[Paper Review] Synergistic Energy Absorption Mechanisms of Architected Liquid Crystal Elastomers

Seung‐Yeol Jeon, Beijun Shen+6 more|arXiv (Cornell University)|Oct 14, 2021

Advanced Materials and Mechanics4 citations

TL;DR

This study demonstrates that architected liquid crystal elastomers (LCEs) exhibit synergistic energy absorption through viscoelasticity and geometrically induced nonuniform buckling. At 600 s⁻¹ strain rate, the LCE unit cell achieves 5 MJ/m³ energy absorption—two orders of magnitude higher than PDMS and comparable to dense metals—enabling lightweight, extreme-energy-absorbing materials.

ABSTRACT

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.

Motivation & Objective

• To develop lightweight, high-performance energy-absorbing materials using architected liquid crystal elastomers (LCEs).
• To understand the rate-dependent energy absorption mechanisms in LCE-based structures under dynamic loading.
• To explore how viscoelasticity and geometric design synergistically enhance energy dissipation.
• To identify structural parameters that enable unbounded energy absorption scaling with stacking number.

Proposed method

• Designing a unit cell structure composed of bistable tilted LCE beams sandwiched between stiff supports to enable controlled buckling.
• Engineering mesogen alignment during synthesis to tune the viscoelastic response and strain-rate-dependent energy absorption.
• Using a power-law relationship to model the rate-dependent energy absorption behavior of the LCE material.
• Stacking multiple unit cells to investigate the effect of structural hierarchy on energy absorption and buckling nonuniformity.
• Varying beam geometry to promote nonuniform buckling and enhance energy absorption in stacked configurations.
• Comparing energy absorption performance against PDMS and dense metals to benchmark mechanical efficiency.

Experimental results

Research questions

• RQ1 How does viscoelasticity in LCEs contribute to rate-dependent energy absorption in architected structures?
• RQ2 What is the maximum achievable energy absorption density in LCE-based unit cells under high strain rates?
• RQ3 How does stacking multiple unit cells affect energy absorption and buckling behavior?
• RQ4 Can geometric tailoring of LCE beams enable unbounded energy absorption scaling with stacking number?
• RQ5 How does the energy absorption of LCEs compare to that of PDMS and dense metals?

Key findings

• At a strain rate of 600 s⁻¹, the LCE unit cell achieves an energy absorption density of 5 MJ/m³, two orders of magnitude higher than PDMS.
• The energy absorption increases with strain rate following a power-law relationship, modifiable via mesogen alignment during synthesis.
• Stacking up to three unit cells enhances energy absorption due to viscoelasticity-induced nonuniform buckling of LCE beams.
• By varying beam geometry, nonuniform buckling is further promoted, enabling energy absorption to increase without bound as stacking number increases.
• The energy absorption performance of the LCE structure rivals that of denser metals undergoing irreversible plastic deformation.
• The synergistic interplay between viscoelasticity and geometric design enables unprecedented energy dissipation in lightweight materials.