Adhesive Bond Testing By Laser Induced Shock Waves

Adhesive bonding of metal sheets presents many practical advantages when compared to other joining methods, but its application for critical components is limited by the absence of reliable nondestructive methods that can assure the bond strength of the joint. In this paper, a method based on shock waves produced by pulsed lasers is applied to the evaluation of adhesive bond strength of two aluminum plates joined with different adhesive types. Shock wave, produced by short laser pulse, propagates through the aluminum plates and adhesive layer and after reflection, can cause a delamination at the adhesive/plate interface. The laser pulse energy can be scanned to probe the adhesion strength. A good joint will be unaffected by a certain level of tensile stress whereas a weaker one will be damaged. The method is made quantitative by optically measuring the aluminum surface velocity with a Doppler or velocity interferometer. Interferometer signals first give a clear signature of damaged or undamaged interfaces. In addition, these signals can be correlated with numerical simulation in order to give an estimation of the bond strength. Results show that the proposed test is able to differentiate bond quality. The proposed testing method may help a broad adoption of adhesive bonding throughout the automotive and aerospace industries.