Plasticity in NiTi Martensite

At the current advent of advanced empirical and numerical techniques for studying NiTi deformations, new understandings are being brought to light regarding inelastic microstructure deformation mechanisms and their contributions to superelastic and shape memory phenomena. In this presentation, new characterization methodologies developed by coupling in situ diffraction experiments with theoretical calculations of monoclinic deformation mechanics will be introduced. The capabilities of using these methodologies to study plasticity in NiTi martensite will be demonstrated by applying them to empirical results from straining NiTi specimens to large tensile and compressive strains ( > 16%). Using the new combined numerical-empirical analysis technique, the contributions of each elasticity, transformation twinning, deformation twinning, and slip are quantified over the entire range of the deformations. These results are used to better understand plasticity in NiTi as well as its effect on subsequent phase transformation. The presentation will conclude with discussion as to the significance of applying this new knowledge in formulating new NiTi models, including a new continuum model we have developed for simulating plasticity-transformation interactions in SMAs.