Experimental and Computational Rotary Bend Fatigue to Characterize Very High Cycle Fatigue of Nitinol

The use of superelastic Nitinol in implants continues to grow as physicians, scientists, and engineers design more novel medical devices to utilize its unique characteristics. As many of these devices are expected to be long-term implants, it becomes critically important to increase our understanding of Nitinol fatigue mechanisms beyond 10⁷ cycles. In this study, the fatigue behavior of Nitinol wire in rotary bend testing was characterized by experimental methods and computational modeling. Fractures occurred in high strain regions as predicted by computational modeling. Furthermore, fractures beyond 10⁷ or 10⁸ cycles were observed and seem to have been initiated by nonmetallic inclusions.