Attenuating liquid crystal elastomers’ stress concentration by programming initial orientation

Abstract

Liquid crystal elastomers (LCEs) are a kind of soft smart materials with fascinating programmability and have a broad application prospect. The monodomain LCEs under loading exhibit the semi-soft elasticity due to the stress-induced director rotation and the resulting spontaneous strain. In this article, we aim to reduce the severe stress concentration of LCEs by programming the initial director orientations. We numerically studied the stress concentration behaviors of a LCE sheet containing a small circular hole with different distribution of initial director under uniaxial loading. For monodomain LCE sheets, the stress concentration factor monotonically decreases as the initial director orientation deviates from the loading direction, and achieves its minimum when the deviation angle reaches 45°. This reduction of stress concentration is attributed to the smaller relative net director rotation and the lower resulting spontaneous strain near the hole edge as the deviation angle increases. Since the director rotation near the hole edge is critical for the attenuation of stress concentration, we only program the initial director orientation near the hole edge, and achieve up to 50% reduction in stress concentration factor. Increasing the size of programming area also enhances the attenuation of stress concentration. This work provides a new strategy to reduce the stress concentration in LCEs with geometric defects.