Non Destructive Evaluation of Urethane-Epoxy Coating Systems using the Scanning Kelvin Probe Technique

High performance aircraft are subjected to harsh environmental factors during operation including impacts with water and other particles, as well as high temperature and humidity. Rain erosion coatings (REC) made from polyurethane (PU) are used to protect the metal and other coatings from these damaging elements by absorbing the force of impacts and providing a barrier against corrosive substances. Over time these coatings break down and may fail in flight by delamination. Traditional lifecycle estimates fail to predict coating life due to the variety of environmental conditions aircraft are exposed to. 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. Previous studies have shown that it is possible to detect change in alkyl chain length in polymers using a Scanning Kelvin Probe (SKP) system. Additionally, Hansen et al. demonstrated the ability to detect the changes in length and conformation of DNA molecules using an SKP system. These, and other experiments, show the sensitivity of the SKP to changes in surface material and indicate that the SKP should be able to detect chemical changes in a degraded PU coating as well. The objective of this research is to determine if the SKP can be used to detect the changes in polymer coating structure associated with degradation as well as characterize the degradation of PU RECs as a function of time exposed to elevated temperature and humidity. 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. Having a reliable method to assess degradation will increase the service life of coatings, saving time and money by reducing preemptive reapplication.https://ecommons.udayton.edu/stander_posters/1900/thumbnail.jp