Bondline Integrity Monitoring of Adhesively Bonded Joints in Aircraft Structures

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Bondline integrity monitoring is one of the most critical concerns in the design of aircraft structures up to date. Although adhesively bonded joints have demonstrated superior properties over mechanically fastened joints, current standards still require fasteners even with bonded joints because of the lack of confidence on the bondline integrity both during fabrication and service. This award supports fundamental research to provide needed knowledge for the investigation of a novel approach for bondline integrity monitoring of adhesively bonded joints. If successful, this project will lead to greatly benefit the design of aerospace and mechanical structures by providing increased confidence on the use of bonded joints leading to a significant weight reductions when compared to bolted joints, reduced assembly cost, increased fuel efficiency, and improved aircraft performance. Therefore, this technology will enhance the economic competitiveness of the US on the novel structural systems front across all industries. This research involves several disciplines including sensor technologies, manufacturing, computational models, and signal processing. Therefore, this multi-disciplinary approach will help broaden participation of underrepresented groups in research and will promote partnerships between academia and industry. The objective of this project is to develop an innovative "intelligent" adhesive for the integrity monitoring and self-diagnosis of adhesively bonded joints in aircraft structures. The implementation will be based on the development of a stretchable micro/nano-sensor network that can be embedded inside the adhesive layer and is capable of monitoring the integrity of the adhesive bondline interfaces and diagnose their integrity status. Throughout this research special emphasis will be given to the early detection and monitoring of weak ("kissing") bonds, for which no mature solutions have been so far proposed by the nondestructive evaluation and structural health monitoring communities. The work involves: (i) development of new types of nano/micro active sensors and actuators that can be integrated into adhesive films without causing adhesive degradation, (ii) characterization of the presence of sensor arrays on the integrity of the intelligent adhesive, and (iii) development of appropriate diagnostic signal processing techniques to detect bondline degradation, and particularly to identify the existence of weak bonds. The diagnostic algorithms as well as the analytical models to be developed will lead to the comprehensive understanding of complex interaction between embedded micro-sensors and the bonded structure and the postulation of a complete structural health monitoring system for bondline monitoring of adhesively bonded structures.