Tension-Induced Soft Stress and Viscoelastic Bending in Liquid Crystal Elastomers for Enhanced Energy Dissipation

TL;DR

This paper explores how tension-induced soft stress in liquid crystal elastomers can be harnessed to improve energy dissipation in architected materials, combining experimental and simulation approaches to optimize impact protection structures.

Contribution

It introduces a novel mechanism of tension-induced soft stress in LCEs for enhanced energy dissipation, supported by experimental characterization and nonlinear viscoelastic modeling.

Findings

Optimized LCE lattice structures dissipate 2-3 times more energy.

Non-monotonic energy dissipation depends on horizontal to tilted member thickness ratio.

Tension-driven soft stress combined with viscoelastic bending improves impact energy absorption.

Abstract

Architected materials that exploit buckling instabilities to reversibly trap energy have been shown to be effective for impact protection. The energy-absorbing capabilities of these architected materials can be enhanced further by incorporating viscoelastic material behavior into the buckling elements using liquid crystal elastomers (LCE). In addition to conventional viscoelastic behavior, LCEs also exhibit a highly dissipative rate-dependent soft stress response from mesogen rotation under a mechanical load. However, the buckling elements cannot take advantage of this dissipation mechanism because buckling occurs at strains below the threshold for mesogen rotation. In this study, we investigate tension-induced soft stress behavior as an additional dissipation mechanism in horizontal members of lattice structures composed of tilted LCE beams under compression. Viscoelastic properties of LCEs with two crosslinking densities were characterized experimentally, and a nonlinear viscoelastic model was implemented in Abaqus/Standard as a user-defined element to simulate finite-strain behavior of monodomain LCEs, including soft stress response. Simulations and experiments revealed a non-monotonic dependence of energy dissipation on the thickness ratio between horizontal and tilted LCE members. Optimized structures with stretchable horizontal bars dissipated 2-3 times more energy than rigid-bar counterparts by balancing tension-driven soft stress with viscoelastic beam bending. These findings demonstrate a new design strategy for LCE-based architected materials to enhance energy dissipation.