The gas gun at NASA's ballistic impact facility. Photo: NASA-GRC

The last time government cannon boomed across the shores of Lake Erie was during the War of 1812, but a new laboratory at NASA's Glenn Research Center, Cleveland, OH, is now experimenting with ballistics of a different kind.

Building 49 houses Glenn's new ballistic impact facility. Its main features are a 40-foot-long gas gun that can eject projectiles at speeds up to 1,500 feet per second, or over 1,000 mph, and a high-speed camera that can capture 2.5 million images per second.

"The whole idea is to watch the impact and see how the materials struck by the projectiles behave," said Dale Hopkins, a structures engineer and team leader for the design and buildup of the new facility. "It's not just whether they survive, but how they deform and fail."

One of the facility's main tasks is testing materials for aircraft engine housings. During rare in-flight events, if the engine is hit by hail or birds, the engine housing must contain any fragments and withstand the severe loads, or forces, that otherwise could cause the engine to separate from the wing of the airplane. Current engine housing materials, usually high-strength metal alloys and non-metal ballistic fabrics, do this job very well but are very heavy. The new, lighter structures being considered for this duty must be evaluated for their ability to withstand such catastrophic events.

"The new facility allows us to use larger, heavier, irregularly shaped projectiles that look and behave more like fragments of an engine's rotating parts. The testing is much more realistic than before," Hopkins said.

A drawing shows the gas gun design. Photo: NASA-GRC

The facility is also being used to evaluate flywheel containment materials. The disk in a flywheel, a new type of energy storage device being considered for use in satellites and other advanced applications rotates at over 50,000 revolutions per minute. Should the disk fatigue and rupture, the high-speed particles released would need to be contained to avoid damaging other equipment or injuring people.

The materials to be tested include intermetallic alloys, fiber-reinforced composites and cloth-like polymers. New engine concepts require materials that can withstand higher temperatures and higher-speed projectiles than current containment materials. Similar work at Glenn over 20 years ago helped prove the worth of the ballistic materials used in jet engines today, as well as in bullet-proof vests.

The data taken during these impact tests will also be used to verify and improve the accuracy of computer models that predict material response to impacts. Manufacturers can use these more accurate models to shorten the time and reduce the cost of bringing new designs to market.