Development of a laser shock adhesion test for the assessment of weak adhesive bonded CFRP structures

Adhesive bonding has a great potential for future lightweight high-loaded structures in the aeronautic industry. A prerequisite for such an application is that the bond quality of the adhesive joint can be assessed in a non-destructive way. However, the use of classical Non-Destructive Techniques (NDT) does not allow the evaluation of the adhesion strength of an adhesive bond yet. This paper presents an investigation made on weak composite bonds in order to develop a laser shock wave adhesion test. First, the procedure to produce controlled weak bonds is described. CFRP bonded samples are prepared in a specific way and characterized by ultrasonic techniques to assess the absence of any detectable defect. Then, for some of the samples, their bond strength is evaluated by mechanical destructive tests and other samples are loaded by various intensity lasers shocks. The obtained results help to understand the behavior of the composite bonds under laser shock loading, thanks to two post-mortem techniques. The correlation between the laser parameters and the induced damage is demonstrated. The potential of the laser shock technique to discriminate different bond qualities is shown, and the need for the test optimization is discussed.