Nondestructive evaluation of adhesive joints by using nonlinear ultrasonics

Adhesive bonding technology has now gained much attention in many industries as a very versatile assembling technique. However, to be used for structural joining and critical application, high reliability is needed. Thus, efficient non-destructive control strategy should be proposed to evaluate the nominal bonding quality but also possible progressive in-service degradations. Promising results have been presented in the literature using ultrasound-based methods. While linear ultrasound is efficient to detect decohesion or voids in a structure, it is barely sensitive to bond strength. In this work, we present a method to generate high amplitude plane wave, which may produce nonlinear phenomenon that are able to reveal kissing bonds or other types of adhesion defects. In this purpose a method based on a chaotic cavity transducer has been developed to generate high energy plane wave. Then the method is evaluated on metallic bonds with bonding defects. Combined with the pulse inversion technique, nonlinear phenomenon can be measured in the form of harmonic generation in the defect zone. We use this method to image a defect created by spraying PTFE on one adherent prior to bonding.