Numerical simulation and experimental validation of bending and curling behaviors of liquid crystal elastomer beams under thermal actuation

Abstract

The exceptional actuation properties of liquid crystal elastomers (LCEs) have made these materials highly attractive for various emerging applications such as soft robotics and artificial muscles. The large strain gradients occurring under thermal stimuli induce bending and curling of initially flat LCE films. Due to the complex physics behind the spontaneous deformation in nematic liquid crystal elastomers, there is no single universal finite element-based method for the simulation of the behaviors of LCE actuators. In this work, we developed a simple layered 2D model for modeling and simulation of the bending and curling characteristics of LCE beams based on the gradient of the temperature-dependent equivalent thermal expansion. The appropriate parameters were derived by measuring the radius of curvature of the LCE film aligned unidirectionally at one surface produced on a rubbed Kapton film. It was found that in a large range of thicknesses (12–134 μm) of the LCE beams, the equivalent thermal expansion coefficients tend to approach a similar value. It was demonstrated and experimentally validated that the thermal expansion model is very effective in predicting the nonlinear curling behavior of LCE beams of various thicknesses. Remarkably, the model is also capable of simulating the rolling behavior of LCE beams with tapered thickness variation. The proposed method offers good flexibility in terms of the geometric shape and expansion parameters, computational efficiency, and accuracy.