Architected materials that exploit buckling to trap energy are effective for impact protection, and their performance can be enhanced by incorporating liquid crystal elastomers (LCEs). Beyond conventional viscoelasticity, LCEs exhibit a highly dissipative, rate-dependent soft stress response in tension associated with mesogen rotation. Because buckling typically occurs at strains below the onset of this soft stress behavior, we introduced an LCE horizontal bar into a hexagonal structure composed of tilted LCE beams. Under compression, stretching of the horizontal bar reduces the angle of the tilted beams and suppresses buckling; however, the viscoelastic softening behavior of LCEs creates the opportunity to design geometries that activate both the buckling of the tilted beams and the large stretching of the horizontal bar. In this work, we characterized the rate-dependent uniaxial tensile response of two monodomain LCE materials with different crosslink densities and used these data to parameterize a nonlinear viscoelastic model for monodomain LCEs implemented in Abaqus/Standard as a user-defined element. Finite element simulations of the compression response of the hexagonal structures showed that energy absorption is maximized at an optimal thickness ratio between the horizontal bar and the tilted beams, which shifts with the relative moduli of the two structural components. This optimized configuration allows the beams to buckle before substantial stretching develops in the bar and absorbs up to 2.5 times the energy of a rigid-bar counterpart, depending on the effective strain rate and material pairing. The same optimized thickness ratio applies to lattices composed of stacked unit cells, which undergo sequential buckling and lateral stretching across adjacent layers. These interactions create local load-unload-reload cycles that increase per-layer dissipation with increasing number of layers and become more pronounced under repeated loading. Together, these results demonstrate that LCE-based lattice structures can be designed to hierarchically nest competing dissipation mechanisms across unit-cell and lattice length scales, providing a new strategy for optimizing energy absorption.

https://doi.org/10.1016/j.jmps.2025.106497