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Strain controlled fatigue tests of a pseudoelastic nickel–titanium (NiTi) shape memory alloy (SMA) have been carried out in this investigation. In particular, flat dog-bone shaped specimens, obtained from commercial NiTi sheets, have been analyzed, under pull–pull loading conditions, in two subsequent steps: (i) material stabilization and (ii) fatigue life estimation. The first step was carried out to obtain a stable pseudoelastic response of the SMA, i.e. with no residual deformations upon unloading, and it can be regarded as a preliminary processing condition of the alloy. Results on functional fatigue, i.e. in terms of stabilized pseudoelastic response, and on structural fatigue, in terms of cycles to failure, are reported and discussed. Furthermore, a modified Coffin–Manson approach for fatigue life estimation of SMAs is proposed, which takes into account the strain mechanisms involved during repeated stress-induced martensitic transformations.

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Temperature dependent fracture properties of NiTi-based Shape Memory Alloys (SMAs), within the pseudoelastic regime, were analyzed. In particular, the effective Stress Intensity Factor (SIF) was estimated, at different values of the testing temperature, by a fitting of the William’s expansion series, based on Digital Image Correlation (DIC) measurements. It was found that temperature plays an important role on SIF and on critical fast fracture conditions. As a consequence, Linear Elastic Fracture Mechanics (LEFM) approaches are not suitable to predict fracture properties of SMAs, as they do not consider the effects of temperature. On the contrary, good agreements between DIC results and the predictions of an ad-hoc analytical model were observed. In fact, the model takes into account the whole thermo mechanical loading condition, including both mechanical load and temperature. Results revealed that crack tip stress-induced transformations do not represent a toughening effect and this is a completely novel result within the SMA community. Furthremore, it was demonstrated that the analytical model can be actually used to define a temperature independent fracture toughness parameter. Therefore, a new approach is proposed, based on the analytical model, where both mechanical load and temperature are considered as loading parameters in SIF computation.

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The crack tip stress‐induced martensitic transformation and the resulting stress distribution in a nickel–titanium (NiTi)‐based shape memory alloy have been analysed. In particular, the effects of temperature, within the stress‐induced transformation regime, in single edge crack specimens have been studied by a recent analytical model, finite element simulations and experimental measurements. The results of the analytical model have been compared with those obtained from finite element simulations, carried out by using a special constitutive model for shape memory alloys, and good agreements have been observed. Furthermore, full field numerical results have been used to better understand the evolution of the volume fraction of martensite in the crack tip region. Finally, experimental measurements have been carried out, by using single edge crack specimens obtained from commercially available NiTi sheets by electro‐discharge machining. The results have been analysed by linear elastic fracture mechanics theory, and the analytical model has been used to calculate modified stress‐intensity factors for shape memory alloys. A slightly increase of the critical stress‐intensity factor has been observed with increasing the testing temperature, and this result is in accordance with the model calculations, which indicate a toughening effect, i.e. a reduction of the crack tip stress intensity factor.

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