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For Release: March 19, 1998

Michael Finneran

(757) 864-6121/23/24

RELEASE NO. 98-013

Lightweight and Durable Structures


Researchers at NASA Langley are testing a new material that may one day be used to build a future supersonic passenger jet. The materials used to build this future jet must endure speeds of more than 1,500 mph, altitudes of 65,000 feet, and aircraft surface temperatures over 300°F. The materials must be strong, lightweight, durable and tolerant to damage.

In a recent test, two 40 inch by 80 inch panels were subjected to more than 400,000 pounds of force before they cracked. "We are testing these panels to study the effects of damage from foreign objects that may penetrate through an aircraft structure," said David McGowan, a NASA aerospace engineer in charge of the tests. "The structure must be able to support the proper amount of load with this type of damage to receive FAA certification. The tests we perform determine if the structure can meet these design requirements, which it did in both cases."

The two test panels were built by The Boeing Co. in St. Louis, Mo. with a new material called PETI-5, developed at NASA Langley. LaRC PETI-5 is a resin material that is combined with graphite fibers to make what's called 'prepreg' tape. Many layers of this tape are then heated under pressure to form a piece of composite structure.

"It was necessary to develop a new [composite] material under NASA's High-Speed Research (HSR) Program because no material existed that met the temperature and durability requirements," said Rodney Ricketts, manager of the HSR Structures and Materials program.

"In the HSR Program we have developed resin and adhesive materials that meet the requirements for the high-temperature composite structures. NASA started with test-tube quantities in the laboratory just 3 years ago, and now commercial material suppliers are producing 1,000 lb. quantities for Boeing, Northrop-Grumman and Lockheed," Ricketts said.

Since 1990, NASA and its industry partners have been working to develop technologies for a future supersonic passenger jet. The jet conceived by NASA's High-Speed Research Programwould carry 300 passengers across the Pacific Ocean in just four hours, at tickets prices only 20 percent over comparable, slower flights.

"During earlier parts of the program, we studied many different structural concepts," Ricketts said. "Now, after much design, analysis and testing, we have selected two. This has allowed us to focus on the lightest weight, highest performance designs and move from testing small coupons and elements to testing large panels such as this. Eventually we will test a large section of a fuselage, approximately 15 ft in diameter and 30 ft in length."

"We have an entire series of tests planned at NASA Langley to evaluate skin panels with foreign object damage," McGowan said. "We will be repeating the first two tension tests on other panels, and we will also be testing a series of flat and curved panels using compression. All of these tests are leading up to the tests of a full section of the fuselage."

"These [recent] tests also give us much needed data to determine if our analytical models are capable of predicting what will happen when the panel is loaded with [foreign object] damage," McGowan said. "The predictions for the ultimate failure loads of the panels that we obtained from our analyses were very close to the actual values. We've realized though, that there are parts of our analyses that need to be refined to better predict certain aspects of the structural response. We are addressing that right now, and we're confident that we'll have even better predictions for the next series of tests. The confidence in our analytical models to predict the behavior of these panels lets us reduce the number of expensive tests to be performed in the future."


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