Developing a self-bending kirigami structure driven by liquid crystal elastomers
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Liquid crystal elastomers (LCEs) are promising smart materials capable of undergoing large anisotropic deformations in response to external stimuli. When exposed to heat, the material's microstructure transitions from an ordered to an isotropic state, resulting in shrinkage along the director and expansion in the perpendicular directions. Despite their potential, the practical implementation of LCEs remains challenging due to the complexity of predicting their mechanical behavior. This research investigates the design of thermally responsive LCE patches to induce controlled deformation in plastic kirigami structures. Kirigami, a Japanese art form, involves cutting and folding a flat sheet into a three-dimensional shape. The same principle can be applied to plastic foils containing embedded electronics to create deployable or shape-morphing devices. The study begins with the material characterization of both the LCE and the polyethylene naphthalate (PEN) substrate. Based on the obtained material properties, a finite element model of a kirigami structure consisting solely of PEN is developed and validated against experimental results. The resulting strain fields are subsequently used to determine the optimal placement and director orientation of the LCE patches. These patches are then incorporated into the numerical model to predict the resulting deformation and to provide insight into the required patch dimensions. The proposed design workflow enables the systematic determination of the placement, size, and director orientation of LCE patches on kirigami structures and is validated through a physical prototype. Although the prototype exhibited a lower-than-desired deformation, the experimental results showed good agreement with the simulation predictions, demonstrating the effectiveness of the proposed design approach.
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