Quality assessment of bonded primary CFRP structures by means of laser proof testing

The use of adhesive bonding as an assembly technology is still limited because of the absence of NDT method to assess the quality of the adhesion. This work evaluates the state-of-the-art of potential NDT technologies and focuses on laser proof test techniques. The theory of this approach aiming at debonding weak adhesive bond and leaving strong adhesive bond unaffected is introduced. A preparation technique and a characterization strategy for bonded CFRP specimens with defined adhesion levels is presented. Two laser proof test setups are then investigated experimentally. A first test focuses on the determination of threshold energy for debonding of the different adhesive bond states. Further tests (repetition of laser shocks, different laser energy levels, mechanical test after laser shock) are performed to evaluate the effects on the CFRP structures. The main objective is the evaluation of the NDT character of laser proof test. With both laser setups, a debonding intensity threshold was achieved, but not without affecting the CFRP substrates. Ultrasonic inspections and mechanical tests conducted before and after laser shocks are compared to analyze the role of each laser setting in the observations. This study shows the feasibility of the concept with a high potential of improvements for the laser technologies and for approaches towards the industrialization.