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Nondestructive Evaluation of Thick Outer Mold Line Paints and Coatings


OBJECTIVE: A nondestructive evaluation tool for aircraft outer mold line (OML) urethane and epoxy integrity assessment to address and identify premature failures. DESCRIPTION: Many paints and coatings are employed on modern military aircraft with functionalities such as rain erosion resistance or p-static dissipation. These paints and coatings experience a wide variety of environmental conditions in flight and on the ground. While performance degradation over time is expected, 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. Standard material lifetime predictions fail to estimate urethane lifetime on operational aircraft due to the wide variety of environmental factors and combinations of factors that trigger degradation at different rates. While signs of urethane aging may not be visible, the onset of chemical composition and physical properties changes can occur. A significant ongoing Air Force investment is being made to understand the cause and extent of these material failures. While these studies will serve to characterize failure mechanisms and evaluate material performance under a variety of relevant conditions, permitting a better understanding of environmental degradation and a refinement of lifetime prediction models, there is no currently demonstrated technology capable of evaluating the in-place integrity of epoxy or urethane materials on a fleet. Representative damage modes that need to be detected are mentioned below. Therefore, the focus of this topic is not on cause and effects studies. The Air Force desires a nondestructive capability for the rapid in-place determination of the integrity of Aircraft OML urethanes and epoxies. The measurement technology must be capable of interrogating a variety of multi-layer coating systems and providing an assessment of total coating system integrity as well the ability to discriminate and characterize individual sub-surface layers. The assessment of coating material state and system integrity should be based on the analysis of measurable quantities which change with respect to the type and degree of material degradation. Detection of changes such as corrosion of fillers and pigments as well as bond breaking and out-gassing of the matrix are the focus of this solicitation for determining the material state of a paint or coating system. The measurement technique must be nondestructive and non-invasive and permit early detection and trending of a detrimental parameter associated with degradation. This measurement capability is desired so that aging materials can be assessed in-place enabling accurate planning and budgeting for sustainment operations. PHASE I: Develop a laboratory urethane based paint and coating integrity evaluation tool for measurement and analysis of a two or more layer material subjected to various degradation conditions. The applicability of the method for epoxy based paints should also be addressed with an experimental plan for phase II. The ability to differentiate and determine the integrity of each coating is required. PHASE II: Demonstrate a nondestructive measurement capability on a stack of four representative OML materials subjected to various degradation conditions. No government furnished equipment is anticipated. Demonstrate the ability to track degradation levels of the system and the individual layers. Develop a plan for packaging, ruggedization and commercialization of a man portable inspection tool for on-aircraft measurement. Develop/demonstrate a prototype OML coating inspection and assessment tool. PHASE III: Development of a man portable, ruggedized, in-place coating inspection tool will have military applications for many systems employing epoxy and urathane based paints and coatings. Other applications could include commercial air and automotive industries. REFERENCES: 1. Detection and Characterization of Water-induced Reversion of Epoxy and Urethane Potting Compounds, DTIC Final Report, 10 Oct. 1976 - 10 Oct. 1977, Jakobsen, A. J. 2. Analyses for Mechanical and Electrical Properties of Epoxy Resins Used as Potting Compounds, Polymer Engineering & Science, Vol. 14, Issue 6, PP. 478-480, June 1974, Fountain, R. 3. Failure Analysis of Paints and Coatings, John Wiley and Sons, Ltd., 2009, Dwight G. Weldon. 4. Mechanisms of Military Coatings Degradation, J.A. Escarsega, W.S. Lum, and P.H. Patterson., DTIC Final Report, Aug 2003.
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