Bonding characterization of three layers metal/adhesive/metal using Lamb waves

The studied samples are three layer Aluminum/Epoxy/Aluminum structures, realized with the cooperation of Physico-Chemists, to obtain samples of controlled adhesion properties, and acousticians for ultrasounds characterization. Different mechanical (roughness) and/or chemical (silanisation) surface treatments at the interface substrate/adhesive are performed. A numerical FEM model is achieved to solve a rheological description of the interface as springs distribution. This model allows the study of the sensitivity of Lamb waves to the interface and the determination of their energy in the cross section of the structure, depending on the stiffness values of the springs. The sensitive modes are then looked for to be excited in the experimental study, particularly the vertical modes that are indicative of a more or less coupling in the three layer structure. Experimental results show different adhesion levels, depending on the surface treatments, and correspond stiffness springs value to each sample.