Laser Cut Nitinol Tubing Fatigue Coupon: Design, Testing, and Endurance Limit

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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.

Keywords

advanced characterization fatigue medical device materials by design Nitinol non-ferrous metals stent 
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Notes

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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Copyright information

© ASM International 2014

Authors and Affiliations

  1. 1.DC Devices, Inc.TewksburyUSA

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