Macroscopic Localization Patterns in NiTi: Numerical Reconstruction of Experimental Observations

Mechanical deformation of superelastic NiTi polycrystals can lead to formation of distinct regions of (almost) pure phases separated by macroscopic, albeit spatially confined, transition zones. The different phases also exhibit different extent of deformation, which results in localization patterns on the sample surface detectable by various experimental techniques (XRD, DIC, optical methods). Recently, intriguing localization patterns have been thoroughly documented on several sample geometries (tubes, rods, ribbons) and under distinct loading modes (tension, shear, bending).

In this contribution, we introduce an extension of a well-established constitutive model for NiTi SMA, which attempts to provide a versatile tool for reproduction and even prediction of the localization phenomenona. By tuning of parameters of both the internal energy (with a particular Eshelby’s inclusion-motivated term) and the dissipation function it is possible to impose a strain-softening response in tension and a strain-hardening one in compression simultaneously. Finite element implementation of the model into a software package then allows to simulate particular cases and compare them with experimental data. It also allows to investigate the influence of material parameters and imposed boundary conditions on topology of the patterns.