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Mark Hilburger (left) and Mike Roberts, NASA's Shell Buckling Knockdown Factor (SBKF) program (2011)

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Mark Hilburger (left), senior research engineer in the Structural Mechanics and Concepts Branch at Langley and the principal investigator of the NESC's Shell Buckling Knockdown Factor project, and Mike Roberts, an engineer in Marshall's structural strength test branch and center lead, review real-time data from the "can crush" test.
Credit: NASA/MSFC/D. Higginbotham

ARTICLE by Chris Rink in the RESEARCHER NEWS, NASA Langley Research Center, Hampton, Virginia:
Success - This can is crushed! 03.24.11:

With ominous building-shaking booms and rumbles, the world's largest can crusher put the vertical smack down on a huge aluminum-lithium test cylinder with almost one million pounds of force.

Some of the visitors who witnessed the March 23 successful can crush at NASA's Marshall Space Flight Center in Huntsville, Ala., described it as the sound of an ocean-going ship breaking up or thunder in the next room.

Others referred to it as rocket science.

The NASA Engineering and Safety Center (NESC) based at NASA Langley calls it the Shell Buckling Knockdown Factor Project (SBKF) - an innovative and long overdue research effort that examines the safety margins needed to design future launch vehicle structures. Test results will be used to develop new shell buckling knockdown factors – a complex set of engineering design standards essential to heavy launch vehicle design.

Launch vehicles that will weigh less and have cheaper development costs.

The current aerospace industry's shell buckling knockdown factors date back to Apollo era, when high-tech materials, manufacturing processes and advanced computer modeling were things of the future. The new analyses will update design considerations for large structures like the main fuel tank of a future heavy-lift launch vehicle.

In a throwback to the beginning of the U.S. space program, the full-scale test happened at Marshall's Structural and Dynamics Engineering Test laboratory. Originally built to test Saturn rocket stages, Building 4619 was key in the development of the lightweight space shuttle external tank and tested International Space Station modules.

Mark Hilburger, a senior research engineer in the Structural Mechanics and Concepts Branch at Langley and the principal investigator of the SBKF project, was sealed in the control room located near the roof of the 4619 high bay with key members of the test team. Hilburger occasionally glanced out the control windows, looking almost eye level at the massive test structure -- 27.5 feet in diameter, 20 feet tall -- reaching up three stories when mounted on its base.

It's a white beast with spots, almost 70,000 of them, photogrammetry polka dots that turn a snow leopard pattern into meaningful engineering data showing stress and strain. But most of the time, Hilburger and Mike Roberts, an engineer in Marshall's structural strength test branch and center lead for the test, watched video and computer monitors displaying high-speed camera angles of buckles, ripples tears, graphs, data, data and more data.

More than 800 electronic sensors on the test article sent data to the Stress Analysis Station on the ground floor room and up to Hilburger, who directed the application and withdrawal of hundreds of thousands of pounds of external pressure at a time. And there was pressure inside the test article at 1 pound per square inch, too. It doesn't sound like much, but considering the massive size of the cylinder, it adds up to 32,000 cubic feet of air pressure that stabilizes the shell and simulates the conditions inside a pressurized fuel tank.

"What a great test," said Hillburger. "I was holding my breath the whole time waiting for the next thing to happen. We certainly have a lot of data to review, and we're reviewing for computer models. But just when you think you had it all figured out, there was something new that we had to go uncover. And that's good for us because it keeps us testers in business."

Before the full-scale test, the shell buckling team tested four eight-foot-in-diameter aluminum-lithium cylinders. Current research suggests applying the new design factors and incorporating new technology could reduce the weight of large heavy-lift launch vehicles by as much as 20 percent. Up next, the shell buckling team will test carbon-fiber composite structures that are 20-30 percent lighter than aluminum and widely used in the automotive and aerospace industries. Marc Schultz is an aerospace engineer at NASA Langley and is leading the composite material testing segment of the SBKF project.

NASA Administrator Charlie Bolden said this type of research is critical to NASA's developing a new heavy-lift vehicle. "The Authorization Act of 2010 gave us direction to take the nation beyond low-Earth orbit, but it is the work of our dedicated team of engineers and researchers that will make future NASA exploration missions a reality," Bolden added.

For Hilburger, the NESC, and the rest of the Langley and Marshall engineers, reality is one shell buckle test at a time.
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