Seedcoat-inspired metal lets wings change shape on their own

A research team at Nanjing University of Aeronautics and Astronautics (NUAA) has created an active metal metamaterial to help build aircraft wings able to change shape smoothly in flight. The material is designed to be lightweight, strong, and capable of bending and recovering its shape on its own, which is difficult to combine in previous designs.

The work, published in the International Journal of Extreme Manufacturing, uses a nickel-titanium shape memory alloy shaped through laser powder bed fusion (LPBF), a high-precision form of metal 3D printing. This method allowed the team to create tiny and wavy structural features only 0.3 millimeters across, much smaller and more controlled than what is typically possible in metal metamaterials.

Today's efforts to build morphing aircraft often run into the same problem: the materials cannot adapt easily. Many designs rely on passive structures that cannot shift shape in real time, while others use polymer-based materials that are too weak for aerospace use. To compensate, engineers often add heavy mechanical actuators, which work but make the wings bulkier and less efficient.

The NUAA researchers approached the challenge from a new angle. Instead of relying on soft materials or external actuators, they created an active metal structure that can withstand aerodynamic forces while reshaping itself as needed.

Their idea was inspired by the seedcoat of Portulaca oleracea, whose epidermal cells have embedded features and wavy interfaces that help spread out stress. By translating this natural pattern into a metal network honeycomb, the team produced a structure that is both flexible and robust.

The resulting family of honeycomb structures can be tuned by adjusting how many cell walls meet at each junction. This allows the mechanical behavior to shift across a wide range, with the Poisson's ratio changing from negative to positive values. One design, the hexagonal honeycomb, stood out. It could stretch up to 38% before fracturing and recovered more than 96% of its programmed shape when heated. Such large, repeatable shape changes are rarely seen in metal metamaterials with comparable strength.

To show how the material could be used, the researchers built prototype wing sections. These wings were able to morph smoothly through an angle range of −25° to 25°, even at low temperatures similar to those experienced in flight. Because the shape memory alloy provides its own actuation, the wings did not require the bulky external systems used in most current morphing-wing designs.

This study marks a clear shift from earlier attempts that relied heavily on polymers or passive materials. By combining a nature-inspired structure with the active response of a shape memory alloy, the team has shown a metal metamaterial that is strong, adjustable, and capable of reshaping itself on demand.

The researchers now aim to add sensors and electronic components so that future versions of the material can monitor their own shape and adjust automatically. Their long-term goal is to support the development of smarter, more adaptive aircraft surfaces capable of responding to changing flight conditions in real time.

International Journal of Extreme Manufacturing (IJEM, IF: 21.3) is dedicated to publishing the best research related to the science and technology of manufacturing functional devices and systems with extreme dimensions (extremely large or small) and/or extreme functionalities

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