Adhesive bond testing of carbon–epoxy composites by laser shockwave

Abstract

Adhesive bonding, particularly of composite laminates, presents many practical advantages when compared with other joining methods but its use is limited, since there is presently no non-destructive inspection technique to ensure the quality of the bond. We are developing a technique based on the propagation of high amplitude ultrasonic waves to evaluate the adhesive bond strength at high strain rate. Compression waves are generated by a short and powerful laser pulse under water confinement and are converted after reflection on the assembly back surface into tensile waves. The resulting tensile forces normal to the interfaces can cause a delamination inside the laminates or a disbond. The adhesion strength is probed by increasing the laser pulse energy until disbond. A good bond is unaffected by a certain level of stress whereas a weaker one is damaged. The method is shown completely non-invasive throughout the whole composite assembly. The sample back surface velocity is measured by an optical interferometer and used to estimate stress history inside the sample. The depth and size of the disbonds are revealed by a post-test inspection by the well established laser-ultrasonic technique. Experimental results confirmed by numerical simulations show that the proposed method is able to differentiate weak bonds from strong bonds and to estimate quantitatively the bond strength.