The morphing metal robots of the "Terminator" franchise represent one of the most iconic images in science fiction movies. But surely we're many decades away from such technology, right? Maybe not.
Scientists at Cornell University have developed a metal-foam compound that can change shape then reform itself into a rigid structure. The material has many potential applications, but is particularly promising as the next step in the busy research field of soft robots.
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The upshot with the Cornell material is it could be used to create soft robots that can also turn stiff and rigid when the need arises. The key development is a hybrid material combining both hard metal and soft porous rubber foam.
The process begins with the use of a silicone foam, which is dipped into a soft metal alloy called Field's metal. The foam-metal hybrid is then placed into a vacuum so that air in the foam's pores is sucked out. The metal alloy flows into those pores, and the material is cooled into a hard solid.
Field's metal has one important characteristic - a low melting point of only 144 degrees Fahrenheit. In testing, the hybrid metal showed an ability to deform when heated above 144 degrees, then regain rigidity when cooled. In other words, the material becomes elastic when heated up, but regains its structural strength when cooled back down.
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"Sometimes you want a robot, or any machine, to be stiff," says Cornell engineering professor Rob Shepherd in press materials accompanying the announcement. "But when you make them stiff, they can't morph their shape very well. And to give a soft robot both capabilities, to be able to morph their structure but also to be stiff and bear load, that's what this material does."
The foam-metal material also has the ability to heal itself if it takes damage, researchers say. Cornell's research was published online this week in Advanced Materials and will be featured in an upcoming issue of the journal's print edition.