FEA Study of the Impact of the Shape Setting Strategy on the Fatigue Performance of Nitinol Vascular Implants

To investigate the fatigue performance of a Nitinol vascular implant a common approach is to use diamond shape samples with geometry and shape setting processes similar to the final device. In fatigue tests, the diamond shape samples are dynamically loaded with different mean and alternating strains until they break, to gain insights into the fatigue behavior of the device.

The aim in the present study is to evaluate the impact of the shape setting strategy on the fatigue performance of Nitinol vascular implants. A Finite Element Analysis (FEA) of the shape setting of a generic Nitinol diamond shape sample with different expansion steps is performed, to get samples with and without plastic deformation during shape setting. For the simulation the commercial code Abaqus is used. Several samples are manufactured with different expansion steps and evaluated with a Scanning Electron Microscope. Afterwards a systematic fatigue test is conducted with typical displacement during a cardiac cycle. For every combination the fatigue life is simulated and Goodman diagrams of alternating versus mean strain are plotted and compared to experimental results and literature data to visualize the effect of plastic deformation during shape setting on the fatigue behavior.