Ultrasonic Based Testing Method for the Symmetry and Dissymmetry Analysis of the Bonding Quality of a Three-Layer Bonded Structure

Abstract

The quality control of bonded structures is very important and decisive in the industry, especially in the aeronautics and automotive industries. In this paper, a non-destructive method is proposed in order to evaluate the bonding quality for a three-layer structure such as Plexiglas/Adhesive/Aluminum by using ultrasound. The transmission of tensile and shear stresses through the interfaces of the adhesive layer is different. Indeed, the external stresses on the Aluminum and Plexiglas sheets are generally different. In addition, the high thermal loads on the two sides of the bonded structure are also different. Therefore, the evolution of the bonding forces across the two adherent/adhesive joints is not necessarily symmetrical. In this work, the study of the symmetry and the dissymmetry of the bonding quality across the joints of the structure has been carried out. The analysis of the behavior of the reflection coefficient of this structure subjected to a beam of ultrasound has allowed distinguishing the different qualities of bonding (perfect, medium or weak) of the two joints of the structure. This work has allowed determining the effective criteria to evaluate the normal rigidities through the bonding joints. These criteria are based on the depths of the resonant modes of the plates forming the structure. The results of the simulations performed on the quality control of the bonding interfaces allow the evaluation of the normal rigidities at the joints.