Controlled fragmentation of multimaterial fibers via cold polymer drawing

University of Central Florida associate professor Ayman Abouraddy has unlocked a means of controlling materials at the nanoscale that opens the door to a new generation of manufacturing. Using a pair of pliers in each hand and gradually pulling taut a piece of glass fiber coated in plastic, Abouraddy found that something unexpected and never before documented occurred – the inner fiber fragmented in an orderly fashion.

“While we thought the core material would snap into two large pieces,” said Abouraddy, “instead it broke into many equal-sized pieces.” Featured in the online journal Nature, he refers to the technique as “Breaking Me Softly.”

The process of pulling fibers to force the realignment of the molecules that hold them together, known as cold drawing, has been the standard for mass production of flexible fibers like plastic and nylon for most of the last century. Abouraddy and his team have now shown that the process may also be applicable to multi-layered materials, a finding that could lead to the manufacturing of next-generation materials with futuristic attributes.

“Advanced fibers are going to be pursuing the limits of anything a single material can endure today,” Abouraddy said. For example, packaging together materials with optical and mechanical properties along with sensors that could monitor vital signs like blood pressure and heart rate would enable clothing capable of transmitting vital data to a doctor’s office via the Internet.

The ability to control breakage in a material is critical to developing computerized processes for potential manufacturing, said Yuanli Bai, a fracture mechanics specialist in UCF’s College of Engineering and Computer Science. A co-author on the paper, Bai helped analyze test results on a wide variety of materials, including silicon, silk, gold and even ice.

Robert S. Hoy, a University of South Florida physicist who specializes in the properties of materials like glass and plastic, helped develop a better understanding of what Abouraddy found. Hoy said he had never seen the phenomena, but that it made great sense in retrospect. The research takes what has traditionally been a problem in materials manufacturing and turned it into an asset, Hoy said.

Hoy said that Abouraddy has found a new application of necking — a process that occurs when cold drawing causes non-uniform strain in a material. “Usually you try to prevent necking, but he exploited it to do something potentially groundbreaking,” Hoy notes. The necking phenomenon was discovered by DuPont decades ago, ushering in the age of synthetic fibers and textiles. Abouraddy said that cold-drawing is what makes fibers like nylon and polyester — which are initially brittle — toughen up and become useful in everyday applications.

He notes that only recently have fibers made of multiple materials become possible. That research will be the centerpiece of a $317 Million U.S. Department of Defense program focused on smart fibers that Abouraddy and UCF will assist with. The Revolutionary Fibers and Textiles Manufacturing Innovation Institute (RFT-MII), led by the Massachusetts Institute of Technology, will incorporate Abouraddy’s research findings published in the Nature article.

The UCF research team believes the implications for future manufacturing of smart materials are vast. By controlling the mechanical force used to pull the fiber and therefore controlling the breakage patterns, materials can be developed with customized properties allowing them to interact with each other and external forces such as the sun (for harvesting energy) and the internet in customizable ways. Also, by carefully controlling the loading condition imparted to the fibers, materials can be developed with tailored performance attributes.