Comparison of linear and torsional SMA actuators for morphing applications

Abstract

Multifunctional capabilities of Shape Memory Alloys (SMAs) and, more specifically, their inherent characteristic of producing and recovering transformation strain under thermal stimulus, render them ideal for actuator appli- cations. In fact, SMA actuators are widely used in various fields including but not limited to robotics, medical, civil, and aerospace engineering. Moreover, they are also able to be formed in a wide range of shapes that includes, but is not limited to, wires, ribbons, bars, torque tubes and various spring types. This fact combined with their high-energy density, the noise-less, spark-free, and debris-less operation and their compactness renders them ideal for aerospace morphing structures where weight, volume, energy consumption, and other operational specifications have to be strictly met. In this study, two SMA actuator forms, one linear, i.e., wires of circular cross-section, and one torsional, i.e., torque tubes, are compared in terms of weight/volume, stroke capabilities, developed stresses, cooling requirements, power consumption and overall operation under predefined conditions. The actuators are intended for use in parts of an articulated shape adaptive mechanism envisioned for altering locally the outer mold line of a civil supersonic aircraft. The morphing system is placed on the lower part of the fuselage in order to alter the aerodynamic profile and reduce the sonic boom created during supersonic flight over inhabited areas. The specifications for the design of the actuators are provided and finite element analysis is used to verify the overall response of the SMAs.