Nondestructive characterization of corrosion protective coatings on airframe structures

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 and frequent 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 this dissertation, several methods were considered to identify potential nondestructive evaluation (NDE) metrics. The approach then concentrated on Scanning Acoustic Microscopy (SAM) which contributed to all main research topics: coating inhomogeneity, coating weathering and interface condition. Developing a new data analysis procedure based on acoustic reflectivity, it became possible to determine the acoustic impedance of the coatings as a function of different weathering exposures. In addition, SAM and thermal techniques were employed to detect microscale sites of coating delamination and early stages of corrosion under a visibly intact coating. Here, the newly developed fan (hot air) thermography was introduced for interface studies. The NDE measurements were benchmarked with results from white light interferometry and electrochemical techniques.