Design, Analysis, and Simulated Testing of a Surrogate Nitinol Fatigue Specimen

Endurance limit analysis and testing require an accurate determination of the strain environment a device experiences in its life cycle (crimp strains, mean strain, and strain amplitudes) as well as the strain capability of the processed device. Surrogate fatigue specimens that represent a critical portion of a device can be designed through finite element analysis to experience the requisite strain life cycle, and in addition, can be efficiently tested to failure in a controlled strain environment. The surrogate should be processed in a similar manner as the parent device to ensure accurate material micro-structural properties as well as surface finish characteristics. In this article, we present the design, analysis, and simulated testing of a fatigue test specimen to determine a fatigue endurance limit to be used in the design assessment of a medical device. The Neyer D-Optimal sensitivity test method was used in a simulation to construct a design envelope.