A mechanics model of coating-assisted strategy for shape fixation of 3D mesostructures based on buckling-guided assembly

Buckling-guided three-dimensional (3D) assembly is an attractive manufacturing method that provides a versatile route to complex 3D mesostructures in a wide range of high-performance materials, which has enabled developments of 3D devices with unique functionalities and/or enhanced performances. While an elastomer substrate is required to serve as the platform of 3D assembly, the existence of such a substrate could impede practical uses of assembled 3D mesostructures in certain applications scenarios. As such, several strategies have been proposed to enable the shape fixation of 3D mesostructures after separation from the assembled substrate. Among them, the coating-assisted strategy does not impose additional constraints on structural designs (e.g., incorporating specific mechanical interlocks) or applicable material types (e.g., metals or shape memory polymers/alloys). Moreover, the shape fixation effects of coating-assisted strategy can be effectively controlled by optimizing key design parameters. Although the development of a rational design method that can guide the selection of design parameters related to the coating-assisted strategy is of great importance, it has not been explored. This paper develops a mechanics model of the shape fixation in a bridge-shaped ribbon structure formed through buckling of a straight ribbon structure and coating of an additional fixation layer. An analytical solution of the springback ratio in terms of the modulus ratio and the thickness ratio between structure/fixation layers as well as the prestrain used in the 3D assembly, is obtained, showing good agreements with finite element analyses (FEA) and experimental results. By introducing a modification factor, this solution can be extended to complexly shaped 3D mesostructures, such as cross-ribbon, helical-shaped and crane-like mesostructures. Guided by the developed model, highly complex freestanding 3D mesostructures such as ribbon-shaped mesostructures, and origami/kirigami-inspired mesostructures are demonstrated.