Modifying the torque-angle behavior of rotary shape memory alloy actuators through axial loading: A semi-analytical study of combined tension-torsion behavior

In this article, a semi-analytical modeling approach is presented to study the pseudoelastic response of shape memory alloy rods and tubes subjected to combined tension-torsion loading states. A three-dimensional phenomenological shape memory alloy constitutive model is used to obtain the corresponding two-dimensional constitutive relations. The rod is partitioned into a finite number of narrow annular regions, and the equilibrium equations are found in each region for both loading and unloading paths. The derived equations are then solved based on an iterative algorithm. A set of experiments is conducted on a shape memory alloy thin-walled tube, and the results are then used to evaluate the performance of the modeling approach. Several numerical examples along with a finite element analysis are finally presented to demonstrate the capabilities of the proposed method. Using this approach, it is possible to design active biomedical devices with shape memory alloy actuators under combined loading conditions.