CAMBRIDGE, MA – University engineers are adding to heat-shrinking materials. A team led by Nicholas X. Fang, an associate professor of mechanical engineering at MIT, has manufactured tiny, star-shaped structures out of interconnected beams, or trusses. The sugar-cube-size structures quickly shrink when heated to about 540°F.

The team, including engineers from USC and UCLA, fabricated each beam from one of two ingredients: a stiff, slow-to-expand copper-containing material, and a more elastic, fast-expanding polymer substance. The internal beams were made from the elastic material, while the outer trusses were composed of stiff copper.
 
Each structure’s trusses are made from typical materials that expand with heat. The team realized these trusses, when arranged in certain architectures, can pull the structure inward, causing it to shrink like a Hoberman sphere — a collapsible toy ball made from interconnecting lattices and joints.

In some cases, these structures’ resistance to expanding when heated may be useful. Such materials could find applications in computer chips, for example, which can warp and deform when heated for long periods of time.

“Printed circuit boards can heat up when there’s a CPU running, and this sudden heating could affect their performance,” Fang said. “So you really have to take great care in accounting for this thermal stress or shock.”

Fang’s lab has pioneered a 3D printing technique called microstereolithography, in which the researchers use light from a projector to print very small structures in liquid resin, layer by layer.

“We can now use the microstereolithography system to create a thermomechanical metamaterial that may enable applications not possible before,” said Christopher Spadaccini, director of Lawrence Livermore National Laboratory’s Center for Engineered Materials and Manufacturing. “It has thermomechanical properties not achievable in conventional bulk materials.”

“We can take the same idea as an inkjet printer and print and solidify different ingredients, all on the same template,” Fang said.

This research was supported, in part, by the Defense Advanced Research Projects Agency.

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