Researchers engineer a tougher fiber

Researchers engineer a tougher fiber
NC State University researchers created fibers consisting of a gallium metal core surrounded by an elastic polymer sheath. When placed under stress, the fiber has the strength of the metal core. But when the metal breaks, the fiber doesn't fail - the polymer sheath absorbs the strain between the breaks in the metal and transfers the stress back to the metal core. Credit: Michael Dickey, NC State University

North Carolina State University researchers have developed a fiber that combines the elasticity of rubber with the strength of a metal, resulting in a tougher material that could be incorporated into soft robotics, packaging materials or next-generation textiles.

"A good way of explaining the material is to think of rubber bands and wires," says Michael Dickey, corresponding author of a paper on the work and Alcoa Professor of Chemical and Biomolecular Engineering at NC State.

"A rubber band can stretch very far, but it doesn't take much force to stretch it," Dickey says. "A 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 researchers created fibers consisting of a gallium metal core surrounded by an elastic polymer sheath. When placed under stress, the fiber has the strength of the metal core. But when the metal breaks, the fiber doesn't fail—the polymer sheath absorbs the strain between the breaks in the metal and transfers the stress back to the metal core. This response is similar to the way human tissue holds together .

"Every time the metal core breaks it dissipates energy, allowing the fiber to continue to absorb energy as it elongates," Dickey says. "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.

North Carolina State University researchers have developed a fiber that combines the elasticity of rubber with the strength of a metal, resulting in a tougher material that could be incorporated into a variety of applications. Credit: Michael Dickey, North Carolina State University

"To think of it another way, the fiber won't snap and drop a heavy weight. Instead, by releasing energy repeatedly through internal breaks, the fiber lowers the weight slowly and steadily."

In materials, toughness is a material's ability to absorb energy and deform without breaking. You can think of it as the amount of force a material can absorb as it is deformed over a distance. The new fiber is far tougher than either the metal wire or the polymer sheath on its own.

"There's a lot of interest in engineering materials to mimic the toughness of skin—and we have developed a fiber that has surpassed the toughness of skin yet is still elastic like skin," Dickey says.

In addition, the gallium core is conductive—though it loses its conductivity when the internal core breaks. The fibers can also be reused by melting the metal cores back together.

"We used gallium for this proof of concept work, but the fibers could be tuned to alter their , or to retain functionality at higher temperatures, by using different in the core and shell," Dickey says.

"This is only a proof of concept, but it holds a lot of potential. We are interested to see how these fibers could be used in soft robotics or when woven into textiles for various applications."

The paper, "Toughening stretchable fibers via serial fracturing of a metallic core," is published in the journal Science Advances.


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More information: C.B. Cooper el al., "Toughening stretchable fibers via serial fracturing of a metallic core," Science Advances (2019). DOI: 10.1126/sciadv.aat4600 , advances.sciencemag.org/content/5/2/eaat4600
Journal information: Science Advances

Citation: Researchers engineer a tougher fiber (2019, February 22) retrieved 23 July 2019 from https://phys.org/news/2019-02-tougher-fiber.html
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Feb 22, 2019
I see two issues. Gallium is pretty expensive, so this fiber would likewise be pretty spendy. In addition, the breaks are permanent, so when the fiber is stretched the breaks permanently weaken the fiber for repeated use.

Feb 22, 2019
So, Robots that can beat Humans are on the anvil !

Feb 22, 2019
or, at least the robots will be looking mighty snazzy in their stylish, ultra-modern togs!

Feb 22, 2019
I received a patent on a bone-shaped fiber that does much of that of the gallium fiber above. You have the right nonlinear strain idea upon the fracture of the host media. Our bone-shaped fibers cost a tiny fraction of the fiber of the article. Testing at 3M and the South Dakota School of Mines and technology proved that we had the best fiber. We sold tonnes. A joint venture funded the rollout but not enough money was be found to build a larger factory to make the ton size orders sought by pipe makers, plastics people, and general construction. I applied a Green's probabilistic elastodynamic tensor with relativistic manifold extensions, an Eshelby's tensor convolved with a neo-Hookean tensor with a Frobenius foliation to predict nonlinear strain tensor and pull out of the applied anisotropic inclusion (the fiber) in an isotropic host. The relativistic 4-D Schrodinger-Dirac delta equation was applied. Taylors series approximations by others occurred. FEA does not work.

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