Experimental and Numerical Investigations on the Acoustoelastic Effect on Lamb Waves in Aluminum

Abstract

Damage detection in thin-walled components is a common application of guided ultrasonic waves, such as Lamb waves, in today’s structural health monitoring. However, the method requires that external or manufacturing influences such as residual stresses, pre-stresses or stresses due to temperature are taken into account. Therefore, this work focuses on the field of acoustoelasticity and compares the influences of pre-stress on the phase velocities of Lamb waves in numerical studies with experimentally determined results. For this purpose, previous experimental and numerical investigations of the authors are extended by expanding the frequency ranges and load steps considered. The measurements are carried out using laser vibrometry to capture the velocity field of the Lamb waves in aluminum specimens subjected to uniaxial pre-stresses covering the elastic range of the material. The experimental results are thereby characterized by the use of a 2d Fourier transform to evaluate the phase velocity over large frequency ranges. The numerical data are generated using a two-step FE model that combines a nonlinear static and a linear eigenvalue computation to determine the dispersion behavior of Lamb waves subjected to pre-stress. The subsequent comparison of numerical and experimental investigations focuses on the verification of the Neo-Hookean and Murnaghan hyper-elastic material models by comparing the changes in phase velocities induced by the pre-stress. For this purpose, the numerically obtained results for different material models are compared with experimental data. The results of these investigations provide a clear indication of the suitability of the material models used here to represent the acoustoelastic effect in Lamb waves.