Spectral Power Distributions in Accelerated and Natural Weathering Tests and Their Impact on Aerospace Coating Service Life Prediction

Exterior commercial airplane coating systems serve both decorative and protective functions and must retain gloss and color properties as well as provide corrosion and fluid resistance in severe service environments. Commercial aircraft can make up to eight flights per day and cruise at altitudes as high as 13 km for up to 16 h/day. Ultraviolet (UV) radiation exposure can increase by a factor of four and paint surface temperature can range from as high as 75°C down to 60°C between ground and cruise altitudes. Additionally, moisture levels may vary from 100% relative humidity and rain on the ground to completely dry conditions at cruise. At a minimum, the effects of the changes in UV radiation, temperature, and moisture on photooxidation and hydrolysis must be considered and balanced in accelerated test method development, damage mechanism understanding, modeling for service life prediction of these coating systems, and design of future generation coatings. This chapter presents recent investigations aimed at achieving these goals. The first part compares the sensitivity of damage from overlap of polymeric absorption peaks with UV spectral radiance measured at ground level in Southern Florida, predicted at airplane cruise altitudes of 9.1-12.2 km, and produced by xenon arc lamps with various filters (Extended UV and Daylight specified in SAE J2527 and special daylight specified in ASTM D7869). The second part of the chapter assesses aerospace coatings using exposures in Southern Florida, SAE J2527 with daylight filters, and ASTM D7869 and compares these results to expectation based on in service data.