Mechanical Metamaterials with Strain-Rate Adaptive Energy Absorption

A metamaterial is a class of materials that provide new properties that are not observed in natural materials or from a bulk material that the “material” is made of. We report strain-rate adaptive mechanical metamaterials with a power-law relation between specific energy absorption and the strain rate based on liquid crystalline elastomer (LCE). Their power-law exponent can be modulated by changing the degree of mesogen alignment. We did experimental measurements and numerical simulations in a large range of strain rates (~10^-4/s to ~10⁴/s) to understand the strain rate-dependent energy absorption behaviors. Our metamaterials showed up to ~6 MJ/m³ specific energy absorption at ~700 /s strain rate, which is comparable to an irreversible plastic deformation-based dissipation of metals with up to two orders of magnitudes lower weight. Moreover, we can leverage the viscoelastic behaviors of LCE to significantly improve the specific energy absorption. We envision our study can contribute to lightweight extreme energy-dissipating materials with applications including personnel protection and automotive and aerospace parts.