J. Olbricht, A. Schaefer, G. Eggeler, M. F. -. X. Wagner, Ruhr-University Bochum, Bochum, Germany
Pseudo elastic deformation of NiTi shape memory wires and ribbons is associated with the formation and propagation of distinct transformation fronts. This localization of the stress-induced martensitic transformation is closely related to a localization of functional fatigue and consequently to the occurrence of multiple plateaus in macroscopic stress strain data during cyclic loading. While structural fatigue (i.e., crack nucleation and crack growth) in NiTi is well understood by the engineering and materials science communities, localization phenomena remain largely elusive. In this contribution, we present detailed experimental results on how these transformation bands evolve during extended mechanical cycling (up to 120 cycles) and how they are affected by different ambient temperatures above the austenite finish temperature. We combine several experimental approaches (thermal imaging, in-situ optical microscopy and alternating current potential drop detection) for characterization. Our results document the effects of thermal and mechanical interactions on the cyclic behavior of NiTi. We highlight and discuss the importance of localization phenomena for modeling and design of NiTi-based components and devices that are subjected to cyclic loading.
Summary: In this contribution, we present detailed experimental results on how transformation bands evolve during extended mechanical cycling (up to 120 cycles) of pseudo elastic NiTi, and how they are affected by different ambient temperatures above the austenite finish temperature. We combine several experimental approaches (thermal imaging, in-situ optical microscopy and alternating current potential drop detection) for characterization. Our results document the effects of thermal and mechanical interactions on the cyclic behavior of NiTi. We highlight and discuss the importance of localization phenomena for modeling and design of NiTi-based components and devices that are subjected to cyclic loading.
