Innovating for Structural Adhesive Bonding Evaluation and Analysis with Ultrasounds : A Summary

In this paper we summarize results from the French research project ISABEAU (Innovating for Structural Adhesive Bonding Evaluation and Analysis with Ultrasounds). The goal of this ANR project (20 13-2017) is to overcome the technical obstacles to the verification of the inte grity of adhesively bonded joints using ultrasonic NDT methods. For instance, the cas e of kissing bonds remains a major scientific challenge years after years. The d evelopment of an acoustic method quantifying the adhesivion “level” of a bonded join t is also one of the ultimate objectives of this research. Three NDT laboratories and one chemical laboratory gather their experience to achieve a leap in the qu antitative analysis of the interfacial adhesion between assembled substrates and the adhes ive layer. Surface treatments were chosen to modify the adhesion properties. The project focuses on aluminium/epoxy/aluminium assemblies, which are rep resentative of the difficulties that one may come across in structural bonding. Three well identified levels of adhesion were obta ined and qualified by mechanical tests (lap shear test). Numerous bonded samples were manufactured to make it possible to use various ultrasonic methods, most of them with various levels of adhesion. Several through-transmission ultrasoni c techniques were used to evaluate different properties of these assemblies: (1) the m aterial properties of the aluminium and epoxy, (2) the bond homogeneity and thickness, (3) the state of the substrateadhesive interfaces together with mechanical parame ters, which are representative of the interfacial adhesion. Lamb waves and SH waves w re used to investigate the variations in the adhesion level, which depends on the treatments carried out on the metal/epoxy interface. As part of this study, the i ssue of surface roughness was