Development of Multi-Physics Models for Actuation of Liquid Crystal Elastomer (LCE) Slender Structures under Various External Stimuli

This thesis investigates the dynamic behavior and actuation mechanisms of liquid crystal elastomer (LCE) slender structures, focusing on the development of finite element models to gain a deeper understanding of their response to various external stimuli, such as light and heat. The research begins with the development of a reduced-order model to study the photo actuation of LCE beams under light illumination, incorporating both photochemical and photo thermal effects. This model involves various physics, such as light absorption, chemical reactions, heat transfer, and mechanical deformation. The study is then extended to analyze self-oscillations under alternating illumination of the top and bottom surfaces of the LCE beam, where a one-degree-of-freedom (1-DOF) model and a linearized approach provide insights into critical oscillation frequencies and intensity thresholds. In collaboration with an experimental group, the thesis also examines the thermal response of liquid crystal fibers (LCFs) due to Joule heating under different heating conditions by developing a three-dimensional model. This model considers the interplay between electrical input, heat transfer, and mechanical deformation. The study investigates both steady-state and transient heating scenarios, revealing key deformation modes and the influence of thermal gradients on actuation. Additionally, periodic electrical heating is examined to induce oscillatory behavior, providing insights into the potential of LCFs for soft robotic applications. Furthermore, the research explores the self-oscillation behavior of an LCE beam immersed in water by developing a two-dimensional fluid-structure interaction (FSI) model. This model couples the beam’s photothermal response with surrounding fluid dynamics, allowing for the investigation of oscillatory motion driven by self-shadowing effects. The study explores how beam length and light intensity influence critical oscillation intensity, frequency, and amplitude. Building upon this foundation, the final stage of the research focuses on exploring the propulsion and steering behavior of light-powered LCE swimmers. This study shows that propulsion (in the presence of perturbations) and steering of LCE beam swimmers lead to instabilities. To counteract these effects, a modified LCE beam swimmer is introduced by attaching an opaque rigid beam to the bottom surface of the LCE beam, generating a self-shadowing mechanism that produces a restoring torque for enhanced stability. The optimized design enables controlled navigation, demonstrating a viable approach for bioinspired swimming systems driven purely by light.