Active sensors for health monitoring of aging aerospace structures

Abstract

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 used to compare 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 identifying additional reflection generated from the damage site and changes in transmission velocity and phase are used. Both approaches benefit from the use of artificial intelligence neural networks algorithms that can extract damage features based on a learning process. Design and fabrication of a set of structural specimens representative of aging aerospace structures is presented. Three built-up specimens, (pristine, with cracks, and with corrosion damage) are used. The specimen instrumentation with active sensors fabricated at the University of South Carolina is illustrated. Preliminary results obtained with the E/M impedance method on pristine and cracked specimens are presented.

Development and Validation of Bonded Composite Doubler Repairs for Commercial Aircraft

“…Prime candidates for sensors based on active-material principles utilize thin piezoelectric wafers of 0.125"-0.25" diameter with thicknesses of 0.010" -0.030". They can be easily attached to existing aging structures without changing the local and global structural dynamics [40][41][42]. PZT sensors can also be embedded inside composite structures to closely monitor for internal flaws.…”

Piezoelectric wafer active sensor embedded ultrasonics in beams and plates

“…Figure 21 shows PWAS calibration in the range 10-600 kHz; their use at up to 2.6 MHz has been also demonstrated. 23 Thus, a variety of guided waves can be generated with the same PWAS installation.…”

“…Osmont et al 22 used Lamb wave propagation in sandwich plates to identify the effect of impact damage in sandwich skins and core. Giurgiutiu et al 23 outlined the general methodology for using piezoelectric active sensors for health monitoring of aging aircraft structures.…”

“…In order to keep the problem tractable, simple geometries (beam and plates) were used. In addition, since the focus of our sponsored research was on aging-aircraft damage detection, 23 our active-sensor experiments were conducted on thin metallic plates. However, the findings of this study can be easily extended to practical geometries and composite material structures.…”

Use of Macro Fibre Composite Transducers as Acoustic Emission Sensors

“…To ensure continued safe operation during long term service, large amounts of inspection and maintenance must be performed on the ground, accounting for up to one quarter of a commercial fleet's running costs [1]. A Structural Health Monitoring (SHM) system for aerospace structures would offer great potential for maintenance cost savings and a potential reduction in the safety factor required for optimized structures.…”