Coupled Electro-Thermo-Mechanical Modeling of Shape Memory Polymers

Abstract

Shape memory polymers (SMPs) are extensively studied for self-folding origami due to their large strain recovery, low cost, and low activation energy. SMPs utilize viscoelastic material behavior to change shape in response to an applied stimulus, for instance light or electricity. Electrical actuation is desirable due to its higher energy density and shorter response time. Previous studies reported empirical results on shape recovery of conductive polymer composites actuated by specific applied voltage or current conditions, which required rigorous experimentation. Here, we introduce a finite element framework capable of predicting the coupled electro-thermo-mechanical response of electrically actuated SMPs. As inputs, this framework requires material properties, such as electrical conductivity and viscoelastic parameters. The viscoelastic response is implemented using a Prony series model that is fit to experimental dynamic mechanical analysis (DMA) data. Using this framework, we predict the shape recovery behavior of electrically actuated SMPs subject to various thermal, electrical, and mechanical loads and evaluate the sensitivity of the response to the material properties. Additionally, we show the effects of material pre-straining conditions and localized conductive pathways on shape recovery and self-folding. This computational framework provides a fundamental understanding of the electro-thermo-mechanical response of electrically actuated SMPs and can be used to design electrically actuated self-folding origami for aerospace applications.