Thermo-mechanical characterization of shape memory alloy torque tube actuators

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.