Rotary-bending fatigue characteristics of medical-grade Nitinol wire

Rotary bending curves for Ni50.8Ti49.2 bright wire with Af=2 °C tested at −25 °C, 23 °C, and 60 °C, with corresponding ∆T (=T−Af) values of −27, 21, and 58 °C, respectively. Data at ≥107 cycles did not fracture and are considered run-out conditions. Trend lines from regression analyses are drawn to delineate strain amplitude regions for these three sets of data. Note that for conditions of pseudoelasticity (stress-induced Austenite to B19' Martensite) there are four distinct regions in the curves, whereas there are only two regions for the data from the lowest test temperature (R-Phase). These regions are correlated to differences in strain accommodation mechanisms for the phases. 90