A team of scientists at Bingham University, led by Asst. Prof. Pu Zhang developed a liquid metal lattice with a silicone “exoskeleton” that can be crushed but return to its original shape when heated. The new material could be used in many applications, such as soft robotics, aerospace engineering, or to make metallic devices (like foldable antennas) easier to transport.
Carmel Majidi, a mechanical engineer at Carnegie Mellon University, said:
There’s been growing interest in machines and structures that can change their shape, stiffness, and ability to bear a load. These architectures have potential use in emerging applications like soft robots that mimic biological organisms, wearable computing systems that can conform to the body’s natural motion, or wearable robotics that can assist in human motor tasks. [This work] nicely builds on past research in stiffness tuning and shape-memory materials. It is an excellent demonstration of how low melting point metals can be used for creating smart and adaptive structures.
The scientists made the liquid metal lattice out of Field’s alloy – which is a unique blend of bismuth, indium, and tin. The alloy melts when heated to just 62°C (144°F), hence why they call it liquid metal. And as quickly as it melts, it re-solidifies upon cooling. All it takes is hot water for the melting take place and removal from the heat for solidification. Field’s alloy is already in use as a liquid-metal coolant for advanced nuclear reactors.
Next, they coated the metal lattice with a silicone shell (rubber) through a hybrid manufacturing process – a combination of conformal coating (a technique used to cover circuit boards) and vacuum casting. This shell is what gives the lattice its “memory” capabilities, enabling it to deform and crush when heated and also restore to the desired shape when reheated. Whenever the temperature is below 62°C (144°F), the structure remains rigid. When above that temperature, the structure can be compacted (pressed flat or otherwise) or left to unfold back to its intended form.
Zhang said:
Without the shell, it won’t work, because the liquid metal will flow away. The shell skeleton controls the overall shape and integrity, so the liquid metal itself can be confined in the channels. We spent over half a year developing this manufacturing process because this new lattice material is very hard to process. You need to find the best materials and processing parameters.
The ability for the metal to compress makes it ideal for use in space missions. For example, it could be used to make antennae that can be packed tightly onto a spaceship, then expand on arrival out in space. Also, future lunar or Mars settlements could have structures made with this material so they can be made on Earth and easily transported. Even parts of the spacecraft could be made of this material.
Zhang explained:
A spacecraft may crash if it lands on the moon or Mars with some kind of impact. Normally, engineers use aluminum or steel to produce the cushion structures, but after you land on the moon, the metal absorbs the energy and deforms. It’s over — you can use it only once. Using this Field’s alloy, you can crash into it like other metals, but then heat it up later to recover its shape. You can use it over and over again.
The team made several demonstration structures to illustrate the potential of lattice technology. Among them were a spiderweb-like mesh, honeycombs, letters BUME (for Binghamton University mechanical engineering), soccer balls, and a lattice-shaped like a human hand. They all crushed when heated and returned to their original form when reheated. In solid-state, they were very strong, sturdy, and safe.
Zhang said:
Our dream is to build a liquid metal lattice robot, and now we have a hand, so we’re one step further.
Enthusiastic about the results of the study, the researchers have since been exploring how to improve the strength, durability, and energy absorption capacity of the liquid metal lattice, as well as improving the coating material and exploring different structure types.
