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Material Design: The Incredible Shrinking Lattice

by Cat McClintock

Replacing solids with lattices  can be a good way to take weight off a product design—especially now that 3D printing makes manufacturing intricate structures so easy. But weight isn’t the only reason to enlist lattices in a design. They may also prove useful for making materials with unusual properties. At least that’s what one group of researchers thinks. Consider this challenge:

Most solids expand when heated, and that creates havoc on everything from circuit boards to railroad tracks.

A novel use of lattice structures and 3D printing may help solve problems that arise from thermal expansion.

Thermal expansion of rail tracks is the driving force for rail buckling, which resulted in 190 train derailments during 1998–2002 in the US alone. Image by By Lankyrider via Wikimedia Commons

 

But lately researchers at MIT have been experimenting with composites that get smaller as temperatures rise.

The team brings together two different materials (roughly, copper and polymers) in lattice structures and 3D prints them via micro-stereolithography.

“Each material has a different rate of expansion upon heating,” explains this recent university publication . “When the whole structure is heated, one material should expand faster and pull the other material inward, shrinking the entire structure as a result.” 

Lattice constructed with micro-3D printer shrinks when heated.

3D printed lattice structure that shrinks when heated. Screenshot from the video Heat-induced Shrinkage, by MIT.

 

It’s not a new idea. In the mid-1990s, scientists proposed theoretical structures whose arrangement should exhibit a property called “negative thermal expansion.”  

“These theoretical papers were talking about how these types of structures could really break the conventional limit of thermal expansion,” says Nicholas X. Fang, an associate professor of mechanical engineering at MIT. “But at the time, they were limited by how things were made.”

Now with new micro additive manufacturing techniques, researchers can design and manufacture tiny star-like shapes about the size of a sugar cube, which quickly become smaller when heated to about 282°C.  

Of course, most design engineers are just getting started with designing for additive manufacturing, and it remains to be seen what happens as lighter weight forms replace traditional solids. But at the same time, it’s fascinating to see novel uses of 3D printing and complex structures. Used in tiny ways, they may lead to big impacts.  

The Future of Design

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