Pre-strain and Mean Strain Effects on the Fatigue Behavior of Superelastic Nitinol Medical Devices

Where are we at with shape-memory alloys in this ‘high-tech’ world?

“…While there have been many materials discovered which exhibit the property of shape memory as a consequence of a martensitic transformation, only relatively few, for example, Nitinol and Ni 2 MnGa, have evolved to the extent that they have a sustainable and viable future in terms of industrial applications. According to a recent review of this field, as was reported in a 2022 publication in the journal Shape Memory and Superelasticity (Pelton et al 2022), the global Nitinol medical devices market was estimated to be of order US$15 billion in 2018.…”

The impact of modeling choices on the assessment of Ni‐Ti fatigue properties through surrogate specimens

“…Indeed, these devices are still reported to fail in clinical service, despite extensive studies over the last decade. [2][3][4][5][6] Lifetime predictions of Ni-Ti stents remain an open issue for academics, industry and regulators: this might be due to the intrinsic complexity related to the non-linear material response that greatly differs from that of standard metals, starting from the strain-based approach for the fatigue assessment. 2 To obtain quality certifications, peripheral stents should withstand about 10 7 fatigue cycles which correspond to about 10 years of survivance without exhibiting failure.…”

“…These cause the application of multiple loads on the stent causing the bending of the v‐struts with localized high‐stress regions at the apices. Indeed, these devices are still reported to fail in clinical service, despite extensive studies over the last decade 2–6 . Lifetime predictions of Ni‐Ti stents remain an open issue for academics, industry and regulators: this might be due to the intrinsic complexity related to the non‐linear material response that greatly differs from that of standard metals, starting from the strain‐based approach for the fatigue assessment 2 …”