In polymer manufacturing, a technique known as cold drawing is used to imbue polyester and nylon fibers with high tensile strength. It involves pulling the fiber so that its diameter is reduced and the polymer chains are aligned. Nobody ever really considered doing this with composite materials because no one imagined that it would lead to anything useful.
But researchers at the University of Central Florida (UCF), in Orlando, believed that seeing what would happen was worth an experiment. In a paper published in the journal Nature, the researchers recall that what they discovered was not at all what they were expecting. And the result could change nanomanufacturing by enabling the production of new kinds of materials.
The unexpected development, said Ayman Abouraddy, an associate professor and co-author of the research, in a press release:
While we thought [that when they performed the cold drawing on the composite fiber, which consisted of a brittle core and ductile outer coating] the core material would snap into two large pieces, instead it broke into many equal-sized pieces.
Though a surprise to Abouraddy, Robert S. Hoy, a University of South Florida physicist who specializes in the properties of materials like glass and plastic, wasn’t shocked by the UCF professor’s the initial findings. Hoy recognized this behavior as something familiar to those in the polymer business—a phenomenon called “necking,” which occurs when cold drawing causes non-uniform strain in a material.
“Dr. Abouraddy has found a new application of necking,” said Hoy in the press release. “Usually you try to prevent necking, but he exploited it to do something potentially groundbreaking.”
So what’s the big deal about breaking a fiber? This new twist on necking could lead to new approaches to manufacturing smart materials. For instance, the amount of mechanical force used to pull the fiber will affect the breakage patterns in a way that will change the physical properties of the material.
“Processing-structure-property relationships need to be strategically characterized for complex material systems,” says Ali P. Gordon, an associate professor at UCF and co-author of the paper. “By combining experiments, microscopy, and computational mechanics, the physical mechanisms of the fragmentation process were more deeply understood,” says Gordon.
The UCF team has shown that this process may also be applicable to multi-layered materials. That could lead to the packaging of hybrid materials with sensing, optical, and mechanical properties that no single material could achieve.