Standardized Test Methodologies for Specialty Coating Durability

Dr. Karen Schultz | Boeing



Replacing exterior coating systems that no longer meet their performance requirements generates a significant environmentally hazardous materials waste stream composed of the combined coating material with solvents and media used to remove the coatings as well as the release of hazardous materials used to prepare the surface and reapply the coating system components. Specialty coating systems, in particular, are proving to be less durable in service than predicted by current accelerated test methods. The more frequent replacement of these coatings is a cost and waste management issue for Department of Defense (DoD) depot and field operations. The objective of this project is to develop a fundamental understanding of the root cause of coating system degradation and failure and to develop an accelerated test protocol and analysis methodology to accurately replicate failure modes observed and predict performance lifetime of the coating systems in service environments.

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Technical Approach

Current accelerated testing methods for specialty coating systems do not accurately simulate damage modes that are relevant to field failures and do not generate data that can be used to accurately quantify specialty coating performance lifetime. To overcome this issue, the researchers will use in situ monitoring of coating system characteristics and substrate corrosion that can be associated with moisture ingression as well as in situ and ex situ measurements of physical and chemical changes in the individual coating system components to determine the causes and damage modes of failure. Using this data along with modeling to understand transport mechanisms and properties change rates, the researchers will design temperature and humidity cycles where they control moisture gradients across the coating system and understand changes in intra and interlayer properties. A test coupon and fixture will be designed so that mechanical stresses can be applied to the coating system in the exposure environment to evaluate the combined effects of mechanical stresses and environmental exposure (photochemical, temperature, humidity, corrosives). The experimental and damage accumulation modeling data will support coating development, selection, and certification for use in a variety of service environments. The data will form the basis for a follow-on effort to develop a lifetime prediction tool that can be used by coatings developers to speed development of high performance coating components and systems and by vehicle designers to predict maintenance intervals and sustainment costs.

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This project will advance the understanding of the interaction of coating systems with their use environment and provide a framework to predict in-service performance based on accelerated laboratory tests. The deliverable for the project is a testing protocol and evaluation tool for specialty coating systems that will accurately recreate observed in-service failure modes and enable reliable prediction of coating system lifetime in service environments. The protocol will be written in a manner that will be suitable for establishment as a standard test method (SAE, ASTM, etc.). Use of the protocol to develop and implement more durable coating systems across DoD will lead to a reduction in hazardous waste over the lifecycle of DoD aircraft while increasing aircraft availability. Although the focus of this project is on specialty coating systems, the methods will be generally applicable to all coating systems.

The science of coating systems degradation is a complex interaction of moisture and contaminant intrusion into the coating materials, ultraviolet light (UV) exposure, thermal effects and cycling, and applied mechanical stresses. The program will quantify the individual and combined effects of these stressors on the overall coating system. Experimental data will be coupled with modeling techniques to understand rate and mode of water migration in coating systems and build relationships between moisture content and mechanical properties of coatings. The individual and combined effects of mechanical stress applied to coating systems, UV, and thermal degradation; thermal mechanical effects; and humidity cycling will provide the basis for construction of a model to predict coating system performance as a function of exposure conditions. (Anticipated Project Completion - 2019)

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Points of Contact

Principal Investigator

Dr. Karen Schultz