Adiabatic Lamb modes in 3D tapered waveguides: Cut-off effects and ZGV resonances

TL;DR

This study explores how higher-order adiabatic Lamb modes propagate in inhomogeneous waveguides with varying thickness, revealing critical effects like cut-off and ZGV resonances, and demonstrates precise profile reconstruction in aluminum plates.

Contribution

It provides new insights into the behavior of adiabatic Lamb modes in inhomogeneous waveguides and introduces an experimental method for accurate profile reconstruction.

Findings

ZGV resonances can be excited beyond the laser source location.

Thickness variations induce anisotropic-like behavior in waveguides.

Reconstructed profiles closely match reference measurements.

Abstract

This paper aims to enhance our understanding of the physical behavior of adiabatic modes in inhomogeneous elastic plates, particularly their remarkable capacity to adapt to gradual perturbations. The study investigates the propagation characteristics of higher-order adiabatic Lamb modes in waveguides with linearly varying thickness, with a focus on the influence of critical thicknesses on their propagation. This is achieved by leveraging the broadband excitation capabilities of a pulsed laser generating higher order Lamb modes to reveal various critical thicknesses, such as the cut-off and Zero-Group Velocity (ZGV) thicknesses. Remarkably, ZGV resonances can be induced at locations well beyond the laser source. Moreover, the mode's behavior is strongly influenced by thickness variations in all directions, imparting the plate an anisotropic-like behavior. Additionally, based on the observed effects, our experimental approach enables precise reconstruction of elastic waveguide profiles in additively manufactured aluminum plates with such thickness variations. The reconstructed profiles show a strong correlation with reference measurements across the scanned area.