Liquid crystal elastomer based mechanical metamaterials for lightweight extreme impact energy absorption*

Liquid crystal elastomers (LCEs) are one of the most promising materials in the field of impact energy absorption, due to their exceptional energy dissipation behavior arising from the coupling of the relaxation dynamics of liquid crystal (LC) molecules and polymer chains. In this study, we report snapping-based metamaterials composed of LCEs for lightweight extreme impact energy absorption. We synthesized LCEs based on a two-stage thiol–acrylate reaction to program the order of LC molecules and chain alignment within beam elements. We characterized the energy absorption behaviors of the programmed LCE beams with bistability at various strain rates. We found that our LCE-based metamaterials show orders of magnitudes better specific energy absorption compared with previous works and their absorption capability is further enhanced as the strain rate increases. We could also tune the metastable energy states by controlling the strain rates. The combination of the inherent enhanced dissipation of LCEs with snapping-based architectures allows a new class of mechanical metamaterials with excellent energy absorbing capabilities.