For large integrated composite structure, the replacement of parts may not be feasible. Thus, the ability to repair the composite structure is important for maintaining its airworthiness. Although adhesively bonded joints have been employed for the repair of secondary structures, the absence of a reliable non-destructive testing (NDT) method for detecting poor bond limits their application to primary structures. Our team has developed smart composite repair patch based on different sensor technologies for monitoring the quality of the repair at the time of application as well as the integrity of the repair patch during the life-time of the structure:
Smart Multi-functional Printed Sensor:
Manual repairs are time-consuming, labour intensive and suffer from the lack of consistency due to human error. These difficulties have given rise in the past decade to development of automated repair technologies. Common issues to all automated systems are the non-destructive inspection and evaluation of damage and verification of the completed repair. Because the bondline between a patch and a repaired surface is so important to the integrity of the repaired structure, our team has developed a novel multi-functional sensor technology for monitoring the curing and service damage of bonded scarf repair patch with minimum disturbance to the structure and the bond-line. The proposed sensor technology is simple, yet reliable, and accurate. The multi-functional sensor is designed with a special pattern to cover different depths of the scarf repaired composite patch. It is inkjet-printed onto the surface of the scarf-repaired area to monitor (i) the curing process of the adhesive film during repair and (ii) the structural integrity of the bondline during service.
PZT based smart repair:
PZT transducers are designed in a ring shape to be attached to the primary structure surrounding the repair patch. Both baseline and baseline free methods based on guided waves are explored for damage detection in a step-sanded repair patch. Most of the diagnostic algorithm developed based of Lamb wave propagation requires baseline measurements taken at a reference state where no damage is present.
The limitation of baseline methods is that Lamb wave signals are affected by environmental and operational conditions of their host structures. Although baseline methods show higher reliability in damage localization, for monitoring repair patch, damage localization is secondary, and damage detection is of much higher importance. Therefore, our group have developed smart repair technologies for damage detection in the repair patch without the need for a baseline measurement.