Assistant Professor Aniruddh Vashisth holds an example of a composite carbon fiber material that heals. This is what his team is currently studying. Credit: Andy Freeberg/University of Washington
Carbon-fiber-based composite materials, which are made from carbon-fiber, are slowly replacing metals because of their strength and light weight. They can be used to advance all sorts of products and applications, including airplanes, wind turbines, and golf clubs. There is a tradeoff. The most common carbon fiber materials can be nearly impossible to recycle or repair once they are damaged.
A research team including Professor Aniruddh Vashisth, UW mechanical engineering assistant, describes a new carbon fiber reinforced material. It is as strong as traditional ones, but can be repeatedly heated to heal fatigue and provide a way for it to be broken down and recycled when it reaches its end.
Vashisth says, "Developing fatigue-resistant materials is a key need in the manufacturing industry." "In this paper we show a material that can be reversed or postponed indefinitely using either radio frequency heating or traditional heat sources."
This material is part a newly developed group called carbon fiber reinforced vitrimers, (vCFRP). Carbon fiber reinforced polymers (CFRP) are the most common materials used in today's sporting goods and aerospace.
Two types of traditional CFRPs are typically available: thermoplastic or thermoset. The epoxy is a glue-like material that hardens permanently. The "plastic" variety contains a softer type of glue that can be melted down and reworked. However, this is a disadvantage for its high strength and stiffness. Vitrimers can link, unlink, and re-link to provide a middle ground.
Vashisth used simulation software at atomic scale (seen in the background) for understanding the mechanics of the healing vitrimer. Credit: Andy Freeberg/University of Washington
Vashisth says, "Imagine that each of these materials is a large room full of people." "In the thermoset area, all the people are holding hands and will not let go. People are moving around in the thermoplastic room shaking hands. The vitrimer room is where people can shake hands with each other, but they also have the ability to make new friends and exchange handshakes so that there are no more interconnections. This re-connection is what repairs material and this paper is the first to use atomic scale simulations to study the underlying mechanisms.
Research team believes vitrimers may be an alternative to many products made from thermosets. This is a critical need as thermoset composites are accumulating in landfills. According to the team, healable vCFRPs could be a significant shift towards a dynamic material that has a different set if considerations in terms life-cycle cost, reliability and safety.
"These materials could translate the linear plastics life cycle to a circular one, and that would be a great step toward sustainability," Nikhil Koratkar, John A. Clark and Edward T. Crossan Professor in Mechanical, Aerospace and Nuclear Engineering at Rensselaer Polytechnic Institute, (RPI), and Vashisth's coauthor on the new paper.
The research team included Koratkar, Vashisth, Mithil Kamble, Professor Catalin Picu of RPI and Hongkun Yang, as well as Professor Dong Wang of Beijing University of Chemical Technology.
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More information: Mithil Kamble and colleagues, Reversing fatigue within carbon-fiber reinforced vitrimer compounds, Carbon (2021). Information from the Journal: Carbon Mithil Kamble and colleagues, Reversing fatigue within carbon-fiber reinforced vitrimer compounds, (2021). DOI: 10.1016/j.carbon.2021.10.078
