A finite element study on localized deformation and functional fatigue in pseudoelastic NiTi strips

Thin tensile specimens of pseudoelastic NiTi shape memory alloys deform by the formation and propagation of distinct martensitic bands. During cyclic loading, functional fatigue (i.e., degradation of functional properties due to the repeated martensitic transformation) is limited to the regions that participate in the transformation. In this study, we present finite element calculations based on a simple elasto-plastic approach that utilizes strain softening to simulate localized transformation/deformation. We investigate the effect of typical experimental factors (clamping conditions and small superimposed bending moments during tensile testing) on the macroscopic mechanical behavior and on the propagation mode of the macroscopic phase interfaces. Moreover, we study how localized functional fatigue influences the macroscopic stress–strain data. The simulations demonstrate that a detailed understanding of experimental conditions and of cyclic experiments can be obtained by finite element modeling of localized deformation.