Sensitivity of the guided waves to the adhesion of lap joints: Finite element modeling and experimental investigations

Abstract

Despite considerable efforts in the last decades to find reliable NDT methods for the control of adhesive joints, the durability and the quality of the adhesive bonding remains troublesome to be determined by ultrasonic nondestructive methods knowing that both the cohesion and the adhesion aspects must be considered. In this paper, the adhesive lap joints between two aluminum plates are first investigated by a finite element approach to compute the transmission and reflection coefficients of Lamb modes. The cohesion is taken into account by the characteristics of the adhesive layer and the adhesion by the interfacial conditions. Two methods are used to compute the energy dissipation: one based on the orthogonality relations and the other based on a signal processing procedure that involves a 2D Fourier transform. Then they can be used to verify the sensitivity of the guided waves to the presence of a contaminant. This model is compared to experimental measurements performed on adhesive lap joints. In order to get reproducible measurements, the detection of the fundamental ultrasonic guided modes is performed with air-coupled transducers.