Materials Science and Engineering A 378
- M. Wagner, T. Sawaguchi, G. Kaustrater, D. Hoffken, G. Eggeler
It is a generally held belief that controlled strain fatigue life is independent of wire diameter. This has led to the widespread use of general S-N curves for Engineering metals. Independence of wire diameter on fatigue life may not hold true for Nitinol. If so care must be used when applying generic Nitinol S-N curves to product design. To provide a more comprehensive understanding of this issue, a comparison study was conducted on the fatigue properties of various diameters of NiTi (Ti-55.8/55.9 wt%Ni) wire drawn from the same starting material. S-N curves were generated for various diameters. The wire diameter reduction from 0.030” to 0.010” increased the 0.8% strain 80k cycle survival rate from 35% to 96% as shown in Figure 3. For the scope of this study, all factors that may have an effect on fatigue life except for wire diameter were held constant.