The Effect of Uniaxial Cyclic Deformation on the Evolution of Phase Transformation Fronts in Pseudoelastic NiTi Wire

Experiments are presented of the response of pseudoelastic NiTi wires subjected to displacement controlled cycles. A custom-built thermo-mechanical testing apparatus is used to control the background temperature field of the wire specimen while allowing the evolution of transformation fronts to be tracked by full-field infrared imaging. Two experiments under similar end-displacement histories, but at temperatures approximately 8oC apart, are shown to give remarkably different cyclic responses. The mechanical response for the lower temperature experiment continued to soften but retained its shape through 43 partial transformation cycles, and the pattern of transformation fronts seemed to reach a steady state. The response for the higher temperature experiment showed a change in shape of the mechanical response and distinct changes in transformation front patterns over 31 partial transformation cycles.