Effect of plasticity on superelasticity and hysteretic dissipation of NiTi shape memory alloy

This paper experimentally investigates the effect of plastic deformation on superelasticity and hysteretic dissipation of NiTi shape memory alloy (SMA). First, NiTi SMA wires were stretched at an extremely high stress to explore the plastic yielding and fracture mechanism. Results show that plastic yielding and fracture took place at stresses of 1260 MPa and 1550 MPa, due to the formations and mergers of the dislocation slipping bands. Then, the SMA wires were plastically treated at different stresses near the plastic yield limit. Finally, the specimens after 'plastic treatment' were subjected to cyclic tensile loading to estimate the effect of the plastic deformation on the material features such as superelasticity, hysteretic dissipation, residual deformation, temperature variation. Results show that most of the material features degraded with the increasing magnitude of plasticity except the residual deformation. From the physical view of point, the plasticity-induced internal stress field facilitates the formation of martensite variants and obstructs the reverse phase transformation from martensite variants to their parent austenite phase. (author)