Multimodal characterization of adhesion within thermoplastic welded composites using Lamb waves

The characterization of interfaces within assemblies using non-destructive methods is a subject of interest for both academic and industrial purposes. Most of the work and methods developed are based on qualitative approaches, often designed to characterize bonding. When it comes to quantitative adhesion characterization, the number of studies remains limited. This contribution presents results related to the characterization of the adhesion of thermoplastic composite welded assemblies. For this purpose, a theoretical model computing the dispersion characteristics of both Lamb and SH waves has been developed. The dispersion curves of the different modes are first obtained by taking into account the mechanical properties and anisotropy of each layer. This is followed by a sensitive study that demonstrated the sensitivity of A0 and S0 modes to variations in the interface layer’s properties depending on the frequency domain considered. An estimation of the normal and tangential interface stiffnesses is obtained with an inverse problem based on air-coupled measurement of the propagation of the involved guided modes. This work shows, through the analysis of various samples from the aeronautics industry, that considering several modes of guided wave propagation over a sufficiently wide frequency range yields results consistent with those obtained with destructive mechanical testing. • Adhesion within thermoplastic welded composites is determined. • A contactless ultrasonic nondestructive characterization method is developed. • Monoclinic and orthotropic symmetries are modelled to provide an exact solution. • Ultrasonic and mechanical test results are successfully compared.