measurements (λ_(1i),f_i) withdifferent frequencies and/or different modes are required to calculate them. The suitability ofdifferent Lamb modes to determine each parameter when the others are known is studied, as wellas the conditions that the experimental set of values must fulfill to calculate all three parameters.Numerous Lamb modes at different frequencies are generated in each plate, and a fitting is madebased on the minimization of the error function, resulting in an accuracy better than 1%.