Simulation-Based Design of a Self-Folding Smart Material System

Abstract

Origami engineering — the practice of creating useful three-dimensional structures through folding operations on two-dimensional building-blocks — is receiving increased attention from the science, mathematics, and engineering communities. The topic of this paper is a new concept for a self-folding material system. It consists of an active, self-morphing laminate that includes two meshes of thermally-actuated shape memory alloy (SMA) separated by a compliant passive layer. The goal of this paper is to analyze several of the key engineering tradeoffs associated with the proposed self-folding material system. In particular, we examine how key design variables affect folding behavior in an SMA mesh-based folding sheet. The design parameters we consider in this study are wire thickness, mesh wire spacing, thickness of the insulating elastomer layer, and heating power. The output parameters are maximum von Mises stress in the SMA, maximum temperature in the SMA, and minimum folding angle. The results show that maximum temperature in the SMA is mostly dependent on the total heating power per unit width of SMA. The results also indicate that through-heating — heat transfer from one SMA layer to the other through the insulating elastomer — can impede folding for some physical configurations. However, we also find that one can mitigate this effect using a staggered mesh configuration in which the SMA wires on different layers are not aligned. Based on our results, we conclude that the new staggered mesh design can be effective in preventing unintended transformation of the non-actuated layer.