Effects of Temperature on Fatigue Crack Propagation in Pseudoelastic NiTi Shape Memory Alloys

The effects of temperature on fatigue crack propagation in a pseudoelastic NiTi shape memory alloy (SMA) were analyzed. Single edge crack specimens were used and near crack tip displacements were captured by in situ digital image correlation (DIC). The effective stress intensity range was estimated from displacement data by a fitting procedure involving the William’s solution. Stress intensity range was also estimated using a recent analytical model that accounts for the complex thermo-mechanical response of SMAs. In addition, comparisons with the linear elastic fracture mechanics (LEFM) solution were made. Results revealed an important role of temperature on crack propagation rate, that is, the higher the temperature the longer the fatigue life. However, it was demonstrated that these effects are attributed to the marked influence of temperature on near crack tip fields and, consequently, on the effective stress intensity range. This trend is correctly captured by the DIC method as well as by the analytical model. On the contrary, LEFM does not consider the effects of temperature and, consequently an apparent change in the material properties is observed. Therefore, a novel approach is proposed to analyze crack propagation in SMAs, where both stress and temperature are considered as significant loading parameters.