Being messy on the inside keeps metamaterials from folding under stress

A disordered design keeps the whole material from collapsing under heavy loads

crystalline lattice structure illustration

DAMAGE CONTROL  Metamaterials with internal lattices containing regions with different sizes, types or orientations of crystal structure (divvied up by yellow lines in the illustration above) could be more durable than materials with neat and tidy designs.

M. Pham et al/Nature 2019

Human-made metamaterials with messy internal designs may be more resistant to damage than those with neatly patterned structures.

Metamaterial lattices, usually composed of struts that form identical, repeating “unit cells,” can exhibit properties that normal solids don’t (SN: 1/19/19, p. 5). But under heavy loads, overstressed struts can collapse, and that breakage quickly splinters through the whole grid, causing it to crumble.

Materials scientist Minh-Son Pham of Imperial College London and colleagues realized that this kind of collapse is similar to the way metallic crystals with atoms arranged in identical unit cells deform under heavy loads. In these materials, defects in the crystal can travel freely through its atomic lattice like dominoes falling in a row, weakening the crystal (SN: 9/11/10, p. 22).

To create more resilient metamaterials, Pham and colleagues drew inspiration from the irregular atomic arrangements inside crystalline metals. In these materials, described in the Jan. 17 Nature, different regions contain unit cells with different orientations, sizes or types of crystals. The boundaries between these regions serve as roadblocks to stop defects from moving. Metamaterial lattices patterned after these atomic setups could make more reliable components for cars and airplanes, Pham says.

Pham’s team 3-D printed lattices with unit cells arranged either in perfect order, as in conventional metamaterials, or in motley groups of different atomic structures. When the researchers squeezed lattices between metal plates, the mixed lattices proved sturdier than those with regular unit cell arrangements.

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