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Researchers at North Carolina State University have developed a fiber that combines the elasticity of the tire with the strength of a metal, resulting in a tougher material that could be incorporated into soft robotics, packaging materials, or next-generation fabrics.
"A good way to explain the material is to think of rubber and metal tapes," says Michael Dickey, a corresponding author of a paper on the project, and Alcoa Professor of Chemical and Biomolecular Engineering at the NC State.
"A rubber band can be stretched too far, but it does not need much force to stretch it," says Dickey. "A metal wire requires a lot of power to stretch it, but it can not get much pressure – it breaks before you can stretch it too far. Our fibers have the best of both worlds."
The researchers created fibers composed of a core of metallic gallium surrounded by a flexible polymeric casing. When placed under tension, the fiber has the strength of the metal core. But when the metal breaks, the fiber does not fail – the polymer sheath absorbs the stem between the metal fragments and transfers the tension back to the metal core. This response is similar to the way the human tissue holds the broken bones.
"Every time the metal core breaks down, it dissolves energy, allowing the fibers to continue to absorb energy as it lengthens," says Dickey. "Instead of breaking into two when stretched, it can stretch up to seven times its original length before failure, while causing many additional breaks in the cable along the road.
"To think otherwise, the fibers will not break and fall into a heavy weight. On the contrary, with the release of energy repeatedly through internal fractures, the fibers reduce weight slowly and steadily."
In materials, resilience is the ability of the material to absorb energy and deform without cracking. You can think of it as the amount of force that can absorb a material as it distorts itself at a distance. The new fiber is much stiffer than the metal wire or polymer sheath itself.
"There is a lot of interest in engineered materials that mimic the skin's resistance – and we have developed a fiber that has outgrowed the skin's durability but is still elastic like the skin," says Dickey.
In addition, the gallium core is conductive – although it loses its conductivity when the inner core breaks. The fibers can also be reused by melting the metal cores.
"We used gallium for this proof of virtual work, but the fibers could be adjusted to change their mechanical properties or maintain functionality at higher temperatures, using different materials in the core and the shell," says Dickey.
"This is just a demonstration of the concept, but it has many possibilities. We are interested in seeing how these fibers could be used in soft robotics or when weaving textiles for various applications."
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Materials provided by University of North Carolina. Note: Content can be edited for style and length.
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