Thermo-mechanical characterization of shape memory alloy torque tubes

The thermo-mechanical characteristics of four NiTi based Shape Memory Alloy (SMA) torque tubes are investigated under simple torsional (uniaxial) loading. Results from the thermo-mechanical tests are presented for samples when fully martensitic (room temperature T<M-f), fully austenitic (T>A(F)), and recovery torque measurements. Test results indicate that wall thickness plays a prominent role in the results. An analytical model was developed as a function of geometry and experimentally determined material properties. The model predicts the torque versus angular deformation for a wide range of tube geometries when in martensite and austenite. The distribution of strain through the thickness is assumed to vary non-linearly as an exponentially with the radius. The analytical results reflect the mechanical behavior reasonably well.