Over the past several years, NiTi alloys in both the shape memory and superelastic form have seen a tremendous increase in applications, which exploit the materials' ability to repeatedly recover inelastic strains up to 8 percent. Despite our understanding of the relationship between the deformation modes and the transformations in NiTi, we do not have a clear understanding of the fracture processes influencing fatigue limits. In this paper, we present a methodology to obtain calibrated material constitutive relations and the approach to determine the effects of the polycrystalline structure. The approach involves a combination of texture mapping, full-field strain measurements using Moire interferometry, and stochastic finite element modeling applied at different length scales. We also explore the effects of localized stress raisers such as grain boundaries and sharp corners, and discuss implications on the fatigue performance of medical devices.