Smart structure application in bonded repairs

Abstract

In the aerospace industries bonded composite patches are being increasingly used to extend the operational life of aging aircraft. The application of bonded composite patches to repair or reinforce defective metallic structures is widely acknowledged as an effective and versatile procedure. Such patches have been successfully applied to the repair of cracked structures, to the reinforcement of components subject to material loss due to corrosion damage and as a general means of stress reduction through the provision of a supplementary load path. However, certification requirements mandate the need for a methodology for monitoring the damage state of both the defective underlying structure and of the repair. In this case, the concept of smart structures can be used to detect damage in the repair itself as well as monitor damage growth in the parent structure. This paper will report on the development of a ‘perceptive repair’ or ‘smart’ system which will provide information on the in-service performance of the repair and the associated structure. In this respect, this paper will focus on the detection of disbond in the adhesive layer between adherend and the metallic parent structure. Since this is a relatively new area, a series of numerical studies were initially performed to reveal the salient features of the signals expected. These numerical findings were subsequently confirmed experimentally.