N. Rebelo, Dassault Systemes Simulia Corp. Western Region, Fremont, CA; A. Zipse, M. Schlun, G. Dreher, J. Zum Gahr, Bard Peripheral Vascular, Karlsruhe, Germany
In recent years, many studies on the fatigue behavior of NiTi have been published. The complexity of the fatigue behavior of NiTi was increasingly taken into consideration by enhanced test methods, more sophisticated test-equipment, improved test specimen and better constitutive models for Shape Memory Alloys. This investigation has the goal to continue these studies and to provide accurate results in all respects regarding the fatigue behavior of stents. Therefore, each individual aspect ranging from the test specimen to the constitutive model was considered and further improved.
The test specimens were processed similarly to real stents and embedded in a stent like structure. This enabled the use of a process identical to stent manufacturing without any additional process steps or the use of different equipment. The test specimen geometry, as well as the tubing geometry, are very similar to a real stent geometry in order to get realistic data.
The test rig was designed to achieve a circumferential load onto the struts, similar to the in-vivo deformations of stents resulting from physical body movement and heart-beats.
Furthermore, the Abaqus Nitinol material model, extended to capture some of the phenomena in the uniaxial behavior of Nitinol due to cyclic loading, was utilized for the determination of the strain levels.
This study was conducted in the course of the work of a consortium of several stent manufacturers, SAFE Technology Limited and Dassault Systèmes Simulia Corp., dedicated to the development of fatigue laws suitable for life prediction of Nitinol devices.
Summary: An investigation on small stent-like diamond specimen was performed. It had the goal to continue studies on the fatigue behavior of NiTi and to provide accurate results in all respects regarding the fatigue behavior of stents.
