Nitinol Fatigue Life for Variable Strain Amplitude Fatigue

Nitinol fatigue testing results are presented for variable strain amplitude cycling. The results show that fatiguing in varying strain amplitude can worsen fatigue life as compared to constant strain amplitude. The testing included two types of specimens; diamond shape specimens and Z shape specimens. The diamond shape specimens are made from nitinol tubing with stent-like manufacturing processes and the Z shape specimens are made from heat set nitinol wire.

The study explores the hypothesis: duty cycling can have an effect on nitinol fatigue life. Stents are subjected to different loadings in vivo resulting in more complex strain amplitudes. The main focus in this study is whether a combination of small and large amplitudes alters the fatigue life of a component due to additional damage.  This study is conducted in the course of the work of a consortium of several stent manufacturers, SAFE Technology Limited and Dassault Systèmes Simulia Corp.