Fracture control parameters for NiTi based shape memory alloys

In this paper new fracture control parameters for Nickel–Titanium (NiTi) based shape memory alloys (SMAs) are proposed, based on a recent literature analytical model on fracture mechanics of SMAs. In fact, the stress induced martensitic transformation, occurring in the crack tip region of NiTi alloys, causes a complex and unusual stress distribution with respect to common engineering materials. For this reason two different stress intensity factors (SIFs) have been defined to describe the stress distribution in both transformed and untransformed regions, i.e. in the martensitic and austenitic phases, respectively. Systematic studies have been carried out to analyze the effects of the main thermo-mechanical parameters of NiTi alloys on the two proposed SIFs, i.e. on the crack tip stress distribution, and comparisons with linear elastic fracture mechanics have been illustrated. Finally, the proposed model was used to analyze different loading conditions of a commercial superelastic NiTi alloys, which demonstrated a marked effect of the temperature on the crack tip stress distribution.