3D printed metamaterial
An example of the 3D-printed structure Nicholas Fang and his team produced which shrinks when exposed to heat
A team of researchers from a range of American Universities has manufactured small 3D-printed structures which shrink when heated, rather than expand.
Engineers from Massachusetts Institute of Technology (MIT), University of Southern California and University of California were led by Nicholas Fang, associate professor of mechanical engineering at MIT.
Each structure is about the size of a sugar cube and quickly shrinks when heated to about 282 degrees Celsius (540 degrees Fahrenheit). The trusses of each structure are made from typical materials that expand with heat. Fang and his fellow researchers noticed these trusses, when arranged in certain architectures, can pull the structure inward, causing it to grow smaller.
The researchers consider the structures to be ‘metamaterials’ – composite materials whose configurations exhibit strange, often counterintuitive, properties not normally found in nature. They believe the structures’ resistance to expansion when exposed to heat may be especially useful. Such materials could find applications in computer chips, for example, which can 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,” said Fang. “So you really have to take great care in accounting for this thermal stress or shock.”
The researchers used a 3D printing technique called microstereolithography. This method uses light from a projector to print very small structures in liquid resin, layer by layer. A stiff, slow-to-expand copper-containing material makes up the outer beams, while the inner trusses are made from a more elastic, fast-expanding polymer substance.
When the structures are heated to a temperature of 282 degrees Celsius, the beams gradually bend inward, causing the construction to shrink with 0.6%. Though this seems a small decrease in size, the team of researchers stress that it is more important that the material does not expand, rather than the amount in which it shrinks.
It would be possible to control the amount of shrinkage by either changing the dimensions of the trusses or the relative stiffness of the outer materials. The technique could even produce metamaterials that do not change size at all when heated.
Fang and his team believe the printing technique could even advance methods in the dental and architecture industries, whether it be tooth fillings or gap fillings in a bridge or building.
