The team used a nickel-titanium shape memory alloy processed with laser powder bed fusion, a high-precision metal 3D-printing technique. This method allowed them to form wavy internal features only 0.3 millimeters across, providing finer structural control than is typical for metallic metamaterials.
Many morphing-wing efforts have struggled because passive structures cannot adapt in real time and polymer-based systems lack sufficient strength for aerospace use. To produce usable deformation, engineers often add heavy mechanical actuators, which increase weight, complexity, and drag.
The NUAA researchers instead designed an active metal network that can bear aerodynamic loads while reshaping under the actuation provided by the shape memory alloy itself. This approach removes the need for external actuator systems and keeps wing structures more compact.
The concept takes inspiration from the seedcoat of Portulaca oleracea, whose epidermal cells contain embedded features and wavy interfaces that distribute mechanical stress. By translating this biological pattern into a metal honeycomb architecture, the team obtained a structure that combines flexibility with mechanical robustness.
Within this bio-inspired family, the researchers tuned mechanical behavior by changing how many walls join at each honeycomb node. Adjusting this connectivity allowed the Poisson's ratio to span from negative to positive values, covering a broad range of deformation modes.
A hexagonal honeycomb variant showed particularly notable performance. Tests indicated it could stretch by up to 38 percent before fracture while recovering more than 96 percent of its programmed shape upon heating, a level of repeatable deformation rarely reported for metallic metamaterials with comparable strength.
To demonstrate a practical application, the team fabricated prototype wing sections that incorporate the active honeycomb core. These test wings morphed continuously over an angle range from about -25 degrees to 25 degrees, including at low temperatures similar to those encountered in flight.
Because the shape memory alloy provides internal actuation, the morphing wings did not require the external actuator assemblies used in many previous designs. The study points to a shift away from polymer-dominated or passive morphing concepts toward metal-based, actively reconfigurable structures.
The researchers now plan to integrate sensors and electronic components into future versions of the material so that the structures can monitor their own state and adjust shape automatically. Their long-term goal is to support aircraft surfaces that adapt in real time to changing aerodynamic and environmental conditions.
Research Report:Laser printed bio-inspired active flexible metallic metamaterials with reconfigurable deformation capability
Related Links
Nanjing University of Aeronautics and Astronautics
Space Technology News - Applications and Research
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