Researchers have developed a fiber that combines the elasticity of rubber with the strength of a metal, resulting in a tougher material. The fibers consist 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. Instead, 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 broken bones.
Each time the metal core breaks, it dissipates energy, allowing the fiber to continue to absorb energy as it elongates. 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.
In materials, toughness is a material’s ability to absorb energy and deform without breaking — the amount of force a material can absorb as it is deformed over a distance. The new fiber is tougher than either the metal wire or the polymer sheath on its own. 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.
While gallium was used for the proof of concept, the fibers could be tuned to alter their mechanical properties, or to retain functionality at higher temperatures, by using different materials in the core and shell.