New soft robot material to morph from ground to air vehicle using liquid
metal
Date:
February 9, 2022
Source:
Virginia Tech
Summary:
Researchers have developed a new approach for shape changing at
the material level. They use rubber, metal, and temperature to
morph materials and fix them into place with no motors or pulleys.
FULL STORY ========================================================================== Imagine a small autonomous vehicle that could drive over land, stop,
and flatten itself into a quadcopter. The rotors start spinning, and the vehicle flies away. Looking at it more closely, what do you think you
would see? What mechanisms have caused it to morph from a land vehicle
into a flying quadcopter? You might imagine gears and belts, perhaps a
series of tiny servo motors that pulled all its pieces into place.
==========================================================================
If this mechanism was designed by a team at Virginia Tech led by Michael Bartlett, assistant professor in mechanical engineering, you would see a
new approach for shape changing at the material level. These researchers
use rubber, metal, and temperature to morph materials and fix them into
place with no motors or pulleys. The team's work has been published in
Science Robotics.
Co-authors of the paper include graduate students Dohgyu Hwang and
Edward J.
Barron III and postdoctoral researcher A. B. M. Tahidul Haque.
Getting into shape Nature is rich with organisms that change shape to
perform different functions.
The octopus dramatically reshapes to move, eat, and interact with its environment; humans flex muscles to support loads and hold shape;
and plants move to capture sunlight throughout the day. How do you
create a material that achieves these functions to enable new types
of multifunctional, morphing robots? "When we started the project, we
wanted a material that could do three things: change shape, hold that
shape, and then return to the original configuration, and to do this
over many cycles," said Bartlett. "One of the challenges was to create
a material that was soft enough to dramatically change shape, yet rigid
enough to create adaptable machines that can perform different functions."
To create a structure that could be morphed, the team turned to kirigami,
the Japanese art of making shapes out of paper by cutting. (This method
differs from origami, which uses folding.) By observing the strength of
those kirigami patterns in rubbers and composites, the team was able to
create a material architecture of a repeating geometric pattern.
========================================================================== Next, they needed a material that would hold shape but allow for that
shape to be erased on demand. Here they introduced an endoskeleton made of
a low melting point alloy (LMPA) embedded inside a rubber skin. Normally,
when a metal is stretched too far, the metal becomes permanently bent,
cracked, or stretched into a fixed, unusable shape. However, with this
special metal embedded in rubber, the researchers turned this typical
failure mechanism into a strength.
When stretched, this composite would now hold a desired shape rapidly,
perfect for soft morphing materials that can become instantly load
bearing.
Finally, the material had to return the structure back to its original
shape.
Here, the team incorporated soft, tendril-like heaters next to the
LMPA mesh.
The heaters cause the metal to be converted to a liquid at 60 degrees
Celsius (140 degrees Fahrenheit), or 10 percent of the melting temperature
of aluminum.
The elastomer skin keeps the melted metal contained and in place, and
then pulls the material back into the original shape, reversing the
stretching, giving the composite what the researchers call "reversible plasticity." After the metal cools, it again contributes to holding the structure's shape.
"These composites have a metal endoskeleton embedded into a rubber with
soft heaters, where the kirigami-inspired cuts define an array of metal
beams. These cuts combined with the unique properties of the materials
were really important to morph, fix into shape rapidly, then return to
the original shape," Hwang said.
The researchers found that this kirigami-inspired composite design could
create complex shapes, from cylinders to balls to the bumpy shape of
the bottom of a pepper. Shape change could also be achieved quickly:
After impact with a ball, the shape changed and fixed into place in less
than 1/10 of a second. Also, if the material broke, it could be healed
multiple times by melting and reforming the metal endoskeleton.
One drone for land and air, one for sea The applications for this
technology are only starting to unfold. By combining this material with
onboard power, control, and motors, the team created a functional drone
that autonomously morphs from a ground to air vehicle. The team also
created a small, deployable submarine, using the morphing and returning
of the material to retrieve objects from an aquarium by scraping the
belly of the sub along the bottom.
"We're excited about the opportunities this material presents for multifunctional robots. These composites are strong enough to withstand
the forces from motors or propulsion systems, yet can readily shape morph, which allows machines to adapt to their environment," said Barron.
Looking forward, the researchers envision the morphing composites playing
a role in the emerging field of soft robotics to create machines that
can perform diverse functions, self-heal after being damaged to increase resilience, and spur different ideas in human-machine interfaces and
wearable devices.
This project was funded through Bartlett's DARPA Young Faculty Award
and Director's Fellowship.
========================================================================== Story Source: Materials provided by Virginia_Tech. Original written by
Alex Parrish. Note: Content may be edited for style and length.
========================================================================== Related Multimedia:
* Video_and_images_of_morphing_material ========================================================================== Journal Reference:
1. Dohgyu Hwang, Edward J. Barron, A. B. M. Tahidul Haque, Michael D.
Bartlett. Shape morphing mechanical metamaterials through
reversible plasticity. Science Robotics, 2022; 7 (63) DOI: 10.1126/
scirobotics.abg2171 ==========================================================================
Link to news story:
https://www.sciencedaily.com/releases/2022/02/220209154810.htm
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