Shape memory alloy laminate for design of self-folding reconfigurable structures
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QinetiQ Ltd 2013. In this work, we examine a self-folding material system that consists of an active laminate including two outer layers of thermally-actuated shape memory alloy (SMA) separated by a compliant passive layer. Localized SMA actuation enables control of the local Gaussian curvature anywhere in the sheet, allowing the initially planar laminate sheet to reconfigure into a 3D structure. The laminate extends the "programmable matter" concept since it can be formed and reconfigured in three dimensions without external manipulations. Two designs have been considered for the self-folding laminate sheet: one design proposes pre-strained thin SMA films for the outer layers of the laminate while the other proposes meshes of pre-strained SMA wires for such layers. The folding performances of these two designs are compared via finite element simulations. The results show that the mesh-based design provides tighter folds at any orientation than the film-based design for the same amount of volume-specific applied power. The mesh-based design shows other attractive qualities such as lower laminate density, less difficult SMA pre-straining process, and reduction of negative effects due to heat transfer between the SMA layers. However, the film-based design provides the advantage of a homogeneous and isotropic folding performance unlike the mesh-based design, where the folding performance depends on orientation and location of the heating zone.