Experimental Characterization of Unimorph Shape Memory Polymer Actuators Incorporating Transverse Curvature in the Substrate

Shape memory polymers (SMP) have the potential to be utilized as a lightweight, solid state actuator in modern reconfigurable structures including as a deployment system for satellite solar panels or morphing aircraft wings. This paper is primarily concerned with the use of Veriflex-SA (R) shape memory polymer and bi-directional carbon-fiber-reinforced-polymer (CFRP) in a flexural unimorph actuator configuration. One of the major deficiencies of SMP unimorphs is the permanent set (unrecovered shape) after a single or multiple temperature cycle(s). The novel concept of incorporating transverse curvature in the CFRP substrate, similar to that of an extendable tape measurer, is proposed to improve the shape recovery by increasing the bending stiffness of the unimorph actuator to compensate for the lack of recovery of the SMP. A set of experiments was designed to investigate the influence of transverse curvature, the relative widths of SMP and CFRP substrates, and shape memory polymer thickness on actuator recoverability after multiple thermo-mechanical cycles. The performance of SMP unimorph actuators with varying degrees of transverse curvature were evaluated versus that of traditional SMP unimorphs incorporating a flat substrate. Digital image correlation was implemented to quantify the out-of-plane deflection of the unimorph composite actuators (UCAs) during the actuation cycle. Experimental results indicate that an actuator with transverse curvature significantly reduces the residual deformation by at least two orders of magnitude which could be further tailored to enhance the performance of shape memory polymers in reconfigurable arrangements.