Experimental investigation of the cyclic degradation of the one-way shape memory effect of NiTi alloys

Based on stress- and strain-controlled cyclic tension-unloading-heat-cooling tests, cyclic degradation of the one-way shape memory effect (OWSME) of NiTi shape memory alloys (SMAs) was investigated. It was seen, in thermo-mechanical coupled cyclic tests, that residual strain after each cycle accumulated, but the martensite reorientation stress and dissipation energy-per-cycle decreased as the number of cycles increased. Meanwhile, the cyclic degradation of OWSME was aggravated by increasing the stress/strain amplitude. In addition, the stress-strain response of NiTi SMAs was further investigated by performing simultaneous thermo-mechanical coupled cyclic tests with various phase-angle differences between the mechanical and thermal cyclic loadings. It can be concluded that such cyclic response depends significantly on prescribed phase-angle differences. Obtained experimental results are helpful for both the development of constitutive models and engineering applications of NiTi SMAs.