On the partial recovery of residual strain accumulated during an interrupted cyclic loading of NiTi shape memory alloys

It is well known that the behaviour of shape memory alloys (SMAs) evolves when subjected to cyclic loading. For instance, during superelastic cycling of an SMA, an increasing residual strain is observed, mainly during the first cycles. This paper first reports that (i)?this residual strain, believed to be irreversible, can be partially recovered and (ii)?a stress increase is observed after a pause during cyclic loading. Also, it suggests an explanation of these experimental observations based on the endo and exothermic phase transformations of the alloy, the heat exchange by convection around the sample and the Clausius?Clapeyron relation characterizing the SMA.