Publications
Active sensors for health monitoring of aging aerospace structures
A project to develop non-intrusive active sensors that can be applied on existing aging aerospace structures for monitoring the onset and progress of structural damage (fatigue cracks and corrosion) is presented. The state of the art in active sensors structural health monitoring and damage detection is reviewed. Methods based on (a) elastic wave propagation and (b) electro-mechanical (E/M) impedance technique are cited and briefly discussed. The instrumentation of these specimens with piezoelectric active sensors is illustrated. The main detection strategies (E/M impedance for local area detection and wave propagation for wide area interrogation) are discussed. The signal processing and damage interpretation algorithms are tuned to the specific structural interrogation method used. In the high-frequency E/M impedance approach, pattern recognition methods are proposed for comparing impedance signatures taken at various time intervals and to identify damage presence and progression from the change in these signatures. In the wave propagation approach, the acousto-ultrasonic methods for identifying additional reflections generated from the damage site and changes in transmission velocity and phase are suggested. Design and fabrication of a set of structural specimens representative of aging aerospace structures (pristine, with cracks, and with corrosion damage) are presented. Their instrumentation with piezoelectric-wafer active sensors is discussed. Damage detection results obtained with the E/M impedance and wave propagation techniques on simple-geometry specimens and on the realistic aging aircraft specimens are presented.