Corrosion protective polymeric aircraft coating systems are continuously subject to ultraviolet radiation, thermal cycling and humidity exposure causing the coating to fail. This leaves the Aluminum alloy aircraft skin unprotected; paint replacement becomes necessary creating huge amounts of hazardous waste. Current efforts are directed to enhance the coating lifetime and new nondestructive inspection methodologies are needed for monitoring the coating performance periodically.

In the scope of an SBIR Phase II effort, a new NDE approach based on acoustic reflectivity analysis was developed to study aircraft coating degradation. These degradation processes cause alterations in the mechanical and physical properties of the coating which will influence ultrasonic wave reflection. A NDE metric to study these properties is acoustic impedance. Developing a new data analysis procedure based on acoustic reflectivity, it became possible to determine the acoustic impedance of the coatings for different weathering exposures. Acoustic reflectivity measurements were conducted on two different polyurethane type topcoat materials that were exposed to different combinations of UV radiation, humidity and temperature. The NDE measurements were benchmarked with results from dynamic mechanical analysis (DMA) and electrochemical techniques (EIS). Results obtained for coating material environmentally exposed up to 5000 hours will be presented.