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Localization Phenomena in NiTi Shape Memory Alloys - Finite Element Modeling of Lueders-like Shear Bands during quasi-static and cyclic loading

Christian Großmann 1,2Andreas Schäfer 1,2Gunther Eggeler 1Martin F. Wagner 1,2

1. Ruhr-University Bochum, Universitaetsstrasse 150, Bochum 44801, Germany
2. Emmy Noether Research Group Twinning, Bochum 44801, Germany


Several reasons for the occurence of localized deformation (as opposed to an evenly spaced "homogeneous" deformation) of pseudo elastic NiTi shape memory alloys have been proposed in the literature. Grain size and texture may well favour localized deformation (microstructural sceanrios). Stress and strain states at the martensite/austenite interface are envisioned to promote the transformation in adjacent regions (mesoscopic and micromechanical models). The specimen shape, overall stress state and heat transfer to ambient media may well have an important effect on the deformation behavior (macroscopic approaches). While there exists a vast body of experimental data on the mechanical behavior of NiTi shape memory alloys, a clear understanding of the individual contributions of these effects is yet to be developed.

In the present contribution, we use a simple Finite Element model in order to study the macroscopic mechanical aspects of the formation and propagation of martensitic transformation regions in thin tensile specimens (wires and ribbons) and in plate specimens with and without notches during quasi-static and cyclic loading. Based on detailed experimental data (also presented in a companion paper in these Proceedings), we include the effect of localized functional fatigue (i.e., changes of transformation behavior due to repeated cycling through the forward and reverse transformation). We study the effect of different specimen geometries and uniaxial versus bi-axial load cases on localization of the stress-induced transformation. Finally, we discuss how uniaxial tensile deformation differs from the more general stress and strain states in plate specimens, and how these subtle differences have a distinct effect on localization of transformation, deformation, and functional fatigue.


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Presentation: Oral at E-MRS Fall Meeting 2007, Symposium E, by Christian Großmann
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-14 22:21
Revised:   2009-06-07 00:44