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NRL Tests Polyurea Coatings for Corrosion Protection in Amphibious Assault Vehicle Armor

Published on 2015-04-09. Author : SpecialChem

The U.S. Naval Research Laboratory (NRL) has found that some types of rubber provide corrosion protection—and potentially better ballistic protection—for amphibious assault vehicles (AAVs). This is important to the U.S. Marine Corps (USMC) as they look to extend the AAV, introduced in 1972, through 2035. "Innovative sustainment concepts, like those NRL is investigating, enable us to avoid the cost of new design, development, and production of new components," says Tim Bergland of the USMC Advanced Amphibious Assault (AAA) office.

Dr. Mike Roland and Dr. Ray Gamache led the research for NRL. "What makes [AAVs] unique is they can go in water and land," says Roland. "They give the Marine Corps a capability that no other service has."

Roland and Gamache found rust and corrosion start at cracks in the paint. "You've got steel, rubber, steel—and these things are thermally expanding and contracting differently," says Roland. "In addition to which, AAVs aren't driven like expensive Volvos; they're banging into stuff—and now you've got a way for water ingress."

NRL showed that certain types of rubber, called polyureas, could better protect the armor from corrosion by stretching with it, instead of cracking like brittle paint.
They also showed polyurea coatings slow bullets and blast fragments. "They take kinetic energy from the bullet," says Roland. "So the bullet, to keep penetrating, it's meeting an increasingly resistant medium. And if it slows down enough—it always makes it to the steel plate, but it doesn't have enough velocity to get through it."
NRL's research could help extend the life of today's AAVs, and may also guide the next generation of ship to shore connectors. "We solved the corrosion problem," says Roland. "And with a negligible increase in weight, we also provided a higher payload capacity and the potential for better ballistic protection."

By exposing steel test pieces to saltwater in their lab, Roland and Gamache also showed polyurea protects armor from corrosion much better than paint.

The U.S. Naval Research Laboratory coated steel samples of amphibious assault vehicle armor with paint or polyurea, and exposed them to saltwater at its Key West facility. On the bent pieces, "The paints tend to crack," says Dr. Mike Roland, who led the project. "The polyureas don't because they're elastomeric, rubbery." "We wanted to simulate what happens in the field, so we bent some of the test pieces," says Roland. In addition to flat test pieces, "we had a gentle bend and we had a 90° acute bend." They tested five coatings: two types of paint, a polyurea NRL's been using in other armor applications, and two polyureas developed by a private company. "We set up aquarium tanks filled with sea water. We raised the temperature to 40 and 50 centigrade [104 and 122°F], just to accelerate the corrosion, and we bubbled air so there was plenty of oxygen."

The polyurea worked much better than paint. "If you just put the plate in flat, they'll all work," says Roland. But with the bent pieces, "the paints tend to crack. The polyureas don't because they're elastomeric, rubbery; so they stretch and don't open up a pathway for the water."

While having a long-term solution is very important, the USMC also needs to know how best to maintain the AAVs in use now. "We quantified how much they're going to lose, in ballistic performance, with the corrosion," says Roland. "This will guide the Marine Corps in when they need to replace or repair the armor, saving a lot of money."

NRL continues to monitor samples in actual seawater troughs at NRL's Key West facility. "The ones that performed the best in salt water tanks in the lab are performing best at Key West," says Roland.

About the U.S. Naval Research Laboratory
The U.S. Naval Research Laboratory is the Navy's full-spectrum corporate laboratory, conducting a broadly based multidisciplinary program of scientific research and advanced technological development. The Laboratory, with a total complement of approximately 2,500 personnel, is located in southwest Washington, D.C., with other major sites at the Stennis Space Center, Miss., and Monterey, Calif. NRL has served the Navy and the nation for over 90 years and continues to meet the complex technological challenges of today's world.

Source: U.S. Naval Research Laboratory

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