Fatigue Life Assessment of Ni-Ti Stent-Like Devices: Investigation of a Fracture Mechanics Approach

Abstract Damage-tolerant approaches, relying on fracture mechanics, are powerful tools adopted in many engineering sectors to predict the initiation and propagation of fracture. In the last two decades, there has been a growing interest in extending these methods to shape memory alloy (SMA) components despite their greater complexities related to phase transformation and the thermomechanical coupling characterizing material response. SMA devices for actuation, damping, and energy absorption are the most appropriate applications of fracture mechanics, being large enough to sustain crack growth before fracture. Nevertheless, also the biomedical field is moving toward these methods for a more accurate prediction of device failure. This work investigates a damage-tolerant approach for predicting the fatigue fracture of Nickel-Titanium (Ni-Ti) stent-like devices. In the case of stenotic lower limb arteries, Ni-Ti SMAs are the top choice for designing self-expanding stents for mini-invasive deployment. The stents throughout their lifespan are subjected to cyclic loads mainly due to gait (106 cycles/year at 1 Hz) causing fatigue failures related to dramatic drawbacks. Since fatigue fracture is typically related to crack growth from manufacturing-related defects, this research aims to identify the basic ingredients needed to apply fracture mechanics, highlighting the critical aspects that should be considered given the particular features of the material and its application in the cardiovascular field.