Eagles can store energy in their feet without having to continuously contract their muscles to then jump high or hold on to prey. New materials have been created that can store energy this way. The materials, called auxetics, behave quite differently from regular materials. Instead of bulging out when squeezed, they collapse in all directions, storing the energy inside.
Current auxetic material designs have sharp corners that enable them to fold onto themselves, achieving higher density. This is a property that has been recognized recently in lightweight armor designs, where the material can collapse in front of a bullet upon impact. This is important because mass in front of a bullet is the biggest factor in armor effectiveness. The sharp corners also concentrate forces and cause the material to fracture if squeezed multiple times, which is not a problem for armor, as it is only designed to be used once.
Auxetic materials were redesigned with smooth curves that distribute the forces and make repeated deformations possible for other applications where energy-storing and shape-changing material properties are required. The work lays the basis for designs of lightweight 3D supports, which also fold in specific ways and store energy that could be released on demand.
The nature-inspired designs could be used in energy-efficient gripping tools required in industry, reconfigurable shape-on-demand materials, and even lattices with unique thermal expansion behavior. A major problem for materials exposed to harsh conditions, such as high temperature, is their expansion. A material could now be designed so its expansion properties continuously vary to match a gradient of temperature farther and closer to a heat source. This way, it will be able to adjust itself naturally to repeated and severe changes.
The flexible auxetic material designs, which were not possible before, were adapted specifically to be easily 3D-printed.