Development and Experimental Validation of Thermally Stable Unimorph SMP Actuators Incorporating Transverse Curvature

Abstract

Shape memory polymers (SMP) have the potential to be utilized as a lightweight, solid state actuator in modern reconfigurable structures including as deployment systems for satellite solar panels or morphing aircraft wings. This paper is predominantly focused on the use of Veriflex-S®, a thermally activated SMP, and bi-directional carbon-fiber-reinforced polymer (CFRP) in a flexural unimorph actuator configuration. The disadvantage of a unimorph composite actuator (UCA) as opposed to an actuator with a SMP matrix or a SMP composite sandwich structure is that UCA behaves like a bimaterial strip when heated or cooled. This means that large temperature swings, like those seen in space environments, will result in large out-of-plane curvature. These deformations can greatly affect the effectiveness of reconfigurable structures. This paper explains the development and experimental validation of a closed-form solution for a thermally stable unimorph actuator which exhibits minimal out-of-plane deformation when subjected to a thermal stimulus. A closed-form solution of the SMP actuator was developed and a set of UCA actuators were experimentally evaluated utilizing digital image correlation (DIC) to validate the conceptual model created. The experimental results indicate that the closed-form solution appears to be accurate as the maximum out-of-plane deformations for several non-ideal thermally stable actuators were less than 0.6 mm for a 65 °C temperature change.