ORNL researchers found a way to double the tensile strength of carbon-fiber composites by reinforcing the material with a thin layer of PAN nanofibers. A human hair is approximately 100 times wider than one of these fibers. Credit: Carlos Jones/ORNL, U.S. Dept. of Energy
Stronger than steel and lighter than aluminum, carbon fiber is a staple in aerospace and high-performance vehicles — and now, scientists at the Department of Energy’s Oak Ridge National Laboratory have found a way to make it even stronger.
ORNL researchers simulated 5 million atoms to study a novel process for making carbon-fiber composites stronger and more cost efficient by incorporating a reinforced layer of polyacrylonitrile nanofibers, or PAN nanofibers. Led by ORNL’s Carbon and Composites group, the team combined fundamental science with molecular dynamics simulations using the Frontier supercomputer to better understand how the reinforcement process works at the atomic scale. Their findings, published in the journal Advanced Functional Materials, could lead to new, ultradurable materials for airplanes, vehicles and a wide range of manufacturing applications that require stronger, more lightweight materials.
Carbon-fiber composites are made by embedding thin strands of carbon — each thinner than a human hair — into a polymer matrix. Carbon fiber strands are incredibly strong; however, their bond with the surrounding polymer is somewhat weak by comparison.
“When a carbon-fiber composite fails, it typically begins at the interface between the carbon-fiber strands and the polymer matrix,” said Tanvir Sohail, a postdoctoral researcher at ORNL’s National Center for Computational Sciences. “By incorporating a layer of PAN nanofibers at the interface, we redirect stress from the carbon fibers into the surrounding polymer, which improves load distribution and enhances the composite’s overall strength.”
The process of reinforcing the carbon-fiber composites involves a technique called electrospinning, which uses an electric field and a spinning drum to create a spool of PAN nanofibers no larger than 10 nanometers. For comparison, a single sheet of paper is about 100,000 nanometers thick.
Carbon fiber is expensive to manufacture and test, and running extensive physical experiments can quickly become time consuming and cost prohibitive. That’s where supercomputing can drastically accelerate the search for materials with the desired characteristics and help guide the experimental development. But simulating the synthesis process is also expensive — computationally, that is.
“Carbon fiber is extremely dense, and modeling it with molecular dynamics requires tracking the behavior of millions, if not billions, of atoms,” said ORNL computational scientist Swarnava Ghosh, who led the Frontier simulations along with Sohail.