<p>Nitinol has been used extensively in the design of cardiovascular implantable devices owing to its superelasticity, biocompatibility and fatigue resistance. Finite element analysis is often used to evaluate strain response and fatigue life of nitinol-based devices under various loading conditions. Typically, the computational models are validated using global load - deflection behavior. Most recently, material strains are characterized using Moire interferometry or digital image correlation (DIC) techniques. Because of the small device dimension and the highly non-linear behavior of Nitinol, DIC local material strain characterization presents unique challenges such as appropriate speckle patterns and imaging quality. The goal of this study is to investigate the reliability and repeatability of strain measurements from DIC technique with respect to key factors that drive the resolution and accuracy of DIC strains. Specifically, fatigue specimens with dimensions typical of endovascular stent struts are characterized under varying loads, geometrical location, speckle patterns to derive the salient features of the strain measurements. The main motivation of this study is to develop confidence on the strain measurements from DIC so that the technique can be reliably used to validate FEA computational model and to facilitate fatigue life prediction of Nitinol implants under varying preconditioning and in-vivo using conditions.&nbsp;</p>

Reliability and Repeatability of Strains Measured by Digital Image Correlation for Nitinol Specimen

Paper Proceedings: https://asmedigitalcollection.asme.org/VVS/VVS2021/volume/84782

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