Improving the Deformability and Recovery Moment of Shape Memory Polymer Composites for Bending Actuators: Multiple Neutral Axis Skins and Deployable Core

Shape memory polymer composite (SMPC) actuators have received significant attention for applications in space deployable structures because of their light weight and simple actuating process without any additional components. However, conventional SMPC actuators exhibit limited deformation owing to damages caused by the slight elongation of fibers and microbuckling. In this study, we designed a sandwich-structured SMPC bending actuator to increase deformability and the recovery moment with two novel features: multiple neutral axis (MNA) skins and a deployable core. The MNA skins were fabricated as layered structures of a soft layer (the polydimethylsiloxane/ethoxylated polyethylenimine layer) and hard layers (the SMPC layer) based on the MNA effect derived from the large modulus difference between the soft and hard layers. Under the bending deformation, the large shear strain in the soft layer significantly decreases the axial strain in SMPC layers and increases deformability. Applying the deployable core on the sandwich-structured SMPC bending actuator increases the recovery moment owing to the deploying force of the core. To the best of our knowledge, the sandwich-structured SMPC bending actuator composed of two MNA skins and a deployable core yielded the world's largest width-normalized recovery moment of 51.2 N·m/m with the smallest bending radius of 15 mm.