Electro-thermo-mechanical behavior of carbon nanopaper shape memory polymer composites

An electro-active composite based on carbon nanopaper (CNP) shape memory polymer (SMP) composite is proposed for actuating deployment of composite deployable structures. Carbon nanopaper shape memory composites are stimuli-responsive materials that can change between programmed shapes and the original shape by a voltage input. The proposed composite is a sandwich structure where the CNP layer acts as a flexible electrical heater when a voltage difference is applied. The shape change behavior of CNP-SMP composite presents a coupled electrical-thermal-structural problem. This paper presents a combined experimental, numerical, and analytical study of the time-dependent shape programming, stowage, and actuation of the CNP-SMP composite. The governing equations for the multiphysics behavior are derived. Characterization of the electrical and mechanical properties of the materials are carried out and employed in a nonlinear, fully coupled electrical-thermal-structural finite element model. Shape programming, stowage and actuation characteristics of the composite are investigated experimentally under axial loading. An analytical model is derived for the thermo-mechanical behavior of the composite which directly expresses the recovery over time through the creep compliance function. Close correlation is obtained between experimental measurements and numerical simulations. The proposed model can accurately predict the load and shape characteristics throughout programming, stowage, and actuation.