Investigation of interfacial stiffnesses of a tri-layer using Zero-Group Velocity Lamb modes

TL;DR

This paper investigates how Zero-Group Velocity Lamb waves can be used to evaluate interfacial stiffnesses in bonded layered structures, combining theoretical modeling and laser ultrasonic experiments for non-contact assessment.

Contribution

It introduces a method to determine interfacial stiffnesses in tri-layer structures using ZGV Lamb modes, validated by experimental laser ultrasonic measurements.

Findings

Theoretical dispersion curves match experimental data well.

Interfacial stiffnesses can be accurately estimated from ZGV resonances.

The technique offers a promising non-contact evaluation method.

Abstract

Zero-Group Velocity (ZGV) Lamb waves are studied in a structure composed of two plates bonded by an adhesive layer. The dispersion curves are calculated for a Duralumin/epoxy/Duralumin sample, where the adhesion is modeled by a normal and a tangential spring at both interfaces. Several ZGV modes are identified and their frequency dependence on interfacial stiffnesses and on the bonding layer thickness are numerically studied. Then, experiments achieved with laser ultrasonic techniques are presented. Local resonances are measured using superimposed source and probe. Knowing the thicknesses and elastic constants of the Duralumin and epoxy layers, the comparison between theoretical and experimental ZGV resonances leads to an evaluation of the interfacial stiffnesses. A good agreement with theoretical dispersion curves confirms the identification of the resonances and the parameter estimations. This non-contact technique is promising for the local evaluation of bonded structures.