Experimental Study of Mechanical Hysteresis of NiTi During Ferroelastic and Superelastic Deformation

Abstract
Shape memory alloys are known to exhibit a range of novel thermomechanical behaviour associated with the unique thermoelastic martensitic transformation. Such behaviour includes the superelasticity associated with stress-induced martensitic transformation at relatively high temperatures and the ferroelasticity associated with a martensite reorientation process at low temperatures. Both the stress-induced martensitic transformation and the martensite reorientation are energy-dissipative processes, i.e., hysteretic between the forward and reverse processes. This work was aimed at studying the hysteretic behaviour of the ferroelasticity and superelasticity observed in a polycrystalline NiTi alloy by carrying out simple shear deformation tests through both major and subloop cycles. It was found that subloops are always closed and enclosed inside the major loop and that the stress hysteresis of a subloop is only dependent on the strain amplitude of the subloop, regardless of the position of the subloop inside the major loop.