Finite element simulation of the influence of TiC inclusions on the fatigue behavior of NiTi shape-memory alloys

In fatigue experiments of NiTi shape-memory alloys (SMAs), TiC inclusions have been found to cause cracks. Based on bending-rotation fatigue (BRF) experiments, which have evolved as one standard method to study the structural fatigue of superelastic NiTi wires, the influence of TiC inclusions on the fatigue behavior of NiTi SMAs has been analyzed quantitatively in this article. Aurichio's superelastic model was implemented into the finite element (FE) code ABAQUS. One specimen without inclusion and seven specimens with inclusions, at different distances with respect to the neutral axis of the wire specimens, have been analyzed. The stress distributions at the cross sections are nonlinear, and there is a stress plateau in the cross section when the phase transformation occurs. The stress distribution in the cross section of the specimen without inclusion is not only dependent on the load, but also dependent on the loading path and loading history. On the other hand, the maximum stress of the specimen without inclusion is not always at the surface, which is due to the phase transformation behavior of SMAs. The existence of the inclusions changes the stress distributions in the cross section. The maximum stress is dependent on the position of the inclusions, the load, and the loading path. It has been found that the maximum stresses increase as the distance from the inclusion to the neutral axis increases. When the inclusion is at the specimen surface, the maximum stress is the highest among all the studied cases. Such high stresses caused by the inclusions can easily induce fatigue cracks. The simulation can explain the fatigue behavior of BRF experiments and provide a deep insight into the fatigue fracture mechanism of SMAs.