Laser Cut Nitinol Medical Device Material: Non Zero Mean Strain Fatigue Life
Stephen J. Forcucci, MSME
DC Devices, Inc., Tewksbury, MA
Building upon previous work presented at 2013 SMST, the effect of a non-zero mean strain on the fatigue limit is explored. Fatigue coupons were fabricated from laser cut Nitinol tubing and tested to 10 million cycles. FEA (finite element analysis) was used to determine the strain versus alternating displacement amplitude for the coupon. The coupons where then fatigue tested in a 37°C temperature water bath at alternating strain levels ranging from 0.85% to 4.0% at zero mean strain, and testing was also performed with 1% and 2% mean strain. The median alternating strain fatigue limit for these situations was determined. Confidence and reliability with maximum likelihood statistics are used to present a strain-based endurance limits for the material at zero and non-zero mean strain levels.