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|NDT.net Issue - 2019-03 - Articles ||NDT.net Issue: 2019-03|
Publication: 10th International Symposium on NDT in Aerospace, Oct 2018, Dresden, Germany (AeroNDT 2018)
On detecting kissing bonds in adhesively bonded joints using electric time domain reflectometryPhilip Johannes Steinbild, Robin Höhne, René Füßel, Niels Modler3
Institut für Leichtbau und Kunststoff-technik; Dresden University of Technology (TU Dresden)80, Dresden, Germany
Abstract: The use of fibre reinforced plastics to achieve low mass aircrafts calls for suitable joining technologies. The joining technology with the highest potential in lightweight construction with fibre reinforced plastics is adhesive bonding. However, in today’s aircrafts the potential of adhesive bonding is limited due to the additional use of rivets as crack arrestors for regulation and safety issues. To meet the regulations and reduce the number of joint-weakening, heavy rivets, an adhesive bond needs to be monitored during its production and throughout its lifetime in operation. State of the art are ultrasound and thermal imaging technologies for non-destructive testing of adhesive bonds. The use of such technologies in a structural health management system is not practical. Additionally, ultrasound and thermal imaging technologies are only capable of detecting gross defects like areas of uncured adhesive and voids. The detection of adhesion defects like kissing bonds still pose a serious problem. This paper describes a novel adhesive sensor principle based on the electric time domain reflectometry, which can detect differences in the deformation of the adherents in an adhesively bonded joint under load to infer that a kissing bond is taking effect. The sensor is integrated into the joint. Results of the experimental validation by shear tension testing of single lap shear specimens with the adhesive sensor integrated into the joint are presented. The deformation of the adherents is monitored by digital image correlation and compared to the data obtained by the electric time domain reflectometry. The results show that by integrating the proposed sensor into an adhesively bonded joint the joint can be monitored operando. This novel technology can be used in a structural health management system to raise the confidence in adhesive bonds and reduce the number of rivets thus reducing mass. Further developments will include the use of a finite difference time domain model to numerically test sensor configurations regarding its geometry and electrical properties.