Programming shape changes in tri-stable bilayer structure

The programmable shape transition in response to external stimuli has attracted increasing attention. Multi-stable structures represent a stimuli-responsive structure that features more than one stable shape and transition from one to another, appropriate for applications such as in micro-robotics. Although bi-stable structures have been extensively investigated, very few studies have been focusing on tri-stability of such structures. Here we design a partially bonded bilayer structure composed of a SMP layer and a rubber strip. When subjected to changes in temperature, this structure exhibits tri-stability and transits between hemihelical, left-handed and right handed-helical shapes. Theoretical analysis, experiments, and finite element simulations are conducted to identify the mechanism of the tri-stability and used to predict the deformed configuration given geometric and material parameters. Our work provides a facile strategy for fabricating smart reconfigurable structures for a broad range of applications in intelligent materials.