Impact of Pretension on Fatigue of Nickel Titanium (NiTinol) Wire

Modern medical implantable devices made of NiTinol such as stents, filters and transcatheter valve frames are crimped to small diameters for minimally invasive delivery. Crimping constrains the device and subjects critical fatigue locations to high pretension loads. The impact of high pretension is known to affect the fatigue strength for other metallic materials. However, its impact on NiTinol have not been studied. The purpose of this research focuses on this study.

A baseline of NiTinol fatigue strength at various mean strains are obtained. The same material is subjected to various high pretension loads before they are fatigue tested at the same conditions to the baseline tests. Results are compared so that the impact of the pretension on the fatigue strength is addressed.