Mechanics of magnetic-shape memory polymers

Magnetic-shape memory polymers (M-SMPs) can not only undergo rapid and reversible deformation in response to magnetic actuation but also lock the actuated shape upon cooling, which has great potential in applications such as soft robotics, active metamaterials, and shape-morphing systems. In this work, we develop a constitutive model for M-SMPs with finite deformation. The constitutive model considers the Helmholtz free energy contributed by the thermally responsive shape memory polymers and the magnetically responsive particles, leading to a magneto-thermomechanical framework. It is shown that the developed model can capture the thermomechanical as well as magneto-elastic responses of M-SMPs at different temperatures. Simplified beam models for M-SMPs are presented to show the material's versatile functionalities including fast and reversible deformation, selective/sequential actuation, and shape locking. We envision that the constitutive framework and the simplified beam models presented in this work can serve as useful tools to guide the rational design of M-SMP-based functional structures and devices.