Phase-Changing Metamaterial Capable of Variable Stiffness and Shape Morphing

Herein, a metamaterial is introduced that achieves tunable stiffness properties according to uploaded instructions, which control the phase of low-melting-temperature metals embedded in elastomeric spherical shells at selected locations within the lattice's microarchitecture. A macroscale cubic lattice of gallium-filled silicone rubber spheres is fabricated as a proof of concept. Nickel-chromium (nichrome) wires are threaded through the spheres within each row in the lattice so that current can be applied to specific rows to melt their gallium cores, thereby achieving a drop in the lattice's stiffness. Using this approach, the lattice can achieve a 3.7x increase in stiffness at 7% strain when the gallium cores are all solid compared with when they are all liquid. Larger increases in stiffness are possible for larger compression strains and with thinner silicone shells. Lattices with solid gallium cores experience buckling when compressed, but lattices with liquid gallium cores do not. Simulations demonstrate that cores can be liquified and resolidified much faster as they are scaled down in size, thus enabling rapid metamaterial stiffness control. Shape reconfiguration is also possible by liquifying select gallium cores at desired locations within the lattice, deforming it, and then resolidifying the cores to passively retain the lattice's shape.