A modified energy-based approach for fatigue life prediction of superelastic NiTi in presence of tensile mean strain and stress

Fatigue behavior of superelastic NiTi (i.e. Nitinol) is experimentally investigated and an energy-based fatigue model is proposed to account for the effects of tensile mean strain and stress on fatigue resistance. Several zero and nonzero mean strain tests at various strain amplitudes were conducted on cylindrical fatigue specimens with uniform gage sections. Experimental results revealed significant detrimental effects of the tensile mean stress on the fatigue life of the superelastic NiTi. On the stress plateau, where a change in the mean strain did not significantly influence the stress value, fatigue lives were observed to be similar. A modified energy-based model is proposed to account for the effects of mean stress and strain on the fatigue behavior of superelastic NiTi. Among all the models investigated in this study, the proposed energy approach was able to better correlate the fatigue data with and without mean strains/stresses.