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PRSEUS Composite Survives Torturous Testing

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Posted August 8, 2015

An aircraft section built by sewing together layers and rods of composite material was recently bent, twisted and otherwise stressed to the breaking point and beyond, and so far the test results show it survived its tortuous ordeal quite well.

NASA technicians conduct a non-destructive inspection of the keel section of the PRSEUS multi-bay box inside the Combined Loads Test System (COLTS) facility. Credits: NASA Langley/David.C Bowman

NASA technicians conduct a non-destructive inspection of the keel section of the PRSEUS multi-bay box inside the Combined Loads Test System (COLTS) facility. Credits: NASA Langley/David.C Bowman

“We hit the ball out of the park, all the way across,” said Dawn Jegley, a senior aerospace engineer at NASA’s Langley Research Center in Virginia.

Jegley is leading the research into this technology, called Pultruded Rod Stitched Efficient Unitized Structure, or PRSEUS, which is taking place at Langley as part of NASA’s Environmentally Responsible Aviation Project.

PRSEUS enables a new way for aircraft components to be assembled, reducing or even eliminating the need to use rivets and bolts driven through metal as fasteners, which over time can lead to cracks and other safety concerns.

The COLTS control room team busy gathering data during the middle of a test run. Credits: NASA Langley/David. C. Bowman

The COLTS control room team busy gathering data during the middle of a test run. Credits: NASA Langley/David. C. Bowman

The technique could enable unique aircraft shapes to be built, such as an airplane in which the wing seamlessly blends into the main fuselage.

Another benefit: Composites are much lighter than the conventional aluminum alloys that are used, and lighter aircraft would require its jet engines to burn less fuel, resulting in fewer harmful emissions.

A key feature of PRSEUS, at least theoretically, is that should any tears or holes open up in the aircraft structure for whatever reason, the unique design of the stitched composite material will arrest the damage and not allow it to get worse.

Researchers intentionally damaged a critical part of the PRSEUS composite structure to see if the damage wouldn't grow. After seeing that PRSEUS behaved as planned, the part was exposed to stresses well beyond what it would ever see in flight until it finally failed, resulting in the tear seen here. Credits: NASA

Researchers intentionally damaged a critical part of the PRSEUS composite structure to see if the damage wouldn’t grow. After seeing that PRSEUS behaved as planned, the part was exposed to stresses well beyond what it would ever see in flight until it finally failed, resulting in the tear seen here. Credits: NASA

“We’re still compiling all the data we gathered during the tests, but just visually you can see instances where we intentionally damaged the structure and the damage stopped where it was supposed to,” Jegley said.

But just as importantly the composite aircraft structure demonstrated it could sustain the loads and forces it would experience in flight, including those it would see in the most extreme cases of violent turbulence.

“And then having covered all the tests we intended to do, we did some bonus tests to find out what the ultimate limits of the structure were by exposing it to levels you would never see in flight, and even as it finally failed it still worked like a charm,” Jegley said.

The 30-foot PRSEUS composite article arrived at Langley aboard NASA's Super Guppy aircraft from Boeing's manufacturing site in California. Credits: NASA Langley/Kathy Barnstorff

The 30-foot PRSEUS composite article arrived at Langley aboard NASA’s Super Guppy aircraft from Boeing’s manufacturing site in California. Credits: NASA Langley/Kathy Barnstorff

The section tested at Langley was made up of 11 panels assembled together and stretching 30 feet long and eight feet wide and 14 feet high. It was built by Boeing in California and shipped to Virginia in December 2014 aboard NASA’s oversized Super Guppy cargo plane.

Once at Langley it was installed in the center’s Combined Loads Tests System (COLTS), a large, hydraulically powered test fixture that essentially serves as an aircraft torture chamber for researchers to put airplane parts through their paces.

Testing of the 30-foot-section in the COLTS took place between January and June.

The PRSEUS-1 multi-bay box being lowered into the COLTS prior to testing. Credits: NASA Langley/David. C. Bowman

The PRSEUS-1 multi-bay box being lowered into the COLTS prior to testing. Credits: NASA Langley/David. C. Bowman

These tests followed a step-by-step evolution during the past few years in which first, many panels were manufactured and tested using the PRSEUS technique, and then a 4-foot-cube was assembled and tested.

At each step the idea has proved itself and provided a number of lessons learned as to how the materials behave and how best to manufacture increasingly larger structures.

“This brings up the technology to a certain level, but there is still more work to be done,” Jegley said.

For example, composite materials can be particularly vulnerable to damage if struck by lightning. Building lightning protection into the materials used by PRSEUS, and testing to see how lightning-induced damage might be minimized by PRSEUS, hasn’t yet been done.

Source: NASA

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