TuFF — Tailored Universal Feedstock for Forming — is a strong, highly aligned, short-fiber composite material that can be made from many fiber and resin combinations. Created at the University of Delaware’s Center for Composite Materials (CCM), it can be stamped into complex shapes, just like sheet metal, and features high-performance and stretchability up to 40%.

Since its introduction, CCM researchers have explored applications for TuFF, from materials for repairing our nation’s pipelines to uses in flying taxis of the future.

Now, armed with $13.5 million in funding from the U.S. Air Force, UD mechanical engineers and co-principal investigators Suresh Advani and Erik Thostenson along with industry collaborators Composites Automation and Maher and Associates are working on ways to improve manufacturing methods for TuFF. 

“I am really excited at the opportunity to mature the TuFF pre-pregging process and demonstrate high-throughput composite thermoforming for Air Force relevant components,” said David Simone of the U.S. Air Force.

The goal is to enable lighter-weight composites to become cost-competitive with aluminum for creating small parts found in air vehicles.

Advani explained that when it comes to making aircraft materials more cost-efficient, reducing a material’s weight even a mere kilogram, just 2.2. pounds, will reduce fuel consumption and emissions and can result in thousands of dollars in savings over time. 

This is because aircraft are heavy. A Boeing 747, for example, weighs a whopping 404,600 pounds. A B2 Stealth Bomber in the U.S. Air Force, meanwhile, tips the scale at over 43,000 pounds.

“In general, the aerospace industry wants to reduce weight and replace metals,” said Advani, George W. Laird Professor of Mechanical Engineering. TuFF is a good option because the material can achieve properties equivalent to the best continuous fiber composites used in aerospace applications. 

Advancing TuFF thermosets

Until now, most of the work around TuFF has focused on thermoplastic composite materials that melt when heated, becoming soft and pliable, which is useful for forming. By contrast, TuFF thermosets have a higher temperature threshold, making them useful for aerospace applications. But TuFF thermosets have manufacturing challenges, too, including the long manufacturing times necessary to make a part. 

In this new project, Thostenson and Advani will work on ways to improve the viability of thermoset TuFF composites. To start, the researchers will characterize the starting materials’ mechanical properties to understand how to make TuFF thermosets reliably and consistently. The research team will explore whether they can make the material in a new way, using thin resin films and liquid resins. They will test the limits of how the material forms and behaves under pressure and temperature, too.

“How does it stretch during forming in a mold? What shapes can we make? When does it tear or thin or develop voids that can compromise material integrity?” said Advani.

Having a database for such properties and behaviors will be useful in understanding TuFF material capabilities and limits, and to inform efforts to model and design parts with TuFF.

Thostenson, professor of mechanical engineering, is an expert in structural health monitoring of materials. He will advance ways to embed sensor technology into TuFF thermosets. This would allow the researchers to see from the inside how the material is forming and curing during its manufacture, in hopes of being able to gauge—and improve— the material’s damage tolerance. 

It’s intricate work. To give you an idea of scale, a single layer of TuFF material is approximately 100 microns thick, about the diameter of the average human hair. The carbon-nanotube sensors Thostenson plans to integrate into the material are smaller still—one billionth the width of a human hair. 

“This would allow us to do health monitoring for the materials and parts during service life, but you could also imagine using sensor technology to detect a defect during manufacturing,” said Thostenson. 

While it remains to be seen whether this is possible, Thostenson said having this ability could result in real cost savings for manufacturing methods, where real-time knowledge of how a material is curing could help the researchers speed up production. Additionally, if there is a material failure, such as a tear, the sensors could point the researchers where to look in the process.

The research team also plans to develop a virtual modeling system to refine the material-forming process through computer simulation instead of by trial and error. In this way, the team will better understand each step in the material-forming process, enhancing the team’s ability to make TuFF materials consistently and reliably — a must for aerospace applications.

“I am hoping this work will allow us finally to make composites cost competitive with the metal industry,” said Advani.

In addition to Thostenson and Advani, the team includes, from CCM, Jack Gillespie, Dirk Heider, Shridhar Yarlagadda, Thomas Cender, John Tierney and Pavel Simacek, along with four to five graduate students.