Experimental Characterization of Shape Fixity in Transversely Curved Unimorph Shape Memory Polymer Actuators

摘要

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 study is predominantly focused on the use of Veriflex-S, a thermally activated shape memory polymer, and bi-directional carbon-fiber-reinforced polymer (CFRP) in a unimorph actuator configuration. One of the deficiencies of shape memory polymer structures is the lack of recovery after a single or multiple thermo-mechanical cycle(s). The novel concept of incorporating transverse curvature in the CFRP substrate, similar to that of an extendable tape measurer, has demonstrated the ability to improve shape recovery by increasing the bending stiffness of the unimorph composite actuator to compensate for the lack of recovery of the SMP. Another deficiency of SMP actuators is the lack of retention of the stored or deformed shape over time. This paper is concerned with the effect of transverse curvature on the shape fixity when the unimorph composite is mechanically deformed into a stored configuration. A set of experiments was designed to determine the influence of transverse curvature, the relative widths of SMP and CFRP substrate, and SMP thickness on actuator fixity after a thermo-mechanical cycle. The performance of SMP unimorph actuators with varying levels of transverse curvature in the substrate were evaluated versus SMP unimorph actuators with a flat substrate. The ability of the unimorph actuator to minimize shape retention loss was evaluated by determining the deflection angle over time after being released from the stored configuration. Experimental results indicate that in most circumstances transverse curvature does not negatively affect the ability of the unimorph actuator to retain its shape fixity. Cases of 100 % or greater retention of shape fixity were documented which could lead to the expanded use of transversely curved shape memory polymer unimorph actuators in reconfigurable structures.