A novel experimental method to assess the fatigue behavior of pseudoelastic NiTi wires

Abstract

A new experimental method for characterizing intrinsic uniaxial pull-pull pseudoelastic fatigue life of commercial NiTi wires is proposed. It consists in the generation of a virtual dog-boned shaped specimen combined with the use of snubbing type of gripping action in order to completely eliminate earlier failures induced by grip-sample interactions. The generation of a virtual dog-boned specimen is based on the localized character of the stress induced martensitic transformation and the evolution of the transformation stresses with further cycling. Reduced pseudoelastic cycles are performed to evaluate functional and structural fatigue with this method. Consistent longer fatigue lives have been obtained compared to traditional gripping methods with fractures occurring inside the region of interest. The present study clearly points to the role of the stress induced transformation in determining the fatigue life. This treatment of the structural fatigue considerable departs from classical approaches but takes into account essential facts like the localized character of the stress induced transformation, the heat effects associated with the first order solid to solid martensitic transformation and its impact on the critical transformation stresses.