The cyclic strain evolution and the fatigue prediction in non-proportional multiaxial loadings of NiTi SMAs

Abstract

NiTi shape memory alloy is a kind of smart material which present unique properties of superelasticity, shape memory and excellent biocompatibility. The applications of such alloys are generally the connectors and fasteners, vibration-dampers, and endovascular stents, etc.. The cyclic deformation and fatigue failure of NiTi SMAs are key issues that need to be investigated since they usually endure complex cyclic loadings during the using process. In this paper, the evolutions of the peak/valley strains in non-proportional multiaxial fatigue loadings of NiTi SMAs are considered, and the fatigue failure mechanism is investigated. The results show that the martensite transformation and martensite re-orientation process greatly influence the transformation ratcheting and fatigue life of NiTi SMAs, and a life-prediction model that considers these deformation mechanisms particular for NiTi SMAs is also proposed to give reasonable predictions.