Structural and functional fatigue behavior of Ni49.8Ti50.2 (at. %) wires under various maximum heating temperatures: Experimental and modeling study

Abstract

The presented work investigates structural and functional fatigue behaviors of Ni49.8Ti50.2 (at. %) SMA wires under various maximum heating temperatures. Firstly, a thermo-mechanical fatigue experimental setup is established to test 24 SMA wires under various maximum heating temperatures (Tmax) of 92 °C, 115 °C, 147 °C, 165 °C, 211 °C, 291 °C. Then, the influence of Tmax on the fatigue life, strain evolution and failure type is discussed and a model is developed to simulate the plastic evolution behavior. Several experimental results are summarized. 1) The fatigue life decreases significantly from 26,559 to 35 cycles as Tmax increases from 92 °C to 291 °C. 2) The final plastic strain increases with Tmax rising and the fracture characteristic transfers from brittle mode to ductile mode. 3) Plastic strain in martensite phase becomes saturated in stage I of plastic strain curves and plastic strain in austenite phase contributes most of plasticity after that. 4) A higher Tmax increases the stable recovery strain and the degradation rate of recovery strain. Finally, based on experimental results, the plastic strain evolution behavior in stage I and stage II is simulated through a Tmax based model. This model shows a good quality of simplicity and precision. Keywords: SMA wire, Thermo-mechanical cycling, Structural fatigue, Functional fatigue, Plastic strain evolution