Hybrid fiber combines strength of metal and elasticity of rubber
Metal fibers are strong, but can't be stretched very far. Rubber fibers are stretchy, but they're not very strong. Well, scientists have combined the selling points of both materials into one type of hybrid fiber. It could be used in applications such as soft robotics, packaging materials, or high-tech textiles.
Developed by a team at North Carolina State University, the new fiber has a gallium metal core – a wire, in other words – which is surrounded by a SEBS (styrene-ethylene-butylene-styrene) elastic polymer sheath. When subjected to mechanical stress, the fiber initially has the strength of the core. Once that core does break, however, the polymer is still there to stretch, keeping the fiber as a whole from breaking.
"Every time the metal core breaks it dissipates energy, allowing the fiber to continue to absorb energy as it elongates," says lead scientist Prof. Michael Dickey. "Instead of snapping in two when stretched, it can stretch up to seven times its original length before failure, while causing many additional breaks in the wire along the way."
As an added bonus, until it breaks, the metal core is capable of carrying an electrical current. And after a break has occurred, the gallium can be melted down to form back into a continuous unbroken core. And yes, the polymer does have a higher melting point than the gallium.
"A rubber band can stretch very far, but it doesn't take much force to stretch it," Dickey says. "A metal wire requires a lot of force to stretch it, but it can't take much strain – it breaks before you can stretch it very far. Our fibers have the best of both worlds."
The scientists now plan on experimenting with other materials for both the core and sheath. A paper on the research was recently published in the journal Science Advances.