Metal-Foam Hybrid Brings “Transformers” to Life

Is it possible for an aircraft to dive into the water without damage and then transform into a submarine?

That may seem like something out of the Transformers movies, where cars and jets change into robots, but a new hybrid material could enable transformations that were once unimaginable.

“That’s what this idea is about, to have a skeleton when you need it, melt it away when you don’t, and then reform it,” said Rob Shepherd, professor of engineering at Cornell.

The ability to change shape requires elasticity, while stiffness is needed to maintain shape integrity.

A Metal-Foam Hybrid

The compound combines a soft alloy called Field’s metal with a porous silicone foam. Field’s metal was the preferred choice since it has a low melting point of 144°F and also contains no lead.

“In general, we want the things we make in this lab to be potentially biocompatible,” said Ilse Van Meerbeek, a mechanical engineering graduate at Cornell.

The elastomer foam is dipped into the molten metal, then placed in a vacuum to replace the air in its pores with the alloy. The pore sizes are about 2 millimeters, but they can be altered to create either more stiffness or more flexibility.

Strength and elasticity tests demonstrated the material’s ability to deform when heated above 144 degrees, regain its rigidity when cooled, then return to its original shape and strength when reheated. The material also has the ability to self-heal if damaged.

Using the material as the skin for a morphing wing could give a micro air vehicle (MAV) the ability to become an underwater vehicle on the fly.

“If you have a wing that’s really broad, you can’t do that because the wing will break off when it hits the water,” said Shepherd. “So you need to sweep it back, similar to what a puffin does, and then go under water. And using that new shape, it could be a propeller-driven ship.”

Building Better Rescue Robots

In addition to the morphing-wing application, Van Meerbeek believes the material could be used in soft robotics.

For example it could give a search-and-rescue robot the ability to maneuver through tight spaces.

“It would be able to go into dangerous and/or unpredictable environments and be able to go through narrow cracks, which rigid robots can’t do,” said Van Meerbeek.

“Sometimes you want a robot, or any machine, to be stiff,” said Shepherd. “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.”