Understanding complex stress states in pseudoelastic shape memory alloys - macroscopic modeling considering localization and tension-compression asymmetry

摘要

In order to understand the asymmetric response of pseudoelastic NiTi shape memory alloys (SMAs) during tension and compression loading, i.e. the stress induced martensitic transformation (SIMT) via formation and propagation of martensite bands under uniaxial tension [1, 2] vs. the homogeneous deformation under simple compression [3, 4], advanced constitutive modeling of these materials is necessary. Several attempts have been made during the last decades to model the localized transformation in SMAs [5, 6], Conventional material models (e.g. implemented in Abaqus software) are able to predict the pseudoelastic hysteresis of SMAs, but they do not consider the localization of deformation. The localization phenomenon in pseudoelastic SMAs, however, can place serious effects on macroscopic material behavior in applications of SMAs. Furthermore, confirmed by experiments, a distinct mode of localized deformation can be observed under more complex loading conditions, e.g., bending [7] and combined tension/torsion [2] and shear-compression [8]. In this paper, an isotropic Drucker-Prager type total deformation strain softening model is developed using the Finite Element Method, to allow for modeling of the tension-compression asymmetry in NiTi SMAs, including localization and growth of individual martensite bands. The Finite Element simulation results (obtained using the Abaqus software package) under uniaxial tension and compression are shown and compared to those from experiments. In addition, numerical results for a pure bending test are presented, as a combination of both deformation modes. In an excellent agreement with the experimental observations, our results present a successful modeling possibility of the deformation behavior of pseudoelastic NiTi SMAs under more complex stress states.