Characterization of SMA Torsional Actuators for Active Twist of Tilt Rotor Blades

This paper presents the material modeling and experimental characterization of SMA rod and tube actuators undergoing torsional deformations. The investigation of the torsional characteristics of SMAs was carried out in order to gain fundamental understanding of the behavior of torsional actuators for actively altering the twist distribution of a tiltrotor blade between hover and forward flight. A torsional model involving the extension of the one-dimensional formulation of Brinson’s model for prediction of SMA behavior is presented. The model is shown to have good correlation with experiment over a wide range of thermomechanical conditions including constant temperature torque-angle and actuation tests against torsional springs. Experimental phenomena associated with the torsional behavior of the SMA actuator such as the effects of heat treatment, twist rate and loading pattern are examined, and limitations of the current model pointed out. It is shown that the theoretical model demonstrates good agreement with the experimental data over a wide thermo-mechanical range of conditions.