Fracture of liquid crystal elastomers

Liquid crystal elastomers (LCEs) are anisotropic, viscoelastic materials integrating polymer networks and liquid crystals. While their mechanical responses have been extensively studied, their fracture behavior remains largely unexplored. Specifically, the effect of the deformation-director coupling on LCE fracture paths is unknown, and fracture criteria for LCEs are not yet established. To address this gap, we combine experimental and theoretical approaches to investigate fracture propagation in LCEs. We stretch edge-cracked monodomain LCE samples, recording their stress-stretch responses and crack paths under varying initial directors and stretching rates. Our findings reveal that cracks can change direction during propagation, which are highly dependent on both the initial director and the stretching rate. To further understand LCE fracture behavior, we develop a rate-dependent phase-field fracture model, which is validated through experiments, and demonstrates the ability to predict complex fracture paths. Our study paves the way for designing LCEs with enhanced fracture properties, imperative for their future applications.