Recent work has used self-folding origami inspired composites to produce complex, scalable, affordable, and lightweight morphing structures [1]. These characteristics are of interest for engineering applications, in fields including aerospace [2] and medical devices [3]. Due to these advantages, research on self-folding smart composites has grown, with a particular focus on the use of laminate manufacturing techniques that stack layers of heterogeneous materials to generate functional composites. Previous work used this approach to manufacture self-folding origami inspired robots [1]. A simple shape memory composite design consists of a smart material (e.g. a one-way shape memory polymer, or SMP) sandwiched between patterned rigid layers. These SMPs change their shape in response to an external stimulus (e.g. temperature). Upon heating above the phase transition temperature of the polymer (Tt), the SMP contracts, causing the laminate to fold. The SMPs used in self-folding laminate composites are unidirectional and thus the laminate is unable to recover its original state without application of external force. In this work, we study the use of thermal responsive liquid crystal elastomers (LCE) for reversible self-folding and actuation of origami inspired composites using laminate manufacturing. LCEs are smart materials that exhibit reversible deformation, good strain recoverability, and tailorable properties (i.e. phase transition temperature, strain, and orientation of deformation) [4–6]. We explore two composite hinge designs using laminate manufacturing process [1, 7] with a Joule heating layer to enable self-folding: one where the LCE acts as a tensile actuator connected only on the edges of the rigid layer, which we call a tensional hinge, and a second where the LCE is attached along the patterned rigid layer hinge, which we call a flexural hinge. The angular displacements of these two hinge designs are estimated using geometric models that account for the contraction of the LCE upon heating, and compared against experimental measurements. The maximum blocked torque of the composite hinges is also measured experimentally. To demonstrate the use of LCE as an active layer for origami inspired composites, we also present a laminate crawler robot. The crawling locomotion is controlled with an electrical heating layer laminated on the LCE. These results demonstrate the possibility of using LCE to achieve rapid, reversible folding and to generate similar torques, as compared to previous work in origami inspired self-folding composite.
Constitutive model for epoxy shape memory polymer with regulable phase transition temperature
