The dynamic nature of weather makes predicting when the PU REC will fail is extremely difficult when using traditional lifecycle estimates, since aircraft are exposed to different environmental conditions at different geographical locations or areas of operations. Currently, no method exists for accurately predicting when a particular aircrafts coating will fail. Therefore, there is a need for a reliable non-destructive method to detect the changes in the surface coating that indicate when it is close to failure or has begun to fail.
It is hypothesized that the Scanning Kelvin Probe (SKP) can be used to detect changes in the work function of the REC’s associated with degradation of the polymer structure. If successful, it will serve as the justification for developing a portable scanning unit that can be deployed by maintenance crews to determine when a coating needs to be reapplied. To test this, 4X6 inch 2024 aluminum alloy test panels were exposed in an autoclave to high heat and humidity (121˚C and 100% RH) for a variety of times to simulate the degradation process. They were then scanned with the SKP to characterize the degradation as a function of exposure time. Initial data shows that there is a change in work function with increasing exposure as well as localized areas of higher work function. Raman spectroscopic analysis indicates changes in coating polymer chemistry consistent with hydrolysis of the ester bonds. This data correlates with the changes in work function seen by the Kelvin probe, showing that the SKP can non-destructively detect polymer degradation.