U.S. Army researchers have teamed with Texas A&M University to create a new polymer material that can shape-shift and autonomously heal itself as part of a research effort to improve future unmanned air and robotic vehicles.
In early research, the first-of-its-kind, 3D-printable epoxy-based material can respond to stimuli, and researchers hope it will one day have embedded intelligence allowing it to adapt to its environment without any external control, according to a news release from Army Combat Capabilities Development Command's (CCDC) Army Research Laboratory.
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"We want a system of materials to simultaneously provide structure, sensing and response," said Frank Gardea, an aerospace engineer and principal investigator for the effort, at the CCDC.
Gardea envisions a future platform, suitable for air and ground missions, with the "reconfiguration characteristics of the T-1000 character in the Hollywood film, 'Terminator 2.'"
The hit film featured a Terminator made of liquid-metal that could form its arms into stabbing weapons and heal itself after being shot with everything from a 12-gauge shotgun to a 40mm grenade launcher.
So far, the material has responded to temperature, which researchers first selected because of its ease of use during laboratory testing.
In the real world, applying a temperature stimulus is not as easy or practical, so they introduced light-responsiveness because it is easier to control and apply remotely, Gardea said in the release.
Polymers are made up of repeating units, like links on a chain. For softer polymers, these chains are only lightly connected to each other through crosslinks, according to the release. The more crosslinks between chains, the more rigid the material becomes.
"Most cross-linked materials, especially those that are 3D printed, tend to have a fixed form, meaning that, once you manufacture your part, the material cannot be reprocessed or melted," Gardea said, adding that this new material has a "dynamic bond that allows it to go from liquid to solid multiple times, which allows it to be 3D printed and recycled."
These dynamic bonds result in a unique shape memory behavior, so the material can be programmed and triggered to return to a remembered shape, according to the release.
"The flexibility introduced to the polymer chain allows it to be fine-tuned, in unprecedented ways, to get either the softness of rubber or the strength of load-bearing plastics," the release adds.
Much of the previous work on adaptive materials was for materials systems that are either too soft for structural applications or otherwise not suitable for platform development, Bryan Glaz, associate chief scientist for the lab's Vehicle Technology Directorate, said in the release.
The research is still in the discovery phase. The team started off trying to develop a 3D-printable material for structural applications that could be used to print components of UAVs or even rotorcraft, according to the release.
During this exploratory research, program officials noticed that, after failure, the surfaces became active and "would easily adhere to one another," Gardea said, adding that the discovery prompted researchers to investigate the self-healing capabilities.
The immediate next steps are to enhance the actuation behavior and healing, as well as introducing multi-responsiveness, and have the material respond to stimuli beyond temperature and light, Gardea said.
This effort is just part of an exploratory research program to look at new scientific developments that may disrupt current scientific and technological paradigms 30 to 50 years from now, Glaz said.
But the team's scientific advancement marks "a first step along a very long path toward realizing the scientific possibility for deep future platforms," he added.
-- Matthew Cox can be reached at matthew.cox@military.com.
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