Method for characterization work output of NiTi accounting for application based transient thermo-mechanical behaviour.

The work output of mechanical systems, shape memory based or otherwise, is dependent on the force applied to the load, and the magnitude of the load. For shape memory alloy (SMA) systems, the key factors determining the former are the heat transfer rates for both heating and cooling, geometry of the SMA, and SMA pre-tension in relation to applied load. These factors are challenging to characterize using tensile tests and differential scanning calorimetry, as they do not account for factors such as dynamic transients or biasing elements. This work proposes a testing apparatus which encompasses testing SMA in conjunction with its biasing element and varied load, while accounting for heat transfer rates. This work demonstrates the methodology of the apparatus and gives work output values for equiatomic NiTi with different geometry and thermomechanical history and biasing elements, yielding a true application based performance curve with varied load.