  Here, we report the rate-dependent energy absorption behavior of a liquid
crystal elastomer (LCE)-based architected material consisting of repeating unit
cells of bistable tilted LCE beams sandwiched between stiff supports.
Viscoelastic behaviors of the LCE material cause the energy absorption to
increase with strain rate according to a power-law relationship, which can be
modulated by changing the degree of mesogens alignment during synthesis. For a
strain rate of 600 s-1, the unit cell structure shows up to a 5 MJ/m3 energy
absorption density, which is two orders of magnitude higher than the same
structure fabricated from Polydimethylsiloxane (PDMS), and is comparable to the
dissipation from irreversible plastic deformation exhibited by denser metals.
For a stacked structure of unit cells, viscoelasticity also produces nonuniform
buckling of the LCE beams, causing the energy absorption density to increase
with the stacking number n up to n=3. Varying the beam geometry further
promotes the nonuniform buckling behavior allowing the energy absorption
density to increase with stacking number without bounds. We envision that our
study can lead to the development of lightweight extreme energy-absorbing
materials.
