The TuFF Age

The TuFF Age

UD researchers tackle new task in making complex material more viable for building aircraft

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.

Alumni Spotlight: Nancy Sottos

Alumni Spotlight: Nancy Sottos

Self-healing materials innovator recognized for her influence

Materials scientists and engineers have developed materials with the ability to heal themselves from damage by closing up tiny cracks before they become deep fissures. These materials can be used to protect infrastructure, military equipment, industrial machinery and more.

One of the pioneers behind the development of these self-healing materials is Nancy Sottos, a University of Delaware alumna.

For her impact and influence as an engineer, Sottos, the Department Head, Professor and Swanlund Chair of Materials Science and Engineering at the University of Illinois at Urbana-Champaign, was recently selected as a member of the National Academy of Engineering (NAE).

This is among the highest honors an engineer can receive. “Election to the NAE is an honor and wonderful recognition by my peers,” said Sottos. “I feel very proud and humbled to have the opportunity to participate in the NAE.”

Sottos received a bachelor’s degree and doctoral degree in mechanical engineering from UD in 1986 and 1991, respectively. She received the Department of Mechanical Engineering’s Distinguished Alumni Award in 2007 and is an external advisory council member for the Department of Materials Science and Engineering, which was founded in 1998.

“While at UD, one of the most important things I learned for my future career was how to work a part of a collaborative team,” said Sottos. “All of my current research is part of a collaboration with chemists, materials scientists and aerospace engineers.  UD also gave me a strong foundation in mechanics and materials.”

Her doctoral advisor and a founder of UD’s Center for Composite Materials, the late Roy McCullough, helped Sottos think outside the box. Mechanical engineering professors Tsu-Wei Chou, Mike Santare, Mike Greenberg, and co-advisor Selcuk Guceri—the latter now a professor at Worcester Polytechnic Institute—were also instrumental to her education, said Sottos.

Today, Sottos conducts research centered on polymers and composite materials capable of self-healing and regeneration, mechanochemically active polymers, and materials designed for reliable energy storage.

With her collaborators, Sottos co-founded a company, Autonomic Material Inc., that has commercialized self-healing coatings and paints based on their research.  “Future applications may involve composite structures that can self-heal or self-report damage—for example—a space structure that can autonomously heal damage from the environment,” she said. “Use of self-healing strategies in solid state batteries is another promising application.”

Sottos has previously been recognized with the Office of Naval Research Young Investigator Award, Scientific American’s SciAm 50 Award, the Hetényi Best Paper Award in Experimental Mechanics, the M.M. Frocht and B.J. Lazan Awards from the Society for Experimental Mechanics, the Daniel Drucker Eminent Faculty Award, an IChemE Global Research Award and the Society of Engineering Science Medal. She is a Fellow of the Society of Engineering Science and the Society for Experimental Mechanics