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The torsional behavior of Ni-rich Ni50.3Ti29.7Hf20 (at%) high-temperature shape memory alloy tubes was investigated under pure torsion loading. Torque tubes with varying geometry including outer diameter, wall thickness, and length were subjected to constant-torque thermal cycling at stresses ranging from 0 to 500 MPa (0–175 N m). It was found that the wall thickness had a notable effect on the transformation temperatures where thick-walled tubes transformed at lower temperatures when compared to the thin-walled form. In all tube outer diameters, shear strains were found to be in the order of 6% obtained at stresses above 300 MPa. At lower stresses, little to no effect of wall thickness was observed, but the influence increased at higher stresses where thin-walled tubes generated approximately 2% less strain when compared to the solid forms. Two-way shape memory effect was also evaluated after 20 cycles and was found to reach ~3% strain when cycled at high stresses.

A parametric study was performed on NiTiCu shape memory alloy torque tubes. Four samples with varying wall thickness values were evaluated for their thermo-mechanical response. The torque against the angular displacement was measured for each sample when purely martensitic and purely austenitic. The recovery torque was measured as a function of the pretwist applied during loading in the martensite phase. The trends observed were compared to three models with relatively good agreement. The recovery torque for biaxial tension/compression-torsion tests were measured with values comparable to pure torsional loadings. During the biaxial loading, a time-dependent phenomenon was observed. To evaluate the time dependence, standard creep tests were performed to elucidate the influence of the load on the temporal response of the material.

Shape memory alloy (SMA) actuators deliver high forces while being compact and reliable, making them ideal for consideration in aerospace applications. One disadvantage of these thermally driven actuators is their slow cyclic time response compared to conventional actuators. Induction heating has recently been proposed to quickly heat SMA components. However efforts to date have been purely empirical. The present work approachs this problem in a computational manner by developing a finite element model of induction heating in which the time-harmonic electromagnetic equations are solved for the Joule heat power field, the energy equation is solved for the temperature field, and the linear momentum equations are solved to find the stress, displacement, and internal state variable fields. The combined model was implemented in Abaqus using a Python script approach and applied to SMA torque tube and beam actuators. The model has also been used to examine magnetic flux concentrators to improve the induction systems performance. Induction heating experiments were performed using the SMA torque tube, and the model agreed well with the experiments.