Multiaxial Finite Strain Behavior of Polydomain Liquid Crystal Elastomers

Why It Matters

Accurate multiaxial modeling equips engineers to reliably integrate LCEs into soft‑robotic systems, shortening development cycles and reducing costly prototyping.

Key Takeaways

• Isotropic hyperelastic model matches FEM for multiaxial LCE loading
• Yeoh and Anssari‑Benam capture strain‑softening in large deformations
• Anssari‑Benam predicts all stress components most accurately
• Blocking force and torque formulas aid LCE actuator design
• Balloon instability linked to geometry, guiding safe design

Pulse Analysis

Liquid crystal elastomers (LCEs) blend the orientational order of liquid crystals with the elasticity of polymer networks, making them prime candidates for soft‑robotic components such as artificial muscles and peristaltic pumps. While uniaxial tests have long dominated the literature, real‑world applications subject LCEs to combined stretch, twist, and pressure, creating a gap in predictive modeling. The new study tackles this shortfall by formulating a multiaxial analytical framework that treats polydomain LCEs as isotropic hyperelastic solids, thereby sidestepping the cumbersome step‑length tensors traditionally required for anisotropic analysis.

The researchers evaluated three classic strain‑energy functions—Mooney‑Rivlin, Yeoh, and Anssari‑Benam—within the framework and benchmarked predictions against finite‑element simulations. Both the Yeoh and Anssari‑Benam formulations reproduced the characteristic strain‑softening and large‑deformation response observed in experiments, but the binomial Anssari‑Benam model delivered the most accurate stress‑component forecasts across extension‑torsion, inflation, and combined loading cases. Validation showed near‑perfect alignment with FEM results, confirming that the isotropic assumption does not sacrifice fidelity for polydomain LCEs.

Beyond theory, the paper extracts actionable design metrics: blocking force, longitudinal torque, and a through‑thickness instability map for LCE balloons, all expressed as functions of geometry and material parameters. These insights give engineers a straightforward toolkit for sizing soft actuators and anticipating failure modes in peristaltic pump housings. By bridging the gap between complex multiaxial loading and simple hyperelastic models, the work accelerates the transition of LCEs from laboratory curiosities to reliable components in commercial soft‑robotic systems.