Abstract
Nitinol medical device implants made from a laser cut tubing process (i.e., stents, valve structures, etc.) frequently require a fatigue durability assessment, which necessitates determining the material fatigue properties. Towards the goal of determining the strain-based endurance limit of medical grade superelastic Nitinol tubing, a coupon was designed and evaluated via FEA using Abaqus software, produced via laser cutting, shape setting, and electro-polishing processes, and then fatigue tested to 10 million cycles. FEA was used to determine the strain versus alternating displacement amplitude for the coupon. Error due to dimensional tolerances was determined. The coupons were then fatigue tested in a 37 °C temperature deionized water bath at alternating strain levels ranging from 0.75 to 4.0% at zero mean strain. Sample replication was greater than 90%, and the median alternating strain fatigue limit was determined via two methods. Confidence and reliability with maximum likelihood statistics are used to present a strain-based endurance limit for the material. The results seem to differ from previous published values.
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Acknowledgments
Thank you to DC Devices, Inc. for supporting this work, BDC Labs, Inc. for the fatigue fixture and machine, and LaserAge Technology Corporation for coupon manufacture.
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This article is an invited paper selected from presentations at the International Conference on Shape Memory and Superelastic Technologies 2013, held May 20-24, 2013, in Prague, Czech Republic, and has been expanded from the original presentation.
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Forcucci, S.J. Laser Cut Nitinol Tubing Fatigue Coupon: Design, Testing, and Endurance Limit. J. of Materi Eng and Perform 23, 2523–2532 (2014). https://doi.org/10.1007/s11665-014-1069-6
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DOI: https://doi.org/10.1007/s11665-014-1069-6