FATIGUE-TO-FRACTURE TESTING, FINITE ELEMENT ANALYSIS, AND METALLOGRAPHIC ANALYSIS TO ESTIMATE FATIGUE DURABILITY OF SUPERELASTIC NITINOL STENTS FOR MEDICAL DEVICE USE

摘要

Superelastic medical devices (stents) allow for consistent radial force, flexibility, and wall apposition, thus providing effective treatments for patients. The aim of this study was to develop a methodology to statistically estimate superelastic stent fatigue strength by utilizing fatigue-to-fracture testing computer-aided engineering, and metallographic analysis techniques. To estimate fatigue strength, four load levels (S), based on finite element analysis (FEA) predictions, were chosen and applied. In accordance with ASTM F3211-17, load (represented as stent percent extension [R=0]) versus number of cycles at fracture (N) were determined. S-N data were used to estimate fatigue strength at the design life of the stent (e.g., 10 years of clinical use). Additionally, crack initiation and growth, as well as high-versus low-cycle fatigue characteristics, were examined using scanning electron microscopy (SEM). Results suggest correlations among fatigue-to-fracture data, FEA-predicted fracture location, and SEM evaluations.