Researchers from MIT and the University of Southern California 3D printed tiny, and quite beautiful, sculptures out of two different materials that usually expand when heated. But the specific architectures of these sugarcube-sized sculptures instead enable them to shrink when heated. The
effect is similar to a Hoberman sphere, the wonderful isokinetic toy sculpture that mechanically collapses to a fraction of its original size. From MIT News:
The researchers consider the structures to be "metamaterials" — composite materials whose configurations exhibit strange, often counterintuitive properties that are not normally found in nature.
In some cases, these structures' resistance to expanding when heated — rather than their shrinking response per se — may be especially 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," (MIT mechanical engineer Nicholas X.) Fang says. "So you really have to take great care in accounting for this thermal stress or shock…"
Fang and his colleagues printed small, three-dimensional, star-shaped structures made from interconnecting beams. They 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.
"If we have proper placement of these beams and lattices, then even if every individual component expands, because of the way they pull each other, the overall lattice could actually shrink," Fang says…
"We now have a tuning method for digitally placing individual components of different stiffness and thermal expansion within a structure, and we can force a particular beam or section to deflect or extend in a desired fashion," Fang says. "There is room to experiment with other materials, such as carbon nanotubes, which are stronger and lighter. Now we can have more fun in the lab exploring these different structures."