UI researchers create form of bendable metal

Graduate students Jagannathan Rajagopalan, left, Jong Han, right, and Professor Taher Saif, center, work in a lab. Beck Diefenbach

Graduate students Jagannathan Rajagopalan, left, Jong Han, right, and Professor Taher Saif, center, work in a lab. Beck Diefenbach

By Matthew Richardson

In the popular imagination, car doors that revert back to normal after being damaged go hand in hand with colonies on the moon and pills that become 3-course meals when you add water. But the popular imagination might be coming closer to the popular reality, thanks to researchers at the University.

Mechanical Engineering and Sciences Professor Taher A. Saif along with graduate students Jong Han and Jagannathan Rajagopalan are responsible for research finding that it is possible to produce metals that retain a “memory” that allows them to revert back to their original shape once bent.

Rajagopalan compared their finding to a rubber band. A rubber-band deforms, or loses its shape, elastically but reverts back to its original shape. Metal, on the other hand, deforms inelastically, he said. When a paper clip is bent, it stays in that shape unless it is bent back. He said the answer to getting metal to behave like a rubber band is in the structure of the metal.

“Most metals are poly crystalline, and are made up of grains, which (consist of) a set of atoms,” Rajagopalan said.

Grains in a piece of metal are generally between 20 and 30 microns, an extremely small unit of measurement. For their experiment, the researchers used pieces of gold and aluminum film, about 200 nanometers thick. When gold and aluminum are reduced to films that thin, the grains in the metal aren’t of uniform size, as they would be in a larger piece of metal.

Some of the grains are of the large type that deform plastically and won’t revert back to their original shape if bent, but some of the grains are of the small type that deform elastically, meaning that they spring back into place.

If a large grain was next to a small grain when the metal is bent, the small, elastically deforming grain causes the plastically deforming grain to retain its shape. Rajagopalan said that by pushing against the large grain as it tries to return to its original shape, the small grains make the metal more elastic.

But the likelihood of seeing commercials for car bumpers that smooth out their own dents in the near future is small.

“That will probably take a long time,” Rajagopalan said. “But it is possible, and there are people are making advances towards it.”