Structural health monitoring of composite patch repairs using two-dimensional wavelet maps

The economic constraints on modern day military and commercial air fleets has imposed longer lifecycles and extended environmental exposure on them. Aging aircrafts are more susceptible to damage due to fatigue and environmental corrosion. Adhesively bonded composite patch repairs have been found to be an economic and reliable means of strengthening aging airframes. However, before this technology is adopted by the aircraft industry the long term durability of the composite patch repairs in terms of their structural integrity has to be thoroughly scrutinized. In this paper a structural health monitoring algorithm has been developed that can detect damage in adhesively bonded composite patch repairs using the dynamic response of a structure. The signal-based health monitoring algorithm, wavelet analysis, has been utilized to detect damage using small local variations in the vibration signature of the structure. Specifically, curvature mode shapes, and wavelet maps, are integrated to detect damage at both single and multiple locations. The dynamical characteristics of the test structure are obtained analytically using linear elastic finite element analysis and experimentally with a Laser Doppler Vibrometer. The results obtained are good.