Shape Memory Alloy Torque Tube Design Optimization for Aircraft Flap Actuation and Control

Abstract

Shape memory alloys comprise a unique class of material that is able to undergo a thermally driven, solid-solid phase change. This transformation is characterized macroscopically by the generation of large inelastic strains which may be recovered while supporting significant load. This process can be harnessed to do useful work as an actuator, and indeed, shape memory alloys possess one of the greatest actuation work densities of all active materials. It is because of this that researchers and engineers are interested in using these alloys to create powerful, lightweight actuators for several aerospace applications. In current aircraft designs, hydraulic systems represent a large proportion of the total aircraft mass. However, shape memory alloy torque tubes may provide a lightweight alternative. This thesis documents research done to study and optimize the structural design and PID controller parameters of an inductively heated shape memory torque tube providing feedback control of the aircraft control surfaces. The system electro-thermomechanical response under variable loading is modeled and implemented in Python. The Design of Experiments methodology is utilized to identify important design parameters. Finally, the structural and control design space is explored using particle swarm optimization to achieve an optimum PID controller response. Experiments are used to calibrate the SMA constitutive model and to validate the time-domain control response simulation. It was found that this method is a viable solution for designing SMA torque tubes for use as aircraft control surface actuators.