Replacing exterior coating systems that no longer meet their performance requirements generates a significant amount of environmentally hazardous materials. That waste stream includes the removed coating material, solvents used to prepare surfaces, and other waste media used during the removal process. Specialty coating systems are proving to be much less durable in service than was predicted by current accelerated test methods, leading to increased frequency of replacing these coatings alongside increased costs and waste management issues for Department of Defense (DoD) depot maintenance and field operations. Understanding degradation and failures in these multilayer coating systems is critically important.
Under her SERDP effort, Dr. Karen Schultz and her team from Boeing, Luna Innovations, North Dakota State University, Air Force Research Laboratory, and NAVAIR addressed this challenge by developing a new test method that combines the effects of dynamic mechanical strain and relevant environmental stressors of cyclic temperature and humidity to produce coating cracking with features similar to that observed in-service over structural discontinuities.
Leveraging in situ test methodologies developed under an earlier SERDP effort, the team created a suite of methods for both in situ monitoring of individual coating layers and ex situ measurements of physical and chemical changes to characterize moisture ingress in the individual coating system components and to determine the causes and damage modes of failure.
Using laboratory and outdoor exposure data, along with modeling to understand transport mechanisms and property change rates, temperature and humidity cycles were designed to control moisture gradients across the coating system and understand changes in intra- and inter-layer properties. Test coupons and fixtures were designed so that dynamic mechanical stresses could be applied to the coating system in the exposure environments to evaluate the combined effects of mechanical stresses and environmental exposure (temperature, humidity, etc.).
Specialty coating systems were evaluated during and after exposure to these combined effects, demonstrating the feasibility of this testing approach to:
1) Accurately simulate damage modes relevant to field failures
2) Identify the initiation point of coating failure
3) Improve sub-surface crack detection
4) Enhance the DoD’s capability to select high performance, durable coating components and systems
The test methodologies developed by Dr. Schultz and her team allows DoD a better means to predict performance of current and future coating systems, and to select more durable high performance coating components and systems.
For their efforts in addressing this issue, Dr. Schultz and her team have been awarded the 2019 SERDP Project of the Year from the Weapons Systems and Platforms Program Area for their project titled, Standardized Test Methodologies for Specialty Coatings Durability.
Project Team:
- Karen Schultz (PI) - Boeing
- Lindsey Blohm - Boeing
- Christina Grumbach - Boeing
- David Jackson - Boeing
- Sean Pennell - Boeing
- Thai Sweitzer - Boeing
- Gary Vanbooven - Boeing
- Kristen Williams - Boeing
- Bruno Zamorano Senderos - Boeing
- Fritz Friedersdorf - Luna Innovations
- Brandi Clark - Luna Innovations
- Patrick Kramer - Luna Innovations
- Stuart Croll - North Dakota State University
- Aaron Feickert - North Dakota State University
- Mary Hedrick - North Dakota State University
- Alen Fletcher - U.S. Air Force Research Laboratory
- Kevin Miller - Naval Air System Command
