Nondestructive Evaluation of Thick Outer Mold Line Paints and Coatings

ABSTRACT: The Air Force is experiencing a number of premature failures of urethanes and epoxies used on the Outer Mold Line (OML) of high performance aircraft which cannot be detected by standard lifetime predictions based on visual, electrical, or mechanical inspection. Consequently, changes in chemical composition and physical properties can occur without warning, compromising functionality of the coating. Well established methods for Non-Destructive Evaluation (NDE) of thin films such as hardness tests, and measurements of capacitance and dissipation have been used extensively for NDE of coatings, but incapable of depth profiling, identification, and tracking of chemically based degradation that occurs in-use. Ultrasound, Forward-Looking Infrared Systems (FLIR), and Raman spectroscopy detect oxidation and fracture zones in polymeric structures and coatings, but lack the resolution for detailed chemical depth profiling. To detect early signs of degradation and estimate coating lifetime, ChromoLogic, LLC (CL) proposes to develop a Coating Integrity Monitoring by Spectroscopic Analysis (CIMOSA) system, which utilizes Spatially Offset Raman Spectroscopy (SORS) to detect and grade subsurface defects and estimate remaining lifetime of OML coatings. This enhancement to current NDE analysis techniques will reduce the frequency of paint/depaint operations, resulting in cost savings, reduced environmental pollution and more efficient maintenance planning. BENEFIT: CIMOSA will provide an easy to use tool for the Air Force to rapidly evaluate OML coatings, thereby optimizing maintenance procedures of military aircraft. CIMOSA could be extended to other DOD agencies as well, such as the Army and Navy, for assessment of protective coatings on aircraft carriers, naval ships, and submarines. In the civilian market, CIMOSA could used to detect oxidative corrosion in coatings on commercial airplanes and automobiles, detection of false coatings on counterfeit electrical components, counterfeit drug detection, and forensics.