Debonding of piezoelectric transducers for residue-free ultrasonic non-destructive testing

Abstract

ABSTRACT Components made of fibre-reinforced polymers (FRP) are prone to different types of damages such as delamination or matrix cracks, which can be critical for a component’s functionality. In classical ultrasonic nondestructive testing (NDT), lamb waves (LW) are frequently used to detect imperfections due to their favourable propagation characteristics over long distances. The LW are often excited by piezoelectric transducers, which are either bonded onto the component’s surface using comparatively stiff adhesives so to ensure loss-free LW coupling into the component or laminated directly into the FRP. In both cases the a priori nonseparable connection between the transducer and the substrate may itself be considered a defect when the component is put into service. In addition, laminating the transducers directly into the matrix is accompanied by both additional production effort and corresponding effects on thermomechanical component properties. To provide a cost-effective solution for NDT applications, the study focused on the development of a residue-free bonding concept for piezoelectric transducers. To this end, a total of three application approaches involving 14 commercially available adhesives and one dilatant material were investigated in different rounds of experimental testing. During the scientific campaign, the authors finally identified an adhesive that guarantees both lossless ultrasonic coupling and residue-free bonding, paving the way for much more process control and reusage of tested components for future NDT processes.