Tracking Deformation Processes in Nitinol Using Fast Infrared Imaging

This work deals with the development of a novel method capable of prediction fatigue of NiTi based on the experimental detection of selfheating.  The method, when fully developed, can be potentially applied to any thermomechanical cyclic loading but since we are not that far yet, we will discuss only superelasticity of NiTi wires under uniaxial loading in this paper. NiTi wires, having three different microstructures due to different annealing treatments were tested. A high-frequency infrared camera with high resolution was used to precisely follow the temperature evolution of the material during the tensile tests. In order to localize the start of the phase transformation in one single spot and facilitate thus the temperature measurements, specimens having nonconventional shape of varying cross section were used. Comparisons between force-controlled and displacement-controlled responses are discussed. In the interest of complement the physical interpretation of the results, a modeling effort is presented in the second part. The model proposes the interaction of several hypothetical thermomechanical couplings to reproduce the observed phenomena.