An energy-based fatigue failure model for super-elastic NiTi alloys under pure mechanical cyclic loading

The fatigue failure of a super-elastic NiTi alloy was observed by uniaxial stress-controlled cyclic tests. During the cyclic loading a hysteresis loop with a varied but stabilized size after certain cycles was obtained, which is similar to plastic shakedown. The material exhibits unique brittle fracture with a large transformation strain. The fatigue life of the material greatly depends on the applied peak nominal stress, the nominal stress amplitude and the mean nominal stress. A relation between the dissipation energy at the stabilized stage of cyclic loading and the number of cycles at failure was derived from the experimental results. Based on the obtained experimental results, a uniaxial fatigue failure model based on the energy approach was proposed to predict the fatigue life. It was shown that the proposed model provides good predictions to the uniaxial fatigue lives of super-elastic NiTi alloys with different types of cyclic stressing.