Smart Patches for Monitoring Fatigue Crack Growth in Aircraft Structures.

摘要

A built-in cost-effective diagnostic system for monitoring crack growth in aircraft structures was developed, particularly for riveted fuselage joints and cracked aircraft parts with composite bonded patches. Different smart patch designs for crack growth monitoring at fuselage lab joints and cracked parts with composite bonded patches were developed and integrated with the corresponding aircraft parts. Using the diagnostic software, pre-selected diagnostic signals are propagated from a designated piezoelectric actuator to neighboring sensors. The corresponding sensor signals are recorded and compared with a baseline reference, which was recorded earlier. The signal processing technique and a damage index resulting from an interpretation algorithm were developed and implemented for extracting features related to crack growth conditions at the time of measurement. The damage index was verified by a crack propagation test on a notched aluminum plate which was fatigued under cycling loading. A fatigue test for multi-riveted aluminum lap joint (936 x 462 mm) with smart patches installed was performed and the damage index results were compared with conventional NDT methods including eddy current and ultrasonic scan. The probability of damage detection (POD) was assessed for the damage index comparing with two conventional NDT methods. Also, an aluminum plate repaired with boron/epoxy patch where smart patches were inserted was tested and the results were compared with the crack growth results by a visible inspection. The crack growth prediction of the damage index on both experiments showed a good agreement with NDT predictions as well as visual inspection results.