Non contact probing of interfacial stiffnesses between two plates by Zero-Group Velocity Lamb modes

TL;DR

This paper introduces a non contact laser ultrasonic method to measure interfacial stiffnesses between two plates using Zero-Group Velocity Lamb modes, providing a way to evaluate bonding quality without contact.

Contribution

A novel non contact approach utilizing ZGV Lamb modes to determine interfacial stiffnesses in bonded plates, combining theoretical modeling and experimental validation.

Findings

Successfully measured normal and shear interfacial stiffnesses.

Demonstrated effectiveness with bonded glass plates using laser ultrasonic techniques.

Identified the impact of different bonding layers on ZGV frequencies.

Abstract

A non contact technique using Zero-Group Velocity (ZGV) Lamb modes is developed to probe the bonding between two solid plates coupled by a thin layer. The layer thickness is assumed to be negligible compared with the plate thickness and the acoustic wavelength. The coupling layer is modeled by a normal and a tangential spring to take into account the normal and shear interfacial stresses. Theoretical ZGV frequencies are determined for a symmetrical bi-layer structure and the effect of the interfacial stiffnesses on the cut-off and ZGV frequencies are evaluated. Experiments are conducted with two glass plates bonded by a drop of water, oil, or salol, leading to a few micrometer thick layer. An evaluation of normal and shear stiffnesses, is obtained using ZGV resonances locally excited and detected with laser ultrasonic techniques.