Validation and Application of DIC In Superelastic Nitinol

The strain-localization behavior of nitinol requires robust techniques to assist in understanding experimental results. Digital image correlation (DIC) provides an optimal modality for assessing superelastic nitinol behavior in medical device applications. In this study, a stereo-microscope-based DIC system (Vic-3D Micro; Correlated Solutions) is first validated, and then employed in practical applications. The system can assess a field of view from 1mm to 7mm, and is mounted on a high precision 3-axis stage. Validation consisted of comparing DIC results to those acquired via strain gauging and analytical solutions. A nitinol diamond coupon was then interrogated via DIC and finite element analysis (FEA). Areas of agreement and sources of divergence between DIC and FEA results were identified. Accurate calibration and validation of FEA material models requires detailed and precise material responses. Several new specimens have been designed to probe the anisotropic and elastic-plastic responses of nitinol under DIC visualization. The initial experience with these specimens and agreement with existing FEA models will be presented. Practical considerations and challenges concerning speckling, experimental setup, and data capture will also be addressed.