What it is
Mechanical metamaterials, materials whose behaviour comes from their architecture, are usually built from repeating unit cells with one or a few length scales, while real-world networks such as the Internet or the brain vary in connectivity and link length over orders of magnitude. The authors introduce scale-rich metamaterials, generated by repeatedly growing a straight ligament (a strut) from a random point at a random angle until it meets another ligament or the boundary, with a thickness that can shrink from one ligament to the next. Governed by only two parameters, the resulting networks have ligament lengths, thicknesses and connectivity that follow power-law distributions, spanning orders of magnitude within one sample. In simulations of 2,600 distinct structures they covered 77% of the density-anisotropy map, reaching combinations the square, hexagonal and Voronoi references did not, and the authors report a 190-fold tunable range of elastic anisotropy across densities. In compression experiments on 3D-printed polymer samples, scale-rich samples of constant ligament thickness deformed without the compaction bands that formed in the square and hexagonal lattices, or the localized compaction seen in the Voronoi tessellation, through 25% strain, and under impact they gave the highest specific energy dissipation at the lowest peak force among the architectures compared. In simulations they also steered elastic waves, focusing them through a lens assembled from scale-rich cells.
Why it matters
Architected materials usually rest on one or a few length scales; this framework lets strut size and connectivity vary over orders of magnitude from two parameters. The authors note that its individual linear and nonlinear properties are not unique to scale-rich materials, and that what sets it apart is combining them: among the architectures they compared, it was the only family to span the full anisotropy range (0.2 to 0.9) while keeping deformation delocalized. They suggest uses in adaptive load-bearing structures, protective gear such as helmets, packaging and armour. In one demonstration, a scale-rich layout designed around a fragile acrylic disc suppressed the stress fringes that square and hexagonal lattices produced in it in photoelastic images, and simulations put the stress reduction at up to 4.9-fold. The authors also suggest that such materials could open questions for network science, since in abstract networks a link's length and thickness are undefined or carry no consequence.
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Filed underAdvanced Materials and Mechanics, Cellular and Composite Structures, Acoustic Wave Phenomena Research
