Improving Fatigue: Role of the R-Phase
The medical device community often uses the Austenite finish temperature to tune for loading and unloading stiffness. Hence during cycling, the material goes through a dominantly first-order cubic (B2) to monoclinic (B19') martensitic transformation. This study focuses on the effect of thermomechanical treatments on fatigue behavior. Specifically, the role of R-phase. We demonstrate that by stabilizing the R-phase at body temperature and replacing the Austenite parent phase with the R-phase, fatigue life can be improved. We will show that when the duty cycle is predominantly between the R-phase and B19' martensite, a softening in cyclic modulus will occur. We will present fatigue results in strain–controlled loading conditions over a span of 2% -5% mean strain, relevant to physiological loading conditions. Also, the mechanism responsible for the increase in fatigue life will be discussed.