Dr. Xiaoshi Zhang, Plastics Engineering Technology researcher, and Josh Lutz ’21, PLET lab assistant.
$385,000 grant will support the work of at least ten faculty members
With a $385,000 grant from the National Science Foundation, the School of Engineering has installed an Instron drop tower impact-testing system to advance the work of faculty members developing new approaches to polymer recycling and the formulation of new composites.
At least ten faculty members will use the system to further their research, which includes automotive and aerospace projects. Another will use it to test new polymers for ski boots and bindings.
“This takes us into a whole new kind of materials science,” said Dr. Greg Dillon, chair of the Polymer Engineering and Science program and the principal investigator for the NSF grant. “It allows us to delve very deeply into fracture mechanics: how materials and structures fail under high energy.”
Drop towers are used to determine how materials break. The drop mechanism, or tup, is fired like an arrow into a plastic, metal, ceramic, or gel. The Instron tup drops at a rate of 78 feet per second.
“It’s a lot like a crossbow,” said Dr. Alicyn Rhoades, vice chancellor and associate dean for research and graduate studies and a professor of engineering. She and Dillon wrote the original application for the NSF grant.
For a previous study, Rhoades used a drop tower owned by a corporate partner. The tup on that machine had been customized for the company’s product, however, so it was not practical to collaborate on the machine for university projects.
The Instron system Rhoades and Dillon selected includes a variety of tups—round, flat, and conical—that can be changed based on an individual researcher’s needs. The conditioning chamber can be heated or cooled to test how a material responds at different temperatures, from a high of 302 degrees to a low of -94 degrees Fahrenheit.
“Any time you test, you want to do so in conditions that are as close to the actual product environment as possible,” said Beth Last, research core facilities coordinator at Behrend and the co-principal investigator for the grant.
Automotive plastics, for example, have to retain their properties over a range of temperatures. In an engine compartment, the temperature can exceed 200 degrees. In the bumper, in winter conditions, it can dip below zero. At low temperatures, plastics become brittle and are more likely to break.
“With polymers, the mystery of fracture mechanics is that it’s so difficult to understand all the phases of the event,” Rhoades said. “We generally know when a material is going to fail. But too often, after that happens, we’re left looking for clues on the surface of the sample, trying to trace back to the origin of the fracture.”
A high-speed camera on the Instron system allows Behrend researchers to analyze the entire process. The camera, which can be set to different magnifications, can record 900,000 frames per second.
Like a Harold Edgerton photo—the bullet piercing the apple or the splash of milk forming a perfect white crown—those images essentially stop time: Researchers can see the exact moment a crack or fracture forms. Then, a few frames ahead, they can watch it spread.
“You can see what’s happening within the material,” Dillon said. “Is it bending? Does it deform? Does it in any way resist the impact? Once you know that, you can engineer materials that better absorb that energy.”