Experimental study on whole-life one-way shape memory cyclic degradation and fatigue failure of NiTi shape memory alloy

Abstract

Thermo-mechanical coupling one-way shape memory fatigue experiments of NiTi shape memory alloy (SMA) micro-tubes were carried out in this work, which consisted of both the cyclic mechanical and thermal loading parts. In the mechanical cyclic loading part, different stress levels and stress rates were prescribed, but fixed maximum and minimum temperatures as well as constant temperature rise/drop rate were set in the thermal loading part. The results show that NiTi SMA micro-tubes exhibit obvious cyclic degradation of one-way shape memory effect (OWSME), that is, the residual strain after each one-way shape memory cycle accumulates as the number of cycles increases; the whole-life cyclic degradation of OWSME depends on the stress level and stress rate, and becomes more remarkable with increasing the stress level and decreasing the stress rate; In addition, corresponding fatigue life also relies on the stress level and rate, the higher the peak stress, and the lower the valley stress and stress rate, the shorter the fatigue life is. Obtained results in this work provide a solid experimental database for the fatigue life prediction of NiTi SMAs.