A sensor detecting kissing bonds in adhesively bonded joints using electric time domain reflectometry

The joining technology with the highest potential in lightweight construction is the adhesive bonding. In an adhesively bonded joint different defects can occur. Alongside gross defects like areas of uncured adhesive and voids, adhesion defects like kissing bonds pose a serious problem to the confidence in these kind of joints in the aircraft industry and other industries. Since kissing bonds are small interfacial defects of as few as nanometers in thickness, the detection by conventional nondestructive testing methods is not possible in most applications. In this paper a novel adhesive sensor based on the electric time domain reflectometry is proposed detecting differences in the deformation of the adherents in an adhesively bonded joint to infer that a kissing bond is taking affect. Numerical calculations are used to show that the proposed sensor principle poses a productive approach. For the numerical calculations a finite difference time domain model is used. The sensor is then validated experimentally by shear tension testing of single lap shear specimens with the adhesive sensor integrated into the joint.